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{{Short description|Satellite bus derived out of launch vehicle upper stage}}
{{Use dmy dates|date=July 2023}}
{{Infobox spaceflight
| name = PSLV Orbital Experimental Module
| names_list = PS4 Orbital Platform
| image = PSLV-C11_Fourthstage.jpg
| image_caption = Unmodified PSLV fourth stage for PSLV-C11 campaign.
| mission_type = Technology
| dry_mass = ~920 kg
| payload_mass = up to 30 kg
| dimensions = Length: 3 meter {{line break}} Diameter: 2 meter
| power = 200 to 500 watts
}}

'''PSLV Orbital Experiment Platform''' ('''POEM''') also known as PSLV Stage 4 Orbital Platform (PS4-OP)<ref>{{Cite web |title=Payloads |url=https://www.isro.gov.in/Payloads.html |access-date=2023-07-24 |website=www.isro.gov.in |archive-date=24 July 2023 |archive-url=https://web.archive.org/web/20230724215843/https://www.isro.gov.in/Payloads.html |url-status=live }}</ref> is an orbital [[micro-gravity]] [[Testbed|test bed]] based on spent fourth stage of [[PSLV]]. By adding modular subsystems for power generation, communication and stabilization like [[Solar cell|photovoltaic cells]], Telemetry and Telecommand (TT&C) package, attitude control system, data storage etc to the PSLV fourth stage, it can function as a [[satellite bus]]. This augmented stage can then host payloads for up to six months while in orbit, making it useful for qualifying components, gaining space heritage and conduct experiments in micro-gravity conditions. Usually the fourth stage of PSLV is discarded after deployment of satellite and remains in orbit for a significant duration in a passive state as a piece of [[Space debris#Boosters|space debris]].<ref name=":0" /><ref name=":1" />

== Objective ==
POEM or PS4-OP was conceived by [[Vikram Sarabhai Space Centre|VSSC]]/[[ISRO]] to help Indian academia and start-ups by providing a low cost platform with essential subsystems to support their payloads hence lowering the barriers of reaching orbit. POEM off-loads the burden of designing, qualifying, procuring a satellite bus, setting up a ground station etc. which reduces the development time and costs associated with using space-grade components thus allowing entities to just focus on payload.<ref name=":0" /><ref name=":1" /><ref name=":7" />

== History ==
PSLV fourth stage or PS4 has often been used to carry non-separable payloads like AAM on PSLV-C8,<ref name="PSLV_C8_Brochure">{{cite web |title=PSLV C8 / AGILE brochure |url=https://www.isro.gov.in/sites/default/files/flipping_book/PSLV-C8/files/assets/common/downloads/publication.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200223011646/https://www.isro.gov.in/sites/default/files/flipping_book/PSLV-C8/files/assets/common/downloads/publication.pdf |archive-date=23 February 2020 |access-date=23 February 2020}}</ref> [[Luxspace|Rubin 9.1]]/[[Rubin 9.2]] on PSLV-C14<ref>{{cite web |title=PSLV C14/Oceansat-2 brochure |url=https://www.isro.gov.in/sites/default/files/flipping_book/PSLV-C14/files/assets/common/downloads/publication.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200806094152/https://www.isro.gov.in/sites/default/files/flipping_book/PSLV-C14/files/assets/common/downloads/publication.pdf |archive-date=6 August 2020 |access-date=23 February 2020}}</ref> and mRESINS on PSLV-C21<ref>{{cite web |title=Space-India July 2012 to August 2013 |url=https://www.dos.gov.in/sites/default/files/flipping_book/Space%20India%20July%2012-Aug%2013/files/assets/common/downloads/Space%20India%20July%2012-Aug%2013.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200806152719/https://www.dos.gov.in/sites/default/files/flipping_book/Space%20India%20July%2012-Aug%2013/files/assets/common/downloads/Space%20India%20July%2012-Aug%2013.pdf |archive-date=6 August 2020 |access-date=23 February 2020}}</ref> etc. but such payloads could be supported only for a very short duration as PS4 lacked the capacity to generate power and maintain attitude stability. So it was proposed to augment PS4 with modular subsystems to convert it into a long duration orbital platform after completion of primary mission.