Sure, we all understand that. When people say SSTO they should say it accomplishes its mission without staging.And the advantage for a lunar lander or any vehicle is that fewer stages mean fewer interfaces and fewer vehicle configurations to analyze and develop. It might even mean a safety improvement since there are fewer components (and also because failures often happen at staging events).But anyway, since we aren't stuck with making things expendable, we can also say that single stage makes reuse WAY easier until your delta-v is around twice your exhaust velocity.For the Moon that means you can refuel the reusable lander in orbit.
Quote from: Robotbeat on 10/23/2016 12:03 amSure, we all understand that. When people say SSTO they should say it accomplishes its mission without staging.And the advantage for a lunar lander or any vehicle is that fewer stages mean fewer interfaces and fewer vehicle configurations to analyze and develop. It might even mean a safety improvement since there are fewer components (and also because failures often happen at staging events).But anyway, since we aren't stuck with making things expendable, we can also say that single stage makes reuse WAY easier until your delta-v is around twice your exhaust velocity.For the Moon that means you can refuel the reusable lander in orbit.I agree with your logic, and anything reusable should have as few stages as reasonably possible (e.g. one stage for a reusable lunar lander, and the two-stage ITS - upper stage getting fueled in LEO, taking that all the way to the Martian surface, where it gets refueled again for the return trip).But how do you explain this Spaceworks study in which they concluded that the development costs for a two-stage and single stage lunar lander were almost the same? And yes, reliability was higher, but only slightly; separation only contributed a very small part to risk.
First things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?
Quote from: Hauerg on 05/25/2015 10:26 amFirst things first: SINCE the LEM was planned as being 100% disposable, what would habe been gained by making it a SSTO vehicle?When your maximum feasibly achievable ISP is ~325, it's not like you have much of a choice
I've often wondered if a Hydrazine/LOX mix would be okay - the Lander descends with an excess of hydrazine leftover after landing. Then; LOX is made by splitting CO2 and liquifyng it. This makes up the ascent propellant then - whoosh - off they go!
No; they would not be hypergolic. But hydrazine mixed with LOX would still be pretty flammable stuff - vacuum specific impulse better than 330 seconds if pressure fed, rising to more than 350 seconds if pump fed. A multi-redundant sparkplug system could be used for ignition with perhaps 'cartridge' starters for 'failsafe' on ascent duites. And the type of hydrazine used would more likely be UDMH.
Is there an existing nomenclature that differentiates between an SSTO ascent vehicle that is landed on a descent stage, vs an SSTO that is self-landing, vs a genuine TSTO ascent vehicle?
I would have thought it best to design the lander/ascent craft to use cheap expendable solid fuel boosters. These give the best of both SSTO and multi stage designs.
What's less clear is why one would want to mine water only to covert it to methane for the SSTO lander? We know very well how to handle liquid hydrogen--that's no showstopper--and once you have LH2, you get your oxygen cooling for free.