Yet another Mars architecture

GW Johnson · 2015-05-31 15:37:13

I get very frustrated with NASA and Congress and a whole succession of Presidents myself. It has motivated me to learn some cuss words in Chinese, for use when English just isn't enough.

When I was a young boy, they were still flying the X-1, the X-2, and the D-552 phase 2 Skyrocket, and the F-100 Super Sabre was entering service. The X-15 came later. The lifting bodies, later still. I watched every launch from the very first Mercury flight, but I was actually more impressed with the suborbital X-15 than I was the suborbital Mercury-Redstone.

I do remember the promise of going to Mars. As I recall it was booked for the 1983 opposition at the time of the first moon landings. By the time Apollo was cancelled in the middle of the moon landings, it had been pushed back to the 1987 opposition. Knowing what we know today, I think what they had in mind then would have killed a crew.

But we have since come to know enough, to know what a manned expedition must have, since about 1995. That's 20 years ago! They don't want to go until the late 2030's, if at all, and are behaving as if they do not want to go at all, period.

And that is what frustrates me, because NASA has been and still is doing almost none of the things we now know that we must have. You'd think they would have learned about the expense of dead crews by now, after one Apollo crew and 2 Shuttle crews. But they cannot even summon the gumption to tell a technically (and many other ways) incompetent Congress to quit micromanaging projects.

The odds are getting high that I will not live to see a Mars expedition before I die. I will be 88 in 2038. Quality of life and quality of medical care is now falling in the US. My dad made it to 88, but I doubt I will.

As for my mission design, it was a permutation upon the 1950's proposal from Von Braun and Ernst Stuhlinger. They had proposed a fleet of 6 orbit-to-orbit transports powered by "cesium ion thrusters", with one-shot hydrazine-NTO-powered two-stage landing rockets. The idea was to land and explore 6 different sites, even then. I wouldn't do it exactly that way for many very good reasons, after 60 years of technology advance.

But I do like the orbit-to-orbit transport idea, and I think I'd add electric propulsion to speed transits after a conventional-rocket getaway (and capture). If you plan on aerocapture, you must have a proper aerodynamic heat shield, and that adds inert mass directly and indirectly, so I don't usually include that notion.

I send my landers separately, and let them push their own refueling supplies to Mars. I'd let them push the return propellant too, except that I worry about failed rendezvous in LMO. So my manned vehicle packs all the propellant to return, as a suspenders-and-belt safety item. There is no rescue outside LEO, except self-rescue. You HAVE to plan for that.

Single-stage chemical looks better with LOX-LH2 masswise, but storability of LH2 is a lot worse than storability of LOX. For the designs I looked at, there wasn't a lot of difference between LOX-kerosene and LOX-methane. Both were better than hydrazine-NTO, and worse than LOX-LH2.

My vehicles sized out around 60-70 tons to land a 3-4 ton deadhead payload on Mars from LMO, and return to LMO without refueling. But, I was trying to be conservative with my inerts, in order to make reusability a credible item. I wanted to send 3 landers and make anywhere from 6 to 18 landings with them.

The total lander height is no greater than the landing leg span, for stability on rough ground. Heat shields were 10-15 m diameter, conical vehicle form. There's a huge cargo deck volume available to pressurize for living space, once you land and unload. So I didn't need any other hab but the landing boat.

It's still a rough plan, and needs a lot of work yet.

GW

RobertDyck · 2015-05-31 17:36:50

From what you say, you're 13 years older than me. I only saw the last 2 missions of Mercury because I wasn't borne before that. I saw the first as a baby, with my mother. I had forgotten details of Mercury, but the movie "The Right Stuff" brought old memories back.

My grandparents died at 92, 94, 86, and I forget the age of my paternal grandfather. I keep hoping my mother will live longer, both my parents are showing their age. We hear of medical issues up here in Canada. An American diagnosed with Cancer chose to kill himself by running his car in his closed garage, so his family wouldn't have to pay medical bills. That's disturbing. Our medical system in Canada isn't perfect, but at least you don't have to kill yourself. I'm getting depressed at the number of friends I've lost. One was just 70, but got pancreatic cancer. By the time doctors diagnose that, it's too late. I watched him slowly whither away over a year. Another was depressed, but self-prescribed anti-anxiety pills. I looked up that pill, warnings on the internet were dire: never take more than one per day, and never take it for more than a year. Over doing it can kill you. I warned him many times, but he got a supply "under the table". After taking 3 pills per day for 3 years, he died. I met one man at Toastmasters, barely got to know him, but he had a condition doctors said was inoperable. I thought they could operate, but just didn't want to due to his obesity. Another friend was conically tired, living on long-term disability. Someone I met where I volunteer, became a good friend. His condition became acute. Turned out to be sclerosis of the liver, even though he never touched a drop of alcohol in his life. He couldn't in his adult life; even the smell of alcohol made him ill. A symptom of his condition. Doctors didn't want to believe it was sclerosis until he was dying, so did nothing until it was too late. His doctor tried to schedule a liver transplant, but he died. I'm running out of friends. Most of those listed are older than myself, but the last guy was my age.

