Mars Direct; are we now beating a dead horse?

RobertDyck · 2017-10-09 13:00:04

Boeing proposed ion propulsion because that would keep acceleration down, and hence forces on CBM hatches within limits. Of course an ion would take a lot longer. The Russian corporation Energia came up with a mission plan in 1999 (updated from earlier plans). They proposed using TAL Hall thrusters for solar-electric propulsion. They had developed Hall thrusters to perform as well as NASA's ion thrusters. This gives us an idea how long solar-electric propulsion will require to get to Mars. Their plan would spiral out of Earth orbit for 3 months, but DSG would start in high orbit so wouldn't need that. Then transit to Mars would take 8 months. Then spiral down to LMO for 1 month. A minimum energy trajectory using chemical propulsion would take 8.5 months, so this is reasonable. But forget getting there via express trajectory in 6 months. And solar arrays for the Russia design are huge!

Click on the small orbit image for a larger view. Click on the spacecraft image for the web page where I got both of these.

RobertDyck · 2017-10-09 13:09:30

kbd512 wrote:

Is there any reason why an axial configuration can't be used, even with artificial gravity?
Is there any reason why a descent / ascent vehicle can't dock with the transit vehicle in LMO?
Apart from the attachment points for other modules or propulsion stage(s), is any other internal or external structural reinforcement required?

An axial configuration could. You would have to be careful about lateral forces when steering the spacecraft, keep them within limits of the attachment hatches. Yes, descent/ascent vehicle could dock in LMO. My issue is with modules attached laterally during injection into trans-Mars trajectory. There's no longer talk of an asteroid redirect mission, but any mission to an asteroid would have the same concerns.

You would have to calculate structural forces on solar panels and radiators. They will also hang out. I don't have figures for those. Normally they're folded/stowed during launch, only unfurled in zero-G of space. Orion will use an ATV-based service module; those solar arrays are designed to be unfurled while the service module main engine operates. What acceleration will it produce? Could those solar arrays withstand acceleration? Probably. The longer the solar array, the more you have to worry about forces during acceleration, so what about the DSG arrays?

RobertDyck · 2017-10-09 15:34:36

We could recalculate sheer force based on a Cygnus cargo ship. The image appears the "logistics module" is a Cygnus "enhanced" with larger pressurized cargo module and round solar arrays. Dry mass is 1,800 kg (4,000 lb) for enhanced variant, 3,500 kg (7,700 lb) payload when launched on Atlas V. I think propellant mass is included in payload mass, so total is 11,700 pounds mass. At 0.6g acceleration that works out to 7,020 pound sheer force. That's less than MPLM, but still more than the 5,900 pound sheer force limit of a CBM hatch.

kbd512 · 2017-10-10 18:44:58

Rob,

Thanks for the info.

The Enhanced Cygnus spacecraft's mass breakdown is thus:

3-Segment PCM: 1,995kg (a relatively accurate value)
Service Module: 1,700kg (not an exact value)
Payload: 2,700kg (mass limitations imposed by launch vehicle capability and ascent loadings)

The Cygnus spacecraft's gross mass would include all three relevant mass values. The service module's exact configuration, which includes propellant loading, is variable. The spacecraft's structure is designed to withstand an 8g peak axial load during ascent along with some fairly intense vibration from the solid rocket motors used in ATK's launch vehicle. The service module uses two MegaFlex arrays that generate 3.5kWe at 1AU distances. That power output level would be inadequate for a pair of astronauts at 1.5AU, so larger arrays or perhaps 2 pairs of arrays are required.

There's a proposed 4-Segment "Super" Cygnus PCM configuration that has a whopping 33.5m^3 of internal volume. An expendable Falcon Heavy's upper stage could TMI that thing without issue and it has enough volume for the consumables required to support a free return trajectory. Presumably, two or three pressurized compartments separated by hatches could be built into the module to both improve structural rigidity and limit the loss of pressurized volume from punctures associated with chance impacts from space debris.

