In
post 1283 of this thread, the
@Borg provided
this link to the SpaceX video coverage of Starship 4 launch (for those of us without a direct connect to the
Collective).
For me (and, I think for most), the main plot line for this video is focused on the reentry - something I've been waiting for for over 5 years - for both the technical challenge and as a critical Starship development milestone.
The technical challenge is to protect the reusable ship during reentry with the lowest mass shielding as possible. The development milestone I was focused on was the point at which Starship becomes destined for success - even if Elon and SpaceX. I think we have just passed that milestone. By my guesstimate, Starship's remaining development costs are low enough that if the whole thing was sold off, the new owner would find it far more tempting to finish it off than to scrap it. In short, I don't see anything short of WW3 stopping this thing.
But back to the technical challenge:
What made the reentry key for me was Musk's description of it in
this January 2015 Popular Mechanics article:
On the windward side, what I want to do is have the first-ever regenerative heat shield. A double-walled stainless shell—like a stainless-steel sandwich, essentially, with two layers. You just need, essentially, two layers that are joined with stringers. You flow either fuel or water in between the sandwich layer, and then you have micro-perforations on the outside—very tiny perforations—and you essentially bleed water, or you could bleed fuel, through the micro-perforations on the outside. You wouldn’t see them unless you got up close. But you use transpiration cooling to cool the windward side of the rocket. So the whole thing will still look fully chrome, like this cocktail shaker in front of us. But one side will be double-walled and that serves a double purpose, which is to stiffen the structure of the vehicle so it does not suffer from the fate of the Atlas. You have a heat shield that serves double duty as structure.
My immediate thought was, "You gotta show me that". With Elon's reputation, you had to believe he could make it work - but still ... like a steam iron?
Of course, the stainless steel part worked out very well. For the most part, the unshielded leeward side of the ship stood up well.
So here is what I saw in the reentry video:
This first screen grab (below) is at 2:29:33 in the video. Notice that the time stamp at the top of the video is T+45:17 while the timestamp associated with the telemetry is 45:00. The best evidence of this "time warp" is during the booster landing. Clearly, the commentator reactions to the video off by a few seconds from each other and one commentators claims that the landing burn was late by 17 seconds. During the engine cutoff of the upper stage, the telemetry seemed to precede the video by just over a second.
That "pitch indicator" (small spacecraft outlines with the horizon lines) often seem to indicate something other than an actual pitch measurements. For example, see the video at T+9:11 where the icon does a somersault. This will be important to note when attempting to make sense of the splash down segment.
And one final telemetry quirk: those six thrust indicators will not be functioning from this point on. So don't expect anything from them during splashdown.
I've also moved the YouTube progress bar down and out of the image area.
The speed is over Mach 25 but the altitude is only 107 KM (half its apogee) - that plasma from reentry is just starting to show as a faint pink zone below the belly beneath flap. This is the "flapcam" showing the view of the aft port-side flap form the forward port-side flap. Apparently (but not surprisingly), this camera did not survive reentry.
At T+46:00 (image below) we are faster and lower. The plasma is a lot brighter - but a lot of that is because we have crossed into night and the video system is making brightness adjustments.
This next screenshot was take 6 minutes later at T+52:00, shortly after peak heating. The altitude is 68Km, which it has been for over a minute and which will remain for over another minute. The speed is about Mach 22.
There is a light gray zone above the flap showing some out-gassing. The engine is being chilled, so the out-gassing may be related to that. Also, there have been occasional "sparks" in the wind stream from belly material. There is none showing in this frame, but there will be lots more to come.
Three minutes later (image below) at T+55, we are at Mach 19.5.
Look at the unprotected steel just forward of that flap we are watching. Material from the tiles seems to be coating that metal. The unprotected surfaces seem to become more involved with the destructive wind stream as altitude and speed drop. This is the last screen shot from this camera. It lasted for more than two more minutes - during which time it showed controlled flap movement.
At T+57:15 the trouble starts.
This is another camera, another fin, the other side of the ship. The camera is mounted on the top side (protected half) of the ship on the starboard side. It is looking forward and down at the back edge and unprotected side of the starboard forward flap.
We are down to 57Km and Mach 15.7. those white streaks are intense sparks coming out of the aft underside junction of that flap with the side of the ship. But in addition to the bright white sparks, we are seeing some heat effects of the unprotected flap surface. It is just starting to redden.
The next frame is only 15 seconds later, 1Km lower, and 500 KPH slower. But something abrupt just happened. The bottom edge of the flap, where it meets the ship body, has moved away from the body by an inch or so, tile material was lost, and unprotected steel appears to be in direct contact with the wind stream.
Below: 45 seconds later, Mach 13.9, 56 Km high. The flap steel has been heating up and flaking off continuously. Its trailing edge is now well-separated from the ship.
But notice something else: There are two black dots in the image - and at this point I need to describe something about the camera. The camera along with its lens are behind a window. As we will see, the camera lens will remain survive. All of the effects that are seen from this point on are with the window - not the lens.
So those black dots are material that has separated from the craft and landed on the window.
At T+59:06, the window is so coated with material that the view is best discerned by changes in glows, and at that point it starts cracking. This is where the nail-biting starts. The image is almost useless. Last we saw, the craft was doomed. But the telemetry suggests that things are holding together and the Mach number is down to a slow-searing 12.
At T+1:00:30 we see some glimmers of something (hope?) through the broken window (image below).
We are just under Mach 9, still apparently under control, and a pinkish splotch in the middle of the image tells us that the flap has not yet separated. Those light gray areas are cracks in the window where sparks (from the "flap") can still be seen flying by. So how long will things kinda hold together?
A minute later, we're dropping like a rock but with pitch still stable, the window cracks are bigger, we're just over Mach 6, the Starlink connection is mostly holding, and there is definitely still something there to call a flap.
NASA has noted that the temperatures are coming down fast and the ship is within seconds of maximum aerodynamic pressure.
At T+1:01:37, the video is lost "Awaiting acquisition of signal".
At T+1:02:24 we get the video back - but it's hard to interpret. We're at Mach 3.5 at 33Km over the Indian Ocean at night. But the window is gone. The only sources of light look like remnant cinders.
There are pitch maneuvers and then, at T+1:03:05 some light flashes that suggest to me that they may have been using jets to augment the flap control. At T+1:03:20, telemetry shows a drastic pitch down orientation. Previous simulations had shown some pitch down before the main rockets kicked in, but this seemed extreme. It is also possible that that "pitch icon" was just showing something other than a pitch measurement.
We can also make out the flap from time to time - and it appears to be under control.
Next, at T+1:03:58 we see the trailing edge of that forward flap we've been watching lit up by the initial ignition of the main rockets. The slight down pitch is consistent with simulated renditions. The speed is a very tame 722KPH and altitude is 14Km.
Would you believe that I am only allowed to attach 10 photos to this post??
Guess you'll have to watch the next 2.5 minute of the video - to mission end.
Scott
