ISRO’s ‘zero orbital debris’ milestone
How did ISRO ensure practically zero debris left in earth orbit after the PSLVC58/◣PoSat mission? What is the purpose and function of the PSLV Orbital Experimental Module3 (POEM3)? How does it contribute to space debris mitigation efforts? What are the
The story so far:
The Indian Space Research Organisation (ISRO) has said its PSLVC58/◣PoSat mission has practically left zero debris in earth orbit. The space agency explained that the last stage of the Polar Satellite Launch vehicle (PSLV) used in the mission was transformed into a kind of orbital station — called the PSLV Orbital Experimental Module3 (POEM3) — before it was left to reenter the earth’s atmosphere instead of floating in orbit once its mission was completed. ISRO said that after it completed the primary mission of injecting all satellites into their target orbits, the fourth stage of the PSLV was transformed into the POEM3. It was subsequently deorbited from 650 km to 350 km, rendering it more susceptible to being pulled towards the earth and burning up in the atmosphere. ISRO also said it “passivated the stage,” meaning dumped its fuel, to avoid an explosion that could have flung small pieces of debris into orbit.
What is POEM?
Developed by the Vikram Sarabhai Space Centre (VSSC) as an inexpensive space platform, POEM uses the spent fourth stage of a PSLV rocket as an orbital platform. Used for the first time in the PSLVC53 mission in June 2022, ISRO had POEM orbit the earth to perform inorbit scientific experiments with various payloads onboard.
POEM is powered by solar panels mounted on the fuel tank of the rocket’s fourth stage and a lithiumion battery. It has a navigation, guidance, and control (NGC) system to stabilise its altitude along with helium control thrusters. The NGC system has four Sun sensors, a magnetometer, and gyroscopes, and talks to ISRO’s NavIC satellite constellation for navigation. POEM also has a telecommand system to communicate with the ground station.
ISRO first demonstrated the reuse of the spent fourth stage of its rocket in its PSLV C44 mission in 2019. After satellites were injected into the target orbits, the fourth stage, carrying a student payload called KalamsatV2, was moved to a higher circular orbit of 443 km and stayed there, facilitating the payload’s requirements.
What has POEM3 achieved?
ISRO launched the PSLV C58 mission from the Satish Dhawan Space Centre in Sriharikota on January 1.
After deploying the ◣PoSat satellite in its desired orbit of 650 km, the fourth stage, now called POEM3, was lowered to a 350kmhigh circular orbit. The lower a satellite is in orbit around the earth, the more drag it experiences and the more energy it needs to expend to stay in orbit.
POEM3 featured nine payloads: two each from VSSC and Bellatrix Aerospace Pvt Ltd, one each from the startups TakeMe2Space, Inspecity Space Labs Pvt Ltd., Dhruva Space, and from LBS Institute of Technology, KJ Somaiya Institute of Technology, and ISRO’s Physics Research Laboratory, Ahmedabad.
It completed 400 orbits around the earth by its 25th day. The payloads were operationalised to perform their experiments at this time. ARKA200, RUDRA, and LEAPTD completed their respective experiments while the data from WeSAT, RSEM, and DE◣ were collected after every orbit for further analysis on the ground. Two fuel cells from VSSC demonstrated their ability to generate power. By January 27, 2024, all of POEM3’s payload objectives were completed.
For two months, POEM3 prepared for its reentry while ISRO tracked it with its Telemetry, Tracking and Command Network stations in Bengaluru, Lucknow, Mauritius, Sriharikota, Port Blair, Thiruvananthapuram, Brunei, and Biak (Indonesia) and the MultiObject Tracking Radar (MOTR) at Sriharikota. On March 21, POEM3 reentered the earth’s atmosphere, meeting its fiery end.
Why is this significant?
With the rise in the number of satellites in orbit around the earth, space debris has become a pressing issue. Space debris in the low earth orbit (LEO) mainly comprises pieces of spacecraft, rockets, and defunct satellites, and the fragments of objects that have deteriorated explosively as a result of antisatellite missile tests. This debris often flies around at high speeds of up to 27,000 km/hr. Due to their sheer volume and momentum, they pose a risk to several space assets.
The LEO extends from 100 km above the earth’s surface up to 2000 km above. It includes satellites tracking intelligence data, encrypted communication, and navigation. According to ISRO’s Space Situational Assessment Report 2022, the world placed 2,533 objects in space in 179 launches in 2022.
Debris also exists, but in smaller volumes, in the geosynchronous orbit (GEO) 36,000 km above the earth’s surface. Currently, 7,000 operational satellites are orbiting the earth at different altitudes along with millions of pieces of space debris. The U.S. Space Command tracks and catalogues space debris larger than 10 centimetres in LEO and larger than 0.31 metres in GEO.
How are agencies dealing with debris?
The latest incident of space debris causing havoc was recorded on March 8 when a discarded battery pallet dropped by the International Space Station ripped through the roof of a house in Florida.
As more communication satellites/constellations are launched and more antisatellite tests are conducted, more onorbit breakup and collisions occur, producing smaller fragments in orbit. The number of space objects
(debris or functional equipment) greater than 10 cm in size in LEO is expected to be about 60,000 by 2030, per ISRO estimates. Space debris can also create unusable regions of the orbit where too much debris has accumulated, and which can trigger a cascading avalanche of collisions that produce yet more, but smaller pieces of, debris.
Currently, there are no international space laws pertaining to LEO debris. Most spacefaring nations abide by the Space Debris Mitigation Guidelines 2002 specified by the InterAgency Space
Debris Coordination Committee (IADC), which the U.N. endorsed in 2007.