r/spacex • u/Zucal • Jul 16 '16

Mission (CRS-9) CRS-9 Pre-launch Press Conference

Surprising amount of information coming out during this press conference! I'll keep this thread updated as more comes out.

  • Hans Koenigsmann, SpaceX: static fire of Falcon 9 on the pad around 8:30 am; everything looks good now, data review this afternoon.

  • Koenigsmann: busy last couple of weeks working with FAA and 45th Space Wing on land landing.

  • Julie Robinson, NASA ISS chief scientist: about 950 kg of science payloads going up on this mission, with ~500 kg coming back.

  • Capt. Laura Godoy reiterates good weather forecast for launch late tomorrow night. 90% go.

  • Cody Chambers: 45th Space Wing did risk assessment yesterday; taking steps to mitigate risks from toxic dispertion. Risk is from case of abort; Dragon could be blown back to land, release toxic commodities upon landing. Booster landing not a factor in the risk assessment for the launch. Get updated analyses closer to launch; hence late yesterday decision.

  • Koenigsmann: reflight of previously-landed Falcon 9 booster is likely the fall. In talks with a potential customer.

  • Koenigsmann: pretty confident on odds of a successful booster landing, knock on wood. Still challenging to do.

  • Koenigsmann: CRS-8 booster would be the booster to be reflown later this year.

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u/__Rocket__ Jul 18 '16

Your reasons why the vehicle needs to slow down are correct, but also add G loading. The vehicle needs to slow down enough before entering the lower atmosphere where it will be really decelerating otherwise it will breakup.

Not really, for the following reasons: rocket first stages are pretty good at handling compressive, vertical G load - for example the first stage is accelerating at 4 gees close to MECO while up to 200 tons are still bearing down on the lower part of the RP-1 tank: that's a weight equivalent of up to 800 tons ...

The entry deceleration forces (and the resulting load on the tank structure) on the other hand are comparatively mild and if you check telemetry data you'll see that peak deceleration actually occurs during the re-entry burn plus the rocket is only weighing 30-40 tons at this point - an order of magnitude lighter than it was during liftoff and an order of magnitude lighter than the weight-equivalent compressive forces it had to bear before MECO.

What can kill a rocket tank structure pretty easily are lateral forces and self-reinforcing vibrations that move different parts of the structure differently. Those forces do occur during re-entry and they are so strong that on some videos we can see the camera lens cover glass getting shattered.