The long weekend of May 15-17 was Keycon, the local science fiction convention. I always give a presentation about Mars or real space exploration. This year so many people had not seen my Mars presentation I gave an overview of Mars mission plans. And the convention brought a professional astronomer in from the UK. He asked me to debate him; he called it "primates in tin cans in space". He argued against humans in space. He didn't know who I am; I busted him up. One point he made was that humans cannot survive in space, we would require massive genetic modification. Ah hem! Apollo. ISS. Most people don't realize an MCP spacesuit is enough. I raise this because some seriously argue against humans in space. This scientist is an astronomer, his argument was everything is telescopes. I argued there's more reasons to go into space than science. Extending humans to another planet in case of an asteroid like the one that killed the dinosaurs. And profit from mining metal asteroids for precious metals. He was set back by that. I think there are scientists seriously trying to sabotage human space efforts because they see everything as science, and their idea of science can be done with robotic probes from JPL.

kbd512 · 2015-05-31 19:38:55

RobertDyck wrote:

My comments were strongly worded, but I'm quite frustrated. NASA promised a human mission to Mars would depart Earth in 1981. We got a Space Shuttle instead. That was nice, but not a mission to Mars. Then President George H. W. Bush made his announcement in 1989. NASA asked for everything under the sun, with a price tag Congress would not approve. That killed that. Since we've seen various obstacles, and estimates for Mars keep moving farther into the future. I want to see it in my lifetime. I watched the last 2 missions of Mercury live as they happened, on TV. I watched the entire space program since. I'm beginning to feel I won't see a human mission to Mars in my life.
Yes, Robert Zubrin's idea for ISPP uses local air only. Nothing more. Production is quite slow, but it's finished before astronauts leave Earth. That's the beauty of his system. One reason I want to keep that design in any updated mission plan. Because ERV or MAV propellant tanks are verified before astronauts leave Earth, you don't need anything more than one demonstrator. Some people have argued for using Mars permafrost or ground ice as source material for ISPP. But that has all the issues you raise. I argue for Robert Zubrin's system because it uses just air, which is the same across the planet, so only one unmanned demonstrator is needed. And it's simpler. No digging or melting or filtering, just an atmosphere inlet.
You keep raising retropropulsion. I'm not convinced it's necessary. I cited a study by the ADEPT team that showed parachutes still are the lowest total launch mass. And they do work. With large mass, the size of a Mars Direct ERV or Hab. Two catches to doing that: first aerocapture into Mars orbit, then land. Don't use direct entry. If you try direct entry with a large mass, then you get the problems you talk about. Second, a simple aeroshell is not good enough. It doesn't "catch enough air" so doesn't decelerate enough. Again, same problems you talk about. The solution is an umbrella style heat shield that does catch enough air to slow sufficiently, at high enough altitude, that parachutes can work. They calculated that a 23 metre diameter umbrella heat shield is necessary for the mass of a Mars Direct ERV or Hab. Note: the presentation Robert Zubrin and David Baker made in June 1990 included an umbrella heat shield with carbon fibre fabric, and was 23 metre diameter. Same material, same size, image that! And in the book "The Case For Mars", Robert Zubrin said David Baker designed that part. Let's give credit where credit is due, David Baker came up with a great design.

Rob,

Everyone but NASA seems to think that pursuing ISPP is an enabler for permanent or semi-permanent human presence on Mars. It's more about moving past the politically motivated BS than any real issue with the technology. The technology works, it's worked for more than a century, and there's no serious argument against using it that isn't motivated by spending inordinate amounts of money with whichever vendors profit from inefficiencies in the manned space exploration program.

The problem that GW addresses as it pertains to parachutes involves deployment. If the parachutes are large enough to slow the payload substantially, then the parachutes won't deploy properly because there's not enough "air" to force them open. This basically means you need a technology to force the parachute open, an inflatable ring around your ringsail might work- something I proposed doing although I'm sure someone else thought of it long before I did, or using parachutes in conjunction with retrorockets.

I think the parachute sizes required for soft landing 10t+ payloads would be impractical and retropropulsion of some kind would be required, even if only during the last few seconds of descent. If there is some method to employ parachutes with active deployment systems to soft land on Mars then that would reduce the mass, complexity, and development risks involved with the EDL solution.

I don't think that there are any perfect solutions to all the development challenges involved with doing the mission, but it also doesn't seem like there's any concerted effort from our space program to solve the technical problems, either. At this point, one thing's pretty certain. If we don't have a coordinated set of development programs to put humans on Mars and continuous focus on the objective, no matter which administration comes to office, we'll never get there. We're well into 2015, nearly a half century after mission planners started actively working towards the goal, and we're no closer now than we were in 1970.