<ref name=":0">{{cite web |date=21 February 2019 |title=Opportunities for science experiments in the fourth stage of India's PSLV |url=http://www.unoosa.org/documents/pdf/copuos/stsc/2019/tech-55E.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/http://www.unoosa.org/documents/pdf/copuos/stsc/2019/tech-55E.pdf |archive-date=2022-10-09}}</ref><ref name=":1">{{cite web |date=15 June 2019 |title=Announcement of Opportunity (AO) for Orbital platform: an avenue for in-orbit scientific experiments |url=https://www.isro.gov.in/sites/default/files/orbital_platform-_ao.pdf |url-status=dead |archive-url=https://web.archive.org/web/20200806072033/https://www.isro.gov.in/sites/default/files/orbital_platform-_ao.pdf |archive-date=6 August 2020 |access-date=23 February 2020}}</ref><ref>{{cite web |last=Kumar |first=Chethan |title=2 days after Space Station news, Isro calls for "docking experiments" on PSLV stage-4 |url=https://timesofindia.indiatimes.com/india/2-days-after-space-station-news-isro-calls-for-docking-experiments-on-pslv-stage-4/articleshow/69800354.cms |url-status=live |archive-url=https://web.archive.org/web/20190824073052/https://timesofindia.indiatimes.com/india/2-days-after-space-station-news-isro-calls-for-docking-experiments-on-pslv-stage-4/articleshow/69800354.cms |archive-date=24 August 2019 |access-date=23 February 2020 |work=The Times of India}}</ref>

In 2017 as an early demonstration on [[PSLV-C37|PSLV-C37/Cartosat-2D]]<ref>{{Cite AV media |url=https://www.youtube.com/watch?v=fujsQ5teHJI&t=4094s |title=The launch of PSLV–C37/CARTOSAT – 2 Series Satellite - Live |date=15 February 2017 |time=1 hour 08 minutes 14 seconds}}</ref> and [[PSLV-C38|PSLV-C38/Cartosat-2E]] campaigns,<ref name=":2">{{Cite web |title=In-situ observations of rocket burn induced modulations of the top side ionosphere using the IDEA payload on-board the unique orbiting experimental platform (PS4) of the Indian Polar Orbiting Satellite Launch Vehicle mission - ISRO |url=https://www.isro.gov.in/situ-observations-of-rocket-burn-induced-modulations-of-top-side-ionosphere-using-idea-payload-board |url-status=live |archive-url=https://web.archive.org/web/20220921000216/https://www.isro.gov.in/situ-observations-of-rocket-burn-induced-modulations-of-top-side-ionosphere-using-idea-payload-board |archive-date=21 September 2022 |access-date=2022-06-27 |website=www.isro.gov.in |language=en}}</ref> PS4 was kept operational and monitored for over ten orbits after completion of its primary mission of deploying spacecraft.<ref name=":3">{{cite web |title=Department of Space Annual Report 2017-18 |url=https://www.isro.gov.in/sites/default/files/article-files/node/9805/annualreport2017-18.pdf |url-status=live |archive-url=https://web.archive.org/web/20180213093132/https://www.isro.gov.in/sites/default/files/article-files/node/9805/annualreport2017-18.pdf |archive-date=13 February 2018}}</ref><ref>{{cite web |last=rajasekhar |first=pathri |date=2017-06-20 |title=Isro to lower rocket's altitude |url=https://www.deccanchronicle.com/science/science/200617/isro-to-lower-rockets-altitude.html |url-status=live |archive-url=https://web.archive.org/web/20200806095054/https://www.deccanchronicle.com/science/science/200617/isro-to-lower-rockets-altitude.html |archive-date=6 August 2020 |access-date=23 February 2020 |publisher=Deccan Chronicle}}</ref> Fourth stage on PSLV-C38 hosted IDEA (Ionization Density and Electric field Analyzer) as a non-separable payload by Space Physics Laboratory of VSSC,<ref name=":3" /><ref name=":2" /> two other non-separable payloads were mAMP and 'Earth Pointing Platform'.<ref name="YT_5thMPVM">{{Cite AV media |url=https://www.youtube.com/watch?v=bwV0S7uEPMg&t=3036s |title=5th Manohar Parrikar Vidnyan Mahotsav: Talk By ISRO Chairman Dr. S. Somanath |date=13 December 2023 |time=50 min. 36 sec.}}</ref>
