The case for space – Part 3: Martian delusions

mars-one

Figure 1: Mars One, serious vision or fantasy….or scam? [Source: Mars One, 2014]

I previously discussed the idea of colonising space as a possible solution to climate change and a future resource crunch. I think the conclusion would be that its not really a feasible solution. Yes, I have no doubt space exploration (as opposed to colonisation) will continue and I would argue that any money spent on space science is money well spent. But migrating large numbers of people off the planet, or start to mine other worlds for their resources just isn’t an economically feasible or practical proposal. It is therefore worthwhile looking at some of the proposals for colonisation doing the rounds on the internet, most notably Mars One, as well the proposed missions from the Mars Society and Elon Musk.

Mars One

The central theme of Mars One is “Mars to stay”. They propose a one way mission to Mars, with no immediate return option. There is perhaps an immediate fallacy in this plan – that a one way trip will be cheaper and easier. Actually, the opposite is likely to be true. Think about it, if you have no line of retreat, you need to build more redundancy into all of your hardware. You’ll need to stockpile spares in case something breaks down (a two way mission can simply abort and return to earth, a one way crew lose this option, as it will take months to get replacement parts out, spares will have to be stockpiled). If you’re only planning to send say 4 astronauts to Mars for thirty days, you can get away with a smallish lander. If they are going to be living there for the rest of their lives, it will need to be physically bigger, you’ll need more than one to handle a larger crew (there’s a minimum number of people you’d need for a permanent colony to work, likely at least 20).

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Figure 2: Mars One in a nutshell [Source: MIT (2015), via Businessinsider.uk]

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Figure 3: Mars One compared to Apollo [Source: MIT (2015), via Businessinsider.uk]

Given the impossibility of maintaining any such colony without resupply (as I discussed in a prior post), they will also likely need resupply from earth. So rather than sending one team of astronauts to Mars, were launching multiple cargo ships there on a regular basis. This will very quickly start to stack up in the cost department. And there’s all sorts of hardware that they’ll need that has never been developed, nor flight tested. Even simply landing on Mars with their proposed lander would present all sorts of challenges.

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Figure 4: Mars one cargo requirements. Note the growing percentage of ECLSS (life support) spare parts [MIT, 2014 via extremetech.com]

Now nobody’s saying its impossible, its just there’s a whole bunch of development costs they’d need to go through before they got to the stage of working hardware….which would presumably have to be flight tested multiple times to prove it can work, before a human crew is sent out. Add up the costs of this and suddenly the costs of a Mars One proposed mission start to balloon to levels that make NASA’s proposal’s look cheap.

The wrong stuff

All of this is not helped by Mars One’s frankly bizarre proposals for crew selection. They have relied on various individuals who’ve applied over the internet. Their shortlist includes in its top ten or so, a Libertarian bitcoin bug, a motivational guru and a fifty year old Sushi chef. Not exactly the right stuff! They also have an insane system whereby prospective astronauts can bump themselves up the rankings by buying sweatshirts and other merchandise. When perhaps they should be ranking them on the basis of technical knowledge, skills and experience (which is more important, being able to cut sushi on a planet with no fish….or being able to steer a spacecraft down to a safe landing?), the outcome of physiological profiles, etc.

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Figure 5: Mars One crew selection [Source Outerplaces, 2015]

As anyone who as ever read up on the history of the Apollo programme should be able to tell you, it is crucial the right people are sent on such a mission. This is not a place for amateurs, space does not suffer fools. The last few minutes of Apollo 11’s descent to the Lunar surface being a case in point. As the LEM approached the moon, a whole bunch of alarms started going off and nobody knew why (it later turned out the computer had effectively crashed because it was getting too much data and couldn’t cope). Neil Armstrong about the same time recalls looking out the window and seeing they were heading for a hard landing in a boulder field. Fortunately, NASA had a kick ass crew on the case. They took manual control of the LEM, boosted away from danger and brought the LEM down to a safe controlled landing, likely with just seconds of fuel to spare.

Now Neil Armstrong and Buzz Aldrin pulled that off because they were highly trained and experienced astronauts. They had both been intimately involved in the development of the LEM throughout its design life (Mars One seem to think they can order this sort of hardware out of an RS catalogue!). Armstrong even survived crashing a LEM training vehicle. They knew their craft inside and out. And ultimately, they had an abort option available if everything when pear shaped. Mars one will be several light minutes away from earth, meaning that either they’ll have figured it out or crashed before mission control can do anything. They will have no abort options, they’ll either crash and die…..or land safely and die later!

