Quote from: ZachS09 on 04/05/2017 04:31 amThis is obviously not a finished design of the reusable second stage because there's no landing legs.That image appears to be from this 2008 paper, which puts it back in the parachute recovery era (no legs). Jon Goff had some posts on Selenian Boondocks about it back in the day:http://selenianboondocks.com/2008/11/fun-spacex-paper-and-presentation/http://selenianboondocks.com/2008/12/falcon-ix-upper-stage-recovery-kremlinology/I don't know how applicable that image is to the current Falcon 9 upper stage, but it may be one of the simpler recovery options.
This is obviously not a finished design of the reusable second stage because there's no landing legs.
Quote from: john smith 19 on 04/04/2017 08:49 pmThe problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble."Drag" something behind it.
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.
Quote from: GWH on 04/04/2017 09:23 pmQuote from: john smith 19 on 04/04/2017 08:49 pmThe problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble."Drag" something behind it.That's what my petals do create drag...
F9 is 3.6m diameter, not 5.2m (your number probaboy refers to the PLF, not the stage itself).
Quote from: Rocket Science on 04/04/2017 09:52 pmQuote from: GWH on 04/04/2017 09:23 pmQuote from: john smith 19 on 04/04/2017 08:49 pmThe problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble."Drag" something behind it.That's what my petals do create drag...Part of why a Shuttlecock is stable is because of its mass distribution. Let's see how this works for your idea.Merlin is reported to be about 470Kg. The counter balance would presumably be a layer of PICAX on the nose. PICAX is much lighter than AVCOAT c0.27 g/cm^3 IE 2.7Kg/sq. m.F9 is 5.2m in diameter so that's about 21 sq. metres, needing a mass of more than 22Kg/sq. m of PICAX to keep it nose heavy. That means a layer 8cm thick would be needed to be nose heavy.If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks. And you have put your "petals" on the back end, making it back end heavier still. Does this still sound like a viable idea to you?Keep in mind the angles being talked about are no more than about 5deg below the local horizontal. The trade offs in system design are tricky. It's not between drag/control surface weight and propellant. It's between drag/control surface weight and propellant and TPS mass. The "exchange rates" between the three are a PITA to calculate without detailed mass and thermophysical properties. The easy one is every m/s you can shave off in the upper atmosphere means so many Kg of TPS you don't have to apply to resist such a high level of heating in the lower, denser atmosphere (provided your drag device can survive the heating). But control surfaces are measured in Kgs of mass, not m/sBut every Kg you add means another Kg of dead weight that builds up terminal velocity the Merlin will have to cancel. So to be a net win your drag/control surface (and its control system) has to trade better than 1:1 in terms of mass in order to lower the propellant needed to cancel the terminal velocity of the stage at landing. Anything less and you might as well just leave the TPS layer in place (if that is adequate to do the job).
And of course we have this from a few years back. Be interesting to know the full history of the image.https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198
If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks.
Quote from: CharlieWildman on 04/05/2017 02:04 amAnd of course we have this from a few years back. Be interesting to know the full history of the image.https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198Thanks for posting. These short-small petals may work for controllabilty, but "may not" protect the engine from entry plasma and "may need" to be made longer and around the entire stage with gap seals just like my shuttlecock concept...
...If that was the whole story. But then we have the mass of the propellant. Since the stage is under deceleration it will be urged to the back bulkheads of the two tanks. ...
Quote from: Rocket Science on 04/05/2017 11:45 amQuote from: CharlieWildman on 04/05/2017 02:04 amAnd of course we have this from a few years back. Be interesting to know the full history of the image.https://forum.nasaspaceflight.com/index.php?topic=36440.msg1308198#msg1308198Thanks for posting. These short-small petals may work for controllabilty, but "may not" protect the engine from entry plasma and "may need" to be made longer and around the entire stage with gap seals just like my shuttlecock concept...That depends on the angle of attack, and the angle of plasma departure. Shuttle flew a very high AOA for high lift and drag. F9 US could generate some lift at a very low AOA (or just dive straight into the atmosphere on a ballistic return) and the engine would just sit in the wake. Sure, it gets pretty hot back there, but not hot enough to bother niobium. The other engine parts would need some TPS.
John, you keep "conveniently ignoring" that I stated that the hypergolic tanks, legs and their tanks and actuators are all in the nose... So you have "no definitive" CoG to speak of... My grid-fin idea on S1 worked out pretty good, wouldn't you say?
Lets hear your great concept...
Quote from: Rocket Science on 04/05/2017 11:27 amJohn, you keep "conveniently ignoring" that I stated that the hypergolic tanks, legs and their tanks and actuators are all in the nose... So you have "no definitive" CoG to speak of... My grid-fin idea on S1 worked out pretty good, wouldn't you say? Actually I just looked at the picture of the petals you posted and wondered how exactly were they going to support the whole loaded weight of a stage sitting on them?But you're right putting a bunch of hypergolic tanks and landing legs in the nose will shift the Cg. That will put the nozzles of the super dracos pointing into the airstream but I presume you have a plan to protect them till they get nearer the ground. Quote from: Rocket ScienceLets hear your great concept...Funny you should say that as I posted it a few days ago. TL:DR Sub orbital velocity, near single orbit eliminates retro burn. Large nose grid fins and TPS. If the grid fins size and mass trades for reduced TPS but propellant for hoverslam also has to be factored in to ensure a net win.
I posted this at ars technica, but thought I might also subject it to the flames here. Apologies if it's been done to death already.-----An expedient way to add reusability to the US would be to make a bolt-on "module" containing the complete recovery package--heat shield, reentry RCS, guidance, retracted landing legs, SuperDracos, and prop tanks. The module would mount on the stage exactly as the payload adapter or Dragon, so no major redesign of the stage would be necessary. It would place all of the recovery mass at the front of the stage. Reentry would be nose-first, with no "swoop of death" because the stage would land upside down. The module could be omitted if max performance was required, just as the boosters are still occasionally expended for big payloads.The design would share one issue with other nose-first reentry designs: mounting the payload above (or through) the heat shield. The Shuttle had hatches in its heat shield for connections to the external tank, and a similar arrangement might work for Falcon.
Quote from: robert_d on 04/01/2017 02:06 pmBecause of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage. It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage. How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge. That gives me an idea (sorry if it's been suggested.) Behold, my first NFS Rube Goldberg device. It must be contagious:Rocket LEGO Landing Element. A landing module that connects to the PAF and is used as a PAF for the "real" payload. It includes integrated SDs and landing legs and it's mass shifts the COM forward so it reenters "head first." No idea how to add a heat shield or control the trajectory w/o some sort of fins.Similar idea could use a controllable parafoil instead of propulsive landing (or maybe with propulsive assist.)Basically I like the idea of the PAF as a PAF so that there is only one S2 and you plug on the "reuse option." Some assembly and lots of hand waving required.
Because of the time constraints, I proposed that they could try a system on the Falcon Heavy Demo mission with 4 legs in the payload fairing. Splay them out and perform re-entry from LEO. Spreading the heat over the larger area would be interesting and might inform the development of a fairing/heat-shield combo to protect the second stage. It might be something like a 3 part fairing with two parts recoverable and the 3rd part sliding into position downward to protect the stage. How it would land? Deployable paraglider 'chute like the fairing onto a "bouncy castle" (air-bag like) barge.
Is it like the decent stage on my Dragon 2 lunar lander with a heat shield?