OSO 7
Encyclopedia
OSO 7 is the seventh in the series of American Orbiting Solar Observatory
satellites launched by NASA between 1962 and 1975. OSO 7 was launched from Cape Canaveral on 29 September 1971 by a Delta N rocket into a 33.1° inclination, low-Earth (initially 321 by 572 km) orbit, and re-entered the Earth's atmosphere on 9 July 1974.
It was built by the Ball Brothers Research Corporation (BBRC), now known as Ball Aerospace
, in Boulder Colorado.
While the basic design of all the OSO satellites was similar, the OSO 7 was larger [total spacecraft mass was 635 kg (1397 lb)] than the OSO 1 through OSO 6, with a larger squared-off solar array in the non-rotating "Sail", and a deeper rotating section, the "Wheel".
series satellites, carried two instruments on OSO 7, which continuously viewed the Sun during orbit day.
These were:
Two of these were solar observing instruments, and the other two were cosmic X-ray instruments:
. The nominal plan was for the spacecraft to be separated from the second stage with the spin axis normal to the Sun direction, so that the sail could be oriented to the Sun, allowing the batteries to be fully charged on orbit. As it was, the orbit was slightly eccentric instead of circular, and the orientation of the spacecraft immediately after launch was unknown, so that the sail could not acquire Sun lock. The spacecraft was launched with its batteries fully charged, giving approximately 12 hours for the controllers, directed by NASA's John Thole, to recover before the spacecraft lost power and commandability. Several hours passed as engineers attempted to interpret the signal strength from the tumbling spacecraft in terms of its transmitting antenna pattern. Finally, an hour or two before the end, Thole decided to abandon caution and "start slewing", and by luck and skill control was regained.
Because the resulting orbital apogee was ~572 km instead of the planned ~350 km for the nominal circular orbit, several times each day OSO 7 passed fairly deeply into the Van Allen radiation belt
s, so that bombardment by high energy proton
s made it somewhat radioactive. The activity then decayed slowly during other times of the day. The complexly varying instrument internal radioactivity interestingly complicated the analysis of data from the sensitive X-ray and gamma-ray instruments on board.
(also known as Solwind), the satellite which was shot down by the USAF in a successful anti-satellite missile test in 1985. OSO 7 and P78-1 were not identical in appearance, but more similar to each other than either were to the earlier OSO 1 through OSO 6 spacecraft, or to the final OSO 8.
The content of this article was adapted and expanded from NASA's HEASARC: Observatories OSO 7 http://heasarc.nasa.gov/docs/heasarc/missions/oso7.html and NASA's National Space Science Data Center: OSO 7 http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1971-083A (Public Domain)
Orbiting Solar Observatory
The Orbiting Solar Observatory Program was the name of a series of nine American science satellites primarily intended to study the Sun, though they also included important non-solar experiments. Eight were launched successfully by NASA between 1962 and 1975 using Delta rockets...
satellites launched by NASA between 1962 and 1975. OSO 7 was launched from Cape Canaveral on 29 September 1971 by a Delta N rocket into a 33.1° inclination, low-Earth (initially 321 by 572 km) orbit, and re-entered the Earth's atmosphere on 9 July 1974.
It was built by the Ball Brothers Research Corporation (BBRC), now known as Ball Aerospace
Ball Aerospace
Ball Aerospace & Technologies Corp. is a manufacturer of spacecraft, components, and instruments for national defense, civil space and commercial space applications. The company is a wholly owned subsidiary of Ball Corp...
, in Boulder Colorado.
While the basic design of all the OSO satellites was similar, the OSO 7 was larger [total spacecraft mass was 635 kg (1397 lb)] than the OSO 1 through OSO 6, with a larger squared-off solar array in the non-rotating "Sail", and a deeper rotating section, the "Wheel".
Sail instruments
The "Sail" portion of the spacecraft, which was stabilized to face the Sun in all the OSOOrbiting Solar Observatory
The Orbiting Solar Observatory Program was the name of a series of nine American science satellites primarily intended to study the Sun, though they also included important non-solar experiments. Eight were launched successfully by NASA between 1962 and 1975 using Delta rockets...
series satellites, carried two instruments on OSO 7, which continuously viewed the Sun during orbit day.
These were:
- The GSFC X-Ray and EUV Spectroheliograph (covering the wavelength range 2 to 400 ÅÅngströmThe angstrom or ångström, is a unit of length equal to 1/10,000,000,000 of a meter . Its symbol is the Swedish letter Å....
), under the direction of P.I. Dr. Werner M. Neupert of the NASA GSFC which imaged the Sun in the Extreme Ultraviolet and soft X-ray bands, to determine the temperature and distribution of matter in the coronaCoronaA corona is a type of plasma "atmosphere" of the Sun or other celestial body, extending millions of kilometers into space, most easily seen during a total solar eclipse, but also observable in a coronagraph...
above active regions and during solar flares.
- The NRLUnited States Naval Research LaboratoryThe United States Naval Research Laboratory is the corporate research laboratory for the United States Navy and the United States Marine Corps and conducts a program of scientific research and development. NRL opened in 1923 at the instigation of Thomas Edison...
White-Light Coronagraph and Extreme Ultraviolet Corona Experiment, directed by Dr. Richard Tousey of the US Naval Research Laboratory, which imaged the while light corona, using an occulting disk, allowing comparison between the structure of the corona and the active regions on the solar surface.
