In recent years there has been increasing interest in picosatellites (small satellites typically with a mass of 0.1 to 1 kilogram) which use the latest miniaturized technology to perform useful tasks in orbit. Their diminutive size and relatively low costs make them attractive to an ever larger number of users including educational institutions, small startup companies, DIY satellite builders and even the military. While most might believe that the concept of the picosatellite is a relatively new product of today’s technology, it actually got its start over half a century ago as part of a USAF satellite series known as the Tetrahedral Research Satellite or simply TRS.

Tetrahedral Research Satellite

The TRS satellite was developed by a subsidiary of TRW called the Space Technology Laboratories (STL) in Redondo Beach, CA as an inexpensive, miniaturized satellite that customers could purchase off-the-shelf to perform simple experiments in orbit. The original TRS was a regular tetrahedron (i.e. a pyramid with four equilateral triangular-shaped faces) 16.5 centimeters across on each edge with a pair of deployable, meter-long antennas providing communications with the ground. Since the TRS had no attitude control system, each face of TRS was covered with 28 solar cells that could provide a nearly constant 600 milliwatts of power regardless of the satellite’s orientation with respect to the Sun.

A solid-state analog telemetry system (in this era before integrated circuits, that would mean a “transistor-based” system) provided eight channels of data: five for experiments, one for the spacecraft temperature and a pair for telemetry calibration. In order to minimize the risk of TRS interfering with the communications of other satellites after it had completed its mission, TRS had a built-in timer that would deactivate the transmitter after approximately 90 days in orbit. With a mass of only 667 grams, TRS would be the smallest working satellite ever placed into orbit. For comparison, the Naval Research Laboratory’s solar-powered Vanguard 1 launched in March 1958 (which was the world’s first nanosatellite and the smallest launched before TRS) was a sphere 16.5 centimeters across with a mass of 1.47 kilograms (see “Vintage Micro: The Original Nanosatellite“). Excluding the costs for development, launch and mission operations, each TRS satellite was estimated to cost only $25,000 to build (that would be about $195,000 in today’s money).

STL’s first (and, as it would turn out, only) customer for TRS was the Air Force Space Systems Division (AFSSD) then headed by Col. T. O. Wear. AFSSD bought the first six TRS satellites to be used in their Environmental Research Satellite (ERS) program. These first satellites, which would be launched into orbit as piggyback payloads on larger Agena-based USAF satellites, would be used to assess the effects of radiation on the performance of solar cells and, by using specially calibrated cells, measure the radiation exposure of the satellite. Aside from modifications that were needed to make the satellite’s telemetry system compatible with NASA and USAF ground tracking stations as well as the addition of five calibrated solar cells, the satellites were essentially ready to fly. Additional satellites were constructed to meet AFSSD needs and in the end, a total of ten original TRS satellites were constructed and launched.

TRS Missions

The first TRS launch attempt used the satellite designated ERS-2. It was sent into orbit on September 17, 1962 riding as a piggyback payload on the KH-4 Number 12 of the Corona spy satellite series (codenamed “Big Flight”) launched on a Thor-Agena B from Vandenberg AFB in California. Called TRS 1, it failed to separate from the Agena B once in its 307-by-584 kilometer orbit inclined 81.8° to the equator. But according to reports at the time, TRS 1 managed to return up to 8 minutes of usable data during each favorable pass allowing measurements of the radiation that had been generated from a high altitude nuclear detonation over Johnston Island on July 9, 1962 codenamed “Starfish”. The KH-4 reentry vehicle and its payload of exposed film were returned to Earth on September 18 while TRS 1, still attached to the equipment rack on Agena 1133, continued on until its orbit decayed on November 19.

The next mission, using satellite ERS-1, hitched a ride on the Atlas-Agena B carrying the Samos 11 spy satellite launched on November 11, 1962. Once again, the TRS satellite failed to eject and it remained attached to Agena 2045. Apparently no data were received and the mission was a failure. For the next attempt, a pair of satellites would be simultaneously deployed in orbit for the first time. ERS-3 and 4 rode piggyback on the Atlas-Agena B carrying the Midas 6 experimental early warning satellite launched on December 17, 1962 from Vandenberg AFB. Unfortunately the Atlas veered off course 80 seconds into the flight and was destroyed by range safety along with its payload.

