Kbd512's human mission design for Mars

SpaceNut · 2016-01-31 19:39:29

Breaking out mission design item for further discusion here...

kbd512 wrote:

RobertDyck wrote:
Current proposals by "Old Space" contractors remind me of the 1965 studies for humans to Mars. In 1965 they wanted to "leverage" as much Apollo technology as possible. Result was designs that just wouldn't work. Now they want to "leverage" as much ISS technology as possible. Result are huge habitats that are far too large, too clumsy, too little usable living space, and still have zero gravity. One problem is use of "solar electric propulsion" (SEP). If you do that, what you get is a Russian design. Here is the proposal from Energia for a human mission to Mars. That is an "old space" corporation in Russia, and this mission plan is from 1988.
I just don't understand the requirement to connect absolutely every piece of the mission architecture together and ship all of it to Mars at the same time.
This may not be the ideal way to do a Mars mission, but it takes available technology and funding realities into account:
1. Land the surface habitat and the MAV on Mars.
[1] Falcon Heavy 1 - MAV and SEP tug
[1] Falcon Heavy 2 - MAV and SEP tug (backup sent to secondary landing site)
[1] Falcon Heavy 3 - Surface Habitat
[1] Falcon Heavy 4 - Surface Habitat (backup sent to secondary landing site)
2. Send the MDV and TEI chemical kick stage to HMO using SEP.
[1] Falcon Heavy 5 - TEI and SEP tug
[1] Falcon Heavy 6 - TEI and SEP tug (backup)
3. Send the MTV and TMI chemical kick stage to ISS.
[1] Falcon Heavy 7 - MTV
[1] SLS 1 - TMI chemical kick stage (LOX/LH2)
[1] Falcon 1 - Dragon
4. Send the crew to ISS using Dragon. The crew inspects their MTV and TMI stage at ISS. If the MTV and TMI stage check out, depart for Mars. If not, the Mars crew returns to Earth and we send another MTV and/or TMI stage to ISS.
A potential variation on this is to use the ISS crew to inspect the MTV and TMI stage and then use a SEP tug to transfer the MTV / TMI stack to L1. The crew would be sent to L1 using Falcon Heavy instead of ISS using Falcon.
[2] Falcon Heavy 7 - MTV
[2] Falcon Heavy 8 - TMI chemical kick stage (LOX/LCH4)
[2] Falcon Heavy 9 - Dragon 1
5. The MTV uses SEP integrated into the MTV to spiral in to LMO. The MDV's SEP tug will spiral into LMO and dock with the MTV. The crew will then transfer to the MDV and descend to Mars to perform their surface exploration. A month or two before the crew leaves, the SEP tug that transferred the TEI stage to HMO will spiral in to LMO and dock with the MTV.
6. Upon completion of surface exploration, the MAV ascends to LMO and the crew transfer to the MTV.
7. The MTV departs for Earth using the TEI kick stage.
8. The MTV captures at L1 or LEO using its integrated SEP.
9. If the MTV captures in LEO, then the MTV docks at ISS and the crew returns to Earth using Dragon.
[1] Falcon 2 - Dragon 2
If the MTV captures at L1, then another Falcon Heavy sends another Dragon to L1 to retrieve the crew to return them to Earth. A SEP tug returns the MTV to ISS for inspection and refurbishment.
[2] Falcon Heavy 10 - Dragon 2
10. Refit the MTV for another mission cycle at ISS.
By delivering smaller and lighter individual payloads on affordable rockets like Falcon Heavy, launch costs are kept well within NASA's budget. This permits a regular launch cadence and funding for spares. There is also a degree of modularity achievable using more affordable rockets. If you want more mission hardware, you add launches.
All cargo to Mars (habitats, rovers, MDV, MAV, MTV) can be delivered to LEO using Falcon Heavy. However, if you want to depart from ISS you need a massive chemical kick stage that only SLS can deliver. SLS was intended to deliver payloads that no other rocket could and MTV TMI from LEO certainly qualifies.
If you lose any component of the 4 SLS mission architecture, then the mission is scrubbed because there's no time or funding to build a replacement SLS and payload.
Given the massive cost differential between heavy lift rockets like Falcon Heavy and super heavy lift rockets like SLS, I think the minimum launch architecture is wrong. For exploration, you don't need a minimum number of launches, you need maximum tonnage delivered. I think commodity rockets like Falcon Heavy and SEP tugs best service that requirement.
If you insist on using mega rockets and mega vehicles, this is the result:
RobertDyck wrote:
http://www.energia.ru/english/energia/mars/im/concept-01.gif
http://www.energia.ru/english/energia/mars/im/concept-05.jpg
NASA needs to tightly focus all available funding on enabling technologies:
1. CL-ECLSS - The feasibility of long duration space flight is directly tied to recycling of water and oxygen
2. ISRU - The ability to produce oxygen, water, and rocket fuel on Mars makes every aspect of manned exploration easier and cheaper to accomplish
3. MCP suits - Legacy technology space suits are impractical for use on a planet like Mars and a liability in microgravity environments contaminated with debris
4. Active radiation shielding - There's simply no suitable substitute for deflection of high energy particles
5. Satellite aided navigation - Landing within 100M or so of the intended target is an absolute requirement if the habitat and MAV will be landed separately.

SpaceNut · 2016-01-31 19:40:53

RobertDyck wrote:

Interesting post. My plan would land the MAV separately. You listed a single Falcon Heavy launching the MAV to Mars with an SEP tug. I question whether that would fit on a single Falcon Heavy. This does require direct launch from Earth surface to Mars surface, including Mars atmospheric entry, and Mars surface soft landing. And it has to lift astronauts and samples to Mars orbit, and rendezvous with the Interplanetary Transit Vehicle aka Mars Transit Vehicle. I argued to not pressurize the MAV capsule, which eliminates life support and replaces the capsule pressure hull with a fairing. Astronauts would ride in their spacesuits. That should reduce mass significantly. But my plan would have the MAV carry enough propellant to act as the TEI stage, your plan wouldn't.
My plan assembled the ITV aka MTV, with the TMI stage, and lander / surface habitat. This avoids the problem of orbit rendezvous before landing. Robert Zubrin doesn't like my plan because it requires both surface rendezvous (lander with MAV) and orbit rendezvous (MAV with ITV). Your plan has that, and adds two additional orbit rendezvous for lander and TEI stage. One reason my plan does this is for free return. If a failure like Apollo 13 happens, then you can use the gravity of Mars to swing into a trajectory to return to Earth. Inspiration Mars would use a free return trajectory. It takes a lot more than 3 days to return, but not a lot of propellant. By integrating the TEI stage with crew before they leave ISS, that stage is available in case of emergency. And integrating the surface habitat and intended return habitat, they have food and life support for the entire mission duration. Free return is supposed to take less than the normal mission duration, but carrying food and life support for the entire mission means that if something goes wrong, they have backups.
My plan would also land a separate laboratory before the crew depart ISS. And a pressurized rover with recycling life support. If everything works, the surface habitat will be connected to the lab. Which means landing them sufficiently close together to connect them. If the lab is all inflatable, then equipment could be moved separately. Basically, the lab would be a big tent. Carry equipment separately, and place inside. So the surface habitat doesn't have to land less than a metre away, it can land a significant distance. A safe distance, considering landing rockets will kick up rocks. But if something goes wrong, the lab can be used as a backup lab. And life support in the rover can be connected to the lab. Those arguing for a nuclear rover could chime in here.
Enabling technologies:
1. Life Support
a) Fix the urine processing assembly (the one on ISS got clogged with calcium deposits, from dissolved astronaut bones)
b) Replace the toilet with one that recovers moisture from feces. I have suggested a reality TV show find this as a contest between NASA and the Russian space agency. Electro-resistive oven (aka electric oven) to bake out moisture, or vacuum desiccation?
c) Shower and sink, connected to the water processing assembly to recycle wash water.
d) Laundry machine. You can't wear the same clothing until it's stinky, then throw it out, like they do on ISS. A Mars mission will not get new clothing every couple months. And operating in the dirty environment of Mars surface will put greater demands on clothing. So laundry, and connected to the water processing assembly to recycle that water too.
e) Direct CO2 electrolysis. This doesn't replace the current system, it augments it. The Sabatier reactor is limited by hydrogen from the water electrolysis unit. That means it can only use half of the CO2 recovered from cabin air. The other half is dumped in space. A direct CO2 electrolysis unit will recover oxygen from CO2 that is currently just dumped.
1.5. Demonstrate life support is ready for Mars by operating ISS without any cargo resupply for the entire duration of a Mars mission. - Crew could be swapped, because a Mars mission will not spend all its time in zero-G. It will be on the surface of Mars much of the time. But no cargo. A Mars mission won't get cargo, it will only have what it brings along, or has been pre-positioned.
2. ISRU - Demonstrate this with a robotic Mars sample return mission. But not Mars 2020, that's just insane. Instead a single mission the size of Pathfinder or Phoenix that lands a tiny rover the size of Sojourner, and returns the sample to Earth with a capsule like Stardust or Genesis. This requires ISPP to produce propellant for the return rocket.
3. MCP suit - This year NASA hired Professor Dava Newman from MIT. She's the last researcher actively working on MCP who hasn't retired or died of old age. Great, they have her, now do it. And you don't need anything fancy like contractile polymers or shape memory alloys. Opponents to MCP complain about donning and doffing. Do what Dr. Paul Webb did: just ignore it. Yes, the suit will be uncomfortable when only part way on. The solution is finish putting it on!
4. Active radiation shielding - nice to have, but I argue not required.
5. Satellite aided navigation - not required. Instead put a beacon on modules landed. Later modules can home in on that. Current navigation technology can get close enough without any aid to pick up the signal from a pre-landed module. And crude satellite aided navigation currently exists: MGS, Odyssey, Mars Express, and MRO all have a Mars relay antenna. That includes the ability to range find. You can use intersecting spheres to find your position in 3 dimensions from that. Not as accurate as Earth's GPS, but it is something.
6. Manoeuvring while rotating in tethered flight - this is key to light-weight artificial gravity. If you want to do it Robert Zubrin's way, then you have to do course adjustments while rotating. This can be demonstrated in LEO by connecting a Dragon cargo ship that's destined to be de-orbited anyway, to a Dragon crew ship. Or Progress to Soyuz, but it would be easier to get Congress and NASA to do this with American technology. You could do it with CST-100 connected to Cygnus.
7. Methane thrusters - Orion was supposed to use LCH4/LOX for its service module. When Lockheed-Martin and Boeing (their subcontractor for Orion) ran short of money, they replaced it with MMH/N2O4. Then they completely ran out of money, so made a swap deal with Europe to provide a couple service modules from ATV. That also uses MMH/N2O4, but greater dry mass and less propellant, so even less delta V. We need to demonstrate LCH4/LOX in space; it's key for ISPP.
8. Aerocapture - demonstrate this by placing an unmanned orbiter into Mars orbit. MGS and Odyssey and MRO used rocket fuel to capture into Mars orbit, then aerobraked down to mapping orbit. We need to demonstrate aerocapture before committing human lives to it.

