5 ms·

Is the Starship upper stage boosting itself up to full orbit yet?

by ethbr1 2y ago

deleted 2y ago
[deleted]
- fastball 2y ago
  Orbit is not about distance, it is about speed (perpendicular to gravity). Starship deliberately did not reach orbital velocity on this flight, so although they are fairly certain it is capable of doing so (esp after testing engine relight on this flight), they have not done it yet. Not being at orbital velocity is one reason why they are not delivering payloads. The reason for choosing not to go orbital at this point is indeed as another commenter said: safety. A craft which has not reached orbital velocity is therefore traveling on a parabola, which has a predictable flight path. If they lose control of all systems, they can still be confident that it will crash where they want it to (in this case, the Indian Ocean). If instead you boost enough to get orbital and then lose control, it is much harder (almost impossible) to know where the craft will end up. SpaceX (and the FAA) wants to make sure everything works properly by doing sub-orbital flights, then when they are fairly confident nothing will completely break on them they can start testing in an orbital regime, by powering on Starship's engines long enough to achieve the requisite speed.
  - fixprix 2y ago
    They don't need to relight to reach orbit, they just performed SECO a bit early. For reference at 190 km up which Starship reached, it needs to go 28,000 km/h to stay in orbit. Today it was flying at 26,000 km/h.
    - hnaccount_rng 2y ago
      But then they’d need to relight in order to break orbit. So technically correct ;)
mgsouth 2y ago
No. This and all previous flights have intentionlly been barely sub-orbital, with less than one orbit. Launch in Texas, re-entry over Indian Ocean. A full orbit at that altitude takes about 90 minutes; this was over in a little over an hour. The reason was safety. If it was orbital, then controlling the re-entry would require a sucessful relight of the engines. If that failed then the re-entry point would depend upon the vagaries of orbital decay from residual atmospheric drag. That's no doubt why today's relight was so brief; they didn't want to significantly alter the reentry point.
- deleted 2y ago
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- mohaine 2y ago
  I don't believe this is quite correct. The last few trips are actually orbital, just not of the correct elliptical shape to do more than a half orbit as the perigee is less than the radius of earth. If earth was a point mass, it would have orbited. This means you don't have to do anything to deorbit while proving you could have made a full orbit if you wanted to.
  - Toutouxc 2y ago
    > the perigee is less than the radius of earth Which is what we call "sub-orbital" :)
  - gpm 2y ago
    If the earth suddenly became a point mass except for all the humans, we'd all already be in orbit. At the "top" of a highly elliptical orbit that passes relatively close to that point mass, yes, but an orbit. Everything that was within the Earth's sphere of influence, not moving so fast to be on an escape trajectory, and not with 0 horizontal velocity relative to the point mass would be in an orbit. Orbital means "on a trajectory that doesn't intersect (or escape from) the body you are orbiting", otherwise the word is meaningless.
    - kbelder 2y ago

Is the Starship upper stage boosting itself up to full orbit yet?

by ethbr1 2y ago

Is the Starship upper stage boosting itself up to full orbit yet?

deleted 2y ago

[deleted]

fastball 2y ago
Orbit is not about distance, it is about speed (perpendicular to gravity). Starship deliberately did not reach orbital velocity on this flight, so although they are fairly certain it is capable of doing so (esp after testing engine relight on this flight), they have not done it yet. Not being at orbital velocity is one reason why they are not delivering payloads. The reason for choosing not to go orbital at this point is indeed as another commenter said: safety. A craft which has not reached orbital velocity is therefore traveling on a parabola, which has a predictable flight path. If they lose control of all systems, they can still be confident that it will crash where they want it to (in this case, the Indian Ocean). If instead you boost enough to get orbital and then lose control, it is much harder (almost impossible) to know where the craft will end up. SpaceX (and the FAA) wants to make sure everything works properly by doing sub-orbital flights, then when they are fairly confident nothing will completely break on them they can start testing in an orbital regime, by powering on Starship's engines long enough to achieve the requisite speed.
- fixprix 2y ago
  They don't need to relight to reach orbit, they just performed SECO a bit early. For reference at 190 km up which Starship reached, it needs to go 28,000 km/h to stay in orbit. Today it was flying at 26,000 km/h.
  - hnaccount_rng 2y ago
    But then they’d need to relight in order to break orbit. So technically correct ;)

mgsouth 2y ago

No. This and all previous flights have intentionlly been barely sub-orbital, with less than one orbit. Launch in Texas, re-entry over Indian Ocean. A full orbit at that altitude takes about 90 minutes; this was over in a little over an hour. The reason was safety. If it was orbital, then controlling the re-entry would require a sucessful relight of the engines. If that failed then the re-entry point would depend upon the vagaries of orbital decay from residual atmospheric drag. That's no doubt why today's relight was so brief; they didn't want to significantly alter the reentry point.

deleted 2y ago
[deleted]
mohaine 2y ago
I don't believe this is quite correct. The last few trips are actually orbital, just not of the correct elliptical shape to do more than a half orbit as the perigee is less than the radius of earth. If earth was a point mass, it would have orbited. This means you don't have to do anything to deorbit while proving you could have made a full orbit if you wanted to.
- Toutouxc 2y ago
  > the perigee is less than the radius of earth Which is what we call "sub-orbital" :)
- gpm 2y ago
  If the earth suddenly became a point mass except for all the humans, we'd all already be in orbit. At the "top" of a highly elliptical orbit that passes relatively close to that point mass, yes, but an orbit. Everything that was within the Earth's sphere of influence, not moving so fast to be on an escape trajectory, and not with 0 horizontal velocity relative to the point mass would be in an orbit. Orbital means "on a trajectory that doesn't intersect (or escape from) the body you are orbiting", otherwise the word is meaningless.
  - kbelder 2y ago