TPK

Furthermore, as I discussed previously it is far from proven that its possible for humans to live on Mars permanently. Long duration stays are a possibility, but permanent residence, given the radiation and low gravity they will be exposed to, is a different kettle of fish. Inevitably over a long enough time period the probability of a Mars One crew’s survival drops to zero. If they crash on landing, they’re dead. If any of their key hardware fails, they’re dead. If a key person with technical skills (e.g. the mission doctor or engineer) gets sick, he’s dead, then so is everyone else once nobody’s left to do his job. If they can’t complete a viable life support loop, they’re dead. Given they will lack a line of retreat, its a case of just rolling the dice often enough and eventually we get a TPK.

The supporters of Mars one claim they will fund it by selling TV rights of their mission. The PR generated will inspire generations. Actually the opposite is likely to be true. A Mars one mission, where the public watches the slow gradual drawn outdeaths of a team of astronauts one by one would likely be a PR disaster. And no TV studio is interested in commissioning the most expensive snuff film in history. An MIT study (the same one referenced earlier) even suggested the crew would be dead 68 days after their arrival.

Scam?

All of these inconvenient facts, the lack of anyone with the appropriate technical skills on the Mars One team has led some to question if its all just a massive scam. One of the few team members with in anyway credible qualifications, quit not too long ago, citing issues he had with the ridiculous way they operated and he openly question the credibility of the whole thing

Now I’m not sure if any of this proves its a scam. There’s enough demented space cadet’s around that its possible those behind it are sincere….and a perfect proof of the Dunning–Kruger effect. However to say there’s a few holes in this proposal is to put it rather mildly. It is no surprise that nobody seems to take Mars one remotely seriously.

Mars Direct and Elon Musk

I was originally going to do a separate analysis of both the Mars Society‘s plans, notably Robert Zubrin‘s Mars Direct and Elon Musk’s more recent proposals. However, given that they are broadly similar, I though it would be sensible to combine the two. Certainly, no doubt that both of these plans are significantly more plausible than anything proposed by Mars one.

marsdirect

Figure 6: Mars Direct proposal: The return vehicle (left) and habitat (right) [Source: NASA spaceflight forum, 2013]

The Mars direct plan involves sending a return vehicle out to Mars fuelled with several tons of hydrogen fuel and a small mobile nuclear reactor. This would then spend a year processing the Martian atmosphere to produce a mix of methane and oxygen, sufficient to fuel the return vehicle for the journey home. Once this vehicle is ready and fuelled, a habitat is sent out along with the astronauts. Once there mission is completed, they return in the already fuelled lander. It should be noted that Mars direct is intended to support Mars exploration, as opposed to colonisation. Although given that we’ll be leaving behind plenty of hardware that could be reused by future travellers, its possible it could form a stepping stone towards colonisation.

Elon Musk’s plans are a bit more ambitious, as he’s planning to send larger numbers for longer stays, leading to eventual colonisation. A extremely large reusable booster rocket will lift either an interplanetary vehicle (or a refuelling tanker) up to orbit. This rocket will be huge, with an LEO throw capability of 300 tons (by comparison the Saturn V could only manage a puny 110 tons) and will be powered by 42 first stage engines, running on the same Methane/LOx mixture mentioned earlier. This booster will be reusable, with the first stage flying back to its pad after staging and landing right back from where it started off.

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Figure 7: Elon Musk’s Mars launcher on the pad.

Once in orbit, the Interplanetary craft is fuelled with further launches (using a reusable tanker). It will then head off for Mars and land on the planet. It will then be refuelled in the same manner as discussed for Mar direct, before returning directly to earth. This offers various options in terms of staying on Mars or returning.

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Figure 8: SpaceX’s proposed launch sequence [Source: Spaceflight.com, 2016]

There are a couple of immediate criticisms and questions one must immediately ask, as this space scientist discusses. However I would take a step back and mention a few more obvious practical problems.

