Environmental Research Satellite

Content sourced from Wikipedia, licensed under CC BY-SA 3.0.

The Environmental Research Satellite (ERS) program was a group of tiny U.S. satellites made to ride along with larger missions and then operate in orbit on their own. Between 1962 and 1971, 33 ERS satellites in six series were launched. They did scientific experiments and also tested new spacecraft parts.

TRS Mk. 1 (Tetrahedral Research Satellite)
- A small tetrahedron about 16 cm on each side, with solar cells on its faces.
- It had eight data channels for experiments and telemetry, no internal battery, and a 40-inch antenna.
- Data were sent continuously at 136.771 MHz.
- Cost to build was about $25,000 (in 1960s dollars).
- The Air Force bought six for ERS; ten were made in total.
- TRS-1 was one of the smallest satellites ever placed in orbit, ran in Low Earth Orbit, and sent back eight minutes of data per orbit for up to about 90 days.
- Its purpose was to study radiation and micrometeoroid flux and to test components.

TRS Mk. 2 and Mk. 3
- Mk. 2 was an octahedron about 21 cm on a side; four were built (ERS-11 to ERS-14), but only two were launched with primary payloads.
- Mk. 3 was about 28 cm on a side; two were built (ERS-17 and ERS-18) and were attached to the Vela nuclear test monitoring satellites.
- These satellites studied charged particles and radiation in Earth’s environment, including the Van Allen belts.
- The data helped scientists understand how radiation affects spacecraft and sensors.

Other ERS series (Ors and OV5)
- ORS Mk. 2 (an octahedron) was about 23 cm wide and carried out cold welding experiments on metals. Five were produced (including ERS-15/16 and ERS-23/25), but not all flew.
- ORS Mk. 3 (28 cm octahedron) included ERS-17 and ERS-18, which rode with Vela satellites to study near‑Earth radiation, X‑rays, gamma rays, and cosmic rays. ERS-17 provided thousands of hours of data before the transmitter stopped, and ERS-18 operated longer, contributing important gamma-ray findings; ERS-18 remained in orbit for years and was still trackable in 2022.
- OV5 (Orbiting Vehicle 5) built on the ORS Mk. 3 design. Nine satellites (OV5-1 to OV5-9) were made, launched with other payloads. They added a ground-command receiver and digital telemetry. Most OV5s were built by TRW, with a few exceptions.
- TETR (Test and Training Satellite) was a classroom for Apollo program ground stations. Four satellites were made (TTR-1 to TTR-4, also ERS-30 to ERS-33). TTR-2 supported Apollo missions 8 through 13, while TETR-C failed to reach orbit.

In short, the ERS program pushed the development of very small, early “microsatellites.” They flew with larger missions, returned useful scientific data about space radiation, helped test new spacecraft technology, and even supported the Apollo era by training ground teams.