India’s Small Satellite Launch Vehicle successful on second test flight

India’s Small Satellite Launch Vehicle lifts off on its second test flight. Credit: ISRO

The second test flight of India’s Small Satellite Launch Vehicle was successful Feb. 10, delivering Indian and U.S.-owned payloads into orbit after the new rocket’s first demonstration mission ended in failure last year.

The Small Satellite Launch Vehicle, or SSLV, is designed to carry payloads of up to 1,100 pounds (500 kilograms) into orbit, complementing India’s larger rockets — the Polar Satellite Launch Vehicle and the Geosynchronous Satellite Launch Vehicle.

The SSLV’s second test flight took off at 0348 GMT on Feb. 10 (10:48 p.m. EST on Feb. 9) from the Satish Dhawan Space Center, India’s primary spaceport on the country’s east coast about 50 miles (80 kilometers) north of Chennai.

“Congratulations to the space community of India,” said S. Somanath, chairman of the Indian Space Research Organization. “We have a new launch vehicle.”

The rocket deployed three satellites into an orbit about 280 miles (450 kilometers) above Earth, with an inclination of 37.2 degrees to the equator, according to U.S. military tracking data. ISRO declared the launch a success.

ISRO’s EOS-07 Earth observation satellite was the main payload on the SSLV test flight. The 344-pound (156-kilogram) spacecraft carries two technology demonstration experiments — a spectrum monitoring payload and a millimeter wave humidity sounder — that could help future operational missions monitoring air traffic and weather, according to Ravi Chandra Babu, ISRO’s EOS-07 satellite manager.

The second SSLV test flight, named SSLV-D2, delivered its three satellite payloads into the intended orbit, Somanath said.

“The orbit achieved by the vehicle today, using its very novel cost effective and very innovative guidance and navigation systems, is exceedingly good,” Somanath said.

ISRO first proposed development of the Small Satellite Launch Vehicle in 2016. The development program has cost about $21 million, according to ISRO. The agency aims to manufacture the SSLV for about $4 million per vehicle, good enough to compete with the stable of commercial smallsat launchers from companies like Rocket Lab and Virgin Orbit.

“Design drivers of SSLV are low cost, low turnaround time, flexibility in accommodating multiple satellites, launch-on-demand feasibility, and minimal launch infrastructure requirements,” ISRO said.

The 111-foot-tall (34-meter) Small Satellite Launch Vehicle is powered by three solid-fueled motors and a “trimming module” fueled by hydrazine to maneuver satellites into precise orbits. The SSLV’s first stage motor can produce more than a half-million pounds of thrust during its two-minute firing. The second and third stages completed their burns about eight minutes into the flight.

The rocket’s liquid-fueled trimming module ignited at T+plus 11 minutes and 23 seconds to nudge the mission’s three payloads into orbit. The EOS-07 spacecraft separated from the SSLV trimming module at T+plus 13 minutes and 5 seconds, followed by release of the Janus 1 and AzaadiSAT 2 secondary payloads.

The first SSLV test flight in August failed to place two Indian satellites into a stable orbit. Investigators blamed the failure on unexpected vibrations on the rocket during separation of the second stage about six minutes after liftoff, which saturated accelerometers in the vehicle’s inertial navigation system.

Software algorithms operating in the SSLV’s flight computer detected errant signals from the accelerometers and flagged the problem, then ordered the rocket to continue the mission in a “salvage mode,” according to ISRO.

“Though the salvage mode was initiated with the purpose of saving the mission, it could not inject the satellites to a safe orbit,” ISRO said. The rocket’s guidance system flew the rest of the mission in an open loop mode, without feedback from the accelerometers, which were taken out of the command chain after the computer flagged the errant data from vibrations during second stage separation.

The mission ended with a velocity shortfall of 125 mph, or 56 meters per second, ISRO said, and the satellites were released into a lower-than-planned orbit that brought them back into Earth’s atmosphere, where the spacecraft likely burned up before completing one lap around the planet.

India’s Small Satellite Launch Vehicle is designed to carry a payload of up to 1,100 pounds (500 kilograms) into orbit. Credit: ISRO

“The SSLV had its maiden flight, SSLV-D1, and we had a narrow miss in placing the satellite into orbit because of a shortfall in velocity,” Somanath said. “I’m very happy to report that we have analyzed the problems faced on SSLV-D1, identified the corrective actions, implemented (them) in a very fast pace, qualified all of those new systems, went through model simulations and studies to ensure that the vehicle would become successful this time.”

“A lot of vehicle systems performed well in the first mission,” said S. Unnikrishnan Nair, director of ISRO’s Vikram Sarabhai Space Center. “There was a small glitch during the second stage. The vehicle axial dynamics got excited, thereby leading to a salvage action. The satellite could not be injected into orbit. For a few months, we have been working hard to make all the systems perform as expected, and today we have the results.”

In six months since the first SSLV test flight, Indian engineers had to develop new hardware, a new separation system, and modify the navigation and guidance system ahead of the second demonstration mission Feb. 10, according to Vinod S.S., ISRO’s mission director.

The Janus 1 satellite that flew in a rideshare slot on the SSLV test flight is a briefcase-size CubeSat that hosts five miniature payloads from AICRAFT, Morpheus Space, Netra, SayariLabs Kenya, SpeQtral, Transcelestial, and Zero-Error Systems, according to Astranis, the California-based company that owns the spacecraft. The payloads will perform internet of things communications, laser communications, radio communications, and machine learning functions in orbit.

The AzaadiSAT 2 CubeSat was developed by the student group Space Kidz India, with help from 750 girl students across the country. Aside from its educational goals, the mission will support amateur radio communications and measure radiation levels in space.

Somanath, the ISRO chairman, said in remarks after the SSLV launch that the Indian space agency is preparing for two launches in March, one using the country’s heavy-duty GSLV Mk.3 rocket to loft 40 internet satellites for OneWeb, and another for commercial customers using the workhorse Polar Satellite Launch Vehicle.

Other objectives for ISRO this year include tests for India’s Gaganyaan human spaceflight program, and the first launch of India’s new-generation navigation satellites on a GSLV rocket. Another GSLV launch late this year will launch the NISAR Earth observation satellite, a joint project between NASA and ISRO.

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