India has launched its Resourcesat-2A imaging satellite on Wednesday morning via its Polar Satellite Launch Vehicle (PSLV) rocket. The ISRO launch, from the Satish Dhawan Space Centre, occurred on schedule at 10:24 India Standard Time (04:54 UTC) from the center’s First Launch Pad.
Wednesday’s launch, India’s seventh and final of 2016, caps what was already the country’s busiest year for space launches.
Including Wednesday’s, six of India’s launches this year were made by the workhorse PSLV rocket, with the seventh using the larger Geosynchronous Satellite Launch Vehicle (GSLV) Mk.II.
It is the third year in a row that India has increased the frequency of its satellite launches; making four launches in a year for the first time in 2014, and beating this with five in 2015. All six of India’s 2016 launches to date have been successful.
ISRO began 2016 with a salvo of three launches to complete the Indian Regional Navigation Satellite System (IRNSS), a constellation of geosynchronous navigation satellites. Made by PSLV-XL rockets, these launches took place in January, March and April. A further PSLV-XL launch in June deployed the Cartosat 2C reconnaissance satellite along with a cluster of secondary payloads.
Early September saw the GSLV Mk.II rocket record a third consecutive successful launch, deploying the INSAT-3DR communications satellite. India’s most recent launch, at the end of September, used a PSLV-G rocket to deploy the SCATSAT-1 ocean research satellite and seven small satellites.
The payload for Wednesday’s launch was Resourcesat-2A.
A replacement for the five-and-a-half-year-old Resourcesat-2, this is a 1,235-kilogram (2,723 lb) remote sensing satellite that is expected to provide data to help monitor natural resources. Designed for a five-year mission, the spacecraft will operate in a circular sun-synchronous orbit, 817 kilometers (508 miles, 441 nautical miles) above the Earth at an inclination of 98.718 degrees, completing one revolution every 101 minutes and 21 seconds.
The Resourcesat spacecraft, along with the Cartosat and Oceansat programs, are the successors to ISRO’s Indian Remote Sensing (IRS) series of satellites which began launching in 1988. The first two satellites, IRS-1A and 1B, launched from the Baikonur Cosmodrome aboard Soviet Vostok-2M rockets making the antepenultimate and final flights of the Vostok series.
A third satellite, IRS-1E or P1, was constructed from an engineering model built alongside the original satellites and intended as a relatively low-risk payload for the PSLV’s maiden flight in September 1993. IRS-1E was lost when the PSLV failed to achieve orbit.
The IRS-P2 satellite, launched successfully on the PSLV’s second mission, in October 1994, as a demonstrator ahead of a second-generation pair of satellites. These – IRS-1C and 1D – were launched in 1995 and 1997, the former aboard a Russian Molniya-M/2BL and the latter atop India’s own PSLV. During the IRS-1D launch the PSLV’s fourth stage underperformed, leaving the satellite in a lower-than-planned orbit.
Another experimental IRS satellite, IRS-P3, was launched by a PSLV in March 1996. The IRS-P4, P5 and P6 satellites, launched by PSLVs in May 1999, May 2005 and October 2003 respectively, began the Oceansat, Cartosat and Resourcesat series of spacecraft.
Resourcesat was the direct successor to the primary IRS satellites. Despite being designed for a five-year mission, it remains operational after thirteen years in orbit alongside its replacement, Resourcesat-2, which was deployed in April 2011.
Resourcesat-2A has been built to similar specifications as Resourcesat-2, and carries the same instrumentation as both Resourcesat-2 and Resourcesat-1 before it.
The primary imaging payload is the Linear Imaging Self Scanner 4 (LISS-4), a high-resolution visible and near-infrared camera with a resolution of 5.8 meters (19 feet).
A medium-resolution instrument, LISS-3, will produce images at a resolution of 23.5 meters (77.1 feet) while the lower-resolution Advanced Wide Field Sensor (AWiFS) can image a 740-kilometre (460-mile) swath at resolutions of up to 56 meters (184 feet). The swath width for LISS-4 is 70 kilometers (43 miles), while for LISS-3 it is 141 kilometers (87.6 miles).
All three cameras can operate in multiple spectral bands; all three can capture green, red and near-infrared light, at wavelengths of 0.52-0.59 nanometres, 0.62-0.68 nanometres, and 0.77-0.86 nanometers respectively. LISS-3 and AWiFS have an additional short-wave infrared band, at 1.55-1.70 nanometres.
India’s Polar Satellite Launch Vehicle (PSLV) was used to place Resourcesat-2A into orbit. The rocket used for Wednesday’s launch flew in the PSLV-XL configuration, and had flight number C36.
