OSO 7 or Orbiting Solar Observatory 7 (NSSDC ID: 1971-083A), before launch known as OSO H is the seventh in the series of American
Orbiting Solar Observatory
The Orbiting Solar Observatory (abbreviated OSO) Program was the name of a series of American space telescopes primarily intended to study the Sun, though they also included important non-solar experiments. Eight were launched successfully into ...
satellites launched by NASA between 1962 and 1975. OSO 7 was launched from Cape Kennedy (now Cape Canaveral) on 29 September 1971 by a
Delta N
The Delta N or Thor-Delta N was an American expendable launch system used for nine orbital launches between 1968 and 1972. It was a member of the Delta family of rockets, and the last Delta to be given an alphabetical designation - subsequent roc ...
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
Ball Aerospace & Technologies Corp. is an American manufacturer of spacecraft, components and instruments for national defense, civil space and commercial space applications. The company is a wholly owned subsidiary of Ball Corporation (NYSE: BAL ...
(BBRC), now known as
Ball Aerospace
Ball Aerospace & Technologies Corp. is an American manufacturer of spacecraft, components and instruments for national defense, civil space and commercial space applications. The company is a wholly owned subsidiary of Ball Corporation (NYSE: BAL ...
, in Boulder Colorado.
While the basic design of all the OSO satellites was similar, the OSO 7 was larger
otal 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
OSO series satellites, carried two instruments on OSO 7, which continuously viewed the Sun during orbit day.
These were:
* The
GSFC
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
X-Ray and EUV Spectroheliograph (covering the wavelength range 2 to 400
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
corona
Corona (from the Latin for 'crown') most commonly refers to:
* Stellar corona, the outer atmosphere of the Sun or another star
* Corona (beer), a Mexican beer
* Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
above active regions and during solar flares.
* The
NRL
The National Rugby League (NRL) is an Australasian rugby league club competition which contains clubs from New South Wales, Queensland, Victoria, the Australian Capital Territory and New Zealand. The NRL formed in 1998 as a joint partnership ...
White-Light
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view ...
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 seconds.
Two of these were solar-observing instruments, and the other two were cosmic X-ray instruments:
*
UCSD
The University of California, San Diego (UC San Diego or colloquially, UCSD) is a public university, public Land-grant university, land-grant research university in San Diego, California. Established in 1960 near the pre-existing Scripps Insti ...
Hard Solar X-Ray Monitoring instrument, P.I. Prof.
Laurence E. Peterson. covered the 2–300
keV Kev can refer to:
Given name
* Kev Adams, French comedian, actor, screenwriter and film producer born Kevin Smadja in 1991
* Kevin Kev Carmody (born 1946), Indigenous Australian singer-songwriter
* Kev Coghlan (born 1988), Scottish Grand Prix moto ...
energy range using proportional counter and NaI scintillator detectors, plus three small charged-particle detectors for monitoring the local radiation environment.
*
UNH Solar Gamma-Ray Monitor. P.I. Prof. Edward Chupp, observed 0.3–10
MeV
In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacu ...
solar flare
A solar flare is an intense localized eruption of electromagnetic radiation in the Sun's atmosphere. Flares occur in active regions and are often, but not always, accompanied by coronal mass ejections, solar particle events, and other solar phe ...
gamma rays with a NaI(Tl) scintillation
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
in a CsI(Na) active
anti-coincidence shield.
*
MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
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 (
FWHM
In a distribution, full width at half maximum (FWHM) is the difference between the two values of the independent variable at which the dependent variable is equal to half of its maximum value. In other words, it is the width of a spectrum curve me ...
) about 6°, looked out perpendicular to the Wheel spin axis, sweeping a great circle on the sky every 2 seconds. 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 cm
2 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 maximal rate of 3.2 per second.
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
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
(γ)
line emission, due to electron/positron annihilation at 511 keV, from solar flares in early
August 1972
August 1972 was the eight month of that leap year. It began on a Tuesday and ended after 31 days on a Thursday.
The following events occurred in August 1972:
August 1, 1972 (Tuesday)
*"Bug Suspect Got Campaign Funds", the first article in the f ...
, by the UNH spectrometer.
Long legendary in NASA due to the hazard to human spaceflight, it would have incurred a potentially fatal radiation dose had astronauts been in space at time and outside the Earth's protective
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
(as is the case during much of a lunar Apollo mission).
* The
first clear detection of a
coronal mass ejection (CME), by the NRL instrument.
* Observations of the hard X-ray spectra of the
AGN NGC 4151
NGC 4151 is an intermediate spiral Seyfert galaxy with weak inner ring structure located from Earth in the constellation Canes Venatici. The galaxy was first mentioned by William Herschel on March 17, 1787; it was one of the six Seyfert galax ...
and
Cen A
Cen or CEN may refer to:
People and language
* Cen language
* Cen (rune) (ᚳ), a rune of the Anglo-Saxon fuþorc
* Cen (surname) (岑), a Chinese second name
Acronym
* Certified Emergency Nurse
* Childhood emotional neglect
* Cambridge Even ...
* 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 seconds prior to second-stage engine cutoff. 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 command ability. 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 belts, so that bombardment by high energy
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s made it somewhat radioactive. The activity then decayed slowly during other times of the day. The complexly varying instrument internal radioactivity 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 U.S. Air Force, modified and re-instrumented, and then launched in 1979 as
P78-1
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's mission was extended by several weeks, so that it operated until it was destroyed ...
(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.
OSO 8, with image showing differences from OSO 7 and P78-1
/ref>
References
External links
''The content of this article was adapted and expanded from NASA's HEASARC: Observatories OSO
and NASA's National Space Science Data Center: OSO
(Public Domain)''
{{DEFAULTSORT:Oso 7
Satellites orbiting Earth
Spacecraft launched in 1971
Spacecraft which reentered in 1974