Thanks every one for finding the PicaX density. I went with .27g/cm^3.New drawings show the drag flaps and the start of a modular nose structure and heat shield. Nose heat shield with 3 inch thick PicaX comes in at 637 lbs. Guesstimated aluminum structure is 1,248 lbsDrag flaps are modeled with 2 inch aluminum honeycomb topped with .093 inch thick carbon skins. 2 inches of PicaX cover one surface and three edges. Total weight for each flap is 61.6 lb. Flaps are 4 x 4 feet. Drag flap size is based on the old SpaceX drawing. They look small to me given the CG and stretched 2nd stage. Might make sense to move them farther aft and increase their area. And as RocketScience mentions, there is a lot of wight that will have to go in to the rear end to get the flaps moving.
Here is a comparison showing the rough CG location for nose first and engine first re-entry. I added a painfully guesstimated carbon structure (interstage like) to the engine first model to connect the heat shield aluminum structure to the tank. It weighs in at 153 Kg for the bell jettisoning model and 360 kg for the retracting bell model.Adding Superdracos, prop tanks and plumbing will help the CG situation for both nose first (assuming Dracos in the nose) and engine first methods. Any residual prop in the main tanks, assuming both RP1 and LOX, will also help the CG for both methods.
Quote from: Rocket Science on 04/16/2017 01:24 amNot really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81https://forum.nasaspaceflight.com/index.php?topic=42637.80But is SpaceX interested in such an idea ?
Not really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81https://forum.nasaspaceflight.com/index.php?topic=42637.80
Quote from: macpacheco on 04/16/2017 01:52 amQuote from: Rocket Science on 04/16/2017 01:24 amNot really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81https://forum.nasaspaceflight.com/index.php?topic=42637.80But is SpaceX interested in such an idea ?That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHO
Quote from: Rocket Science on 04/16/2017 04:08 pmQuote from: macpacheco on 04/16/2017 01:52 amQuote from: Rocket Science on 04/16/2017 01:24 amNot really, I posted a concept using an "X-37 like" S2 several pages back to land horizontally on a runway: post#81https://forum.nasaspaceflight.com/index.php?topic=42637.80But is SpaceX interested in such an idea ?That, I can not answer for you... What I can answer is that Elon "is" interested in being successful... What form that architecture will look like will be driven purely by physics and economics, the data will speak for itself. Any approach that may work shouldn't be ruled out at this point. He may ideological, but not foolish IMHOHe has in the past disdained wings as not worth the mass. But grid fins are a kind of wing (if you stretch the definition) and if someone put together a proposal that showed that wings of a certain size were the least mass penalty (integrating across the increased drag on the way up, the probability of success, and all the other variables in the trade space) way to recover S2, I think he'd give it very serious and detailed consideration.So yeah. what Rocket Science said.
No matter what I see, I keep coming back to a tail-first entry. I can't call myself an expert, but the one thing I'm sure SpaceX won't do is add mass primarily to move the CG. If gravity is pulling the upper stage into a tail-first orientation, I think SpaceX will work with it rather than against it.
Re disdain for wings: We do at least know that making use of aerodynamic lift is in favor at SpaceX: They experimented with it on the last Falcon launch. And the ITS designs are clearly 'lifting bodies' with entry attitudes closer to the shuttle orbiter than the tail-first boosters. If SpaceX were designing the Falcon stage 2 now I'd easily believe it would look and behave like a massively scaled down ITS, and part of the justification for that design would be proving/maturing plans for ITS. But what's actually coming in the near term S2 recovery attempts? I've no idea.
Sigh. If I only had an engineering team and a wind tunnel...I was actually playing with the idea of CADing up a 2nd stage with X-37 ish wings and tail and doing some DIY aerodynamic testing. There would be so much structural guess work though... I think any findings would be useless for determining the mass hit. So shelving that idea for now.
The 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads,
Quote from: john smith 19 on 04/15/2017 09:31 amQuote from: rakaydos on 04/14/2017 06:03 pmWhile that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.Watch the video again from 1:18 to 1:59It shows the US flipping, then a de-orbit burn. It does not show it flipping again to do a nose first entry (although that's what it does show). Nor does it show how the US does the 90deg shift from nose front to nose top (or the 180 deg flip post re-entry). Both of which occur when the stage is deep in the atmosphere and GN2 or even Dracos would probably not have the authority to overcome the drag forces without ripping the stage apart. But it does show it landing tail down with no other obvious engines firing apart from the main one. That suggests either it's the main engine doing the work or any separate landing engines are inside the tail skirt. Mechanically and structurally the simplest answer is to use what has to be on the stage anyway IE the main engine, provided it can survive the environment and throttle down enough.Watch it again. First during the flip, see where the thrusters next to the engine bell are that fire during the flip. Then the landing, where you can see 4 of those thrusters firing, not the main bell.
Quote from: rakaydos on 04/14/2017 06:03 pmWhile that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.Watch the video again from 1:18 to 1:59It shows the US flipping, then a de-orbit burn. It does not show it flipping again to do a nose first entry (although that's what it does show). Nor does it show how the US does the 90deg shift from nose front to nose top (or the 180 deg flip post re-entry). Both of which occur when the stage is deep in the atmosphere and GN2 or even Dracos would probably not have the authority to overcome the drag forces without ripping the stage apart. But it does show it landing tail down with no other obvious engines firing apart from the main one. That suggests either it's the main engine doing the work or any separate landing engines are inside the tail skirt. Mechanically and structurally the simplest answer is to use what has to be on the stage anyway IE the main engine, provided it can survive the environment and throttle down enough.
While that can be looked into, it remains a longshot, and even SpaceX's original video does not suggest that they thought it was possible.I've heard that a minimum throttle hoverslam would be at something like 8g for a dry upperstage.
You guys are arguing about a really old video that I am pretty sure Musk himself had said was done with a lot of artistic license.
I wouldn't get hung up on anything.
Quote from: robert_d on 04/17/2017 01:48 pmThe 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads, That's sort of right, but reminds me of something else. Shotwell said there are 2 F9 designs. One is a regular F9 and can serve as the booster for an FH. The other is the design that serves as an FH core. Presumably it can also serve as a regular F9. But now you mention it both core stages would have to be stronger than the base F9 stages to carry the maximum 64 tonnes, unless F9 is built with a lot of structural margin, which I don't think is the case.
Quote from: john smith 19 on 04/17/2017 03:54 pmQuote from: robert_d on 04/17/2017 01:48 pmThe 'secret sauce' might be some dual use capability. Since second stages must already be strong enough to support Falcon Heavy payloads, That's sort of right, but reminds me of something else. Shotwell said there are 2 F9 designs. One is a regular F9 and can serve as the booster for an FH. The other is the design that serves as an FH core. Presumably it can also serve as a regular F9. But now you mention it both core stages would have to be stronger than the base F9 stages to carry the maximum 64 tonnes, unless F9 is built with a lot of structural margin, which I don't think is the case.What does the different S1 structural versions(F9 S1 vs FH S1) have to do with the S2?If the S2 can take 64 tons on the top on the ground then it doesn't make any difference in flight.A heavier payload does not increase the load during flight. The load is just the thrust in flight.What am I missing?