ISRO’s POEM (PSLV Orbital Experiment Module) repurposes the spent fourth stage (PS4) of the Polar Satellite Launch Vehicle as a long-duration microgravity platform By equipping PS4 with solar panels, batteries, sensors and thrusters, POEM can power and stabilize itself after the primary mission, carrying experiments in orbitisro.gov.inisro.gov.in. POEM has flown on four missions (POEM-1 through POEM-4) between 2022–2024, each time after the primary satellite payloads were deployed.
This innovative use of a discarded booster provides a low-cost testbed for startups and academia. It also ensures the stage is de-orbited later to avoid space debris.
POEM-1 (PSLV-C53, June 2022)
PSLV-C53 (DS-EO mission) launched on 30 June 2022 and featured the first POEM flightisro.gov.in. For the first time, the fourth stage remained operational as a 3-axis-stabilized platform, using cold-gas thrusters and solar cells wrapped around the propellant tankisro.gov.in. POEM-1 carried six payloads (all non-separable), including two from Indian startups via IN-SPACe: Digantara’s ROBI (radiation dosimeter) and Dhruva Space’s DSOD-1U (1U cubesat deployer)en.wikipedia.org. Other experiments included a software-defined radio transmitter, a UHF transponder, an optical-visual imaging experiment (OP-VIS) with cameras, and a symbolic Indian flag/preamble to the Constitutionen.wikipedia.org. In-orbit power was ~150 W, and navigation used sun sensors, a magnetometer, gyros and NavIC positioningen.wikipedia.orgisro.gov.in.
POEM-2 (PSLV-C55, April 2023)
On 22 April 2023, POEM-2 rode atop PSLV-C55 (TeLEOS-2 mission)en.wikipedia.org. This flight introduced deployable solar arrays (~500 W) on PS4en.wikipedia.org. POEM-2 hosted seven experiments: an Advanced Retarding Potential Analyzer (ARIS-2) by IIST for ionospheric studies, a PiLOT onboard computer testbed, and a low-cost star sensor (“Starberry”) by IIAen.wikipedia.org. It also carried Bellatrix Aerospace’s ARKA200 xenon Hall thruster, and three devices by Dhruva Space – a 3U cubesat deployer, a 6U deployer, and an S- & X-band transceiver (SatOrbiterLink)en.wikipedia.org. Like POEM-1, it was 3-axis stabilized with Helium cold-gas thrusters. The mission life was planned for ~1 monthen.wikipedia.org, after which natural drag brings the stage down.
POEM-3 (PSLV-C58/XPoSat, Jan 2024)
The third POEM mission flew on PSLV-C58 (XPoSat) launched 1 January 2024isro.gov.in. After deploying the XPoSat observatory, the PS4 stage was deliberately lowered from 650 km to 350 km to expedite re-entryisro.gov.inen.wikipedia.org. POEM-3 carried ten payloads (~145 kg total), seven from non-governmental entities (NGEs) via IN-SPACe and three from ISRO/academiaisro.gov.in. Notable experiments included: Bellatrix Aerospace’s xenon Hall thruster (ARKA200) and green thruster (RUDRA 0.3 HPGP), Dhruva Space’s 3U nano-satellite bus test (LEAP-TD), and VSSC’s 100-W fuel cell power system and silicon-graphite batteryen.wikipedia.orgen.wikipedia.org. Scientific payloads ranged from a Radiation Shielding Module (RSEM) by TakeMe2Space to an interplanetary dust counter (DEX by PRL), a solar UV index sensor (WeSAT by LBS), and an amateur radio repeater (BeliefSat-0 by KJSIT)en.wikipedia.org. All mission objectives were met within about one monthisro.gov.in. On 21 March 2024, POEM-3 re-entered Earth’s atmosphere over the Pacific (impact ~19:34 IST), leaving zero debris in orbitindiatoday.in.
POEM-4 (PSLV-C60/SpaDeX, Dec 2024)
POEM-4 flew on PSLV-C60 (SpaDeX mission) launched 30 December 2024en.wikipedia.org. This mission carried 24 payloads (~120 kg), a three-fold jump from POEM-3isro.gov.in. Ten experiments (from startups and universities) were selected via IN-SPACe, and 14 were ISRO projectsen.wikipedia.org.
Mission carried out in-orbit scientific experiments at an altitude of 350km with a 55-degree inclination.