The next attempt, using ERS-5 and 6, was made on May 9, 1963 with the launch of Midas 7 from Vandenberg AFB. These TRS satellites carried a total of 20 test solar cells that were unshielded or fitted with either 0.5 or 1.0 millimeter thick fused quartz covers to assess their ability to shield solar cells from radiation damage. This time TRS 2 and 3, as they were called, were successfully ejected into their own 1,400-kilometer high orbits inclined about 87° to the equator becoming the first picosatellites in orbit as well as the first pair of piggyback satellites to be simultaneously deployed in orbit. The pair of satellites successfully completed their missions returning useful data on solar cell degradation and radiation exposure in high Earth orbit.

A subsequent pair of satellites, ERS-7 and 8, were launched on June 12, 1963 as a piggyback payload on Midas 9 but were both lost due to another Atlas-Agena B launch failure. The last pair of TRS satellites, ERS-9 and 10, carried five sets of test solar cells that were either unshielded or fitted with 0.15, 0.5 or 1.5 millimeter thick shields. They were launched as piggyback payloads on Midas 9 on July 19 but only ERS-9 was successfully deployed to become TRS 4. It returned 112 days worth of radiation exposure data from its 3,662-by-3,731-kilometer orbit that correlated well with the results of the previous TRS missions

TRS Mk. II

After the first ten TRS satellites were built, a larger version called TRS Mk. II with a mass of 2.0 kilograms (now a small nanosatellite) was designed and built by STL to accommodate larger payloads for the AFSSD. Each edge of the tetrahedron on the TRS Mk. II was now 23 centimeters across with a total of 256 solar cells providing 1.2 watts of power. These satellites, which now had a nominal one-year lifetime, carried an omnidirectional radiation detector to measure electrons in the 0.5 to 5 MeV energy range and protons in either the 10 to 20 MeV or 50 to 100 MeV range. Four of these satellites were built but only two were apparently launched.

The first TRS Mk. II, designated ERS-12, was launched on an Atlas-Agena D from Cape Canaveral in Florida on November 17, 1963 as a piggyback payload with the Vela 1 and 2 satellites. The Vela satellites were fitted with X-ray, gamma ray and neutron detectors designed to monitor compliance with the 1963 Nuclear Test Ban Treaty that limited nuclear tests to underground detonations. The Vela satellites could detect the distinctive radiation signature of any nuclear detonation above the ground or in space. The new TRS Mk. II satellite was successfully deployed into a 208-by-103,600-kilometer orbit inclined 37° to the equator to become TRS 5. TRS 5 successfully returned two weeks worth of radiation data. The final launch in the TRS series, ERS-13, was on July 17, 1964 as a piggyback payload with Vela 3 and 4. TRS 6, as it was called, was successfully deployed and made additional measurements of electron and proton radiation levels in the magnetosphere.

The USAF would continue the ERS program with still larger satellites of various designs over the next five years. But the original three TRS Mk. I satellites that were successfully deployed in 1963 remained the smallest satellites (and only picosatellites) to be orbited for decades to come and be the forerunners of the much more capable picosatellites of today.

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Related Reading

“Vintage Micro: The Original Nanosatellite”, Drew Ex Machina, February 5, 2015 [Post]

“Vintage Micro: The First ELINT Satellites””, Drew Ex Machina, September 30, 2014 [Post]

“The Discoverer Missions: America’s Original (Secret) Satellite Program”, Drew Ex Machina, April 13, 2019 [Post]

General References

Jos Heyman, “ERS”, Directory of U.S. Military Rockets and Missiles Appendix 3: Space Vehicles, last updated 12 April 2005 [Link]

Gunter Dirk Krebs, “TRS Mk. 1 (ERS)”, Gunter’s Space Page, last updated 30 March 2014 [Link]

Gunter Dirk Krebs, “TRS Mk. 2 (ERS)”, Gunter’s Space Page, last updated 26 March 2014 [Link]

Curtis Peebles, The Corona Program: America’s First Spy Satellites, Naval Institute Press, 1997

“TRS 1”, STL Spacelog, Vol. 2, No. 4, p. 45, December 1962

“Six-Inch Satellite”, Flight International, p 172, 31 January 1963

“TRS 2 and 3”, Spacelog, Vol. 3, No. 4, pp. 31-32, December 1963

“TRS 4” and “TRS 5”, Spacelog, Vol. 4, No. 2, pp. 6-8, Summer 1964