SpaceNut · 2015-05-31 19:48:43

I think Nasa is missing the point on ISPP as its not just about fuel from the surround materials that are used and processed into what we need as it can also be the source for Oxygen, Water and so much more, Nasa needs to get the hint as to go without it; as it is not going to be much of a mission or more that one attempt....

Artificial gravity ok a must but spinning anything on the end of a cable is just not going to be the best method as we would be doing cable spinning here on Earth of the masses that we need the parts to be but that is part of the problem in that we do not have firm numbers for what that mass is....so how can we design the cable in the right way to meet the need.

RobertDyck · 2015-05-31 20:01:37

kbd512: I do get frustrated when I have to repeat myself. I understand that GW is concerned about parachute opening before impacting the surface. There are several aspects to this. First aeroshell slowing to speed appropriate to open the parachute. If you deploy the parachute while hypersonic, the fabric will tear or melt. Second is how quickly the parachute can open. How deep will the craft be in the atmosphere by the time the parachute reduces speed to terminal velocity? Will that happen before crashing into the surface? But all previous probes did this: Pathfinder, Phoenix, Spirit/Opportunity, and Curiosity. They proved you can do this. On the other hand, the Beagle 2 lander released by Europe's Mars Express orbiter demonstrated what can go wrong. They used an aeroshell optimized for the Huygen's probe for Titan. But Titan has an atmosphere 1.5 times as dense as Earth, while Mars is 0.7% as dense as Earth. The shape of the aeroshell has to be far more blunt. Beagle 2 opened it's parachute too low, and crashed before it could slow to safe speed. They found it.

Curiosity proved they can open a parachute for a large lander in Mars atmosphere. They still used direct entry, and a simple aeroshell. The landing system for ADEPT makes several changes. It aerocaptures into Mars orbit first, so when it does plunge into the atmosphere it's slower. Second it uses a parasol/umbrella that increases surface area. That ensures opening sequence for the parachute starts at higher altitude.

It will be tested by the ERV/MAV itself, prior to sending humans. I've argued for a Mars sample return mission to demonstrate ISPP. And an orbiter to enter Mars orbit via aerocapture to demonstrate that technology. Do you really think we need another technology demonstrator before sending an unmanned ERV or MAV? How about cargo landers, precision landed at the ERV/MAV landing site, sent before astronauts leave Earth.

But I'm getting into technical stuff again. I think we all agree that the technical stuff could have been solved in the 1990s. The problem is political will.

kbd512 · 2015-05-31 20:19:17

SpaceNut wrote:

I think Nasa is missing the point on ISPP as its not just about fuel from the surround materials that are used and processed into what we need as it can also be the source for Oxygen, Water and so much more, Nasa needs to get the hint as to go without it; as it is not going to be much of a mission or more that one attempt....

I sincerely hope they do "get it", but I doubt they ever will until they're forced to by some external entity- like a Congressman with two connected neurons who understands that not bringing absolutely everything with you saves railcars full of Benjamins.

SpaceNut wrote:

Artificial gravity ok a must but spinning anything on the end of a cable is just not going to be the best method as we would be doing cable spinning here on Earth of the masses that we need the parts to be but that is part of the problem in that we do not have firm numbers for what that mass is....so how can we design the cable in the right way to meet the need.

We do know what the minimum mass is for a mission, though. This isn't a major technical problem, it's simple math. My issue with the tethering solution to providing artificial gravity is what happens if the tether breaks or you lose attitude control. If you can't spin down, you have a major problem. A module rotating perpendicular to the direction of travel solves that problem. If there's ever a problem with the module's rotation or stabilization, you kill power to the motor that rotates the module and the problem resolves itself.

That said, I'm hoping and praying that "em drive" isn't some kind of experimental or measurement anomaly and that Lockheed really can make a fusion reactor the size of a small car. If we had that tech ready to fly in another ten years, our problems with propellant expenditures for attitude control and solar panel orientation for power go away. Then we can use simple tethers in conjunction with ISS modules to provide artificial gravity because we never run out of propellant or power for propulsion. Right now, it's wishful thinking. In another ten years, who knows?

kbd512 · 2015-05-31 20:48:02

RobertDyck wrote:

kbd512: I do get frustrated when I have to repeat myself. I understand that GW is concerned about parachute opening before impacting the surface. There are several aspects to this. First aeroshell slowing to speed appropriate to open the parachute. If you deploy the parachute while hypersonic, the fabric will tear or melt. Second is how quickly the parachute can open. How deep will the craft be in the atmosphere by the time the parachute reduces speed to terminal velocity? Will that happen before crashing into the surface? But all previous probes did this: Pathfinder, Phoenix, Spirit/Opportunity, and Curiosity. They proved you can do this. On the other hand, the Beagle 2 lander released by Europe's Mars Express orbiter demonstrated what can go wrong. They used an aeroshell optimized for the Huygen's probe for Titan. But Titan has an atmosphere 1.5 times as dense as Earth, while Mars is 0.7% as dense as Earth. The shape of the aeroshell has to be far more blunt. Beagle 2 opened it's parachute too low, and crashed before it could slow to safe speed. They found it.

