The giant leap forward

  With the successful launch of the fourth satellite, IRNSS-1D, atop a Polar Satellite Launch Vehicle (PSLV) on March 28 this year from Satish Dhawan Space Center SHAR, Sriharikota, India has reached another milestone in its space program. The PSLVs have made more launches than all of India’s other orbit-capable rockets combined. The 1,425 kg IRNSS-1D satellite was injected to an elliptical orbit of 282.52 km x 20,644 km and successfully separated from the PSLV fourth stage after the flight time of about 19 minutes 25 seconds. After injection, the solar panels of IRNSS-1D were installed automatically as ISRO’s Master Control Facility took over the charge of the satellite. It will soon be positioned in the Geosynchronous orbit at 111.75 degree East longitude with 30.5 degree inclination. IRNSS-1D is fourth in the series of seven satellites comprising of the IRNSS space segment. Its antecedents — IRNSS-1A, IRNSS-1B and IRNSS-1C — were launched by PSLV-C22, PSLV-C24 and PSLV-C26 in July 2013, April 2014 and October 2014 respectively. All the three satellites are completely functional in their designed orbital positions. The navigational system will be a regional one targeted to South Asia and will provide tracking, navigation and mapping services. Having a life span of 10 years, the satellite is powered by two solar arrays and the mission costs approximately Rs.1,400 crore. Built around ISRO’s I-1K satellite bus, the IRNSS spacecraft has a mass of 603 kg and is loaded with 822 kg propellant for orbit-raising and maneuvering. The spacecraft is powered by a pair of solar arrays, capable of generating 1.6 KW power, used to broadcast L5 and S band navigation signals. Each satellite carries C-band transponders and retroreflectors, which can be used for range calibration to determine the spacecraft’s precise position in space. The propulsion and control system of each IRNSS satellite consists of a liquid-fueled apogee motor. which produces up to 440 newtons of thrust to raise the satellite into its operational orbit and 12 reaction control thrusters for three-axis attitude control. IRNSS-1D is expected to have an operational lifespan of 10 years. The next satellite of this constellation, IRNSS-1E is all set to be launched in the coming months, thus completing the entire constellation of seven satellites.

Two solar panels of IRNSS-1D

The two solar panels of IRNSS-1D consist of Ultra Triple Junction solar cells that generate approximately 1,660 W electrical power. Sun and star sensors along with gyroscopes offer orientation reference for the satellite. Further, special thermal control schemes have been designed and implemented for critical elements such as atomic clocks. In addition, the Attitude and Orbit Control System (AOCS) of IRNSS-1D maintains the satellite’s orientation with the help of reaction wheels, magnetic torquers and thrusters. The propulsion system consists of a Liquid Apogee Motor (LAM) and thrusters. After it is injected into this preliminary orbit, the solar panels of IRNSS-1D are deployed automatically in quick succession and the Master Control Facility (MCF) at Hassan takes control of the satellite thereby performing the initial orbit raising maneuvers consisting of one maneuver at perigee (nearest point to earth) and three at apogee (farthest point to earth). Further, for these maneuvers, LAM of the satellite is used which finally places it in the circular geostationary orbit at the designated location.