ISRO Press Brief on GSLV-D1/GSAT-1

The first developmental flight of Geo-synchronous Satellite Launch Vehicle,
GSLV-D1, was successfully carried out on April 18, 2001 from SHAR Centre,
Sriharikota. The flight was primarily intended to validate the vehicle
design and evaluate flight performance parameters. This objective was met
when the experimental satellite, GSAT-1, was successfully placed in the
geo-synchronous transfer orbit as planned. For the first time, validation of
Geo-synchronous launch Mission from SHAR with associated acquisition of
signals at satellite injection and carrying out the orbit raising maneuvers
through a network of international stations, coordinated and controlled by
INSAT Master Control Facility, Hassan, has been achieved.

The preliminary analysis of the flight data indicates that GSLV has
performed well in flight validating the design and functioning of all the
vehicle subsystems in flight, the integration procedures including the safe
handling of large quantities of liquid and cryogenic propellants, the
navigation and control, the flight sequence like ignition of various stages,
separation of spent stages, the heatshield and the spacecraft, besides the
coordinated working of a network of ground stations to track and monitor the
vehicle in flight.

It may be recalled that the first attempt to launch GSLV on March 28, 2001
was aborted one second before the lift-off by the Automatic Launch
Processing System (ALS) after it detected that one of the liquid propulsion
strap-on boosters did not develop the required thrust. Based on the detailed
analysis of the data during the first three seconds of operation of the four
strap-on motors, it was established that the reason for one of the strap-on
boosters not developing the required thrust was due to a defective plumbing
in the oxidiser flow line of the engine, which had escaped detection during
testing. This resulted in reduced flow of oxidiser to the engine. The
anomalous engine was replaced with a standby engine for the relaunch on
April 18, 2001. The successful flight of GSLV-D1 has validated the analysis
and the solution adopted for the relaunch.

The GSLV flight test opportunity was also used to place an experimental
satellite, GSAT-1, in the geo-stationary orbit to prove new spacecraft
elements and conduct a few communication experiments. GSAT-1 was placed in
an orbit of 181 km perigee (nearest point to earth) and 32,051 km apogee
(farthest point to earth) with an inclination of 19.2 degree with respect to
equatorial plane. The satellite was injected with a velocity that was 99.4
percent of the intended 10.2 kilometre per second. But this minor shortfall
of 0.6 % in the overall velocity resulted in reduction of orbital apogee of
the satellite. The perigee of 181 km and inclination of 19.2 deg were close
to targeted values.

This minor deficiency in the apogee altitude was correctable and, in fact,
was corrected during the orbit manoeuvres of the satellite since such
contingencies are provided for in the mission planning. Through a series of
six orbit maneuvers conducted between April 19 and April 23, 2001, the
satellite orbit has now been raised close to near-geo-synchronous height
with an apogee of 35,665 kilometer, perigee of 33,806 kilometer and
inclination of 0.997 degree. All deployments operations like those of
antenna reflector, solar array and the solar sail have been successfully
completed. Further, the satellite has been put in 3-axis stabilisation mode
using momentum wheels.

Several new communication satellite technologies have been evaluated using
GSAT-1. These include: (i) Fast Recovery Star Sensor (FRSS) which provides
enhanced accuracies of measuring satellite orientation and for quick
earth-lock recovery in case of loss of lock, (ii) a new earth sensor using
pyro electric detectors, (iii) a new technique of using 22 Newton thrusters
in a combination of four as an alternate strategy for orbit raising, (iv) a
new technology for thermal control of satellites using heat pipes (v) new
technique of power management through charger arrays for improving the
overall efficiency of power systems and (vi) optimal orbit raising using
perigee firing strategy.

During the orbit raising operations of the satellite, consumption of
propellant was much more than planned resulting in a shortage of about 10 kg
to achieve the geo-stationary orbit. The satellite is presently in a drift
orbit with an orbital period of 23 hr 2 minutes.

In conclusion, (i) GSLV-D1 launch vehicle has fulfilled all its intended
objectives and injected the GSAT-1 spacecraft into the Geo-synchronous
transfer orbit (ii) the shortfall of 0.6% in final velocity of injection was
correctable and was corrected using satellite propulsion (iii) several new
technologies for the spacecraft have already been evaluated. The satellite
will be kept under observation for further operations.