Author Topic: Who's in Favour of Mars Direct?  (Read 34974 times)

Offline Andy L

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Re: Who's in Favour of Mars Direct?
« Reply #20 on: 03/30/2007 02:43 am »
It's a good question, but if NASA insist they need to test the technology on the moon, then I can't argue with that.

Offline Kaputnik

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Re: Who's in Favour of Mars Direct?
« Reply #21 on: 03/30/2007 07:33 am »
I'd have to say I'm with Zubrin on the Moon vs. Mars issue; going to the moon needs to be an end in itself, not just a test-bed for Mars technologies, because we can test those in orbit at lower cost. But, hey, it looks like the moon is where NASA is headed, and I'm not going to argue with that.

My own concept of a Mars Direct style mission would increase launches from two to three, so costs would go up, but it would remove most of the flaws that I perceive in the plan.
First launch: a combined storable propellant stage and manned descent stage; this payload would be equipped with an aeroshell and would aerobrake into high elliptical orbit at Mars, awaiting docking with the manned craft.
Second launch: a combined surface habitat/laboratory and ascent vehicle, equipped with ISRU plant, nuclear reactor, and rover. This payload would make a direct entry and landing on the surface, and the ascent stage would be fully fuelled by the time the crew arrived.
Third launch: a habitat module (probably ISS, Mir, or Bigelow derived) coupled to an Orion return capsule and a storable propellant stage. The crew would probably need to launched separately for launch abort reasons.

When the manned craft arrive, they propulsively brake into orbit, rendezvous with the first payload, and dock with its storable propellant stage; this will be used for the TEI burn. They then board the Mars descent capsule and make their way to the surface, where they will abandon the capsule and take up residence in the habitat on the surface. On departure, they would use the ascent vehicle to rendezvous with the orbiting habitat module, and then jettison the ascent stage, using the storable propellant stage for TEI, and the Orion capsule for Earth return.

This plan has the advantages of having propulsive capture of the manned craft, and of having dedicated space-based and surface-based habitat modules; the crew are also not cooped up in a tiny module for the return journey. Finally, the TEI propellant does not depend on ISRU.
The main potential weaknesses I would forsee in this plan are that there is still no abort-to-orbit capability, and that if the crew's tiny descent module lands off course they will not have the advantage of a large inventory of supplies. Further, rendezvous in high high Martian orbit might present challenges that I am unaware of, e.g. infrequent launch windows, long chase times, etc. There are two high-orbit rendezvous needed, and both of them are mission critical. Is this unacceptable?

I'd be interested to see what other, more knowledgable, people would make of this altered 'Mars Direct' plan?
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline MATTBLAK

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RE: Who's in Favour of Mars Direct?
« Reply #22 on: 03/30/2007 08:13 am »

I think his basic architecture is excellent and some 10 years ago got me re-energised about manned space exploration. Though:

1): He's optimistic on the vehicle masses. But just how optimistic? A detailed re-analysis should clear that up. But you're right about the ERV mass; it'd probably be 3 times that quoted 3-ton mass, even with all-composite strutures.

2): I think he also underestimates (but not massively) the danger of cosmic radiation and coronal mass ejections, the two major rad-dangers.

3): I think 5 would be a good crew number, not 4 -- one crew member would essentially be 'spare'. The loss of life of one member on a 4-person crew would be a terrible blow for mission completion. Losing 1 of 5 -- less so, of course.

4): Re-size Mars Direct vehicles and logistics for 5 crewmembers, increase radiation shielding, and maybe -- adopt a more 'Semi-Direct' architecture which Nasa once touted.

An upgraded Ares V could do a revised Mars Direct -- Regenerative RS-68's, slightly 'stretching' the EDS upper stage and increasing to 2x J-2X, adding some small solids (like those from the Atlas-V) would give a payload increase from 130 to 150 tons, enough for a more realistically revised "Mars Direct Version 3.0".

