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

SpaceNut · 2004-12-13 10:25:36

What would be the change if the fuel to go to mars was not Lox / H2 but Methane does the same problem of boil off occur? Since methane would be used on the ERV why not keep that the constant once you leave Earth instead.

BWhite · 2004-12-13 10:56:25

What would be the change if the fuel to go to mars was not Lox / H2 but Methane does the same problem of boil off occur? Since methane would be used on the ERV why not keep that the constant once you leave Earth instead.

Boil off is only one issue. Keeping methane or LH2 or LOX stored for several years while in orbit seems risky.

Direct return from Mars to Earth has the advantage that the astronuats can stay on Mars (the 2nd safest location for humans in the solar system) unless they KNOW the ERV has full fuel tanks.

But you can blend the architectures. A minimal MAV capable (barely) of Earth return via chemical propulsion and a robust habitat parked in Mars orbit with a nuclear thermal engine.

Dock the MAV to the Earth return vehice and fly both back to Earth. Use the MAV to land on Earth and park the habitat in LEO for future use. Design the nuke thermal engine to be a modular "plug and play" system and you have a re-useable architecture. Dicard the used nuke thermal module and attach a clean engine module and re-use.

GCNRevenger · 2004-12-13 11:27:16

An Earthly cruise liner has exactly zero to do with building spaceships psychologically, because you don't have a huge massive ship to run around on when you are stuck for six months between planets. The HAB's staterooms & bathroom are aproximatly the right size, they aren't the problem, the problem is the rest of the vehicle is too small and devided into too many small rooms. The lab is too small, the "living room" is too small, and there isn't a good place for vehicle control or equipment/storage space acessable during transit. Building the ERV, which will be a good two or three meters smaller anyway, within current mass budget is clearly not feasable to begin with and it suffers from similar "elbow room" problems.

You keep on talking about making the suits durable enough for a daily EVA, which is possible, what I am saying is that the water & gasses consumeables involved will be considerable. You will need to lug along an exhaled water condenser, and you will probobly have to make quite a bit of extra oxygen then you would if you sat in the Hab all day. I also worry about Nitrogen losses from suit pressure regulation, which could add up if the whole crew goes outside every day or two, requiring even more ISRU capacity.

"Mars Direct is not Apollo. I also want to start establishing a permanent presence on Mars, but MD is not Apollo!"

YES,, yes it is... MarsDirect IS a Martian Apollo because it is being thought of and planned in the same exact way... To get there NOW and to do it as simplest, smallest, and fastest acceptable way with absolutely NO serious thought about what happens after we get there. Going to Mars this way would be a horrible mistake and leave us trapped here for another generation or two.

If you don't go from the first day with serious thought and planning to stay, then we shouldn't go at all until we are ready to. The political, technologic, and economic inertia will only be enough for ONE Mars program, that getting there and saying "yay we're here, oh now lets stay, we'll need new this and this and this..." isn't going to fly, the country would not tollerate such a thoughtless rush or deciet and clip your wings for good.

"...send all manned missions to the same spot starting with the first mission. That will enable accumulation of equipment for a permanent base, not as a giant base construction mission but simply accumulating left-overs from science missions. Once started we can send a larger base construction mission later."

This is a perfect example of not being really serious about the future... So you want to dash off to Mars only to throw away all that money and work when you need to "larger missions later??" Certainly not, definatly not when such a larger mission is not unaffordable today. If you are going to stay eventually anyway, don't bother with the smaller missions to begin with. Developing small and large is going to be much more expensive then just doing large!

As for using old worn out HABs and various bits and pieces as some kind of "base," please thats nonsense... MarsDirect is also incapable of delivering large enough payloads to Mars for base building, and if you are using the excuse that humans can do science more efficently then robots, then you WILL be landing all over the surface... Try that one with the science review boards and you'll just get laughed at.

