TAN is a great idea, but becomes unnecessary for SSTO if a (hinted at) 200:1 T/W dense fuel engine like Raptor is available. Raptor would be only ~0.65% of launch mass which is only around 10% of the ~6.5% of GTOW that an SSTO powered by it can orbit. Thought the boost it can give to vacuum isp (through use of higher expansion ratio TAN nozzle) is probably more significant.
TAN is a great idea, but becomes unnecessary for SSTO if a (hinted at) 200:1 T/W dense fuel engine like Raptor is available. Raptor would be only ~0.65% of launch mass which is only around 10% of the ~6.5% of GTOW that an SSTO powered by it can orbit.
Quote from: RobLynn on 02/10/2019 07:19 amTAN is a great idea, but becomes unnecessary for SSTO if a (hinted at) 200:1 T/W dense fuel engine like Raptor is available. Raptor would be only ~0.65% of launch mass which is only around 10% of the ~6.5% of GTOW that an SSTO powered by it can orbit.Where does the ~6.5% figure come from? Off hand, it seems to me that most SSTO proposals have considerably lower payloads fractions.
Quote from: RobLynn on 02/10/2019 07:19 amTAN is a great idea, but becomes unnecessary for SSTO if a (hinted at) 200:1 T/W dense fuel engine like Raptor is available. Raptor would be only ~0.65% of launch mass which is only around 10% of the ~6.5% of GTOW that an SSTO powered by it can orbit. Thought the boost it can give to vacuum isp (through use of higher expansion ratio TAN nozzle) is probably more significant.That leaves the problem of landing.A single engine SSTO design either needs to avoid relighting its engine for landing IE Gliding in, or have an engine capable of throttling to something like 3% of its takeoff thrust. The first is certainly possible the second is at least partly why SX use engine clusters.
Quote from: john smith 19 on 02/10/2019 10:14 amQuote from: RobLynn on 02/10/2019 07:19 amTAN is a great idea, but becomes unnecessary for SSTO if a (hinted at) 200:1 T/W dense fuel engine like Raptor is available. Raptor would be only ~0.65% of launch mass which is only around 10% of the ~6.5% of GTOW that an SSTO powered by it can orbit. Thought the boost it can give to vacuum isp (through use of higher expansion ratio TAN nozzle) is probably more significant.That leaves the problem of landing.A single engine SSTO design either needs to avoid relighting its engine for landing IE Gliding in, or have an engine capable of throttling to something like 3% of its takeoff thrust. The first is certainly possible the second is at least partly why SX use engine clusters.If you are trying to do economic SSTO you need to find every scrap of performance you can.
I like the idea of a net catcher to eliminate mass of precise trajectory control and landing systems: 3 or more big multicopter drones with a net strung between them, dive to intercept (and reduce net impact velocity).
The rocket equation. 9100m/s (typical dense fuel SSTO LEO deltaV). 340s Isp. 6.5%GTOW = total mass in LEO RLV+payload in orbit. Number is not particularly important other than to make point of how small a factor engine mass is with high thrust to weight engine.
With TAN coming off patent soonish, perhaps it's time to revisit nozzle tricks. Specifically a vacuum optimized nozzle with TAN injection of a high density fuel to keep the plume stable and achieve high thrust when it counts, AKA a tripropellant engine but a bipropellant chamber. Say a LOX+methane/RP1 combo. Hrm, I wonder if you could get away with an electric pump for the TAN RP1 injection in the nozzle, and potentially avoid coking?
Quote from: RobLynn on 02/10/2019 07:03 pmThe rocket equation. 9100m/s (typical dense fuel SSTO LEO deltaV). 340s Isp. 6.5%GTOW = total mass in LEO RLV+payload in orbit. Number is not particularly important other than to make point of how small a factor engine mass is with high thrust to weight engine.Oh, right. I had mistakenly thought you were suggesting that an SSTO's payload might be ~6.5% of its GTOW.I would expect, though, that an SSTO's payload as a fraction of GTOW will be quite a bit less than 6.5%. Even the fully-expendable two-stage Atlas 401, for example, has a payload fraction of only about 3.8%. For a reusable SSTO, 0.65% might be the difference between a positive payload and a negative one.
