Merits of Mars Direct - Is it too optimistic?

Mark S · 2002-06-04 18:40:50

After looking at Mars Direct and the NASA Design Reference Mission 3.0, I've noticed some disparity between the mass estimates of the two plans. Namely, the habitat lander in NASA's blueprint is over 12 tonnes heavier than Zubrin's. Some of the difference can be attributed to Zubrin's decision to go with a crew of four instead of six, but I don't think that it can cause that large of a difference. Along the smae line, I think that Zubrin's decision to eliminate the dedicated doctor from Mars Direct is a mistake. On a mission lasting for 2.5 years, a doctor is a necessity. It is also true that with a 5-person crew would have a better "group dynamic" than a crew of four or six. Studies show that odd-numbered groups usually work better than even numbered groups.

I'd really like to hear the forum's thoughts about these subjects, or at least on different facets of Mars Direct. Only constructive criticisms will turn Mars Direct into a reality.

Dayton3 · 2002-06-04 19:32:38

I agree with Dr. Zubrin that having a dedicated doctor aboard is unnecessary. A biologist with medical training would be best. Simply put, what could a doctor do aboard a spacecraft with limited equipment, very little in the way of trained support personnel and et cetera.

A simple illness or injury can almost certainly be treated by a person with a basic level of paramedic training.

A serious illness or injury, an overturned rover with a crushed crewman would probably be well beyond the abilities of even the best surgeon under such conditions.

I do think astronauts on such missions would have to submit to some surgery beforehand to remove things like the appendix and gall bladder which could conceivably become infected during the mission despite any possible precautions.

Shaun Barrett · 2002-06-05 01:32:47

I agree with Dayton3 and Bob Zubrin. In my opinion, much of any early exploratory effort relies on luck. Without wishing to labour the unpopular parallels drawn between the old American West and Mars, how many wagon trains had dedicated medical personnel back in 1875?
Going to Mars is a risky business and you can't possibly cover every conceivable eventuality. Even if you take a general surgeon with you, what can s/he do without a properly equipped O.R. and support staff? What if your geologist dies on the way and you lose the benefit of that expertise for the whole 500 days on Mars? What if your mechanical engineer has an unforeseen massive stroke and can't fix the descent engine for the landing? ... The list goes on and on.
I think Mars Direct would work as it stands. Have everyone able to do lots of different things and just trust to luck. A fifth person makes the mission bigger, heavier, and more costly. And each extra person is another possible medical emergency anyway! ... Who's to say the surgeon won't get sick?!
Let's face it ... WE CAN'T ELIMINATE RISK!! The sooner NASA realises that, the better.

Josh Cryer · 2002-06-05 10:08:46

We can't eliminate risk, yet, we've only had one shuttle accident in the history of the program?

NASA is extremely careful, because it's proven to work. I do agree that they're overcautious sometimes, but I think Zubrin's Mars Direct is a disastor waiting to happen. There's nothing it could achieve that probes themselves couldn't.

Mars Direct is relatively cheap. Why hasn't Zubrin made a proposal to some of the big corps, like Microsoft, Sony, etc? The video rights alone would more than make up the cost.

Oh, one more thing. NASA hasn't even made a plan (outside of speculation) to go to Mars, so you can't condemn them for something they haven't even done yet.

C M Edwards · 2002-06-05 10:55:55

Well, obviously, the Mars Direct mass estimate given in The Case for Mars is very rough and incomplete. It omits several important basics, such as clothing. (Clothing alone can add between 300kg and 700kg to life support for a three year mission, depending on whether it?s treated as disposable and/or extended wear, washing machines & detergents are included, etc.) It?s just an educated guess, and a more detailed analysis reveals that it?s a lot harder to fit the vintage Mars Direct architecture into 140T than Mr. Zubrin lets on.

However, the vintage Mars Direct plan makes a lot of assumptions that add weight to the hab. For example, if you have the guestimate for the ERV crew module, note how much lighter it is than the crew hab. They?re both in interplanetary space for the same amount of time, and presumably have comparable amounts of crew space. But one weighs less than the other by an amount greater than can be accounted for by just supplies & equipment. From what I read, it also ignores the potential of aramid composites, inflatable structures, and other technologies that were still ?exotic? in the early 1990?s. (Recall, Zubrin prefers proven technologies. The list has grown longer since 1996.) And that doesn?t even touch the subject of propulsion.

The vintage plan would be overweight, but there?s still plenty of ways to get the lead out. I think that the Mars Direct mission architecture is feasible using reasonable and reliable changes in the vehicle design.

Does anyone have any good ideas for making the Mars Direct Mission fit within its mass budget?

CME

Mark S · 2002-06-05 14:13:08

Good ideas to trim down the mass of Mars Direct? I have a few. For starters:

1. Use composites wherever they would save weight.
2. The ERV should find something better than the methane/oxygen fuel mixture. You could dispense with some of the tankage and Sabatier reactors if you used a nuclear thermal reactor that heated compressed carbon dioxide. Better yet, you could land at one of the water deposits and use the ice to make hydrogen and oxygen fuel.
3. Use ballutes (inflatable balloon-parachutes) for landing. The parachutes will be heavier than normal but it might eliminate the need for descent engines and propellant on the hab lander.
4. Integrate the aerobrake with the hab's outer skin. This is a key feature of the lander in NASA's DRM 3.0.

