On March 21, 2024, the Indian Space Research Organisation (ISRO) marked a significant achievement with the PSLV Orbital Experimental Module-3 (POEM-3), which successfully concluded its mission by re-entering the Earth’s atmosphere and disintegrating. This event, part of the PSLV-C58/XPoSat mission, is notable for leaving virtually no debris in orbit, demonstrating a commitment to minimizing space clutter.
The PSLV-C58 Mission, which was successfully completed on January 1, 2024, involved deploying all satellites into their predetermined orbits. Following this main objective, the final stage of the PSLV rocket was converted into a stabilized platform, known as POEM-3, by employing a 3-axis stabilization technique. This transformation signifies a strategic utilization of the rocket’s terminal stage beyond its primary satellite launch mission.
“A 3-axis stabilization technique in the context of spacecraft and satellites refers to the method of controlling the orientation of the object in space with respect to all three spatial dimensions — pitch, yaw, and roll. This ensures the spacecraft maintains a stable position and orientation, allowing it to face the desired direction.
It’s achieved through various mechanisms, such as reaction wheels, gyroscopes, and sometimes thrusters, which apply small amounts of force or torque to adjust the spacecraft’s position as needed. This stabilization is crucial for a variety of tasks, including precise pointing of instruments for data collection, communication with Earth, and optimal positioning of solar panels for energy collection,” explains Bengaluru based Girish Linganna, Aerospace & Defence Analyst.
“In the case of POEM-3, employing this technique meant that the final stage of the PSLV rocket was not just passively drifting in space after its primary mission but was actively maintaining a stable orientation, allowing for further experiments or tasks to be carried out,” he adds.
According to Linganna, “The stage was intentionally lowered from its initial orbit of 650 kilometers down to 350 kilometers above the Earth. This strategic maneuver accelerated its re-entry into the Earth’s atmosphere, ensuring that it would not remain in orbit for a prolonged period. Additionally, the stage underwent a passivation process, which involved the safe removal of any leftover propellant. This step was crucial for reducing the risk of accidental explosions or break-ups that could generate space debris, further emphasizing the mission’s commitment to space sustainability and safety.”
POEM-3 was equipped with nine distinct experimental payloads, designed to perform technology demonstrations and scientific experiments on newly developed domestic systems. Six of these payloads were contributed by New Generation Enterprises (NGEs) through the Indian National Space Promotion and Authorization Center (IN-SPACe). Within a month, these payloads successfully achieved their mission objectives, demonstrating the effectiveness and potential of the collaboration between ISRO, IN-SPACe, and the private sector in advancing space technology and research.
The Upper stage of the rocket (POEM-3), after completing its mission in space, gradually moved closer to Earth due to natural forces, mainly the resistance from the thin layers of atmosphere it encountered, which is known as atmospheric drag. This process caused it to slowly lose height from its orbit around Earth. It was anticipated that this module, known by its tracking number NORAD ID 58695, would fall into the North Pacific Ocean near the coordinates latitude 6.4 North and longitude 158.7 West. This event was expected to happen on March 21, 2024, at 2:04 PM UTC, which corresponds to 7:34 PM Indian Standard Time (IST). Essentially, the rocket stage was guided back to Earth safely, avoiding any potential hazards, and it was planned to land in the ocean, away from populated areas.
“The POEM initiative, acting as an economical platform for conducting brief experiments in space, has broadened opportunities for academic institutions, startups, and New Generation Enterprises (NGEs) to test their innovative payloads. Through this approach, ISRO has created new pathways for various sectors to engage in space research and experimentation.This new chance has been taken advantage of by many startups, universities, and new space companies, allowing them to conduct space experiments. These experiments have covered a range of innovations like electric propulsion systems, devices for releasing satellites, and technology for tracking stars, making space research more accessible and diverse,” states Linganna.
What is new in POEM?
POEM has introduced several new features to make space experiments more efficient and versatile. These include simplifying the control electronics into a single streamlined system, using commercial-grade parts in the computer systems that manage the mission, and providing standard connections for electrical power, as well as for sending and receiving data. It also introduces advanced navigation techniques that use gyroscopes, sun sensors, and magnetometers to accurately determine its position in space. To ensure experiments can be conducted without any issues, POEM-3 kept its movements extremely steady, with any twisting or turning kept under half a degree per second. Additionally, it employed creative methods to safely get rid of any leftover fuel, reducing any potential disruptions caused by the fuel disposal process. These advancements make POEM a cutting-edge platform for space research, accessible for a wide range of scientific explorations.
POEM, short for PSLV Orbital Experimental Module, is a pioneering mission undertaken by ISRO that utilizes the fourth stage of the Polar Satellite Launch Vehicle (PSLV) as a platform to conduct scientific experiments in orbit. This innovative approach transforms a segment of the PSLV launch vehicle into a functioning laboratory for space-based research.
The PSLV operates with four stages, with the initial three stages descending into the ocean after their fuel is expended. The fourth and final stage (PS4), which is responsible for placing the satellite into its orbit, traditionally remains as debris in space following its mission completion.
Yet, for the PSLV-C53 mission, the previously discarded final stage will serve a new purpose as a “stabilized platform” for conducting experiments.
The PS4 (fourth stage) will orbit the Earth as a stabilized platform. POEM is equipped with its own Navigation Guidance and Control (NGC) system, designed to manage the spacecraft’s orientation within set boundaries. This NGC system functions as the platform’s “brain,” ensuring it maintains a stable position with precise accuracy.
POEM is equipped with payloads and obtains its power from solar panels installed around the PS4 tank, supplemented by a lithium-ion battery. For navigation, it utilizes four sun sensors, a magnetometer, gyroscopes, and the NavIC system. Additionally, it features specialized control thrusters powered by stored helium gas and is equipped with a telecommand capability for receiving instructions.
POEM vs. Satellites
Satellites are like specialized spaceships built for long-term missions in space, such as weather monitoring, communication, or navigation. They have their own power, communication systems, and advanced controls to stay in orbit for years.
POEM is different, it’s a temporary orbital lab created by repurposing the final stage of a rocket. It carries scientific experiments into space for a short period, using basic controls for stability. Instead of staying in orbit long-term, POEM is designed to safely re-enter Earth’s atmosphere after completing its experiments, leaving no debris behind,” explains Linganna.
Clean Orbit, Successful Mission
The Vikram Sarabhai Space Centre (VSSC) played a pivotal role in the development and implementation of the POEM concept by enhancing the fourth stage of the PSLV rocket. The PSLV-C58/XPoSat mission represents the third instance (POEM-3, means 3rd time) in this series, with each mission featuring a POEM that has achieved success. This initiative demonstrates the VSSC’s continuous commitment to advancing space technology through innovative use of existing resources. The payload activities were successfully managed by the spacecraft operations team from the Mission Operations Complex (MOX) at ISTRAC. Meanwhile, ISRO’s System for Safe and Sustainable Spacecraft Operations Management (IS4OM) continuously observed and assessed the gradual descent of the orbit throughout the mission. Until it was close to re-entering the atmosphere, POEM-3 was monitored by ground stations at ISTRAC. Additionally, the PS4 stage was tracked by the Multi-Object Tracking Radar (MOTR) at Sriharikota until the morning of March 21. Other ISRO centers such as URSC, LPSC, and IISU also provided support for POEM-3.