I'm still very much in favor of sending astronauts to Mars in pairs (one man and one woman, to account for consumables limitations) using the Cygnus hardware set for the initial Mars exploration missions. It's just a heavy, durable aluminum drum. A non-structural BNNT liner and water tank can provide the required radiation protection. The 2-Segment PCM's can land on Mars using HIAD attached to the base end and a monopropellant retro-propulsion module attached to the top end. A tether system can provide artificial gravity for both transits.

It's a spartan domicile to be sure, but it should work. And yes, if you confine a man and woman inside a tin can they will inevitably have sex at some point. That simply has to be taken into account. NASA needs to start selecting couples who work well with each other. Anyone who thinks humans should remain celibate for years at a time needs their brain adjusted to account for real life. These volunteers will be further removed from the rest of humanity than anyone has ever been and they need intimate contact with other humans to survive that level of isolation with their sanity intact. Losing any crew members will be devastating to morale, to put it mildly. Prior testing to assure compatibility will necessarily be extreme, much as it was for the original NASA astronauts.

Oldfart1939 · 2017-10-11 09:06:48

kbd512 wrote:

Rob,

It's a spartan domicile to be sure, but it should work. And yes, if you confine a man and woman inside a tin can they will inevitably have sex at some point. That simply has to be taken into account. NASA needs to start selecting couples who work well with each other. Anyone who thinks humans should remain celibate for years at a time needs their brain adjusted to account for real life. These volunteers will be further removed from the rest of humanity than anyone has ever been and they need intimate contact with other humans to survive that level of isolation with their sanity intact. Losing any crew members will be devastating to morale, to put it mildly. Prior testing to assure compatibility will necessarily be extreme, much as it was for the original NASA astronauts.

I fully agree. NASA should rejoin the real world when it comes to these issues. What did sailors do after being confined aboard a ship for certainly less than the 4 year commitment of a Mars mission? They went LOOKING FOR WOMEN.

RobertDyck · 2017-10-11 10:16:20

The European Space Agency said what consenting adults do in space on ISS is their business, no space agency can order them to abstinence. NASA was obsessed, wanted all astronauts to abstain, but after ESA calm adamant insistence that NASA managers behave like adults instead of teenagers, NASA quietly agreed. This may be yet another reason for a Mars mission to be international.

This Victorian attitude toward sex is the result of one powerful woman being frustrated, wasn't able to get her guy. Do to a long elaborate story, when Victoria was young, she couldn't have the guy she had a crush on. Eventually Queen Victoria decided to be stoic, non-sexual, focus on getting her job done. Some teenage girls who go through the same thing will dress in black, become a goth. Victoria chose to dress like a marble statue. Victorian attitudes were the rest of the British empire following the same attitude of this one frustrated woman. In reality, people during the Victorian era were just as sexual as people today, it was just the "public face" they had to put on. Today Queen Elizabeth II is Queen of England and the British Commonwealth. When Elizabeth was only 13 years old she got a crush on a certain guy. He was from a European royal family, so on the "approved" list, but some individuals wanted to control her, didn't want her to date that guy. When Elizabeth II was still a princess at age 21, they announced their engagement. They're now both in their 90s, still married. By reports, Philip wanted to wait before having children, but Queen Elizabeth II got pregnant with their first child when she wanted. They had they had the number of children that she wanted, the number of years between children that she wanted, everything as she wanted. When Queen Elizabeth II wants something, she gets it. Period. And Queen Elizabeth II has reigned longer than any other monarch of England, even Queen Victoria. Can we dispense Victorian attitudes now? The attitudes of a single frustrated woman?

