India's Polar Satellite Launch Vehicle successfully lofted the country's fourth IRNSS Navigation Satellite into orbit on Saturday, continuing a worldwide drive to launch navigation satellites.
Over the course of this week, the United States launched a new Global Positioning System Satellite while Europe launched a pair of Galileo satellites followed by this Indian Launch and an upcoming Chinese launch on Monday that will deliver China's first third-generation navigation satellite into orbit.
PSLV carrying the IRNSS-1D satellite blasted off from the Satish Dhawan Space Center at 11:49 UTC on Saturday and raced into the skies over India's East Coast on a south-easterly flight path.
Using a combination of solid-fueled stages and liquid engines, PSLV packed quite a punch at liftoff and during the initial stages of flight, lifting off under the power of its large Core Stage and six ground and air-lit Solid Rocket Boosters. The four-stage PSLV rocket performed flawlessly over its 19-minute 25-second mission, reaching the target sub-GTO orbit and releasing the IRNSS-1D satellite on its journey.
When finished, the Indian Regional Navigation Satellite System will consist of seven satellites in Geostationary and Geosynchronous orbits covering India and surrounding territories to provide India with independent access to navigation data without relying on foreign programs like GPS or Glonass.
The system is designed to be compatible with the US Global Positioning System and Europe's upcoming Galileo constellation using navigation signals in S-Band and at L5. The deployed constellation will only cover India and surrounding regions with high-accuracy services available about 1,500 Kilometers beyond the Indian territory.
Saturday's launch was preceded by a 59.5-hour countdown sequence that started at 0:19 UTC on Thursday morning and included all the necessary events to load the PSLV with propellants and prepare all systems on the launcher and the ground for the launch.
The first two days of the countdown were dedicated to tanking operations on the second and fourth stages of PSLV as well as the Roll Control Thrusters of the core stage. The first and third stage did not need to be loaded during the countdown since their solid propellants had been loaded during manufacture. PSLV combines the raw power of solid rockets with the precision of liquid-fueled engines to create a highly precise launch vehicle with significant payload capabilities in its weight-class.
Flying in its XL configuration, PSLV consists of the standard PS1 first stage that has six stretched boosters attached to it and a liquid-fueled second stage atop which sits the solid third and the dual-engine liquid-fueled fourth stage. Overall, the rocket stands 44.5 meters tall, has a diameter of 2.8 meters and a liftoff mass of 320,000 Kilograms.
Pressing into the final hours of the countdown on Saturday, teams on the pad started final close outs of the PSLV rocket and the various ground systems while the Launch Team worked on a series of testing operations on the PSLV rocket. Also, ground stations were polled for their readiness before teams committed to press into final countdown operations after looking at the day's weather forecast. The Mobile Service Tower was retracted, first to a stand-off distance of 50 meters before rolling to its launch position, 160 meters from the rocket that was fully fueled at this point. Afterwards, teams made final close-outs on PSLV and the service structure before departing the launch complex.
Throughout the countdown, teams were watching over all systems of the rocket and the payload and completed electrical tests, checkouts of the communications system, control system verifications and Flight Termination System testing. Flight computers were configured for the Terminal Countdown Sequence and the final systems check was performed less than one hour from launch. When all systems were verified in good condition, the formal authorization for launch was given and the countdown headed into its Terminal Sequence at T-12 minutes.
Heading into its Terminal Countdown Sequence, PSLV started the final steps to transition to a launch configuration. The IRNSS-1D satellite was verified to be on internal power and executing its flight program, having transitioned to flight mode in the last 20 minutes of the countdown. At T-5 minutes, the PSLV Flight Computer was transitioned to its flight mode, receiving the proper flight coefficients for the mission. Ground tracking and radar station readiness was confirmed.
Three minutes prior to launch, PSLV made its transition to battery power and started the pressurization of its second and fourth stage tanks for liftoff. At T-1 minute, the onboard Master Sequencer assumed control of the final countdown events with the Real-Time Program beginning execution at T-30 seconds.
Three seconds ahead of T-0, the hypergolic Roll Control Thrusters on the first stage ignited to be used during first stage flight to keep the roll rate of the vehicle in the appropriate corridor. When clocks hit zero, the PS1 stage was commanded to ignite. Two pairs of boosters were ignited at T+0.42 and T+0.62 seconds.
Right on time, at 11:49 UTC, the PSLV Rocket started rising from its pad, powered by its huge core stage and the four ground-lit boosters for a total launch thrust of 700,600 Kilogram-force creating an initial thrust to weight ratio of 2.2 - making for a quick initial ascent completed vertically before PSLV pitched over and rolled onto its precisely calculated course taking it to the south-east across the Indian Ocean. The rocket burned 1,600 Kilograms of propellant per second and successfully acquired its planned ascent path, sticking to a pre-programmed attitude profile for this early portion of the mission.