Anyway, I think that going with a large enough mission for a future perminant presence is not sufficently bigger then MarsDirect to be a fatal impediment... we have spent so much on the Shuttle and the ISS that this kind of investment is simply not foolish. What is foolish though is this "start small" nonsense... either you start with staying in mind, or the price you'll pay for throwing away all the MD hardware and breaking the trust placed in NASA will be too high... and you won't be going anywhere.

BWhite · 2004-12-13 11:32:23

General Simon "Pete" Worden wants to send people to Mars, to stay. Draft him for the new NASA administrator.

GCNRevenger, we need to promote the idea of "staying" as the motivation.

Science? Apollo style may well be fine since three Mars Direct missions gives over 6000 man-days on Mars. National prestige? Plant the flag in the red dust. No reason to stay.

But to go bigger and get nuclear propulsion we need political support for going and staying.

Edited By BWhite on 1102959389

GCNRevenger · 2004-12-13 11:50:37

NTR engines are an integral part of the deal. If the mission will be flying on a pair of "light" HLLVs going chemical won't buy you enough payload I don't think. They are really non-negotiable if we're serious about sending heavy payloads.

They are NOT too sensitive either, we have been launching much more dangerous Plutonium payloads for years. Rebuilding NERVA or Timberwind will not be a huge expense either, and will be well worth it.

I am curious about using Timberwind style PBR reactors instead of NERVA style "graphite block" with their higher Isp. If the TMI engine(s) were powerful enough to leave orbit in one burn, then the improved performance and lower engine complexity could greatly reduce engine prices.

Using NTR both ways on the ERV would be great, but I think that adds excess risk and headache. Storing LOX and CH4 over essentially indefinate times shouldn't be a problem, and they are much safer then Hypergolics in use today. Making the NTR stage with cryogenic fuel cooler will add signifigant weight and complexity... not to mention that if it failed, the crew would be in big trouble. Oh, and expendable high-temp Timberwind engines have high Isp to start with and are cheaper then fancy Bimodal NERVA-style engines. And last but not least, you would have to put the NTR stage on course back to Earth with hot reactors, which might be a political issue.

There is enough payload mass to put chemical TEI fuel with the ERV in Mars orbit. Oh, and as nice as it would be have the MAV big enough to go all the way back to Earth on its own, that isn't practical... you just have to trust it the ERV this time.

Edit: If you are having to launch an HLLV for the fresh TMI stage, and another launch for sending up fresh supplies & refurbishing gear, you probobly may as well send up a new ERV.

RobertDyck · 2004-12-13 14:04:26

If you really stop and think about what we're saying, the mission plan you want isn't much different from what I want. I'ld love a Timberwind TMI stage. In fact, Timberwind had both a lighter engine and higher Isp, but Isp was achieved by temperature. I haven't raised the issue of nuclear propulsion with NASA, but they do include it in several funded research programs. Do you have any contacts with the military? Could you find the guys involved with Timberwind and get them to propose reactivating their design?

Cryogenic storage is a concern. There is boil-off during transit, but the vacuum of space makes hydrogen boil-off less. Temperature recorded by Pathfinder varied from -8°C to -78°C (day/night) but it can vary more than that. Oxygen boils at -182.96°C at 1 atm pressure. Methane boils at -161.6°C at 1 atm, and actually solidifies at -182.5°C. The critical point of methane is -82.7°C @ 45.96 bar pressure. How much pressure are the ERV tanks designed for? The Shuttle ET LOX tank operates at 20-22 psig, the LH2 tank 32-34 psia. The unit psig is pressure in psi relative to ambient pressure outside the tank, psia is absolute pressure. Since Shuttle launches from sea level the ambient pressure will be 14.7, so hydrogen tank pressure at lift-off will be 17.3-19.3 psig. So we'll have to reliquify for Mars surface storage.

RobertDyck · 2004-12-13 14:46:53

I should add, the Mars Homestead project includes Mars Society members but is not a Mars Society project. Many members are from MIT. That project's goal is to design the first permanent settlement. The design is to use Mars Direct habitats as construction shacks while building a much larger habitat from Mars materials. 12 construction crew.