Firstly, why fly the booster back to the launch tower? Why not fly it back and land it at some other location? Why not do parachute recovery into the ocean like NASA does with its SRB’s? After all, what if it, say, crashes into the launch tower (or the tank farm!). Already SpaceX lost a few rockets in tests due to retrofire failures or legs failing to deploy. And any accident would jeopardise the mission by paralysing the launch process. Also the rocket would need to be checked out and inspected prior to re-use. So presumably you’d land it somewhere else (on the top of a barge or crawler vehicle) take it indoors for such checks and repairs, then deploy it to the launch site. Not least because Florida (from where they propose to launch) is prone to hurricanes and storms. And speaking of which, why not move down closer to the equator, such as the ESA launch centre in French Guiana? This would be a more fuel efficient location to launch from.

As Jeff Bell recently pointed out, Elon appears to be channelling Sergei Korolev and copying his failed N1 booster. This rocket, used the same idea of clustering multiple engines around a single rocket stage, meaning you’re rolling 42 dice every time you launch and running the risk of one or two engine failures destroying the launch vehicle. With the N1 this configuration meant it proved impossible to test fire the whole assembled rocket on the ground, so they had to work things out in actual test flights…..four extremely expensive and embarrassing failures later (including one of the largest non-nuclear explosions in history) and the Russian manned lunar programme was finished before it even started. Jeff Bell also discusses the extremely ambitious design of the proposed Raptor engines, which will use a staged combustion process operating at extremely high chamber pressures. Not exactly the sort of thing that would boost reliability.

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Figure 8: The Russian N1 Rocket [Astronautix.com, ND]

But I would raise a more obvious question, why use Methane/Lox for earth ascent and trans Mars Injection? Surely LH2/LOx with an Isp of 450s v’s the 360s he’ll get from his raptor engines (if they don’t blow up!), would be a better idea? His proposal incurs a massive weight penalty right from the start. In theory the only bit of the vehicle that needs to be powered by LCH4/LOx is the section of the flight where astronauts are boosted back up off Mars (or where fuel is ferried up for the transfer vehicle’s flight back to earth). This would have the additional benefit of cutting down the weight landed on Mars considerably, as we’d only be taking a small capsule up/down v’s the entire spacecraft.

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And since we’re talking about it there’s a certain swiss army knife nature to this Interplanetary vehicle. It has to withstand launch on a booster from earth (carry the crew one assumes), keep the crew alive for many months on end by meeting all of their life support requirements. It has to survive re-entry through both the Martian atmosphere and the Earth atmosphere (and do both in the one mission, sitting on Mars exposed to the elements for several months prior to return to earth and doing a re-entry there). It must be capable of boosting itself off Mars and perform the Trans Mars and return injections. That’s an absurdly long list of mission requirements.

Playing around with the numbers from Musk’s proposal shows its going to need a mass fraction of at least 0.19, not far off that for an SSTO. I discussed the technical difficulties of developing such a vehicle in a prior post. But in this case Musk is lumbering his vehicle with a whole raft of additional requirements (notably several months of food and consumables has to come out of that 19% mass budget….along with any any payload and crew….and the vehicle’s empty weight as well!).

To my mind breaking the job up into three separate spacecraft, an ascent module, a transfer vehicle and a descent stage would solve a whole host of problems. Quite apart from the obvious fact that if the transfer vehicle is designed to be reusable, then if it stays in space we skip the need for another launch to send it back into earth orbit again. Indeed, I’d go further and point out that direct flights to Mars using chemical rockets are extremely fuel inefficient (meaning our space craft ends up being mostly fuel tanks, as discussed), limiting the amount of cargo the ship can carry. There are alternative ways of getting there with a lower fuel burn, but they increase the time in space and thus exposure to radiation.

Using alternatives to chemical rockets (nuclear rockets, M2P2, solar thermal rockets, etc.) would however speed things up considerably and also have the advantage of cutting the fuel requirements down yet further (Isp’s of 900s or higher, twice that of LH2/LOx, at least three times better than what Musk is proposing).

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Now you may say, am I not forgetting something, we don’t have nuclear engines, nor M2P2 (nor photon torpedoes!), so not a realistic proposal? Yes, but both Mars Direct and Elon Musk’s Mars plan also involve a an unproven element – that nuclear reactor to process the Martian atmosphere and create fuel. Then store that fuel in a cryogenic liquefied state for over a year on the surface of Mars. Has anyone built such a thing? How sure our we about Zubrin’s weight calculations? Has anyone built such a processing plant and sent it to Mars to check the concept will work? Yes the basic theory is sound on paper, but theory and practice are two different things. If I were Elon Musk I’d quit rocket and engine development and send a boiler plate test article to Mars ASAP and test the basic concept. If its not feasible he’ll be building in a massive weight penalty right from the start. To the point where this could be a potential show stopper.

