Rusty Schweickart has written an open letter to NASA Administrator Michael Griffin that discusses the recent NASA NEO Analysis of Alternatives (AoA) report.
Beyond the issues addressed by Rusty in his commentary I agree with some of his issues on the release of the full 200+ page NASA NEO AoA report. If the U.S. Congress can see this unclassified report about the government's response to the threat from a potentially large natural disaster but the public cannot, I have some issue with that. I would urge those in the know including Lindley Johnson (NASA NEO program office), Bill Claybaugh (lead person at NASA PA&E involved with the study as far as I can tell), and of course NASA Administrator Mike Griffin to release the full study. I would not want this to turn out like NASA's Exploration Systems Architecture Study (ESAS), where we got a very large report but were missing some very interesting and relevant appendices.
On to some of my initial comments on Rusty's paper.
To me it seems like this retort by Rusty was in the making before the NASA NEO AoA report was released. I need to be convinced of the estimates he make of the gravity tractor. Several people have told me that designing the spacecraft is not the main problem, hand-waving the issue in essence. Yes the design of a gravity tractor spacecraft could potentially be simple, but at this point, with all the talk of the gravity tractor in the media, I think we need a conceptual design with mission analysis, mass breakdown, power budget, operations plans, and life cycle cost assessments. The papers out there talk about the simple gravitational equations that initially describe the problem (though Eugene Fahnestock, a PhD student under Danial Scheeres at the Univ. of Michigan did present an very interesting gravity tractor dynamical analysis at the recent 2007 Planetary Defense Conference).
I believe Rusty's criticisms may be spurred from some of the slides presented at the 2007 Planetary Defense Conference from the NASA NEO AoA study. Some of these slides had results that are not in the report that was publicly released. This data on these slides did show large costs for various mitigation options including the gravity tractor.
He states that he has conducted a "parallel analysis of the various alternatives for diverting a threatening NEO to that which NASA submitted to the Congress. In it I [Rusty] provide the basic logic and resultant conclusions and then juxtapose them with the NASA response commenting on why the apparent difference."
In this letter, Rusty (representing only himself and not the B612 Foundation or Association of Space Explorers) brings up the concept he discussed at the recent 2007 Planetary Defense Conference, namely a gravity tractor combination mitigation approach coupled with either a kinetic impactor or nuclear option. As he states: "The characteristics of the gravity tractor and kinetic impactor are such that they nicely compensate for each others' limitations." He also states: "Consideration should be given in the future to flight testing the kinetic impactor/gravity tractor combination to validate the capability and provide confidence to the world public."
Later on, Rusty states that he has issues with the perceived cost estimates in the report (since we do not have the full report). In commenting on this issue, he discusses the cost of the Gravity Tractor (or GT): "The GT concept, as presented in NASA's NEO Workshop held in Vail, Colorado in June-July 2006, is adaptable to any size spacecraft and was specifically presented and evaluated in White Paper 42 (the only professional paper presented on the gravity tractor) based on NASA's Deep Space 1 spacecraft flown successfully from 1998-2000 and costing (based on the official NASA website, http://nmp.nasa.gov/ds1/quick_facts.html) $149.7 million (FY 95-99). Given that the presentations at NASA's Vail Workshop explicitly presented and evaluated the GT concept based on the Deep Space 1 mission technology, and not on the cancelled Prom"etheus, it is mystifying why, in NASA's Report to Congress the GT was presented as technically immature and extremely costly. Without access to the Final Report it cannot be stated with certainty but it appears that NASA inappropriately used the low technological readiness level and extreme cost of the cancelled Prometheus spacecraft as a proxy for the GT. In this analysis I use the GT as it was presented to the NASA study team in the NASA NEO workshop in Vail, Colorado."
Another issue he addresses is resonant returns or keyholes, and the potential failure of the NASA NEO AoA report to examine this aspect of mitigation missions.
Independent Analysis of Alternatives To Divert a NEO on a Likely Collision Course With Earth
19 March 2007
Source: Russell L. Schweickart
Link: Rusty Schweickart's Letter and Limited Analysis (Source: SpaceRef)
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