Vela was the name of a group of satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s developed as the Vela Hotel element of Project Vela

Project Vela

Project Vela was a project by the United States to develop and implement methods to monitor compliance with the 1963 Partial Test Ban Treaty. The development work was primarily performed by the Advanced Research Projects Agency and was overseen by the United States Air Force.Project Vela consisted...

 by the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 to monitor compliance with the 1963 Partial Test Ban Treaty

Partial Test Ban Treaty

The treaty banning nuclear weapon tests in the atmosphere, in outer space and under water, often abbreviated as the Partial Test Ban Treaty , Limited Test Ban Treaty , or Nuclear Test Ban Treaty is a treaty prohibiting all test detonations of nuclear weapons...

 by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

, and other nuclear-capable states. It means vigil or "watch" in Spanish

Spanish language

Spanish , also known as Castilian , is a Romance language in the Ibero-Romance group that evolved from several languages and dialects in central-northern Iberia around the 9th century and gradually spread with the expansion of the Kingdom of Castile into central and southern Iberia during the...

.

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

Defense Support Program

The Defense Support Program is a program of the U.S. Air Force that operates the reconnaissance satellites which form the principal component of the Satellite Early Warning System currently used by the United States....

 (DSP) system, and in the late 1980s, augmented by the Navstar Global Positioning System

Global Positioning System

The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...

 (GPS) satellites. The program is now called the Integrated Operational Nuclear Detection System (IONDS

Nuclear MASINT

Nuclear MASINT is one of the six major subdisciplines generally accepted to make up Measurement and Signature Intelligence , which covers measurement and characterization of information derived from nuclear radiation and other physical phenomena associated with nuclear weapons, reactors, processes,...

).

Deployment

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 initiations 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

TRW

TRW Inc. was an American corporation involved in a variety of businesses, mainly aerospace, automotive, and credit reporting. It was a pioneer in multiple fields including electronic components, integrated circuits, computers, software and systems engineering. TRW built many spacecraft,...

 and launched in pairs, either on an Atlas-Agena

RM-81 Agena

The RM-81 Agena was an American rocket upper stage and satellite support bus which was developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program...

 or Titan III

Titan III

The Titan IIIC was a space booster used by the United States Air Force. It was launched from Cape Canaveral Air Force Station, FL., and Vandenberg Air Force Base, CA. It was planned to be used as a launch vehicle in the cancelled Dyna-Soar and Manned Orbiting Laboratory programs...

-C boosters, and placed in 63,000 to 70,000 mile orbits, well above the Van Allen radiation belt

Van Allen radiation belt

The Van Allen radiation belt is a torus of energetic charged particles around Earth, which is held in place by Earth's magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is named after its discoverer, James...

s. The first Vela Hotel pair was launched on October 17, 1963, one week after the Test Ban Treaty went into effect, 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.

Instruments

The original Vela satellites were equipped with 12 external X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 detectors and 18 internal neutron

Neutron

The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...

 and gamma-ray detectors. They were equipped with solar panel

Photovoltaic module

A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

s generating 90 watts.

The Advanced Vela satellites were additionally equipped with two non-imaging silicon

Silicon

Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 photodiode

Photodiode

A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area 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

Meteoroid

A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...

 strike triggering a lightning

Lightning

Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

 superbolt in the Earth's atmosphere, as may have occurred in the Vela Incident

Vela Incident

The Vela Incident was an unidentified "double flash" of light that was detected by an American Vela Hotel satellite on September 22, 1979....

.

They were also equipped with sensors which could detect the electromagnetic pulse

Electromagnetic pulse

An electromagnetic pulse is a burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation usually results from certain types of high energy explosions, especially a nuclear explosion, or from a suddenly fluctuating magnetic field...

 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 burst

Gamma ray burst

Gamma-ray bursts are flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several minutes, although a typical...

s.

Some controversy still surrounds the Vela program since on 22 September 1979 the Vela 6911 satellite detected the characteristic double flash of an atmospheric nuclear explosion. Still unsatisfactorily explained, this event has become known as the Vela Incident

Vela Incident

The Vela Incident was an unidentified "double flash" of light that was detected by an American Vela Hotel satellite on September 22, 1979....

. The now-declassified report of the scientific panel appointed to evaluate the event concluded that it was "probably not from a nuclear explosion."

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. In front of each crystal was a slat collimator providing a full width at half maximum (FWHM) aperture of ~6.1 x 6.1 degrees. The effective detector area was ~26 cm². The detectors scanned a great circle every 60 s, and covered the whole sky every 56 hr. Sensitivity to celestial sources was severely limited by the high intrinsic detector background, equivalent to about 80% of the signal from the Crab Nebula

Crab Nebula

The Crab Nebula  is a supernova remnant and pulsar wind nebula in the constellation of Taurus...

, one of the brightest sources in the sky at these wavelengths.

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 2 good candidates were found, GB720514 and GB740723. The X-ray detectors failed on Vela 6A on 12 March 1972 and on Vela 6B on 27 January 1972.

Role of Vela in discovering Gamma Ray Bursts (GRBs)

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. Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos Scientific Laboratory, led by Ray Klebesadel

Ray Klebesadel

Ray Klebesadel is a scientist, now retired, who was a member of the gamma-ray astronomy group at the Los Alamos National Laboratory in New Mexico that discovered cosmic gamma-ray bursts using data from the Vela satellites, which were deployed by the United States after the Nuclear Test Ban Treaty...

, 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

Star position

Star position in the sky is defined by a pair of angles. These two angles - which refer to the celestial equator - are called declination and right ascension ....

 of sixteen bursts and definitively rule out a terrestrial or solar origin. The discovery was declassified and published in 1973 as an Astrophysical Journal

Astrophysical Journal

The Astrophysical Journal is a peer-reviewed scientific journal covering astronomy and astrophysics. It was founded in 1895 by the American astronomers George Ellery Hale and James Edward Keeler. It publishes three 500-page issues per month....

article entitled "Observations of Gamma-Ray Bursts of Cosmic Origin". This alerted the astronomical community to the existence of gamma-ray bursts (GRBs), now recognised as the most violent events in the universe.

External links

• Includes material from NASA Goddard's Remote Sensing Tutorial