What is POEM?
The PSLV Orbital Experimental Module is a platform that will help perform in-orbit experiments using the final, and otherwise discarded stage of ISRO’s workhorse rocket, the Polar Satellite Launch Vehicle (PSLV).
The PSLV is a four-stage rocket where the first three spent stages fall back into the ocean, and the final stage (PS4) — after launching the satellite into orbit — ends up as space junk. However, in PSLV-C53 mission, the spent final stage will be utilised as a “stabilised platform” to perform experiments.
“It is the first time that the PS4 stage would orbit the earth as a stabilised platform,” ISRO said in a statement prior to the launch. After the primary mission, the fourth stage will “write some poems in orbit”, ISRO Chairman S Somanath said in a post-launch address from Mission Control.
POEM is carrying six payloads, including two from Indian space start-ups Digantara and Dhruva Space.
How will ISRO keep POEM ‘alive and stable’ in orbit?
According to ISRO, POEM has a dedicated Navigation Guidance and Control (NGC) system for attitude stabilisation, which stands for controlling the orientation of any aerospace vehicle within permitted limits. The NGC will act as the platform’s brain to stabilize it with specified accuracy.
POEM will derive its power from solar panels mounted around the PS4 tank, and a Li-Ion battery. It will navigate using “four sun sensors, a magnetometer, gyros & NavIC”.
“It carries dedicated control thrusters using Helium gas storage. It is enabled with a telecommand feature,” ISRO said.
Has ISRO repurposed and used PS4 rocket junk earlier?
The Indian space agency first demonstrated the capability of using PS4 as an orbital platform in 2019 with the PSLV-C44 mission that injected Microsat-R and Kalamsat-V2 satellites into their designated orbits. The fourth stage in that mission was kept alive as an orbital platform for space-based experiments.
In a statement after the successful PSLV-C44 launch, ISRO had said: “Subsequently, the fourth stage (PS4) of the vehicle was moved to a higher circular orbit of 453 km after two restarts of the stage, to establish an orbital platform for carrying out experiments. Kalamsat-V2, a student payload, first to use PS4 as an orbital platform, was taken to its designated orbit about 1 hour and 40 minutes after lift-off.”
While in that mission, the fourth stage had Li-Ion batteries solar panels are an addition this time. The latest repurposing and upgrade of the fourth stage of the PSLV rocket involves stabilization of the orbital platform.
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