New Horizons 2 (also New Horizons II, NHII, or NH2) was a proposed mission to the trans-Neptunian objects by NASA. It was conceived as a planetary flyby mission in 2002, based on the New Horizons spacecraft, which was in development at the time. [1] [2] In March 2005, the proposal was not selected for further development because of a shortage of plutonium-238 needed for the radioisotope thermoelectric generator (RTG). [3] The New Horizons 2 study was funded by the New Frontiers program, and delivered to the U.S. Congress in June 2005. [4]
New Horizons 2 was included in the tentative budget for the New Frontiers program missions. [5] In 2004, the United States Senate on Appropriations Committee provided additional funding for New Horizons 2, a new Kuiper belt mission. [6] As early as 2004, there was a conference on how to make the most use of New Horizons 2's Uranus flyby. [7]
Candidate targets included 47171 Lempo, a system that, like Pluto–Charon, contains multiple bodies. [5] The mission plan for Lempo also included flybys of Jupiter and Uranus, [5] and perhaps four Kuiper belt objects (KBO). [2] There was a lot of flexibility: even without a gravity assist, any KBO within 50 AU and a 20-year flight time was possible. [3] A flyby of Neptune's largest moon Triton was also considered, with 66652 Borasisi as a potential follow-on. [3] 55637 Uni was also considered for a visit, as it had a similar orbit to Lempo. [8]