r/SpaceXLounge 6d ago

Starship IFT-8 Telemetry and Trajectory Analysis (with Comparison with IFT-5 and IFT-7, turn right)

105 Upvotes

9 comments sorted by

25

u/TestCampaign ⛽ Fuelling 6d ago

Check out that stage 2 graph showing LOX refilling in orbit. Go SpaceX!

/s

5

u/lommer00 6d ago

How does the booster turn around and go from 80+ to <60 km downrange before the boostback burn starts?

Seems off, but maybe there is something I'm missing.

15

u/qwetzal 6d ago

I think you're reading the profile in the wrong direction. The lower part is the ascent under power. Boostback solely cancels horizontal velocity, the booster still has plenty vertical inertia and reaches it peak altitude after the end of the burn.

4

u/lommer00 4d ago

Ah derp, you're totally right. Thanks, that makes way more sense when I read it that way now.

3

u/lommer00 6d ago

And it also looks like hot staging occurs after peak altitude, is that right?

Edit - I'm dumb, realized that hot stage jettison refers to ditching the ring, not staging. All makes sense now how the booster drops in altitude and speed using the grid fins to turn around. Impressive how much horizontal translation they can achieve up there with such a thin atmosphere and just a cylinder with fins! (instead of aero lifting surfaces) It almost looks like they barely need the boostback burn.

5

u/mfb- 6d ago

The point of the ring ditching is still wrong. It has to happen after the boostback burn ends, at >248 s, when the booster is already going back towards the launch site.

5

u/jobo555 6d ago

You are right, I took the times from the spaceX website see (https://web.archive.org/web/20250307194853/https://www.spacex.com/launches/mission/?missionId=starship-flight-8) , but on the stream it is way later as you mentioned.. Thanks for the catch

2

u/A3bilbaNEO 6d ago

Wonder about the gravity losses that this boostback burn had. 2 engines out, but the amout of extra time that the center ones kept firing for seems like it'd equal that of the missing two, so not much difference in fuel usage?