-
#1980
by
Herb Schaltegger
on 03 Jan, 2016 03:22
-
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...
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.
-
#1981
by
deruch
on 03 Jan, 2016 03:42
-
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...
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.
Watch from time mark 14m04s:
-
#1982
by
sewebster
on 03 Jan, 2016 03:47
-
Another 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?)
-
#1983
by
Herb Schaltegger
on 03 Jan, 2016 03:52
-
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...
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.
Don't generalize beyond what I said and then compare apples to oranges. We're talking about a VERY lightly loaded F9 1.1 FT stage decelerating here, not a heav Mars-entry vehicle.
-
#1984
by
meekGee
on 03 Jan, 2016 04:42
-
Another 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?)
Yup. That's what it is - nice. (Back of the rocket, not back of the picture, to those who still haven't found it.)
-
#1985
by
Rocket Science
on 03 Jan, 2016 08:42
-
My take was all three engines in-line were fired during entry and landing. The vertical three in the photo above (reply# 2005): 12 and 6 o'clock and then center for touchdown...
-
#1986
by
ppb
on 03 Jan, 2016 08:51
-
From the update thread:
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...
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?
Not to mention the uneven pitching moment that could only be addressed by throttling down 2 engines 40% or by some severe gimbal bias that may not even be possible. IOW, must have symmetric layout for 3 engine controllability.
-
#1987
by
Dante80
on 03 Jan, 2016 10:07
-
I'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.
-
#1988
by
Johnnyhinbos
on 03 Jan, 2016 11:58
-
I'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.
That's a great picture. I hadn't seen it before. One interesting thing is that you can see the engine number printed for each engine position.
-
#1989
by
Endeavour126
on 03 Jan, 2016 15:32
-
Is it already been stated, or estimated, the horizontal velocity of the first stage at MECO?
-
#1990
by
ugordan
on 03 Jan, 2016 15:40
-
-
#1991
by
Endeavour126
on 03 Jan, 2016 15:45
-
-
#1992
by
mtakala24
on 03 Jan, 2016 16:19
-
Some great discussions and behind the scenes feelings of the landing were included in the latest episode of the TMRO show.
-
#1993
by
llanitedave
on 03 Jan, 2016 16:37
-
I'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.
Just noticed the guy snatching donuts over on the left hand side...
-
#1994
by
the_other_Doug
on 03 Jan, 2016 16:55
-
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.
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.
Well, kerolox has a lot sootier exhaust than the Shuttle's hydrolox main engines. I grant you, there was likely soot from the SRB exhaust, but that was blasted away from the base of the orbiter by the SSME exhaust, with whatever got back up to the orbiter body hitting on the belly and body flap tiles. Any soot on those tiles would burn off cleanly during entry.
So, yeah -- there are lots of reasons why the Shuttle orbiters didn't show a lot of soot buildup.
-
#1995
by
gadgetmind
on 03 Jan, 2016 17:05
-
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!
-
#1996
by
kch
on 03 Jan, 2016 17:14
-
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!
"Welcome to NSF" ...
(don't worry -- you'll get used to it (it's like tap-dancing on marbles))
-
#1997
by
OxCartMark
on 03 Jan, 2016 17:27
-
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.
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.
That shuttle thing you refer to never really had to fly into its own exhaust. The only time it fired while traveling backward was to de-orbit, which was in a full vacuum atmosphere. Even if it did get sooty during the de-orbit burn it would have been decarbarized a bit by flying into the oxygen(y) plasma during re-ently, a luxury that F9's 1st stage doesn't have. And as you point out F9's exhaust is more carbony than the shuttles' was. All RP-1 fueled engines have a bit of a sooty nature. They burn rich so some carbon and heavy hydrocarbons are produced. No surprise there to SpaceX or most anyone. I think that the soot on the exterior is easily dealt with but the bigger problem with RP-1, and one of the reasons for the migration to methane is soot (coke) building up in the hot parts of the engine thus limiting heat transfer, flow, and function - more troublingly obviously so in multiply re-use-able engines. It serves one well to not use shuttle as an example of how things work, better to reference back to basic physics and engineering in my opinion.
-
#1998
by
WindnWar
on 03 Jan, 2016 17:28
-
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!
-
#1999
by
Herb Schaltegger
on 03 Jan, 2016 17:52
-
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!
Layered shades of gray with an airbrush - train modelers solved this looooong ago (my step-dad was one of those - his day job for many years was commercial artist and industrial designer).
