Design efforts in the United States and in Europe for the next-generation TeV Čerenkov telescope, AGIS and CTA, respectively, are underway and follow a recent worldwide explosion of activity in gamma-ray astrophysics, with the U.S.-led Fermi Gamma-ray Space Telescope (FGST) in space and a host of TeV Čerenkov telescopes on the ground (VERITAS, HESS, MAGIC, Milagro, CANGAROO, and HEGRA). The proposed new instruments would increase sensitivity and field of view by an order of magnitude. Because the two designs have similarities and complementarity (including the location of VERITAS and HESS in different hemispheres), opportunities for collaboration exist and discussions are underway. This is yet another example in which common scientific interests, current capability, and design complementarity make collaboration not only a means of reducing cost to each partner, but also a way of creating a more capable observatory.
The Laser Interferometer Space Antenna (LISA) and the International X-ray Observatory (IXO) are two transformational missions where the convergence of scientific goals, complementarity of expertise, and the desire to produce more science per dollar has made partnering essential. LISA is a relatively mature NASA/ESA collaboration, while IXO is the result of a more recent merger of the U.S. Con-X and the ESA XEUS missions, with JAXA as an additional partner. NASA will consider Astro2010 advice on the relative rankings of LISA and IXO, and in Europe the two are competing for the first L(arge)-class launch slot (scheduled for 2020) against the Europa Jupiter System Mission (EJSM) (an outer planets mission) in the ESA Cosmic Vision program, whose down-select process is beginning in 2010. From the U.S. perspective, the committee would like to see both LISA and IXO go forward, and an implementation plan for NASA is given in Chapter 7. ESA, on the other hand, may choose a different prioritization, or choose to go with EJSM.
Even more complex is the potential partnering between NASA, DOE, and ESA on a dark energy mission. Because of the common interests in the science of dark energy, as well as complementary technical capabilities, NASA and DOE have been planning for the Joint Dark Energy Mission (JDEM) since 2003. Euclid is a European mission concept aimed at cosmology and dark energy, which is competing for one of two M(edium)-class launch slots, with a decision expected in late 2011 and launches scheduled for 2018 and 2019. The overlap in goals and scope between the proposed U.S. and European missions is significant, and there is potentially a grand partnering arrangement involving NASA, DOE, and ESA if the expanded scientific priorities set by Astro2010 for such a mission can be aligned among the partners, and assuming that the arrangement is consistent with the United States