Rob,

How much more will ADEPT lower the velocity of a payload in comparison to the rigid fixed geometry aeroshells currently in use?

RobertDyck wrote:

Curiosity proved they can open a parachute for a large lander in Mars atmosphere. They still used direct entry, and a simple aeroshell. The landing system for ADEPT makes several changes. It aerocaptures into Mars orbit first, so when it does plunge into the atmosphere it's slower. Second it uses a parasol/umbrella that increases surface area. That ensures opening sequence for the parachute starts at higher altitude.

Curiosity was landed using retropropulsion. I wonder why. Could it have been the parachute deployment issue that GW brought up?

RobertDyck wrote:

It will be tested by the ERV/MAV itself, prior to sending humans. I've argued for a Mars sample return mission to demonstrate ISPP. And an orbiter to enter Mars orbit via aerocapture to demonstrate that technology. Do you really think we need another technology demonstrator before sending an unmanned ERV or MAV? How about cargo landers, precision landed at the ERV/MAV landing site, sent before astronauts leave Earth.

Using retropropulsion and radio beacons, we could precision land vehicles in close proximity to each other on Mars. I think one ADEPT technology demonstrator should be landed on Mars. Ideally, it should be an ISS derived node module that has CL-ECLSS, spare suits, a rover, power, and an ISPP demonstrator to fuel Mars surface exploration vehicles. If it works, it's as much of a demonstration of Mars EDL and surface habitation tech that we require prior to sending humans.

RobertDyck wrote:

But I'm getting into technical stuff again. I think we all agree that the technical stuff could have been solved in the 1990s. The problem is political will.

Well, we still don't have ISPP, CL-ECLSS, and active radiation shielding in mid 2015. I think internal mis-management at NASA is the primary problem. Congress and the President may have their pet projects, but those named technologies are enablers for all manned space exploration missions and you'd think that after more than five decades of manned space flight that that tech would rate higher on the to-do list than new rockets or new spacecraft. It's still not a priority for NASA's management, as hard as that is to believe. When NASA's management puts its money where it's mouth is, I'll believe that something has changed.

RobertDyck · 2015-05-31 21:54:58

Here is video of Curiosity landing...
https://youtu.be/oNviFQpRvwQ

Notice the sequence: direct entry, aeroshell, parachute, landing rockets, wheels. Viking and Phoenix used landing legs with shock absorbers. Curiosity was suspended by cables from a skycrane, but finally landed on its wheels. So its wheels needed some suspension to absorb that final shock of touch down on the surface. The point is it *DOES* require a parachute. It isn't retropropulsion without a parachute. I'm saying a Mars Direct hab will do the same thing. With rockets built-in like the Apollo LM rather than a skycrane, so landing more line Viking or Phoenix, but still very much like this. Debris kicked up from the rocket exhaust will require a robust underside to the hab, able to withstand rocks kicked up into it. And the hab will use rockets around the periphery like the Curiosity skycrane, or Viking lander, rather than the single engine of Apollo.

RobertDyck · 2015-06-01 06:04:02

kbd512 wrote:

Well, we still don't have ISPP, CL-ECLSS, and active radiation shielding in mid 2015.

Robert Zubrin argued to go to Mars with life support available at that time. NASA wanted 95% closed oxygen and water recycling, but Robert Zubrin argued if we wait for that then it'll be the 21st century before we're ready to go! Well, it is the 21st century now. And I've argued that the system on ISS, with addition of just a few components, is enough.

Specific additions:
- zero-G shower and "sink" to wash hands. Skylab had a shower, and a "sink" that looks like a glove box. The water processing assembly on ISS is able to process wash water. All we need is something to collect wash water.
- toilet to recover moisture from solid human waste. I've already posted about this several times.
- direct CO2 electrolysis, to recover O2 from CO2 that can't be processed by Sabatier. Currently that CO2 is dumped in space. The ISPP Precursor on the Mars 2001 lander did that. That lander was rebuilt to become Phoenix. The ISPP Precursor was removed.
- methane pyrolysis to recover hydrogen from methane produced from the Sabatier. That hydrogen can be recycled into the Sabatier.
- laundry

louis · 2015-06-01 17:37:17

RobertDyck wrote:

kbd512 wrote:
Well, we still don't have ISPP, CL-ECLSS, and active radiation shielding in mid 2015.
Robert Zubrin argued to go to Mars with life support available at that time. NASA wanted 95% closed oxygen and water recycling, but Robert Zubrin argued if we wait for that then it'll be the 21st century before we're ready to go! Well, it is the 21st century now. And I've argued that the system on ISS, with addition of just a few components, is enough.
Specific additions:
- zero-G shower and "sink" to wash hands. Skylab had a shower, and a "sink" that looks like a glove box. The water processing assembly on ISS is able to process wash water. All we need is something to collect wash water.
- toilet to recover moisture from solid human waste. I've already posted about this several times.
- direct CO2 electrolysis, to recover O2 from CO2 that can't be processed by Sabatier. Currently that CO2 is dumped in space. The ISPP Precursor on the Mars 2001 lander did that. That lander was rebuilt to become Phoenix. The ISPP Precursor was removed.
- methane pyrolysis to recover hydrogen from methane produced from the Sabatier. That hydrogen can be recycled into the Sabatier.
- laundry

