Space Technology

   Space Technology -2001  


When India's polar Satllite Vechile (PSLV)-D3 was launched on march 21 in the year,1996 it signalled the country's entry into the exclusive club of five-hi tech powers controlled the commerical Satellite launch market.The first launch of the PSLV in september 1993, was a failure due to a defect in the guidance  software.

Indian space engineers wored hard to rectify the flaw and in october 1994, PSLV-D2 lifted off successfully from the launch pad at Sriharikota. But the PSLV-D3 launch was more than a proving flight. In that it had do demonstrate the soundness of the PSLV desing, as well as sent the Indian Remote Sensign(IRS)P-3 satellite into Orbit.The successful third lauch of the PSLV was also of great importance to the Indian space effort as a failure at this stage would have adversely affected the geostationary satellite launch vehicle (GSLV).

The GSLV uses the PSLV's first two stage combined with a ygenic third stage and four liquid engine strap-ons.

The country's earlier launch vehicles,the SLV-3 which was launched in August 1979,and  the Augmented satellite launch vehicle (ASLV) launched in march 1987,where exprimental space shorts, and were used to master launched vehicle technologies. The conservatism evident in PSLV's design stems for the failures of the first two ASLV's  and the limited launch exprience available to the Indian launch vehicle designeers let's take a closer look at thise launch vehicles which make a turning point in India's space research programme.
   The44-metre tall  PLSV has four stages :
The first stage carries 129 tonner of propellant and measure 2.8 meters in diameter. It is one of the largest solid propellant boosters in the world. Its indgenously produce motor casing is of maraging steel and the booster develops a thrust of 41500KN from Hydroxyl  Terminated poly butadiene (HTPB) fuel,Six solid propellant strap-on motors augment the first stage thrust, together producing over 660KN.
The indigenously produced Vikas engine power the PSLV's second stage.Its 725KN thrust is derived from the 37 tonnes of the liquid propellantunsymmetric Dimethyl Hydrozine-it carrier, over seven tonnes of  HTPB based sold propellant power the third stage to its 340 KN thrust. And the fourth,and the terminal stages of  PSLV has a train engine conflagration, using liquid propellant that generates a minimum thrust of 7.4KN.
   To protect the space from atomos-pheric friction the metallic bulbous heat shield of the PSLV is of isogrid construction-a method that has been tried and tested by the world's premier space agencies.The primary controls of the PSLV during fight comprise the following.The first stage's pitch and year movement are controlled by the secondary injection thrust vector control ,While roll is monitored by the Reaction control thrusters,In the second stage pitch and yaw are controlled by Engine Gimbal control  (EGC), and roll by hot gas reacting control. the corresponding control for the third stage are Flex Nozzle control and Reaction control system (RCS),and for the fourth, EGC and  RCS, the latter operting the coast phase.

 To guide the PSLV, the equipment bay has guidance system along with a Redundant Strap down Intrtial Navination System. These offer directional control to the vehicle right from the movement it lifts off till the PSLV in injected into Orbit in a three axis guided more. Tracing telemetry and command function of the PSLV are monitored by on-board instrumentation packages that comprise PCM/S-band telemetry systems and C-band transponders.There also a large number of power and signal conditioning packages.For purposes of stage separation,heat sheild separation. Jettisoning etc., the PSLV employes a host of stage auxiliary systems.

 The PSLV was designed and developed by the liquide propulsion system center the Trivandrum and the SHAR center in Sriharikota,with the Vikram Sarabhai Space center in Trivandrum as the lead center in the efforts.The vehicle navination systems were also developed by the ISRO Inertial system unit at Trivandrum. After launch, the PSLV's flight path was monitored by the ISRO Telemetry. Tracking and Command Network (ISTRAC) with the help of its station at Trivandrum, Mauritius and Shiharikota. It look hundreds of thousends of manhour's put in by tecnicians, to made the SLV programme  sucessful. Over 150 public and private sector Industries have been involed in the PSLV's febrication. These industries supplied a variety of hardware, such as light alloy structures for interstages,motor cases electronic packages, heat shields,and precision congruent radars. The Industries played a vital role even in the supply of chemicals and materials such as, for instance, producing the maraging steel and HTPB resin.
  The latest feat achieved by ISRO ahs been the successful developement of a design for a cryogenic engine. Scientist at the liquid propulsion System centre (LPSC) of the ISRO has thus facilitated and early launch of GSLV by side-stepping the controversial cryogenic entire technology transfer from Rusia.
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