Wednesday, December 7, 2016

India’s Newest Remote Sensing Satellite Launches atop PSLV Booster

PSLV-C36 launch. Photo Credit: ISRO

The Indian Space Research Organisation (ISRO) has successfully launched its workhorse PSLV launcher carrying the country’s Resourcesat-2A remote sensing spacecraft. Liftoff occurred as planned at 10:25 a.m. local time (04:55 GMT) on Dec. 7 (11:55 p.m. EST on Dec. 6) from the First Launch Pad (FLP) at ISRO’s Satish Dhawan Space Centre in Sriharikota, India.

The mission, designated PSLV-C36 in ISRO’s numbering system, has faced several postponements. Resourcesat-2A was initially scheduled to fly aboard the PSLV-C35 mission, which was eventually launched on Sept. 26, 2016, and the satellite was assigned to PSLV-C36. However, this mission was later rescheduled two times: Nov. 23 to Nov. 28, then finally to Dec. 7.

It was also decided that Resourcesat-2A will be the only passenger of the PSLV-C36 mission. Earlier plans envisioned several other smaller payloads that could piggyback on the mission; however, their flight was postponed to 2017. ISRO originally had planned to launch two additional Indian satellites: the IITMSAT, designed for ionospheric research, and an Earth-observing spacecraft named NIUSAT. The Italian Max Valier Sat nanosatellite for X-ray astronomy research and a Latvian nanosatellite Venta-1 built for ship tracking purposes were also on the list of optional payloads.

With the assembly of the rocket completed and the spacecraft installed on top of the launch vehicle in late November, the Mission Readiness Review (MRR) committee and Launch Authorisation Board (LAB) on Dec. 5 gave the green light for liftoff. It allowed the engineers to commence a 36-hour countdown necessary for final pre-launch preparations and reconfigurations.

During the countdown campaign, the launch vehicle was fueled, and last comprehensive checks were conducted in order to ensure a flawless flight to space. All the preparatory activities culminated 14 minutes ahead of liftoff when an automated sequence began which handed control over the mission to computers.

The automated sequence led to the ignition of the rocket’s core stage which was followed by the ignition of four of the six strap-on boosters about one second later. The PSLV launch vehicle soared into the sky, starting a short vertical ascent during which the remaining duo of additional boosters began their burn at about 25 seconds after liftoff.

After a brief vertical climb, the rocket started heading southeasterly to avoid flying over Sri Lanka. During its detour over the island, the strap-on boosters were jettisoned, leaving the launch vehicle powered by its core stage alone. The quartet of ground-lit motors separated at one minute and 10 seconds after launch at an altitude of about 17.3 miles (27.8 kilometers), while the two air-lit boosters were detached some 22 seconds later when at an altitude of 31 miles (50 kilometers).

Afterward, the core stage continued the flight for 18 seconds until it separated from the launch vehicle at one minute and 50 seconds after liftoff. Then the second stage almost immediately ignited its Vikas 4 engine, giving the required boost to carry on with the mission. Next, the payload fairing was jettisoned some two-and-a-half minutes into the flight, and the second stage burned out its fuel nearly two minutes later, leaving the launch vehicle at T+4 minutes and 22 seconds.

The third stage took control over the mission one second after separation of the second stage at an altitude of about 171 miles (275 kilometers). This phase of the flight lasted four minutes and 18 seconds, during which the launch vehicle accelerated to a velocity of 12,750 mph (20,520 km/h) and climbed to an altitude of 385 miles (620 kilometers) above the Earth’s surface.

The third stage separated at nine minutes and 41 seconds into the flight, releasing a stack consisting of the rocket’s fourth stage and the Resourcesat-2A spacecraft attached to it. The fourth stage started burning its two L-2-5 engines at T+9 minutes and 51 seconds. The duo of motors burned for 8 minutes and 17 seconds until they were cut off, allowing the stack to drift for nearly one-minute in order to adjust its flight path toward the targeted orbit.

The satellite was released as planned into a polar Sun-synchronous orbit (SSO) at an altitude of about 514 miles (827 kilometers) after a flight lasting roughly 18 minutes. Now, the Resourcesat-2A spacecraft will enter an important phase of checkouts lasting several weeks until it becomes fully aligned with previous satellite in the series currently orbiting Earth. The new satellite is expected to continue remote sensing data services for global users provided by Resourcesat-1 and Resourcesat-2 – launched in 2003 and 2011, respectively – operating as a trio in orbit for as long as possible.

Resourcesat-2A is a remote sensing satellite designed for resource monitoring. The spacecraft, built by ISRO, is based on IRS-1 platform and weighs around 1.24 metric tons. The satellite features two deployable solar arrays that generate up to 1,700 watts of power for a designed lifetime of five years.

Resourcesat-2A carries three imaging cameras: two Linear Imaging Self Scanners (LISS-4 and LISS-3) and the Advanced Wide Field Sensor (AWiFS). Moreover, it is equipped with two Solid State Recorders with a capacity of 200 gigabits each to store images taken by the cameras.

LISS-4 is a high-resolution camera operating in three spectral bands in the Visible and Near-Infrared Region (VNIR) with a 5.8-meter spatial resolution and steerable up to about 26 degrees across track to achieve a five-day revisit capability.

LISS-3 is a medium resolution camera. It operates in three spectral bands in VNIR and one in Short Wave Infrared (SWIR) band with 23.5-meter spatial resolution.

AWiFS is a coarse resolution camera operating in three spectral bands in VNIR and one band in SWIR with 56-meter spatial resolution.

The four-stage PSLV booster is India’s most reliable launch vehicle. The rocket has been used to deliver more than 40 satellites into space for some 19 countries. PSLV is capable of lofting up to 3.25 metric tons to low-Earth orbit and about 1.42 metric tons to a geosynchronous transfer orbit (GTO).

The rocket uses an Earth-storable, liquid-fueled rocket engine for its second stage, known as the Vikas engine; it was developed by the Liquid Propulsion Systems Centre. The third stage of the PSLV is powered by a solid rocket motor that provides the upper stage’s high thrust after the atmospheric phase of the mission. The fourth stage is composed of two Earth-storable liquid-fueled engines.

The 144-foot (44-meter) tall XL version of the PSLV that was used for Wednesday’s mission is the upgraded variant of the rocket in its standard configuration. Its thrust is increased by the addition of more powerful, stretched strap-on boosters.

The vehicle has a mass of 320 metric tons at liftoff and uses the larger strap-on motors (PSOM-XL) that provide the capability of hoisting heavier payloads into orbit. PSOM-XL uses the larger 1-meter (3.3-foot) diameter, 13.5-meter (44-foot)) length motors. This version of the rocket carries 12 metric tons of solid propellants instead of the nine metric tons that were used on an earlier configuration of the PSLV.

The PSLV rocket in its XL configuration was launched for the first time on Oct. 22, 2008, when it sent India’s Chandrayaan-1 lunar probe toward the Moon.

Wednesday’s mission was India’s seventh launch this year and the sixth orbital flight for PSLV in 2016. The country’s next flight is currently scheduled to take place on Jan. 18, 2017, when a GSLV Mk III rocket will send ISRO’s GSAT-19E communications satellite into orbit.

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