ISRO’s ‘zero orbital debris’ milestone

Context: Indian Space Research Organisation (ISRO) announced that its PSLV Orbital Experimental Module-3 (POEM-3) re-entered the Earth's atmosphere in March 2024 without leaving any debris in orbit.

Major Highlights: 

• Mission launch: The PSLV-C58 mission was launched on January 1, 2024.
• Primary Mission: The mission's main objective was to deploy XPoSAT satellite into the intended orbit of 650 km, which it successfully accomplished.
• POEM-3: After deploying the satellite, the leftover part of the PSLV rocket, the terminal stage (fourth stage), was not discarded. Instead, it was ingeniously repurposed into a stabilised platform named POEM-3 (PSLV Orbital Experimental Module-3).

PSLV Orbital Experimental Module (POEM):

• Developed by: Vikram Sarabhai Space Centre (VSSC).
• POEM is an experimental mission or space platform to perform in-orbit experiments using the final, and otherwise discarded, stage of ISRO’s PSLV.
  • 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. 
  • In POEM, the spent final stage will be utilised as a stabilised platform to perform experiments. 
• POEM has a dedicated Navigation Guidance and Control (NGC) system which will act as the platform’s brain for attitude stabilisation 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.

Zero orbital debris milestone:

• Deorbiting POEM-3: To ensure POEM-3 would not remain as space junk, its orbit was lowered from a high altitude of 650 km to a much lower one at 350 km. This significantly reduced the time it took for POEM-3 to re-enter Earth's atmosphere and burn up.
• Passivation: To further minimise risks, any leftover fuel on POEM-3 was eliminated in a process called passivation. This reduced the chance of an accidental explosion during re-entry that could create debris.
• Zero-Debris Goal Achieved:  On March 21, 2024, POEM-3 re-entered the earth’s atmosphere, meeting its fiery end. Due to the well-planned deorbiting and passivation manoeuvres, the PSLV-C58/XPoSat mission resulted in practically zero debris left behind in Earth's orbit. This is a significant achievement in space sustainability, reducing the potential hazards of space debris for future missions.

Space Debris: 

• 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 anti-satellite missile tests.
• This debris often flies around at high speeds of up to 27,000 kilometres per hour. Due to their sheer volume and momentum, they pose a risk to several space assets.
• With the rise in the number of satellites in orbit around the earth, space debris has become a pressing issue, particularly in the Low Earth Orbit (LEO).
  • Currently, there are 7,000 operational satellites orbiting the earth at different altitudes along with millions of pieces of space debris.
  • According to ISRO’s Space Situational Assessment report 2022, the world placed 2,533 objects in space in 179 launches in 2022, up from 1860 objects in 135 launches in 2021.
• As more communication satellites/constellations are launched and more anti-satellite tests are conducted, more on-orbit breakup and collisions occur, producing smaller and 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 also leads to two major risks – it creates unusable regions of the orbit due to excessive debris, and leads to the ‘Kessler syndrome’ – creation of more debris due to cascading collisions resulting from one collision.

How are space agencies dealing with debris?

• Currently, there are no international space laws pertaining to LEO debris.
• However, most space-exploring nations abide by the Space Debris Mitigation Guidelines 2002 specified by the Inter-Agency Space Debris Coordination Committee (IADC), which the U.N. endorsed in 2007.
• The U.S. Space Command tracks and catalogues space debris larger than 10 centimetres in LEO and larger than 0.3-1 metres in geosynchronous orbit (GEO).