India launches PSLV rocket with CMS-01 communications satellite

by Joseph Navin

The Indian Space Research Organisation, ISRO, has launched their second mission of 2020 using their workhorse rocket: the Polar Satellite Launch Vehicle, or PSLV. 

The mission carried the CMS-01 replacement communications satellite to orbit on Thursday, 17 December at 10:11 UTC, or 05:11 EST.  The launch occurred locally at 15:41 IST (Indian Standard Time) from the Second Launch Pad at the Satish Dhawan Space Centre on India’s east coast.

The flight was only the second — and last — from India this year as the country continues to grapple with the ongoing COVID-19 pandemic that has seen a slew of launches delayed for personnel protection.

As with the previous flight in November, the PSLV rocket launched a single primary passenger: the CMS-01 communications satellite, previously named GSAT-12R.

The mission marked the 52nd flight of the PSLV rocket, which took CMS-01 into a Geostationary Transfer Orbit, or GTO.

In order to lift the payload to its designated orbit, the PSLV rocket flew in its “XL” variant, which consisted of six side-mounted boosters — the maximum possible for the PSLV.

This was the 22nd launch of the PSLV in the “XL” configuration, the 77th mission to launch from the Satish Dhawan Space Centre, and the 42nd communications satellite for India.

GSAT-12, which CMS-01 is replacing and is reported to be closely related to, seen prior its launch in 2011. (Credit: ISRO/Arianespace)

CMS-01, once deployed to its full Geostationary orbit, or GEO, will provide Extended-C Band coverage for the Indian mainland as well as the Andaman-Nicobar and Lakshadweep islands.  The C Band ranges from 4.0 to 8.0 gigahertz and is commonly used in cordless phones, wi-fi devices, satellite communication, and surveillance and weather radar.

ISRO has not released many details about the satellite; however, it is a replacement for the aging GSAT-12 platform which launched on 15 July 2011 and was supposed to serve for seven years.

Over nine years later, its replacement has now launched.  GSAT-12 itself was a replacement for INSAT-3B.

CMS-01 is reported to have similar features to GSAT-12, with a mass of 1,410 kilograms built around an I-1K satellite bus with two deployable solar arrays capable of 1500 W power generation.

The satellite will take up position at the 83° East GEO location, directly above the Indian Ocean.


The CMS-01 mission lifted off from the same launch pad that its predecessor, GSAT-12, launched from.

The rocket and payload were rolled out from their vertical integration facility to the Second Launch Pad on 14 December for final launch preparations.

After arriving at the launch pad, crews connected the rocket’s mobile launch stand to its ground support equipment for purge and fuel operations as well as electrical/data connections for personnel at the launch and mission control center.

The 25 hour countdown began on 16 December at 09:11 UTC (14:41 IST at the launch site) and was followed 90 minutes later by the start of fueling of the fourth stage with its highly toxic propellants.

Second stage fueling started seven hours before liftoff.

Once the countdown reached T0, the first stage, known as the PS1, ignited.  This was followed in quick succession by the ignition of the four ground lit PSOMs, which are the strap-on boosters.

The first two PSOMs ignited 0.42 seconds after the PS1 booster, and the third and fourth PSOMs lit 0.62 seconds after the first stage.

At T+25 seconds, the two air-lit PSOMs were ignited.  All six PSOMs carried 12.4 tonnes of propellant called Hydroxyl-terminated polybutadiene, or HTPB.  This is the same solid propellant used in the PS1 core booster.

Between T+1 minute 9 seconds and T+1 min 10 seconds, the four ground-lit PSOMs separated in a staggered sequence.  This was followed by the separation of the two air-lit PSOMs at T+1 minute 32 seconds. 

At T+ 1 minute 49 seconds, the PS1 core booster burned out, and the rocket separated the first and second stages.  At this point, the vehicle had a velocity of 2,401.5 m/s.

After staging, the single Vikas engine on the PS2 second stage ignited. 

Unlike the solid propellant first stage, the second stage used liquid fuel to produce 803.7 kN (180,700 lbf) of thrust.  The engine ran on toxic propellants, including nitrogen tetroxide and a mixture of 75% unsymmetrical dimethylhydrazine and 25% hydrazine hydrate.

A PSLV-XL rocket launches from the Satish Dhawan Space Centre in February 2017. (Credit: ISRO)

At T+3 minutes 23 seconds, the fairings separated.  At this time, the vehicle was traveling 3,705.4 m/s.  Exactly one minute later, the second stage shut down and separated.

Ignition of the solid propellant third stage, PS3, occurred at T+4 minutes 24 seconds.  The PS3 ran on HTPB like the first stage.

The PS3 stage took the craft to a velocity of 7,722 m/s.  At this point, the rocket coasted for approximately four minutes before separating the third sage and igniting the PS4 fourth stage for the climb to Geostationary Transfer Orbit. 

The fourth stage burned for 8 minutes 35 seconds and increased the remaining vehicle’s velocity to 9,910 m/s — throwing the apogee (highest point from Earth) outward toward Geostationary orbital distance at 35,786 kilometers.

PSLV, however, purposefully left the satellite not quite in true Geostationary Orbit, dropping it off in a 283 x 20,653 km sub-Geostationary Transfer Orbit.

After the fourth stage shut down, the CMS-01 satellite separated at T+20 minutes 11 seconds, completing the rocket’s mission.

Now, the satellite will be responsible for raising its apogee and perigee up to Geostationary Orbit over the course of the following weeks.

Teams will use this time to unfurl the satellite and check out its systems while the craft arcs outward to its final orbit.

CMS-01 is intended — like the GSAT-12 platform it is replacing — to serve for at least seven years.

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