It was the thirty-eighth PSLV launch since the rocket was introduced in 1993; thirty-five of its previous launches have been successful; its maiden flight failed and another early launch – with the IRS-1D satellite, a predecessor of the Resourcesat series – was a partial failure due to upper stage underperformance. Since the IRS-1D launch the PSLV has achieved thirty-three consecutive successful launches in nineteen years.
PSLV C36 launched from the First Launch Pad at the Satish Dhawan Space Centre (SDSC) on Sriharikota, an island on India’s east coast about 70 kilometers (40 miles) north of Chennai.
Formerly known as the Sriharikota High Altitude Range (SHAR), the facility was renamed in 2002 following the death of former ISRO chairman Satish Dhawan. All of India’s orbital launches have been made from the site.
The First Launch Pad was constructed ahead of the PSLV’s début launch in 1993, replacing the launch pads to the south which had been used for the earlier Satellite Launch Vehicle (SLV) and Augmented Satellite Launch Vehicle (ASLV).
Both the First Launch Pad, and the nearby Second Launch Pad, can accommodate the PSLV and the larger Geosynchronous Satellite Launch Vehicle (GSLV), although since the second pad became operational in 2005, it has been used for all GSLV launches; with the PSLV continuing to use both pads. At the First Launch Pad, rockets are integrated at the launch pad within a mobile service tower; in contrast to the Second Launch Pad where assembly takes place in a separate integration building with the rocket being transported vertically to the pad for final preparations.
PSLV is a four-stage rocket, using a mixture of solid and liquid-fuelled stages. The first and third stages use solid propellant, as do the six strap-on boosters which augment the first stage as the rocket climbs through the lower regions of Earth’s atmosphere, while the second and fourth stages are liquid-fuelled.
The first stage, or PS1, uses an S-138 motor. The six boosters which provide additional thrust during the early stages of flight are PS0M-XL rockets, powered by S-12 motors. The PSLV-XL uses PS0M-XL boosters in placed of standard PS0M motors used on the rocket’s standard, or PSLV-G, configuration.
First stage ignition occurred at the zero mark in the countdown. Four of the strap-on motors are ground-lit, igniting in pairs 0.42 and 0.62 seconds after the first stage, while the final pair are air-lit. These are started twenty-five seconds after liftoff.
The ground-lit solids were jettisoned at the end of their burn; with the first pair separating 69.9 seconds after liftoff and the second pair following two tenths of a second later. The air-lit motors separated 92 seconds into the flight.
Burnout and separation of the first stage occurred one minute and 50.48 seconds after liftoff. Two tenths of a second later the second stage’s Vikas engine ignited, beginning an approximately two-minute, 30-second burn.
Vikas burns a mixture of hydrazine hydrate and unsymmetrical dimethylhydrazine (UDMH) – designated UH25 – oxidized by dinitrogen tetroxide. It is a license-built version of the Viking engine that was used by Europe’s Ariane family of rockets prior to the introduction of the modern Ariane 5.
Forty seconds into the second stage’s burn, the payload fairing separated from around Resourcesat-2A at the nose of the rocket. At this point the vehicle was at an altitude of around 126 kilometers (78 miles, 68 nautical miles) and the fairing was no longer be needed to protect the satellite from Earth’s atmosphere.
Two minutes and 31.28 seconds after the second stage ignites, it shut down its engine and separated. The third stage – or PS3 – ignited its S-7 motor 1.2 seconds after stage separation, burning for around 70 seconds.
Once the third stage burned out, the vehicle coasted towards the apogee of its trajectory. The spent third stage remained attached during this coast, separating at eight minutes, 41.72 seconds mission elapsed time. The fourth stage, PS4, ignited ten seconds later.
The PS4 uses monomethylhydrazine (MMH) propellant, oxidized by mixed oxides of nitrogen (MON). It burned for eight minutes and 16.54 to establish a circular deployment orbit at an altitude of 827 kilometers (514 miles, 447 nautical miles) and an inclination of 98.719 degrees; slightly above what will become the satellite’s operational orbit. Forty-seven seconds after the end of the fourth stage burn, Resourcesat-2A separated from the PSLV.
The launch of Resourcesat-2A concluded India’s scheduled launches for 2016. ISRO’s next launches are scheduled for January; with 18 January a possible date for the first orbital launch of the new Geosynchronous Satellite Launch Vehicle Mk.III. A PSLV launch with the Cartosat-2D imaging satellite is also scheduled for the start of the year.
(Images via ISRO).