SpaceNut · 2016-01-31 19:42:08

kbd512 wrote:

RobertDyck wrote:
Interesting post. My plan would land the MAV separately. You listed a single Falcon Heavy launching the MAV to Mars with an SEP tug. I question whether that would fit on a single Falcon Heavy. This does require direct launch from Earth surface to Mars surface, including Mars atmospheric entry, and Mars surface soft landing. And it has to lift astronauts and samples to Mars orbit, and rendezvous with the Interplanetary Transit Vehicle aka Mars Transit Vehicle. I argued to not pressurize the MAV capsule, which eliminates life support and replaces the capsule pressure hull with a fairing. Astronauts would ride in their spacesuits. That should reduce mass significantly. But my plan would have the MAV carry enough propellant to act as the TEI stage, your plan wouldn't.
A 15t pressurized MAV with seating for four crew members, ADEPT aeroshell, and modified Block 1A SEP tug will all fit within Falcon Heavy's payload shroud. The MAV will be approximately 3M in diameter and 4M in length with the landing legs stowed. I'm not in favor of pressurized MAV's, nominal use being 60 minutes or less, but some people are insistent on pressurized vehicles.
RobertDyck wrote:
My plan assembled the ITV aka MTV, with the TMI stage, and lander / surface habitat. This avoids the problem of orbit rendezvous before landing. Robert Zubrin doesn't like my plan because it requires both surface rendezvous (lander with MAV) and orbit rendezvous (MAV with ITV). Your plan has that, and adds two additional orbit rendezvous for lander and TEI stage. One reason my plan does this is for free return. If a failure like Apollo 13 happens, then you can use the gravity of Mars to swing into a trajectory to return to Earth. Inspiration Mars would use a free return trajectory. It takes a lot more than 3 days to return, but not a lot of propellant. By integrating the TEI stage with crew before they leave ISS, that stage is available in case of emergency. And integrating the surface habitat and intended return habitat, they have food and life support for the entire mission duration. Free return is supposed to take less than the normal mission duration, but carrying food and life support for the entire mission means that if something goes wrong, they have backups.
Orbital rendezvous is not the major problem that Dr. Zubrin makes it out to be. Every single crew and cargo transfer to ISS is another successful orbital rendezvous. We've done it many times and we're very good at it. ISS would not have been completed if orbital rendezvous posed any significant problems.
Name a MTV failure that a free return abort somehow makes survivable. I can't think of any. We already have a backup MAV and backup surface habitat. Once you get to Mars, you need to land on Mars. Speaking of which, I forgot to include the MDV and that's one more Falcon Heavy flight. With eleven Falcon Heavy flights, we've officially matched or exceeded the cost for one SLS and have officially orbited five times as much tonnage.
If an Apollo 13 type failure happens aboard the MTV, the result is loss of crew and loss of mission. With my MTV, the TMI and TEI stages will be the only likely sources for Apollo 13 type failures. If TMI or TEI fails, the result is loss of crew and loss of mission for any realistic architecture.
Some things have to work properly or you don't come home.
Do we want to spend billions of dollars on super heavy lift rocket development and leave ourselves with no funding for payloads or do we want to spend billions of dollars on payloads and then figure out how to break those payloads into pieces that comparatively low cost commodity rockets can deliver? Personally, I'd rather fund payloads than rockets. If there's no payload development, then the rocket development was pointless.
RobertDyck wrote:
My plan would also land a separate laboratory before the crew depart ISS. And a pressurized rover with recycling life support. If everything works, the surface habitat will be connected to the lab. Which means landing them sufficiently close together to connect them. If the lab is all inflatable, then equipment could be moved separately. Basically, the lab would be a big tent. Carry equipment separately, and place inside. So the surface habitat doesn't have to land less than a metre away, it can land a significant distance. A safe distance, considering landing rockets will kick up rocks. But if something goes wrong, the lab can be used as a backup lab. And life support in the rover can be connected to the lab. Those arguing for a nuclear rover could chime in here.
If you want to send more hardware to Mars using my mission architecture, you add Falcon Heavy launches.
I think nuclear powered rovers are a fantastic idea, provided that the shielded reactor mass stays sane. Unlimited range surface vehicles would be very nice to have, but vehicles are not required.
I simply want us to go to Mars. I think the greatest possibility for that to occur in a reasonable time frame would come about as a result of using our strengths (orbital rendezvous and docking, SEP), not attempting to address every aspect of the mission at the same time with the same hardware stack (combination MDV/MAV, MDV/MTV/TMI/TEI), and spending development funding on technologies critical to success (CL-ECLSS, ISRU, MCP).

SpaceNut · 2016-01-31 19:43:04

RobertDyck wrote:

kbd512 wrote:
Orbital rendezvous is not the major problem that Dr. Zubrin makes it out to be.
True. That was an issue in the 1960s. Dr. Zubrin and his partner David Baker developed Mars Direct in the last quarter of 1989, and the first half of 1990. They presented it to NASA at a conference in June 1990. That was before ISS, and before Shuttle rendezvoused with Mir. However, even then Shuttle had rendezvoused with Hubble a couple times. At that time we didn't have automated rendezvous, the Shuttle required a pilot. Now we do. So 21st century technology makes that easier. That's one point I've made several times.
kbd512 wrote:
Name a MTV failure that a free return abort somehow makes survivable. ... If an Apollo 13 type failure happens aboard the MTV, the result is loss of crew and loss of mission.
Apollo 13 had an explosion in the service module. They never did determine the exact cause. The two possibilities were either stirring the hypergolic aerozine 50 fuel tank caused it to explode, a hypergolic explosion, or a meteoroid hit it causing that same fuel tank to explode. The Apollo service module used MMH for RCS thruster quads, but aerozine 50 for the primary engine. That's a 50:50 mixture UDMH and simple hydrozine. NASA was worried that zero-G would cause separation of the fuel into layers, so they included a "stir" mechanism. Russia avoided that by using pure UDMH. Aerozine 50 is slightly more dense, and slightly higher Isp. Wikipedia says the AJ10-137 engine used by Apollo SM had Isp=314s, while Astronautix says 312s. Fuel density 0.903 g/cc (g/ml). Astronautix says Soyuz TMA main engine has Isp=304s. Soyuz TMA-M used currently and the Soyuz MS to be introduced this year both use the same engine. UDMH density 0.791 g/cc. So one way to avoid an Apollo 13 type accident is don't use aerozine 50. MMH has density 0.875 g/cc. Main engine of the European ATV, or Orion's ATV-based service module, Isp=312s. So MMH is a safe compromise.
However, to put it bluntly, shit happens. Every Apollo mission had something go wrong. The sole exception was Apollo 17. The very last Apollo had everything work correctly, but only the last one.
Apollo 9 was a test of the CSM and LM in high Earth orbit. Apollo 10 was a dress rehearsal: everything to the Moon, and the LM descended with crew to approach the surface, but they deliberately activated the abort. The LM abort caused the ascent stage to separate from the descent stage, and the ascent stage returned to lunar orbit. Apollo 8 was going to be an unmanned test of the Apollo CSM. They had tested the Apollo CM and its heat shield from high Earth orbit, but this would be the first time it returned all the way from the Moon. So this would test that the CSM could survive the trip all the way to the Moon and back. But Russia tested their Soyuz spacecraft with the exact same manoeuvre, the mission was called Zond-5. Yes, it was the Soyuz L1 spacecraft rather than the Soyuz LOK, but the Soviets were seen to be ahead in the space race. The next mission after Zond-5 would have been a manned flyby with one cosmonaut in a Soyuz L1 spacecraft. Zond-5 launched September 15, 1968, Apollo 8 launched December 21 of the same year. So NASA asked for volunteers for Apollo 8. Absolutely every astronaut volunteered, NASA had to pick crew. But the point is if an Apollo 13 type failure occurred with Apollo 8, crew would have died. Apollo 13 used the LM as a life boat. The LM was not ready in time for Apollo 8.
My plan would carry the surface habitat with the ITV. So if an Apollo 13 style failure happens, then crew can use the surface hab just like Apollo 13 did.
We already have bureaucrats in NASA claiming NATO won't be ready to go to Mars for at least 20 years, if not longer. Statements like "Apollo 13 type failure...result is loss of crew" simply reinforces their claim that we can't go to Mars.
kbd512 wrote:
Do we want to spend billions of dollars on super heavy lift rocket development and leave ourselves with no funding for payloads
This is a contradiction. I don't know the solution, but you don't want to even face the problem. Congress wants to keep jobs in their congressional districts, and I suspect "Old Space" contractors donate funding to their election campaigns. That means they want to keep SLS. But they're also concerned about cost. Abandoning SLS in favour of Falcon Heavy will reduce cost, but that cost basically means voter salaries. And those jobs are highly skilled jobs for NASA and their contractors. Congress has already overruled Presidential budget requests, giving NASA more money to finish SLS and Orion. Ok, they want SLS. So we have to find an excuse to use SLS. Even my mission plan could be broken into smaller launches, not assembled exactly your way, but could use Falcon Heavy instead of SLS. The question is whether Congress would approve it.
kbd512 wrote:
If you want to send more hardware to Mars using my mission architecture...
To be blunt, I presented my mission architecture at the Mars Society convention of 2002. I've tweeked it a bit, but it's essentially the same. We came to the same conclusion, I'm not taking your ideas.
kbd512 wrote:
nuclear powered rovers...
My mission plan includes life support in the pressurized rover as a backup. I don't specify whether the rover is nuclear or conventional fuel. It could generate power using LCH4/LOX, or even batteries. The idea is the lab could be used as backup habitat, and life support for the rover could provide life support to the lab. Normally the surface hab would do that, but this is a backup in case the surface hab fails.
kbd512 wrote:
I simply want us to go to Mars. I think the greatest possibility for that to occur in a reasonable time frame would come about as a result of using our strengths (orbital rendezvous and docking, SEP), not attempting to address every aspect of the mission at the same time with the same hardware stack (combination MDV/MAV, MDV/MTV/TMI/TEI), and spending development funding on technologies critical to success (CL-ECLSS, ISRU, MCP).
We both want to go, and we're coming up with the same ideas. Our differences are few. So yea. But now the question is what is Congress willing to pay for.

