The test was done in the lower atmosphere to ensure that there is no space debris. Whatever debris that is generated will decay and fall back onto the earth within weeks.
When you boost an orbiting object in this manner there's only two possibilities for what can happen next:
a) you give it enough energy to reach escape velocity, in which case there's no problem.
b) you blow out the circular orbit into a long ellipse. The far end, apogee, can be very far out depending on how much energy you added, but the near end, perigee, is always at the same altitude as it was at the moment of impact. Therefore, as long as the satellite is "within" thin atmosphere at the moment of impact, the fragments will periodically pass through thin atmosphere as well.
To properly boost yourself into a higher (circular) orbit you need to give yourself two kicks: one to raise your apogee, and then half an orbit later another to raise your perigee to match.
Yeah it will come down... nobody is disputing that. The worry is that in the meantime it could hit some other satellite, causing more debris. Yes the likelihood is vanishingly small. But the consequences of an unlucky event could be large.
V. Does the test create space debris?
The test was done in the lower atmosphere to ensure that there is no space debris. Whatever debris that is generated will decay and fall back onto the earth within weeks.
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