Has Dr. Zubrin Addressed Mars Direct Objections? - A few questions?

GCNRevenger · 2004-12-17 18:47:12

Now for mission particulars... I want to start out by saying that MarsDirect as currently envisioned is IMPOSSIBLE.

You must not have read much about DRM... the MAV vehicle would have been fueled by the ISRU unit before the crew left Earth in the same way that MarsDirect does. The DISadvantage of MarsDirect's ERV is that the entire mass of hardware needed for Earth return must be lifted from the surface. NASA DRM is superior, because only the crew and boxes of rocks and HDDs would need to be sent from the surface, which permits you to use a much more robust ERV.

To subscribe to the notion that not using ISRU for the entire return trip is a "bad" thing is to willfully overlook its disadvantages or even a minimal reasoned comparison... Also, if you may have been reading previous posts, you may have learned that the entire ERV crew cabin, LSS system, and consumeables would have to weigh about as much as a Soyuz capsule. For up to 2.5 years.

This is a best-case senario, with the unshielded nuclear reactor being half of the optimistic goals of the progenitor SP-100 program, almost no consideration of the reentry systems, and no signifigant capacity for sample return.

In short, the MarsDirect ERV is not possible by any stretch of the imagination reguardless how rosey your glasses. It cannot be taken seriously by any level-headed apraisel... hence why the DRM MAV/ERV concept on a per-crewmen basis is the obvious choice.

The HAB is not in good shape either; it isn't likly that you could carry the required pressurized rover on either payload as envisioned, or the drill needed to hunt for bugs or water. There isn't even enough room for a proper glove box, much less the electron & optical microscopes, the mass spectrometer, perhaps an autoclave, and the biochemical detectors. You do want to look for life and study geology don't you?

Next, the idea that MarsDirect could somehow be upgraded into somthing more is not credible either. The Ares launch vehicle is already at the upper limit of any concieveable SDV launcher, and cannot be improved upon. Building a base 25MT at a time is just not going to happen, payloads in the 50+ tonne range will likly be commonplace. The monolithic ERV also precludes any upgrade of ERV reuseability down the road. With the HAB being too small to begin with, and too small for a larger construction crew, it isn't worth it to build it or any of the MarsDirect componets at all.

Now about those human factors... "There is very little substance to any of the claims made on the human factors subject..."

There isn't any substance to your assertion that this isn't a problem. There is a real risk that the astronauts could be mentally impared or incapacitated because of the extended isolation and poor living conditions, especially when cooped up in zero-G during transit. Shooing away this concern could be fatal if an astronaut isn't able to focus, and the "oh it'll be okay, your overreacting" excuse is the same mindset that got the Columbia and Challenger crews killed. We MUST err on the side of caution where possible when dealing with big question marks.

No going outside, no getting out of the little tin can, you can't even sit down to enjoy your meal... No, the HAB and even moreso the ERV are much too small. I think that it would be common sense to be critical of a HAB structure where there isn't any contiguous space much bigger then 3m wide or sufficent storage space. I believe that the MarsDirect HAB is too small by about 50%, and the ERV by a much larger amount with its smaller diameter.

And finally the radiation issue... what you don't seem to be willing to accept is that radiation shielding is a fundimental physical problem, and not one that can be stepped around by improved technology. There is no practical passive defense against cosmic radiation except to put atoms between you and space. Atoms that are practical to wrap your space ship with are heavy, and there is no magical silver bullet to fix this situation... You either bring enough radiation shielding mass or you don't, there isn't going to BE a superlight shield.

Oh, which reminds me... Doc Zubrin, being a nuclear engineer by trade and not a medical doctor or biologist, should not be making "oh this is good enough" assumptions about shielding. Nor does he include any in his reactor budgets in the event there aren't any rocks or dunes to park the thing behind. Whoops.

BWhite · 2004-12-17 19:46:15

Since a mission architecture based on 2 shuttle C+ is most likely cheaper than building Ares (if Delta "V" can come close to shuttle C+ well that's okay also) and 2 shuttle C+ can throw more to Mars than one Ares, then that is what we should be looking at for mass budget numbers.

Shuttle C+ will absolutely be cheaper if it is used for something in addition to Mars, such as lunar cargo support missions, JIMO class missions (and I still believe an orbiter can "play catch" with a shuttle C launched truss payload for ISS completion) etc. . .

