Even at suborbital velocities, putting debris into the path of an existing satellite that is traveling at orbital velocity is enough to trigger a cascade.
No. An object in orbit colliding with anything threatens to create debris in orbit. Debris in orbit collides with other objects in orbit, creating debris in orbit. That's a cascade.
> Debris in orbit collides with other objects in orbit, creating debris in orbit. That's a cascade
For the same reason not every nucleus that fractures on neutron bombardment sustains chain reactions not every orbital configuration supports a Kessler cascade. In LEO, it’s virtually impossible: you get a nuisance, not SOL.
Note that Kessler posited his syndrome before we could computationally verify it. We can now. It’s not a real threat in the long term, and is more of an insurance question than existential issue for spaceflight in the medium term. It’s pertinent in the very short term, militarily, which is partly how we know it’s very difficult to trigger across even limited orbits.
LEO is the exact place you need to be careful. Higher orbits have more space and have fewer satellites overall so it's less of a concern.
Obviously not a problem for IFT6 since it's sub-orbital, but the original comment was about why we need a deorbit burn rather than just triggering the flight abort system.
> LEO is the exact place you need to be careful. Higher orbits have more space and have fewer satellites overall so it's less of a concern
No. In LEO orbits degrade in single-digit years at most. There is no known solution for rendering an orbit in LEO inaccessible with a Kessler cascade—the best you can do is blind an area with repeated ASAT fire.
In higher orbits debris last longer. That makes cascades possible, though again it only denies a limited area and requires almost active effort.
At least in LEO you need to keep expending DeltaV to keep stuff in orbit. Trace atmosphere slows everything down and would eventually clean LEO at 500km of relevant junk in about 25 years depending on altitude.
If you have debris in geostationary orbit, it will stay there basically forever whereas in low earth orbit it will burn up within a few years at worst.