Highlights include two robotic demos by ISRO/Inertial Systems Unit: a Relocatable Robotic Manipulator (Walking Robotic Arm) with 7 DOF for in-orbit servicing, and a Debris-Capture Arm (VSSC) to snag and handle space junkisro.gov.in
Other ISRO payloads: a reaction-wheel assembly for attitude controlisro.gov.in, a multi-sensor inertial reference package (MIRS) testing miniaturized gyros and magnetometersisro.gov.in, and a lead-free DC-DC power converter (LEXS) to validate RoHS-compliant electronics in spaceisro.gov.in. SPL developed an Ionospheric IDEA-V2 suite (Langmuir probes, electron temperature analyser, neutral wind sensor), and ISRO tested an advanced NavIC-based plasmaspheric density measurement (PLASDEM)isro.gov.inisro.gov.in.
NGE payloads (not all listed here) covered plant growth, biology and imaging (e.g. automated plant module CROPS, gut microbiology, amateur radio transmitter, SAR demos, AI lab). By early April 2025, POEM-4’s orbit decayed to ~174×165 km and it re-entered safely on 4 Apr 2025 over the Indian Oceanndtv.comndtv.com. Engines had been reignited post-deployment to lower the orbit to 350 km, and residual fuel was vented for passivationndtv.comindiatoday.in. ISRO reports all 24 payloads performed as expected, yielding valuable datandtv.com.
IN-SPACe, which is the autonomous nodal agency under Department of Space to promote NGE’s undertake space activities.
De-orbiting & Debris Mitigation
A key feature of POEM is its debris-safe end-of-life. After experiments conclude, the PS4 stage is actively de-orbited: in each mission ISRO has reignited the remaining stage engine to drop altitude (e.g. to ~350 km) and then vented any leftover propellant to passivate the tankindiatoday.inndtv.com. Tracking data (via ISTRAC, MOTR and USSPACECOM) was used to predict the re-entry pathndtv.com. For POEM-3 the stage naturally decayed and burned up on 21 Mar 2024, and for POEM-4 it re-entered on 4 Apr 2025, both times leaving essentially “zero debris”indiatoday.inndtv.com. These steps embody ISRO’s Debris-Free Space Mission ethos: reusable launchers with responsible disposal. In fact, ISRO’s space policy (2023) mandates compliance with international debris mitigation guidelines and the development of de-orbiting technologiesisro.gov.inisro.gov.in. POEM has therefore become a practical demonstration of sustainable spacecraft operations (managed by IS4OM) and safe disposal.
Microgravity Science & Space Sustainability
By offering a stable, powered platform in LEO, POEM enables short-duration microgravity experiments without building a full satellite bus. The experiments range from life sciences to advanced tech: plant and microbiology modules test growth in microgravity (e.g. CROPS and Amity’s plant cell payload)isro.gov.inen.wikipedia.org, while startups demonstrate cutting-edge systems (green/hydrogen thrusters, SA fusion for SAR imaging, AI data processing) in real space conditions. Electric propulsion (Hall thrusters and green-propellant thrusters) and fuel cells tested on POEM directly feed into ISRO’s strategic R&D (e.g. fuel cells for the upcoming Bharatiya Antariksh Stationswarajyamag.comisro.gov.in). Repurposing the PSLV stage dramatically lowers cost and schedule: payload developers need only focus on their experiment, since POEM supplies power, comms and attitude controlisro.gov.inisro.gov.in. This cost-effective approach “opens new vistas for academia, startups, and NGEs to experiment in space” as ISRO notesisro.gov.in. Importantly, using a spent stage (rather than launching a new mini-sat) also cuts down space junk, advancing the space sustainability agenda.
Public-Private Collaboration & IN-SPACe
POEM exemplifies India’s public–private space synergy. The payloads come from a mix of ISRO and NewSpace players (Bellatrix, Dhruva Space, Inspecity, TakeMe2Space, GalaxEye, Piersight, and universities)isro.gov.inen.wikipedia.org. IN-SPACe has played a pivotal role: it solicited and facilitated NGEs to join POEM. For POEM-3, 6 of 9 experiments were from IN-SPACe-selected entitiesisro.gov.in; for POEM-4, 10 of 24 were selected via IN-SPACeen.wikipedia.org. NSIL (ISRO’s commercial arm) arranged the launches (PSLV C53/C55 were NSIL missions)isro.gov.inisro.gov.in. This model mirrors India’s 2020s space reforms: a level playing field for private players, and active support for start-ups and academic institutesisro.gov.inisro.gov.in. Notably, ISRO incorporated industrial-grade avionics (standardized interfaces, heritage components) into POEM to streamline payload integrationisro.gov.in. In effect, POEM provides a proven “ride” for private R&D – lowering barriers for NewSpace firms to qualify technologies in orbit.
