The first stage is not orbital so there isn't a de-orbiting burn, so it doesn't look like one. [opinion] It isn't using the exhaust as a heat shield either as heating isn't the issue with first stage reentry. It's and speed for aerodynamic pressures and downrange distance for boostback (the goal but not in practice here). [/opinion]
Currently there's no "boost-back" either and the way it looks the stage is reaching atmospheric interface which has been "assumed" to involve taking the reentry heating on the forward stage TPS. With all that entails. IF as would be shown in the video, the stage is going to "enter" engines first then that changes a lot of the base assumptions that have been circulated on the operational recovery sequence.If, once the stage rotates to engines down position it remains that way for the entire recovery sequence that's differenet than what most folks were assuming in other words.Randy
Quote from: RanulfC on 09/29/2014 03:36 pmCurrently there's no "boost-back" either and the way it looks the stage is reaching atmospheric interface which has been "assumed" to involve taking the reentry heating on the forward stage TPS. With all that entails. IF as would be shown in the video, the stage is going to "enter" engines first then that changes a lot of the base assumptions that have been circulated on the operational recovery sequence.If, once the stage rotates to engines down position it remains that way for the entire recovery sequence that's differenet than what most folks were assuming in other words.RandyI have always "assumed" that the atmospheric interface was always going to be engine first as depicted in their CGI re-entry video. This is backed up by the Orbcomm F9 First Stage return video showing the re-entry burn from 15:23:45 to at least 15:24:17 (32 sec burn) before SpaceX jumps to the landing burn at 15:25:40, 83 seconds later. I thought the engine first re-entry burn was obvious, Am I miss-reading your statement above?
Quote from: Exclavion on 09/28/2014 06:37 pmThe first stage is not orbital so there isn't a de-orbiting burn, so it doesn't look like one. [opinion] It isn't using the exhaust as a heat shield either as heating isn't the issue with first stage reentry. It's and speed for aerodynamic pressures and downrange distance for boostback (the goal but not in practice here). [/opinion]Currently there's no "boost-back" either and the way it looks the stage is reaching atmospheric interface which has been "assumed" to involve taking the reentry heating on the forward stage TPS. With all that entails. IF as would be shown in the video, the stage is going to "enter" engines first then that changes a lot of the base assumptions that have been circulated on the operational recovery sequence.If, once the stage rotates to engines down position it remains that way for the entire recovery sequence that's differenet than what most folks were assuming in other words.
I have always "assumed" that the atmospheric interface was always going to be engine first as depicted in their CGI re-entry video. This is backed up by the Orbcomm F9 First Stage return video showing the re-entry burn from 15:23:45 to at least 15:24:17 (32 sec burn) before SpaceX jumps to the landing burn at 15:25:40, 83 seconds later. I thought the engine first re-entry burn was obvious, Am I miss-reading your statement above?
I'm confused too - it's definitely engines first... and what "forward stage TPS"? do you mean?
Quote from: sheltonjr on 09/29/2014 04:47 pmI have always "assumed" that the atmospheric interface was always going to be engine first as depicted in their CGI re-entry video. This is backed up by the Orbcomm F9 First Stage return video showing the re-entry burn from 15:23:45 to at least 15:24:17 (32 sec burn) before SpaceX jumps to the landing burn at 15:25:40, 83 seconds later. I thought the engine first re-entry burn was obvious, Am I miss-reading your statement above?The former is the "boost-back" burn (reuse CGI) while I'd not previously SEEN the Orbcomm "reentry burn" video SpaceX hadn't "said" as much but when the original idea of reentring "engines first" was discussed Musk (IIRC) tweeted that no one had ever SAID the stage would enter that way and speculation drifted to "top" first reentry since we were aware that there was TPS there. (More I suspect to protect the upper tank dome from damage when the US fired but that's the ONLY thing that made sense at the time and was reinforced when there was the issue of "tumbling" on entry which suggested an aerodynamically unstable entry angle was being used.)Combined with the obvious (CGI again) reentry of the upper stage "forward" tank first it had become assumed the the first stage did the same thing.The main point of contention has been if the engines could handle the heating load but after to above tweet it was figured that they simply didn't bother and were using some sort of active control to hold the stage "top" first for reentry. As I pointed out, confirmed "engine first" entry is something new to the non-L2 discussions Quote from: somepitch on 09/29/2014 05:11 pmI'm confused too - it's definitely engines first... and what "forward stage TPS"? do you mean?The direction hasn't been obvious for the above reasons though it makes all sorts of sense it was NOT something that was clear. There was mention of beefing up the forward tank TPS at one point and this was "assumed" to be for reentry purposes though I now suspect it was to reduce damage from the upper stage seperation and engine firing. And you, (again) have the CGI example of the second stage reentry so it seemed that SpaceX was "comfortable" with that entry position.No it doesn't make a lot of "sense" to try reentring with the engines NOT facing "forward" because of the aerodynamic forces involved and the extra stress' generated in doing so. Which is why I argued that no matter what "eventually" SpaceX was going to have to do it that way. But I was under the impression given the rather "vehment" denial noted above and the question of whether the engines would be damaged during entry in that position that they had decided to attempt it with the engines-aft and do a turn over prior to the landing burn. The video shows this not to be the case so at the very least MY arguments need to be reconsidered Randy
Launch and acceleration out of the atmosphere.MECO and stage separation.180 degree maneuver to engine first attitude while still outside of the atmosphere.Ballistic coast.(Added in: {In-Real-use} Boost-Back-Burn to return Booster To Launch Site Just thought I'd keep that in everyones mind as THE goal )Braking/entry burn at atmospheric interface.Unpowered drag deceleration to lower atmosphere.Landing deceleration burn.If such a long and lightweight aluminum stage attempted an end over end flip while at high mach within even the high, thin atmosphere, it would be instantly shredded by aerodynamic forces.
The second stage is much shorter and conversely, should be better able to take the stress of an inter atmospheric "flip" at (what I would assume will be) very low mach. That should be a fun one to watch! Also, the second stage will enter the atmosphere at much greater velocity and the aerothermal environment would quickly destroy the engine/stage without additional protection.
I will assume that they will have to add in an additional boost back burn before the ballistic coast and then a second flip maneuver before braking when they do attempt an actual 1st stage recovery.
No, that may be different from *your* perception, but not most people. The first stage enters engines first. It always has in all promotional materials.
Who is this informer that "informed you" otherwise? Stop being obtuse. If you claim that you were right originally but everyone else convinced you that you had to be wrong, then you have a *very* unique recollection of the F9 reusable speculation threads.
(And now you are pulling the same stunt on the second stage reuse thread, missing the forest for the trees)
Yes, the animation didn't show everything, but the gist of it was there in plain sight. How else did you imagine it would work, with the giant air scoop of a trunk attached? How was that possibly going to work?
I read a lot of the re-entry threads. No one ever thought they were going to perform any part of the reentry with the engines at the rear.
You are missing one absolutely enormous and completely obvious reason why:Boost back. Reusability has always targeted landing close the the original launch pad so the stages can be reused without moving them very far. Otherwise, there is no point. Elon has always talked like this. Landing on a barge has just come up recently, and seems to be related to the fact that the pad in NM is still not done so they have not been able to prove to the FAA they have the chops to bring it home.
MECO and stage separation.180 degree maneuver to engine first attitude while still outside of the atmosphere.Ballistic coast. Braking/entry burn at atmospheric interface.Unpowered drag deceleration to lower atmosphere.Landing deceleration burn..