ISRO’s module re-entered the atmosphere and impacted the Indian Ocean on April 4, 2025. Name the module.
- (a)POEM-X-R
- (b)POEM-4
- (c)POEM-6
- (d)POEM-K
Correct — B, POEM-4.
POEM is the PSLV Orbital Experimental Module: the rocket's spent PS4 fourth stage, kept alive in orbit as a platform for experiments instead of being cast off. The digit in the name is a serial for the platform's flight.
POEM-4 rode on PSLV-C60, launched 30 December 2024 with the twin SpaDeX satellites. After injecting them at 475 km, the stage was restarted down to a nearly circular 350 km orbit and passivated by venting its leftover propellant.
It hosted 24 payloads — 14 from ISRO and 10 from non-governmental entities. ISRO recorded its re-entry and impact at 08:03 IST (02:33 UTC) on 4 April 2025 over the Indian Ocean.
Carry away the link that fixes the name: a POEM's number comes from the flight that launched it, not from the date it came down.
- (a)POEM-X-R — The module is identified by the flight that put it up — PSLV-C60, on 30 December 2024 — and ISRO's account of the 4 April 2025 re-entry names that platform POEM-4.
A letter tag inside the name belongs to a different ISRO habit: the PSLV's configuration suffixes, CA, DL, QL and XL, which describe how the rocket is built rather than count a platform's flights.
- (c)POEM-6 — The serial counts the platform's flights, so it is fixed at launch and not by the year of re-entry. POEM-3 went up on PSLV-C58 with XPoSat on 1 January 2024; the SpaDeX flight of December 2024 is the one after it.
Six would point to a flight of the platform further along the series than SpaDeX's, so it does not name the stage ISRO tracked down into the Indian Ocean in April 2025.
- (d)POEM-K — A bare letter carries no flight information, and the serial digit is the part of the name that says which mission is meant. Here that mission is PSLV-C60's, launched on 30 December 2024.
In ISRO designations a letter usually does other work — the "C" in PSLV-C60, which marks an operational flight of the vehicle and says nothing about the module riding on it.
A PSLV normally finishes its job by releasing its satellites and leaving the fourth stage, PS4, adrift in orbit. POEM — PSLV Orbital Experimental Module — is the practice of keeping that stage useful instead.
The stage is stabilised and powered so it can host experiments once the primary satellites are away. Its engine is then restarted to drop it into a lower orbit, and the propellant still in its tanks is vented.
This sits where launch-vehicle engineering meets debris management. An abandoned upper stage is a large uncontrolled object with fuel still aboard; venting the tanks removes the risk of an accidental break-up, and a lower orbit shortens the time it spends in a crowded shell of space.
It is also cheap access to orbit. A small experiment that would otherwise wait for a satellite of its own gets a berth on hardware that has already flown, with power and pointing supplied by the stage.
- POEM stands for PSLV Orbital Experimental Module — the launch vehicle's spent PS4 fourth stage reused in orbit as a hosted-payload platform.
- POEM-4 flew on PSLV-C60, launched 30 December 2024, the mission that placed the twin SpaDeX satellites in a 475 km orbit.
- After injection the PS4 stage was restarted to bring POEM-4 into a nearly circular orbit at 350 km altitude, inclined 55.2 degrees.
- The stage was passivated by venting its leftover fuel, cutting the risk of an accidental break-up in orbit.
- POEM-4 hosted 24 payloads — 14 from ISRO and 10 from non-governmental entities.
- ISRO recorded POEM-4's re-entry and impact at 02:33 UTC (08:03 IST) on 4 April 2025, in the Indian Ocean.
- ISRO's radar tracking fed the re-entry prediction, and ISRO logged the impact at 02:33 UTC on 4 April 2025.
- POEM-3 flew on PSLV-C58 with XPoSat, launched 1 January 2024, and was also lowered to a 350 km circular orbit.
Dropping the stage to 350 km shortened its stay in orbit; drag brought it down a little over three months after launch.
- The date in the stem is the re-entry date; the number in POEM-4 comes from the launch, PSLV-C60 on 30 December 2024.
- POEM is not a satellite with a launch of its own — it is the launch vehicle's own upper stage, left in orbit and put to work.