1 shuttle C+ lifts the Mars hab and some fuel. The 2nd lifts fuel and engines. A Delta IVH (or Kliper) carries up crew, spacesuits and extra food. The total mass available will be much higher than Ares.

Edited By BWhite on 1103334416

John Creighton · 2004-12-17 19:59:54

I think one advantage of shuttle C over a 250 metric ton clean slate option is it is better suited size wise to a JIMO class mission. Then again the clean slate option GCNRevenger proposed had options for reduced launch weight.

John Creighton · 2004-12-17 20:07:46

I wonder if three shuttle C’s would be too much orbital assembly. First one delivers the vehicle. Second delivers a methane tank. Third one delivers the engines and a hydrogen tank.

GCNRevenger · 2004-12-17 20:25:21

I am split on if a superlauncher would be worth the trouble or not. Shuttle-C would be nice, IF it could perform as advertised. If this isn't the case, then the tossup is between clean sheet "super-heavy" or smaller numbers of clean sheet "light-heavy."

Superheavy will be more efficent on a per-weight basis because of its larger size, but I can see advantages to launching only a few smaller vehicles. There aren't many options to making a "light" version of the superheavy other then dropping boosters.

The problem with dividing up the vehicle into three parts or more is the liquid hydrogen. Any Mars payload requires about 70-80% of that mass in propellant (for 900sec NTR) to orbit. If you divide up the vehicle into three, then some of the Hydrogen would have to be sent up on the second flight, where it would have to sit for a while.

NASA DRM estimates a 90 day turn-around between Magnum flights, which is about 2-3 times too long for light weight passive LH2 stowage. It also will make the whole departure schedule tight overall.

One flight or two, but no more then that for Hydrogen unless you could send up the third flight within weeks of the second.

John Creighton · 2004-12-17 20:34:49

But if the second flight delivers methane fuel and the third flight delivers hydrogen fuel then you don’t have the boil off problem. How many pound of methane would you have to lift to get the same delta V as hydrogen? The other possibility is better storage. Didn’t you previously suggest that the boil off rate could be significantly improved? How would you do this? Some kind of condenser?

John Creighton · 2004-12-17 20:39:22

What about the possibility of using multiple launch pads to get a better turn around time? Probably only one launch pad could launch a heave lift vehicle but could an upgraded medium launch vehicle lift a big enough fuel tank to help at all or would the size of the tank sent not be worth the cost and complexity?

GCNRevenger · 2004-12-17 20:58:05

Using Methane for TMI isn't such a good idea, its Isp in combustion hardly tops 400sec, and it isn't very good in nuclear engines at all. You'd need ALOT of methane to get the same push as Hydrogen/NTR.

Another issue is docking. Each launch you make has to have its own RCS system, docking adapters, fuel lines maybe, communications systems and power supplies. The fewer launches the better complexity wise. This pretty much kills medium launchers for Mars ships.

The boiloff rate could be improved or even eliminated for Hydrogen with the use of a condenser, but that is a big energy hog and would add signifigant weight to the rocket.

Multiple pads would mean multiple flight crews and would get expensive FAST.

John Creighton · 2004-12-17 21:24:21

Using Methane for TMI isn't such a good idea, its Isp in combustion hardly tops 400sec, and it isn't very good in nuclear engines at all. You'd need ALOT of methane to get the same push as Hydrogen/NTR.

Doesn't triton use oxygen in one mode of its nuclear thermal rocket. Oxygen has about the same molecular mass as methane. But perhaps the majority of the delta V comes from hydrogen. I was more interested in a comparison with chemical rockets. If you are launching the mars payload in two pieces and using nuclear thermal rockets you should be able to get a lot of mass to mars with a shuttle derived vehicle. But I suspect you are right that methane is not very good for nuclear thermal.

Another issue is docking. Each launch you make has to have its own RCS system, docking adapters, fuel lines maybe, communications systems and power supplies. The fewer launches the better complexity wise.

I think there must be a payload size the cost of this added complexity becomes small in comparison to the cost of launching the vehicle. I am just not sure what payload is.

The boiloff rate could be improved or even eliminated for Hydrogen with the use of a condenser, but that is a big energy hog and would add significant weight to the rocket.