SpaceNut · 2004-12-13 15:03:12

The only thing I see against adding in nuclear components is the much higher cost to accomplish any mission initially but if the devices can be used and re-used over and over again then we only need to worry about the waste products.

BWhite · 2004-12-13 15:11:46

As for using old worn out HABs and various bits and pieces as some kind of "base," please thats nonsense... MarsDirect is also incapable of delivering large enough payloads to Mars for base building, and if you are using the excuse that humans can do science more efficently then robots, then you WILL be landing all over the surface... Try that one with the science review boards and you'll just get laughed at.

Taken from The Case for Mars, page 89:

Using nuclear thermal, a 140 tonne HLLV can deliver 46 tonnes to the surface of Mars. Go with 210 tonnes from using 2 Shuttle C+ instead of Ares and that is 69 tonnes in payload.

How many of those cargo shots would be needed to get a permanent base up for 12 people and running?

Page 91:

If chemical propulsion is used, then the unmanned cargo flight launched by a single 140-tonne-to-LEO booster can deliver 28.6 tonnes to the Martian surface, while the faster piloted flight can deliver 25.2 tonnes. Can a manned Mars mission be designed within these mass limites? if it can't, we could alwasy design a bigger booster or go ahead and develop the NTR stage. But let's see if we can make it with nothing better than a Saturn V and chemical propulsion. If we can, then more advanced technologies or propulsion capabilities and their associated benfits are icing on the cake.

GCNRevenger, very few Mars Society types will oppose nuclear propulsion. Or building bigger boosters.

The question is how to build momentum when the NASA, Boeing/Lockmart propaganda is that we need 30-40 years of practice on the Moon before we even begin thinking about Mars.

If the VSE included nuclear thermal development from the beginning, few would argue against waiting for it.

GCNRevenger · 2004-12-13 15:19:37

Ultimatly perhaps, but there are two or three points of obvious contention...

1: MarsDirect is not capable of delivering or sustaining large enough payloads or construction crews on its own, nor does the arcitecture have much room for improvements. Ares may also prove to be prohibitive to develop due to the extensive modifications to the Shuttle stack.

This is assuming that the fatal faults in MarsDirect are corrected somehow, which would probobly cause a large increase in vehicle mass and size, which Ares could not support in a single throw.

2: NASA DRM is capable of delivering big enough payloads and larger crews, plus since the design is devided up there are more options for evolutionary improvements and to eliminate infrastructure items down the road.

3: NASA only has enough fiscal and political capital for only one Mars program or the other, but it does have enough to do either one. It makes no sense to me nor will it make sense to Congress to say that we should build the dinky MarsDirect now, only to say that we will have to throw it away later for somthing bigger.

But most of all is the idealogy perhaps... That you seek to put humans on Mars as soon as possible as the goal, and staying is not an issue, somthing only to be thought of after we get there. If it takes more time and money to do it right, then it does, and that is the price to be paid.

I think that this way of thinking is dangerous, because the means of getting there and the means of getting there to stay are sufficently different that the "just enough" arcitecture is not practical for anything else... Politically too, that if you press hard to just explore, then you suddenly change your tune, then the credibility you expended was for nothing. If we say that we want to go to stay up front, yes it will cost more political capital, but not as much as spending it on exploration and then tossing it only to ask for more.

SpaceNut · 2004-12-13 15:22:16

That in its self may be the problem of pay as you go to funding the goal. That future technology can not be afforded near term.

RobertDyck · 2004-12-13 16:38:28

I was the ISRU guy for Mars Homestead. They're trying to recruit more people and I don't have the time they were hoping for. But remember my mission plan calls for establishing reusable vehicles for Mars, collecting Habitats at a single location and designing them from the beginning to last multiple years. Include an ambient light inflatable greenhouse with the first mission and test ISRU. When you send the construction crew they already have habitats and greenhouses waiting for them, and scientists scouted out resources and tested ISRU technology before sending production scale ISRU equipment.

SpaceNut · 2004-12-15 14:43:56

Here is a modified thought for another board that the one in the same Bwhite had I think but here is the thought any ways.

