Fifty minutes after the satellites are injected into the orbit from the fourth stage of the vehicle, its engine will be re-ignited for five seconds.

The Polar Satellite Launch Vehicle (PSLV-C34), which will lift off at 9.25 a.m. on June 22 from Sriharikota, is an important mission for the Indian Space Research Organisation (ISRO).

The vehicle will not only put 20 satellites into the same orbit — the highest number of satellites to be put into orbit by a PSLV — but it will perform two tricky experiments of the same nature. Fifty minutes after the satellites are injected into the orbit from the fourth stage of the vehicle, its engine will be re-ignited for five seconds. Then it will be shut down for 50 minutes and re-ignited for another five seconds, according to K. Sivan, Director, Vikram Sarabhai Space Centre, Thiruvananthapuram.

The ISRO wants to master this complex manoeuvre so that it can put multiple satellites into different orbits using the same rocket. A forthcoming PSLV launch will put the ISRO’s SCATSAT-1, meant for forecasting weather and cyclone detection, and a foreign satellite in two different orbits.

On December 16, 2015, after the PSLV-C29’s fourth stage put six Singapore satellites into the same orbit, the ISRO re-started the fourth-stage engine for four seconds. At that time, Dr. Sivan called it a “small experiment” to master the manoeuvre of putting multiple satellites into different orbits with the same vehicle.

On June 22, eight minutes after the PSLV-C34 lifts off, the fourth stage engine will sizzle into life, taking the stage to an altitude of 514 km. The fourth stage engine will be cut off 16 minutes and 30 seconds after the lift-off. Over the next 10 minutes, 20 satellites will be injected into the same orbit from the fourth stage, one after another.

Dr. Sivan said: “After each satellite is injected into orbit, the vehicle will be re-oriented if required and the next satellite will be put into orbit with a varying velocity so that the distance between the satellites grows monotonically. We will do this to ensure that there is no collision of satellites. Then, after a huge gap of 3,000 seconds, PS-4 [the fourth stage] will be re-ignited for five seconds. Then, it will be switched off for another 3,000 seconds. It will be re-ignited for another five seconds.”

On April 28, 2008, the PSLV-C9 deployed 10 satellites, but in the same orbit.

P. Kunhikrishnan, Director, Satish Dhawan Space Centre, Sriharikota, said the PSLV-C34, with the 20 satellites, was moved to the launch tower on Saturday morning. “Everything is going on smoothly,” he said.