Has anyone suggested the possibility of SpaceX's announcement including "a reusable, nuclear (fission, fusion, either or) upper stage for the BFR" yet?
I think a nuclear fusion engine using magnetic control of the plasma and having one end expel the plasma for propulsion with the other end feeding liquid hydrogen in and continuously making plasma for propulsion would work. It would still require a lot of power just to use lasers to create the fusion at one end. However if you are going to use some other type of power source to create the fusion for the engine, one still needs a lot of power, and you have to have heavy hydrogen to operate. How much I don't know? So it seems SEP with very large arrays and a cluster of a lot of ion engines and a large tank of propellant could also make a very large in space, higher speed cargo or even human run to Mars. A small NEP reactor, sealed, use for several years, and throw away, by shooting it to the Sun. It might be somewhat smaller and could make several Mars runs before depleting its fuel. Technology for small sealed reactors should be improved first.
I think the biconic shape is the way to go. I do think concentric fuel/oxygen tanks running the entire length of the MCT in the center would allow for more balance. Say with liquid methane in the center tube and the lox in a donut tube around the methane. Cargo, solar panels, landing legs, thrusters and thruster fuel, etc could be around this central tanking system. The picture on post 733 is what I like except with concentric center fuel/lox tanking. One can still dock on the nose, as tank dome could stop short of the nose. Heavy cargo could be stored near the bottom for easier unloading. Instead of the plug nozzle engine as shown, standard Raptors vacuum engines could be on the bottom. The interstage could double as heat protection flaps when coming back through the atmosphere.
Quote from: meekGee on 10/13/2015 05:07 amI'll also add that in addition to the trip duration, there's the "land the whole thing" mentality. If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.But again, this is about MCT.We KNOW SpaceX is considering SEP for Mars, and as it is impossible to land a SEP, that mean IPSO FACTO that they are have ALSO considered a Semi-Direct architecture of a transit-vehicle and a separate landing vehicle. And that such a vehicle trades very well against a single massive direct vehicle.
I'll also add that in addition to the trip duration, there's the "land the whole thing" mentality. If you're talking about ISS-esque solar array and radiator array, the idea of stowing them before EDL is not practical.If instead you have a "Hermes"-type orbit-to-orbit ship in mind, then now SEP starts making sense.But again, this is about MCT.
It's not, in fact, impossible to land an SEP on Mars. Just kind of odd and mass inefficient. But with a sufficiently good solar array, you could do it. I should point out that an "ISS-esque" solar array is, in fact, retractable!
Quote from: Rocket Surgeon on 10/13/2015 06:44 amTo go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area. Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?I do like that image, it is close to what I have in mind for an MCT. But I think a lengthy tunnel through a cryogenic tank might have issues.If you insist on have a nose-mounted LAS, another way around it might be to have just a giant central tank (split between oxidizer and fuel), and then have a lower cargo bay (just above engines), and an upper cargo bay in the nose. It would force some level of cargo balance, but that would allow you to put all the pressurized volume up top. And as a bonus the unpressurized/heavy cargo would be easily offloaded near the surface.
To go back to balancing the Biconic for a bit, would it be possible to have a configuration similar to the Phoenix (see attached), except applied to a Biconic and with some sort of escape system in the nose (sorry, really like the idea of the nose section being a dedicated 'lifeboat'. I just see it as a way to solve so many problems) It would still have the central column, as a way to move down to the main pressurized area. Not sure what this would do to the mass in total, but wouldn't it allow for a more evenly distributed mass during EDL?
Just on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight,
but it allows for something I've been worried about, Abort during transit. If we assume these things are traveling in a fleet (say 10 MCT's for 1000 colonists to Mars?), if one suffers a mishap during flight, then the colonists can load up and punch out from the failing MCT and rendezvous with another nearby one. Granted, depending on the mishap, the 'other' MCT could just come to them anyway, but there may be issues necessitating a quick departure, for example during Mars approach and entry...I'm pretty sure you can't keep 100 people alive on an MCT for 2 years waiting for free-return to Earth if you miss. The other MCT would have to put up with 200 people for a short time, while they can be distributed amongst the rest of the fleet, giving you 9 MCT's with 110 people each for the rest of the trip.