By the way, Robert Zubrin is now a vocal proponent of using lunar oxygen to fuel direct return flights to Earth. Land a large vessel with a methane fuel supply but no LOX. This allows a much larger lunar payload and presence and will test equipment that can be used for Mars.

How about making the lander use the martian atmosphere though some sort of intake to mix with a fuel that would use the martian air as an oxidizer. This would save on the mass. You might need to carry a little synthetic oxidizer tank but could save on the down mass by not needing to carry all of it.

RobS · 2004-12-15 18:43:32

Silane and borane both burn in CO2, but with a lower specific impulse than methane/oxygen, and you'd have to haul the silane (about 30% of the propellant mass) to Mars, as opposed to hydrogen (about 5.5% of the propellant mass). And you'd have to spend a few hundred million or more to develop and test silane/CO2 engines, since they have never been used before.

-- RobS

Ad Astra · 2004-12-15 22:32:13

How dangerous would silane and borane be when compared with methane or kerosene? I get the impression that these are very nasty fuels.

Methane / LOX initially looks like the best fuel combination, but appearances can be deceiving. What if you were to haul kerosene or methane or propane to Mars, instead of hydrogen? Less fuel would boil off, and more fuel could be stored in smaller tanks. The oxidizer would come from electrolyzed carbon dioxide. The idea is worth a trade study.

GCNRevenger · 2004-12-15 22:37:04

The only reason we'd haul hydrogen to Mars is for ISRU use, not rocket fuel. The bennefits of Hydrogen rockets drop as the tanks get smaller and heavier (per volume), and there isn't a practical way to passively store large amounts for long periods. Any liquid hydrogen shipped from Earth will likly suffer 25% boiloff after 6mo even with the best passive insulation in small tanks like a lander would use.

For ISRU conversion use, you'd be hauling alot of carbon with you from Earth just to make that hydrogen easier to bottle.

Ad Astra · 2004-12-15 22:46:17

If my last post was misunderstood, I apologize.

The hydrogen would still be used as feedstock, while the hydrocarbon fuel would be a fuel. The tradeoff is CH4/LOX (produced on Mars, including the H2 feedstock) versus the LOX/Hydrocarbon reaction which would make LOX from Mars's atmosphere and bring the hydroarbon fuel from earth.

GCNRevenger · 2004-12-15 23:00:24

Huh? I don't follow...

What I am guessing you were thinking: Instead of bringing Hydrogen from Earth as Liquid Hydrogen, which boils off and requires bulky tanks, that instead bring Liquid Methane or a light Hydrocarbon and remove the Hydrogen from it on Mars as it is denser and has better thermal stability. Less prone to gas leakage too.

But, for these bennefits, you have to carry the carbon as the Hydrogen "binder" and this would add substantial weight to the feedstock, more then is saved by reduced storage difficulties.

Maybe you are thinking that the Methane or Hydrocarbons could be burned as fuel for energy and then use the resulting water for the ISRU machine too? But the Hydrogen would just be used to make more Methane for fuel, so this doesn't make thermodynamic sense.

RobS · 2004-12-15 23:45:08

I think the suggestion is, haul up just the methane and a device to crack carbon dioxide into oxygen and carbon monoxide to make the oxidizer. The methane will be more stable thermally than hydrogen. It would also be much heavier, though; rather than hauling 5.5% of your propellant mass, you'd be hauling up 22%. You also wouldn't save much energy, as the reaction to convert CO2 and hydrogen into methane and water is mildly exothermic. Making the oxygen's the energy-intensive step.

-- RobS

Ad Astra · 2004-12-16 01:03:57

Rob, you've hit the nail on the head. Methane or kerosene or propane coul be brought from earth to use as rocket fuel for the ascent from Mars. I have no desire to extract hydrogen from it, and no desire to run the Sabatier reaction.

Of course, if the numbers justify Zubrin's propellant production scheme, I will gladly support it. But I got the idea from a NASA study on sample return, which would make LOX from the CO2 atmosphere and bring propane fuel from earth to use for the fligh back home.