SpaceNut · 2016-01-31 19:44:06

GW Johnson wrote:

KDB512 and RobertDyck:
You two are talking about variations on the same basic mission design. I think you both already know that. And I think you both have gone way further than Zubrin ever did with his 1990-vintage Mars Direct scheme. Zubrin is smart, but he is not god. I would caution about thrusting maneuvers on a spinning tethered design. That's a development item. A rigid spinning baton design is far less of a development item.
As for NASA, its troubles are both technical and management, but the management is by far the dominant problem. It traces directly to the "corporate welfare state" problem that I despise so much, and have railed against in these forums. The only thing holding Musk back is not totally embarrassing his biggest customer (the US government/its various agencies).
That being the case, I'd be less interested in what Congress is willing to pay for, and a whole lot more in what Musk (and some others) are willing to pay for when the government will not. That's what sets when men finally go to Mars. Not NASA or any other government agency.
GW

SpaceNut · 2016-01-31 19:52:21

Gw I do agree with you on some of the elements of the mission in that we use a capsule for earth return, a capsule for earth taxi to orbit, a TMI stage to push the deep space habitat to mars with a return TEI and for the mars end of the equation we have Insitu propellant manufacturing plus MAV, a Mars lander for the crew if we do not land in the habitat, Mars habitat and consumables for the stay with everything else being extra....

All these must be within a cost bracket for a first mission to allow for any chance of a follow up being done.

As for having the things we need for a mission we are close but no cigar....so that means R&D money beyond the costs of launch vehicles regardless of what ones are used....for this mission....

SpaceNut · 2016-01-31 21:17:53

kbd512 wrote:

RobertDyck wrote:
True. That was an issue in the 1960s. Dr. Zubrin and his partner David Baker developed Mars Direct in the last quarter of 1989, and the first half of 1990. They presented it to NASA at a conference in June 1990. That was before ISS, and before Shuttle rendezvoused with Mir. However, even then Shuttle had rendezvoused with Hubble a couple times. At that time we didn't have automated rendezvous, the Shuttle required a pilot. Now we do. So 21st century technology makes that easier. That's one point I've made several times.
Use of massive chemical rockets for one-shot assembly of interplanetary exploration vehicles is 20th century thinking. We're in the 21st century now and NASA's budget is what it is and it is unlikely to be substantially increased. Let's update our thinking to include orbital rendezvous to keep launch costs well within NASA's budget by using commodity rockets whenever we reasonably can.
For light cargo, use the old "lift, throw, and let it go" method. For heavy cargo, use the new "lift, spiral out, spiral in" method. Both methods clearly function as intended.
RobertDyck wrote:
Apollo 13 had an explosion in the service module. They never did determine the exact cause. The two possibilities were either stirring the hypergolic aerozine 50 fuel tank caused it to explode, a hypergolic explosion, or a meteoroid hit it causing that same fuel tank to explode. The Apollo service module used MMH for RCS thruster quads, but aerozine 50 for the primary engine. That's a 50:50 mixture UDMH and simple hydrozine. NASA was worried that zero-G would cause separation of the fuel into layers, so they included a "stir" mechanism. Russia avoided that by using pure UDMH. Aerozine 50 is slightly more dense, and slightly higher Isp. Wikipedia says the AJ10-137 engine used by Apollo SM had Isp=314s, while Astronautix says 312s. Fuel density 0.903 g/cc (g/ml). Astronautix says Soyuz TMA main engine has Isp=304s. Soyuz TMA-M used currently and the Soyuz MS to be introduced this year both use the same engine. UDMH density 0.791 g/cc. So one way to avoid an Apollo 13 type accident is don't use aerozine 50. MMH has density 0.875 g/cc. Main engine of the European ATV, or Orion's ATV-based service module, Isp=312s. So MMH is a safe compromise.
My MTV has integrated SEP propulsion for spiral in and attitude control. There are no hypergolic propellants or fuel cells aboard. The MDV and MAV both use hypergolic propellants. The kick stages are LOX/LH2 (for LEO TMI from ISS; requires SLS) or LOX/LCH4 (L1 TMI and LMO TEI; only requires Falcon Heavy).
RobertDyck wrote:
However, to put it bluntly, shit happens. Every Apollo mission had something go wrong. The sole exception was Apollo 17. The very last Apollo had everything work correctly, but only the last one.
I always count on that, but question the idea that any habitat short of a second MTV is a suitable replacement for the MTV.
RobertDyck wrote:
Apollo 9 was a test of the CSM and LM in high Earth orbit. Apollo 10 was a dress rehearsal: everything to the Moon, and the LM descended with crew to approach the surface, but they deliberately activated the abort. The LM abort caused the ascent stage to separate from the descent stage, and the ascent stage returned to lunar orbit. Apollo 8 was going to be an unmanned test of the Apollo CSM. They had tested the Apollo CM and its heat shield from high Earth orbit, but this would be the first time it returned all the way from the Moon. So this would test that the CSM could survive the trip all the way to the Moon and back. But Russia tested their Soyuz spacecraft with the exact same manoeuvre, the mission was called Zond-5. Yes, it was the Soyuz L1 spacecraft rather than the Soyuz LOK, but the Soviets were seen to be ahead in the space race. The next mission after Zond-5 would have been a manned flyby with one cosmonaut in a Soyuz L1 spacecraft. Zond-5 launched September 15, 1968, Apollo 8 launched December 21 of the same year. So NASA asked for volunteers for Apollo 8. Absolutely every astronaut volunteered, NASA had to pick crew. But the point is if an Apollo 13 type failure occurred with Apollo 8, crew would have died. Apollo 13 used the LM as a life boat. The LM was not ready in time for Apollo 8.
I don't want anything explosive aboard the MTV. It's simply not required for this mission. If there's funding to build and launch a second MTV, then fly both MTV's in formation to Mars. Complete redundancy won't hurt the mission if the individual components and launch costs are affordable.
You're really talking about connecting two MTV's together and therefore require sufficient propellant to push that stack to Mars and back to Earth, unless you can guarantee that a failure that would require use of the redundant MTV won't prevent you from discarding the stricken MTV. I don't think you can make that guarantee.
So, how big a rocket do you need to throw two MTV's connected to each other and how much will that rocket cost?
RobertDyck wrote:
My plan would carry the surface habitat with the ITV. So if an Apollo 13 style failure happens, then crew can use the surface hab just like Apollo 13 did.
The Apollo 13 astronauts survived due to their close proximity to Earth. If our Mars mission astronauts don't have a functional duplicate of the MTV, they're not coming home. What functionality would your approach provide that a spare MTV would not better provide?
I would say we ship the Mars surface habitats directly to Mars and then fly MTV's in formation to Mars if redundancy is an issue. I've already indicated that we should ship two TEI kick stages to HMO.
RobertDyck wrote:
We already have bureaucrats in NASA claiming NATO won't be ready to go to Mars for at least 20 years, if not longer. Statements like "Apollo 13 type failure...result is loss of crew" simply reinforces their claim that we can't go to Mars.
I had no idea that NATO was involved in the manned mission to Mars effort and was unaware that there were any people there for them to stand around and watch while other people slaughtered them. Maybe we should just call this whole thing off if NATO is involved.
RobertDyck wrote:
This is a contradiction. I don't know the solution, but you don't want to even face the problem. Congress wants to keep jobs in their congressional districts, and I suspect "Old Space" contractors donate funding to their election campaigns. That means they want to keep SLS. But they're also concerned about cost. Abandoning SLS in favour of Falcon Heavy will reduce cost, but that cost basically means voter salaries. And those jobs are highly skilled jobs for NASA and their contractors. Congress has already overruled Presidential budget requests, giving NASA more money to finish SLS and Orion. Ok, they want SLS. So we have to find an excuse to use SLS. Even my mission plan could be broken into smaller launches, not assembled exactly your way, but could use Falcon Heavy instead of SLS. The question is whether Congress would approve it.
It's not a contradiction. You can pay a startup aerospace company to develop an affordable heavy lift rocket and use a little creativity to maximize what you can do with that affordable rocket or you can wait for a decade or two for a government agency to pay an established aerospace company to develop an unaffordable super heavy lift rocket that still requires a bit of creativity to maximize what you can do with that unaffordable booster.
All the money lavished on these shiny new toys called Orion and SLS prevent NASA from developing payloads that require SLS.
RobertDyck wrote:
To be blunt, I presented my mission architecture at the Mars Society convention of 2002. I've tweeked it a bit, but it's essentially the same. We came to the same conclusion, I'm not taking your ideas.
Ok. I never stated that you were. In fact, we can call it your idea if you like. To reiterate, I care less who gets credit as long as we do the mission. I'm no more or less enamored with the idea of using commodity rockets. Regarding your ideas, I'm not aware of what your ideas are until you post them in response to my posts on this forum. I don't go hunting for other peoples' ideas. Maybe I'm only the 100th monkey, but I still like to think for myself. If you posts links to your mission architecture plans, I'd be interested to read your thoughts on this matter.
My ideas, which I'm pretty sure I arrived at on my own, were arrived at by taking account of hard fiscal reality. These mega rockets that NASA and Congress are so enamored with have choked off all available funding for payloads that would require such massive rockets.
RobertDyck wrote:
My mission plan includes life support in the pressurized rover as a backup. I don't specify whether the rover is nuclear or conventional fuel. It could generate power using LCH4/LOX, or even batteries. The idea is the lab could be used as backup habitat, and life support for the rover could provide life support to the lab. Normally the surface hab would do that, but this is a backup in case the surface hab fails.
I specify nuclear until our solar panel power density and battery energy density improves to the point to where there's no practical requirement for nuclear power. We're not there yet.
RobertDyck wrote:
We both want to go, and we're coming up with the same ideas. Our differences are few. So yea. But now the question is what is Congress willing to pay for.
Agreed.

