After Elon's Mars schedule announcement, I was wondering about this (I don't know if this has been discussed before, I presume so but perhaps not in this specific context) : A way to speed up the development of the first manned Mars mission (to keep up with the aggressive 2024/5 schedule) would be to bring molecular H to the Martian surface (which could also serve as a radiation shield on the way there). If the BFS must have a dV capacity of 6 km/s and has a dry mass of 200 tons, it will need about 800 tons of fuel for the return journey. Since only about 5% of a stochiometric Methane/LOX fuel is hydrogen, they could bring down about 40 tons of molecular H with each BFS, well within its payload capacity (of 100 tons). Even if we add a few percent of that for the mass of the tank, this is still very feasible.All that the first SpaceX astronauts would then have to do after landing is react the H with the atmospheric CO2 in the Sabatier reaction - this could virtually been done without any human supervision or involvement. This is also a much simpler and cleaner (and less energy intensive) process than having the crew looking for water ice, digging it out, cleaning it, testing it for any potential chemical agents (e.g., peroxides, salts, etc.) and removing them before electrolysis, etc. This is also a technology that 1) is already in development and 2) would be reasonably easy to demonstrate with a precursor Red Dragon mission. The same cannot be said of actively digging for water ice on Mars. While I am certain the plan is for a Mars base to eventually provide BFS's with fuel synthesized from martian water ice and atmospheric CO2, the very first landings could / should skip this step and bring the H from Earth instead.
Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....
@kch: sure, I am aware that the idea of bringing in H is from Mars Direct (and as such I should perhaps have said so), but I mean in the specific context of the BFS and speeding up the schedule to make a 2024/5 manned SpaceX mission to Mars feasible. ISRU is (well, presumably so) an integral part of the SpaceX architecture, but some of it (like digging up water ice) has very low technological readiness and this is unlikely to change before 2024/5. Also, consider that the initial crew would have to dig up 360 tons of water ice to produce the fuel, or 60 tons each if they are 6 astronauts.... Hard even if you bring some landmoving equipment....Envy887 made an excellent point on the volume and cooling systems this would require. This is the kind of answer and input I was going after. A tank this size would only be 3 m high at 15 diameter for the BFS. Even if cooling etc take up 10 tons or more, at 100 tons total you still have some serious payload capacity left.
Did Musk say humans would LAND on Mars, or just be sent TO Mars in 2024? That later leaves open a purely orbital mission.
Assuming its a landing in 2025, ISRU water from martian ground ice has still extremely low technological readiness,
I wonder if Elon is an investor in Boston Dynamics...
The other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.
So... while SpaceX may get plenty of kudos for landing the first humans on Mars, it will pretty much kill their colonization plans if those first humans end up on a one-way trip with no hope of either survival or return. I'm therefore awfully confident that they will have anticipated most, if not all, of the obvious common-sense precautions we're all coming up with here, and will have plans in place to cope with those situations if they arise.
Quote from: su27k on 06/04/2016 02:48 pm I wonder if Elon is an investor in Boston Dynamics...That rings a bell - will do some searching and report back if it turns out to be factual.
Why do you think bringing down H to the surface is a weak point of Mars Direct? The motivation is not so much that there is no H on Mars, it's that this allows you to take one big unknown (how youw get from sub-surface dirty ice to CH4 in your tanks) out of the equation.
Quote from: nadreck on 06/03/2016 03:58 pmThe other option is to land enough propellant on Mars for the ascent of the escape vehicle. This is possible, but not nearly as economical, potentially requiring one MCT to stay in low Mars Orbit with its payload of propellant that came from Earth and 3 or 4 cargo MCTs arriving with just propellant for the emergency ascent vehicle. The complexity of this is that propellant transfer from landed craft is required. The ISRU example might be accomplished with the ISRU MCT refueling itself and it being the emergency return vehicle not just an ascent to orbit vehicle.The emergency ascent spacecraft can be very small, like a Dragon, without the heat-shield and SDs. Launch it to reach the Earth-return MCT in low Mars orbit will not require an enormous amount of fuel. If the capsule + ascent stage is 10 t dry, then 30 t wet is enough. The ascent stage can be derived (shortened) from F9 second stage, so the ascent vechicle need not be developed from scratch. A single MCT can land the fueled ascent vechicle together with extra cargo, or even the hab modul.