SpaceNut · 2004-12-16 05:58:18

So the ship in orbit around mars would have carried just the hydrogen or methane from earth, while the lox would come from Mars insitu Co2 cracking for the return trip. If the Co is kept for other uses rather than releasing into the atmosphere making things more toxic to any crew on the planet or colonization efforts in future years, ok.

SpaceNut · 2004-12-16 08:11:51

There have been a couple of points in this thread that has talked about the use of aerobraking the vehicles into mars orbit.

Andrews Space, Inc. Wins Contract to Flight Test a Variable-Drag Ballute

A Ballute is a pressure-stabilized, inflatable membrane that provides a large, blunt, high-drag surface for aerobraking systems. Ballutes offer significant advantages over rigid shells for aerocapture and reentry of spacecraft by providing simplified packaging and lower total weight.

Another use for inflatables? ??? Very simular to the one the russians are working on under the technology thread.

GCNRevenger · 2004-12-16 08:34:58

Rob, you've hit the nail on the head. Methane or kerosene or propane coul be brought from earth to use as rocket fuel for the ascent from Mars. I have no desire to extract hydrogen from it, and no desire to run the Sabatier reaction.

Mmmmm thats alot of Methane to drag all the way from Earth though, I think it'll put MarsDirect way way over budget and likly kill DRM, Sabetier reactor or no.

For really small payloads like Mars sample return it might make more sense, where your payload is only a few kilos.

Mad Grad Student · 2004-12-17 16:57:01

What I want to see happen for Mars?
-Ditch the "direct" part of the return leg. Combining the ERV and MAV as in MarsDirect places unrealistic restraints on the ERV, and so the NASA DRM three-ship aproach should be employed. This lends to future modification of re-use of the ERV someday perhaps, and sending "bulk" MAVs without ISRU plants & gear is easier than ERVs once a base is established.
-Double the payload of MarsDirect, make it on the order of 50MT as in NASA DRM, which is the kind of payload masses needed to establish perminantly, like a ~1MWe refuelable reactor, a pre-built HAB dome, or ISRU capabilities an order of magnetude beyond "exploration-class" stuff.
-Six crew minimum, which gives you much more manpower per mission while still being affordable... the size of crew needed for serious science or base construction, since robots will not likly be advanced enough for the task alone. Preferably with the option for eight if the HAB is launched without laboratory space/equipment once a base is established.
-Employ either the two-shot "light HLLV" (~100MT, like Shuttle-C with RS-68 & five-segment SRB) or build a vastly more powerful "super HLLV" with 200-250MT capacities in order to achieve this. Building a Shuttle-derived vehicle above 100MT like Ares may involve excessive modification. Solid-core NTR engines for TMI should likly be standard, with investigation of simplified high-thrust expendable Timberwind style engines.
-Don't skimp on the crew safety. Either include an escape option or don't launch the crew on the HAB. Sufficent floor space for psychological concerns. Radiation shielding aproved by medical scientists and not zealous nuclear engineers. Include the full 3-year LSS supply on the ERV. Etcetera.

Okay, so there is a difference of opinions.

Seperating the surface ascent and TEI parts of Earth return really only leaves you with many disadvantages over a direct return system. If the ISRU system has a problem than the whole mission is a bust even if you still have all the fuel to get from Mars orbit to Earth; there is no safety benefit here. All Mars Semi-Direct really does is use up more money and an extra rocket launch to accomplish the same task by deliberately not taking advantage of the full use of in-situ resources. Granted, the mass of a Mars Direct-style ERV will be greater than a MAV, but the mission is still doable. If it's not with an Ares-type launcher then I suppose we can just upgrade or use nuclear rockets, but sticking with direct return offers big advantages over a MAV/ERV setup.

More payload, heavier stuff is always great, but you need to keep this in perspective. The more you expect out of the first system the harder and longer it's going to be until it is launched, and every year a project is delayed is another round or Russian roulette at the hands of Congress. Are you feeling lucky today?