SpaceNut · 2016-01-31 21:20:54

MTV Spiral out is the time line that is in this image....12 months to get into Mars orbit....

That gets you only 1 month on the surface....can you say flag and foot prints.....

Also Ion drive means no artificial gravity tumbling end over end as perferred by GW....

So basically a sick astronaut returns to earth.......

SpaceNut · 2016-01-31 22:21:46

RobertDyck wrote:

My mission architecture includes a reusable habitat. The in-space habitat is separate from the surface habitat. And both habitats have life support. This allows use of the surface habitat as backup. And allows the in-space habitat dedicated to in-space use.
I like Robert Zubrin's idea for artificial gravity. That's light, it doesn't involve a truss or pipe or other connection arm. It does require manueovring while rotating in tethered flight. That technology requires some work. An easy way is to time thrusters so they "pull" the module, providing tension on the tether. And to ensure the "pull" force is less than the acceleration due to centripetal effect (artificial gravity). That ensures no hard bounce.
I have argued for laundry. The laundry machine can be an RV style single appliance washer/dryer. This requires gravity to work. When washing, clothes fall into and are pulled out of soapy water. That moves soap and water through clothes. When drying, clothes fall from the drum as it rotates slowly. During zero-G, just don't use the laundry machine. If artificial gravity fails, you have to wear the same stinky clothes.
Use of artificial gravity requires a hab with a flat floor. It can be sideways like an ISS module.
I have argued for aerocapture to enter Mars orbit, or Earth orbit. If you use this for an asteroid, then aerocapture into Earth orbit from that too. Use a deployable and reusable heat shield, such as ADEPT.
One reason for making the propulsion separate is so it can be replaced. It can be chemical, or SEP, or NEP, or nuclear thermal, or even microwave/water. Whatever the latest technology is. The propulsion stage could be expendable; that makes the tether easy. As described in Mars Direct, don't recover the stage. Just cut the cable/rope/strap/chain and let the spent stage fly off into space. It will enter orbit around the Sun. The hab then has to de-spin to prepare for aerocapture. A reusable stage has to be reeled-in, which makes de-spin more challenging.
Life support can be based on the system currently on the American side of ISS. It will require a few additions. I listed additions several times, the latest is the previous page of this discussion.
A reusable habitat can rendezvous and dock with ISS. Then any spacecraft that can carry crew to ISS, can return crew from this habitat. However, in case of aerocapture failure, you need an emergency escape pod aka lifeboat. That means a capsule. As an emergency vehicle, you want that to be as low mass as possible. Options: Dragon, CST-100, Orion, Soyuz. Since this is in case of aerocapture failure only, you would want the capsule only, no service module or orbital/mission/resource module.
Dragon: 4.2 tonnes dry mass + 1.29 tonne propellant = 5.49 tonne. Crew 7. That's for the cargo resupply ship, but official statements from SpaceX claim Dragon v2 will have the same mass. I suspect it will mass more once you add launch escape system, life support, seats, control consoles.
CST-100 Starliner: 13 tonnes, but that includes service module. Crew 7.
Orion: 8.6 tonnes. Crew 6.
Soyuz: 2.95 tonnes. Crew 3.

kbd512 · 2016-02-01 04:51:43

SpaceNut wrote:

MTV Spiral out is the time line that is in this image....12 months to get into Mars orbit....

We're using SEP to spiral in to LMO on the outbound trip from Earth and SEP to spiral in to L1 or LEO on the inbound trip from Mars. Ideally, SEP tugs mate the MTV to the TMI stage at L1. The crew then uses Falcon Heavy and Dragon to transfer to the MTV at L1. The transit takes a few days. The TMI and TEI kick stages are both chemical, so no spiral time is required. Ideally, both TMI and TEI kick stages use the same LOX/LCH4 propellants and make use of ZBO technology NASA is working on for long term cryogenic propellant storage. You only lose 2 months with the spirals.

This architecture maximizes practical application of SEP and ZBO technology that NASA is actively developing and uses affordable commodity rockets for launch services.

SpaceNut wrote:

That gets you only 1 month on the surface....can you say flag and foot prints.....

Flags and footprints is still more than what we're capable of right now, but we're not using SEP for TMI or TEI.

SpaceNut wrote:

Also Ion drive means no artificial gravity tumbling end over end as perferred by GW....

Using SEP only equates to no AG if you insist on using tumbling to generate AG. My MTV concept uses a rotor. The rotating module is a hub with two to four pressurized blades. The hub is connected to a primary module and secondary module.

FRONT

^
S
M
O
D
[ROTOR]-[HUB]-[ROTOR]
P
M
O
D
^
[SEP]
^
[TMI]
^^
REAR

Each rotor blade is covered with solar cells. At the tip of each rotor blade is a small compartment for an astronaut to sleep in. For 8 hours each day, the astronauts receives 1G. Each rotor blade stores water for use as crew provisions and to provide counter mass if there is not an astronaut occupying an opposing rotor blade. Each rotor tip contains electric thrusters for attitude control. An electric motor in the hub rotates the assembly. The hub would also contain an active radiation shielding device, when such a device becomes available. The blade tip mounted thrusters could also expel ionized propellant to increase the effectiveness of the active radiation shielding device.

SpaceNut wrote:

So basically a sick astronaut returns to earth.......

Sick astronauts don't return to Earth from ISS when they follow the recommended exercise regimen.

RobertDyck · 2016-02-01 09:59:01

kbd512 wrote:

Use of massive chemical rockets for one-shot assembly of interplanetary exploration vehicles is 20th century thinking. We're in the 21st century now and NASA's budget is what it is and it is unlikely to be substantially increased. Let's update our thinking to include orbital rendezvous to keep launch costs well within NASA's budget by using commodity rockets whenever we reasonably can.

Wrong. Physics is universal. It isn't the latest fad. Life support is expensive: food, oxygen, water, heat, humidity control, all the needs to keep crew healthy. And yes, gravity. There's protection from radiation and micrometeoroids. Cargo can be delivered the way you described, but crew need fast transit.

I met someone at the Humans In Space symposium at Banff. He was from the European Space Agency. I described using ion propulsion to spiral out of Earth orbit, head toward the Moon, then use the Moon for gravity assist to continue on to Mars. Using ion propulsion would take longer than a Hohmann transfer orbit, but it's still efficient. That individual was interested. Shortly after that ESA used a spiral trajectory to send a probe to the Moon. So he used my idea, although not for Mars. I'm not opposed to spiral transfer, it's just not for crew.

kbd512 wrote:

I always count on that, but question the idea that any habitat short of a second MTV is a suitable replacement for the MTV.

So what is the purpose of your backup when it isn't needed as a backup? Not for some future mission, but the first one. None? Then you just doubled the cost for no reason.

kbd512 wrote:

You're really talking about connecting two MTV's together and therefore require sufficient propellant to push that stack to Mars and back to Earth, unless you can guarantee that a failure that would require use of the redundant MTV won't prevent you from discarding the stricken MTV.

No. You're wrong. The ITV (Interplanetary Transit Vehicle) is used to transit to Mars, and back to Earth. The name comes from NASA's Mars design reference mission. It's reused, and intended for multiple missions from ISS to Mars and back. The surface hab is one way only, left on Mars. It is not hauled back to Earth. You could place it on Mars ahead of crew, but why? It'll take the same propellant whether you send it with crew or not. With crew, it acts as a backup. If free return is necessary, it will come back to Earth. But if it is used for that, it won't go to Mars again.

kbd512 wrote:

So, how big a rocket do you need to throw two MTV's connected to each other and how much will that rocket cost?

I estimate the TMI stage will require a singe Falcon Heavy to lift the stage alone to ISS.

kbd512 wrote:

The Apollo 13 astronauts survived due to their close proximity to Earth. If our Mars mission astronauts don't have a functional duplicate of the MTV, they're not coming home. What functionality would your approach provide that a spare MTV would not better provide?

No, it wasn't proximity. It was use of the LM as a lifeboat. My mission plan carries the surface habitat as a spare, but only to Mars. If nothing goes wrong up to and including Mars orbit, then crew will ride the surface hab down to the surface of Mars. Once on Mars, it won't lift off again. A spare MTV is double expense, and double propellant required to deliver it.

kbd512 wrote:

It's not a contradiction. You can pay a startup aerospace company...

It is contradiction. People worry about losing their jobs. Congress knows Old Space companies, doesn't know any startup. So Congress wants to keep people employed at their current company. But they also want to keep cost down. But they don't want existing Old Space companies to lose employees. But they want to keep cost down. But they don't want people to have to seek employment at a new company. But they want to keep cost down. Getting it yet?

kbd512 wrote:

All the money lavished on these shiny new toys called Orion and SLS prevent NASA from developing payloads that require SLS.

