ATS-6

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ATS-6
ATS-6 Satellite Ats-6.jpg
ATS-6 Satellite
ATS-6 satellite.
Mission type Communications
Technology
Operator NASA
COSPAR ID 1974-039A
SATCAT no. 07318
Mission duration5 years
Spacecraft properties
Bus ATS-6 Bus
Manufacturer Fairchild Aircraft
Launch mass930.0 kilograms (2,050.3 lb)
Power645 W
Start of mission
Launch dateMay 30, 1974, 23:37:00 (1974-05-30UTC23:37Z) UTC [1]
Rocket Titan-3(23)C
Launch site Cape Canaveral LC-40
End of mission
DeactivatedJune 30, 1979 (1979-07-01)
Orbital parameters
Reference system Geocentric
Regime GSO
Semi-major axis 41,691.1 kilometres (25,905.6 mi)
Perigee 35,184 kilometers (21,862 mi)
Apogee 35,444 kilometers (22,024 mi)
Inclination 13.1º
Period 1,412 minutes
 
ATS-6 during radio-frequency tests. Ats6.jpg
ATS-6 during radio-frequency tests.

ATS-6 (Applications Technology Satellite-6) [2] was a NASA experimental satellite, built by Fairchild Space and Electronics Division [3] [4] It has been called the world's first educational satellite as well as world's first experimental Direct Broadcast Satellite as part of the Satellite Instructional Television Experiment between NASA and Indian Space Research Organisation (ISRO). It was launched May 30, 1974, and decommissioned July 1979. At the time of launch, it was the most powerful telecommunication satellite in orbit. [5] ATS-6 carried no fewer than 23 different experiments, and introduced several breakthroughs. It was the first 3-axis stabilized spacecraft in geostationary orbit. It was also the first to use experimentally with some success electric propulsion in geostationary orbit. It also carried several particle physics experiments, including the first heavy ion detector in geostationary orbit.

Fairchild Industries was created from a name change from Fairchild-Hiller Corporation, division and subsidiaries: Fairchild Aircraft Marketing Company, Fairchild Aircraft Services Division, Fairchild Republic Division, Fairchild Space and Electronics Division, Fairchild Stratos Division, Burns Aero Seat Company, Inc., Fairchild Arms International, Ltd., Fairchild Aviation (Asia) Ltd., Fairchild Aviation (Holland) N.V., Fairchild-Germantown Development Company, Inc. and S.J. Industries, Inc. Prior to 1971 Fairchild Industries was a term used to include many of the companies of its founder Sherman Mills Fairchild.

Satellite Instructional Television Experiment

The Satellite Instructional Television Experiment or SITE was an experimental satellite communications project launched in India in 1975, designed jointly by NASA and the Indian Space Research Organization (ISRO). The project made available informational television programmes to rural India. The main objectives of the experiment were to educate the financially backward and academically illiterate people of India on various issues via satellite broadcasting, and also to help India gain technical experience in the field of satellite communications.

NASA space-related agency of the United States government

The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research.

Contents

During its five-year life, ATS-6 transmitted connection programming to various countries, including India, the United States and other regions. The vehicle also conducted air traffic control tests, was used to practice satellite-assisted search and rescue techniques, carried an experimental radiometer subsequently carried as a standard instrument aboard weather satellites, and pioneered direct broadcast TV.

India Country in South Asia

India, also known as the Republic of India, is a country in South Asia. It is the seventh largest country by area and with more than 1.3 billion people, it is the second most populous country as well as the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the southwest, and the Bay of Bengal on the southeast, it shares land borders with Pakistan to the west; China, Nepal, and Bhutan to the northeast; and Bangladesh and Myanmar to the east. In the Indian Ocean, India is in the vicinity of Sri Lanka and the Maldives, while its Andaman and Nicobar Islands share a maritime border with Thailand and Indonesia.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.

Air traffic control A public service provided for the purpose of maintaining the safe and orderly flow of air traffic

Air traffic control (ATC) is a service provided by ground-based air traffic controllers who direct aircraft on the ground and through controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of air traffic, and provide information and other support for pilots. In some countries, ATC plays a security or defensive role, or is operated by the military.

ATS-6 was a precursor to many technologies still in use today on geostationary spacecraft: large deployable antenna, 3-axis attitude control with slewing capabilities, antenna pointing through RF sensing, electric propulsion, meteorological radiometer in geostationary orbit, and direct to home broadcasting. It is also possible that ATS-6 was a forerunner of the large ELINT satellites such as Mentor.

Launch

ATS-6 Launch Titan III-C launches with ATS-6.jpg
ATS-6 Launch

ATS-6 was launched on May 30, 1974, by a Titan III-C launch vehicle. The spacecraft was inserted directly in the geosynchronous orbit. This reduced the on-board fuel requirements to less than 40 kg (for a total mass at launch of nearly 1400 kg). The highly accurate orbit insertion further lowered the amount of fuel required for final positioning to 9 kg. This enabled a life extension from the original 2 year to 5 years, even accounting for the premature failure of the electric propulsion subsystem (the station-keeping fuel requirement being around 1.6 kg/year).