Strategic Vision & Policy Alignment
POEM strongly aligns with India’s space strategy. The 2023 Space Policy emphasises advanced R&D, a robust private sector, and debris managementisro.gov.inisro.gov.in. POEM puts these into action: it advances indigenous technology (e.g. propulsion, power, robotics) through rapid flight-demonstration, while engaging academia and industry. By disposing spent stages responsibly, POEM supports the goal of “safe and sustainable space operations” outlined in policyisro.gov.in. ISRO explicitly cites POEM as evidence of its “Debris-Free Space Mission” commitmentndtv.comisro.gov.in. Further, the data from POEM experiments (e.g. fuel cells, robotic arms, life-support demonstrations) feed directly into India’s future programs (Gaganyaan, space station). In summary, POEM embodies a low-cost, reusable infrastructure approach and a vibrant space ecosystem – key pillars of India’s current space vision.
Key Facts (Prelims)
- POEM Definition: PSLV Orbital Experiment Module (POEM) is the spent fourth stage (PS4) of the PSLV repurposed as an on-orbit platformen.wikipedia.org.
- Missions: POEM-1 (PSLV-C53, June 2022)isro.gov.in; POEM-2 (PSLV-C55, April 2023)en.wikipedia.org; POEM-3 (PSLV-C58, Jan 2024)isro.gov.in; POEM-4 (PSLV-C60, Dec 2024)en.wikipedia.org.
- Capabilities: POEM provides ~28 V power bus, 1 GB storage, ~200–500 W solar power, and 3-axis attitude control (±1° sunlit accuracy)en.wikipedia.org.
- Payloads: Each POEM can carry up to ~30 kg (≤3U) of non-separable experiments. POEM-1 carried 6 payloadsen.wikipedia.org; POEM-2 – 7 payloadsen.wikipedia.org; POEM-3 – 9–10 payloadsisro.gov.in; POEM-4 – 24 payloadsisro.gov.in.
- De-orbit: All POEM stages are actively de-orbited after use. For example, the C58 stage was lowered to 350 km and passivated, burning up on re-entry to leave no debrisindiatoday.inndtv.com. POEM-4 similarly decayed and re-entered Apr 2025indiatoday.in.
- IN-SPACe & Startups: IN-SPACe selected private payloads for POEM. POEM-3 had 6 experiments from NewSpace/startups via IN-SPACeisro.gov.in. POEM-4 had 10 such NGEs (start-ups/universities)en.wikipedia.org.
- Use Cases: POEM is used for microgravity and tech demos (thrusters, fuel cells, sensors), boosting space science and validating technologies for future missionsisro.gov.inswarajyamag.com.
Analytical Insights (GS III)
POEM is a striking example of innovation through reuse and collaboration. Instead of discarding the PSLV’s upper stage, ISRO upcycles it into a science platform – saving cost and enabling rapid experiments. This model democratizes access to space for Indian researchers: startups need not build full satellites, and academic experiments can fly as “hosted payloads.” The public–private R&D ecosystem benefits greatly: Bellatrix and Dhruva successfully space-qualify new thrusters and buses, ISRO validates life-support tech for the future space station, and ISAC/IIST hone small-sat controllers, all under one mission framework.
In strategic terms, POEM advances India’s low-cost space infrastructure. It underwrites broad research (from medical biology to Earth observation tech) at a fraction of a dedicated satellite program. It also underlines India’s responsible role in space: by engineering zero-debris re-entries, POEM showcases leadership in orbital sustainability (complementing ISRO’s debris monitoring and de-orbit researchisro.gov.inisro.gov.in).
Finally, POEM embodies current policy goals. The 2023 Space Policy calls for greater NGE participation, private innovation, and debris mitigationisro.gov.inisro.gov.in – all realized by POEM. It aligns with “Make in India” for space hardware and with international norms (IADC) on space sustainability. As a result, POEM not only achieves its own scientific objectives but also strengthens India’s broader space capabilities and ecosystem.
Sources: ISRO mission releases and reportsisro.gov.inisro.gov.inndtv.com; Wikipedia and news summaries of POEM-1–4en.wikipedia.orgindiatoday.in; Indian space policy documentsisro.gov.inisro.gov.in.
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