Or, you could adapt my own Mission Architecture, which nods to Zubrin anyway. ;)

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Offline lambda0

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Re: Who's in Favour of Mars Direct?
« Reply #23 on: 03/30/2007 11:05 am »
Hi
I am not really a fan of "Mars Direct", although I admit that it could work, but at the expense of too much risks. It seems to me that 3 years is much too long for a first mission to Mars, and this scenario also includes hazardous phases, such as aerocapture.
Another possibility would be a "short stay" mission, lasting about 400 days, but that would imply an unrealistic IMLEO with classical propulsion.
However, it seems that such missions are possible with near term electric propulsions and not so high electric power. Most "fast missions" to Mars with electric propulsion are based on a very high power nuclear generator that is not realistic for near term (100-200 MW for a 250 days mission), but opposition trajectories may require far less power : 4 MW for a 145+30+270=445 days missions.
The following document describes such missions :
http://myfreefilehosting.com/f/0168848ecc_1.59MB
30 days on Mars for a 445 days mission is not very efficient, but this could probably be improved to 60 days with a 10 MW generator, which is also credible for near term. The other thing is that this solution seems to be also more secure than Mars Direct from abort options point of view.


Offline CuddlyRocket

Re: Who's in Favour of Mars Direct?
« Reply #24 on: 03/30/2007 12:48 pm »
Quote
Kaputnik - 30/3/2007  8:33 AM

...not just a test-bed for Mars technologies, because we can test those in orbit at lower cost.
No, you can't. (Well, you can test them in LEO, but such a test is not definitive).

Equipment designed for use in LEO has gone through extensive and apparently exhaustive testing on Earth to make sure it will function for specified periods. Then it goes into orbit and regularly fails well within those periods. And we don't know why!

Obviously, it has something to do with the differences between the LEO environment and Earth (0g versus 1g in particular). Mars is a different environment again - so testing on Earth and in LEO will not validate equipment meant for use on Mars.

We get things back from the ISS and try and figure out what the problem is, and sometimes we can guess at a fix, but we don't understand the problem. (And we still haven't come up with a fix that makes things reliable enough for long missions.)

Will fixes for 0g work for 0.33g on Mars? Who knows? Will they work at 0.167g on the Moon? Again, who knows? But if they fail on the Moon it's a lot less likely to be disastrous than it would on Mars. And three data points should give us a much better handle on the problem. Once we have a theoretical understanding, we can extrapolate from Earth, LEO and Lunar conditions and testing to Mars.

Offline aftercolumbia

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Re: Who's in Favour of Mars Direct?
« Reply #25 on: 03/30/2007 08:17 pm »
Oooookaaaay...where do I start?

The big problems that I find with Mars Direct (which Orbiter Mars Direct Project tried to solve):

- Aerocapture is silly, we went with direct landing
- No earth launch LES, we went with separate crew ascent on the Sprint spacecraft (After Columbia's CEV, which predates the VSE by about six months)
- The landers are so far beyond current landing technology, that they might be too expensive to develop, OMDP went inactive before I found this out.

On some of the ideas mentioned so far, there are unvoiced problems:

- SEP: there is an eclipse on most orbits, and it is usually just after periapsis, knocking your engine out for part of the "drag pass"
- Aerocapture: We can't predict the state of the Martian atmosphere well enough for a liftless aerocapture to be reliable.  If you miss high, you are stranded in deep space.  If you miss low, you must land and are stuck with whatever landing site happens to be downrange of the approach periapsis.
- Liftless Entry: it is very difficult to enter accurately with no lift, however, with lift and good guidance, it should be possible to hit a parachute deploy zone several kilometres in diameter.  0.18:1 should be enough, but 0.5:1 would be ideal.


Offline Kaputnik

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Re: Who's in Favour of Mars Direct?
« Reply #26 on: 03/31/2007 09:17 am »
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aftercolumbia - 30/3/2007  9:17 PM
- Aerocapture is silly, we went with direct landing

I don't know the figures, but I think direct landing would subject the crew to unacceptable decceleration loads. The use of direct entry might mean that artificial gravity on the outbound trip becomes essential.
"I don't care what anything was DESIGNED to do, I care about what it CAN do"- Gene Kranz

Offline RedSky

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RE: Who's in Favour of Mars Direct?
« Reply #27 on: 03/31/2007 01:23 pm »
What I worry about with any direct entry landing scheme (i.e., no orbit insertion first before landing) is what is the contingency if a few weeks before entry, it is determined that a landing as scheduled is unsafe.  This could be anything from a global dust storm, to some suspect equipment that may need troubleshooting.  With a direct entry, there is no option for a wave off, is there?  