Yes. Orion is way too heavy. Apollo Command Module massed 5,560 kg, without Service Module. Orion Crew Module is estimated at 19,000 lb or 8,600 kg. You would expect modern materials would allow reduction of mass, but it's just fat. And ridiculously expensive. But the worry is that SLS has no manifest other than Orion. So if Orion is cancelled, SLS could be too. That would leave is with no rocket capable of delivering useful mass to Mars.

There is SpaceX, but at this point I'm very hesitant to commit to just one supplier. There were multiple companies in the 1960s; they merged into just a handful today. Each time the number of companies declined, NASA got screwed more. It's called "monopoly". SpaceX looks great today, but could become just as corrupt if they become the new monopoly.

My ideas are a modification of Mars Direct and NASA's DRM (aka Semi-Direct). And I took principles of "Lunar Orbit Rendezvous" from Apollo. I called it "Mars Orbit Rendezvous" but one member of this forum asked Dr. Zubrin about my plan. He said Dr. Zubrin called it "Hybrid Direct". I consider the fact Dr. Zubrin came up with a nick-name for my plan is a complement. I posted it a few times. The recent complete discussion is here... Yet another Mars architecture

Last edited by RobertDyck (2016-02-01 17:19:35)

kbd512 · 2016-02-01 11:32:20

RobertDyck wrote:

Wrong. Physics is universal. It isn't the latest fad. Life support is expensive: food, oxygen, water, heat, humidity control, all the needs to keep crew healthy. And yes, gravity. There's protection from radiation and micrometeoroids. Cargo can be delivered the way you described, but crew need fast transit.

The crew do make a fast transit. As fast as reasonably achievable from a cost standpoint. Funding is not unlimited. Why is that so difficult to accept?

RobertDyck wrote:

I met someone at the Humans In Space symposium at Banff. He was from the European Space Agency. I described using ion propulsion to spiral out of Earth orbit, head toward the Moon, then use the Moon for gravity assist to continue on to Mars. Using ion propulsion would take longer than a Hohmann transfer orbit, but it's still efficient. That individual was interested. Shortly after that ESA used a spiral trajectory to send a probe to the Moon. So he used my idea, although not for Mars. I'm not opposed to spiral transfer, it's just not for crew.

We're not spiraling out using SEP. We're spiraling in. You lose two months. So what?

RobertDyck wrote:

So what is the purpose of your backup when it isn't needed as a backup? Not for some future mission, but the first one. None? Then you just doubled the cost for no reason.

Complete redundancy is about giving hand wringers something to prevent arthritis.

kbd512 wrote:

You're really talking about connecting two MTV's together and therefore require sufficient propellant to push that stack to Mars and back to Earth, unless you can guarantee that a failure that would require use of the redundant MTV won't prevent you from discarding the stricken MTV.

RobertDyck wrote:

No. You're wrong. The ITV (Interplanetary Transit Vehicle) is used to transit to Mars, and back to Earth. The name comes from NASA's Mars design reference mission. It's reused, and intended for multiple missions from ISS to Mars and back. The surface hab is one way only, left on Mars. It is not hauled back to Earth. You could place it on Mars ahead of crew, but why? It'll take the same propellant whether you send it with crew or not. With crew, it acts as a backup. If free return is necessary, it will come back to Earth. But if it is used for that, it won't go to Mars again.

You just stated that you intend to use the surface habitat as a lifeboat. Short of creating a fully functional ITV, how do you intend to do that? Apollo 13 was a power/propellant issue. If your ITV experiences a similar power/propellant issue, how do you intend to get the crew home when their vehicle has no power or propellant? The answer is or should be pretty obvious.

RobertDyck wrote:

I estimate the TMI stage will require a singe Falcon Heavy to lift the stage alone to ISS.

Have you seen what ICPS and LUS are estimated to be able to throw from LEO to Mars?

You either have the lightest ITV / Surface Habitat / Capsule / TMI / TEI stack on the planet or there's a problem with your mass budget. If it's not clear, I'm talking about TMI from LEO, not TEI.

RobertDyck wrote:

No, it wasn't proximity. It was use of the LM as a lifeboat. My mission plan carries the surface habitat as a spare, but only to Mars. If nothing goes wrong up to and including Mars orbit, then crew will ride the surface hab down to the surface of Mars. Once on Mars, it won't lift off again. A spare MTV is double expense, and double propellant required to deliver it.

Doubtful.

RobertDyck wrote:

It is contradiction. People worry about losing their jobs. Congress knows Old Space companies, doesn't know any startup. So Congress wants to keep people employed at their current company. But they also want to keep cost down. But they don't want existing Old Space companies to lose employees. But they want to keep cost down. But they don't want people to have to seek employment at a new company. But they want to keep cost down. Getting it yet?

We're not going anywhere until Congress substantially increases NASA's budget for payload development or we start using affordable rockets. Since NASA's not going to receive more funding and Congress insists on development of an unaffordable rocket, we're not going anywhere. Getting that yet? SLS is not a float, it's an anchor.

RobertDyck wrote:

Yes. Orion is way too heavy. Apollo Command Module massed 5,560 kg, without Service Module. Orion Crew Module is estimated at 19,000 lb or 8,600 kg. You would expect modern materials would allow reduction of mass, but it's just fat. And ridiculously expensive. But the worry is that SLS has no manifest other than Orion. So if Orion is cancelled, SLS could be too. That would leave is with no rocket capable of delivering useful mass to Mars.

We don't need SLS to deliver useful mass to Mars. We need SEP tugs and orbital assembly. ISS wasn't built with a Saturn V class rocket. It was built with commodity rocket payloads delivered in the most unaffordable way imaginable.

RobertDyck wrote:

There is SpaceX, but at this point I'm very hesitant to commit to just one supplier. There were multiple companies in the 1960s; they merged into just a handful today. Each time the number of companies declined, NASA got screwed more. It's called "monopoly". SpaceX looks great today, but could become just as corrupt if they become the new monopoly.

Yes, let's throw some more money at some companies so we can wait another decade or two before there's funding for payloads. SpaceX's leadership is serious about affordability and reliability. If Elon gets hit by a truck tomorrow, that might change in an instant, but I kinda doubt it.

RobertDyck wrote:

My ideas are a modification of Mars Direct and NASA's DRM (aka Semi-Direct). And I took principles of "Lunar Orbit Rendezvous" from Apollo. I called it "Mars Orbit Rendezvous" but one member of this forum asked Dr. Zubrin about my plan. He said Dr. Zubrin called it "Hybrid Direct". I consider the fact Dr. Zubrin came up with a nick-name for my plan is a complement. I posted it a few times. The recent complete discussion is here... Yet another Mars architecture

SLS is the Mars Direct heavy lift booster, so Mars Direct is unaffordable because it uses unaffordable rockets. I don't care what Dr. Zubrin calls any plan that uses unaffordable rockets. Any plan that uses unaffordable rockets may as well be called Unaffordable Direct.

NASA will not receive the budget increase required to fly these rockets often enough for whatever mass increase they provide over commodity rockets to matter. Let's say NASA is given enough money to fly 4 SLS rockets per year and let's say the cost to fly drops to $1B and each rocket can lift 125t to LEO. That's magical thinking since SLS has yet to fly, but let's pretend.

That's $4B for 500t to LEO. If the Falcon Heavy costs $125M per flight and each rocket can lift 50t to LEO, that's 1600t. If the commodity rocket required a SEP tug to deliver the payload and the SEP tug cost $125M per flight, that's still 300t greater lift capability per year.

RobertDyck · 2016-02-01 12:42:10

kbd512 wrote:

You just stated that you intend to use the surface habitat as a lifeboat. Short of creating a fully functional ITV, how do you intend to do that? Apollo 13 was a power/propellant issue.

A free return trajectory is designed deliberately that you don't need propellant. You launch the spacecraft into a trajectory where it will loop around your intended target (Moon or Mars), not stop, and return directly back to Earth. Entering orbit requires expending energy to get out of the free return trajectory. That can be done with propulsion, or aerocapture. Apollo used this to go to the Moon, and its good that they did. It was used for Apollo 13. A 6 month transit to Mars does the same thing, that's one reason you don't want to go faster. Any faster and you don't get free return. So if an Apollo 13 style failure occurs, you continue to drift past Mars, and the gravity of Mars itself redirects your path (trajectory) to return to Earth. That's why it's called "free".

Not my idea. Apollo already did this. And Robert Zubrin has argued for a free return trajectory for Mars. I just think it's a good idea.

kbd512 wrote:

You either have the lightest ITV / Surface Habitat / Capsule / TMI / TEI stack on the planet or there's a problem with your mass budget. If it's not clear, I'm talking about TMI from LEO, not TEI.

If you want to help flesh it out, please do. But that means helping, not trying to trash the plan.

My plan pre-lands the MAV. Direct launch from Earth surface to Mars surface. The MAV uses ISPP, and launches with extra propellant so it will be the TEI stage. No on-orbit propellant transfer. Instead the MAV just docks to the ITV, and when they're ready to depart the MAV fires its engine to push the ITV into trans-Earth trajectory.

The laboratory with pressurized rover is also pre-landed. Again direct launch from Earth surface to Mars surface. No stop in Earth orbit.

The ITV is launched to LEO. Then the surface habitat is launched and docked to the ITV. The TMI stage is launched and docked to the stack. Then crew is delivered via capsule. You could dock a capsule to act as an emergency escape pod, then launch crew separately. Or just use the capsule to deliver crew. The simplest solution is to launch crew in a Dragon, dock it to the stack. The Dragon will remain docked to Mars orbit, and all the way back to Earth orbit. When the ITV docks with ISS, the Dragon will still be attached. At that point you can either leave it attached for the next mission, and return crew with some other vehicle, or just return crew with that Dragon. If you use Dragon for return, then the next mission will need a fresh Dragon.

