This might just be a definitions issue. If there's a biconic capsule sitting on top of a Reusable Booster Stage, is the biconic capsule a second stage? What if the biconic capsule doesn't contribute to the ascent?Actually, looking at the slides, it's unclear if the RBS is one stage or two...
Quote from: neilh on 04/30/2012 11:31 pmThis might just be a definitions issue. If there's a biconic capsule sitting on top of a Reusable Booster Stage, is the biconic capsule a second stage? What if the biconic capsule doesn't contribute to the ascent?Actually, looking at the slides, it's unclear if the RBS is one stage or two...It looks pretty obviously like it's two stages. There's a long, skinny cylinder between the top of the first stage and the bottom of the spacecraft. Every indication is that it's TSTO.
Quote from: Robotbeat on 04/30/2012 11:36 pmQuote from: neilh on 04/30/2012 11:31 pmThis might just be a definitions issue. If there's a biconic capsule sitting on top of a Reusable Booster Stage, is the biconic capsule a second stage? What if the biconic capsule doesn't contribute to the ascent?Actually, looking at the slides, it's unclear if the RBS is one stage or two...It looks pretty obviously like it's two stages. There's a long, skinny cylinder between the top of the first stage and the bottom of the spacecraft. Every indication is that it's TSTO.That seems reasonable.
Yep, its pretty clear that the biconic capsule is not some sort of derivative of DC-X with integral rocket engines and propellant. Too bad.
If we had spent as much money and effort on designing a TSTO RLV as we have collectively designing efforts at SSTO RLVs (including Shuttle, which was kind of a SSTO and kind of an RLV), we'd wouldn't be having this conversation right now.
Quote from: Robotbeat on 04/30/2012 09:44 pmIf we had spent as much money and effort on designing a TSTO RLV as we have collectively designing efforts at SSTO RLVs (including Shuttle, which was kind of a SSTO and kind of an RLV), we'd wouldn't be having this conversation right now.Shuttle was kind of an SSTO only if you're allowed to stretch the definition until it's meaningless. NASA defined the SRBs as first stage.
Quote from: Jorge on 05/01/2012 03:48 amQuote from: Robotbeat on 04/30/2012 09:44 pmIf we had spent as much money and effort on designing a TSTO RLV as we have collectively designing efforts at SSTO RLVs (including Shuttle, which was kind of a SSTO and kind of an RLV), we'd wouldn't be having this conversation right now.Shuttle was kind of an SSTO only if you're allowed to stretch the definition until it's meaningless. NASA defined the SRBs as first stage.The core is ground-launched and reaches essentially all the way to orbit. Sure, it's not technically SSTO
, but the SRBs don't contribute that much to delta-v, just initial thrust (like the Atlas classic outer engines... and Atlas was a pseudo-SSTO).
Not just technically. It's a parallel-staged TSTO, by any reasonable definition.
Quote from: Robotbeat on 05/01/2012 05:45 amQuote from: Jorge on 05/01/2012 03:48 amQuote from: Robotbeat on 04/30/2012 09:44 pmIf we had spent as much money and effort on designing a TSTO RLV as we have collectively designing efforts at SSTO RLVs (including Shuttle, which was kind of a SSTO and kind of an RLV), we'd wouldn't be having this conversation right now.Shuttle was kind of an SSTO only if you're allowed to stretch the definition until it's meaningless. NASA defined the SRBs as first stage.The core is ground-launched and reaches essentially all the way to orbit. Sure, it's not technically SSTONot just technically. It's a parallel-staged TSTO, by any reasonable definition.Quote, but the SRBs don't contribute that much to delta-v, just initial thrust (like the Atlas classic outer engines... and Atlas was a pseudo-SSTO).Velocity at SRB burnout was about 20% of orbital velocity (SSME contribution during first stage was minimal, all three combined were about a third of an SSME). And that understates the contribution of the SRBs to delta-v, since first stage absorbed most of the gravity losses.Your other points about the SSME needing aggressive performance are valid, and this would be a characteristic of any parallel-staged TSTO, but it's not nearly as aggressive as an SSTO would require. Don't call it an SSTO.
There's a lot to be said for: - Reusable VTVL first stage - Cheap expendable second stage - Reusable VL spacecraft with a significant contribution to final ascent