NASA tried to negotiate with Russia for use of Proton rockets to launch the spacecrafts, in exchange for carrying Russian "Drop Zond" probes to Pluto. Another idea, emanating from the Max Planck Institute, would have had Germany contribute funding for the launch, in exchange for Pluto Express carrying a German probe to be dropped at Io during the Jupiter gravity assist. The timing of the mission was important, as it would have passed Pluto shortly before its atmosphere froze, which it was thought to do for a considerable part of its orbit. The mission's main objectives would have been to map Pluto's surface and examine the double system's geology and geomorphology, as well as determining the composition of Pluto's atmosphere. This last task would have been considerably more difficult after the start of atmospheric freezing. Scientific equipment on board would have included visible light imaging systems, infrared and ultraviolet spectrometers, and an ultrastable oscillator (USO) for use in a radio occultation experiment. The spacecraft was to have been a simple hexagonal prism shaped structure weighing some 220 kg (485 lb), powered by radioisotope thermal generators (RTGs) similar to those used on the "Galileo" and "Cassini" missions. On-board control and data collection would have been maintained by a 1.5 MIPS RISC-based computer system capable of processing data at 5 Mbit/s. This would have allowed for the transmission of over one gigabyte of data over a one-year period. Communications would have been via a fixed 1.47 m (5.6 ft) high-gain antenna, directionally corrected using a wide-field star tracker. Early in the mission's planning there was suggestion of combining efforts with the Russian space agency and including Zond probes to study the Plutonian atmosphere. This plan was later abandoned. The Pluto Express was predicted to be launched in 2001, but it was not ready until late 2004. The spacecraft was to have been launched via either a Delta rocket or the Space Shuttle, most likely in December 2004. Had that happened, the only option would have been to use a Delta rocket, as the Shuttle fleet was grounded after the "Columbia" disaster. The course would have been initially via Jupiter, whose gravity well would have been used to increase the probe's velocity via a gravity assist. The closest approach distance to Pluto would have been about 15,000 km (9320.6 mi) at 17–18 km/s (38,027.9–40,264.9 mph), so as to allow for 1 km (0.6 mi) resolution mapping.