Note the TEI stage is not docked when crew depart Earth orbit. TEI is done with the MAV, which is pre-landed on Mars.

kbd512 wrote:

We're not going anywhere until Congress substantially increases NASA's budget for payload development or we start using affordable rockets. Since NASA's not going to receive more funding and Congress insists on development of an unaffordable rocket, we're not going anywhere. Getting that yet? SLS is not a float, it's an anchor.

SLS development is taking way too long, and cost way too much. Cost estimate for Mars Direct was $20 billion in 1990 dollars for research, development, construction of infrastructure, and the first mission. Then $2 billion per mission thereafter, with one mission every 26 months. That initial $20 billion would be spread over 8 years, so NASA could afford it. And that $20 billion included development of Ares. SLS block 2 is essentially Ares. How much has SLS alone cost?

But Orion is worst of all. It cost more than Apollo, but is essentially a redo of Apollo. Considering it isn't anything new, just redo of existing technology, why would it cost more? And to make matters worse, they only built the capsule and launch escape system. They ran out of money before developing the service module. They had to arrange a swap deal with Europe to provide theirs.

And we don't need Orion. If you want to go to the Moon, we have Dragon and CST-100. Both were competitors for the Crew Exploration Vehicle (CEV), intended to go to Lunar orbit and back. Dragon would need a service module instead of a trunk, and CST-100 would need a larger service module, but both were originally designed with them. We could use those to replace Orion.

But there are members of Congress who want to protect Orion. If you argue to scrap Orion, they will view you as the enemy, refuse everything you ask, and actively fight against you. So I have pointed out NASA could use a Mars habitat as a Moon base, Orion to deliver crew to Lunar orbit, and develop a small, light lunar lander similar to the Apollo LM. Of course I hope they would do so with Dragon or CST-100 instead, but give them the option of Orion just to appease those who want to champion Orion.

In year 2000, I pointed out military spending was $288 billion, NASA got $14 billion. In dollars of that day. Actually the budget request was $14.something, what they got was $13.5784 billion. I said if they could cut military spending by 10%, give half to NASA and use the other half for tax cuts. That would double NASA's budget. But they didn't. Once George W. got elected, he massively increased military. And that started in February 2001, right after his inauguration. It wasn't due to 9/11. Military and National Security spending in 2007 was $700 billion, in 2008 it was $799 billion, and in 2009 (first approved by Obama) it was $901 billion! And some people wonder why America is broke. They have trimmed it a bit; for 2016 it's $625 billion. The last year America had a balanced budget was year 2000. Bill Clinton claimed surpluses in 1998, 1999, and 2000. Reality is he raided the US federal government employee's pension fund. When you treat that as a loan that has to be repaid, 1998 and 1999 were still in deficit. In 2000 he raided the pension fund again, but the surplus was larger than what he took. After you reduce the surplus by that amount, the surplus in year 2000 was so pitifully puny it was practically non-existent. But at least the budget was balanced. So part of my argument is that year's budget has to be used as the example. Converting that year's military budget to 2015 dollars (inflation calculator doesn't go to 2016 yet) you get $396.4 billion. That's what military spending should be. If you did that, you could afford to increase NASA's budget. But there are Republicans who don't want to touch the military budget, so good luck with that.

kbd512 · 2016-02-01 14:28:56

RobertDyck wrote:

A free return trajectory is designed deliberately that you don't need propellant. You launch the spacecraft into a trajectory where it will loop around your intended target (Moon or Mars), not stop, and return directly back to Earth. Entering orbit requires expending energy to get out of the free return trajectory. That can be done with propulsion, or aerocapture. Apollo used this to go to the Moon, and its good that they did. It was used for Apollo 13. A 6 month transit to Mars does the same thing, that's one reason you don't want to go faster. Any faster and you don't get free return. So if an Apollo 13 style failure occurs, you continue to drift past Mars, and the gravity of Mars itself redirects your path (trajectory) to return to Earth. That's why it's called "free".
Not my idea. Apollo already did this. And Robert Zubrin has argued for a free return trajectory for Mars. I just think it's a good idea.

Are any course corrections required on the free return trajectory?

What's the mass differential between heat shield material required to survive aerocapture vs propulsive capture?

If the ITV loses power, does the surface habitat have backup avionics and solar panels to provide power?

There are three events I can think of that would require permanent abandonment of the ITV:

1. Irreparable damage from space debris

2. Fire from batteries or electrical equipment

3. Damage from an explosion in the ACS/RCS that punctures the ITV or severs power/cooling

RobertDyck wrote:

If you want to help flesh it out, please do. But that means helping, not trying to trash the plan.

I'm not trying to trash your plan. I don't think Falcon Heavy can lift a TMI stage large enough to throw your stack to Mars. I can't figure this out until I know the mass of the ITV, surface habitat, and capsule. What type of propellants and engines will the TMI stage use?

RobertDyck wrote:

My plan pre-lands the MAV. Direct launch from Earth surface to Mars surface. The MAV uses ISPP, and launches with extra propellant so it will be the TEI stage. No on-orbit propellant transfer. Instead the MAV just docks to the ITV, and when they're ready to depart the MAV fires its engine to push the ITV into trans-Earth trajectory.

Only the ITV and capsule are leaving Mars, right?

RobertDyck wrote:

The laboratory with pressurized rover is also pre-landed. Again direct launch from Earth surface to Mars surface. No stop in Earth orbit.

Ok.

RobertDyck wrote:

The ITV is launched to LEO. Then the surface habitat is launched and docked to the ITV. The TMI stage is launched and docked to the stack. Then crew is delivered via capsule. You could dock a capsule to act as an emergency escape pod, then launch crew separately. Or just use the capsule to deliver crew. The simplest solution is to launch crew in a Dragon, dock it to the stack. The Dragon will remain docked to Mars orbit, and all the way back to Earth orbit. When the ITV docks with ISS, the Dragon will still be attached. At that point you can either leave it attached for the next mission, and return crew with some other vehicle, or just return crew with that Dragon. If you use Dragon for return, then the next mission will need a fresh Dragon.

This ITV and surface habitat will be at least 60t. Dragon 2's dry mass is 4.2t. I don't know what its wet mass is, but let's call it 7t to be safe because we're gonna pack that sucker if we take it with us. That's 67t. Falcon Heavy can deliver 13t to Mars. Am I missing something?

RobertDyck wrote:

Note the TEI stage is not docked when crew depart Earth orbit. TEI is done with the MAV, which is pre-landed on Mars.

Good.

louis · 2016-02-02 04:49:26

If anyone wants to post a mission design against the categories in this doc I set up

https://www.docdroid.net/137mm/mars-mis … f.pdf.html

...then just set the details out against the listed categories (first column) and I will update the doc.

Last edited by louis (2016-02-02 04:53:01)

SpaceNut · 2016-02-02 17:46:48

Is there a way to solve the spiral out speed that the ion will be at when its at L1 for the crew to try and catch it to link up with as its not stationary. If its stationary its of no difference for fuel use for crew, only the total ship would change by the amount of the ion section which had been used to push it from earth to L1 versus just directly leave from earth orbit....

kbd512 · 2016-02-02 18:41:36

SpaceNut wrote:

Is there a way to solve the spiral out speed that the ion will be at when its at L1 for the crew to try and catch it to link up with as its not stationary. If its stationary its of no difference for fuel use for crew, only the total ship would change by the amount of the ion section which had been used to push it from earth to L1 versus just directly leave from earth orbit....

Combined SEP and chemical kick is more than sufficient for Mars.

There are ways to minimize transfer energy using so-called halo orbits and ballistic capture. Hohmann transfers are really expensive in terms of dV requirements, but well understood and easy to do from a technical perspective.

A LEO Hohmann transfer for the weight class representative of any realistic MTV requires super heavy lift or fuel depots and there's no way around that. Heavy lift and chemical propulsion work, but only from a higher orbit than LEO. That's why SEP tugs are so important for affordability.

Ship your cargo to Mars using SEP tugs and ship your MTV and chemical kick stage to L1 using SEP tugs.

SpaceNut · 2016-02-02 19:30:46

ION drive spiral to L1 calculation search located several papers on moving cargo to L1 and its not fast.....

SOLAR ELECTRIC PROPULSION VEHICLE DESIGN STUDY FOR CARGO TRANSFER TO EARTH-MOON L1

mass of approximately 36 metric tons from Low Earth Orbit to the first Earth-Moon libration point (LL1) within 270 days.

Concept Design of High Power Solar Electric Propulsion Vehicles for Human Exploration paper describes the unique challenges associated with developing a large-scale high-power (300-kWe class) SEP vehicle and design concepts that have potential to meet those challenges.

Spiral Transfer

Solar Electric Propulsion Demonstration Mission Trajectory Solar Electric Propulsion Demonstration Mission Trajectory

The Design of a 4-Gridded Ion Engine for the Deployment of a EM-L1 Space Harbor

kbd512 · 2016-02-02 20:36:32

SpaceNut,

With my architecture you need to be ready to launch a year ahead of time. There are trade-offs with every architecture. I traded some simplicity and some lead time to permit use of commodity heavy lift launch vehicles like Falcon Heavy and Vulcan. The launch costs and technology development costs are well within NASA's existing budget.

No technology development programs are required that are not already on NASA's critical path for manned Mars exploration. In other words, the architecture is workable because it uses existing launch vehicles and existing technology development programs to maximize ROI on tech that NASA has already heavily invested in.

Apart from the MTV, there is no orbital assembly of any other mission component. The MTV is mated to the TMI at L1 for the outbound trip and then mated to the TEI at LMO for the return trip. That's the extent of orbital assembly required by my architecture. Note that my MTV design is not required for my architecture. Substitute NASA's DSH or an inflatable habitat and the overall architecture still works.

