"Show me how you put together a non-ISRU Mars Ascent Vehicle without needing some Sea-Dragon sized LV to get it there."Well, you are overstating things a tad:a non-ISRU Ascent Vehicle need not be a 'Battlestar Galactica' sent there on a rocket twice as powerful as Ares V!! First of all, I only said that a non-ISRU Ascent Vehicle was an
option, and
not the preferred one at that.
Following figures approximate; since Mars mission mass numbers are still debated - The
dry mass of the Mars Ascent Vehicle (MAV) according to the
NASA Mars DRM-3 study - is 20 tons, give or take consisting of both the Descent and Ascent portions, plus 20 tons of cargo sent as down mass:
http://ares.jsc.nasa.gov/HumanExplore/Exploration/EXLibrary/docs/MarsRef/addendum/index.htmThis down mass includes the ISRU 'feedstock', a Rover, scientific equipment, tools, spares, the nuclear reactor for ISRU etcetera. If this vehicle is landed with 6 tons of LH2 feedstock for ISRU creation of LOX/Methane, this is leveraged to produce more than 30 tons of propellants to launch the ascent vehicle to a Mars Transfer Vehicle or a dedicated Earth Return Vehicle in Martian orbit. We're assuming that the MAV would use this approx 30 tons of propellant to liftoff only the crew cabin, the Ascent stage motor, the crew and their Martian regolith & rocks, all massing about 15 tonnes at Martian liftoff - leaving the legs, descent motors and cargo pallet behind.
Since hypergolic propellants are between 10 and 15% percent less efficient than LOX/CH4, if we halved the vehicle's cargo downmass load - including deleting the nuclear reactor - we could more than make up for the loss in efficiency.
But if the Ascent Vehicle is made as basic and bare-bones as possible: a small cabin derived from Dragon or another, all-composite capsule, bolted to an Ascent engine, RCS sets and fuel tanks. Think of it as a "Apollo Lunar Module Ascent Stage on Steroids".
Apart from the hypergolic propellant load, all this craft would be lifting to Martian orbit would be a crew (2 or 3?) and their load of Martian rocks and regolith and maybe some data storage blocks. So it doesn't have to be as big or complex as the 44 ton (landed), 15 ton (ascending) NASA DRM-3 design for 6 crew.
Or if you wanted to meet ISRU halfway and only produce LOX oxidizer to supplement some landed kerosene or ethanol - this could use a 5 metric ton combined solar and RTG package to slowly produce the LOX only. And you could trade some of that 5 tonne increase in mass for cargo down mass; as you'd be using more powerful LOX/Kerosene/Ethanol for descent propulsion, not less efficient storables, to compensate for the mass of the ISRU package in the first place.
But let me state for the record: I am in favour of ISRU for Mars.
But an all-hypergolic Ascent Vehicle doesn't have to weigh 60 or 70 tonnes at Trans-Mars Injection. Launched on an uprated EELV or Falcon Heavy, the Hypergolic 'basic' MAV with
Empty propellant tanks would mass about 16 metric tons, Descent/Ascent stages all up with little or no cargo. I say make a separate, dedicated Cargo Lander by deleting the weight of the 4 ton composite crew cabin. Before Earth Departure, load it with fuel from a Prop. Depot or Propellant Delivery Modules until it contains enough hypergolics to descend to the Martian Surface. For a bare-bones 2 or 3 person Ascent vehicle weighing
half that of the 6 person DRM-3 design, total hypergolic propellant loading would be about 35 tons - 15 tons for a descent assisted by frictional slowing and parachutes, plus 20 tons to later get the craft into orbit to meet the ERV or MTV.
As I said, by making the MAV basic with no 'bells & whistles' and keeping bulk cargo for another lander, you don't need a 'Sea Dragon' to send it to Mars!! A couple Phase 1 EELVs, Falcon Heavies or one SLS Block 1B could do it. But yes, if you wanted a 6x person version with lots of cargo down mass, expect a much heavier vehicle. If you wanted to lift a hypergolically propelled big, 6 person MAV then yes, get a bigger rocket than even Ares V would have been.
