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Budget

NASA FY 2019 Budget Hints: SLS Alternatives Sought

By Keith Cowing
NASA Watch
January 24, 2018
Filed under

NASA Watch founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.

18 responses to “NASA FY 2019 Budget Hints: SLS Alternatives Sought”

  1. Daniel Woodard says:
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    Astronishing is the only word. The FH cleared its throat today, who knows?

    • ThomasLMatula says:
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      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 🙂

  2. DougSpace says:
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    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.

    • Paul451 says:
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      Has anyone written up an Europa mission using the Falcon Heavy?

      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.)

      • Daniel Woodard says:
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        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?

        • fcrary says:
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          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.

          • Daniel Woodard says:
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            How can you have too much thrust?

          • fcrary says:
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            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.)

          • Daniel Woodard says:
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            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.

      • fcrary says:
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        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.

    • Daniel Woodard says:
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      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.

    • fcrary says:
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      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.

    • Not Invented Here says:
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      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.

    • Zed_WEASEL says:
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      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.

      • fcrary says:
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        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.

  3. ThomasLMatula says:
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    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.

  4. Charlie X Murphy says:
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    There are better alternatives than FH and they were already in the works before this announcement as backup .

  5. Steven Rappolee says:
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    BFR for Europa