[AR] Re: India shoots down satellite, declares itself a space power .

  • From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
  • To: Arocket List <arocket@xxxxxxxxxxxxx>
  • Date: Thu, 28 Mar 2019 17:17:38 -0400 (EDT)

On Thu, 28 Mar 2019, Rand Simberg wrote:

...nearly the most benign ASAT anyone has ever done.
While this is true, it's still not great.  In particular, it's *not*
impossible for a fragment from such a test to end up in a long-lived
high orbit -- rather less likely than for a test higher up, yes...

How does that happen without a second impulse? Another collision?

As Jon has already mentioned, just boosting the apogee can considerably lengthen the life of a fragment, as well as exposing higher-orbit objects to it. A 300km perigee is not low enough to reliably bring things down quickly.

Such an object's *perigee* can't then increase without some other delta-V, but there are ways that can happen. Another collision, perhaps with another fragment from the same original collision, although it's not too likely. Outgassing of surfaces that weren't meant to see vacuum. Leaks in, or explosions of, things with stored energy (batteries, pressurized tanks, perhaps charged capacitors) that were benign when they were undamaged and their temperature was controlled. Light-pressure thrust on very lightweight fragments.

And Earth's gravity field is not pure inverse-square. In particular, the equatorial bulge can cause an elliptical orbit's eccentricity to vary, moving perigee up or down -- this is periodic in principle, so what goes up comes down again, but the time scale can be substantial. This is more of an issue for things with higher eccentricity to begin with, e.g. GTO (where the changes in perigee can be hundreds of kilometers), but I wouldn't rule out a more modest effect in an elliptical LEO without running the numbers...

My (dim) recollection is that there have been occasional cases of presumed collision fragments in orbits entirely above the collision altitude, although exactly how this happened was not clear. When a collision produces thousands of fragments, that's enough rolls of the dice that it's not too surprising if unlikely things happen to a few of them.

Henry

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