Dayton3 · 2002-06-05 18:16:56

I don't get it. If everyone thinks Zubrins mass estimates are too low, just increase the booster size.

During the Saturn V era, many well laid plans existed for increasing the LEO capability of the Saturn V to over 300,000 lbs. with relatively minor modifications.

I would wager the original Ares design could be stretched in capability as much as 20%. By adding a second pair of SRBs and replacing the four SSMEs with the already designed Advanced Launch System Main Engines (basically shuttle engines, not reusable, with very few moving parts) and capable of 650,000 lbs. of thrust.

Sure it would probably add a couple of hundred million to the overall development, but next to the Hab and ERV development costs it would be minor.

Shaun Barrett · 2002-06-05 19:40:53

OHHH!!! Now I get it! At last I understand NASA's procrastination.
They've figured out that if they just keep stalling with this Mars exploration thing, they'll have better rockets with more thrust pushing spacecraft made of lighter, stronger materials!
H***!! If they wait long enough, say another 30 years, we'll probably have warp-drive and be able to get to Mars a few days before we leave Earth!!
You can probably forget Mars Direct and the NASA Reference Mission. Seems to me NASA ain't goin' no place 'til they've invented a better mouse-trap!!

Dayton3 · 2002-06-05 21:39:17

By the way, in Mars Direct, the ERV Cab actually has only half the space that the Habitat Module has.

About 125 square feet per person.

I think Dr. Zubrin originally called for using artificial gravity on the return leg with the ERV, but given that zero g would allow more space to be utilized by the crew and it would only be six months, he dropped the artificial G for the return leg.

That would save on weight as well.

Mark S · 2002-06-06 08:21:19

The Mars Direct hab structure actually weighs more than the NASA hab structure, but apparently Zubrin didn't factor in the weight of the descent engines or propellant.

My critique of the hab doesn't end there, however. It doesn't provide a cockpit for the astronauts to sit in during launch from earth, nor are there any control panels. In all of the interior drawings of the hab, only the top floor is shown. What about the lower decks?

Mars Direct is over ten years old, and we know a lot more about spacecraft design now than we did in 1990. The Mars Society should prepare a "Mars Direct 2.0" which takes advantage of advances in life support, materials, nuclear power and propulsion, and engines and construction techniques developed for the Atlas V and Delta IV.

For example, an Ares rocket built with a Super-Light Weight ET (introduced in 1998) and powered by four RS-68 engines (to fly this July) would kick the pants off the original Ares. It might even be possible to replace each SRB with two Atlas V Common Core Boosters, which will improve the safety margins of the booster. Having a pro-nuclear president will help, as a nuclear thermal rocket in the upper stage may boost its lift capacity by 20 tonnes.

RobS · 2002-06-17 01:39:44

The weights for the hab and ERV given in *Case for Mars* are a bit misleading because they don't include the aerobrake, landing engine, and landing fuel. But those weights have been included in the plans. Of the 140 tons in low earth orbit, 40.6 tonnes can be put in Mars orbit and 25.2 tonnes on the surface for the piloted option (page 89). The difference between 40.6 and 25.2 tonnes is the mass of the aerbraking system, engines, and fuel.

I agree that a redesigned "Mars Direct 2" plan would be nice to have. But politically, I suspect it is a waste of time. Mars Direct 1 exists to give everyone a rough idea of what can be done. A Mars Direct 2 design will similarly become out of date before anything can actually fly, and will cause people to compare the two and debate their relative merits. What's needed now is effort to find the money, and that means acquiring experience and building trust. Once those exist, you can revise Mars Direct to build something that will actually fly.

-- RobS

Bill White · 2002-06-17 12:36:39

What's needed now is effort to find the money, and that means acquiring experience and building trust. Once those exist, you can revise Mars Direct to build something that will actually fly.

Spot on! - IMHO

Mark S · 2002-06-19 09:37:48

After some cosiderable thought, I think that nuclear thermal rockets are a bad idea for the earth return vehicle. In order for the rocket to reach Mars orbit and return to earth, it will need two or possibly three stages. It is also true that a nuclear thermal rocket using carbon dioxide as a working fluid actually has a lower ISp than methane/oxygen chemical rockets. The extra weight of the nuclear thermal rocket then becomes a bane. Putting it all into the rocket equation, it means that it would be more difficult to build a nuclear thermal ERV.

Michael Bloxham · 2002-06-20 20:14:56

If Zubrins weight estimates are too low, just launch from a higher altitude! Launching from 5000 or 10,000ft would improve payload capacity considerably.

Dayton3 · 2002-06-22 18:57:14

When a Manned Mars Mission is launched, it WILL have alot in common with Mars Direct.