Wheel instruments
The rotating, "Wheel", component of the spacecraft, which provided overall gyroscopic stability to the satellite, carried four instruments which looked radially outwards, and scanned across the Sun every 2 sec.Two of these were solar observing instruments, and the other two were cosmic X-ray instruments:
- UCSD Hard Solar X-Ray Monitoring instrument, P.I. Prof. Laurence E. Peterson. covered the 2—300 keVKevKev can refer to:*Kev Hawkins, a fictional character.*Kevin, a given name occasionally shortened to "Kev".*Kiloelectronvolt, a unit of energy who symbol is "KeV".* Krefelder Eislauf-VereinKEV can refer to:...
energy range using proportional counter and NaI scintillator detectors, plus three small charged particle detectors for monitoring the local radiation environment.
- UNHUniversity of New HampshireThe University of New Hampshire is a public university in the University System of New Hampshire , United States. The main campus is in Durham, New Hampshire. An additional campus is located in Manchester. With over 15,000 students, UNH is the largest university in New Hampshire. The university is...
Solar Gamma-Ray Monitor. P.I. Prof. Edward Chupp., observed 0.3—10 MeVMEVMeV and meV are multiples and submultiples of the electron volt unit referring to 1,000,000 eV and 0.001 eV, respectively.Mev or MEV may refer to:In entertainment:* Musica Elettronica Viva, an Italian musical group...
solar flareSolar flareA solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...
gamma rays with a NaI(Tl) scintillation spectrometer in a CsI(Na) active anti-coincidence shield.
- MIT Cosmic X-Ray Experiment, P.I. Prof. George W. Clarke, observed cosmic X-ray sources in the range 1.5 to 9 Å. This instrument used proportional counters to observe cosmic X-ray sources in the 1 to 60 keV range, in five broad logarithmically-spaced energy bands, with about 1° angular resolution.
- UCSD Cosmic X-ray Experiment, P.I. Prof. Laurence E. Peterson. This instrument, which had a field-of-view (FWHMFull width at half maximumFull width at half maximum is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value....
) of about 6°, looked out perpendicular to the Wheel spin axis, sweeping a great circle on the sky every 2 sec. As the Wheel spin axis moved to keep the Sail instruments pointed at the Sun, it scanned the whole sky every 6 months. It featured a 1 cm thick NaI(Tl) scintillation detector that covered the energy range from ~7 keV to ~500 keV in 126 PHA channels, with an effective area of 100 cm2 at the lower energies. The detector was enclosed in a thick CsI(Na) anti-coincidence scintillation shield with 10 holes bored through it which defined the optical field of view of the detector. Events were individually recorded and telemetered, with time and pulse height tagged for each, at a maximum rate of 3.2 per sec.
Scientific results
Among the notable scientific results from OSO 7 were:- All-sky hard X-ray surveys by the MIT and UCSD cosmic instruments.
- The first observation of solar gamma-ray line emission, due to electron/positron annihilation at 511 keV, from a solar flare in April 1972, by the UNH spectrometer.
- Observations of the hard X-ray spectra of the AGNActive galactic nucleusAn active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...
NGC 4151NGC 4151NGC 4151 is an intermediate spiral Seyfert galaxy located 43 million light years from Earth in the constellation Canes Venatici, discovered by Frederick William Herschel on March 17, 1787...
and Cen A - Position and spectral variability of the 14 May 1972 cosmic gamma-ray burst
Near loss at launch
The OSO 7 was nearly lost at launch, due to a loss of hydraulic pressure in the second-stage guidance control system ~7 sec prior to SECOSeco
Seco may refer to:* Seco, Kentucky, a small town in the United States* Seco Herrerano, the national alcoholic beverage of Panamá* Seco Rail, a French railway company* Figueira Seco, a village on Maio in the Republic of Cape Verde...
. The nominal plan was for the spacecraft to be separated from the second stage with the spin axis normal to the Sun direction, so that the sail could be oriented to the Sun, allowing the batteries to be fully charged on orbit. As it was, the orbit was slightly eccentric instead of circular, and the orientation of the spacecraft immediately after launch was unknown, so that the sail could not acquire Sun lock. The spacecraft was launched with its batteries fully charged, giving approximately 12 hours for the controllers, directed by NASA's John Thole, to recover before the spacecraft lost power and commandability. Several hours passed as engineers attempted to interpret the signal strength from the tumbling spacecraft in terms of its transmitting antenna pattern. Finally, an hour or two before the end, Thole decided to abandon caution and "start slewing", and by luck and skill control was regained.
Because the resulting orbital apogee was ~572 km instead of the planned ~350 km for the nominal circular orbit, several times each day OSO 7 passed fairly deeply into 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, so that bombardment by high energy proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s made it somewhat radioactive. The activity then decayed slowly during other times of the day. The complexly varying instrument internal radioactivity interestingly complicated the analysis of data from the sensitive X-ray and gamma-ray instruments on board.
P78-1
The flight spare for OSO H was later acquired by the US Air Force, modified and re-instrumented, and then launched in 1979, to become P78-1P78-1
P78-1 or Solwind was a United States satellite launched aboard an Atlas F rocket from Vandenberg Air Force Base in California on February 24, 1979. The satellite operated until September 13, 1985, when it was shot down in orbit by an F-15 Eagle fighter aircraft during an US Air Force ASM-135 ASAT...
(also known as Solwind), the satellite which was shot down by the USAF in a successful anti-satellite missile test in 1985. OSO 7 and P78-1 were not identical in appearance, but more similar to each other than either were to the earlier OSO 1 through OSO 6 spacecraft, or to the final OSO 8.
External links
The content of this article was adapted and expanded from NASA's HEASARC: Observatories OSO 7 http://heasarc.nasa.gov/docs/heasarc/missions/oso7.html and NASA's National Space Science Data Center: OSO 7 http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=1971-083A (Public Domain)