NASA Study Casts Some Doubt on Sat Shootdown

By Noah Shachtman
See video at bottom

Former NASA scientist Yousaf Butt didn't buy his former employer's explanation for why a dying satellite had to be shot out of orbit. Publicly, the space agency and the military insisted that the satellite's payload of hydrazine rocket fuel was a significant risk to public health. Butt -- now an astrophysicist at Harvard -- wasn't so sure. So he filed a Freedom of Information Act request, to force the space agency to disclose the documents related to its shootdown rationale.

The other day, Butt got back a key study, examining whether that hydrazine tank might survive reentry into Earth's atmosphere. The primary question: How will heat (either from the Sun, or from reentry) transfer into the hydrazine tank's titanium coating?

Two models were considered and analyzed, the paper notes. But only the more dire case -- more likely to lead to the tank's survival -- gets any play in the study, Butt notes in a new Bulletin of the Atomic Scientists article.

[And] even with this oversimplification that biases toward tank survival, the study's authors still find that four out of the titanium tank's five concentric finite-element nodes would melt off since the reentry temperature exceeds titanium's melting point. Thus, even as modeled, out of an initial 3.56 millimeters tank thickness, only 0.7 millimeters remains, making it highly unlikely that the tank would survive the high g-forces and dynamic pressure of reentry.

Veteran satellite-watcher Peter J. Brown is similarly dubious. And he notes that health warnings from the Centers for Disease Control and Prevention about the satellite's reentry "relied heavily on DoD [Department of Defense] projections."
Still, officials didn't argued at the time of the shootdown that the hydrazine risk was high. They insisted (and continue to insist) that the chance of fatalities was just large enough (more than 1 in 10,000) that the space and defense agencies were duty-bound to act. Is that central assertion true? This new paper, unearthed by Butt, doesn't definitevly answer that, as far as I can tell. So the debate goes on.