Vela 5B Satellite in Orbit.
Country of originUnited States
OperatorU.S. Air Force
RegimeHighly elliptical orbit
Design life15 years
Maiden launchVela 1A
Last launchVela 6B
Related spacecraft
Derived fromProject Vela & Integrated Operational Nuclear Detection System (IONDS)

Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to detect nuclear detonations and monitor Soviet Union compliance with the 1963 Partial Test Ban Treaty.

Vela started out as a small budget research program in 1959. It ended 26 years later as a successful, cost-effective military space system, which also provided scientific data on natural sources of space radiation. In the 1970s, the nuclear detection mission was taken over by the Defense Support Program (DSP) satellites. In the late 1980s, it was augmented by the Navstar Global Positioning System (GPS) satellites. The program is now called the Integrated Operational NuDet (Nuclear Detonation) Detection System (IONDS).


Twelve satellites were built, six of the Vela Hotel design and six of the Advanced Vela design. The Vela Hotel series was to detect nuclear tests 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 an AtlasAgena or Titan III-C boosters. They were placed in orbits of 118,000 km (73,000 miles)[1] to avoid[2] particle radiation trapped in the Van Allen radiation belts. Their apogee was about one-third of the distance to the Moon. The first Vela Hotel pair was launched on October 17, 1963,[3] one week after the Partial Test Ban Treaty went into effect, and the last in 1965. They had a design life of six months, but were only 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 seven 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 Vela series began with the launch of Vela 1/2 on October 17, 1963, a flight also marking the maiden voyage of the Atlas-Agena SLV-3 vehicle. The second pair of satellites launched on July 17, 1964, and the third on July 20, 1965. The last launch miscarried slightly when one Atlas vernier engine shut down at liftoff, while the other vernier operated at above-normal thrust levels. This resulted in a slightly lower than normal inclination for the satellites, however the mission was carried out successfully. The problem was traced to a malfunction of the vernier LOX poppet valve.

Subsequent Vela satellites were switched to the Titan IIIC booster due to their increased weight and complexity. Three more sets were launched on April 28, 1967, May 23, 1969, and April 8, 1970. The last pair of Vela satellites operated until 1985, when they were finally shut down, the Air Force claimed them to be the world's longest operating satellites. They remained in orbit until decaying at the end of 1992.

Table of Vela launches:[4]
Launch Date Satellite COSPAR ID Launch vehicle Serial Launch mass Instruments Satellite photo
17 October 1963 Vela 1A 1963-039A Atlas-Agena-D 197D 150 kilograms (330 lb) 3 instruments
Vela 1B 1963-039C
17 July 1964 Vela 2A 1964-040A Atlas-Agena-D 216D 150 kilograms (330 lb) 8 instruments
Vela 2B 1964-040B
20 July 1965 Vela 3A 1965-058A Atlas-Agena-D 225D 150 kilograms (330 lb) 8 instruments
Vela 3B 1965-058B
28 April 1967 Vela 4A 1967-040A Titan IIIC 3C-10 231 kilograms (509 lb) 9 instruments
Vela 4B 1967-040B
23 May 1969 Vela 5A 1969-046D Titan IIIC 3C-15 259 kilograms (571 lb) 8 instruments
Vela 5B 1969-046E
8 April 1970 Vela 6A 1970-027A Titan IIIC 3C-18 261 kilograms (575 lb) 8 instruments
Vela 6B 1970-027B


Vela-5B All-Sky Monitor Instrument

The original Vela satellites were equipped with 12 external X-ray detectors and 18 internal neutron and gamma-ray detectors. They were equipped 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, often called a "double-humped curve": 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, it cools down becoming more transparent allowing the much hotter and brighter fireball to become visible again.

No single natural phenomenon is known to produce this signature, although there was speculation that the Velas could record exceptionally rare natural double events, such as a meteoroid strike on the spacecraft that produces a bright flash or triggering on a lightning superbolt in the Earth's atmosphere, as may have occurred in the Vela incident.[5][6][7]

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 cosmic gamma ray bursts.

Role in discovering gamma-ray bursts

On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature.[8] Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos Scientific Laboratory, led by Ray Klebesadel, filed the data away for investigation. As additional Vela satellites were launched with better instruments, the Los Alamos team continued to find inexplicable gamma-ray bursts in their data. By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of sixteen bursts[9] and definitively rule out a terrestrial or solar origin. Contrary to popular belief, the data was never classified.[10] After thorough analysis, the findings were published in 1973 as an Astrophysical Journal article entitled "Observations of Gamma-Ray Bursts of Cosmic Origin".[9] This alerted the astronomical community to the existence of gamma-ray bursts, now recognised as the most violent events in the universe.

Vela 5A and 5B

The scintillation X-ray detector (XC) aboard Vela 5A and its twin Vela 5B consisted of two 1 mm thick NaI(Tl) crystals mounted on photomultiplier tubes and covered by a 0.13 mm thick beryllium window. Electronic thresholds provided two energy channels, 3–12 keV and 6–12 keV.[11] In addition to the x-ray Nova announcement indicated above the XC Detector aboard Vela 5A and 5B also discovered and announced the first X-Ray Burst ever reported.[12] The announcement of this discovery predated the initial announcement of the discovery of gamma-ray bursts by 2 years. In front of each crystal was a slat collimator providing a full width at half maximum (FWHM) aperture of ~6.1 × 6.1 degrees. The effective detector area was ~26 cm2. The detectors scanned a great circle every 60 seconds, and covered the whole sky every 56 hours.[13] Sensitivity to celestial sources was severely limited by the high intrinsic detector background, equivalent to about 80% of the signal from the Crab Nebula, one of the brightest sources in the sky at these wavelengths.[13] The Vela 5B satellite X-ray detector remained functional for over ten years.

