But it does show it landing tail down with no other obvious engines firing apart from the main one.
Quote from: john smith 19 on 04/15/2017 09:31 amBut it does show it landing tail down with no other obvious engines firing apart from the main one.Disagree, video shows a number of thruster plumes around the edge of the stage quite clearly.
I have and you're right there does appear to be some non main engine firing from inside the main skirt. However what's still missing is how the US goes from being engine first to being nose first (and how it's kept nose first) during reentry and how it goes from nose first to tail sitting to fire whatever engines are being used for landing.
My instinct is SX will use what they know and what works. Grid fins, being mostly drag devices should keep the nose down during most of the deceleration following a main engine burn.
Quote from: john smith 19 on 04/17/2017 10:24 pmMy instinct is SX will use what they know and what works. Grid fins, being mostly drag devices should keep the nose down during most of the deceleration following a main engine burn.I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps. Also seems like a lifting entry is more desirable, so center of gravity would be somewhat off center. In this scenario, the transition to vertical flight can be accomplished by increasing angle of attack until stall.
The cleanest way to achieve active guidance during reentry is c.g. shifting.
Quote from: meekGee on 04/18/2017 04:41 amThe cleanest way to achieve active guidance during reentry is c.g. shifting. Yes, but when this is not feasible shifting center of drag is good as well. IMO PicaX covered drag and steering flaps at the bottom will do that nicely. Similar to the 2 flaps on ITS. They may need more than two lacking the wing like extensions on ITS.
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps. Also seems like a lifting entry is more desirable, so center of gravity would be somewhat off center. In this scenario, the transition to vertical flight can be accomplished by increasing angle of attack until stall.
I'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps.
Quote from: ArbitraryConstant on 04/18/2017 01:58 amI'm skeptical any reasonable grid fin would survive full reentry heating, it would need to be some other material like PICA-X flaps.Titanium is fairly durable with heating. For example, see X-33 as an example of a titanium SSTO vehicle.
Both wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.
Quote from: Robotbeat on 04/19/2017 01:20 amBoth wrong twice. X-33 wasn't SSTO, and its main structure was carbon fiber.I think Gliderflyer might be referring to the Inco "tiles" that covered the carbon fiber frame on the windward side.http://www.styleofspeed.com/images/space/x-33/tps_c.jpg
Another idea would be a Rogallo wing, like that employed on the Gemini TT-1 test vehicle:- I am more of the belief that they'll try with a simple parachute and grab it with a helicopter. Seems to me that it would be the lightest and most practical solution.
I have to agree that a parachute in air recovery would be the lightest weight option. It's a reasonable starting point. Get some S2's back, learn, iterate.
Yeah the grid fins have sharp edges, but they're going to be behind the main shockwave. The blunt main heat shield will take the bulk of the heating. Actually, more accurately, the atmosphere compressed by the blunt main heat shield will take the bulk of the heating. The blunt main heat shield will take less of it, but still a lot more than any grid fins back on the body will.Look at how the main shock wave is far to the side as you go back for a re-entry capsule. For S2 the sides are straight, not angled back, but they are still far from the shock wave. The grid fins wouldn't reach out far enough to get the kind of heating the main heat shield will get.http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/blunt-body-shockwave.jpg?itok=dDTHT4aH
Quote from: ChrisWilson68 on 04/19/2017 07:58 amYeah the grid fins have sharp edges, but they're going to be behind the main shockwave. The blunt main heat shield will take the bulk of the heating. Actually, more accurately, the atmosphere compressed by the blunt main heat shield will take the bulk of the heating. The blunt main heat shield will take less of it, but still a lot more than any grid fins back on the body will.Look at how the main shock wave is far to the side as you go back for a re-entry capsule. For S2 the sides are straight, not angled back, but they are still far from the shock wave. The grid fins wouldn't reach out far enough to get the kind of heating the main heat shield will get.http://www.popsci.com/sites/popsci.com/files/styles/large_1x_/public/blunt-body-shockwave.jpg?itok=dDTHT4aHIf the grid-fins are deep in the wake they won't help solve the pitch/yaw control problems S2 appears to have; you need to keep it upright with the heat shield facing into the airstream. So... spin stabilize S2 for entry, and only use the grid fins for terminal guidance a la S1.In fact spinning up the S2 for entry might be something you could do with a stock stage. I guess it depends where the thrusters are and if it naturally spins in the desired axis.