Geosynchronous orbit Satellite orbit keeping the satellite at a fixed longitude above the equator

A geosynchronous orbit is an orbit around Earth of a satellite with an orbital period that matches Earth's rotation on its axis, which takes one sidereal day. The synchronization of rotation and orbital period means that, for an observer on Earth's surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day. Over the course of a day, the object's position in the sky traces out a path, typically in a figure-8 form, whose precise characteristics depend on the orbit's inclination and eccentricity. Satellites are typically launched in an eastward direction. A circular geosynchronous orbit is 35,786 km (22,236 mi) above the Earth's surface. Those closer to Earth orbit faster than Earth rotates, so from Earth, they appear to move eastward while those that orbit beyond geosynchronous distances appear to move westward.

ATS-6 inside the Space Environment Simulation Laboratory at the Johnson Space Center (JSC) during antenna deployment tests Applications Technology Satellite Testing - GPN-2000-001264.jpg
ATS-6 inside the Space Environment Simulation Laboratory at the Johnson Space Center (JSC) during antenna deployment tests

Structure, power subsystem and Antenna

One of the major innovations of ATS-6 was an in-flight deployable antenna of more than 9 m in diameter. The antenna reflector was furled during launch under the launch vehicle fairing, and was deployed in orbit much like an umbrella. The antenna reflector was built from 48 aluminum ribs, supporting a metallized Dacron mesh. The antenna feeds (in C, S, L, UHF and VHF bands) were placed on the spacecraft body, facing the antenna reflector, and linked to the antenna and the solar panels masts by a carbon-fiber reinforced plastic (CFRP) truss. The solar panels were rigidly mounted on two deployable masts. They were of hemi-cylinder shape, thus providing a relatively constant power (595 W beginning of life). Electric power was supplied during eclipses by two Nickel cadmium batteries of 15-A·h capacity, powering a regulated 30.5-V bus. The satellite dimensions in orbit were 15.8-m width by 8.2-m height.

Eclipse astronomical event where one body hides another

An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. Apart from syzygy, the term eclipse is also used when a spacecraft reaches a position where it can observe two celestial bodies so aligned. An eclipse is the result of either an occultation or a transit.

This deployable antenna parabola was designed and developed by Lockheed Missiles and Space Company (LMSC), now Lockheed Martin, under subcontract to Fairchild Aerospace, after several years of small study contracts at LMSC. The program manager at LMSC was GKC (Colin) Campbell. The deployment of the reflector was initiated by pyrotechnically operated SQUIB cable cutters. Deployment time was on the order of 2.5 seconds producing 2500 Ft Lbs of torque at the spacecraft interface. The reflector surface was designed for optimal operation at S-Band frequencies.[ citation needed ] It weighed 182 lbs at launch and stowed into a toroidal volume (doughnut shaped) approximately 6 feet in diameter and 10 inches thick. Three models were fabricated, the STM or structural test model, the F reflector and the G reflector. The STM was destroyed by Fairchild shortly after the program was finished and the F model was launched with the spacecraft in 1972. The G model sat unprotected in the Farchild parking lot for several years before it was donated to the Smithsonian.[ citation needed ] Bill Wade, the assistant program manager and test manager on the program supported The Smithsonian in the restoration by providing a complete set of drawings and specifications and visited the Silver Hill facility to provide technical guidance.[ citation needed ]

At the time of launch it was the largest parabolic surface launched into orbit.[ citation needed ]

Three-axis stabilisation

ATS-6 has been the first geostationary satellite with three-axis stabilization and pointing., [6] This subsystem was capable of a highly accurate pointing (better than 0.1° through the inertial measurement units, down to 0.002° by using a radio-frequency interferometer. [7] ). Furthermore, the satellite was able to follow low earth orbit satellites through slewing, [8] by tracking the low earth-orbit satellite through an S-band RF sensing. The system was also able to perform orbitography of the tracked satellite, and was a precursor to the operational system TDRSS. This highly advanced (for the time) pointing subsystem used earth and sun sensors, a star tracker pointed to the pole star, Polaris, and three inertial sensors. The sensor measurements were fed to two digital computers (nominal and redundant), as well to a back-up analog computer. It was also possible to orient the satellite by using radio-frequency sensors. Actuators were three momentum wheels, and hot gas (hydrazine mono-propellant) thrusters. One of the momentum wheels having failed in July 1975, an alternative scheme was developed, allowing station-keeping with the two remaining wheels and thrusters.

Radiometer

A radiometer was on board ATS-6, mounted on the earth-facing panel. [9] This instrument was (for the time) of very high resolution. It operated on two channels: infra-red (10.5 to 12.5 µm) and visible light (0.55 to 0.75 µm). Images taken with the radiometer covered the whole earth disk, with a resolution of 1,200 lines of 2,400 pixels each (11 km square pixel in infra-red, and 5.5 km square in visible light). The IR detector was passively cooled at 115K, and the visible light detector maintained at 300K. A complete image of earth's disk was transmitted to ground every 25 minutes. Several hundreds images were taken and transmitted, until a mechanical component of the radiometer failed, two and a half months after launch.

