PSLV ORBITAL EXPERIMENTAL MODULE-3 (POEM-3)

POEM, developed by the Vikram Sarabhai Space Centre (VSSC), serves as a cost-effective space platform leveraging the spent fourth stage of a PSLV rocket. Initially introduced during the PSLV-C53 mission in June 2022, POEM orbits the Earth, conducting in-orbit scientific experiments with various payloads onboard.

Key Features

• Utilizes solar panels mounted on the fuel tank of the rocket's fourth stage and a lithium-ion battery.
• Ensures altitude stabilisation and includes helium control thrusters. Equipped with four Sun sensors, a magnetometer, and gyroscopes, the NGC system communicates with ISRO's NavIC satellite constellation for navigation.
• Facilitates communication with ground stations.

ISRO's pioneering reuse of the spent fourth stage of its rocket was demonstrated during the PSLV C44 mission in 2019. Following the successful deployment of satellites into their designated orbits, the fourth stage, carrying the student payload Kalamsat-V2, was manoeuvred to a higher circular orbit of 443 km. It remained there, catering to the payload's operational needs.

ISRO launched the PSLV C-58 mission from the Satish Dhawan Space Centre in Sriharikota on January 1.

• Following the successful deployment of the XPoSat satellite into its designated orbit of 650 km, the fourth stage of the rocket was repurposed into POEM-3 and manoeuvred to a circular orbit 350 km above Earth's surface. Lower orbits entail increased atmospheric drag, demanding higher energy consumption to maintain orbit.
• POEM-3 carried nine payloads, including contributions from various organisations such as VSSC, Bellatrix Aerospace Pvt Ltd, and several startups and educational institutions. By its 25th day, completing 400 orbits, the payloads were activated for experimentation. Notably, ARKA200, RUDRA, and LEAP-TD finalized their experiments, while data from other payloads were collected after each orbit for subsequent ground analysis. Additionally, fuel cells from VSSC demonstrated their power generation capabilities.
• over two months, POEM-3 underwent preparations for re-entry while being tracked by ISRO's Telemetry, Tracking, and Command Network stations across various locations. The Multi-Object Tracking Radar (MOTR) at Sriharikota was also utilised for tracking purposes.

4. Significance of Minimizing Space Debris

As the number of satellites orbiting Earth continues to rise, the issue of space debris has become increasingly critical. Space debris, predominantly found in the low Earth orbit (LEO), encompasses fragments of spacecraft, rockets, defunct satellites, and remnants from anti-satellite missile tests. With velocities reaching up to 27,000 km/hr, these debris pose a significant threat to various space assets due to their mass and momentum.

• The LEO, spanning from 100 km to 2000 km above the Earth's surface, hosts satellites crucial for intelligence gathering, encrypted communication, and navigation. According to ISRO's Space Situational Assessment Report 2022, the global space community launched 2,533 objects into space through 179 launches in 2022. Additionally, while space debris exists in smaller quantities in the geosynchronous orbit (GEO) at 36,000 km altitude, it still poses risks to operational satellites.
• Presently, around 7,000 operational satellites orbit Earth at various altitudes, alongside millions of space debris pieces. Tracking and cataloguing efforts, led by entities like the U.S. Space Command, focus on debris larger than 10 centimetres in LEO and larger than 0.3-1 meters in GEO.
• ISRO's successful implementation of the PSLV-C58/XPoSat mission, particularly the utilization of POEM-3 to minimize space debris, marks a significant step in addressing this pressing issue. By repurposing the final stage of the PSLV rocket into an orbital platform and subsequently de-orbiting it, ISRO has demonstrated a proactive approach towards mitigating space debris accumulation. This achievement not only ensures the safety of existing space assets but also sets a precedent for responsible space exploration and satellite deployment practices.

5. Approaches to Addressing Space Debris

The latest incident involving space debris occurred on March 8, highlighting the growing concern over its impact. A discarded battery pallet from the International Space Station caused damage to a house in Florida.

• With the launch of more communication satellites/constellations and the conduct of anti-satellite tests, instances of on-orbit breakup and collisions are on the rise. These events generate smaller debris fragments, contributing to the overall debris population. ISRO estimates that the number of space objects larger than 10 cm in size in LEO could reach approximately 60,000 by 2030. Additionally, the accumulation of debris in certain regions of orbit can create unusable zones, potentially leading to a cascading effect of collisions and further debris generation.
• Currently, there are no specific international space laws governing LEO debris. However, most spacefaring nations adhere to the Space Debris Mitigation Guidelines 2002 established by the Inter-Agency Space Debris Coordination Committee (IADC), which the U.N. endorsed in 2007. These guidelines serve as a framework for mitigating the generation of space debris and minimizing its impact on space operations.

Key Strategies

• Active Debris Removal (ADR): Several agencies and organizations are researching and developing technologies for actively removing debris from orbit. ADR methods include capturing debris with nets, harpoons, or robotic arms, and then either de-orbiting it or moving it to a graveyard orbit.
• Space Traffic Management (STM): Efforts are underway to improve tracking and monitoring of space objects to minimize the risk of collisions. STM involves enhancing communication and coordination among satellite operators and space agencies to mitigate the risk of collisions and avoid generating additional debris.
• Design for Demise: Satellite manufacturers are exploring ways to design satellites and rocket stages to safely re-enter Earth's atmosphere at the end of their operational lives, ensuring they burn up completely and minimize the generation of debris.