I thought hygiene is dealt mostly by moist wipes these days in space? A shower would be nice but that can wait till they get to Mars. We can ensure a tonne or more of water is pre-landed on Mars. With waste water processing, the amount of water needing to be carried could be pretty minimal for the transit flight - maybe less than a tonne on a 3 person flight. However we may need more water for use as a radiation barrier.

GW Johnson · 2015-06-01 18:07:52

The parachute thing has a lot of aspects to it.

There is opening the chute, for chutes big enough to have a subsonic terminal velocity in the thicker "air" close to the surface of Mars. I kind of like the idea of an inflatable structure to force the bigger chute open to lower that terminal velocity. But it cannot be too extreme an inflatable, as this still needs to be a ringsail geometry, if you expect it to survive opening at local Mach 2.5. Even on Mars the forces are too big to open such a chute at local Mach 3.

Coming out of hypersonics can leave you either very little or lots of time-to-impact, depending upon your ballistic coefficient, your path angle relative to horizontal, and the initial speed when you first entered sensible "air".

Curiosity in its aeroshell exceeded crudely 100 kg/sq.m ballistic coefficient, and needed some form of fairly significant retropropulsion in addition to its chute. The bizarre skycrane was just the way they chose to do that at min weight, needing only the rover and noting else to survive touchdown. The timeline was shorter than they liked, I remember what a "nail-biter" they claimed Curiosity's EDL sequence was. Bigger ballistic coefficient delays your deceleration pulse deeper into the atmosphere, closer to the ground. That's inherent.

Path angle does the same thing, steeper delays the deceleration pulse until deeper down, which is lower altitude. Inherent.

Higher speed at entry interface has the same effect. Faster means the deceleration pulse is delayed deeper, which is lower altitude. Again, inherent.

You "come out of hypersonics" at around Mach 3 local (on Mars at modest altitudes, about 2 km/s). Max chute opening is about Mach 2.5 even with the ringsail. You are past the big deceleration pulse, so your deceleration by drag on your aeroshell is quite modest once again, while your path angle is very rapidly steepening toward vertical downward. You will be at quite the low altitude by the time you reach a feasible chute deployment speed.

Once you open a chute (which takes at least a little time), it requires significantly yet more time to decelerate you at a rather modest rate to terminal speed, whatever that is. If you can open a chute in the 10-20 km range of altitudes like the earlier probes that were under 100 kg/sq.m did, you will be at some high subsonic terminal speed at a decent altitude like 5 km.

On the other hand, if you come out of hypersonics at low altitude like 5-10 km, you'll pretty much smack the ground while still supersonic, or maybe even before decelerating to a feasible chute opening speed. (Every mission is different in detail; I'm just trying to illuminate trends and physics here.)

That last is why I say that heavy objects with large ballistic coefficients (300+ kg/sq.m) need to use supersonic retropropulsion instead of worrying about chutes. You only have mere seconds left to impact, while still moving way too fast to deploy one.

Objects that use inflatables or foldables to lower ballistic coefficient will reach feasible chute speed at altitudes high enough to do some good. But those (and the small objects) still need either retropulsion or airbags to survive touchdown, because the chute terminal velocities are nearly always high subsonic. Just barely subsonic. Mach 1 at low altitude on Mars is about 0.7 km/s.

Airbags for landing (not car wrecks) are very high gee shock, so that's not feasible with men at all. They are feasible for only very shock-hardened gear like the Spirit and Opportunity rovers. Most equipment is not shock-hardened for 100+ gee. Hardening is very heavy.

So to me one option looks like something to lower ballistic coefficient (which might be light but still adds nonzero inert mass), followed by chutes, followed by a short terminal pulse of retropropulsion to touchdown. That would be for both men and for ordinary non-hardened gear unmanned. That's one limiting case.

The other option is leave out the low-ballistic coefficient gear and the chutes (saving their weights), but adding back in the weight of the extra propellants to do retropropulsion from the point you come out of hypersonics (or even earlier, if forced). That's the other limit: the plain rocket landing, just not all the way from orbit. Most of your deceleration delta-vee is the hypersonic pulse.

I honestly don't know which might be lighter, but I have a hunch they're really not very different in weight. Either could be made to work. I think the retropropulsion is techologically further along in development.

The other option is a mix-and-match somewhere between those two limit extremes. A bit of inflatable or foldable to your heat shield, followed by a chute that gets you down to about Mach 1, then some (serious) retropropulsion to survive the touchdown. You can even add a small pulse of retropropulsion to slow you from Mach 3 to max chute opening speed of Mach 2.5 more quickly.

