OLYMPUS

Introduction

OLYMPUS (Figure 5.1) is an ESA telecommunications satellite launched on July 12, 1989. British Aerospace was the prime contractor and Alenia Spazio's predecessor company, Selenia Spazio, was responsible for the communications payload. The OLYMPUS communications payload has four components described below.

The Television Broadcast ("TVB") Payload provides high power direct broadcast satellite (DBS) TV at 12 GHz on two 27 MHz channels, TVB1 for Italy and TVB2 for all of Europe. The Italian channel is used for High Definition TV (HDTV) experiments, including tests of a compression algorithm based on inverse cosine transforms. The initial goal for the TVB transponder output power was 220 W (59 dBW equivalent isotropic radiated power, EIRP). This was lowered to 180 W, and that figure has been achieved. Two tubes in the same transponder have failed, one immediately after launch and one after the "cold soak" discussed later.

The Communications ("COM") Payload supports 30/20 GHz point-to-point or point-to-multipoint video conferencing on two 40 MHz channels. It can also be reconfigured to provide a single 700 MHz bandwidth channel for high data rate (up to 800 Mbits/sec) transmission experiments. The COM package operates with two steerable high gain antennas and two transponders, functioning as a two-way "bent pipe in the sky" that can connect two small stations anywhere in Europe. In the basic point-to-point video-conferencing mode, the system provides two-way 8.448 Mbits/sec service.

The Specialized Service ("SS") Payload provides two 18 MHz channels or one 36 MHz channel for Ku-band business communications using "thin route" satellite-switched time division multiple access (SS-TDMA). Its antenna provides five fixed-pointing spot beams that together cover Europe. Switching and other on-board processing are by ground command; the SS payload is not autonomous.

The "PP" Payloadis a propagation package incorporating coherent beacons at 12, 20, and 30 GHz. The polarization of the 20 GHz beacon is switched at 933 Hz; this allows receiving stations to measure the full (matrix) depolarization properties of the 20 GHz channel.


Figure 5.1. The OLYMPUS Satellite (Courtesy ESA)

Operational Problems

In addition to the high-power tube problems, OLYMPUS has suffered several other failures and one long service interruption. In January 1991, the south solar panel failed, reducing available primary power to 1800 W. It is still possible to operate all payloads using the north solar array, cycling the batteries occasionally. The failure left the spacecraft in an unbalanced state that requires thruster pulsing and thus a greater expenditure of fuel for attitude control, which will further reduce life on station.

Because ground controllers used an unapproved procedure, spacecraft control was lost later in 1991, the satellite froze and went on its well known "round the world tour." During the tour the satellite was tumbling and endured a "cold soak." One array saw the sun at a 5 degree incidence angle on each tumble. This produced sufficient voltage to bring up the telemetry transmitter at each peak; a great deal of effort went into decoding the resulting bursts of telemetry data. From this information the controllers figured out how to make the command receivers respond and then get the arrays pointing toward the sun. Then the heaters were commanded to turn on in a slow, careful sequence that avoided trapping liquid in any region bounded by two solids.

Significance

OLYMPUS is an impressive demonstration of 30/20 GHz technology. ESA hopes that it will have the same influence on later communications satellites that OTS had on ECS and MARECS.

Some of the OLYMPUS effort may turn out to have been misdirected because DBS technology did not evolve in the way everyone anticipated when OLYMPUS was planned. (COMSAT Corporation's unsuccessful DBS endeavor took place at about the same time.) Besides the lack of a strong DBS market, other trends that were not anticipated include the success of low power DBS and the development of TV satellites by France and Germany.

The OLYMPUS propagation package has been extremely successful, supporting experiments by researchers all over Europe and at one U.S. site (Virginia Tech).


Published: July 1993; WTEC Hyper-Librarian