Powering away from the coastline and racing uphill, PSLV ignited the remaining two boosters at T+25 seconds, increasing its total thrust to 803 metric tons to accelerate on its way into orbit. Each of the six boosters measured 13.5 meters in length and one meter in diameter, burning 12,000 Kilograms of solid propellant over the course of a 50-second burn.
The ground-lit Solid Rocket Boosters concluded their burn at T+50 seconds when thrust tailed off. PSLV held the boosters for another 20 seconds to ensure a clean separation and off-shore impact of the four boosters that were jettisoned in pairs with just a 0.2-second spacing. At that point, PSLV was close to 24 Kilometers in altitude traveling nearly 1.5km/s. The two air-lit boosters tailed off 75 seconds into the flight and were separated at T+1 minute and 32 seconds at an altitude of 40 Kilometers, heading for a splashdown in the Ocean.
With all six boosters gone, the PS1 stage continued firing on its own, delivering 495,600 Kilogram-force of thrust, burning through 138 metric tons of propellant. Overall, the stage stands 20.34 meters tall with a diameter of 2.8 meters using two Roll Control Thrusters and a Secondary Injection Thrust Vector Control system for three-axis attitude control.
Thrust on PS1 began tailing off one minute and 45 seconds after launch with separation from the second stage taking place five seconds later using a series of pyrotechnic devices.
Ignition of the Vikas engine of the PS2 stage occurred less than half a second after staging that took place 56 Kilometers in altitude with the stack traveling 2.4km/s.
The second stage of the PSLV is 12.8 meters long and capable of holding 40,700 Kilograms of Unsymmetrical Dimethylhydrazine fuel and Nitrogen Tetroxide oxidizer. The Vikas 4 engine provides 81,500 Kilograms of thrust operating at a chamber pressure of 58.5 bar, consuming 278 Kilograms of propellant per second.
Three seconds after ignition of the second stage, PSLV went from flying a pre-programmed attitude profile to Closed Loop Control, processing navigation data to dynamically adjust its flight path to meet the required cutoff targets.
Three minutes and 25 seconds after launch, PSLV separated its payload fairing because the vehicle had departed the dense atmosphere, flying 113 Kilometers in altitude where aerodynamic forces are no longer a concern. Shedding the no longer needed weight of the fairing, PSLV exposed the 1,425-Kilograms IRNSS-1D satellite on its way uphill.
The second stage shut down its Vikas engine four minutes and 22 seconds into the mission followed less than a second later by the pyrotechnic separation of the second stage that fell back to Earth. Another second later, the PS3 stage ignited on a 113-second burn of its Solid Rocket Motor to increase the vehicle's speed from 5.4 to 7.7km/s. The stage has a reduced diameter of 2.02 meters, being 3.54 meters long. It is loaded with 6,700 Kilograms of HTPB based propellant and provided 24,900 Kilogram-force of thrust over the course of its burn.
Thrust on the third stage started tailing off at T+6 minutes and 16 seconds and PSLV headed into the standard Stage 3-4 Coast Phase that is designed to allow the stack to climb in altitude for the 4th stage burn and also ensures that any thrust residuals on the third stage tail off ahead of stage separation. The coast phase was five minutes and 45 seconds in duration during which the fourth stage attitude control system provided three-axis stabilization. Coasting on its south-easterly trajectory, the launcher climbed from 130 to about 180 Kilometers.
Ten minutes and nine seconds after launch, the third stage was separated using pyrotechnics and a spring loaded system. Ignition of the two L-2-5 engines of the fourth stage occurred at T+10 minutes and 19 seconds on a burn of 8 minutes and 29 seconds to boost the stack into an elliptical orbit.
In the PSLV XL configuration, the PS4 stage launches with a full fuel load of 2,000 Kilograms of Monomethylhydrazine and Mixed Oxides of Nitrogen. PS4 is 2.02 meters in diameter and 2.6 meters long and its two L-2-5 engines provide 1,490 Kilogram-force of thrust.
Measuring the achieved velocity, the fourth stage was programmed to accelerate the stack to an injection speed of 9.64km/s. Engine shutdown came just before T+19 minutes when the stack had reached an altitude of 455 Kilometers.
The mission was targeting an insertion orbit of 284 by 20,650 Kilometers at an inclination or 19.2 degrees. The achieved orbit matched very nicely with the targeted parameters, marking another very precise mission performed by the PSLV.
After fourth stage shutdown, the stack performed a quick re-orientation for release of IRNSS-1D 19.5 minutes into the flight, marking the beginning of a mission of at least ten years as one of four Geosynchronous Satellites in the IRNSS constellation.
>>>IRNSS Satellite & Constellation Overview
Once in orbit, IRNSS-1D deployed its two power-generating solar arrays, established communications with ground stations and entered a stable three-axis orientation using its reaction control system. Over a period of days, the satellite will complete initial checkouts and start orbital maneuvers. One maneuver using the Liquid Apogee Motor will be conducted at perigee to boost the apogee followed by three maneuvers that are done to raise the perigee and place the spacecraft in a Geosynchronous Orbit at 111.75 degrees East and an inclination of 30.5 degrees.
