Vela (satellite)
Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means watchman in Spanish.
Vela started out as a small budget research program in 1959. It ended 26 years later as a successful, cost-effective space system. In the 1970s, the nuclear detection mission was taken over by the Defense Support Program (DSP) system, and in the late 1980s, by the Navstar Global Positioning System (GPS) satellites. The program is now called the Integrated Operational Nuclear Detection System (IONDS).
The total number of satellites built was 12 — six of the Vela Hotel design, and six of the Advanced Vela design. The Vela Hotel series was to detect nuclear explosions in space, while the Advanced Vela series was to detect not only nuclear explosions in space but also in the atmosphere.
All spacecraft were manufactured by TRW and launched in pairs, either on a Atlas-Agena or Titan III-C boosters, and placed in 63,000 to 70,000 mile orbits, well above the Van Allen radiation belts. The first Vela Hotel pair was launched in 1963, three days after the Test Ban Treaty was signed, and the last in 1965. They had a design life of six months, but were actually shut down after five years. Advanced Vela pairs were launched in 1967, 1969 and 1970. They had a nominal design life of 18 months, later changed to 7 years. However, the last satellite to be shut down was Vehicle 9 in 1984, which had been launched in 1969 and had lasted nearly 15 years.
The original Vela satellites were equipped with 12 external X-ray detectors and 18 internal neutron and gamma-ray detectors. The were equpped with solar panels generating 90 watts.
The Advanced Vela satellites were additionally equipped with two non-imaging silicon photodiode sensors called bhangmeters which monitored light levels over sub-millisecond intervals. They could determine the location of a nuclear explosion to within about 3,000 miles. Atmospheric nuclear explosions produce a unique signature: a short and intense flash lasting around 1 millisecond, followed by a second much more prolonged and less intense emission of light taking a fraction of a second to several seconds to build up. The effect occurs because the surface of the early fireball is quickly overtaken by the expanding atmospheric shock wave composed of ionised gas. Although it emits a considerable amount of light itself it is opaque and prevents the far brighter fireball from shining through. As the shock wave expands, so the amount of light it emits increases with its surface area. No natural phenomenon is known to produce this signature.
They were also equipped with sensors which could detect the electromagnetic pulse from an atmospheric explosion.
Additional power was required for these instruments, and these larger satellites consumed 120 watts generated from solar panels.
Serendipitously, the Vela satellites were the first devices ever to detect Gamma ray bursters.
The 1979 Vela incident
Some controversy still surrounds the Vela program since on 22 September 1979 at 00:53 GMT, the Vela 6911 satellite detected the characteristic double flash of an atmospheric nuclear explosion of about 3 kilotons apparently over the Indian Ocean or South Atlantic. Vela 6911 was one of the pair launched on 23 May 1969, over ten years before the possible explosion. It was operating two years past its designed lifespan and its electromagnetic pulse (EMP) sensor had failed. It had also developed a fault in July 1972 where around half a second of its recording memory had failed. This had cleared itself in March 1978.
The Vela satellites previously detected 41 atmospheric tests, each of which had been subsequently confirmed through other means. There was some other data which seemed to confirm the explosion. For instance, hydrophones detected a signal which was consistent with a small nuclear explosion on, or slightly under, near Prince Edward Island. The radio telescope at Arecibo, Puerto Rico also detected an anomalous traveling ionospheric disturbance at the same time.
Many scientific and policy experts at that time (during the Carter Administration) took pains to debunk the data as a false reading. The panel set up to review the evidence, the Ruina Panel, released its report in summer of 1980 and concluded that the signal "was probably not from a nuclear explosion. Although we cannot rule out that this signal was of nuclear origin".
In 1994 Commodore Dieter Gerhardt, a convicted Soviet spy was released from prison and emigrated to Switzerland. At the time of the Vela flash he had been the commander of the Simonstown naval base. In February 1994 he told the Johannesburg City Press that the flash was produced by an Israeli-South African test code-named "Operation Phenix". The test was supposed to be hidden by cloud but at the last minute the weather changed and it was detected.
This has not completely ended the controversy, since on 20 April 1997 the Israeli daily newspaper Ha'aretz, quoted South African Deputy Foreign Minister Aziz Pahad was quoted as confirming that the flash over the Indian Ocean was indeed from a South African nuclear test. However, according to documents passed by South Africa to the IAEA, South Africa did not construct its first nuclear device until November 1979, two months after the flash was detected.
Includes material from NASA Goddard's Remote Sensing Tutorial (http://rst.gsfc.nasa.gov/)
See also: Report on the 1979 Vela Incident (http://nuclearweaponarchive.org/Safrica/Vela.html)
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