National

Sept. 26 PSLV launch to be doubly special

On September 26, the PSLV satellite launcher will for the first time place its multiple passengers in two different orbits.

The flight is also significant as it will last two hours and 15 minutes, making it the PSLV’s longest ever.

A routine PSLV launch lasts about 20 minutes.

Three Indian and five foreign commercial spacecraft will ride in it together. Only the main passenger, ISRO’s 370-kg Scatsat-1 ocean and weather tracker, will get off first at a slightly higher orbit at 720 km. It will be out in the first 17 minutes, as is customary.

The remaining smaller satellites, weighing between 5 kg and 110 kg, will be ejected at 670 km — but after about two hours.

To make this possible, launch team engineers will shut down and restart the fourth and last stage of the vehicle (called PS4) twice during the flight, according to two senior officials in the know.

ISRO had tested this new techique during a PSLV flight in June this year. It then said the added versatility of reaching satellites to different orbits will enlarge its customer base: sometimes, different launch customers need to reach their satellites to different orbits or distances from Earth.

P.Kunhikrishnan, Director of the Satish Dhawan Space Centre, which handles launches at its two launchpads, said, “The campaign is in full swing for the launch of the PSLV-C35 on September 26. We have planned to release its different payloads [or spacecraft] at two different orbits this time. This will be a first multiple orbit launch in a single PSLV mission using the PS4 restart method.”

The PSLV has so far launched 39 remote-sensing satellites of ISRO, including the Chandrayaan-1 of 2008 and the Mars mission of 2013-14. It has also orbited 74 foreign commercial and university satellites in a global trend where the demand for its category of launch services is increasing.

About the spacecraft

Scatsat-1 370 kg [Indian; main payload]

Alsat-1B 103 kg

Alsat-2B 110 kg

Alsat Nano 7 kg

[All 3 Algerianearth observation satellites]

Pathfinder-1 44 kg [BlackSky, U.S.]

NLS-19 8 kg [University of Toronto, Canada]

PISat 5.7 kg [Student sat from PESIT Bengaluru]

Pratham 10 kg [IIT-Bombay's Dept of Aerospace Engg[

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