I remember when Mariner 9 got to Mars, it took a month or two for a global dust storm to settle down so that the surface became visible. Since the crew will be at Mars for 18 months or more, being in orbit and able to wait out such events seems wise.

Offline KNebergall

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Aerocapture and staged landings
« Reply #28 on: 03/31/2007 11:21 pm »
A couple quick points.

We tend to compartmentalize between direct entry and a year of aerobreaking after a propulsive capture, because our probes fall in these categories.  Orbiters are not given aeroshells for aerocapture.  A crewed mission capable of direct entry could keep its cruise phase RCS capability and either aerocapture or directly enter depending on surface conditions at the time.  We could then either save propellant or deal with either problems with the planet or problems with the craft from the relative safety of orbit for a bit.

As for someone's proposal of landing an uncrewed hab loaded with equipment, I personally think this is an excellent opportunity to test the vehicles before sending crews - send a workshop Hab with all the equipment you couldn't fit into the crewed hab, and send an ERV with similar capability and equipment - maybe as a massive Mars Sample Return mission (since this would flight-test the return mission).  Imagine 3-4 Mars Science Labs running across the surface and bringing back a few hundred kilos of samples to be packed into a capsule capable of returning a crew of four.  The main thing to keep in mind here, though, is that whatever is sent this way for future crews needs to be non-perishable.  No food, no chemicals - maybe inflatable structures like those recently designed for lunar use, maybe a workshop, maybe scientific gear, maybe a greenhouse made with materials that will not erode badly if exposed to dust storms or radiation.  

Something I find beautiful about Mars Direct is that we all have the same image from the book in our heads but it seems everyone has improvised off this theme like Jazz musicians.  Even if it's never built, we owe Dr. Zubrin much for creating a theme that allows so many people to learn to play and is compelling enough that we put the effort into learning.  
Kent Nebergall

Offline kraisee

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Re: Who's in Favour of Mars Direct?
« Reply #29 on: 04/01/2007 11:27 pm »
I'm also in general favour of using the same basic lander design for all parts of a Mars mission - whether it is delivering crew or cargo.   Such a concept would allow unmanned testing of most of the crew vehicle's systems, while delivering useful unmanned cargo for later missions to utilise.

I personally keep coming back to the Viking/Pathfinder/MER aeroshell concept - just expanded to ~8.4m diameter.   A combination of parachutes & descent engines looks suitable to me - although crew abort options on descent are extremely limited without launching a LOT more payload to LEO initially (something I'm not actually against!).

I've got an idea for a reusable transit habitation module, with a permanently affixed heatshield for aerobraking.   It would require a replacement propulsion module for each mission, and a replacement lander, but the hab should be able to be re-used many times for aerobraking at both ends of Mars missions.   This reduces the per-mission IMLEO requirements, and also removes the need for a crew return vehicle to be dragged all the way through the mission just to be used in the last 30 minutes returning to Earth.

I'm still working designs, but everything I've done so far is tailored for DIRECT.

Ross.
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Offline Kaputnik

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Re: Who's in Favour of Mars Direct?
« Reply #30 on: 04/03/2007 08:37 am »
I can't seem to find very much information on the 'VISITOR' scheme as proposed by John Neihoff in the 1980s. The idea was to have four heloicentric-obriting space stations whose paths ensured that they would shuttle regularly between Mars and Earth to coincide with the launch and nreturn windows. Neihoff envisaged huge, spinning, nuclear-reactor powered stations, but I presume the concept would work for a simple Mir-sized module modified for the trip.
My only source for the VISITOR scheme is the rather excellent book 'Race to Mars' which I must have read over a thousand times since I got it in 1987. The main advantage of the scheme is that the crew can be afforded a large habitat facility for the interplanetary transit, without this having to be launched anew with each mission. Thus the crew could leave Earth in a much smaller craft, rendezvous with the VISITOR, and then use that same smaller craft to descend to Mars on arrival. Cargo would be launched separately using simpler hohmann trajectories and (probably) direct entry.
Neihoff envisaged the use of a two-stage 'Biconic' craft whilst I've investigated the use of a single-stage reusable version of the same, which would rely on ISRU be refuelled on the surface. If the Biconics could be made reliable enough and within the required mass fraction (these would be pretty advanced craft) then the mission plan becomes very elegant indeed, with a single heavy launcher sending a reasonable sized crew to Mars in one launch, without any NTR, NEP, SEP etc being necessary.

