(83K)ATS-5 was the final attempt at a synchronous gravity-gradient spacecraft by the ATS program. The spacecraft used the same basic cylindrical bus as its predecessors with the additional booms for gravity-gradient stabilization. The size was the same as ATS-2 and ATS-4, but the weight had increased to 431 kg.
ATS-5 was launched on August 12, 1969 on an Atlas-Centaur vehicle. Problems developed in its parking orbit where large amounts of propellant were expended to stabilize the spacecraft. To try to salvage the mission, the satellite was injected into its final orbit ahead of schedule.
Although ATS-5 was to be a gravity-gradient stabilized satellite, spin stabilization was used during orbit insertion (a common practice). A despin device was carried by the spacecraft to remove the spin after it reached its final orbit. The yo-yo despin device deployed booms to slow the spin, much like a spinning figure skater slows down as she extends her arms. ATS-5 was successfully placed in synchronous orbit, however the spin on the spacecraft was in the wrong direction for the despin device to work. The gravity- gradient stabilization experiment was useless and the communications experiments were severely affected since the antennas were spinning with the spacecraft and could only work like a lighthouse beakon rather than as a spotlight. Some communications experiments were later carried out in a pulse mode and some secondary experiments were conducted as late as 1977 [McCeney, Pg. 324].
Experiments carried by ATS-5 included an ion engine, solar cell investigation, and space environment investigations of particles, electric fields, magnetic fields, and solar radio waves.