NASA FY 2019 Budget Hints: SLS Alternatives Sought
Sources report that the #NASA FY 2019 budget will advise @NASA to look into non-SLS options to launch missions to Europa. One would assume that @CongCulberson will have an opinion on this. #astrobiology pic.twitter.com/K1YG9sgXg1
— NASA Watch (@NASAWatch) January 24, 2018
Astronishing is the only word. The FH cleared its throat today, who knows?
Yes, and it would be great for FH to hit a home run on its first flight, and maybe a grand slam if it does it before the State of Union so it gets a shout out by the President 🙂
Has anyone written up an Europa mission using the Falcon Heavy? I have always regarded the time savings of using the SLS for Europa as hard to justify compared to the cost of using the SLS. I don’t see that we lose much by waiting something seven years versus three. It’s mostly just scientific curiosity.
Apparently it would need a hydralox 3rd stage to squeeze into a 20t HEO payload limit. The only suitable candidates are DCSS/ACES. They should be able to send about 6-7 tonnes direct to Jupiter on FH. But it means modifying the FH launch site to allow LH2 loading.
Current estimates for Clipper/Lander are around 13 tonnes. NASA prefers separate launches, the orbiter mapping for the later lander, so it’s do-able with two FH launches, but the primary sponsor, Culberson, wants a single launch.
(We really need orbital-refuelling/distributed-launch.)
I agree, but as the FH is likely to be limited by volume rather than mass a LOX/methane upper stage (with much denser fuel) might be equally effective. Didn’t the DOD pay for some studies on such an upper stage for the FH?
Now that you mention it… Yes. A Centaur is about 12.5 m tall plus payload, and the Falcon payload shroud is only 11 m long (and starts tapering at 6.5 m.) You’d need something at least as big as a Centaur.
I think it’s the Air Force, but SpaceX does have funding to develop a smaller version of the Raptor engine (oxygen/methane). But even that may be too high thrust for this application, and I don’t think the contract was for a full upper stage, just the engine.
How can you have too much thrust?
You can have too much of just about anything. (I once saw a study proving that distilled water, in sufficient quantity, is carcinogenic.)
In this case, too much acceleration. We’re talking about a hydrocarbon/oxygen kick stage for a Europa Clipper (or equivalent) spacecraft, launched on a Falcon Heavy. That implies a total mass (spacecraft, rocket and empty fuel tank) at the end of the kick stage burn of about 7 or 8 tonnes. A Raptor is planned to have a thrust of 1900 kN, which would be an acceleration of around 250 m/s^2 (about 25 gs) at cutoff. Building a spacecraft to survive that would mean a huge waste of mass on mechanical structure.
On the other hand, too little thrust is also a problem. For efficiency, you need the burn to be much shorter than an orbital period. Say a factor of ten or twenty. For this, 6.4 km/s from LEO to a direct trajectory to Jupiter, if I did the math right, I’d say an average acceleration of 10 to 15 m/s^2 would be about right, which implies a thrust of around 400 kN (20% that of the planned Raptor.)
I was under the impression the Raptor powered stage would replace the existing second stage rather than being added as a third stage. This permits several alternatives. The second stage can have a much larger fuel tank, as permitted by the FH thrust, increasing the empty mass and reducing final acceleration. Or, the spacecraft mass could be increased by adding a lander, or the original solid kick stage intended for the Atlas could be carried. Finally, we don’t know how much throttling capability is possible with the full flow staged combustion cycle. Finally, a subscale development Raptor with a 1MN thrust is the only one that has been tested, and could be adapted for flight.
Actually, the Europa Clipper is only a bit over 4 tonnes (well, a hair under plus margin), unless it’s grown substantially in phase A and B. (Ok, that’s likely)
If it is 4 tonnes, and placed in low Earth orbit with a fully fueled Centaur, that just barely works for a direct trajectory to Jupiter. It also greatly under utilizes the Falcon Heavy, since it only requires 30 tonnes to LEO. If you used to full lift capability of a Falcon Heavy, you could get away with a RP-1 and oxygen. But that means a custom kick stage, and that could cost more than a SLS launch.
The 13 tonne number isn’t for Clipper. That’s _just_ the lander as a separate mission (plus a carrier vehicle/relay, deorbit stage and sky crane. Yes, sky crane…) Even on an SLS, that requires a deep space maneuver and an Earth flyby.
With the FH the mission has not been examined, but the wait would probably be a lot less than seven years, although the science community never said the Atlas was unacceptable. But until now the Europa mission was considered a political anchor for the SLS. As long as that was the case, there was not much to be gained by examining the technical suitability of the FH.
I don’t think there have been any formal studies, but the back of the envelope calculations say a direct trajectory with a Falcon Heavy launch would work. But it would involve adding a upper (kick) stage, so it wouldn’t be as easy as you think.
As for the savings, it’s about two and a half to three years difference, not four. But operating costs are not trivial for a mission like this. I don’t know what the numbers for Europa Clipper, but something like $75 million per year is a reasonable guess based on other missions. So the savings is considerable. From the mission’s point of view, and if the Planetary Science Division were only charged the incremental cost of a SLS launch, it much look good.
According to GAO report, Europa Clipper hasn’t selected a launch vehicle yet, the current design is compatible with both FH and D4H, in addition to SLS. They’ll have to select a launch vehicle later this year though, that’s when things will get interesting.
The original Europa Clipper mission was baseline with the Atlas V 551 with a solid motor kick stage. So the Falcon Heavy is over qualified.
The Atlas V option, which the Clipper project still retains as a backup, involves a five year cruise to Jupiter and has to do a deep space maneuver and a Earth flyby along the way. The SLS launch option gives them a two and a half year cruise, going directly to Jupiter.
You know, if NASA really wanted an alternative for the SLS they could just use that money to fund both the New Armstrong/BFR and accelerate the development of both. Then instead of just having a very expensive way to make short visits to a DSG every couple years NASA could have HSF access to the entire inner Solar System.
There are better alternatives than FH and they were already in the works before this announcement as backup .
BFR for Europa