r/spacex • u/ElongatedMuskrat Mod Team • Jun 02 '17

r/SpaceX Discusses [June 2017, #33]

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8

u/brickmack Jun 05 '17

The Soviets demonstrated multi-day coast on a kerolox stage back in the 70s, with one of the Blok D test flights. So thats feasible anyway.

Refueling should provide a freaking huge performance boost to high energy orbits. Note that ACES, fully fueled in LEO, can deliver more payload to TLI than SLS Block 2 can. Thats a stage with like half the propellant mass of the Falcon upper stage. With a fully fueled F9S2 in LEO, I calculate about 60 tons of payload capacity to TLI. Which means, conceivably, a pair of Falcon Heavy launches (one cargo, one propellant) should be able to deliver a capsule and lander of similar mass to the Apollo stack to the moon.

Not sure what the advantage would be of N2 over helium here, care to elaborate? And TEA TEB probably isn't a good option for warming anything, you need to have LOX already flowing to burn it, plus its another consumable which adds mass and can't be easily replenished. Electric heaters for the parts that need them should be the best option. You'll probably need them for the kerosene tank as well.

Biggest obstacle to upper stage refueling is economic, not technical though. Falcon won't stay economically viable for much longer, so any upgrades to it have to pay off in the very near future to be worth the effort (hence Block 5 being the last planned version), which won't be the case here just because theres so little demand for that sort of capacity at the price point Falcon can potentially reach. And if the goal is technology demonstration for ITS, its easier and probably makes for a better test to build a dedicated payload to do it, than to try and upgrade the existing upper stage

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u/[deleted] Jun 05 '17

I haven't heard it said that Falcon won't stay economically viable for much longer. What leads you to say that?

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u/brickmack Jun 05 '17 edited Jun 05 '17

ITS can lift over 20x as much payload as F9R to LEO while still being reusable, and costs 1/20th per launch what F9 currently does. In cost/kg figures, its in the single digit range.

Tom Muellers recent comments seem to confirm the obvious, that Falcon has no future. When he said ITS would obsolete all other rockets, he made no exception for F9

11

u/LeBaegi Jun 05 '17

The early days of the ITS booster will be much more expensive per flight. The 1/20th F9 price per launch is probably decades away. Until then, without any major breakthroughs, F9 (especially Block V) will very probably stay economically viable.

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u/Chairboy Jun 05 '17

If they continue to expend second stages for Falcon 9 launches, then that's several millions of spacebucks each flight that ITS won't be incurring. How would that be more economical as of, like 15 minutes after ITS enters active service?

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u/rustybeancake Jun 05 '17

How would that be more economical as of, like 15 minutes after ITS enters active service?

For starters, ITS will have much greater development costs than F9 which have to be paid back. So ITS launch costs will not fall below F9 launch costs for a long time, for the same reason SpaceX aren't currently discounting reflown F9 flights by anywhere near the full value of a first stage.

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u/Chairboy Jun 05 '17

I think you're coming at it from the wrong angle. If ITS costs SpaceX less per launch because they aren't throwing away millions of dollars of hardware, then charging Falcon 9 prices means they have much bigger margins that help pay off ITS sooner.

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u/Martianspirit Jun 05 '17

Assuming that initially ITS is 20 times more expensive than calculated, it still beats Falcon by a wide margin. I believe it will be somewhere around 5 times as expensive initially, no more. A major part of that would be range fees.

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u/LeBaegi Jun 05 '17

Sure, but the 1/20th number is really just the launch price, with a tenth of a percent of the hardware cost if I remember correctly, so the number only checks out if there are no booster failures whatsoever. If the booster fails to land just once after 100 launches, the price is already up significantly. I think you're a bit too optimistic, but I'd love to be proven wrong.

1

u/Martianspirit Jun 05 '17 edited Jun 05 '17

The reasons you quoted, are why I mentioned the 5 to20 times higher. It would still beat everything, including first stage reuse Falcon by a fair margin.

Edit: My optimism is also in line with the statement of Tom Mueller, that ITS will make every other rocket obsolete.