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The Transit Improvement Program (TIP) was established in 1969 to test improvements to the Transit Navigation System with the goal of providing a redundant, radiation-hardened satellite that could continue to provide its correct position for over five days without update from the ground. This "drag-free" satellite would use a Disturbance Compensation System (DISCOS) developed at Stanford. Substantial improvements to Transit were demonstrated in the three satellites flown, followed by three production Nova satellites. These evidently were intended to provide ballistic missile submarines with a minimum Transit capability even after a nuclear exchange. However they did not replace the earlier model of Transit satellites, which continued to be launched. The TIP 150- and 400-MHz transmitters had the output power raised to 3 W at 150 MHz and 5 W at 400 MHz. Each TIP satellite was equipped with a redundant, radiation-hardened, fully programmable minicomputer with 64 KB of memory, a formidable technical accomplishment at the time. To correct for orbital precession over the long life of the Transit satellites, TIP was equipped with a main hydrazine thruster to make orbital corrections as needed to keep the satellite in its polar orbit. The DISCOS sensor consisted of a mass floating inside a cavity. Small thrusters were automatically fired to keep the floating mass in the middle of the cavity. These thrusters were an innovative pulsed-plasma design developed by Republic Aviation, and used solid Teflon as the fuel. The Teflon was vaporized by an electrical arc, then heated, focused, and expelled by a magnetohydrodynamic bottle. The resulting jet had a specific impulse of 500 seconds, and 1 kg of Teflon, divided between two thrusters, was adequate for ten years of DISCOS operation. Each thruster generated a discrete impulse of 0.38 mN within one second of command. The TIP satellite also demonstrated a lighter-weight, more accurate oscillator and an improved incremental phase shifter to improve spacecraft timing. A quadrifilar helix antenna of near-ideal configuration was introduced. In 1977, the Navy awarded a contract to RCA for the production of three Nova spacecraft with the option to build two more. These satellites were nearly identical to the TIP satellites, with minor improvements, including the addition of magnetic damping to DISCOS and a stiffening of the lower boom assembly. However the basic Transit system had been upgraded in accuracy over the years through improvement of the ground and processing segment and met fleet requirements. Therefore further Nova satellites were not orbited, or only three were needed for the post-strike strategic navigation mission. Instead, six Transits built in the 1960's were orbited two at a time in the late 1980's, and this kept the system in operation until all surface users could convert to GPS and the Transit system was shut down. Typical orbit: 1100 km circular orbit, 90 deg inclination. Mass: 170 kg (370 lb). TIP Chronology
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