So that's a lot of options, but they all involve retropropulsion at one or the other level, and at least as an aid to surviving touchdown. I really don't see a chute big enough to get an Earthly touchdown speed as something feasible on Mars. I can't rule that out, but it does seem rather unlikely to me.

A final note: Spacex is working retropropulsion in two scenarios (Falcon stage recovery and landing Dragon v2). ULA is not. NASA has ignored retropropulsion other than terminal touchdown applications, since 1960, when they ran some wind tunnel tests to find the effect a retro plume had on the drag of a Mercury capsule (it lowered drag).

GW

RobS · 2015-06-01 19:31:18

It seems to me, GW, that if one needs retropropulsion, unless one is sure the EDL mass is much more than an EDL including parachutes, one is better off eliminating the parachutes and keeping the system simpler. Why have two potential system failures when you can have one?

RobertDyck · 2015-06-02 06:18:25

On page 12 of this very discussion thread, I posted this:

Slide 6 for ADEPT has a little graphic to land on Mars, with 4 options to land 40 MT (assume metric tonnes) landed payload.
#1: 23m umbrella heat shield during aerocapture, then expand to 44m at transition between hyper- & supersonic, then subsonic retro-thrust. Finally terminal descent and landing. Total mass before entry: 90mT
#2: 33m aerocapture, remain 33m during hyper- & supersonic, begin retro-thrust at transition between super- & subsonic. Terminal descent and landing. Total mass: 87mT
#3: 23m aerocapture, remain 23m hyper- & supersonic, supersonic retrothrust. Terminal descent and landing. Total mass: 81mT
#4: 23m aerocapture, parachute opens supersonic, subsonic retrothrust. Terminal descent and landing. Total mass: 78mT

I could post links to NASA's ADEPT project. They go into excruciating detail about the stuff GW just posted about.

::Edit:: I found the presentation. There's a lot about ADEPT on the internet. Here's the the chart I referred to...
http://www.lpi.usra.edu/vexag/Nov2012/p … cinski.pdf

An interesting twist is use of the parasol ribs as landing legs...

Last edited by RobertDyck (2015-06-03 09:17:23)

SpaceNut · 2015-06-04 16:50:37

louis wrote:

RobertDyck wrote:
kbd512 wrote:
Well, we still don't have ISPP, CL-ECLSS, and active radiation shielding in mid 2015.
Robert Zubrin argued to go to Mars with life support available at that time. NASA wanted 95% closed oxygen and water recycling,
I've argued that the system on ISS, with addition of just a few components, is enough.
Specific additions:
- zero-G shower and "sink" to wash hands. Skylab had a shower, and a "sink" that looks like a glove box. The water processing assembly on ISS is able to process wash water. All we need is something to collect wash water.
- toilet to recover moisture from solid human waste. I've already posted about this several times.
- direct CO2 electrolysis, to recover O2 from CO2 that can't be processed by Sabatier. Currently that CO2 is dumped in space. The ISPP Precursor on the Mars 2001 lander did that. That lander was rebuilt to become Phoenix. The ISPP Precursor was removed.
- methane pyrolysis to recover hydrogen from methane produced from the Sabatier. That hydrogen can be recycled into the Sabatier.
- laundry
I thought hygiene is dealt mostly by moist wipes these days in space? A shower would be nice but that can wait till they get to Mars. We can ensure a tonne or more of water is pre-landed on Mars. With waste water processing, the amount of water needing to be carried could be pretty minimal for the transit flight - maybe less than a tonne on a 3 person flight. However we may need more water for use as a radiation barrier.

The trip out would benefit from recycling waste into returning fuel and if wipes gives the chance to take along less mass in the process all the better to do so on the out and return legs of the mission where it matters.

SpaceNut · 2015-06-04 20:04:29

Mars Rover Curiosity's Retro Parachute

MSL’s parachute is the main source of atmospheric drag. It’s a 64.7 foot (19.7 meter) disk-gap-band style chute deployed by a mortar. The main disk is a dome-shaped canopy with a hole in the top to relieve the air pressure. A gap below the main canopy also lets air vent out to prevent the canopy from rupturing. Under the gap is a fabric band designed to increase its lateral stability by controlling the direction of incoming air.

With Nasa working on another system to slow the craft in Mars atmosphere a Low-Density Supersonic Decelerator, or LDSD which seems to be targetting an even larger parachute that is being torn up on the way down.

GW Johnson · 2015-06-06 09:16:27

Rob S wrote:

"It seems to me, GW, that if one needs retropropulsion, unless one is sure the EDL mass is much more than an EDL including parachutes, one is better off eliminating the parachutes and keeping the system simpler. Why have two potential system failures when you can have one?"

That's exactly why I only looked at the all-retropropulsion option when I looked at reusable Mars landing boats. I used multiple engines to have the redundancy which multi-engine confers.

Besides, if the landers are reusable and you use chutes, you have to bring all the chutes for all the landings. They do not weigh zero.