No super heavy lift is required. It's really nice to have so you can depart from LEO, but certainly not required.

kbd512 · 2016-02-03 00:03:07

louis,

Affordable Human Exploration of Mars Program

MISSION SIZE: 4 Astronauts per mission

PRE-MISSION CONTENT:

Three Phased 5 Year Development and Demonstration Programs:

Phase I:

Deep Space Habitat (DSH) with Artificial Gravity (AG)

Closed-Loop Environmental Control and Life Support System (CL-ECLSS)

High Efficiency Solar Cell and Battery Systems

Passive Radiation Shielding System (PRSS)

Phase II:

SEP Cargo Transfer Vehicle (SEP-CTV)

SEP Integrated Transfer Vehicle (SEP-ITV)

Mars Surface Habitat (MSH)

Adaptable Deployable Entry and Placement Technology (ADEPT)

Phase III:

Trans-Mars Injection (TMI) and Trans-Earth Injection (TEI) Kick Stages

Mars Descent Vehicle (MDV) / Mars Ascent Vehicle (MAV)

Active Radiation Shielding System (ARSS)

Mechanical Counter-Pressure Space (MCP) Suits

LAUNCH:

Phase I Demonstrators:

DSH-1 (LEO)

DSH-2 (L1)

Phase 2 Demonstrators:

CTV-1 (150kW-class SEP 30t cargo transfer of 1 MSH using ADEPT for aerocapture and reentry)

Phase 3 Demonstrators:

CTV-2 (150kW-class SEP 40t cargo transfer of 1 TEI stage to LMO)

CTV-3 (150kW-class SEP 30t cargo transfer of 1 MAV to Mars using ADEPT for aerocapture and reentry)

DSH-3 (tele-robotically operated DSH-ITV equipped with ARSS transfers to Mars using TMI stage, captures in LMO, tele-robotically operated MAV simulates transfer of crew after completion of surface missions, CTV-2 mates TEI stage to DSH-3, transfers to Earth using TEI stage, and captures at L1)

TRANSIT TO MARS:

7 Month transfer to Mars using chemical kick stage followed by DSH-ITV spiral in to LMO

TRANSIT FROM MARS:

7 Month transfer to Earth using chemical kick stage followed by DSH-ITVE spiral in to L1

ENTRY, DESCENT, LANDING:

3t MDV (pressurized MAV without fuel tanks and engines for ascent) transferred to Mars using SEP-CTV, docked to DSH-ITV for crew transfer after DSH-ITV arrives in LMO, and landed using ADEPT / super-sonic parachute / retro-rocket

ASCENT:

15t pressurized MAV transferred to Mars using SEP-CTV and landed using ADEPT / super-sonic parachute / retro-rocket

RETURN:

MAV docked to DSH-ITV for crew transfer, TEI mated to DSH-ITV, capture at L1 using SEP

ENERGY AND LIFE SUPPORT:

DSH-ITV uses solar panels for power

DSH-ITV is equipped with next-generation CL-ECLSS, intended to replace current ECLSS on ISS, for life support

MSH uses solar panels for power

MSH equipped with next-generation CL-ECLSS, intended to replace current ECLSS on ISS, for life support

MSH equipped with oxygen generation demonstrator

MSH equipped with Martian regolith water extraction demonstrator

MISSION CONTENT:

Focuses on technology development that maximizes use of critical path technologies already identified by NASA for human exploration of Mars

Directs funding towards payload, rather than launch vehicle development

Sacrifices some measure of simplicity to avoid further launch vehicle development

Permits sustainability initiatives (ISRU and ISPP) for permanent habitability of Mars, but does not rely on sustainability to land humans on Mars

Intended to achieve the goal of landing humans on Mars for surface exploration, not colonization

Each major mission hardware component has a replacement as backup

Uses commercial launch services and capsules for affordability

COST/INCOME:

This plan requires present levels of funding for NASA. Each 5 year technology development phase spreads the cost of research, development, and demonstration as evenly as possible, given the logical horse/cart requirements for achieving the ultimate goal of landing humans on Mars.

I put the development phase costs in the $50B to $75B range, over the course of 15 years. At the high end, that's 25% of NASA's budget. I think it's reasonable for NASA to devote a quarter of their budget towards a real space exploration program. NASA has repeatedly said that Mars is the prize. I say it's long past time for them to put their money where their mouth is.

OTHER ASPECTS:

I think it's reasonable to orbit a constellation of advanced TDRS and GPS satellites over a planet we intend to make our own. Obviously there's quite a ways to go to establishing an infrastructure required to colonize Mars, but the first steps have to be taken and must be taken by our government.

Subsequent missions can land advanced pressurized rovers for mobile surface exploration and various sustainability experiments, but the first order of business is to simply prove that we can get there and come back. This mission architecture is intended to do that and nothing further.

louis,

If you require launch schedules that include launch vehicle and payload descriptions, mission objectives, etc, please let me know.

SpaceNut · 2017-03-06 20:54:38

I knew we had a topic with kbd512's work for mission elements with in it so here are the posts for turning the cygnus into a mars surface habitat for a minimal design crew mission.

kbd512 wrote:

GW,
IRVE-3 used rotation for stability and cold-gas RCS for attitude control at the entry interface. Spinning humans may not work so well. MSL used spin for stability and RCS for attitude control. Could spin negate or lessen the RCS requirement, or is that a bad idea?
A new method for HIAD control NASA is working on is called the Cable-Controlled Aeroshell Deceleration System (CCADS). It is intended to provide coarse and fine HIAD flight control during descent by varying L/D to adjust cross-range, a concept much like using the body flap on the orbiter to adjust aerodynamic lift (CCADS basically uses cables to "pinch" the HIAD):
CCADS Presentation
CCADS Technical Paper Final Draft
The "HEART Flight Test Overview" report said shallow angles of attack (10 degrees or less) negated the requirement for thermal protection of the exposed portion of the Cygnus. Is that an error with the Thermal Desktop heating model used to determine peak heating or is that possible? The CCADS flight profile uses entry angles greater than 10 degrees. Is it possible to use a 10 degree or less followed by actuation of CCADS to increase lift and establish a more horizontal glide path to the ground?
The computer models indicate that HIAD (no parachutes or CCADS) is subsonic at 15km, but then velocity is nearly constant between .3km/s and .2km/s all the way to the ground. There is virtually no deceleration from .2km/s at approximately 5km. Apparently, high subsonic flight speeds are required to generate lift. CCADS lengthens flight duration considerably, permitting astronauts to actually "fly" Cygnus to a landing target, but it's either traveling at .2km/s or it ceases to generate lift and subsequently falls out of the sky.
A subsonic parachute and mortar system would weigh more than rocket engines and propellant with .25km/s dV. I give up. There's no better way to do this.
My proposed propulsion module is mounted atop Cygnus over the docking ring since HIAD is on the bottom. It has 8 MR-80C's (AeroJet-Rocketdyne MR-80B's modified to use HAN / AF-M315E monopropellant) for retro-propulsion and 16 MR-104D'S (AeroJet-Rocketdyne MR-104C's modified to use HAN / AF-M315E monopropellant) for attitude control. Isp (vac) for MR-80C and MR-104D is presumed to be 250s. AF-M315E's density is 1.47g/cm^3. A US gallon of AF-M315E weighs approximately 12.26774lbs, so 450kg of the stuff is slightly less than 81 gallons. My retro-propulsion engines are radially mounted over the docking ring in a sort of "nosecone" for the Cygnus PCM (a misnomer since Cygnus is traveling base forward throughout EDL).
Notes:
1. Cygnus won't fly aboard Antares, thus no requirement for the structure to withstand 8.5g peak acceleration, so it'll be a bit lighter
2. HIAD is separated just prior to retro-propulsion and Cygnus becomes 1,000kg lighter
3. RCS module is permanently attached to Cygnus, but hinged so the crew can ingress / egress through the PCM's top hatch
4. Cygnus is modified with the addition of a bottom hatch for normal ingress / egress on the surface of Mars
5. Solar panels for surface power are stowed inside Cygnus and manually attached by the crew to the top hatch
6. Cygnus landing gear consists of composite struts with small wheels containing electric hub motors for 2.5km/h max speed
7. Cygnus lands several kilometers from the ascent stage to avoid potentially damaging the ascent stage during retro-propulsion
8. Consumables mass assumes the crew consists of 1 average man and 1 average woman
9. Service Module provides power and propulsion for transit
10. Apart from providing transit power and mid-course correction burns, the primary purpose of the service module is to decelerate the PCM approximately 1km/s just prior to reentry, at which point in time it detaches from the PCM
11. My previous mass estimates for a scaled-up HIAD were used for the ascent stage. Mass was greater because the ascent stage has a greater mass. I mistakenly added that mass to the Cygnus reentry mass. My Cygnus PCM is within the 5600kg limit imposed by the HEART HIAD precursor mission design.
12. Cygnus is positioned atop the ascent stage
13. Ascent Stage uses 4 AeroJet-Rocketdyne AJ10-190's (the uprated OMS-E / OME engine developed for Orion); essentially a reprise of MIT's Scott Alan Geels Mars Ascent Vehicle, 4.2km/s dV (accounts for drag and gravity losses); requires a 10% or less inert mass fraction; nearly maxes out Falcon Heavy's throw capability, requiring 13t to TMI
14. Earth Return Stage uses 1 AeroJet-Rocketdyne AJ10-190 (the uprated OMS-E / OME engine developed for Orion)
15. Consumables and HIAD #2 for Earth return are delivered with the Earth Return Stage (some assembly required)
Mass Estimates:
Service Module (1 AeroJet RocketDyne AJ10-190): 4,750kg
Gross Reentry Mass: 5,250kg
HIAD: 1,000kg
Cygnus PCM gross mass (reentry; includes RCS module): 4,250kg
Cygnus PCM (structure, avionics, life support - CAMRAS / MOXIE / IWP, batteries, solar arrays for surface power): 1,650kg
Consumables (food and water): 1,850kg
Astronauts (we're sending small people to Mars): 150kg
RCS Module: (450kg HAN, 68kg for 8 MR-80C, 30kg for 16 MR-104D, 52kg for structures): 600kg
Well, there it is. It's quite minimalist, but it should get the job done. I would feel better about this if there was another Cygnus loaded with consumables and parked in the landing area. A Mars orbital station like Lockheed-Martin's Mars Base Camp would be nice, too. All the Falcon Heavy payloads range from 11t to 13t. If I had 15t to work with, the mission hardware elements could be more robust. Unfortunately, 13.6t is all Falcon Heavy can deliver. C'est la vie.