[[File:Render of PS4 Orbital Platform payload deck.webp|thumb|300x300px|'''Render of PS4 Orbital Platform payload deck''']]
In January 2019, [[PSLV-C44|PSLV-C44/Microsat-R]] became the first campaign where PS4 functioned as an independent orbital platform for short duration as the provisions for on-board power generation capacity were not yet made.<ref>{{cite news |last=Rajwi |first=Tiki |date=2019-01-12 |title=PSLV lift-off with added features |newspaper=The Hindu |url=https://www.thehindu.com/news/national/kerala/pslv-lift-off-with-added-features/article25981654.ece |url-status=live |access-date=23 February 2020 |archive-url=https://web.archive.org/web/20200806161530/https://www.thehindu.com/news/national/kerala/pslv-lift-off-with-added-features/article25981654.ece |archive-date=6 August 2020 |issn=0971-751X}}</ref> It hosted a 1U cubesat called KalamSAT-V2 as a non-separable payload by Space Kidz India based on [[Interorbital Systems]] kit.<ref>{{cite web |title=PSLV-C44 - ISRO |url=https://www.isro.gov.in/launcher/pslv-c44 |url-status=dead |archive-url=https://web.archive.org/web/20190117013408/https://www.isro.gov.in/launcher/pslv-c44 |archive-date=17 January 2019 |access-date=26 June 2020 |website=isro.gov.in}}</ref><ref>{{cite tweet|number=1088526772109422592|user=interorbital|title=Congratulations to ISRO and SpaceKidzIndia on getting their CubeSat into orbit! The students modified their IOS CubeSat kit, complete w/ their own experiments!|author=Interorbital Systems|date=25 January 2019}}</ref><ref>{{cite web |last=Singh |first=Surendra |date=16 December 2018 |title=In a first, ISRO will make dead rocket stage "alive" in space for experiments |url=https://timesofindia.indiatimes.com/india/in-a-first-isro-will-make-dead-rocket-stage-alive-in-space-for-experiments/articleshow/67067817.cms |url-status=live |archive-url=https://web.archive.org/web/20201108132514/https://timesofindia.indiatimes.com/india/in-a-first-isro-will-make-dead-rocket-stage-alive-in-space-for-experiments/articleshow/67067817.cms |archive-date=8 November 2020 |access-date=23 February 2020 |work=The Times of India}}</ref> Later in April, the fourth stage on [[PSLV-C45|PSLV-C45/EMISAT]]<ref>{{Cite web |title=PSLV-C45/EMISAT Mission Press-kit |url=https://www.isro.gov.in/sites/default/files/pslv-c45_launch_kitv5.0_fn_23.03.19.pdf |archive-url=https://web.archive.org/web/20190323093804/https://www.isro.gov.in/sites/default/files/pslv-c45_launch_kitv5.0_fn_23.03.19.pdf |archive-date=23 March 2019 |access-date=23 July 2023 |url-status=dead }}</ref> had its own power generation capacity as it was augmented with an array of fixed [[solar cell]]s wrapped around the propellant tank of PS4 generating about 200 watts of power.<ref>{{cite web |last=Clark |first=Stephen |title=Indian military satellite, 20 more Planet imaging CubeSats launched by PSLV |url=https://spaceflightnow.com/2019/04/01/indian-military-satellite-20-more-planet-imaging-cubesats-aboard-successful-pslv-launch/ |url-status=live |archive-url=https://web.archive.org/web/20190406042135/https://spaceflightnow.com/2019/04/01/indian-military-satellite-20-more-planet-imaging-cubesats-aboard-successful-pslv-launch/ |archive-date=6 April 2019 |access-date=2020-02-23 |publisher=Spaceflight Now}}</ref><ref name="PSLV_C55_Presser">{{Cite AV media |url=https://www.youtube.com/watch?v=lGyCpYFS90o&t=81s |title=Press briefing by S Somanath (Chairman, ISRO) |date=22 April 2023 |time=1 minutes 22 seconds}}</ref><ref>{{Cite web |title=PSLV-C45/EMISAT Mission Curtain Raiser video (English) |url=https://www.isro.gov.in/mission_PSLV_C45_CameraView.html |access-date=2023-07-23 |website=www.isro.gov.in |archive-date=26 July 2023 |archive-url=https://web.archive.org/web/20230726171613/https://www.isro.gov.in/mission_PSLV_C45_CameraView.html |url-status=live }}</ref> Three payloads hosted on PS4-OP were, Advanced Retarding Potential Analyzer for Ionospheric Studies (ARIS 101F) by IIST,<ref>{{cite web |title=Department of Avionics, R. Sudharshan Kaarthik, Ph.D (Assistant Professor) |url=https://www.iist.ac.in/avionics/sudharshan.kaarthik |url-status=live |archive-url=https://web.archive.org/web/20200213005932/https://www.iist.ac.in/avionics/sudharshan.kaarthik |archive-date=13 February 2020 |access-date=23 February 2020}}</ref> experimental [[Automatic identification system|AIS]] payload by ISRO and AISAT by [[Satellize]].