I wonder if there is a practical way to dump the condenser just before trans mars injection.

Multiple pads would mean multiple flight crews and would get expensive FAST.

Don’t we already have multiple pads and multiple flight crews? Is it impossible to coordinate them?

GCNRevenger · 2004-12-17 21:33:53

The TRITON's "LANTIR" LOX-augmented mode increases thrust, but it also reduces Isp by about 20-25%, requiring you to haul more propellant mass overall.

You could leave the condenser in orbit, but the thing will be fairly big & heavy, and the fuel lines involved would present some signifigant additional complexity.

I think we only have one operational Shuttle pad, with the other being some trouble to make workable again. You don't want multiple pads because of the cost to operate them both.

John Creighton · 2004-12-17 22:32:18

I think we only have one operational Shuttle pad, with the other being some trouble to make workable again. You don't want multiple pads because of the cost to operate them both.

Maybe by the time the US launches a mars mission China will have a heavy lift launch pad too. Russia of course has the latitude penalty. Of course I know you think international cooperation is not worth the effort. I am kind of neutral on the point. But I am wondering what is the advantage of one huge vehicle with lots of crew instead of dividing the crew up between multiple vehicles. How big a vehicle is needed? http://www.newmars.com/forums/viewtopic.php?t=1808]Well that is the subject of another thread.

RobertDyck · 2004-12-17 22:44:17

First, the single floor version of the Mars Direct habitat is enough. Someone who wants a luxury cruise ship isn't the person for the first exploration mission to Mars. Yes, you do need more lab space than the little lab in the single floor version. That's why Robert Zubrin proposed using the lower floor as the lab, EVA prep, and airlock after the rover, garage tent, and inflatable greenhouse were removed. Remember I called for sending a dedicated inflatable lab in a cargo lander as a separate launch. Yes, the Mars Direct ERV is a bit tight. I'm the one who asked where's the zero-G exercise equipment. You need that if you don't have an artificial gravity tether. But to be fair, others have pointed out to me that the ERV has exercise equipment. Mars Direct is possible.

Landing location: we have Mars pretty well mapped out. We will know exactly where the dunes are before landing.

As for assembly launches, if you use Shuttle-C you get the launch facilites at KSC. That includes 2 launch pads. Prepair 2 vehicles and launch them a day apart. I've advocated Shuttle-C before, but the down side of any SDV is potentially maintaining the extreme cost of Shuttle facilities.

Mad Grad Student · 2004-12-17 23:00:42

I don't have much time right now so I'll just make one point.

GCN, I read your posts and you actually seem to have some good points to make. But why do you have to pepper every post with patronizing language and personal insults? Good golly, I don't know how you expect me to take you seriously if you start throwing temper tantrums like a hyper first grader.

John Creighton · 2004-12-17 23:05:02

I don't have much time right now so I'll just make one point.
GCN, I read your posts and you actually seem to have some good points to make. But why do you have to pepper every post with patronizing language and personal insults? Good golly, I don't know how you expect me to take you seriously if you start throwing temper tantrums like a hyper first grader.

You mean language like , “Oh another thing”. I just ignore that “patronizing” language. I am much more interested in hearing well thought out arguments. I think GCNRevneger is one of the more knowledgeable people here and I enjoy his posts the most.

GCNRevenger · 2004-12-17 23:10:58

MarsDirect is NOT possible. The ERV imparticularly is simply not reasonable. Period. And with the heavier ERV comes bigger fuel tanks, bigger hydrogen needs, bigger ISRU, etc. Its not a linear relationship.

No, no I don't think it is big enough. There is insufficent space on the first floor alone. There is too little space for a solid six months. I don't think you have a sufficent mental image of how small it is... Even if you do, you are making this assertion out of hand because it HAS to be big enough to make MarsDirect fly. It must be at minimum 50% larger for a four-man crew or around 100% bigger for a six-man crew and have emphasis on contiguous living space.

Yes yes inflatable this, inflatable that... you can't have an inflatable lab space easily because of the equipment that doesn't fold up neatly. A glove box should be rigid and it will be fairly large. An electron microscope and its pumps is a washing-machine sized piece of equipment. A nice TOF mass spectrometer is aproximatly that size as well, and must have a long dimension for the flight tube. As well as the sample chaimber, perhaps an autoclave, a rock grinder (at least a small one), etc etc etc... A laboratory is not just an empty room with a place to sit and poke at rocks.