I rather doubt that astronauts in clumsy full pressure suits can effectively repack very large chutes for reuse. That would be tough, even in an optimal MCP suit design. That's an example of indirect inert weight growth.

GW

RobertDyck · 2015-06-06 12:24:50

My mission plan calls for a habitat attached to the Interplanetary Transit Vehicle (ITV). Astronauts land in it. Once down, it never leaves the surface. That habitat is the beginning of a permanent human base. An MAV is pre-landed, unmanned. It produces propellant with ISPP, using Robert Zubrin's idea. Only when propellant tanks are full do astronauts leave Earth. The MAV docks to the ITV, and acts as the TEI stage. Once empty, it acts as counterweight for rotation, for artificial gravity. Upon approach to Earth, the tether is cut, discarding the MAV in space. The second mission can carry a second habitat, or just a landing capsule, but the ITV is reused. Propulsion stages are not. The second mission will start by pre-landing another MAV. The MAV lands only once. After launch from Mars, it never lands again, so no need to repack a parachute.

The MAV will use ISPP using Mars atmosphere only. No use of resources from Mars surface. Again, Robert Zubrin's idea as detailed in Mars Direct.

Long after the permanent base is established, surface resources will be characterized and utilized. Once a reliable means of delivering propellant to the ITV is established, then the expendable TEI stage can be replaced with a reusable stage. That means the tether will have to "reel it in" on approach to Mars. And the MAV will be replaced by a reusable rocket, a Mars shuttle. I had envisioned one based on DC-XA, but now that SpaceX is building reusable rockets, it would be one of theirs. Obviously a reusable land-on-tail rocket will not use a parachute. However, that's not for the first mission. That's after a reliable source of propellant is established, and reliable means to deliver it to the ITV. Propellant could come from Mars surface, or one of its moons. Definitely not for the first mission.

Multi-engine? Definitely! The Apollo LM descent stage used a single engine, embedded within the stage, and because there was only one it had to be in the centre. I argue a manned Mars lander would be more like the Curiosity propulsion stage: multiple engines around the periphery. Even Viking landers in the 1970s used multiple engines. For one thing, you want the crew lander to carry a rover. That requires a large storage area in the centre as garage. Curiosity had 2 engines on each corner, but only needed one on each corner. So every engine had a backup. Good idea, duplicate that. But instead of a skycrane, use a lander with legs. The reason for the skycrane was so they wouldn't need a lander with legs and shock absorbers and a ramp. They reduced mass by landing the rover on its wheels. For a human mission, a lander like Viking or Phoenix.

RobS · 2015-06-06 13:03:56

I like your approach, Robert. I think all of us want to work toward a reusable architecture, but the question is how quickly. If the first mission uses reusable equipment, the up front cost is higher and that may not be sustainable. If reusability is introduced later, equipment has to be replaced by new items and they require additional development time and cost. Who knows which will prove politically more feasible.

I do have a question for GW, though. Is there an easy way to estimate the retropropulsion needed for a vehicle based on its beta? For example, a 25 tonne lander with a 6-meter base would have 28 square meters of heat shield, so the beta is 25/28 of a tonne/sq m, or 892 kg per square meter. That's a lot, but if the retropropulsion needed is a delta-v of 1 km/sec, with methane/oxygen that's a mass ratio of about 1.3, which is maybe 6 or 7 tonnes of propellant.

GW Johnson · 2015-06-06 14:51:35

I used 1.4 to 1.5 km/s delta-vee for the terminal maneuvers of the lander, to cover errors, and some hover time looking for a clear site to touch down. That would be in addition to that required to get from 2 km/s down to the terminal maneuver conditions, which are essentially subsonic.

That means more propellant, of course, but not so much as to make the design infeasible. I also stayed around 20% inert mass fraction, in order to "confer" the structural robustness one would expect of a reusable landing boat. That's why my landing boats mass 60-70 tons but only land 3-4 tons dead-head payload.

My mission "plan" was for 3 landers to make 6 landings at 6 sites with propellant brought from Earth. If propellant ISPP actually proves to work in-situ, then you might make up to 18 landings pretty easily, or a few more landings plus a Phobos visit (about equivalent to one landing), or even visit several more sites by suborbital "hop".

I had thought to spend the first half of the year-plus at Mars based from orbit, exploring multiple sites from LMO with 3 of my 6 crew alternating, and then picking one site as the best spot to establish a base and leave ISPP/ISRU running to serve the next expedition. I have essentially zero confidence that mission 2 would be a government-sponsored mission. That would be a Spacex or similar visionary private concern.

6 crew is 2 groups of 3, each group a geologist, a biologist, and an engineer/pilot. All cross-trained, of course. One crew watches from LMO in a spinning habitat, while the other spends 2 weeks to a month on the surface at its designated site. I send 3 landers in order to have a backup for rescue, and also so as not to abort the mission, if 1 of the 3 landers fails in some way.

