|
Transit
|
Program: Transit. Objective: Navigation. Spin-stabilized Transit satellites were developed by the US Navy into the first operational navigation satellite system, for use by ballistic missile submarines and surface vessels. Early Transits carried a variety of piggy-back payloads, many still classified. Transit was also known as the Navy Navigation Satellite (NNS). Transit provided continuous navigation satellite service from 1964, initially for Polaris submarines and later for civilian use. Transit receivers used the known characteristics of the satellites orbit, measured the Doppler shift of the satellite's radio signal, and thereby calculated the receivers position on the earth. Individual satellites operated for over 10 years. Technical breakthroughs during the program included gravity gradient stabilization, the use of radio-isotope thermoelectric generators (RTG), and navigation satellite technologies used in the later GPS series. The TRIAD satellite was launched in 1972 to test improvements. Transit was superseded by the Navstar global positioning system. The use of the satellites for navigation was discontinued at the end of 1996, but the satellites continued transmitting and became the Navy Ionospheric Monitoring System (NIMS).
Major Events:
- 1961 February 22 - Transit 3B. Spacecraft: Transit. Mass: 112 kg (246 lb). Launch Site: Cape Canaveral. Launch Vehicle: Thor Able-Star.
Lofti 1 piggyback payload did not separate. Nevertheless Transit 3B returned useful data needed for design of the operational satellites. It carried a digital clock driven by the same oscillator that drove the transmitters. It transmitted timing signals governed by the clock and a 384-bit memory. This allowed testing of the techniques for loading the memory from the ground, the ability of the memory to hold a message in orbit, and the ability to encode the memory contents by means of a frequency modulation on one of the main transmitters. It was also shown that ±60° phase modulation could be used to transmit the contents of the satellite memory without degradation of the accuracy of the Doppler signal and Doppler measurements.
- 1961 November 15 - Transit 4B. Spacecraft: Transit. Mass: 86 kg (189 lb). Launch Site: Cape Canaveral. Launch Vehicle: Thor Able-Star.
Together, Transits 4A and 4B allowed the determination of harmonics in the Earth’s gravity field that had not yet been evaluated, and they also allowed firm navigational ties to be established from continent to continent as well as to isolated islands. As a result, it was discovered that the position of Hawaii was incorrect by 1 km. Carried SNAP 3 nuclear power source.
- 1963 June 16 - Transit 5A-3. Spacecraft: Transit. Mass: 55 kg (121 lb). Launch Site: Point Arguello. Launch Vehicle: Scout X-3.
First operational prototype with a redesigned power supply. A malfunction of the memory occurred during powered flight that kept it from accepting and storing navigation messages, and the oscillator stability was degraded during launch. The satellite could not be used for navigation, but it was the first to achieve gravity-gradient stabilization, and its other subsystems performed well.
- 1963 September 28 - Transit 5BN-1. Spacecraft: Transit. Mass: 70 kg (154 lb). Launch Site: Vandenberg. Launch Vehicle: Thor Able-Star.
First test of nuclear-powered Transit operational prototype. Carried SNAP-9A nuclear power source. The satellite achieved gravity-gradient stabilization, but upside down, making the signal level too low for operational users with low-gain antennas. However, geodetic and navigational evaluation data were obtained.
- 1963 September 28 - Transit 5E-1. Spacecraft: Transit. Mass: 61 kg (134 lb). Launch Site: Vandenberg. Launch Vehicle: Thor Able-Star.
The missions of Satellite 1963-038C were to measure omnidirectional flux of protons and electrons at various energy levels, radiation effects on transistors, and the effectiveness of thermal coatings. The satellite was launched together with a classified Department of Defense spacecraft on September 28, 1963. Its planned orbit was apogee 1120 kilometres, perigee 1070 kilometres, inclination 88.9 degrees. The satellite weighed 62 kg; its body was in the shape of an 0.46 m x 0.25 m octagonal prism. It was powered by four solar blades and transmited on 136, 162, and 324 mcs. The spacecraft was built for the Bureau of Naval Weapons. In 1967 it was still sending usable data from all systems.
- 1967 September 25 - Transit O-14. Spacecraft: Transit. Mass: 60 kg (132 lb). Launch Site: Vandenberg. Launch Vehicle: Scout A.
- 1968 March 2 - Transit O-18. Spacecraft: Transit. Mass: 60 kg (132 lb). Launch Site: Vandenberg. Launch Vehicle: Scout A.
First RCA-built Transit.
- 1970 August 27 - Transit O-19. Spacecraft: Transit. Mass: 18 kg (39 lb). Launch Site: Vandenberg. Launch Vehicle: Scout A.
- 1981 May 15 - Nova 1. Spacecraft: TIP. Mass: 170 kg (370 lb). Launch Site: Vandenberg. Launch Vehicle: Scout G.
Improved Transit.
- 1985 August 3 - Transit O-30. Spacecraft: Transit. Mass: 55 kg (121 lb). Launch Site: Vandenberg. Launch Vehicle: Scout G.
- 1987 September 16 - Transit O-29. Spacecraft: Transit. Mass: 59 kg (130 lb). Launch Site: Vandenberg. Launch Vehicle: Scout G.
- 1988 April 26 - Transit O-32. Spacecraft: Transit. Mass: 64 kg (141 lb). Launch Site: Vandenberg. Launch Vehicle: Scout G.
- 1988 August 25 - Transit O-31. Spacecraft: Transit. Mass: 59 kg (130 lb). Launch Site: Vandenberg. Launch Vehicle: Scout G.
|
Contact us with any corrections, additions, or comments.
Conditions for use of drawings, pictures, or other materials from this site..
To contact astronauts or cosmonauts.
© Mark Wade, 1997 - 2007 except where otherwise noted.
|
|
|
|