Mapped out down to meters? This is assuming you can land with precision too.

GraemeSkinner · 2004-12-17 23:19:30

Yes yes inflatable this, inflatable that... you can't have an inflatable lab space easily because of the equipment that doesn't fold up neatly. A glove box should be rigid and it will be fairly large. An electron microscope and its pumps is a washing-machine sized piece of equipment. A nice TOF mass spectrometer is aproximatly that size as well, and must have a long dimension for the flight tube. As well as the sample chaimber, perhaps an autoclave, a rock grinder (at least a small one), etc etc etc... A laboratory is not just an empty room with a place to sit and poke at rocks.

Forgetting the size problems of lab equipment I don't think we have the skill at the moment to land equipment such as a electron microscope in one piece and expect it to work 'out of the box' as it were. A lot of lab equipment needs setting up correctly in order to get any accurate data from it, that means if we send a lab with a manned mission they'll have to have someone who can set up the equipment correctly as well as operate it. This says nothing about the extra power requirements for all the lab equipment. We do need lab equipment on a manned mission in my view, we just have to be careful about what we send and when.

Graeme

Mad Grad Student · 2004-12-17 23:32:34

You must not have read much about DRM... the MAV vehicle would have been fueled by the ISRU unit before the crew left Earth in the same way that MarsDirect does. The DISadvantage of MarsDirect's ERV is that the entire mass of hardware needed for Earth return must be lifted from the surface. NASA DRM is superior, because only the crew and boxes of rocks and HDDs would need to be sent from the surface, which permits you to use a much more robust ERV.
To subscribe to the notion that not using ISRU for the entire return trip is a "bad" thing is to willfully overlook its disadvantages or even a minimal reasoned comparison... Also, if you may have been reading previous posts, you may have learned that the entire ERV crew cabin, LSS system, and consumeables would have to weigh about as much as a Soyuz capsule. For up to 2.5 years.

And how exactly does not taking full use of in-situ resources offer advantages? The ERV in Mars Semi-Direct has to haul a considerable amount of propellant all the way from Earth to Mars orbit. That's a lot of mass, that could be avoided almost entirely if it were made on Mars. Going direct from the surface yields more payload capacity and hence more possible science return, as well as fewer launches and hence less chance for failure.

I'll just come right out and say it. I'm not a rocket scientist. I'm not quite sure what a reasonable estimate of system mass is, but I doubt that many other people here can give a better guess than I can. (NOTE: you DO NOT have to yell something like "I bet you're not a rocket scientist, you don't know what you're talking about!!!!" in your next post, GCN. It's really not going to help your case if you do) If Zubrin's mass estimates are on the low side we can always use a bigger booster or go nuclear, but no matter what the system will mass more with semi-direct and the science return will be less per pound.

Who said anything about extended zero-g time? If you just take the kick stage and attach a tether to it you can make a pretty decent centrifuge to replicate gravity. Before you start screaming and using the bold, underline, and italicized writing all at the same time, I'd like to say that I in fact do realize that this will add a token amount to the system mass, but it would be worth it to eliminate the zero-g dragon. Under no circumstances would the crew be under worse conditions than those endured by U-boat crews or (Ant)Arctic researchers. Of all the things that could possibly go wrong on a mission to Mars this is one is towards the bottom of plausibility.

There would still be many parts of Mars Direct that could be used in future missions. Perhaps not entire vehicles like the hab and ERV, but practically all of the subsystems, the LSS, the ISRU setup, the radiation sheilding, engines, the launch vehicles, etc etc could be implemented in future scaled up versions of Mars exploration. Apollo happened because of a very complicated set of circumstances, many of them unique to its time frame. Its unrealistic to say that exactly the same loss of interest would occur again "just because," and if the day after the first landing everyone at NASA starts lobbying congress with the next scaled up hardware it would at least stand a fighting chance of making it off the drawing board.