However, I lack details on the delta-v required to reach a VISITOR rendezvous; I also do not know what the propulsion reqirements of the VISITORs would be. Whilst theoretically zero, the regular planetary flybys would presumably tend to throw the spacecraft into higher energy orbits.
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Offline KNebergall

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RE: Who's in Favour of Mars Direct?
« Reply #31 on: 04/03/2007 04:05 pm »
Buzz Aldrin has been working on an update to that.  The main objection is the amount of Delta-V it takes to catch up to the cycler station.  At any rate, his group advanced the design to take fewer vehicles on more complex paths that also speed the transfer.  

My concern would be the low-mass launches of crews and maintenance parts in an environment where the ISS requires tons of new and rebuilt equipment every year - I'd be hesitant to trust current technology and methods to the design of a cycler - I think we'd have to do something big, dumb, and simple or small, complex, and very highly redundant to make this concept work.

While I think magnetic shielding against cosmic rays is the way to go with Mars and other long term deep spaceflight, if we HAVE to resort to 4 meter water shields, some sort of cycler station would probably be the only practical Mars transfer solution.  Also, some magnetic shields may be massive, so they, too, may fall in this category if we build vehicles for crews larger than 4-6 people.  I'm just happy that MIT "Magnetic Faraday Cage" design exists to demonstrate that most of the problem can be solved for a small habitat without the crew experiencing magnetic flux in the cabin or on EVA.
Kent Nebergall

Offline CEV Now

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Re: Who's in Favour of Mars Direct?
« Reply #32 on: 04/04/2007 01:27 am »
Mars direct would get the public imagination back into the game, although their apathy with the moon is misplaced.

Offline aftercolumbia

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RE: Who's in Favour of Mars Direct?
« Reply #33 on: 04/05/2007 03:51 am »
Quote
RedSky - 31/3/2007  7:23 AM

What I worry about with any direct entry landing scheme (i.e., no orbit insertion first before landing) is what is the contingency if a few weeks before entry, it is determined that a landing as scheduled is unsafe.  This could be anything from a global dust storm, to some suspect equipment that may need troubleshooting.  With a direct entry, there is no option for a wave off, is there?  

Free return flyby.  It results in a lost landing, and a really long deep space cruise, but it can be achieved.  A propulsive correction maneuver would adjust the mission's course so that the approach orbit results in a post-encounter orbit that leads back to Earth.  The total mission duration is most likely to be 3 years, but can be 2 (give or take a few days.)

Quote
I remember when Mariner 9 got to Mars, it took a month or two for a global dust storm to settle down so that the surface became visible. Since the crew will be at Mars for 18 months or more, being in orbit and able to wait out such events seems wise.

I would recommend using a propulsive insertion maneuver rather than aerocapture.  It should be possible to provide oxyhydrogen propulsion (perhaps even the Ares V upper stage) for this maneuver.  Oxyhydrogen propulsion is far more mature at this scale than aerocapture at any scale.  Also, given the mass penalties of having the extra aerocapture shield (or heavier single shield), plus the vagaries of retaining or doubling up on deep space power (probably solar, but even nuclear would still involve external radiators), the question of which option is heavier needs more study.

To another post: Direct entry liftless is about 6-8g, depending on the arrival speed.  A liftless entry won't happen because the chances are too good you will land quite far from the ERV/MAV (up to 100km).  An L/D=0.16 entry can probably reduce it to 4-6g.  L/D=0.5 could reduce it perhaps to less than 1g (theoretically, about 2.5-3g(Mars).)

