SpaceX to Mars!

This story keeps getting more interesting as I trawl around the Mars-Soc web-site. Bob Zubrin discusses the plan in more detail…

Discussion of Using SpaceX Hardware to Reach Mars

2. Technical Alternatives within the Mission Architecture

a. MAV and associated systems

In the plan described above, methane/oxygen is proposed as the propulsion system for the MAV, with all the methane brought from Earth, and all the oxygen made on Mars from the atmosphere. This method was selected over any involving hydrogen (either as feedstock for propellant manufacture or as propellant itself) as it eliminates the need to transport cryogenic hydrogen from Earth or store it on the Martian surface, or the need to mine Martian soil for water. If terrestrial hydrogen can be transported to make the methane, about 1.9 tons of landed mass could be saved. Transporting methane was chosen over a system using kerosene/oxygen for Mars ascent, with kerosene coming from Earth and oxygen from Mars because methane offers higher performance (Isp 375 s vs. Isp 350 s) than kerosene, and its selection makes the system more evolvable, as once Martian water does become available, methane can be readily manufactured on Mars, saving 2.6 tons of landed mass per mission compared to transporting methane, or about 3 tons per mission compared to transporting kerosene. That said, the choice of using kersosene/oxygen for Mars ascent instead of methane oxygen is feasible within the limits of the mass delivery capabilities of the systems under discussion. It thus represents a viable alternative option, reducing development costs, albeit with reduced payload capability and evolvability.

b. ERV and associated systems.

A kerosene/oxygen system is suggested for Trans-Earth injection. A methane/oxygen system would offer increased capability if it were available. The performance improvement is modest, however, as the required delta-V for TEI from a highly elliptical orbit around Mars is only 1.5 km/s. Hydrogen/oxygen is rejected for TEI in order to avoid the need for long duration storage of hydrogen. The 14 ton Mars orbital insertion mass estimate is based on the assumption of the use of an auxiliary aerobrake with a mass of 2 tons to accomplish the bulk of braking delta-V. If the system can be configured so that that Dragon’s own aerobrake can play a role in this maneuver, this delivered mass could be increased. If it is decided that the ~1 km/s delta-V required for minimal Mars orbit capture needs to be done via rocket propulsion, this mass could be reduced to as little as 12 tons (assuming kerosene/oxygen propulsion). This would still be enough to enable the mission. The orbit employed by the ERV is a loosely bound 250 km by 1 sol orbit. This minimizes the delta-V for orbital capture and departure, while maintaining the ERV in a synchronous relationship to the landing site. Habitable volume on the ERV can be greatly expanded by using an auxiliary inflatable cabin, as discussed in the Appendix.

c. The hab craft.

The Dragon is chosen for the primary hab and ERV vehicle because it is available. It is not ideal. Habitation space of the Dragon alone after landing appears to be about 80 square feet, somewhat smaller than the 100 square feet of a small standard Tokyo apartment. Additional habitation space and substantial mission logistics backup could be provided by landing an additional Dragon at the landing site in advance, loaded with extra supplies and equipment. Solar flare protection can be provided on the way out by proper placement of provisions, or by the use of a personal water-filled solar flare protection “sleeping bag.” For concepts for using inflatables to greatly expand living space during flight and/or after landing, see note in Appendix.

…which gratifyingly echoes my own thoughts. Landing a Dragon directly on Mars has a great appeal and as a Mars Descent Vehicle it’s a good system, given the modifications Zubrin outlines. But is it a Mars Habitat? The Inflatable extensions make it viable and I was wondering if Bigelow, SpaceX and Mars-Soc couldn’t combine forces on a design. Zubrin argues for eventual extensions of the architecture itself, calling for eventual Heavy Lift systems able to throw 30 tonnes to Mars, but IMO the Falcon Heavy Tanker modification is sufficient to launch ~24.7 tonne payloads now and with an LH2/LOX Stage II it might easily launch ~30-40 tonnes. Alternatively two FHTs can be ganged to launch 55-60 tonnes directly now. However such modifications are deployed is perhaps irrelevant. What’s needed is the political will to commit to Mars Colonization, not just a one-off stunt. All the good ideas to improve how we get there are irrelevant until we actually do…

8 thoughts on “SpaceX to Mars!

  1. Hi Adam,

    When watching the latest video from SpaceX, I notice some interesting equipment on the surface of Mars. What do you make of that odd looking craft (in the middle) which appears to have three engines?

    Also, what are your views re: Mars vs Moon colonization? Risking humans to search for evidence of life on Mars makes no sense to me. Certainly one could send dozens of rovers to dozens of diverse locations on the surface of Mars. A flags and footprint affair has some PR value but moving towards a self-sustaining colony, IMO, would provide a very valuable insurance policy for the human race. But we ought to be able to do that on the lunar surface for far less cost and far less risk and sooner too all the while developing a valuable cis-lunar economy.

  2. Hi John
    Mars has many more advantages than the Moon for long term habitation – stronger gravity, some atmosphere, diurnal cycle like ours, more water, perhaps more deuterium, and probably a more developed hydrological cycle to plant ore bodies at interesting concentrations around the surface.