RobertDyck · 2017-10-11 10:29:33

Robert Zubrin's Mars Direct habitat is just an aluminum-lithium alloy cylindrical hull. The only difference between that and Cygnus, is that the Mars Direct hab has the same diameter as the core stage of the Ares launch vehicle that was supposed to launch it. SLS block 2 is basically Ares. The Ares from 1990 was based on a Shuttle ET, same diameter. It had 5 SSME, 2 advanced solid boosters, and an upper stage with the same diameter as the core stage and used a single J-2S engine. The S-IVB stage that propelled Apollo into a trans-lunar trajectory used a single J-2 engine. In 1979 NASA designed an update of the J-2, the result was J-2S. So Mars Direct simply used the newest latest version of the same engine as Apollo. When SLS was announced at the joint NASA/Senate presentation, it was stated SLS block 2 would have a core stage the same diameter as a Shuttle ET, would have 5 SSME, 2 advanced solid boosters, an upper stage with the same diameter and a single J-2X engine. J-2X is simply the 21st century update of the same J-2 engine. So SLS block 2 *IS* Ares. So why not expand the habitat to the same diameter as the launch vehicle? Just like the Apollo SM, that dispenses with any fairing. That's the only difference between a Cygnus PCM and MD hab.

Last edited by RobertDyck (2017-10-11 10:44:49)

elderflower · 2017-10-11 12:18:35

Robert, you have discussed the public façade of Queen Victoria. Privately she was really quite horny!

GW Johnson · 2017-10-11 15:55:01

The Bigelow B330 inflatable has 330 cu.m internal volume in a module that can be sent to LEO by an Atlas-5 or a Falcon-9 at 15 metric tons. The inflatable has an 18-inch (near 0.5 m) thickness that has twice the radiation shielding of the BEAM that has already demonstrated itself to be the radiation equivalent-or-better than any spam-can module on the ISS.

With 330 cu.m, you have a lot of space to put crew and gear or supplies. Plus, you can dock them end-to-end and build an enormous volume rather quickly.

It wouldn't take much of a modification to the core to add fold-out decks. Use the Cygnus tin can plus some structural beef inside it, modified with a stout docking port on each end, to house a couple of electric-driven flywheels, and dock two B-330's to each end. The total volume is 4x330 + 35 cu.m or 1355 cu.m. You can put a decent crew and a whole lot of equipment and supplies inside that. Spin it end-over-end at 4 rpm, and you have pretty close to 1 gee artificial gravity at the outermost fold-out deck at each end.

5 current-booster launches, and we could have a space station with far more internal volume than ISS, artificial gravity, and twice the radiation shielding they have now. Add a 6th launch for the crew that docks it together. Now, wild-guess $100M each for the 5 modules, plus $80M each for 6 launches, plus $50M for the capsule that brings the assembly crew and returns them.

Total price for a new space station bigger than the one we have now, with better shielding, and with artificial gravity at every level from 0 to 1 gee: something like $1B. Not $110B. $1B!!!!!!!

Why the hell would we not want to do that?

Especially since pretty much the same design could be an orbit-to-orbit transport to Mars and back.

GW

Last edited by GW Johnson (2017-10-11 15:57:24)

SpaceNut · 2017-10-11 19:33:13

Private Space Habitat to Launch in 2020 Under Commercial Spaceflight Deal

aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzA1NC83MDkvb3JpZ2luYWwvYmlnZWxvdy1hZXJvc3BhY2UtQjMzMC1jdXRhd2F5LmpwZw==

https://www.nasaspaceflight.com/2016/04 … -stations/

Oldfart1939 · 2017-10-11 22:11:44

GW-

Have you looked at the energetics of the Moxie system, the conversion of CO2 to O2 and CO? I don't have much primary source information on this process.

2 CO2 --------------------> O2 + 2 CO

elderflower · 2017-10-12 04:52:27

I looked for info on thermal conversion of CO2 to CO and O2 using catalysts. I saw about 15% conversion max (one pass) and no coking, which is encouraging. Temperatures required are high, though. Up to 900C was quoted. With better catalysts this might come down. High temperatures might be achieved using steered solar concentrators rather than just photovoltaics.
I also looked for work on CO/O2 rockets and found a practical test using an existing test stand design. It gave Isp vac of around 260-280 against theoretical just over 300. This is adequate to get a surface exploration ship back to LMO and doesn't need hydrogen.
What's not to like?

