Chair Force Engineer

Monday, February 25, 2008

Going to Pieces

The destruction of USA 193 by a US Navy SM-3 missile and LEAP impactor has worked a lot of people into a tizzy, for what is a tempest in a teapot for all intents and purposes.

On the US side, there was a lot of hype and hysteria about the spacecraft's fall from orbit and the consequences. There were several concerns about classified hardware surviving atmospheric entry, or the damage that could be caused by falling debris, or the health hazards posed by dispersion of hydrazine.

The most interesting aspect of this was the large quantity (estimated to be one ton) of frozen hydrazine that was expected to be entering the earth's atmosphere. I don't recall any spacecraft entering the atmosphere with such large quantities of frozen hydrazine aboard. The situation was unique in that the spacecraft had been powerless on-orbit for over a year, and the propellant was frozen solid. I'm not aware of any entering spacecraft going through similar conditions with such a large propellant load. The ballistic coefficient of the propellant tank(s) might be sufficient so that some quantity of the propellant could survive into the lower atmosphere.

While I can't say who the source of the hype over USA 193 was, it stands to reason that the news media has a duty to serve as a fact-check and defuse unjustified fears. But the history of news reporting in this country gives no reason to be so optimistic. The incredibly small risk that anybody would be harmed was definitely overblown in the media, and the testimony of experts in downplaying the risk was insufficient to stop the story from spiraling out of control.

Of course, the usual suspects (Russia & China) balked at the prospect of shooting down USA 193. The predictable complaints about the militarization of space were aired. But it must be emphasized that destroying a satellite in a low, decaying orbit does not represent the capability to destroy a satellite in a higher, stable orbit. The risk to other spacecraft was minimal as the debris largely continued to dip through denser regions of the upper atmosphere as it passed through perigee.

Moreover, the domestic missile-defense critics claimed the missile shot would not work. The destruction of USA 193 is also very different from missile defense tests. While satellites travel faster than reentry vehicles, their flight paths (or orbit tracks, in the satellite's case) are far more predictable and can be known with great precision several days from the planned intercept. In the case of shooting down USA 193, it was sufficient to launch the LEAP interceptor to the precise point in space at the precise point in time when USA 193 was expected to be there. It should be noted that the LEAP vehicle required new sensors which may not have any application to operational sea-based missile defenses.

The death of USA 193 is another strange twist in a secretive but tragic MilSpace story. The satellite's early failure was a massive waste of taxpayer dollars. Its death was a spectacular display of capabilities, but it may not have any military relevance.