For Friday’s launch, the Polar Satellite Launch Vehicle – flight number PSLV C40 – flew in its PSLV-XL configuration. This is the same configuration that was used for the unsuccessful launch last August. PSLV is a four-stage rocket, using a mixture of solid and liquid-fuelled stages. The rocket’s first stage, or PS1, consists of an S-138 solid rocket motor which ignited when Friday’s countdown reached zero. Six PS0M-XL boosters provide additional thrust during the early stages of flight, each using an S-12 solid rocket motor. Four of these motors are ground-lit, igniting 0.42 and 0.62 seconds after the first stage. The remaining two boosters ignite twenty-five seconds into the flight.
The first pair of ground-lit boosters separated from the PSLV 69.9 seconds after liftoff, with the second pair separating two-tenths of a second later. The air-lit boosters continued to burn, before they were jettisoned at 92 seconds mission elapsed time. The first stage continued to burn for the first 108.62 seconds of the flight, at which point the stage separated. Second stage ignition occurred two-tenths of a second after staging.
The liquid-fuelled second stage, designated PS2 or L-40, is powered by a Vikas engine – a license-built version of the French Viking rocket engine which powered earlier versions of the Ariane rocket. Vikas burns UH25 propellant – a mixture consisting of three parts unsymmetrical dimethylhydrazine to one-part hydrazine hydrate – which is oxidized by dinitrogen tetroxide. The second stage burned for two minutes and 32.52 seconds.
It is during second-stage flight, about 42.9 after the Vikas engine ignited, that the payload fairing – also known as the heat shield – separated from the rocket. This event occurred at an altitude of 115.63 kilometers (71.85 miles, 62.44 nautical miles), with the rocket clear of the dense lower regions of Earth’s atmosphere, from which the fairing protects its payload. This is the point at which August’s launch failed, as part of the separation mechanism did not pressurize as expected and the two halves of the fairing remained attached to the rocket.
At the end of the second stage burn, the spent stage was jettisoned. The third stage – or PS3 – ignited 1.2 seconds later and burned for about 70 seconds. This is another solid-fuelled stage, consisting of an S-7 motor. After this stage burned out, the vehicle continued to coast until eight minutes and 11.72 seconds mission elapsed time, when the third and fourth stages separated. The fourth stage ignited ten seconds after staging.
Designated PS4, or L-2.5, the PSLV’s fourth stage is a restartable liquid-fuelled stage capable of inserting its payloads into precise orbits. Its twin engines burn monomethylhydrazine, oxidised by mixed oxides of nitrogen (MON). The first burn lasted eight minutes and 15.08 seconds, establishing an initial deployment orbit for Cartosat-2F. The primary payload separated forty-two seconds after the burn concluded.
Most of the secondary payloads separated into the same orbit as Cartosat-2F. Fifteen seconds after Cartosat has separated, the upper section of the PSLV’s dual launch adaptor, or DLA-U, was jettisoned. LEO-2 was deployed after a further fifteen seconds with ICEYE-X1 following 0.22 seconds later. Beginning 87.78 seconds after ICEYE-X1, Tyvak-61C, Carbonite-2, INS-1C and CICERO-7 were deployed at ten-second intervals. Deployment of all remaining satellites, except for ISRO’s Microsat-TD, occurred over the course of 195 seconds, starting 55 seconds after CICERO separated.
Over half an hour later, at 58 minutes, 18.24 seconds after liftoff, the PS4 stage began its second burn. This maneuver lasted 4.72 seconds, lowering the orbit’s perigee. The next burn was made 46 minutes, 35.78 seconds later, once the vehicle reached perigee, in order to reduce its apogee. This burn also lasted 4.72 seconds. The Microsat-TD satellite was released 37 seconds after the end of the third burn.
The PS4’s fourth burn, beginning 14 minutes and 32.28 seconds after Microsat separated, lasted 13.6 seconds and served to deorbit the upper stage. These latter events were later confirmed by ISRO due to the live webcast ending after the first batch of deployments.
Friday’s launch took place from the First Launch Pad (FLP) at India’s Satish Dhawan Space Centre. Formerly the Sriharikota High Altitude Range, the Satish Dhawan Space Centre is named after former ISRO chairman Satish Dhawan.
The First Launch Pad is one of two PSLV launch complexes at the site, along with the nearby Second Launch Pad (SLP). FLP was built for the PSLV, with the first launch from the pad being the PSLV’s maiden flight in 1993. Rockets are integrated vertically at the launch pad, using a mobile service tower that is retracted before launch.
Friday’s launch was India’s first of 2018, following five launches in a 2017 campaign that was truncated by the PSLV’s failure in August. ISRO’s next launch is expected to be that of the GSAT-6A communications satellite, using a Geosynchronous Satellite Launch Vehicle (GSLV) Mk.II.
The next PSLV launch will carry the IRNSS-1I navigation satellite, replacing the IRNSS-1H spacecraft lost in last year’s failure which was itself a replacement for the IRNSS-1A satellite that had malfunctioned on orbit. No dates for either of these two launches have been announced.