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SLS And Europa

25 Comments

What a mess.

A dual FH launch would give them a direct trajectory, at far lower cost.

And why does no one ever question the provenance of that $1B estimate per flight for SLS?

25 thoughts on “SLS And Europa”

  1. The SLS is a rocket in search of a mission. If they can’t find a mission for it, they’ll create one. There is no rational reason why this mission can only fly on an SLS, but politics and pork are hardly rational.

    As for the cost per mission, the billion dollar per mission price tag is probably the most bare-bones estimate of the hardware costs that doesn’t include any of the labor or facilities costs to actually launch it. Even that is suspect. Those multiple RS-25s, 5 segment SRBs, and multiple RL-10s don’t come cheap.

  3. Even without Starship, change is coming. Even if SLS flies, SuperHeavy + Starkicker (the expendable 3-engine upper stage) will undercut it completely, and maybe undercut New Glenn as well.

    1. Musk could ask NASA if he could launch Europa Clipper for free because he needs a mass simulator for a test launch of Superheavy.

      The offer would probably give them ulcers as they compare $0 to $1,500,000,000 dollars, and then realize that they are likewise using Europa Clipper as a mass simulator for a test launch.

      2. It’s a fun idea, but NASA would have to break its own requirements to launch a Flagship level mission on a launcher not certified for Cat 3 missions.

        That’s all right, though. Falcon Heavy expendable will be plenty cheap enough, even with the Star 48 kick stage.

        1. The Falcon 9 was certified for Cat 3 missions last fall. I have no idea when or if Falcon Heavy will get certified, but so far it’s flown three successful missions, which is the minimum number for Cat 3 certification. To fly Europa Clipper on the SLS’s third launch obviously requires tossing that rule aside.

          1. Apparently, FH is in the process of being certified now.

            Heck, it’s got more flights under its belt than Delta IV Heavy did when it got certified.

            To fly Europa Clipper on the SLS’s third launch obviously requires tossing that rule aside.

            Apparently, it doesn’t apply to NASA operated launchers!

  4. One of the puzzling things about Europa Clipper is the use of solar panels rather than an RTG to provide power. The spacecraft requires 150 W of power, which is exactly what an RTG supplies – continuously – from a 37.7 kg unit.

    Since the solar intensity at Jupiter is roughly 3.7% of what it is at the Earth’s distance from the Sun, 150 W of solar power takes 27 times as large a solar panel as one for an Earth satellite. Europa Clipper will have at least 18 m^2 of solar panels (that’s an initial estimate), which, based on the DAWN spacecraft solar array weight, would come in at about 59.4 kg. Not a killer in and of itself, except that use of solar requires the addition of batteries for the time the spacecraft is behind Jupiter. Clipper’s orbit around Jupiter will be highly elliptical, to minimize its time in the radiation environment at Europa’s orbit. That means that the time in Jovian shadow will be much longer than the 2.9 hours per orbit it would experience were it orbiting Europa – roughly 26 hours, worst case. Li-ion batteries for this would add at least 43 kg (based on the MER rovers’ battery specific energy), not to mention the weight of power conditioning equipment. These are unnecessary with an RTG.

    So they’re adding at least 102.4 – 37.7 = 64.7 kg (2.2 % of the dry mass of the spacecraft) which translates into 130.8 kg added launch mass compared to what they could do with an RTG.

    It doesn’t sound like much, but little bits of mass on this energetic a mission really impact the launch vehicle performance requirements.

    1. Maybe the SLS has to be certified to some standard to launch an RTG? Which it couldn’t possibly be pencil whipped by the second or third flight?

    2. They say they went with solar cells because of cost, but if cost is the issue why did they size EC so it had to launch on the world’s most expensive rocket instead of a Falcon Heavy, a choice that adds at least a billion dollars to the mission? I suspect it’s a case of “But that money is over there in that NASA budget, not here in our NASA budget.” And if they’ve been told that it has to launch on the SLS to help justify SLS, then the switch to solar does lower the overall cost of the mission.

      From an engineering standpoint it’s a bad decision because the solar cells will degrade due to the passes through Jupiter’s intense magnetic fields, limiting the mission duration, though the science team may view extra lifetime with the same sensor set observing the same moon as diminishing returns.

      1. They say they went with solar cells because of cost, but if cost is the issue why did they size EC so it had to launch on the world’s most expensive rocket?

        Lots of instruments on this probe, and lots of radiation shielding to survive the Jovian electromagnetic field.

        I expect, though, that NASA’s dwindling supply of plutonium is the real culprit, more than price. I think they want to save the RTG’s for missions where it’s basically necessary – like multi-billion dollars rovers facing Martian dust storms, and probes that go out beyond Jupiter – at least until their supply gets built back up.

    3. There were apparently a number of factors in using solar over RTG, cost being the chief one:

      A solar-powered Europa Clipper would be less expensive than one that used an RTG, Magner said, although he did not quantify the difference in costs. It would eliminate the need for an environmental impact statement that is required for nuclear-powered spacecraft and launch approval from the director of the Office of Science and Technology Policy. It would also free up constrained supplies of plutonium-238, the isotope used in RTGs, for other potential missions.

      Magner said after his presentation that using solar power would increase the spacecraft’s mass in order to accommodate the panels and structures, although it remained well within current design margins. A few other tweaks would be needed to the spacecraft’s design to incorporate the solar panels, he said.

      Link: https://spacenews.com/42121europa-clipper-opts-for-solar-power-over-nuclear/

      All that said, given how little plutonium NASA has on hand for deep space missions, I have the sense that there was pressure put on JPL to find a way to do it with solar. Much of what little remains is already committed to Mars 2020 and Titan Dragonfly.

  5. So the rocket built from components of the rocket that could not reach the current ISS orbit, will somehow be the only one capable of making this mission a success? I lack confidence.

  6. I suspect the $1 billion estimate that’s been kicking around for years dates from when they were assuming a production rate of two per year. With a $2 billion / year run rate that puts the marginal cost at $1 billion each, ignoring amortization of development cost (which they would ignore since they don’t have to recover it – hey, we’re the Federal Government).

  8. As for the Europa Clipper option, what about Star 48 as an upper stage for FH? That might still require a grav assist, but only from Earth, not Venus. It’s also based on, I think, Block4 specs, so I’m not totally convinced that there isn’t a way to do a direct shot with a fully expendable Block5 FH plus Star48 and a lunar grav assist prior to Star 48 ignition.

    FH + Centaur could do it, but that’d require launchpad mods for fueling, plus some R&D work. Still, probably a lot cheaper than an SLS launch, and more timely, too.

    1. Well, you have to compare the difficulty of adapting a Centaur to a Falcon Heavy versus the simpler option of developing a giant LH2 core first stage that uses four expendable RS-25’s and two five segment solid rocket boosters, plus a crawler and a giant launch tower.

      Elon Musk once Tweeted that it would be trivial to add two more side boosters to Falcon Heavy, which according to his numbers would increase the LEO payload capacity by 63%. That would be about 205,800 lbs for a fully expendable mission, right on par with a block 1 SLS. He’s says he’s not pursuing it because he chose to focus on Starship, but I’m sure if they threw some money at him he could have it flying before Europa Clipper is even ready. My estimate for the launch price of a 5-booster Falcon Heavy is $130 million.

  9. Why not just have Congress pass a law mandating that each SLS launch shall cost $1B? That seems like a simple solution.

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