    Is the Moon any easier? Thanks to aerobraking Mars is easier to get to in delta-vee terms and thanks to easier ISRU it’s easier to get back from. Another factor is that a thin atmosphere is all that’s needed to cut the micrometeorite flux down dramatically, which simplifies suit design somewhat. I think Mars is a much better option, aside from the distance aspect.

  3. As for the vehicles in the background, they’re obvious modifications of some designs which I think James Cameron came up with. Or Frassinato. Cute solution to how to get Dragons back into orbit.

  4. > Found the source of the Ascent vehicle in the SpaceX vid… Beyond Apollo post on Bimodal NTR to Mars…the visualization was done by Frassanito.

    Good catch. Yes. I believe that you are referring to the next to last image on the left-hand column and the fifth from the last picture. So…apparently that small blunt acute triangle in the center of the center piece of equipment is the ascending capsule.

    > Mars has many more advantages than the Moon for long term habitation

    Certainly yes. What I wonder is which is the logical destination for the first base…more later.

    > stronger gravity

    Somewhat yes. I’m not sure that the difference is decisive. They’re both a fair bit less than on Earth. For industrial processes, the small amount of gravity on the Moon is sufficient to settle material. For osteoporosis, my guess is that it would happen on Mars too but would simply be delayed. For fetal development, my guess is that 37% gravity on Mars is probably also problematic. Some sort of centrifuge will be needed for either (just a guess).

    > atmosphere

    IMO, probably the greatest advantage due to easy access to carbon, though ice on the Moon does contain methane, CO, and ammonia.

    > diurnal cycle

    For people I don’t think that this is relevant since that cycle can be produce in the undergound living quarters. For power, the Peaks of Eternal Light can provide power up to 90% of the month. Again, short-term this would work. Long-term Mars is better.

    > more water

    Yes, but short and medium term, the Moon will provide far more than enough water.

    > Thanks to aerobraking Mars is easier to get to in delta-vee terms

    Very true. But my feeling is that the launch windows, greater delta-V getting off Mars, and the hazards and mass of long-duration travel negates this advantage.

    > and thanks to easier ISRU it’s easier to get back from

    True, hadn’t considered this. However, the lunar poles contain water ice from which one should be able to produce the oxygen. Given that lunar gravity is as low as it it, one would not need to produce as much compared with trying to get off Mars. However, sucking in Martian air is easier than digging up lunar ice. Still, from what Elon said in his Press Club speech, a Mars mission would entail more launches than that for the Moon.

    Taking all things into account, don’t you think that (for the same amount of money) a lunar base could be developed sooner? Especially consider the frequent launch windows. Also, would you agree that near real-time teleoperations on the Moon could go a long ways to providing safe and relatively inexpensive scale-up of operation on the Moon that probably couldn’t be achieved for Mars. Also, the development of a cis-lunar economy could draw commercial enterprise to invest in the development of the Moon but not Mars.

    ——

    Agreed, Mars wins from a long-term colonialization goal and from a scientific goal. I know that most people look at our space goals from either a scientific or a do-something-historic standpoint. But I strongly believe that we should first seek to establish a self-sufficient off-Earth base first as insurance for humanity. If this were our goal, do you think that developing a lunar self-sufficient base would be the quickest way to achieve this?

  5. > For pace the Moon wins, but Mars wins for long term insurance IMO.

    Yes, you are correct. So, here’s how I view it. An off-Earth self-sufficient base is a very valuable form of insurance since several of the expected existential risks this century would involve an uninhabitable biosphere of the Earth (e.g. self-replicating chemical, nanodevice, biotech). So, I figure that the sooner that we achieve a self-sufficient, off-Earth base at any location, the better. In my thinking, even a decade earlier might make the difference since we are dealing with technology (even accidental technology) that could be upon us by mid-century plus or minus. As you note, pace would indicate that this should be the Moon.

    But, thanks to SpaceX, Mars isn’t looking that far away any more. So, I think that the issue comes down to which (the Moon or Mars) can be achieved politically first. I believe that we probably need NASA-level funding for either the Moon or Mars. Mars is more exciting and has stronger and more organized supporters. But the Moon can more easily fit in the budget and can have a commercial justification (Lunar Ice To LEO). Between, the two, I believe that, politically, a lunar colony can be achieved first since I think that a Lunar COTS can fit within a Flexible Plan context provided that HLV funds went into the Lunar COTS. But a near-term Mars colonization program would probably be incompatible with a Flexible Plan. Even Zubrin is only talking about a one-off science and inspirational mission.

    The downside with a lunar self-sufficient colony is that individuals from the colony would eventually have to migrate to Mars whereas a Mars-first architecture would establish the Mars colony earlier. However, escaping the gravity of the Moon should be fairly easy and much of the technology to get to the Moon would be applicable for a later Mars mission.

    I’ve tried to look somewhat into the issue of whether self-replicating technology could make it to the Moon via every day asteroid impacts, atmospheric skipping bodies, and loss along Earth’s magnetic fields. Some bacteria can survive lengthy exposure to space. Though I am uncertain about chemicals and nanodevices and whether anything would survive beyond our magnetic fields or (perhaps more importantly) impacting the lunar surface.

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