Yeah, and other huge impact of rocket mass is the vehicle centre of mass - and requirement for heavy wings or other planform area to balance all the tail mounted engines. Maybe it is worth chasing engine T/W uber alles? A TAN version of Raptor might get up to 3-400:1 T/W with Vac Isp of ~380s.
Have you got any idea how big and expensive those "drones" need to be?
Quote from: RobLynn on 02/11/2019 07:00 pmYeah, and other huge impact of rocket mass is the vehicle centre of mass - and requirement for heavy wings or other planform area to balance all the tail mounted engines. Maybe it is worth chasing engine T/W uber alles? A TAN version of Raptor might get up to 3-400:1 T/W with Vac Isp of ~380s.With the proviso this is always in the context of a VTOL SSTO system.HTOL SSTO systems can have options.
HTOL really only makes sense if airbreathing is involved - which comes with huge aero and gravity losses,
high dynamic pressures , high developmental complexity and long development cycles all of which mean
huge cost with marginal likelihood of success (technical or commercial).
HL might be viable, though with terrible abort options and
typical estimates for wings and wheels at around 10% of landed mass vs as little as 5% for a 'fluffy' rocket powered VL and ability to land anywhere, it is now tough to make a convincing case for HL.
The arguments for HL used to hold more water in pre-spaceX day due to lack of familiarity, but propulsive VL has been very well proven now and is almost certainly going to be the standard going forward.
I think it's very telling that despite arguably the best design team in US rocket building industry (in terms of current applied skills experience, as opposed to something, somewhere, inside the corporate memory that was done long ago) and a very strong desire by the Chief Designer to avoid wings at all costs SX still ended up with a winged US design.
Quote from: john smith 19 on 02/14/2019 06:56 amI think it's very telling that despite arguably the best design team in US rocket building industry (in terms of current applied skills experience, as opposed to something, somewhere, inside the corporate memory that was done long ago) and a very strong desire by the Chief Designer to avoid wings at all costs SX still ended up with a winged US design.As I understand it (and I may be wrong), the "wings" on Starship won't provide any lift, but are simply control surfaces, much like the gridfins on the Falcon 9. I don't think they're a very good argument for the utility of lifting surfaces on an orbital craft.
As I understand it (and I may be wrong), the "wings" on Starship won't provide any lift, but are simply control surfaces, much like the gridfins on the Falcon 9. I don't think they're a very good argument for the utility of lifting surfaces on an orbital craft.
Quote from: Tulse on 02/14/2019 02:03 pmAs I understand it (and I may be wrong), the "wings" on Starship won't provide any lift, but are simply control surfaces, much like the gridfins on the Falcon 9. I don't think they're a very good argument for the utility of lifting surfaces on an orbital craft.I do so admire anyone who can confidently describe a set of control surfaces that have to operate over a rage of 23 Mach numbers, with operating temperatures into the 1200-1400c range, creating control forces in the 10s, if not 100s of tonnes range, as "simple"
Quote from: john smith 19 on 02/14/2019 09:13 pmQuote from: Tulse on 02/14/2019 02:03 pmAs I understand it (and I may be wrong), the "wings" on Starship won't provide any lift, but are simply control surfaces, much like the gridfins on the Falcon 9. I don't think they're a very good argument for the utility of lifting surfaces on an orbital craft.I do so admire anyone who can confidently describe a set of control surfaces that have to operate over a rage of 23 Mach numbers, with operating temperatures into the 1200-1400c range, creating control forces in the 10s, if not 100s of tonnes range, as "simple"They are not "simple", but they are "simply" control surfaces, and not wings, a point you don't seem to dispute but which you seemed to claim earlier. Let's try to discuss in good faith, rather than score rhetorical points.
Quote from: Nighthawk117 on 01/28/2019 02:28 amLuckily, XS-1 is the spiritual successor to X-33.No, it is not.
Luckily, XS-1 is the spiritual successor to X-33.