- POEM-3 and POEM-4 sit in consecutive New Year windows, XPoSat on 1 January 2024 and SpaDeX on 30 December 2024.
- 350 km is the orbit the stage was lowered into; the SpaDeX satellites were injected higher up, at 475 km.
- ISRO numbers POEM platforms serially (POEM-1 to POEM-4), so a letter-suffixed name such as POEM-X-R or POEM-K does not correspond to any POEM flight ISRO has flown.
This is a one-join recall: a date, or an ocean, has to be matched to a mission name. The durable anchor is the flight the module belongs to, since the re-entry date changes nothing about its designation.
The same material can be set as a statement item on what POEM is — the launch vehicle's own upper stage rather than a separate satellite — and on why the stage is lowered and its tanks vented before it is abandoned.
MPPSC_2021_PRE_PaperI_Q82021Same organisation, very different depth. The MPPSC item asks only for the expansion of ISRO — Indian Space Research Organisation — while this one needs a named module tied to a specific mission and date. Both reward keeping ISRO's vocabulary straight: there, the acronym for the agency; here, the acronym POEM for the PSLV's reused upper stage.
- practice — not a real PYQ
POEM, associated with ISRO's PSLV missions, refers to which one of the following?
- (a)A ground-station network that tracks spent rocket stages
- (b)The PSLV's spent fourth stage, kept in orbit as a platform for hosted experiments
- (c)A solid propellant developed for the PSLV's strap-on boosters
- (d)A series of communication satellites operated from Sriharikota
Answerb — POEM expands to PSLV Orbital Experimental Module: the PS4 fourth stage, stabilised in orbit after satellite injection and used to carry payloads.(a) fails because POEM is not a ground network at all — it is the flight hardware itself, the PSLV's PS4 stage kept alive in orbit.
(c) fails because the name expands to a module, not a propellant. (d) fails because POEM stays part of the launch vehicle and carries no communication satellite series.
- practice — not a real PYQ
The POEM-4 platform reached orbit on which flight, and alongside which primary payload?
- (a)PSLV-C58, along with XPoSat
- (b)PSLV-C60, along with the twin SpaDeX satellites
- (c)PSLV-C55, along with Aditya-L1
- (d)PSLV-C61, along with Chandrayaan-3
Answerb — PSLV-C60 lifted off on 30 December 2024 with the twin SpaDeX satellites, and its PS4 stage was then operated as POEM-4.(a) fails because PSLV-C58 flew XPoSat on 1 January 2024, and the platform on that flight was POEM-3. (c) fails because Aditya-L1 was launched by PSLV-C57 in September 2023. (d) fails because Chandrayaan-3 was launched by an LVM3, not by a PSLV.
- practice — not a real PYQ
Consider the following statements about POEM-4: I. After the primary satellites were injected, the stage was manoeuvred into a lower, nearly circular orbit. II. It hosted payloads from ISRO as well as from non-governmental entities. III. It re-entered the atmosphere and impacted the Indian Ocean in April 2025. Which of the statements given above are correct?
- (a)I and II only
- (b)II and III only
- (c)I and III only
- (d)I, II and III
Answerd — all three hold. The stage was restarted after SpaDeX separation to reach a nearly circular 350 km orbit; it carried 24 payloads, 14 from ISRO and 10 from non-governmental entities.ISRO logged the re-entry and impact on 4 April 2025 in the Indian Ocean, which settles III. Each of the other three options leaves out one statement that is true, so none of them is complete.
- practice — not a real PYQ
Lowering a spent upper stage from about 475 km to about 350 km before abandoning it has which one of the following effects?
- (a)It increases the atmospheric drag acting on the stage, shortening its orbital life
- (b)It places the stage in a graveyard orbit reserved for retired spacecraft
- (c)It raises the stage above the band used by earth-observation satellites
- (d)It makes the stage's orbit more elliptical so that the stage can be recovered
Answera — the residual atmosphere is denser lower down, so a stage parked near 350 km meets more drag than one at 475 km and decays sooner. POEM-4 came down a little over three months after launch.(b) fails because graveyard orbits lie above the geostationary belt, tens of thousands of kilometres higher.
(c) fails because 350 km is below, not above, the sun-synchronous band many earth-observation satellites use. (d) fails because the burn made the orbit nearly circular, and the stage was not recovered.