With its constellation of Astra spacecraft, Société Européenne des Satellites (SES)
of Luxembourg is delivering analog as well as digital television and radio services across
Europe.
SES ordered its first Hughes HS-601 satellite,
called Astra 1C, in late 1990, after a six-month competitive bidding process. That was
followed in late 1991 by an order for a second spacecraft, Astra 1D.
The Hughes' 601 satellite was designed for the higher-power missions of the 1990s. The
model was introduced in 1987 to meet anticipated requirements for high-power,
multiple-payload satellites for such uses as direct television broadcasting to small
antennas, mobile communications, and private business networks.
The Astra satellites are similar in appearance to other 601 models, with each having a
cube-shaped body and two solar array wings oriented along its north-south axis and the
antennas located on the east-west axis.
All the satellites operate in Ku-band and use traveling-wave tube amplifiers (TWTAs)
for power. On Astra 1C and 1D, the TWTAs provide 63 Watts each;
Astra 1C ans 1D each carry 18 operating transponders and six spares.
The satellites enable SES to provide analog and digital television programs together.
Most operate at 19.2 degrees East longitude. On Astra 1C, the 18 transmission frequencies
can be selected on-orbit from 34 possibilities. On Astra 1D and 1E, the on-orbit
transmission frequency selection is increased to 66 possibilities.
The 1C and 1D satellites each measure 7.4 meters across with antennas deployed and 21
meters long from the tip of one three-panel solar array wing to the tip of the other.
These solar arrays generate a combined 3500 Watts of electrical power, backed up by a
28-cell nickel-hydrogen battery for power during eclipse.
On the spacecraft, a flight-proven bipropellant propulsion system with an integral
490-Newton (110-lbf) Marquardt liquid apogee motor and 12 thrusters provides the impulse
to achieve and maintain the orbit and attitude necessary for geosynchronous operation.
