TPF and Europa Orbiter: a tale of two unfunded missions

A lot of attention in the week since the release of NASA’s FY2007 budget proposal as been on cuts to NASA’s science programs. Two efforts that have attracted a lot of attention have been the Terrestrial Planet Finder (TPF) and a Europa orbiter. The former has been “deferred indefinitely”, while NASA did not include a Europa orbiter in the budget as a new start, despite specific direction to do so from Congress in the conference report on the FY06 budget.

Needless to say, scientists and groups like The Planetary Society aren’t pleased by these developments. TPS is particularly unhappy about the lack of funding for a Europa mission: “NASA’s robotic exploration program is being flat-lined, setting aside a mission to Europa to search for its ice-covered ocean and perhaps for life itself,” executive director Louis Friedman said in a press release. Later, in an interview for Technology Review magazine, Friedman said, “The ones I’m most concerned about are the mission to Europa and the Terrestrial Planet Finder.” Exoplanet hunter Geoffrey Marcy told the AP that the decision to delay TPF and a precursor mission, SIM, was disappointing since it showed that “our society can’t put more resources into answering the glorious question of whether we humans are alone in this universe.” Keith Cowing was critical of the decision to defer TPF, writing on SpaceRef.com that “This is a bad decision. A really bad one. In making it, one has to question whether this White House really meant what it said 2 years ago when it raised everyone’s expectations, invoking an expansion ‘into the cosmos’ in so doing.”

The temptation here is to lump a Europa orbiter (hereafter simply “EO”) and TPF together as signs that NASA and/or the administration is somehow abandoning science. That argument, though, seems a little simplistic. TPF and EO are very different programs facing very different challenges. EO has long been a priority of planetary scientists; a planetary sciences decadal survey report, issued in 2002, ranked a “Europa Geophysical Orbiter” mission as the highest-priority “large” mission (excluding Mars missions) for the 2003-2013 period. NASA had planned an EO mission in the late 1990s, for launch as early as 2003, as part of its “Ice and Fire” program that included a Pluto flyby and solar probe missions; that fell by the wayside because of cost growth. Europa was then going to be explored by the Jupiter Icy Moons Orbiter (JIMO) mission, part of the Project Prometheus nuclear power and propulsion program, but JIMO died last year as NASA sharply curtailed Prometheus.

TPF, on the other hand, has always been a long-range program at NASA. TPF is actually two separate missions: a single large space telescope with coronagraph (TPF-C), and several space telescopes flying in formation to serve as an interferometer. TPF-C was planned for launch as early as 2014 before the budget release, although that date would have almost certainly slipped several years, particularly given that JWST is now scheduled for launch in 2013. The TPF interferometer, meanwhile, was planned for launch “before 2020″, a date that would have likely slipped too. TPF faced a number of serious technological hurdles, including the ability for large space telescopes to perform wavelength-precise formation flying. It’s interesting to note that the AAS, which included TPF in its list of high-priority astronomy missions in its 2001 decadal survey (a study separate from the planetary science decadal survey mentioned above), priced TPF at $1.7 billion. However, the same report priced JWST (then known as the Next Generation Space Telescope, NGST) at about $1.5 billion, including international contributions; JWST is now expect to cost around $4 billion, even after its primary mirror was shrunk from 8 meters (the size used for the 2001 NGST cost estimate) to 6.5 meters. Given that cost growth, how much would the two TPF missions cost now? Or ten years from now?

By contrast, EO doesn’t face a lot of those technology issues: orbiters are a lot simpler, and have a lot more flight heritage, than formation-flying space telescopes. Given that, as well as the high priority scientists have given for studying Europa, it’s hard to see its exclusion from the 2007 budget as anything other than the result of a budgetary squeeze. TPF, on the other hand, is a project many years down the road, with several near-term exoplanet projects—the Keck Interferometer and the Kepler mission—still on track. It’s tough to mourn for TPF to the same degree as EO.