This problem perhaps hints at a wider fundamental problem with both Musk and Mars Direct. It explains why NASA estimates for the cost of a Mars mission come in at hundreds of billions, while Musk/Zubrin/Mars One come in at a price of tens of Billions (or less!). To draw an analogy from mountaineering, NASA propose to climb the Martian mountain the same way they did with the Moon, what would sometimes be called the Mallory method in mountaineering circles. Here we lay siege” to the mountain. A large base camp is established (e.g. the NASA development centres) from where we make increasingly ambitious forays up the mountain. Based on the experience of these missions we eventually send a team of suitably equipped, acclimatised, experienced and well supported climbers, up to a high camp, from where they make an attempt on the summit.

By contrast what Zubrin and Musk propose is to climb the Martian mountain alpine style. This means taking the minimum of gear and climbing the mountain in one continuous push. This is a much more physically arduous task to perform, it requires a higher level of technical skill and it is much more risky (largely because your lines of retreat are limited if something goes wrong). Keep in mind there are several mountains worldwide that have never been climbed alpine style (and it would be suicidally stupid to even try!). By contrast the best analogy I can think of for Mars One is the fate (and cautionary tale) of Maurice Wilson, an eccentric amateur who tried to climb Everest unsupported in the 1920’s and ultimately descended into madness and died on the mountain.

But I digress, the bottom line is that to maximise ones chance of success on Mars, it would be sensible to conduct a serious of shakedown cruises and dress rehearsals first, much as happened during Apollo. Missions to the moon first, an extended space soak (e.g. to an asteroid, Mars or Venus flyby’s), test runs of the descent vehicle in the upper earth atmosphere (or on the moon) would gradually build up to the main event. Of course this would take longer and cost a lot more, but it would make the chances of success significantly higher. The reason why Aldrin and Armstrong didn’t pull the abort lever during those last few minutes prior to landing is because they had confidence in what they were doing. Confidence built up on the past missions they and their colleagues had performed.

Space central planning

Also there’s the obvious question why Mars? Musk say’s its in case some disaster renders earth uninhabitable. Well even any of the disasters he lists would still make the earth a more hospitable place to live than Mars. And there’s a whole host of issues I raised previously about human habitation of space which we’ve not looked into. But suffice to say there’s more than a few holes in this plan.

Perhaps the key myth we need to debunk here is the notion that you can build a space colonisation program without involving the government. It doesn’t help that many space cadets are rabid libertarians who see it as their way of breaking free from the shackles of government…..only some of them seem to think that said big government and its NASA’s resources and budget should now be turned over to Elon Musk. Ah, no! When did we vote to end democracy?

NASA I’m quite sure would like to work with anyone on Mars, they’ve incorporated parts of Robert Zubrin’s plans into their own mission designs, but their experts may decide to do things differently. They may want to go away and do some testing first. Almost certainly I suspect they’ll opt for their own SLS system for earth launch as well as stretch out the launch schedule, shrink the size and complexity of the main spacecraft (yet still bulk up the budget for its development) and generally downside the ambitions. They may offer elements of any future contracts to SpaceX (one assumes a competitive bidding process will be put in place), they made decide to go with someone else. The point is they know what they are doing, we’d be fools to ignore them.

But space cadets seem to want to skip this important process of technical review and democratic discussion. Going to Mars would be a big decision, not least because of the costs involved. That decision needs to be made in a democratic way, particularly if you are looking to taxpayers to bankroll it. Personally, I’d have no objection to a crewed Mars mission, so long as it was justified by well supported proposal of potential research outputs and it wasn’t overly expensive and its goals and objectives were realistic and achievable. However, there are plenty of people who won’t be willing to do so. And Musk and Mars one are proposing something more along the lines of colonisation of Mars and a blank cheque to go with that. Without the necessary justification and democratic mandate it would be insane to even try such a thing.

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About daryan12

Engineer, expertise: Energy, Sustainablity, Computer Aided Engineering, Renewables technology
This entry was posted in aviation, future, politics, space, transport and tagged , , , . Bookmark the permalink.

