Again, as I've said before, I am questioning the center engine being used during the three engine burn (as in, I think it's only used for final burn). For supersonic retrograde you want the engines on the periphery to not impact aero drag. A center engine would deform the shockwave, thereby reducing drag and therefore associated slowing...
Quote from: Johnnyhinbos on 01/03/2016 01:34 amAgain, as I've said before, I am questioning the center engine being used during the three engine burn (as in, I think it's only used for final burn). For supersonic retrograde you want the engines on the periphery to not impact aero drag. A center engine would deform the shockwave, thereby reducing drag and therefore associated slowing... Think through what you just said ... Your claimed "reducing drag and therefore associated slowing" is going to have a significantly lower effect on overall deceleration than, you know, the engine thrust. Form drag of an essentially blunt body (which is what the stage can be reasonably modeled as in the absense of thrust) is well understood and characterized.
Another wonderment - what's the instrument in the background, visible under the rocket under the blue slash of the X of the SpaceX logo?
Quote from: Herb Schaltegger on 01/03/2016 03:22 amQuote from: Johnnyhinbos on 01/03/2016 01:34 amAgain, as I've said before, I am questioning the center engine being used during the three engine burn (as in, I think it's only used for final burn). For supersonic retrograde you want the engines on the periphery to not impact aero drag. A center engine would deform the shockwave, thereby reducing drag and therefore associated slowing... Think through what you just said ... Your claimed "reducing drag and therefore associated slowing" is going to have a significantly lower effect on overall deceleration than, you know, the engine thrust. Form drag of an essentially blunt body (which is what the stage can be reasonably modeled as in the absense of thrust) is well understood and characterized.Depending on the amount of thrust he is correct.
Quote from: meekGee on 01/03/2016 02:39 amAnother wonderment - what's the instrument in the background, visible under the rocket under the blue slash of the X of the SpaceX logo?I think there is another one directly above the step stool at the back... Rolls the stage around on the mounting ring? (do they do that?)
Quote from: Lars-J on 01/03/2016 01:42 amFrom the update thread:Quote from: Johnnyhinbos on 01/03/2016 01:34 amAgain, as I've said before, I am questioning the center engine being used during the three engine burn (as in, I think it's only used for final burn). For supersonic retrograde you want the engines on the periphery to not impact aero drag. A center engine would deform the shockwave, thereby reducing drag and therefore associated slowing...It is certainly used in the boost-back burn. And visual evidence from the stage 1 rocket cam footages that have been released certainly make it look like 3 parallel engines burning during the reentry/braking burn. (Exhaust interaction)And the drag reduction properties of a center engine depends on the thrust level (low thrust has that effect) and the reentry speed and atmospheric density. It also assumes a single engine, the combination with outer engines is far less obvious.The other problem with using three peripheral engines is that the octoweb design doesn't allow for even spacing between them. Each engine is spaced at 45 degrees, so if two engines are fired at 90 degrees, the third will be at 135 degrees from those two. The vector triangle will not be equilateral, and the resulting shape of the shock wave... who knows?
From the update thread:Quote from: Johnnyhinbos on 01/03/2016 01:34 amAgain, as I've said before, I am questioning the center engine being used during the three engine burn (as in, I think it's only used for final burn). For supersonic retrograde you want the engines on the periphery to not impact aero drag. A center engine would deform the shockwave, thereby reducing drag and therefore associated slowing...It is certainly used in the boost-back burn. And visual evidence from the stage 1 rocket cam footages that have been released certainly make it look like 3 parallel engines burning during the reentry/braking burn. (Exhaust interaction)And the drag reduction properties of a center engine depends on the thrust level (low thrust has that effect) and the reentry speed and atmospheric density. It also assumes a single engine, the combination with outer engines is far less obvious.
I'm looking at the building... That is the first pic I have seen released of the inside on that building...
Quote from: John Alan on 01/03/2016 02:10 amI'm looking at the building... That is the first pic I have seen released of the inside on that building... It is big indeed. Here is an image from the SLC-40 HIF.
Is it already been stated, or estimated, the horizontal velocity of the first stage at MECO?
Based on this http://forum.nasaspaceflight.com/index.php?topic=38149.msg1467411#msg1467411 I estimate it at 600 m/s.
Quote from: Steven Pietrobon on 01/03/2016 03:02 amQuote from: cartman on 01/03/2016 01:08 am1) Can we guess which are the outer engines that fired for the boost back burns? my guess is the 1o clock and 7o clock ones.In the enhanced image below, the insides of those engines definitely appear to be lighter in colour.maybe someone can chime in on this. Don't recall the Shuttle being this dirty. Better get that Raptor engine up and running ASAP Noticed for some time the Merlin "combustion" is dirty. Sure the returned F9 has some ablative burnoff on it, but also elements from the dirty combustion. Wonder if this is will reflect in reuse.
Quote from: cartman on 01/03/2016 01:08 am1) Can we guess which are the outer engines that fired for the boost back burns? my guess is the 1o clock and 7o clock ones.In the enhanced image below, the insides of those engines definitely appear to be lighter in colour.
1) Can we guess which are the outer engines that fired for the boost back burns? my guess is the 1o clock and 7o clock ones.
It's amazing how quickly the target changes. First it's get the 2nd stage and payload to orbit successfully, then it's do this and get back to the ASDS (ideally without inconvenient RUD issues) then after flamboyantly achieving RTLS and landing undamaged, we're quibbling over whether it's still got the showroom shine after all of that!
Imagine the challenge now for the modelers to perfect that perfect just launched patina on their model rockets meant to look like a returned stage. Their job just got a lot harder!