Vela 6A and 6B

Like the previous Vela 5 satellites, the Vela 6 nuclear test detection satellites were part of a program run jointly by the Advanced Research Projects of the U.S. Department of Defense and the U.S. Atomic Energy Commission, managed by the U.S. Air Force. The twin spacecraft, Vela 6A and 6B, were launched on 8 April 1970. Data from the Vela 6 satellites were used to look for correlations between gamma-ray bursts and X-ray events. At least two good candidates were found, GB720514 and GB740723. The X-ray detectors failed on Vela 6B on 27 January 1972 and on Vela 6A on 12 March 1972.

Controversial observations

Main articles: Vela incident and Bell Island boom

Some controversy still surrounds the Vela program. On 22 September 1979 the Vela 5B (also known as Vela 10 and IRON 6911[14]) satellite detected the characteristic double flash of an atmospheric nuclear explosion near the Prince Edward Islands. Still unsatisfactorily explained, this event has become known as the Vela incident. President Jimmy Carter initially deemed the event to be evidence of a joint Israeli and South African nuclear test, though the now-declassified report of a scientific panel he subsequently appointed while seeking reelection concluded that it was probably not the event of a nuclear explosion.[citation needed] In 2018, a new study confirmed that it is highly likely that it was a nuclear test, conducted by Israel.[15][16] An alternative explanation involves a magnetospheric event affecting the instruments.

An earlier incident occurred when an intense solar storm on August 4, 1972, triggered the system to event mode as if an explosion occurred, but this was quickly resolved by personnel monitoring the data in real-time.[17]

See also


  1. ^ "The Vela 5A satellite". NASA Goddard Space Flight Center. Retrieved 28 October 2015.
  2. ^ "Vela satellite measurements". Los Alamos Scientific Laboratory. Retrieved 17 March 2024.
  3. ^ Encyclopedia Astronautica, Vela nuclear detection surveillance satellites.
  4. ^ Gunter's Space Page. "Vela 1, 2, 3, 4, 5, 6". Retrieved 21 September 2019.
  5. ^ New York Times. South Africa Stops Short Of Denying Nuclear Test, The Ledger, Lakeland, Florida, originally from The New York Times, 27 October 1979
  6. ^ Lightning Superbolts Detected By Satellites, Science Frontiers, September 1977, No. 1, which in turn cites:
    Turman, B. N (1977). "Detection of lightning superbolts". Journal of Geophysical Research. 82 (18): 2566–2568. Bibcode:1977JGR....82.2566T. doi:10.1029/JC082i018p02566..
    Retrieved from website July 24, 2010.
  7. ^ Dunning, Brian. "Skeptoid #190: The Bell Island Boom". Skeptoid. Retrieved June 19, 2017. quote (emphasis added): "They also picked up large lightning flashes, and it was in part from the Vela satellites that we learned about lightning superbolts. About five of every ten million bolts of lightning is classified as a superbolt, which is just what it sounds like: An unusually large bolt of lightning, lasting an unusually long time: About a thousandth of a second. Superbolts are almost always in the upper atmosphere, and usually over the oceans."
  8. ^ Schilling 2002, pp. 12–16
  9. ^ a b Klebesadel, Ray W; Strong, Ian B; Olson, Roy A (1973). "Observations of Gamma-Ray Bursts of Cosmic Origin". The Astrophysical Journal. 182: L85. Bibcode:1973ApJ...182L..85K. doi:10.1086/181225.
  10. ^ Bonnell, J. T.; Klebesadel, R. W. (1996). "A brief history of the discovery of cosmic gamma-ray bursts". AIP Conference Proceedings. 384: 979. Bibcode:1996AIPC..384..977B. doi:10.1063/1.51630.
  11. ^ Conner JP, Evans WD, Belian RD (1969). "The Recent Appearance of a New X-Ray Source in the Southern Sky". The Astrophysical Journal. 157: L157–159. Bibcode:1969ApJ...157L.157C. doi:10.1086/180409.
  12. ^ Belian RD, Conner JP, Evans WD (1972). "A Probable Precursor to the X-Ray Nova Centaurus XR-4". The Astrophysical Journal. 171: L87–90. Bibcode:1972ApJ...171L..87B. doi:10.1086/180874.
  13. ^ a b Priedhorsky WC, Holt SS (1987). "Long-term cycles in cosmic X-ray sources". Space Science Reviews. 45 (3–4): 291–348. Bibcode:1987SSRv...45..291P. doi:10.1007/BF00171997. S2CID 120443194.
  14. ^ "Vela 7, 8, 9, 10, 11, 12 (advanced Vela)".
  15. ^ Wright, Christopher M.; De Geer, Lars-Erik (2017). "The 22 September 1979 Vela Incident: The Detected Double-Flash" (PDF). Science & Global Security. 25 (3): 95–124. Bibcode:2017S&GS...25...95W. doi:10.1080/08929882.2017.1394047. ISSN 0892-9882.
  16. ^ Weiss, Leonard (2018). "A double-flash from the past and Israel's nuclear arsenal". Bulletin of the Atomic Scientists. Retrieved 2018-08-14.
  17. ^ Knipp, Delores J.; B. J. Fraser; M. A. Shea; D. F. Smart (2018). "On the Little‐Known Consequences of the 4 August 1972 Ultra‐Fast Coronal Mass Ejecta: Facts, Commentary and Call to Action". Space Weather. 16 (11): 1635–1643. Bibcode:2018SpWea..16.1635K. doi:10.1029/2018SW002024.