NASA Ares V cargo launch vehicle (CaLV) integration manager Steve Creech visibly shook and his voice wavered with a very nervous answer to my question about why, when they already have a 6,000kg payload margin to trans-lunar injection (TLI), they were considering changes to the CaLV to add another 3,000kg of margin?
I suspect that the reason is that NASA’s Altair Lunar Lander is going to go all-hypergolic
With an Altair design that is not yet even a “point of departure” that is not at all clear, admittedly
Going hypergolic would repeat the Apollo programme experience. Its lunar module used nitrogen tetroxide (NTO) and Aerozine-50 (a 50/50 mixture of hydrazine (N2H4) and unsymmetrical dimethylhydrazine (UDMH)) for its hypergolic propellants – meaning they ignite on contact
While NASA has yet to decide officially whether Altair’s ascent stage will be cryogenic or use hypergolic fuels, an industry technical exchange meeting in November last year indicated an NTO and monomethylhydrazine (MMH) engine for the early conceptual designs with a longer term goal of liquid oxygen (LOX) and liquid methane (LCH4). An industry day a few weeks later in December presented the ascent propulsion system as an NTO/MMH engine
That NTO/MMH ascent engine was adopted for the “minimal functional” 711-A design that is the starting point for companies contracted by NASA to carry out a study that would see recommendations for safety improvements but is still not for the point of departure
The argument for switching to cryogenics is the almost 1,000kg (2,200lb) mass saving that comes with those propellants. So unsurprisingly NASA has a project underway to solve the problems of long duration storage of liquid oxygen and methane and hydrogen
The descent stage, however, had to be made cryogenic and specifically LOX, liquid hydrogen (LH2) because of Ares V’s payload capability. An all hypergolic descent stage would simply be too heavy and this, I suspect, is where the problem lies
Talking to NASA’s exploration launch project office’s advanced planning manager and former Apollo programme rocket engineer Phil Sumrall in February he explained how high hopes for the 2005 Exploration Systems Architecture Study’s (ESAS) Ares V design’s capability were whittled away
That while at the end of ESAS they were able to show a 73,000kg TLI throw weight, (though only declared 65,000kg capability) the TLI deltaV budget was “not great” and they had to add flight performance reserve to that
Other mission requirements also ate into the TLI capability. The Ares team were given a 29degree orbital plane to widen the launch window and that cost them 7,500kg in payload margin
Then the decision to allow Altair to go anywhere on the Moon saw a need for a lot more deltaV capability and the emergency return requirement to come back “anytime from anywhere” further eroded the rocket’s TLI margin
A decision to be able to inject 130,000kg into low Earth orbit, up from ESAS’s 125,000kg requirement, did not help matters either
Interestingly Sumrall told me about how a “55,000kg to 60,000kg lander” had been considered
It was rejected and NASA’s lunar architecture team were told to go back and think again about what payload they wanted taken to the lunar surface
But I wonder if maybe things are not swinging back the scientists way. The Lunar Capability Concept Review presentation at the Lunar and Planetary Institute’s website indicates that the Altair Lander Design Analysis Cycle (LDAC)-2 design (seen above) could return 100kg of rock sample but Apollo’s lander could help bring back 110kg
So the pressures on Sumrall and Creech and the Ares V design are just not going away
So what can they do to increase that margin?
Beyond the publicised change from PBAN to HTPB for the solid rocket fuel, at a presentation at the 44th AIAA Joint Propulsion Conference on Ares I first-stage solid rocket motor (SRM) and Ares V SRM booster reusability it was indicated that a 4,400kg payload increase could be achieved for the CaLV by having expendable boosters
Another option is to increase the amount of composite structures used in the Ares V. Over the last year the current design has shifted slightly in the presentations’ vehicle descriptions from saying aluminium lithium (Al Li) tanks and structures to now saying Al Li tanks and composite structures. I suspect that composite tanks is the next move
This use of composites for tanks is referred to as a technology challenge in the Ares V presentation given at the November 2007 Galveston, Texas, technical echange conference. Click on the presentation slide below to see a larger version in the same browser window