9 Responses to The case for space – Part 3: Martian delusions

  1. anejati says:

    Daryan, I love your blog and I’ve enjoyed all of your posts so far. You’re probably right that Mars One is a scam, and that Mars direct is probably unfeasible as of yet because the nuclear reactor hasn’t been developed. But you’re wrong about SpaceX’s plan. Please don’t take this the wrong way, but they know way, way more about space than you do.

    > why fly the booster back to the launch tower?

    So it can be ready to fly again in just a matter of minutes or hours. This is a critical part of the plan.

    > Why not do parachute recovery into the ocean like NASA does with its SRB’s?

    It’s baffling to me that a person like you who seems to try to do their homework would ask a naive question like this. There are multiple issues with parachute recovery (mass, vehicle damage, etc.) that are solved via a retrorocket recovery system.

    > you’re rolling 42 dice every time you launch

    So far, SpaceX’s engines have been pretty reliable and as far as I remember not a single one has failed catastrophically in that way. The N1’s issues were mostly in controlling the engines and making them work together without in a nice way. We are in a much better position to solve these problems now than in the 60’s.

    > why use Methane/Lox for earth ascent and trans Mars Injection?

    This has been covered by a lot of people before. Basically, the gist of this is that LH2 is a hell of a pain to work with. It is low density so you need very large, thick pipes and you have very high volume flow rates. You have metal embrittlement issues – very very bad for a reusable rocket, as the Space Shuttle found out. And the need for a very large tank mostly cancels out the Isp and energy density arguments.

    Plus, don’t forget that the ITS needs to hold cryogenic fuel for six months in its tanks. This is far, far easier to achieve with CH4 than LH2. And it’s far easier to achieve when the fuel system uses a single mixture as opposed to multiple mixtures for ascent, TMI, and deceleration.

    > Using alternatives to chemical rockets (nuclear rockets, M2P2, solar thermal rockets, etc.) would however speed things up considerably

    Citation needed. Current electrical rockets are hilariously and ridiculously bad at anything other than very long (read: multiple year) missions, even assuming a nuclear reactor on board. Last time I did the calculation, I think a realistic ion rocket could (in the best scenario) shave about a day or so off of the Mars mission duration. Big whoop.

    • daryan12 says:

      I accept that I’m not an expert, but I’m assuming that NASA are experts and do know alot more and I cannot help but notice that the proposed SLS, Ariane 6 and the existing EELV (Atlas & Delta IV) & Ariane 5 all rely on LH2. Which suggests these problems aren’t the insurmountable obstacles Musk claims them to be. Yes none of these rockets go to Mars, but neither does this launch rocket either.

      You imply the plan is to launch several times a day, that would require an absurd level of reliability and yes falcon engines (which operate at much lower pressures than those proposed for the Raptor) have failed in flight. Listen to the audio from Jeff Bell, or one or two of the other space scientists I quote, they have good reasons to question the practicality of this rocket. Not saying its impossible, but it does highlight its not as straightforward as Musk proposes.

      And okay, if we want to up the launch schedule, just build more rockets. You could have one on the pad being fuelled, one or two in the VAB being checked out and prepped and one or two more between either the landing site and the VAB or the VAB and the pad. Keep in mind that as the shuttle showed the flyaway unit costs of a Reusable launch vehicle are usually only a small fraction of the overall costs (compared to R&D or maintenance).

      As for alternative propulsion, I make a clear distinction in an earlier post between low thrust options like Ion thrusters and other alternatives such as Nuclear thermal rockets, solar thermal or M2P2. There’s been a long held assumption within NASA that any mission to Mars, beyond a simple cheap “flags & Fotos” mission will involve nuclear energy. The current Copernicus proposal from NASA is just one of a long line of similar nuclear powered mission studies going back to the Von Braun era. Now I’ll admit, they’ve soften the stance somewhat (largely because I suspect they’ve realised they may not get funding or permission to launch such a mission!), but if you’re planning on bringing the number over Musk is taking about, I think you have to question the practicality of doing that without resorting to alternative propulsion methods. As for M2P2, well Robert Zubrin did quite a bit of research into this himself, so I’m guessing he thinks its a good idea.

