TWRackers
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The earlier discussion about why the Ares-1 (or more specifically, the Ares-1X test vehicle) has no fins made me wonder about a related question:
On the full-scale rockets, what keeps the rocket stable during the few seconds between when the first stage engine(s) cut off and when the second stage ignites?
During that time, there's no thrust being produced with which to control the vehicle (with gimballed motors or vectored thrust), before or after separation of the first stage, until the second stage ignites.
What made me wonder was what happened in the first few seconds after separation of the Ares-1X booster from the upper-stage simulator. The dummy upper stage almost immediately began tumbling, and although no recontact between it and the booster occurred, it sure looked like they (nearly) hit from the ground camera's point of view.
Now I understand the builders expected the upper stage to tumble upon separation, although none of the animations they kept showing us showed any tumbling. So maybe they expected it, maybe they didn't. That's not the point though.
So possible answers to my original question include:
So does anyone have any real knowledge here as to how the big rockets handle this?
On the full-scale rockets, what keeps the rocket stable during the few seconds between when the first stage engine(s) cut off and when the second stage ignites?
During that time, there's no thrust being produced with which to control the vehicle (with gimballed motors or vectored thrust), before or after separation of the first stage, until the second stage ignites.
What made me wonder was what happened in the first few seconds after separation of the Ares-1X booster from the upper-stage simulator. The dummy upper stage almost immediately began tumbling, and although no recontact between it and the booster occurred, it sure looked like they (nearly) hit from the ground camera's point of view.
Now I understand the builders expected the upper stage to tumble upon separation, although none of the animations they kept showing us showed any tumbling. So maybe they expected it, maybe they didn't. That's not the point though.
So possible answers to my original question include:
- With the upper stage full and the booster empty, it's just plain statically stable enough to coast without tumbling for the short time spanning the staging process.
- Separation happens high enough above the atmosphere that static stability is not an issue, it's purely momentum keeping it going straight. (Which would still make me wonder why Ares-1X behaved so differently. Was it much lower in the atmosphere at staging?)
- Reaction control systems in the upper stages come in play after staging and before second-stage ignition.
So does anyone have any real knowledge here as to how the big rockets handle this?