Mars Direct was designed from the ground up to 1) get people to Mars, now, and 2) accomplish a good deal of science in the process. The mission architecture includes enough science payload to make the mission worthwhile, and more importantly is a good first step in human Mars exploration. After the first landing with Mars Direct, ideally an expanded system with bigger science payload, larger crew, and possibly longer stays would be started, with Mars Direct flights continuing until its ready. This is in a way what should have happened with Apollo, but NASA managed to make going to the Moon increadibly boring for the public and Congress, we can't afford to do that with Mars. Can it be done this way? Maybe, but there's a better chance that we'll actually make bootprints on Mars than if we try to go as big as possible from the begining.

Who said anything about skimping on crew safety? The crew will know that their propellant is waiting for them before they even launch, and if something happens on the way they can always come back on a free-return trajectory. If they somehow manage to land wildly off course, the next mission's ERV can be redirected to their new landing site. Human factors? Bleh. Just as it was obvious to some people before the space age that under zero-gravity the heart will fly apart and eyeballs will ooze out of shape, and that astronauts will suffer separation anxiety and never come home, many will have you think that four (or six if you must) good-natured scientists and engineers will bash each others brains out if you send them to Mars. There is very little substance to any of the claims made on the human factors subject, the MD hab is fine.

Radiation protection is a bit of a sticky point. But then again it would take at least nine or ten years to go from drawing board to launch, so that should leave us enough time to develop a decent radation shield. We landed on the Moon when cars had tail fins but no airbags and room-size computers had less power than a graphing calculator. There is no reason to think that with today's technology we couldn't go to Mars within a decade.

GCNRevenger · 2004-12-17 18:10:42

Lets see, where to begin... "Mars Direct was designed... to get people to Mars, now"

This is the underlying problem I think, a true textbook example of getting in a "blind rush" without considering the consequences, or even properly thinking about the motivation. Getting people to Mars as soon as humanly possible would be a horrible mistake, a tragedy of Shakespearian proportion. NO, getting there "now now now!" is not the mission we should want, we could do that today with EELVs if we only wanted to send two people and be sending the first crews early next decade.

I think that Zubrin privately prefers such a mission, but he knows for fact that it would purely be a flags & footprints mission, with just enough capacity left over for a box of museum pieces. He proposed MarsDirect as the absolute minimum acceptable mission that would stand more then a snowballs' chance on the sun of working.

It is really very simple. We have to go to Mars to stay. Not on the first missions, but with a definate time table before the first piece of hardware is built. I reiterate, leaving the goal of going to stay as some nebulus item down on the "to do" list of mission planning is entirely unacceptable. There is only enough fiscal and political capital for ONE Mars program, not two.

MarsDirect cannot ever be more then a basic science/scouting mission, and its very dubious if it could even do that. In order to stay on Mars, systems with more capacity and growth options - such as NASA DRM - would be needed. The larger system will be more expensive and the larger system will take longer to get off the ground... so the issue about "every year a project is delayed is another round or Russian roulette at the hands of Congress." is not an issue at all.

Because, it is better that we not go at all until we are serious about staying

MarsDirect was concieved for the same mission that Apollo was concieved for the Moon, to send and retrieve humans from the Moon in a gainful way in the shortest possible amount of time. And we all know what happend with Apollo... the same would happen with MarsDirect. Since the arcitecture has no future beyond scouting missions, the prior higher but affordable cost of a more capable system is no longer an option as the money and political good will was squanderd in the blind rush... There wouldn't be enough left to start over.

So, we'd be stuck here again for another generation or two (or more) thanks to Doc Zubrin's overzealousness and lack of introspection... Which you seem to share.

Edit: I'd like to expand on somthing breifly... if we are going to be building a bigger mission arcitecture later, in order to fulfill the true mission of establishing and not just exploring, why bother with MarsDirect in the first place? It would be cheaper just to send additional "big" ships instead of developing and sending MarsDirect seperatly.

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

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