As for radiation sheilding: there are in fact other ways to shield out radiation than putting an atom at every point in the hab. http://www.spacedaily.com/news/rocketsc … .html]This article proposes using superconducting magnets to create a magnetic "bubble" around the hab to keep out charged particles. Granted, that won't do much against high-energy gamma rays, but it would ward off the bulk of what the Sun spits out, especially during solar storms. As you said, it's unreasonable to try to completely sheild the crew from all sources of radiation, so why bother? If we can protect them from solar radiation and the bulk of alpha- and beta-particles that's really the best we can do without sending them in a giant tank of water. Sometimes that's just the way the cookie crumbles.

Let me clarify what I said in that last post. The amount of personal insulting in this thread has simply gotten out of hand. We all want to go to Mars (or at least get people to Mars), right? What are we really arguing about?

RobertDyck · 2004-12-18 00:47:05

Ok, before I get pushed into defending Mars Direct without change, let me say I advocate going to Mars. I said before that landing all the food, life support, exercise equipment, heat shield, parachute, etc. for the return to Earth all the way on the surface of Mars just to lift it off again is a waste of propellant. It's more efficient (less fuel) to leave it parked in Mars orbit. Once you do that, you can use the same vehicle for interplanetary transit each way. In fact, why bring the Earth atmospheric entry vehicle all the way to Mars and back? Just park the ITV in Earth orbit and use something (capsule or Shuttle) to return crew to Earth surface. Once you've done all that, it's easy to make the ITV reusable. A separate ITV lets you design a dedicated Mars surface habitat, one that doesn't require zero-G operation or micrometeoroid shield. You can reduce heatshield by compacting the hab for landing, and every weight reduction will reduce the parachute, legs, and landing rockets. This means sending all habitats with the crew, no ERV left unattended for transit to Mars and multiple months sitting on the surface.

Using the MAV as the TEI stage reduces launch mass from Earth. You can land large empty tanks by using collapsable tanks. Kel-F bladder supported by a basket. The basket can be made of bi-material members, compressible but non-elastic on the inside, bendable outside. That should curl up for storage but can't completely straighten out. Interwoven, pressed down into a circle, and curled up. Release the spring material to deploy the basket. LOX and methane are very close temperature, put the LOX bladder (colder) inside the methane bladder. Reduced tank volume means reduced heatshield size for landing, which means reduced mass for the parachute, legs, and landing rockets. Just add a structural member to push up when it docks with the bottom of the ITV.

What's the real difference from what you're saying, GCNRevenger? I'm saying 4 crew instead of 6, and volume of a single floor MD hab or single ISS module is enough for transit. For additional space on the surface you have the lab and great outdoors. Mars is a big planet.

Dayton3 · 2004-12-18 11:46:40

^So is it my understanding Robert that your preferred mission plan is Mars Semi-Direct rather than Mars Direct since if I read it right, you are advocating parking an unfueled vehicle in Martian orbit?

Or, are you advocating Mars Hybrid Direct in that you want all the return fuel manufactured on the surface?

Once again, I say this the original Mars Direct I believe is the best mission plan.

Now, you can want a more massive Earth Return Vehicle with greater room for mass growth.

You can want a six man instead of a four man crew.

If thats the case, why jack with the mission plans at all? Just build a larger booster in the first place?

I hate to use the metaphor, but when we talk about building a larger booster than the Ares, its not really rocket science. Its easily doable from an engineering standpoint.

RobertDyck · 2004-12-18 12:40:55

You'll notice I started with Mars Direct, tried to address what I perceive as weaknesses (ERV too small, and dropping it on Mars surface is a waste of fuel), and updating it with new technology developed in the last 14 years. What I ended up with is very similar to Mars Semi-Direct, except it uses the MAV as the TEI stage. That's what's called Mars Hybrid Direct, my preferred plan. Fuel saved by not dropping the ERV on Mars permits a larger return vehicle, no need for a larger booster. It also permits a reusable ITV, and can be easily assembled with medium lift launch vehicles like Delta IV Large. You can always build a bigger launch vehicle, but who's going to pay for it?

BWhite · 2004-12-18 13:27:06

I hate to use the metaphor, but when we talk about building a larger booster than the Ares, its not really rocket science. Its easily doable from an engineering standpoint.

Politics and finding money are the show stoppers, not the engineering.

