Let's say I have a reusable methalox vehicle ... I want to deploy the ISRU unit ... then re-stow the unit back inside and take it back to orbit. ...Doable?
I asked this over on the main Missions to Mars thread, but perhaps there will be insights here as well....I've read a lot of studies on Martian ISRU, but I haven't seen many clear figures on what's realistic for a reusable ISRU unit.Let's say I have a reusable methalox vehicle which can deliver up to 40 tonnes of payload to the Martian surface in a 10 meter long, 4 meter wide cross section. I want to deploy the ISRU unit out of the cargo bay and onto the surface (potentially using a robotic arm), use it to refuel my vehicle's tanks, then re-stow the unit back inside and take it back to orbit. Once in orbit, the vehicle will transfer excess propellant to a tanker before re-entering, landing at a new location, and starting over.The number of useful cycles varies with the dry mass of the ISRU unit. That is, a heavier ISRU unit needs to be able to survive more autonomous refueling cycles than a lighter one.Doable?
How did this become a thread about some weirdly shaped ITS variant? What's wrong with just using the regular ITS shape?I guess it's better than what this thread was about immediately before that.Carry on.
Quote from: sevenperforce on 04/28/2017 04:23 pmI asked this over on the main Missions to Mars thread, but perhaps there will be insights here as well....I've read a lot of studies on Martian ISRU, but I haven't seen many clear figures on what's realistic for a reusable ISRU unit.Let's say I have a reusable methalox vehicle which can deliver up to 40 tonnes of payload to the Martian surface in a 10 meter long, 4 meter wide cross section. I want to deploy the ISRU unit out of the cargo bay and onto the surface (potentially using a robotic arm), use it to refuel my vehicle's tanks, then re-stow the unit back inside and take it back to orbit. Once in orbit, the vehicle will transfer excess propellant to a tanker before re-entering, landing at a new location, and starting over.The number of useful cycles varies with the dry mass of the ISRU unit. That is, a heavier ISRU unit needs to be able to survive more autonomous refueling cycles than a lighter one.Doable?Not sure this is on topic here either but why would you want to do this? Why wouldn't you deliver an ISRU unit and leave it there, running? If you want to do multiple sites, deliver multiple units. Picking things up and taking them back to orbit isn't how you colonise things.
Quote from: Robotbeat on 04/30/2017 01:11 amHow did this become a thread about some weirdly shaped ITS variant? What's wrong with just using the regular ITS shape?I guess it's better than what this thread was about immediately before that.Carry on.Size? The regular ITS cannot be launched on Falcon 9 or Falcon Heavy; a smaller one with bisymmetry rather than trisymmetry could.
I was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).
Quote from: Robotbeat on 04/30/2017 04:18 pmI was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.
Quote from: RonM on 04/30/2017 04:59 pmQuote from: Robotbeat on 04/30/2017 04:18 pmI was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.
Wings for Earth good, wings for Mars meh...
Would you give it any lifting body characteristics at all? Earth and Mars entries both will require a lot of -ΔV from aerodynamic drag, though the flight profiles will have to be very different. On Earth, the ability to glide offers ability for airplane-like landing (with skids possibly better than wheels), while on Mars the ever increasing angle of attack at low altitude to maintain lift as V bleeds off could requires some modicum of aerodynamic profile that does generate that lift.In that this is likely an experiment to obtain data, I imagine that what flies may not look like the final design. I know you believe they may have been working on this for longer than most think, but still, it has to be pretty prototypical in nature. If so, I have to wonder if they have strayed from pure cylindricality. If it does have the mini-raptor that you believe it might, does it have a larger diameter to accommodate the lower density CH4? (IDNT it can be longer due to bending loads on total LV.) What kind of overall design do you think it might be? Would any landing legs be like F9-S1 or like ITS? If it cannot land on Vac engine, will it have Super Dracos, fore or aft? Do you have a TPS plate to shield the main nozzle, jettison the nozzle, jettison most of the nozzle and use the remnant as a SL engine? How do you envision the thing?
Quote from: sevenperforce on 04/28/2017 04:23 pmLet's say I have a reusable methalox vehicle ... I want to deploy the ISRU unit ... then re-stow the unit back inside and take it back to orbit. ...Doable?If you want to make chemical fuel (e.g. methalox or CO/O2), then that takes a lot of energy. Zubrin and NASA DRM-5 assume the fuel plant will have nuclear power and will be remotely located and non-retrievable (i.e. no radiation shielding). If you like the solar option, then plan to invest a lot of man-hours setting up the PV panels, even robotically, plus many months to collect enough energy.An additional problem is that for Methalox (which is a much better propellant combo than CO/O2, with Isp=380s), you also need hydrogen. Zubrin and NASA DRM-5 assuming you'll bring a load of LH2, just enough for one mission. Maybe it's also possible to dig for perma-frost, then melt and electrolyze the water to make hydrogen (i.e. more man-power).
The ITS is supposed to have ten-tonne RCS thrusters, so these would work very well as landing engines. If you use winglike extensions to drive down terminal velocity, you can place the landing thrusters biaxially in the wings and land this way:
Quote from: Robotbeat on 04/30/2017 06:18 pmQuote from: RonM on 04/30/2017 04:59 pmQuote from: Robotbeat on 04/30/2017 04:18 pmI was indeed thinking of a smaller BFS on top of FH. 5.6m in diameter instead of 12m (plus fins).How large would the payload to Mars be on this mini-ITS? It would only need to carry a crew of four plus supplies to do a NASA-style exploration mission.Pretty small if you had one or two cargo ITSes beforehand and/or in parallel carrying power and ISRU equipment. I'm thinking like 3 total mini-ITSes: 2 cargo and one crew. 30-45 tons of payload each.That's a good way to get the initial base started while still working on the full-size ITS.No reason for Congress to fund the colonization of Mars, but they might chip in some cash for the mini-ITS as long as NASA astronauts get to do the flag-and-footprints thing. Then SpaceX can use the new Mars infrastructure and start working on their colonization plans.
Quote from: sevenperforce on 05/01/2017 01:57 pmThe ITS is supposed to have ten-tonne RCS thrusters, so these would work very well as landing engines. If you use winglike extensions to drive down terminal velocity, you can place the landing thrusters biaxially in the wings and land this way:Are you going to land it that way on both Earth and Mars?