Indian PSLV launches two British satellites

by Chris Bergin and William Graham

India’s Polar Satellite Launch Vehicle (PSLV) rocket has launched two British satellites into a 583 km Sun Synchronous Orbit on Sunday. The lofting of SSTL S1-4 and NovaSAR-1 took place from the First Launch Pad of the Satish Dhawan Space Centre with T-0 occurring at 16:37 UTC.

ISRO’s return to action is set to mark an upturn in launch activity for the Indian space agency.

“We are going to conduct 19 missions, including 10 satellites and nine launch vehicles, between September and March,” noted ISRO chairman K Siva to the Times of India ahead of this launch. “For ISRO, this will be the highest density period for launches as never before we had launched two satellites within 30 days consecutively for months. ”

To kick off that launch salvo, the PSLV was employed to launch two commercial satellites, which is a rare use for the rocket.

It was 2007 when ISRO launched its first commercial mission when a PSLV carried Italy’s astronomical satellite AGILE as the main payload. The most recent came in July of 2015 when ISRO launched its heaviest commercial mission when the PSLV-XL lofted five UK satellites with a total mass of 1,439 kg.

The PSLV – which can fly in a number of configurations, such as the XL – flew as a Core Alone variant for the first time in three years. The low payload mass to orbit requirement avoided the need for the more powerful XL rocket.

PSLV first flew in September 1993 – its maiden flight failing to deploy the IRS-1E remote sensing satellite after a guidance problem. The maiden flight is one of only two outright failures that the PSLV has suffered – the other being the loss of IRNSS-1H last August when the rocket’s payload fairing failed to separate – in forty-three launches prior to this mission.

PSLV also recorded a partial failure in 1997, placing the IRS-1D satellite into a lower-than-planned orbit after a helium leak on the fourth stage.

PSLV launches take place from ISRO’s Satish Dhawan Space Centre, located on Sriharikota Island, about seventy kilometers (45 miles) north of Chennai.

Satish Dhawan Space Centre

The center, named the Sriharikota High Altitude Range prior to 2002, has been used for all of India’s orbital launches. Two launch pads are currently used for orbital missions – the First Launch Pad is used for PSLV launches, while the Second Launch Pad also accommodates the PSLV, as well as the larger GSLV Mk.II and GSLV Mk.III.

Despite its name, the First Launch Pad is not the oldest launch complex at the Satish Dhawan Space Centre – it is a separate complex to the pads used for India’s earlier launches with the smaller SLV and ASLV rockets. When launching from the First pad, PSLV rockets are stacked vertically directly atop the launch pad, with the aid of a mobile service tower. The tower was moved away from the launch pad prior to PSLV’s thirty-two-hour-long countdown getting underway.

The rocket performed the launch had the flight designation PSLV C42.

The launch vehicle during pre-launch processing – via ISRO

At the conclusion of the countdown on Sunday, PSLV’s first stage ignited.  The solid-fuelled first stage, designated PS1, consists of a single S-138 motor which burned for just under two minutes.

PSLV uses a liquid-fuelled second stage – designated PS2 or L-40 – which is powered by a single Vikas engine – which is derived from the French Viking engine that powered the European Ariane 1, 2, 3 and 4 rockets – burns UH25 propellant and dinitrogen tetroxide.

During this part of the ascent, PSLV’s payload fairing was commanded to separate at just after the three minute mark. The fairing, termed a “heat shield” by ISRO, protects PSLV’s payload as the rocket climbs through Earth’s atmosphere. With the rocket now in space, at an altitude of about 115 kilometers (71 miles, 62 nautical miles), the fairing was no longer be needed and will be discarded to save weight.

During last August’s IRNSS-1H launch, part of the fairing separation mechanism failed to pressurize, resulting in the fairing remaining attached to the rocket.

Carrying the extra mass of the fairing for the remainder of its flight resulted in August’s launch attaining a lower-than-planned orbit. When IRNSS-1H separated from the rocket, it was still contained within the fairing, unable to maneuver or deploy its solar arrays or antennae.

A minute after fairing separation, the second stage cut off and separated. The solid-fuelled PS3 third stage ignited its S-7 motor 1.2 seconds after separation to continue the ascent. The third stage burn was followed by a short coast.

Mission Profile for the PSLV

The fourth stage – known as PS4 or L-2.5 – is liquid-fuelled and burns monomethylhydrazine and mixed oxides of nitrogen and provided the final powered flight to the orbital destination. It cut off at the 16 minute, 56 second mark.

The launch target was a sub-synchronous transfer orbit for the two passengers, both of which are British satellites. Spacecraft Separation came just under 18 minutes into the flight.

NovaSAR-1, a small Synthetic Aperture Radar (SAR) satellite, and SSTL S1-4, a high-resolution Earth observation satellite. It is classed as a technology demonstration satellite mission designed to test the capabilities of a new low cost S-Band SAR platform.

The spacecraft was designed and manufactured by SSTL, with an S-Band SAR payload developed by Airbus Defence and Space in Portsmouth, and an Automatic Identification Receiver (AIS) supplied by ComDev to track ships at sea.  NovaSAR-1 will be operated from SSTL’s Spacecraft Operations Centre in Guildford, UK.

The two satellites during encapsulation – via ISRO

“The UK Space Agency has invested £21M in the development of NovaSAR-1 and will benefit from access to data from the spacecraft, significantly boosting the UK’s sovereign Earth observation capabilities and leveraging additional inward investment to the UK by creating highly skilled jobs in the UK space industry, and stimulating the growth of data analysis services,” noted SSTL.

Also on the PSLV-C42 launch will be the SSTL S1-4 satellite. With a mass of 440kg, the spacecraft will further enhance SSTL’s existing in-orbit observation capabilities.

S1-4 is a high-resolution Optical Earth Observation Satellite used for surveying resources, environment monitoring, urban management and disaster monitoring.

Related Articles