Offline Kaputnik

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RE: Who's in Favour of Mars Direct?
« Reply #34 on: 04/05/2007 02:27 pm »
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aftercolumbia - 5/4/2007  4:51 AM
Oxyhydrogen propulsion is far more mature at this scale than aerocapture at any scale.  Also, given the mass penalties of having the extra aerocapture shield (or heavier single shield), plus the vagaries of retaining or doubling up on deep space power (probably solar, but even nuclear would still involve external radiators), the question of which option is heavier needs more study.

To another post: Direct entry liftless is about 6-8g, depending on the arrival speed.  A liftless entry won't happen because the chances are too good you will land quite far from the ERV/MAV (up to 100km).  An L/D=0.16 entry can probably reduce it to 4-6g.  L/D=0.5 could reduce it perhaps to less than 1g (theoretically, about 2.5-3g(Mars).)

What are mass penalties fo using a cryo stage that has to store its propellants for c.9 months? Presumably there is a break-even point (in terms of storage time) when the active cooling and/or extra LH2 for boil-off loses you any performance advantage over a storable stage (e.g. N204/UDMH).

The g-loads for direct entry aren't as bad as I had feared- didn't Apollo have a L/D of 0.3? If so then presumably a similar craft could do direct Mars entry with a g-load of 2-3g, which I think must be within acceptable limits.
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Offline mong'

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Re: Who's in Favour of Mars Direct?
« Reply #35 on: 04/05/2007 03:01 pm »
the arrival velocity relative to mars for a minimum energy trajectory is around 3 km/s, direct entry wouldn't be that hard on the crew

Offline Verio Fryar

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Re: Who's in Favour of Mars Direct?
« Reply #36 on: 04/05/2007 04:37 pm »
Direct entry when returning to Earth is in the baseline of almost every mission plan. It should be much harder on the astronauts because of the higher velocity and they being weaker after 2+ years in space.

Offline kevin-rf

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Re: Who's in Favour of Mars Direct?
« Reply #37 on: 04/05/2007 05:19 pm »
Quote
Verio Fryar - 5/4/2007  11:37 AM

Direct entry when returning to Earth is in the baseline of almost every mission plan. It should be much harder on the astronauts because of the higher velocity and they being weaker after 2+ years in space.

I think they are talking about mars direct entry instead of spending the fuel (mass) on going into orbit arround the small blush red dot.
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Offline kfsorensen

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RE: Who's in Favour of Mars Direct?
« Reply #38 on: 04/05/2007 05:27 pm »
All of these issues with aerobraking, propulsive capture, human adaptation to weightlessness, abort scenarios, and robustness between mission opportunities are some of the reasons why I came to favor the artificial-gravity nuclear-electric propulsion vehicle over Mars Direct.

Also issues with the development of the heavy-lift rocket and the fact that Mars Direct needs a nuclear reactor anyway.  Why not build a good one and use it to get there?

Offline aftercolumbia

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Re: Who's in Favour of Mars Direct?
« Reply #39 on: 04/05/2007 05:36 pm »
Quote
Verio Fryar - 5/4/2007  10:37 AM

Direct entry when returning to Earth is in the baseline of almost every mission plan. It should be much harder on the astronauts because of the higher velocity and they being weaker after 2+ years in space.

I see where you're coming from, but direct entry at Earth isn't as much of a problem.  Where L/D problems happen over Mars, your drag coefficient starts to drop fast at L/Ds over 0.18.  This is a big problem with Mars' thin atmosphere.  Earth has a much thicker atmosphere, and compared to landing on Mars, landing on Earth is a non-issue.  Apollo got 0.5:1 with its shape, while Soyuz gets a barely adequate 0.3:1.  The former results in about 4g, the latter about 6g for entries returning from Mars.  A liftless entry from Mars, I'm guessing about 11-12g, which is survivable for returning astronauts if they are equipped with custom-built g-suits and oscillating respirators (standard equipment in the F-16 Falcon, I think.)  The problem is that this, and the spacecraft's tougher structure, add mass to the very top of the mission, with the biggest IMLEO multiplier.  A lifting entry (skip-glide) is a much better idea.

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