Cryogenic gains for GSLV

ISRO announces its arrival in the global satellite launch market with the successful flight of the GSLV-Mk II rocket with an indigenous cryogenic engine to put a 2,211-kg weather satellite into orbit. This success also gives an impetus to Chandrayaan-2, which will put a lander and a rover on the moon.

The GSLV-F05 carrying INSAT-3DR takes off from the Satish Dhawan Space Centre in Sriharikota on September 8.

THE bespectacled D. Sujatha, an engineer in the Satish Dhawan Space Centre (SDSC), Sriharikota, radiated confidence on September 8. As she stood on the terrace of the Brahm Prakash auditorium, situated in the space port of the Indian Space Research Organisation (ISRO), she was prepared for the occasion. At 4:50 p.m., when ISRO’s Geosynchronous Satellite Launch Vehicle (GSLV-F05) lifted off from its launch pad and roared into a cloudless sky, she calmly filmed the rocket riding on plumes and smoke on her mobile phone. When the rocket was a mere dot in the sky and several minutes before the mission ended, she waved the Indian tricolour to indicate its success.

Her confidence in the GSLV-F05 was not misplaced. At the end of a smooth 17-minute flight, it put the 2,211-kilogramme INSAT-3DR weather satellite, the heaviest satellite to be launched from Indian soil, into orbit. The GSLV-F05 belonged to the GSLV-Mk II generation of rockets that use indigenous cryogenic engines. This flight, an operational one, was the third success in a row for the GSLV-Mk II generation of vehicle. The two earlier successes, on January 5, 2014 and August 27, 2015, were developmental flights.

“The indigenous cryogenic engine in this mission performed very well,” said Mission Director Umamaheswaran R. “For the sub-assemblies also, it was a satisfying mission. Our effort will be to improve the capability of the GSLV-Mk II to put into orbit satellites weighing between 2,600 kg and 2,800 kg,” he added.

Ready for Chandrayaan-2

The mission’s success signalled two things. One, the GSLV-Mk II with an indigenous cryogenic upper stage is “more than qualified”, as M. Annadurai, Director, ISRO Satellite Centre (ISAC), Bengaluru, described it, to put Chandrayaan-2 into orbit. The other, the GSLV-Mk II rocket has become a candidate in the launch market to put the two-tonne class of satellites into orbit. It is all set to complement ISRO’s Polar Satellite Launch Vehicle (PSLV), which, with its string of 35 consecutive successes, has consolidated itself as a robust, reliable vehicle for putting small satellites into orbit.

ISRO also notched up a success in another complex mission on August 28. On that day, its launch vehicle engineers successfully flight-tested a supersonic ramjet (scramjet) engine on board a 3.2-tonne RH-560 rocket as part of their endeavour to develop an air-breathing propulsion system. As the second stage of the two-stage RH-560 flew at a velocity of Mach 6, that is, six times the speed of sound, two scramjet engines strapped around the stage ignited when air from the atmosphere was rammed into them, and the flame held for five seconds as planned (see box). The scramjet engines used hydrogen as fuel and oxygen from the atmosphere as oxidiser.

The real significance of the GSLV-F05 mission’s success is that it has cleared the road for the Chandrayaan-2 mission and boosted the morale of the Chandrayaan-2 project team at ISAC, Bengaluru. Chandrayaan-2 will be a totally indigenous mission, with the launch vehicle (GSLV-Mk II), the spacecraft, the lander and the rover, all made by ISRO.

While the Vikram Sarabhai Space Centre (VSSC) will build the GSLV-Mk II that will put Chandrayaan-2 into orbit, teams in ISAC are busy building the orbiter, the lander and the rover.

Annadurai said: “Basically, Chandrayaan-2 calls for a GSLV. The latest [GSLV-F05] success indicates that the GSLV is also in the category of the PSLV, which has had a string of successes. It was the PSLV, its XL version, which put both Chandrayaan-1 and our spacecraft to Mars into orbit. Thus, the PSLV played a major role in the successes of both Chandrayaan-1 and our Mars spacecraft missions. Similarly, the GSLV-F05 mission’s success gives us the confidence that a GSLV-Mk II vehicle will put Chandrayaan-2 into orbit. The GSLV-F05’s triumph will galvanise us to realise the Chandrayaan-2 spacecraft, the lander and rover at the earliest so that we can aim for a lift-off by 2017-end from Sriharikota.”

Teams are working in full swing at ISAC to realise the orbiter, lander and rover. The interfaces between the orbiter and the GSLV-Mk II have been finalised and the rover’s engineering model is ready. The rover will have six wheels made of aluminium, a navigation camera and an inclinometer. The orbiter, the lander and the rover together weigh 3,280 kg; the rover weighs 25 kg and the lander 935 kg.

G. Nagesh, Project Director, Chandrayaan-2, said the orbiter, the lander and the rover were together called the composite module. The GSLV-Mk II will first place this composite module in an orbit of 170 km by 19,500 km, called earth-parking orbit. “From there, with the help of the liquid engines in the orbiter, we will take Chandrayaan-2 to the moon’s orbit of 100 km,” he said. It is exactly the same as Chandrayaan-1’s orbit. Once Chandrayaan-2 (that is, the composite module) is in the lunar orbit, ISRO will beam commands to it for the lander to fly out of the orbiter. This will happen at an identified time, depending on the Sun-Moon-Earth gravity. The lander has a pyramidal structure.

“The lander will land at an identified site on the moon. Once the lander touches down, a ramp will deploy and the rover will come out, rolling down the ramp. Both the lander and the rover will perform experiments on the moon,” said Nagesh.

Annadurai said that for the lander to make a soft landing on the lunar soil, matching the lunar gravity, it needs to have throttle-able engines. “This is a major technology. Over and above that, the lander should do in-place navigation and [be able to] find hazards. In case of hazards, it should go around and land [in a suitable] place. These two things are new to us,” he said.

The rover will roll down a ramp from the lander on six aluminium wheels which should interact properly. “If they don’t interact properly, there is a possibility that the rover will sink into the lunar soil,” Annadurai said. The rover has batteries which are charged by solar panels. Each wheel will be driven by a motor. “This is what makes the rover move forward and backward. We use the principle of skid-steering to enable the rover to take turns, negotiate hazards, etc.,” he said.

The rover will move at a speed of one to two cm a second. After it traverses a distance of say, five metres, the navigation cameras on board will take pictures of the lunar surface and the images will be sent to the ground. Annadurai said, “We will analyse the [best] path to follow and direct this command [to the rover] to move on that path.” The rover will do all the operations during the lunar day. Its life is one lunar day, or 14 earth days. It has two payloads to analyse the chemical properties of the lunar soil.

The lander will perform three experiments: analyse seismic activity on the moon’s surface; measure plasma and electron content on the lunar surface; and study temperatures below the moon’s soil. The orbiter, from its perch in the lunar orbit, will do mineralogical mapping of the moon’s soil.

Asked how a GSLV-Mk II vehicle could take the 3,280-kg Chandrayaan-2 into orbit when even future GSLV-Mk II rockets could carry only satellites weighing around 2,800 kg into orbit, Umamaheswaran replied that since Chandrayaan-2 would be first parked in its initial orbit of 180 km by 20,000 km, it would indeed be possible. It would be different from the GSLV-F05 mission, where the 2,211-kg INSAT-3DR had to be put into a geosynchronous transfer orbit of 170 km by 35,000 km.