Orbital Test Satellite

OTS-2
Start date	May 11, 1978, 22:59 UTC
Launcher	Delta 3914
Launch site	Cape Canaveral LC-17
COSPAR-ID :	1978-044A
Takeoff mass	approx. 865 kg
Dimensions	2.39 m × 2.13 m (W × H)
Span in orbit	9.26 m
Manufacturer	BAe / MESH
Satellite bus	OTS / ECS
lifespan	approx. 12.5 years
Stabilization	Three-axis stabilization
operator	ESA , Eutelsat
Playback information
Transponder	6 Ku-band transponders
Transponder performance	6 × 20 W.
Bandwidth	2 × 40 MHz, 2 × 120 MHz, 2 × 5 MHz
Others
Ground stations	u. a. Fucino , Usingen
position
First position	10 ° East
Actual position	Cemetery orbit
List of geostationary satellites

Orbital Test Satellite ( OTS for short ) was a communication satellite project of the European Space Research Organization ( ESRO ), which was continued by ESA from 1975 . It served to prepare the satellite programs ECS and MARECS and pioneered the communications provider Eutelsat . The satellites were built by the MESH consortium, led by British Aerospace .

The first OTS-1 satellite was destroyed in 1977 when the launcher exploded. OTS-2 started in 1978 and was in operation for twelve and a half years, of which around five years were in regular use for communication services.

Mission objectives

OTS was intended as a demonstration and test project for the new ECS satellite platform ( European Communications Satellite ). These were ESA's first communications satellites. You should demonstrate the commercial viability of the system and try out various communications innovations. In addition to the time division multiplex method , the transmission of telephone calls, data and television programs in the Ku frequency band (11-14 GHz ), which was intended as an alternative to the increasingly congested C band , was to be tested . This also included testing the dual use of this frequency band by polarizing the carrier waves .

Mission history

On September 13, 1977 at 11:31 p.m. UTC , OTS-1 took off from Cape Canaveral AFS Launch Complex 17 . The Delta launcher exploded 52 seconds later , presumably as a result of damage to the casing of one of its two solid fuel boosters .

OTS-2 took off on May 11, 1978, 22:59 UTC, in the same configuration. After the satellite successfully completed a transfer orbit with a Perigäumshöhe had reached km 184, be promoted him Aerojet -SVM-7 - apogee in the planned geostationary orbit at 10 degrees east longitude .

In the first years of operation, OTS-2 demonstrated the use of the Ku band as planned. The communications services were marketed through the intergovernmental consortium Interim Eutelsat , founded in 1977 , the forerunner of the Eutelsat company . Among other things, the time-division multiplex method for the transmission of user data and, from 1980, video conferences as well, were tested. Antennas 2–3 meters in diameter were sufficient on the ground, which enabled mobile use. For example, OTS-2 was used as an emergency telephony system within a few hours after a fire in 1981 destroyed parts of Lyon's telephone network . Ultimately, however, the satellite was mainly used for television broadcasts. According to Encyclopedia Astronautica, the geostationary position was moved 5 ° to the west in 1982.

OTS-2 remained in commercial use at Interim Eutelsat until the end of 1983 and thus exceeded the planned minimum useful life of three years. Various maneuvers were then tried out, including the use of awning for more precise positioning without additional fuel consumption. In 1984 the satellite was put into an energy-saving and gentle resting state ( hibernation ) in order to be able to examine the aging of the systems over a longer period of time. In 1988 it went into operation again briefly and broadcast the celebrations for its 10th anniversary.

After the last useful data communication system failed at the end of 1990, the satellite was moved to a cemetery orbit above the geostationary orbit.

Satellite technology

The OT satellites were based on a bus in the shape of a hexagonal prism 2.39 meters wide and 2.13 meters high . They were stabilized with inertia wheels , hydrazine thrusters, and a biaxial gyroscope aimed at the earth . Four solar modules , each with an area of ​​1.9 m ² , each consisting of 4000 solar cells and in pairs, each formed a foldable “wing”, were used for power supply . At the start of the mission, they delivered a total of 830  watts of electrical power at 50  volts , which decreased to around 550 watts within three years. A nickel-cadmium accumulator bridged the 72-minute shadowing when the earth passed through the sun. The span of OTS-2 including the solar panels supplied by AEG-Telefunken was 9.26 meters.

The heart of the satellites was the 20 kg communication unit. It consisted of four message transponders and two “beacon” transponders , each with 20 watts of transmitting power, which were connected in pairs to three antennas. With the OTS-2, two 11.5 GHz transmitters, each with a 40 MHz bandwidth, served most of Europe and Northeast Africa via the “Eurobeam-A” antenna. Two 11.6 GHz transmitters, each with a bandwidth of 120 MHz, were focused on Western Europe via the “spot beam” antenna. In contrast to the communication systems, the beacon system was used for measurement purposes and for narrow-band data transmission. With two 11.8 GHz transmitters with 5 MHz bandwidth each and the "Eurobeam-B" antenna, it covered a wide area from Iceland to North Africa to the Middle East. According to ESA, these systems were able to transmit a total of 7200 telephone calls or eight television channels simultaneously.

OTS was the first triaxial stabilized communications satellite platform for the Ku band. For the first time, integrated microwave circuits were used in space, as well as various amplifier components developed by AEG-Telefunken.

The satellite weighed 865 kg at launch. About half of this was accounted for by the apogee engine including fuel.

Ground stations

The control ground station for the OTS program was located in the Fucino space center in Italy. It was built by AEG-Telefunken and the Italian satellite company Telespazio and was connected to the European Space Control Center (ESOC) in Darmstadt . The Deutsche Bundespost had a ground station with an 18-meter antenna built in the Usingen earth station for the OTS transmissions .

Individual evidence

1. ↑ ^{a b} Launch / Orbital information for OTS 2 in the NSSDCA Master Catalog , accessed on November 6, 2017 (English).
2. ↑ ^{a b c d e f g h i j k l} ESA Achievements (BR-250) , ESA, June 2015. Pages 70–73. (PDF)
3. ^ ^{A b} Nicolas Matte: Aerospace Law: Telecommunications Satellites. In: Recueil Des Cours, Collected Courses of the Hague Academy of International Law , Sijthoff & Noordhoff, 1981, p. 192f ( limited preview in the Google book search).
4. ↑ ^{a b c d e f} Second European test satellite (OTS-2) launched , Schweizerische Bauzeitung , 96th year, issue 32, pages 611f; August 10, 1978 (PDF)
5. ↑ ^{a b} ECS / OTS in the Encyclopedia Astronautica , accessed on November 6, 2017 (English).
6. ↑ David Harland, Ralph Lorenz: Space Systems Failures: Disasters and Rescues of Satellites, Rockets and Space Probes . Springer Science + Business Media , 2007, page 27 ( limited preview in Google book search).