Oldfart1939 · 2017-10-12 08:28:45

In an earlier thread regarding one of my mission models, I suggested taking along the fuel component as either MMH or UDMH. Look at the Oxygen ratios in the fuel requirements also posted elsewhere. I'll try to find those figures and update this post later.

RobertDyck · 2017-10-12 11:19:17

The Raptor engine developed by SpaceX uses LOX/CH4, producing Isp=375s in vacuum. That's a lot more than the Isp you site for carbon monoxide. NASA had studied ISPP before Dr. Zubrin did, that's where Dr. Zubrin got the idea. But NASA looked at carbon monoxide, Dr. Zubrin said if we bring a little hydrogen from Earth and use the Sabatier process developed in the first decade of the 1900s we can dramatically increase Isp. In fact, Dr. Zubrin's plans to produce extra O2 to top-up the LOX tank is the method NASA developed to produce CO/O2, but Dr. Zubrin would vent the CO back into the Mars atmosphere. At 1 atmosphere pressure, methane is liquid at -161.48°C while CO requires -191.5°C. Methane remains liquid at warmer temperature than LOX, CO requires colder. So LCH4 is easier to handle, as well as dramatically higher performance. Why would we take a major step backward?

elderflower · 2017-10-12 12:04:11

My proposal is to minimise landed mass by leaving the return ship and return fuel in orbit. A couple of smaller units would be used to land in a few places of interest using LOX CO and hopping between these or returning to the ship using LOX CO generated on the surface to top up.
Such a mission would allow selection of a good place, with a large water ice resource, well characterised to improve the chances of success of the next mission which would be direct to the surface with 150 te of kit, people and stores.

RobertDyck · 2017-10-12 12:06:56

Bringing return propellant from Earth does not reduce mass, that increases it. ISPP reduces mass.

elderflower · 2017-10-12 12:17:21

The return propellant is methane and LOX. To make that on Mars you will need to find water or to import hydrogen from
earth. The first requires a search mission and some digging to prove a deposit, the second requires you to land a large tank and you lose a lot of its contents on the way.
Landing the return ship and making hydrogen based propellant without first doing the ground work is a huge gamble. We need to establish, beyond doubt that the water is there where we land and available to be mined, or take a big hit on the mass we can ship by bringing a tank of low density gas with us.

RobertDyck · 2017-10-12 14:02:52

NASA Design Reference Mission (DRM) also known as Mars Semi-Direct was designed to bring return propellant from Earth. It required more launches per mission, and dramatically increased cost. The cost estimate for Mars Direct was $20 billion in 1989 dollars for the first mission including development, infrastructure, and the first mission. Then $2 billion per mission thereafter. Or $30 for 7 mission if you commit up-front. Yes, that works out to buy 6 missions, get 1 free. Mars Semi-Direct cost $55 billion, so practically double before any hardware was even built. That's what you get when you drag propellant from Earth.

That's also why Congress wouldn't approve it in the 1990s. They believed NASA would manipulate anything they do to become the 90 Day Report, together with it's $450 billion price tag. In 1989 dollars. That works out to $750 billion today. When NASA came up with Semi-Direct and it's doubled price tag, even before anything was built, they believed NASA would increase the price back to $450 billion. And they would not approve that. Ever. Period.

You could argue for stupid stuff. Doing so means you will sit at home typing on an internet forum forever, never seeing anyone on Mars.

louis · 2017-10-12 17:00:18

I still find it that saga of the 90 Day Report quite shocking. These were supposed to be serious people doing a serious job. That was pure sabotage wasn't it? Someone must have known exactly what they were doing. It's a bit like a parent wanting to show the world their children are too demanding - and so to prove it, they encourage the kids to write a list of everything they would ever like to have for Christmas if there really was a Santa Claus...just so they can say "there you go - I told you they were too demanding!"