C M Edwards · 2004-12-18 13:28:06

An electron microscope and its pumps is a washing-machine sized piece of equipment. A nice TOF mass spectrometer is aproximatly that size as well, and must have a long dimension for the flight tube.
Forgetting the size problems of lab equipment I don't think we have the skill at the moment to land equipment such as a electron microscope in one piece and expect it to work 'out of the box' as it were. A lot of lab equipment needs setting up correctly in order to get any accurate data from it, that means if we send a lab with a manned mission they'll have to have someone who can set up the equipment correctly as well as operate it.

The people you're talking about are often referred to as "the crew" or "astronauts". :;):

Yes, the average electron microscope is somewhat bigger than a washing machine. Further, the equipment needed to keep it calibrated and operating is about the same size. But we needn't send an average one. To an extent, capacity can be traded for size and still send something considerably better than a high school caliber optical microscope. I have no doubt that a passable electron microscope can be fit into a smaller package. (Regarding how much should be sacrificed, I recall being just as fond of an unsafe, barely functional, desktop-sized design that could be built for less than $100 as I was of LSU's old half-million dollar, top of the line baby, so perhaps I lack perspective! )

Decreasing the size of the microscope will not decrease the labor necessary to calibrate it. However, I have confidence that the crew will include members skilled enough to do that.

That said, I can't get past the notion that an electron microscope isn't likely to be used either going to or coming from Mars, no matter how small you make it. For one whole year or more, it's dead weight. Why send it along with the crew at all? For that matter, why send any lab equipment with the crew that you don't expect to need in orbit? Ship it ahead and let them pick it up on Mars.

Dayton3 · 2004-12-18 14:42:14

You'll notice I started with Mars Direct, tried to address what I perceive as weaknesses (ERV too small, and dropping it on Mars surface is a waste of fuel), and updating it with new technology developed in the last 14 years. What I ended up with is very similar to Mars Semi-Direct, except it uses the MAV as the TEI stage. That's what's called Mars Hybrid Direct, my preferred plan. Fuel saved by not dropping the ERV on Mars permits a larger return vehicle, no need for a larger booster. It also permits a reusable ITV, and can be easily assembled with medium lift launch vehicles like Delta IV Large. You can always build a bigger launch vehicle, but who's going to pay for it?

In Mars Hybrid Direct then, since all the fuel must be manufactured on the Mars surface, then the Mars Ascent Vehicle must hard dock with the Earth Return Vehicle and then use its engines to propel both back to Earth Orbit right?

Perhaps its a better plan. Who can say.

But for gods sake can't we all one or another just agree on a plan and lobby for it?

How big a crew? Can we all live with 5?

Conjunction flight plan? Can we live with that?

No more than three launches per mission? Can we live with that? Note, I'm not including the shuttle or crew return vehicle flight that takes the astronauts back down to Earth after the mission.

How much scientific equipment can we carry along? Can we do the job with one metric ton? Two metric tons? Three?

Whats the total mass of samples we wish to be able to return with?

I hope the time between the first manned Mars mission and the one to Callisto is considerably less than between the moon and Mars.

RobertDyck · 2004-12-18 17:13:21

I saw video of Robert Zubrin's testimony before congress. He called for a study for a detailed mission plan, and competition between contractors. I may see a few details differently than he, but the objective is the same. Keep it small enough to be affordable, and let's get moving now. Keep it within NASA's current budget, and possible in just a few years. Actually, that's one reason I want a mini-shuttle; NASA wants a reusable space transportation system and I want to free funds for planetary exploration. I agree with NASA, in the long term a reusable system is more affordable than an expendable one. The key is to keep it small and special purpose; it can't be everything to everyone. I submitted the mini-MAKS/HL-20 paper to NASA in the hope they will build it and retire the full-size Shuttle early. We may argue over the development cost of such a mini-shuttle, but even the most pessimistic estimate is less than a single year operation budget for the current Shuttle. Operation budget of the mini-shuttle space taxi will be even less. I want to redirect Shuttle funds to manned exploration of the Moon and Mars. I would prefer going directly to Mars and skip the Moon, several NASA people at the November 30 workshop want to go to Mars as well, but George W. Bush said the Moon. Ok, so Moon and Mars; let's get going.

Dayton3 · 2004-12-18 18:04:42

What would be the crew and cargo capacity of the mini-shuttle you mention?

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