Quote from: Ionmars on 07/17/2017 04:43 pmIf this approach were used to establish a platform for testing BFS, there may be two basic questions. First, how much mass will Falcon 9R block 5 boost to stage separation, and (2) how much volume could be built into a partially-fuelled, empty stage 2-to-orbit vehicle that resembles the BFS. This will tell us how closely this testbed BFS could resemble a final BFS with usable payload that could be launched by an intermediate BFR.Why launch on F9 if FH is available and could launch it fully fueled?
If this approach were used to establish a platform for testing BFS, there may be two basic questions. First, how much mass will Falcon 9R block 5 boost to stage separation, and (2) how much volume could be built into a partially-fuelled, empty stage 2-to-orbit vehicle that resembles the BFS. This will tell us how closely this testbed BFS could resemble a final BFS with usable payload that could be launched by an intermediate BFR.
Anything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?
Quote from: envy887 on 07/17/2017 08:50 pmAnything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?just stop. NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules.
There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.
Would it ever happen that no-one wants to play by those rules any more? Or charges so much money to stick to the rules that even the NSS thinks they are taking the piss. Would/could the rules be changed?Not saying they should do one or the other, just commenting that just maybe, over the next few years, rules could change.
Quote from: Jim on 07/18/2017 02:12 amQuote from: envy887 on 07/17/2017 08:50 pmAnything else? Building integration facilities doesn't seem to be beyond the realm of possibility, as SpaceX needs them anyway for commsats. What particular requirements do NSS payloads have for integration that a commercial bird wouldn't?just stop. NSS has their requirements, if others want to play in their sandbox, then they have to play by NSS rules. There was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements.
Quote from: rakaydos on 07/18/2017 03:44 amThere was a recent video of Elon telling the Arkansas govenor that one of the downsides of oldspace is that they will never say no to awful requirements. And that is why it is unlikely that the NSS will use Falcon Heavy
One thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does? Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).
Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.John
Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.
Quote from: livingjw on 07/19/2017 11:39 amStudies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?
Quote from: mikelepage on 07/19/2017 07:17 amOne thing I'm curious about - and SpaceX would have data on this now - is to what extent supersonic retro-propulsion reduces peak heating on the returning stage? and to what extent it reduces the need for shielding?If the exhaust plume from the engine is creating a tear-drop-shaped protective interface around the returning stage, does this help to protect the stage? and/or create additional deceleration over & above the thrust itself in the same way a drogue chute does? Basically I'm wondering to what extent the requirement for S2 shielding can be removed by just changing the reentry procedure (timing/throttling of reentry/landing burns).Supersonic retro-propulsion will not be used, a heat shield will be. The only reason supersonic retro-propulsion is used for the booster is to keep it from exceeding about Mach 3.5. Much faster and the booster would get to hot. Reentry from orbit is 7 times faster than that and must use the atmosphere to slow down. Not enough propellant to do anything else. For landing it will either be parachutes or subsonic retro propulsion (the landing burn).Studies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.John
Quote from: Lars-J on 07/19/2017 04:28 pmQuote from: livingjw on 07/19/2017 11:39 amStudies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.
Quote from: envy887 on 07/19/2017 05:10 pmQuote from: Lars-J on 07/19/2017 04:28 pmQuote from: livingjw on 07/19/2017 11:39 amStudies have been done which show that a rocket firing from the center does not increase drag, but that drag can be increased if rockets are fired from around the perimeter. I cannot remember if heating was reduced. I will see if I can't dig up the study.No, no, no. People keep misunderstanding this. This observed effect was only at low throttle levels. It does not mean that braking is impossible with a center mounted engine. Surely you have observed the F9 braking burns?Those do not rely to any significant extent on drag. Drag is most important in the hypersonic and high supersonic phases of entry.Right. But the problem is that some people interpreted the paper on drag reduction using a central thruster as proof that retro propulsion at supersonic speeds is impossible with a central thruster. ("you'll never get thrust, only reduce drag!")