RobertDyck wrote:

NASA Design Reference Mission (DRM) also known as Mars Semi-Direct was designed to bring return propellant from Earth. It required more launches per mission, and dramatically increased cost. The cost estimate for Mars Direct was $20 billion in 1989 dollars for the first mission including development, infrastructure, and the first mission. Then $2 billion per mission thereafter. Or $30 for 7 mission if you commit up-front. Yes, that works out to buy 6 missions, get 1 free. Mars Semi-Direct cost $55 billion, so practically double before any hardware was even built. That's what you get when you drag propellant from Earth.
That's also why Congress wouldn't approve it in the 1990s. They believed NASA would manipulate anything they do to become the 90 Day Report, together with it's $450 billion price tag. In 1989 dollars. That works out to $750 billion today. When NASA came up with Semi-Direct and it's doubled price tag, even before anything was built, they believed NASA would increase the price back to $450 billion. And they would not approve that. Ever. Period.
You could argue for stupid stuff. Doing so means you will sit at home typing on an internet forum forever, never seeing anyone on Mars.

elderflower · 2017-10-13 04:10:26

I do think that Spacex has made previous estimates out of date. Unfortunately Musk isn't giving out his financial projections in any detail.

GW Johnson · 2017-10-13 10:29:52

It's not just Spacex. It's the commercial launch industry plus 2 decades experience with orbital assembly doing ISS that has made all the fundamental assumptions behind all these earlier Mars mission concepts completely obsolete. Those assumptions are two very-constraining "thinking boxes": (1) we can only afford min thrown mass", and (2) "only a direct shot with a giant rocket is feasible".

Falcon-9 flings up to 22 tons to LEO for about $85-90M per launch, maybe 10-15 tons reusably. That's under $5M/ton of delivered payload, flown expendably, and the recent booster reflights cut that further, by perhaps a factor of two. Atlas-5 with SRB's can fling 20 tons to LEO expendably for about $120M per launch, which is $6M per delivered ton.

Now compare that with SLS: if you believe NASA's projections, block 1 delivers 70 tons to LEO for ~$500M per launch, which is $7M/delivered ton. If you believe their critics, at least double that figure to $14M/delivered ton to LEO. And it will NEVER EVER be reusable in any way at all. So it will always be expensive.

Consider also launch rates: Spacex is edging toward 2 dozen Falcon-9 launches this year alone. NASA projects an SLS to launch maybe once every year or two. Being able to launch lots of payloads quickly is one key to doing Mars for under a trillion dollars. SLS will NEVER EVER do that.

Reusable boosters flying dozens of times a year can put an awful lot of tonnage into LEO very quickly for assembly, especially if the price edges down toward $2-3M/delivered ton. Even without reusability, the demonstrated prices are $5-6M/ton. How is that not affordable, even if the thrown mission mass is not minimized? You can put together a whole fleet of manned and unmanned vehicles in orbit to send to Mars, and you can do it fast and affordably, with orbital assembly by docking.

The unmanned stuff can go there with electric propulsion, another launched mass savings. The natural "drift" of this capability is in two complementary directions: (1) orbital-based missions to Mars become practical and affordable, which allows exploring multiple surface sites in the one trip, like the sea voyages to the New World half a millennium ago. And (2) really big spacecraft become entirely feasible, even without a gigantic rocket (and both Spacex and Blue Origin are working on gigantic reusable-and-affordable rockets, too).

The mission design constraints are no longer what they were in the 1980's and 1990's. Things have changed, and for the better.

One should go with the leaders creating that beneficial change. And it ain't NASA and "old space".

GW

Last edited by GW Johnson (2017-10-13 10:35:46)

GW Johnson · 2017-10-13 10:46:27

Given what I said in post 46 just above, why should not a Mars mission send ahead the return propellant, and the landers and their propellant, ahead to Mars orbit, using electric propulsion? Then send the men in a big assembled craft with conventional rocketry to rendezvous with those assets in Mars orbit.

