A tweet from Musk about F9 performance upgrades coming soon: (we already knew about the densification and M1D thrust upgrade, but the upper stage stretch(?) is new)https://twitter.com/elonmusk/status/572257004938403840QuoteElon Musk @elonmuskUpgrades in the works to allow landing for geo missions: thrust +15%, deep cryo oxygen, upper stage tank vol +10%
Elon Musk @elonmuskUpgrades in the works to allow landing for geo missions: thrust +15%, deep cryo oxygen, upper stage tank vol +10%
Quote from: Lars-J on 03/02/2015 03:53 amA tweet from Musk about F9 performance upgrades coming soon: (we already knew about the densification and M1D thrust upgrade, but the upper stage stretch(?) is new)https://twitter.com/elonmusk/status/572257004938403840QuoteElon Musk @elonmuskUpgrades in the works to allow landing for geo missions: thrust +15%, deep cryo oxygen, upper stage tank vol +10%Well, it was a low hanging fruit.http://forum.nasaspaceflight.com/index.php?topic=36045.msg1285819#msg1285819a stretch is all you need to improve your GTO margins.A two meter stretch would add 20000 kg of propellant to the second stage for a mere 300 kg of extra tankage (only 2m sidewalls added).With 20% more propellant you get at least 1000 kg of extra payload.This would have no influence on first stage T/W, and small influence on second stage T/W; most of this extra mass is masked by GTO payload reduction compared to LEO.And +10% is more like 1 m stretch.
Any insights on how these F9 changes may affect USAF certification, which I assume has been based on F9 v1.1? I don't see SpaceX operating two F9 variants?
It actually could be no stretch if the U/S really has been flying at less than 90% fuel load, which has been speculated before. Perhaps they designed it with subcooling in mind and the lower stage couldn't provide enough for the extra prop to be loaded until subcooling increased the lower stage total impulse enough to make it work.
A two meter stretch would add 20000 kg of propellant to the second stage for a mere 300 kg of extra tankage (only 2m sidewalls added).And +10% is more like 1 m stretch.
I think this is more realistic than stretching the 2nd stage. The latter would require re-tooling, aerodynamic analysis and more. Can't see this happening, at least in the short term.
Quote from: ugordan on 03/02/2015 11:14 amQuote from: FutureSpaceTourist on 03/02/2015 07:34 amAny insights on how these F9 changes may affect USAF certification, which I assume has been based on F9 v1.1? I don't see SpaceX operating two F9 variants?I'll throw in a question about NASA's own certification and how this will play into it? Can anyone in the know comment? Not interested in speculation for the sake of speculation.Just speculation, but EM only mentioned it in the context of GEO missions, so the LEO configuration may be unaffected, and hence certification is unchanged.
Quote from: FutureSpaceTourist on 03/02/2015 07:34 amAny insights on how these F9 changes may affect USAF certification, which I assume has been based on F9 v1.1? I don't see SpaceX operating two F9 variants?I'll throw in a question about NASA's own certification and how this will play into it? Can anyone in the know comment? Not interested in speculation for the sake of speculation.
it seems entirely plausible that SpaceX can increase the total tank volume of the second stage by 10% without increasing the total rocket length through the use of densified LOX.
Yes that's exactly what my post implies. You need less volume of lox to maintain same ratio.
The following paper suggests a 9% increase in LOX mass is possible by supercooling. So maybe they keep the LOX tank volume as is, and increase the RP-1 tank volume 10% to maintain the ratio.http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050203875.pdfIn any case, hard to see how you do that without stretching the stage slightly. As others have pointed out, changing S2 tank length slightly is not a big deal from a manufacturing POV, and probably not a big deal structurally or aerodynamically.
Well, It's only 1 meter. You'd have to lengthen the tank by only about 19 inches on each end to get 1 meter. Perhaps within the current shell, they can reposition some equipment and wiring at either end to squeeze in a slightly bigger tank.