PSLV Orbital Experimental Module (POEM)

Context

ISRO has recently launched three Singaporean satellites in precise orbit through the PSLV Orbital Experimental Module or ‘POEM’.

What is POEM?

• The PSLV Orbital Experimental Module is a platform that aims to 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 has been utilised as a “stabilised platform” to perform experiments.
• POEM is carrying six payloads, including two from Indian space start-ups Digantara and Dhruva Space.
  
  

Key-features

• 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 tele-command feature.

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.
• In that mission, they 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.
• 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.