Quote from: Rocket Surgeon on 10/14/2015 03:02 amJust on the Lifeboat idea, I know it was mentioned back-thread that it would be making things a lot more complex, but I think it would be worth it. Why? Not only can you Abort during Launch and EDL both at Earth AND Mars anywhere through the flight, Don't make the mistake of thinking that all an abort capsule needs to do is taking passengers away from an imminent explosion, to just survive the imminent danger. That works on Earth, because rescue is nearby, and the environment is survivable.But that is NOT enough for Mars. An abort capsule is USELESS if it just dooms you to death a couple of hours later. To be a proper abort/rescue vehicle it basically needs to be a fully independent spacecraft/lander, built into another spacecraft/lander. By adding enough rescue/survival capability, you get into a dark spiral that eventually leads you to conclude that your escape capsule needs another escape capsule.
Being able to abort/rescue during transit is a completely separate aspect from whether or not you have a launch abort capsule. Any reasonable MCT proposal would have a fleet of them going during a launch window, so that rescue would be available even without abort capsules. And no, I don't think you need to have a rapid way to escape your MCT during transit. At some point you just have to accept that there will be riskier times during a trip. Those who cannot accept risks can stay behind.
The fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.
MCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.
My question is, why not send the crew up in traditional capsules to dock and load into the MCT.
How would these children fare if they return to earth with heavier gravity?
Quote from: spacenut on 10/14/2015 01:27 pmMy question is, why not send the crew up in traditional capsules to dock and load into the MCT. Because that'd be way expensive cumulatively than launching the MCT itself, and cost is a factor.
But surely if we're assuming a mostly developed Mars Colony ready to accept 1000 new immigrants, then it is reasonable to assume that they could mount a quick rescue of an abort capsule? Something like a dedicated MCT with enough fuel to do a sub orbital hop, on station and ready to go could make it to the capsules landing site in a few hours, and if the capsule was close enough, you could even go over land. That's why it would only need to sustain the colonists for a few hours, not days or weeks. That keeps the capsule more simplistic. Simple CO2 scrubbers, maybe a dedicated radiator if the base hull rejection rates are naturally too low and batteries for power. Add some pressure fed hypergolic rockets, or methalox ones that are made so the tanks can be 'charged' from the main tanks when they are likely to be needed (for those who don't like hypergols) and a parachute or two to help slow down. Again, I'm not saying it'll be 'cheap' either in terms of mass or money, I'm saying that it is worth it. It would have to cost more than $1.5 billion to save 100 lives for it to be considered 'Grossly improportional' and for SpaceX to have a reasonable argument that is was too expensive.
Quote from: Krevsin on 10/14/2015 06:52 amThe fact that SpaceX were looking into SEP could mean they were looking at an all-in-one vehicle with both SEP and chemical propulsion.As was already mentioned in the thread, that would require the large solar arrays not only somehow be retracted into the MCT itself but also be deployed again after re-launch from Mars, and thus be so reliably shielded from re-entry (and issues on the surface like dust) that you can guarantee they will redeploy for the return trip to Earth. There's simply no advantage to justify that complexity.
Quote from: Krevsin on 10/14/2015 06:52 amMCT will remain a "land the entire thing" architecture, no matter how disagreeable you find the prospect of it.The original land-the-entire-thing comment was made in the context of the typical multi-stage launch/landing architectures. It doesn't mean that Musk has ruled out having a SEP stage that remains in orbit.And given that he's happy to do EOR refuelling, to avoid the restrictions of monolithic launches that are typical of Mars architectures, I can't see why anyone would think he'd arbitrarily rule out such an option just to satisfy one interpretation of a throw away quote.We might find out in a month or so. Until then, these options are on the table... "No matter how disagreeable you find the prospect."
Musk’s architecture for this human Mars exploration effort does not employ cyclers, reusable spacecraft that would travel back and forth constantly between the Red Planet and Earth — at least not at first."Probably not a Mars cycler; the thing with the cyclers is, you need a lot of them," Musk told SPACE.com. "You have to have propellant to keep things aligned as [Mars and Earth’s] orbits aren’t [always] in the same plane. In the beginning you won’t have cyclers."Musk also ruled out SpaceX's Dragon capsule, which the company is developing to ferry astronauts to and from low-Earth orbit, as the spacecraft that would land colonists on the Red Planet. When asked by SPACE.com what vehicle would be used, he said, "I think you just land the entire thing."Asked if the "entire thing" is the huge new reusable rocket — which is rumored to bear the acronymic name MCT, short for Mass Cargo Transport or Mars Colony Transport — Musk said, "Maybe."
around 4:25 "So we're looking at solar-electric propulsion. I think we're gonna umm, look at some other interesting IN-space propulsion technologies..."