      Another feature of many NASA (or Russian or ESA) baseline missions is that they often break up the mission into multiple vehicles, an earth launcher, a transfer vehicle, an excursion vehicle to the Martian surface, etc. This is to get around the problem of trying to turn the one vehicle into a massively overweight and overly complex Swiss army knife. I may be no expert, but one has to suspect they’re doing because they understand the practical problems.

      All in all my guess is that what Musk has proposed is his vision, one that’s not yet been through the mill of scientific and engineering rigour. Much like his early Falcon 5 or Hyperloop proposals, I’d guess that once the scientific and engineering community (and his own engineers and scientists) have had their say, we’ll see it altered somewhat and probably the ambition downgraded a bit.

      • anejati says:

        The SLS uses hydrogen because it uses re-purposed old STS hardware. The Ariane 5 and 6 are medium-lift, disposable vehicles. Not comparable at all to the ITS booster.

        Another problem with hydrogen that I forgot to mention is that for a variety of reasons, ITS uses autogenous pressurization which is very hard to do with hydrogen due to the low boiling point. The helium COPVs used currently are one of the weak points of existing rockets and for reliability concerns it’s important to be able to do without them.

        To wrap it up about hydrogen, low boiling point, high boiloff, low density, metal embrittlement, and other issues basically kill it dead. I don’t really think SpaceX has a choice; methane is the _only_ way to go.

        > You imply the plan is to launch several times a day, that would require an absurd level of reliability

        It definitely would. No argument there.

        > they have good reasons to question the practicality of this rocket.

        Sure, it uses much higher chamber pressures than previous rockets, a technically difficult fuel cycle, and a largely unproven fuel. Which is why SpaceX is being extremely cautious and taking things very slowly with it.

        The Merlin engine was also a large technical advance (highest TWR of any rocket engine) which they pulled off successfully. It would be unwise to underestimate them. They have amazing engineers.

        > And okay, if we want to up the launch schedule, just build more rockets.

        Unlike for instance the STS, the ITS is designed to be an advanced, expensive rocket only requiring minimal maintenance between launches. It wouldn’t make sense to build more of them than necessary.

        > As for alternative propulsion, I make a clear distinction in an earlier post between low thrust options like Ion thrusters and other alternatives such as Nuclear thermal rockets, solar thermal or M2P2.

        All of those technologies have in common the fact that they are nowhere remotely even near the development stage. Why would you go for dubious, risky, expensive, unproven tech just to be able to pack fewer supplies? It doesn’t make sense.

        For missions to the outer solar system, sure, research on those propulsion techniques makes sense.

        It’s kind of unreasonable for a person like you who wrote at length about the infeasible nature of thorium reactor designs (a great blog series btw, I have reposted it often) to suddenly talk about M2P2 and nuclear thermal rockets. Come on.

      • daryan12 says:

        Nuclear
        To quote myself from an earlier post “…this is not to suggest all of the problems with nuclear energy magically disappears just because we are in space. Actually, they get worse.” I reckon that NASA are perhaps underestimating the technical problems they’ll face trying to develop such an engine, nor indeed do they seem to appreciate the political flak they’ll catch when they talk about launching nuclear reactors into space.

        However, I understand the logic of those pushing for these programs, they’ve done the maths, they know that any Mars program reliant on chemical rockets becomes very expensive and imposes very tight design requirements on the all of the hardware. It simply may not be possible to do this with existing technology. So while I may sceptical of the proposed solution, I understand what’s driving them to propose it.

        However Musk’s plan is also reliant on nuclear power. To make Methane on Mars he’ll need nuclear reactors and a chemical plant (and he’ll have to overcome the same opposition NASA face). The only difference is that NASA at least have the results of some (fairly dated and limited) testing from the 60’s into nuclear rockets. While Musk has only some theoretical calculations and some Photoshoped images to go on.

      • daryan12 says:

        Oh, and as for storeable propellants, well the Chinese and Russian space programs are largely based on their military programs which generally require storeable propellants to operate. Do they use Methane? Nope! They use either Kerosene or that god awful UDMH stuff.

        As for relying on one single rocket, well what if it breaks down or is lost by misadventure? That could jeopardise the entire mission and any astronauts already on Mars by delaying the arrival of supplies. They’ll have to have more than one, that’s a given really. So it makes sense to have all of them in play and ready for use if something goes wrong.

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