A follow up …

In 2001 NASA asked me to organize a workshop to evaluate the decision alternatives it faced on TRMM. Our workshop report concluded:

“[W]e recommend that NASA should not base its decision to extend the TRMM mission primarily on quantitative comparisons between “lives potentially saved” through operational exploitation of TRMM data and “potential hazard” associated with uncontrolled reentry.”

We made this recommendation because estimates of reentry risk are simply arithmetic exercises with little connection to reality. As it turns out, so too are estimates of the benefits of the TRMM satellite to hurricane warnings. Comparing two meaningless estimates didn’t make much sense to us.

It turns out that NASA (probably inadvertently) followed our advice, according to this excerpt in the Washington Post article Shep cited earlier:

“In 2002, Asrar asked Bryan O’Connor, NASA associate administrator for safety and mission assurance, to conduct a “disposal risk review.” Did the benefits of using all the fuel to keep TRMM in orbit an additional five years outweigh the hazards of allowing the spacecraft to fall back to Earth without guidance?

In his reply on Sept. 4, 2002, O’Connor said the probability of a TRMM debris casualty would be one in every 5,000 reentries, twice as dangerous as NASA’s standard of one in 10,000. NASA allows about six uncontrolled reentries a year. Despite the heightened danger, O’Connor concluded that “these risks appear to be reasonable when subjectively weighed against the potential public safety benefits of improved storm analysis and forecasting capabilities that appear to be realized by extending the TRMM mission.”

But uncontrolled reentry was never seriously considered, Asrar said, and the O’Connor analysis was used to reaffirm what Asrar described as NASA’s original view: “What if the one in 5,000 becomes a reality?” Asrar said. “Can anybody stand up and say it was worthwhile?” He said he asked for the O’Connor report simply to show that “we had done due diligence” in evaluating TRMM’s potential hazard.”

Our workshop concluded:

“[D]ecision makers lack knowledge necessary to prioritize observational program decision alternatives on the basis of quantitative risk assessment according to the actual and potential contributions to science and society. Absent such information, it is likely that decisions on issues such as TRMM deorbiting will continue to be made on an ad hoc basis. It would be relatively simple to construct a “back-of-the-envelope” calculation of potential lives saved related to TRMM data availability based on a set of simplifying assumptions. However, participants agreed that because of the unverified nature of the cascade of assumptions on which such a calculation would be based, it would have little connection with reality. One reason for the lack of unanimity in the Workshop participants’ estimation of relative risk is the lack of analysis and data on the direct and indirect roles of TRMM data in weather forecast operations. Anecdotes, back-of-the-envelope calculations, and incomple!
te case studies are not a substitute for reasoned conclusions based on rigorous, scientific analyses.”

Finally, while I do agree with Shep that the money saved on TRMM has nothing to do with the President’s Mars mission, it all but certainly has something to do with paying for the next generation of remote sensing satellites.