Send part of the crew down in a lander for maybe a month's stay at each site, with the rest of the crew and landers in orbit, and providing a rescue capability that no other previous plan has ever had?

Try out the ISPP/ISRU and greenhouse stuff at every site you visit this way. Alternate crews, so everybody who makes the trip gets to go to Mars. Leave the equipment running for subsequent visits, at every site you visit. By the time you do this (in the one trip!!), you will find out what ISPP/ISRU items work, how well, and at which sites. My hunch is those answers are very different at every site.

It's on subsequent trips you land the massive ISPP/ISRU equipment that you now know will work at the site you select for each trip, plus the stuff to construct a permanent manned base. That kind of trip is where Musk's BFR/ITS has the overwhelming advantage. Not that first multi-site "find out what is there" trip.

GW

Oldfart1939 · 2017-10-13 11:16:48

GW-

The real weakness in Musk's plan is an absolute lack of any reconnaissance missions. Going ahead balls to the leather is OK once there is adequate data.

Quaoar · 2017-10-13 11:34:39

Oldfart1939 wrote:

GW-
The real weakness in Musk's plan is an absolute lack of any reconnaissance missions. Going ahead balls to the leather is OK once there is adequate data.

Even the landing of a gigantic rocket may be problematic without knowing if the soil of the landing site is stable enough to support its weight

Last edited by Quaoar (2021-06-01 09:10:18)

GW Johnson · 2017-10-13 14:39:31

What Oldfart1939 and Quaoar object to, is quite true, and I totally agree. I think the very first trip should probably not be a BFR/ITS type expedition.

That first trip probably ought to look somewhat like what I posted over at "exrocketman" last year as "Mars Mission 2016". It's a set of vehicles like that which finds out the best place to land "big time" with a cargo container ship like Musk's BFR/ITS.

Basically you need a pathfinder.

GW

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#26 2017-10-09 13:00:04

Re: Mars Direct; are we now beating a dead horse?

#27 2017-10-09 13:09:30

Re: Mars Direct; are we now beating a dead horse?

#28 2017-10-09 15:34:36

Re: Mars Direct; are we now beating a dead horse?

#29 2017-10-10 18:44:58

Re: Mars Direct; are we now beating a dead horse?

#30 2017-10-11 09:06:48

Re: Mars Direct; are we now beating a dead horse?

#31 2017-10-11 10:16:20

Re: Mars Direct; are we now beating a dead horse?

#32 2017-10-11 10:29:33

Re: Mars Direct; are we now beating a dead horse?

#33 2017-10-11 12:18:35

Re: Mars Direct; are we now beating a dead horse?

#34 2017-10-11 15:55:01

Re: Mars Direct; are we now beating a dead horse?

#35 2017-10-11 19:33:13

Re: Mars Direct; are we now beating a dead horse?

#36 2017-10-11 22:11:44

Re: Mars Direct; are we now beating a dead horse?

#37 2017-10-12 04:52:27

Re: Mars Direct; are we now beating a dead horse?

#38 2017-10-12 08:28:45

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#39 2017-10-12 11:19:17

Re: Mars Direct; are we now beating a dead horse?

#40 2017-10-12 12:04:11

Re: Mars Direct; are we now beating a dead horse?

#41 2017-10-12 12:06:56

Re: Mars Direct; are we now beating a dead horse?

#42 2017-10-12 12:17:21

Re: Mars Direct; are we now beating a dead horse?

#43 2017-10-12 14:02:52

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#44 2017-10-12 17:00:18

Re: Mars Direct; are we now beating a dead horse?

#45 2017-10-13 04:10:26

Re: Mars Direct; are we now beating a dead horse?

#46 2017-10-13 10:29:52

Re: Mars Direct; are we now beating a dead horse?

#47 2017-10-13 10:46:27

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#48 2017-10-13 11:16:48

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#49 2017-10-13 11:34:39

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#50 2017-10-13 14:39:31

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