Starship/Superheavy Flight Test 5, 13 October 2024

Note:  a version of this article appeared as a board-of-contributors column in the Waco "Tribune-Herald" for Tuesday,  15 October,  2024.

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I found out after the fact that the test took place this morning.  I watched the SpaceX videos to find out what happened.  While not perfect,  the test was a resounding success! 

The launch was normal with all 33 Raptors working in the Superheavy booster stage.  Hot staging was successful,  and they seemed to keep control of the propellant ullage problem by running 3 booster engines all during the staging event and the flip-around.  The Starship upper stage pulled away on all 6 of its Raptor engines successfully.  Staging took place at approximately 67 km altitude and 5200 km/hr (1.44 km/s) speed (which is actually a bit less speed than I expected to see).

The booster successfully flew back to the South Texas “Starbase” facility,  and successfully made the landing burns (initially 13 engines,  finally 3 engines) and the tower catch,  which was utterly amazing to see!   I did see the methane plume from one vent burning with air along one side of the stage near its base.  That vented material continued to burn for some time after the landing.  (They might consider adding a water spray on the tower to put such fires out.)

The Starship upper stage successfully made the same kind of almost-an-orbit suborbital trajectory,  to come down in the ocean on the other side of the world.  There is no need for a deorbit burn on this trajectory:  entry is automatic.  The video was astonishingly good.  I saw no visible plasma effects at the nominal entry interface altitude 140 km.  Speed was somewhere around 27,000 km/hr (7.5 km/s) at this point,  although I did not recover the speed data on the screen.

I saw a visible plasma glow under the tail and portside aft flap,  starting at about 102 km altitude and at a speed of about 26,727 km/hr (7.43 km/s).  The announcer said the flaps were in control of vehicle attitude at about 85 km altitude and 26,720 km/hr (7.42 km/s).  I started to see the speed readout begin dropping at a noticeable rate (indicating significant deceleration beginning) at about 75 km altitude and 26,350 km/hr (7.32 km/s).  The vehicle is generating lift at about 60 degrees angle of attack,  which shallows the descent angle and makes the entry process longer in time. 

When the announcer said peak heating occurred,  the ship was at about 70 km altitude,  and about 25,500 km/hr (7.08 km/s) speed.  This always occurs before the “max dynamic pressure” (or max deceleration gees) point.  I never heard the announcer say where max dynamic pressure occurred.  But I saw one of the flaps develop a hinge line burn-through!  I’m not sure which one,  there were 4 views of 4 flaps,  the other 3 were unlabeled as to which they were.  That was at roughly 45 km altitude and 9500 km/hr (2.64 km/s),  probably substantially after the max dynamic pressure point.  There is still very significant heating going on,  just not the maximum amount. 

According to the announcer,  the ship was down to about Mach 2,  which I read off the screen as about 25 km altitude and 1400 km/hr (0.39 km/s) speed.  He indicated the ship was in the subsonic “belly-flop”,  for which I read the screen as 3 km altitude and 400 km/hr (0.11 km/s) speed. 

The ship fired up its 3 sea level Raptors successfully,  and flipped tail first rather quickly,  at very low altitude (apparently per plan),  and touched down on the ocean in the proper attitude (nose high).  It hit the target zone,  and a camera on one of the target zone buoys recorded a huge steam cloud obscuring everything,  then a fiery explosion.  Apparently the ship broke up and exploded when it tipped over onto the water.  There was burning cylindrical wreckage visible,  sticking up out of the water at about a 45 degree angle.  The last recorded speed,  which I took to be speed at touchdown,  was 8 km/hr  (2.2 m/s).

All in all,  this was an astonishingly successful test flight.  Kudos to SpaceX,  they did good,  really good!  And,  they are doing things no one has done before,  and accomplishing them faster than anyone has a right to expect.  Well done!

The heat shielding at the flap hinge lines obviously still needs some improvement (see figure).  I do believe it is time to try landing and recovering the Starship on land,  and it is time to try doing Raptor restart burns in space.  Solve those issues,  and they are ready to attempt propellant transfer tests “for real”.

Update 10-15-2024:  Here is the simplest notion I could come up with,  for a “fix” to stop the hinge line burn-through problems.   It’s not a reusable part,  you would install these on the 4 flaps before every launch.  But these are not large items;  they would not “break the bank” on launch costs.  My materials selections are just a start point.  But the final product might be very similar to my sketch.