Wednesday, December 9, 2020

The SN8 Test Flight Was Worth Waiting For

The long awaited and frequently talked about test flight of Starship Prototype Serial Number 8 took place at 4:45 PM CST, after a countdown that went into a long hold at T-2:06 earlier in the day.  They analyzed their data and decided to launch anyway.  

With no feedback from SpaceX, the flight had a lot of events that seemed like problems but could have been planned.  Elon Musk's tweets in the aftermath of the flight make them appear to be planned.  One Raptor engine shut down at 1 minute 45 into flight & the second at 3:15 into flight. One talking head/commenter speculated that this was done deliberately to lower the thrust to weight ratio and keep the vehicle from accelerating too quickly.  It could also be used to judge how well the control systems adapted to loss of two engines. Yes, the vehicle slammed down during the attempt to flip upright and land on its legs.  Elon always said the chance of getting everything right was about 1 in 3.

That's the wreckage of SN8 after its RUD (Rapid Unplanned Disassembly).  In the hour or so after the test, Elon tweeted (oldest to most recent from top to bottom):
Successful ascent, switchover to header tanks & precise flap control to landing point!

Fuel header tank pressure was low during landing burn, causing touchdown velocity to be high & RUD, but we got all the data we needed! Congrats SpaceX team hell yeah!!

SN8 did great! Even reaching apogee would’ve been great, so controlling all way to putting the crater in the right spot was epic!!
From Elon Musk's Twitter account.

On the left edge of that screen capture image, you can see some dark smoke wafting away from the wreckage.  It was still burning an hour and a half later at 7:15 PM EST when I sat down to compose this, but has seemingly burned out now, another half hour later. 

Meanwhile I'll leave you with this: the entire test flight.  Don't rewind this to the beginning. It starts at T-1:00 minute or 1:47:11 into the entire video. 

I bet that SN9 will go to the test pad No Later Than Friday, and will progress through its tests faster than SN8. 


  1. I watched it live, and it was.....almost unbelievable.

    Damn! It looked like they "flew" it back, and then flipped it around to land, almost like the Big Silver Rockets I grew up dreaming about.

    I noticed how the plume turned bright green not long after they relit the engines, and figured it would be an "OOOPS!" landing, and also that they had enough telemetry to know the cause very rapidly.

    Well done, SpaceX! I'm still smiling about it hours later.

  2. I also watched the launch live. That was amazing! The landing was the only thing that did not happen right but it almost did. I daresay that SN9 will probably make the landing without an RUD.

    There are supposed to be major upgrades at SN15. I wonder if that will include improved landing legs?

    1. The only thing I've seen them say about SN15 is that there will be a lot of changes. Elon has said they'll be changing over to legs more like Falcon 9, and that seems that would be a good time to cut them. Rough guess would be each one goes through its tests a little faster and we'll see SN15 ready to fly by summer.

  3. The belly flop reminded me of the whale in Hitchhiker's Guide. Completely at peace while enjoying that 120-mph breeze coming straight out of the ground.

    And we could have used a Slim Pickins mockup on the fuselage for a Stragelove link. Come'on Elon!

    I can't wait for SN9 to incorporate the boatload of lessons-learned.

    Congrats SPACEX!

  4. Scott Manley put up an excellent video with some judicious editing to bring out details he talked about. Shutting down the engines one by one was the flight plan.

    1. Excellent video and narration! Thanks. There's more information here than I've been able to find anywhere else.
      One question I haven't yet seen addressed is did this flight regime go supersonic? With the engine shutdowns I suspect not, but that is a critical flight dynamic to test. On the other hand, with only three engines in that wide open bottom end, it may not be able to withstand supersonic pressures.

    2. You know, I hadn't heard if they went supersonic or not. I found Teslarati has an article up on the flight today
      They don't talk about it but commenters do, pointing out that the ship took longer going up than coming down, so clearly not supersonic. Maybe they shut down the engines like they did to keep from going supersonic.

  5. That was, simply, too cool from start to finish.

  6. S/N9 just fell over in the high bay. The base support structure apparently collapsed, and the building kept it from falling all the way over.

    They were lucky it didn't fall out the door! In any event, it won't be moving by Friday.

    1. Thanks for that! It won't be moving today, and I suspect next week is out, too. They have to figure out how to lift it up, get it out of there and onto another stand to inspect the damages.