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> Musk said Monday that there wasn't enough ignition fluid to light the outer two engines of the booster "after several three engine relights." I don't see a m

> Musk said Monday that there wasn't enough ignition fluid to light the outer two engines of the booster "after several three engine relights." I don't see a mention of whether the previous relights succeeded or not. I'm guessing they did succeed, but the center booster had to perform a higher number of relights than a Falcon 9 booster due to its higher speed.

rory096 9y ago
It's the same amount of relights - boostback burn, re-entry burn, and landing burn. It's possible the re-entry burn used more TEA-TEB than usual because of the high speed, but it's also possible that non-boostback GTO missions re-entered at higher speeds (this is the case at least in flightclub.io's model of the mission). Remember that this wasn't a particularly challenging flight profile for Falcon Heavy, which allowed it to boost back to reduce speed and landing distance from shore. The excessive TEA-TEB use may have been caused by an unrelated engine issue. In any case, Musk reported the fix is 'obvious'.
nickparker 9y ago
By my reading, the center core was using three engine burns for more efficient boost-back and re-entry burns. The side cores and typical F9 boosters (afaik) always use single engines for those and occasionally three-engine burns at landing, so three engine-ing all three burns would be 4 more relights than any previous core. So, an equal number of "relights" of the entire rocket but more engine relights, and engine relights are the relevant unit for ignition fluid consumption.
- rory096 9y ago
  Boostback and reentry burns are always 3 engines. Landing burns are often 2 engine and often 1-3-1, usually on the drone ship. The unique part of the GovSat "failed to expend" mission a few weeks ago was not cutting off the outer two engines some time before hitting the surface, not that it used three engines at all.
- JshWright 9y ago
  No, three engine burns are typical for boostback/re-entry. In many of the webcasts you can see the initial round plume turn into a rectangle as the two outboard engines ignite.

rory096 9y ago

It's the same amount of relights - boostback burn, re-entry burn, and landing burn. It's possible the re-entry burn used more TEA-TEB than usual because of the high speed, but it's also possible that non-boostback GTO missions re-entered at higher speeds (this is the case at least in flightclub.io's model of the mission). Remember that this wasn't a particularly challenging flight profile for Falcon Heavy, which allowed it to boost back to reduce speed and landing distance from shore. The excessive TEA-TEB use may have been caused by an unrelated engine issue. In any case, Musk reported the fix is 'obvious'.

nickparker 9y ago

By my reading, the center core was using three engine burns for more efficient boost-back and re-entry burns. The side cores and typical F9 boosters (afaik) always use single engines for those and occasionally three-engine burns at landing, so three engine-ing all three burns would be 4 more relights than any previous core. So, an equal number of "relights" of the entire rocket but more engine relights, and engine relights are the relevant unit for ignition fluid consumption.

rory096 9y ago
Boostback and reentry burns are always 3 engines. Landing burns are often 2 engine and often 1-3-1, usually on the drone ship. The unique part of the GovSat "failed to expend" mission a few weeks ago was not cutting off the outer two engines some time before hitting the surface, not that it used three engines at all.
JshWright 9y ago
No, three engine burns are typical for boostback/re-entry. In many of the webcasts you can see the initial round plume turn into a rectangle as the two outboard engines ignite.