Remember, that the current NASA Baseline Plan is basic Mars Semi-Direct but substituting the Magnum booster for the Ares and thus requiring six launches instead of three for each mission.

Mark S · 2002-06-28 15:33:07

I've thought of two technologies that have the potential for improving Mars Direct, and I'd like to hear what everybody thinks about them.

1) Use a metal fuel for the ERV. There have been a few Mars mission studies that used Magnesium or preferably Beryllium as a fuel and liquified Carbon Dioxide as an oxidizer. The fuel will be heavier than hydrogen feedstock but you won't need to run the Sabatier reaction or keep everything in cryogenic storage.

2) Replace the parachutes with inflatable balloon-parachutes ("Ballutes.") The extra buoyancy might eliminate the need for descent engines when the ERV and Habitat Lander touch down on Mars.

Phobos · 2002-06-28 18:17:28

2) Replace the parachutes with inflatable balloon-parachutes ("Ballutes.") The extra buoyancy might eliminate the need for descent engines when the ERV and Habitat Lander touch down on Mars.

This could be a good idea for reducing the amount of fuel you need to bring along in order to land. Would the mass of the balloons be less than the mass of the fuel you'd need to safely land a module? Also, I wonder if it still might be better to have fuel because you can control the landing better. This might be one of those rare cases where it's better to have a more complex, but a more controllable landing system. But then again, it's hard to see a whole lot going wrong with balloons unless one of them fails to inflate. :0

Palomar · 2002-07-01 16:34:28

Worst case would be if they brought back a Mars rock with an alien spore and they came back a perfectly healthy green multi-tenticaled entity bent on world domination.

*Well, in that event, the multi-tentacled entity will find plenty of competition already here! Actually, that could be ::the key:: in it leaving Earth!

--Cindy

Palomar · 2002-07-01 16:43:27

Mark S: "Along the same line, I think that Zubrin's decision to eliminate the dedicated doctor from Mars Direct is a mistake. On a mission lasting for 2.5 years, a doctor is a necessity."

*I agree. At the very least, a nurse practitioner [NP] or certified medical assistant [CMA] should be on board, as well as a tiny sickbay with at least a certain amount of surgical instruments, casting and splinting material, etc., "just in case." They've got to have more than just "first-aid kits." Also, if one of the astronauts is on a prescription medication, then acquires a reaction to that medication -- let's say having been on it previously for years with no problems whatsoever, and now mid-flight starts developing hives and dizziness, and NEEDS a replacement medication [and this can and does happen here on Earth, folks!] -- what are they going to do then? Perhaps the medical person should have a good working knowledge of pharmaceuticals as well, and a small laboratory be stocked and set up.

Mark S: "It is also true that with a 5-person crew would have a better "group dynamic" than a crew of four or six. Studies show that odd-numbered groups usually work better than even numbered groups."

*Probably because it makes the tendency to "pair off" more difficult.

--Cindy

Shaun Barrett · 2002-07-03 07:13:25

So, if 5 is good for group dynamics, how did the muslims come to the conclusion after centuries of trial and error that the ideal number of wives in a harem is 4?
:0

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#1 2002-06-04 18:40:50

Re: Merits of Mars Direct - Is it too optimistic?

#2 2002-06-04 19:32:38

Re: Merits of Mars Direct - Is it too optimistic?

#3 2002-06-05 01:32:47

Re: Merits of Mars Direct - Is it too optimistic?

#4 2002-06-05 10:08:46

Re: Merits of Mars Direct - Is it too optimistic?

#5 2002-06-05 10:55:55

Re: Merits of Mars Direct - Is it too optimistic?

#6 2002-06-05 14:13:08

Re: Merits of Mars Direct - Is it too optimistic?

#7 2002-06-05 18:16:56

Re: Merits of Mars Direct - Is it too optimistic?

#8 2002-06-05 19:40:53

Re: Merits of Mars Direct - Is it too optimistic?

#9 2002-06-05 21:39:17

Re: Merits of Mars Direct - Is it too optimistic?

#10 2002-06-06 08:21:19

Re: Merits of Mars Direct - Is it too optimistic?

#11 2002-06-17 01:39:44

Re: Merits of Mars Direct - Is it too optimistic?

#12 2002-06-17 12:36:39

Re: Merits of Mars Direct - Is it too optimistic?

#13 2002-06-19 09:37:48

Re: Merits of Mars Direct - Is it too optimistic?

#14 2002-06-20 20:14:56

Re: Merits of Mars Direct - Is it too optimistic?

#15 2002-06-22 18:57:14

Re: Merits of Mars Direct - Is it too optimistic?

#16 2002-06-28 15:33:07

Re: Merits of Mars Direct - Is it too optimistic?

#17 2002-06-28 18:17:28

Re: Merits of Mars Direct - Is it too optimistic?

#18 2002-07-01 16:34:28

Re: Merits of Mars Direct - Is it too optimistic?

#19 2002-07-01 16:43:27

Re: Merits of Mars Direct - Is it too optimistic?

#20 2002-07-03 07:13:25

Re: Merits of Mars Direct - Is it too optimistic?

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