SpaceNut · 2017-03-06 20:55:19

kbd512 wrote:

SpaceNut,
The article says they're using MR-80B (3100N) and MR-107U (275N) thrusters. MR-80C (3100N) and MR-104D (440N) are thrusters I made up. They're notional variants of the MR-80B (3100N) and MR-104C (440N), both of which are real flight hardware, that have been modified to use materials compatible with the slightly acidic HAN (AF-M315E) monopropellant.
* HAN monopropellant thrusters do not use double valves as do thrusters using N2H4 / hydrazine (MR-80B and MR-104C are examples thereof) use. HAN requires high temperature catalyst beds (200C to 300C) compared to hydrazine (100C to 150C), and thus more electrical power, to decompose the propellant. Hydrazine will start to decompose purely as a function of contacting the catalyst bed, although Isp will be lower without pre-heating. The switch to single valves for HAN-fueled thrusters is principally a characteristic of the high heat requirement to facilitate propellant decomposition. Simply put, propellant leaking through the feed valve won't fire the thruster without a hot catalyst bed. HAN is also less likely to decompose in hot propellant feed lines connected directly to the thruster, compared to hydrazine. This simplifies the propellant feed system.
* HAN does not require continuous heating of the propellant tanks and feed lines. It has a glass transition temperature, but doesn't freeze like hydrazine will if it gets too cold during the deep space transit. Basically, you heat the tanks and feed lines when you intend to use the thrusters.
* AF-M315E (a trade name for a specific HydroxlAmmonium Nitrate or HAN blend / formulation developed by Air Force Research Laboratory or AFRL and AeroJet-Rocketdyne) monopropellant is comparatively non-toxic to humans, in relation to hydrazine. That is another reason for the simplified propellant feed system. Spills or leaks are not events that pose immediate danger to human health during propellant handling. For comparison, a gasoline spill is more hazardous to your health and a hydrazine spill would seriously injure or kill you without protection.

kbd512 wrote:

Further notes:
16. The Cygnus PCM has 4 variable length (extendible) landing legs attached to steel wire wheels that can caster. Each wheel hub has a small electric motor so the PCM can move at low speeds. This is how the Cygnus PCM is mated to the Earth return stage. The PCM drives over to the Earth return stage after landing, extends the legs to raise the PCM above the upper stage, and then rotates about its axis to lock the PCM in place.
17. The empty RCS module stays attached to Cygnus during ascent because it is later required during Earth return to stabilize the Cygnus PCM during Earth reentry. After the Cygnus PCM ascends to Mars orbit using the ascent stage, they have a series of three spacewalks to perform to prep their Cygnus PCM for Earth return.
Space Walk I - Transfer food and water from the Earth Return Stage to the Cygnus PCM
Space Walk II - Refill the empty HAN and GN2 tanks using tanks integrated into the Earth Return Stage
Space Walk III - Attach a new HIAD to the Cygnus PCM for Earth reentry
18. The Earth reentry HIAD is specifically designed for that purpose. All HIAD's have to be constructed specifically for their intended payload mass. It's the same basic technology set and materials, but different donut sizes, material thickness, or material layers. An Earth reentry HIAD may have five layers of thermally protective fabric whereas a Mars reentry HIAD may only have three layers.
19. If SLS and SEP can deliver Lockheed-Martin's Mars orbital station, better known as Mars Base Camp, to LMO, then the spacewalks are performed while the crew stay aboard the space station in Mars orbit. There will be 2 to 4 crews (4 to 8 astronauts) loading supplies at the same time, so an ISS node module with 4 docking ports and an ISS MPLM module to store consumables is the bare minimum required to service 4 Cygnus PCM's. An ISS node module and ISS Destiny (lab habitat) module is more realistic.
20. 1g artificial gravity is provided on the departure flight by tethering off to the expended upper stage. Artificial gravity may or may not be practical for Earth return. The PCM really needs to stay solidly attached to the Earth return stage because that stage is responsible for slowing the PCM just prior to reentry. If that fails, you get BBQ'd during reentry and that's not a good way to end an otherwise successful mission.
21. If NASA is willing to give up 30 to 60 days of surface time by spiraling into LMO using SEP and/or spiraling into LEO using SEP, then reentry velocities drop substantially. If that Mars orbital station ever materializes, it's a good place to inspect PCM's prior to committing to a reentry. If I was an astronaut, I'd want to determine whether or not my PCM, RCS, and HIAD modules were in good working order after my trip through interplanetary space.
22. Using SEP to spiral into both LMO and LEO, I eliminate the requirement to attach a second HIAD to the Cygnus PCM. The RCS tank still requires a refill. The food and water still require replenishment prior to Earth return. Upon Earth return, the PCM's dock at ISS for samples offload, crew de-briefing, and return to their respective countries along with astronauts from ISS. The Americans and Canadians return to America aboard Dragon V2, the Asians return to China aboard Shenzhou (assuming they participate; they seem to be more interested in the moon), and the Europeans and Russians return to Kazakhstan aboard PTK NP. There is no need to store NTO/MMH in the PCM service module or the Earth Return Stage, either. HAN and SEP are sufficient for all mission requirements except the Mars ascent. NTO/MMH, as dangerous as they are, are required by the Mars Ascent Stage to achieve sufficient Isp so that a single Falcon Heavy can deliver the stage to Mars.

SpaceNut · 2017-03-06 20:57:45

Question would the canted draco engine mounting benefit for this engine or is there enough clearence for the surface profiles.....

kbd512 · 2017-03-07 12:59:11

SpaceNut,

Draco and SuperDraco both use NTO/MMH. This bi-propellant combination produces higher Isp than HAN monopropellant alone. The poor vacuum performance is probably due to under-expanded nozzles. The expansion ratio looks like it's optimized for throttling at sea level, probably because it was intended as a launch escape system. However, I'd get a real rocket scientist like GW to confirm that.

SuperDraco is regeneratively-cooled, so if 2 SuperDracos weigh less than 4 uprated AJ10-190, then my ascent stage could use SuperDracos instead of AJ10-190's. It would produce even more thrust (32,000lbf for 2 SuperDracos to 30,000lbf for 4 uprated AJ10-190's). With two properly expanded SuperDraco's producing a 316s or better Isp, assuming two SuperDracos weigh less than 400kg, the inert mass fraction of the tankage and feed system can rise to something inline with commonly used materials.

GW Johnson · 2017-03-07 17:59:02

What you need is a theoretical c* velocity from a thermochemical code at your intended chamber pressure. Then you knock it down slightly by a c*-efficiency factor that reflects reaction completeness in your engine at its operating L*. This c*-efficiency is entirely an empirical thing coming from test data. As knocked down, that's your operating c*.

The same thermochem code tells you what your gas specific heat ratio is (gamma). You need that to determine thrust coefficient at your chamber pressure and whatever backpressure exists. It is a function of that backpressure, coming from F = mdot V + (Pexpanded - Pback)Aexit. Thrust maximizes when Pexit = Pback, obviously. As you climb in altitude, Pback reduces. Pexpanded is a fixed ratio to whatever chamber pressure you are using.

When Pexpanded - Pback is positive, thrust is higher for the same wdot V term, but you could have expanded further (to higher V) to actually optimize things. We call that condition underexpanded. When Pexpanded - Pback is negative, thrust is reduced for the same wdot V term. You need less expansion ratio to increase thrust back to optimal, but it will cost you V. We call that condition overexpanded.

But there is a max Pback limit that causes shockdown flow separation in the exit bell (which just absolutely kills your thrust!). That can be approximated, but not predicted precisely. It is a risk if you are too overexpanded. Being underexpanded is no risk, it just means you get a little less thrust than you could possibly have. Which is why launch vehicle engines have nozzles sized for sea level perfect expansion and max thrust (when the weight to be lifted is maximum), and then operate increasingly underexpanded as the vehicle rises. Thrust increases as they climb, but not all the way to ideal values.

Nozzles that operate in vacuum have much larger expansion bells for much higher V. You cannot expand all the way down to vacuum as the exit Pexpanded, because the device would be of infinite size! You must fit within physical dimension limits of your vehicle. There are NO "perfect-vacuum-expansion" designs, only designs that fit certain dimensional constraints.

Tables and charts exist which have thrust coefficients CF reflecting these phenomena. These usually include the nozzle kinetic energy efficiency (which reflects bell expansion half angle). They are usually available for this or that gamma (specific heat ratio). F = Pc At CF, where Pc = chamber pressure and At = throat area.

Without belaboring derivations, ideally CF c* /g = Isp, except for engine cycle effects! To get those, you calculate ideal chamber-nozzle wdot = Pc At g / c* (where g is the gravity constant that makes units consistent, not an actual acceleration of gravity). Isp = F/wdot as a definition, but you need to add some extra wdot to your ideal amount, to reflect the bled-off massflow that operates your propellant turbopumps. That's how your engine cycle gets into it, really. Turbopump bleeds inherently reduce Isp, because you must inherently flow more propellants than what creates the nozzle thrust forces.

Reported sea level Isp data usually does not reflect engine cycle losses, and usually does not have the nozzle kinetic energy efficiency figured into CF. Reported vacuum Isp data lacks cycle losses, lacks nozzle efficiency, and usually they never tell you what expansion ratio they really used, which is utterly crucial to CF. So beware of other people's Isp. It's usually one or another sort of lie.

Does that help? I hope?

GW

Last edited by GW Johnson (2017-03-07 18:17:05)

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Kbd512's human mission design for Mars

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