My "minimum mass" is the crew=6 orbit-to-orbit transport plus its return propellant, plus the propellant to support 6 landings with 3 landing boats, all pushed there by the reusable landers themselves. If ISPP/ISRU actually works, then we visit more sites. Simple as that.

GW

RobS · 2015-06-06 14:59:37

So you are assuming 2 km/sec retropropulsion, but I am not sure why you are assuming 1.5 km/sec for maneuvering. Mars's gravity is 3.7 meters per second. Thirty seconds of hovering would consume 110 meters per second. Presumably the sites have been extensively characterized from orbit and probably already have landing beacons. Retropropulsion on the way down can steer you to the site and you already will know where the boulders, if any, are.

SpaceNut · 2015-06-06 21:10:42

The table would suggest that each craft would be in orbit at the same distance and speed before entering Mars to landing but that is not quite the case. We know that we can try to compansate for the differences in mass so that they do come in at the same rate of speed at aerocapture but when we see the entry results they still do not come out in the same orbiting distance. Even when we do take the time to use Aerobraking all that is for certain is that we will be lower and slower but it takes time.
I see that we have for a 21 m difference in diameter that we have a 9mt change and with just a 10 m diameter change that we have a 6mT from the 23 m diameter base line but when we use a parachute we will loss 3 mT of down mass starting point in fuel needs or are the columns starting mass switched.

http://en.wikipedia.org/wiki/Aerocapture
AEROCAPTURE DEMONSTRATION AND MARS MISSION APPLICATIONS
Trajectory Guidance for Mars Robotic Precursors: Aerocapture, Entry, Descent, and Landing
A Comparative Study of Aerocapture Missions with a Mars Destination

http://en.wikipedia.org/wiki/Aerobraking

GW Johnson · 2015-06-07 10:20:52

Well, avoiding the boulders on the way down didn't work for Armstrong and Aldrin on the moon. Their biggest problem was running short on propellant. We shouldn't make that mistake again. The boulders that threatened their landing didn't really show up in the photos at that time. We do better now, but it isn't perfect.

I'd have to go back and look at my design analysis for the reusable 1-stage lander. It's been over a year since I did anything with it. Memory fades, so don't trust my recollections of delta vees.

Where you have beacons to home on, you could likely get away with slightly short-loading propellant in favor of some extra payload. But who's to say whether the crew in LMO might not spot something at another site without beacons? Better to have the delta vee capability to cover scenarios like that. It would apply to suborbital hops fueled by ISPP, too.

GW

RobS · 2015-06-07 10:29:40

Presumably manned landings will be occurring at sites that have been selected because of extensive study. Even now we have the ability to spot the wheel tracks of the Mars rovers and the vehicles themselves, so we have a pretty good idea about surface roughness. If each landing site already has a lander with supplies, it would be worth it to send along a small rover--perhaps the size of Spirit and Opportunity--to explore the site. There are also ideas about "tumbleweed" rovers that let the wind roll them around, and balloon rovers that can acquire low-level aerial views. So there are a lot of ways to select virtually boulder-free landing sites. Software that already exists can determine where the vehicle is relative to all local obstacles; it can even recognize uncharted obstacles. This is especially true if a Martian GPS system is set up.

louis · 2015-06-07 14:23:45

RobS wrote:

Presumably manned landings will be occurring at sites that have been selected because of extensive study. Even now we have the ability to spot the wheel tracks of the Mars rovers and the vehicles themselves, so we have a pretty good idea about surface roughness. If each landing site already has a lander with supplies, it would be worth it to send along a small rover--perhaps the size of Spirit and Opportunity--to explore the site. There are also ideas about "tumbleweed" rovers that let the wind roll them around, and balloon rovers that can acquire low-level aerial views. So there are a lot of ways to select virtually boulder-free landing sites. Software that already exists can determine where the vehicle is relative to all local obstacles; it can even recognize uncharted obstacles. This is especially true if a Martian GPS system is set up.

I agree entirely RobS. The difference from the lunar programme will be the extend of pre-knowledge about the landing site.

I would think we would be looking at a identifying a landing zone of 10 sq. miles (for the landing of supplies etc) and within that - following, as you say, robot rover mapping - a landing area (maybe 100mx100m) for the landing craft. The robot rover should also have the ability to clear large rocks from that landing area.

With transponders placed in the landing area an accurate landing should be 100% assured.

SpaceNut · 2015-06-07 15:52:40

Or we could just drop in a rover capable of clearing any such objects in the first place making it a safe landing zone.

Hypersonic space entry: Advanced Hypersonic Entry Guidance for Mars Pinpoint Landing
Hypersonic and Supersonic Static Aerodynamics of Mars Science Laboratory Entry Vehicle
Mars Science Laboratory: Entry, Descent, and Landing System Performance
ADAPTABLE, DEPLOYABLE ENTRY AND PLACEMENT TECHNOLOGY (ADEPT) FOR FUTURE MARS MISSIONS

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