Telecommunication experiments

Zone covered by the SITE Experiment SITE-map-locations.svg
Zone covered by the SITE Experiment

The main mission of ATS-6 was to demonstrate the feasibility of direct-to-home (DTH) television broadcasting. [10] To this end, in addition to the high-gain antenna, the spacecraft payload was able to receive in any of the VHF, C, S and L-bands, and to transmit in S-band (2 GHz) through a 20-W solid state transmitter, in L-band (1650 MHz) at 40W, in UHF (860 MHz) at 80W (which was used for the Satellite Instructional Television Experiment (SITE)), and with a TWTA-based transmitter of 20 W in C-band (4 GHz). The antenna produced two spots on earth of 400,000 km² each, in which the TV broadcast could be received with 3 meters diameter antennas. This payload was first used over the United States for tele-education and tele-medicine experiments, from August 1974 to May 1975 as part of the HET, or Health, Education, Telecommunications experiment developed jointly by NASA and the US Department of Health, Education, & Welfare (now DHHS). The spacecraft was then moved over the geo-stationary arc from 94 °W to 35 °E, in collaboration with the Indian Space Agency (ISRO), who had deployed in India more than 2500 receive ground stations. A tele-education programme was started – Satellite Instructional Television Experiment or SITE [11] – and run for one year. During the experiment, a receive station was offered by the Indian Government to Arthur C. Clarke, who was living in Sri Lanka. This experiment was highly successful, and encouraged ISRO to start building an operational program, with the Indian spacecraft INSAT IB (launched 1983). After the SITE experiment, the satellite was brought back over the United States, and served notably as a data-relay and tracking satellite for low-orbit spacecraft such as Nimbus 6, and for the Apollo-Soyuz flight.

Electric propulsion

ATS-6 was equipped with two electric thrusters based on the acceleration of cesium ions, that were to be used for North-South Station Keeping. [12] This subsystem development followed earlier failed attempts on the previous ATS spacecraft. Each of the thrusters had a mass of 16 kg, used 150 W of electric power, and produced a thrust of 4 mN, with a specific impulse of 2500s. The on-board supply of cesium would have been sufficient for 4400 hours of thrust. Unfortunately, both thrusters failed prematurely, one after 1 hour of operation, one after 95 hours. However, some of the experiments objectives could be met, such as the measurement of the effective thrust, the absence of any interference with the radio-frequency payloads (from 150 MHz to 6 GHz), no cesium redeposition on the critical parts of the payload (such as the radiometer), and the correct neutralisation of the spacecraft versus its environment.

Particle physics experiments

Several particle physics experiments were on board ATS-6. The most significant measured low energy protons (from 25 keV to 3.6 MeV), [13] as well as detected heavy ions (up to 6 MeV). This latter experiment allowed to detect the first heavy ions (Z > 6) with an energy E > 4 MeV, in geostationary orbit.

Propagation experiments

Finally, ATS-6 embarked several beacons, [14] which allowed to measure electromagnetic propagation properties of the atmosphere at 13, 18, 20 and 30 GHz.

See also

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References

  1. McDowell, Jonathan. "Launch Log". Jonathan's Space Page. Retrieved January 24, 2014.
  2. ATS-6 Significance, R.B. Marsten IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  3. "table4.156". nasa.gov. Retrieved 22 March 2015.
  4. Glover, Daniel R. (1996). "NASA Experimental Communications Satellites, 1958-1995". Beyond the Ionosphere. NASA.
  5. http://hdl.handle.net/2060/19820008279 ATS-6 engineering performance report. Volume 6: Scientific experiments
  6. ATS-6 Spacecraft Attitude Precision Pointing & Slewing Adaptative Control Experiment, W.C. Isley; D.L. Endres IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  7. ATS-6 Interferometer, W.C. Isley; D.L. Endres IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  8. Orbit Determination Accuracies Using Satellite-to-Satellite Tracking, F.O. Vonbun; P.D. Argentiero; P.E. Schmid IEEE transactions on Aerospace & Electronic Systems vol.AES-14 N°6
  9. ATS-6 The Very High Resolution Radiometer, W.E. Shenk; C.C Stephanides; G.E. Sonnek; L.D. Howell IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  10. A Dream Come True: Satellite Broadcasting, R. Marsten IEEE transactions on Aerospace & Electronic Systems vol.33 N°1
  11. ATS-6 Satellite Instructional Television Experiment J.E. Miller, IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  12. ATS-6 Cesium Bombardment engine North South Station Keeping Experiment, R.M. Worlock; E. James; R.E. Hunter; R.O. Bartlett IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  13. NOAA Low Energy Proton Experiment, T.A. Fritz; J.A. Cessna IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6
  14. ATS-6 Millimeter Wave Propagation and Communication Experiments, L.I. Ippolito IEEE transactions on Aerospace & Electronic Systems vol.AES-11 N°6