<ref>{{cite web |title=Exseed Sat-2 |url=https://satellize.com/index.php/exseed-sat-2/ |url-status=live |archive-url=https://web.archive.org/web/20200223011624/https://satellize.com/index.php/exseed-sat-2/ |archive-date=23 February 2020 |access-date=23 February 2020 |publisher=Satellize}}</ref> To function as an orbital platform, fourth stage was put in [[Spin-stabilisation|spin-stabilized]] mode using its RCS thrusters.<ref name=":6">{{Cite web |date=16 June 2021 |title=Opportunity for Scientific Experiments on PSLV Upper Stage Orbital Platform |url=https://www.unoosa.org/documents/pdf/psa/hsti/Hyper-Microgravity_Webinar2021/Hyper-Microgravity_Webinar2021/9_RegionalActivities/R._Senan_Hypermicrogravity_ISRO.pdf |url-status=live |archive-url=https://ghostarchive.org/archive/20221009/https://www.unoosa.org/documents/pdf/psa/hsti/Hyper-Microgravity_Webinar2021/Hyper-Microgravity_Webinar2021/9_RegionalActivities/R._Senan_Hypermicrogravity_ISRO.pdf |archive-date=2022-10-09}}</ref> PS4-OP on this campaign had mission life of 3 months and AISAT payload onboard was operational for almost a year.<ref name=":6" /><ref name="PSLV_C55_Presser" /> According to ISRO, the PS4-OP can transmit commands and data to sustain the payloads and regulate its location in three different orientations.<ref>{{Cite web |last=Linganna |first=Girish |date=3 January 2025 |title=While POEM-4 Experiments Run, SPADEX Prepares for Docking Day |url=https://www.india.com/news/india/while-poem-4-experiments-run-spadex-prepares-for-docking-day-7510978/ |access-date=2025-01-03 |website=india.com |language=en}}</ref>

After these initial testing campaigns, ISRO issued an Announcement of Opportunity in June 2019 to carry out in-orbit scientific experiments on PS4 orbital platform.<ref name=":1" /> And in following years POEM-1 aboard [[PSLV-C53]]/DS-EO campaign in June 2022<ref>{{Cite web |title=NSIL's Second Dedicated commercial launch "PSLV-C53/ DS-EO Mission" successfully accomplished on 30th June 2022 |url=https://www.nsilindia.co.in/sites/default/files/Press%20Release%20-%20PSLV%20C-53%20DS-EO%20Mission.pdf |archive-url=https://web.archive.org/web/20230518082810/https://www.nsilindia.co.in/sites/default/files/Press%20Release%20-%20PSLV%20C-53%20DS-EO%20Mission.pdf |archive-date=18 May 2023}}</ref> and POEM-2 aboard [[PSLV-C55]]/TeLEOS-2 campaign in April 2023 were launched.<ref>{{Cite web |title=India's PSLV launches with two Singaporean satellites – Spaceflight Now |url=https://spaceflightnow.com/2023/04/22/indias-pslv-launches-with-two-singaporean-satellites/ |access-date=2023-07-26 |language=en-US |archive-date=6 June 2023 |archive-url=https://web.archive.org/web/20230606165526/https://spaceflightnow.com/2023/04/22/indias-pslv-launches-with-two-singaporean-satellites/ |url-status=live }}</ref> Both of these orbital platforms had mature configurations utilizing 3-axis stabilization and on-board power generation capacity.<ref name=":8">{{Cite web |title=PSLV-C53/DS-EO mission |url=https://www.isro.gov.in/sites/default/files/article-files/pslv-c53-ds-eo-mission/pslv-c53-ds-eo-mission-brochure-english/brochure_pslv_c53-ds-eo_mission_english.pdf |archive-url=https://web.archive.org/web/20220705162540/https://www.isro.gov.in/sites/default/files/article-files/pslv-c53-ds-eo-mission/pslv-c53-ds-eo-mission-brochure-english/brochure_pslv_c53-ds-eo_mission_english.pdf |archive-date=5 July 2022}}</ref><ref name=":9">{{Cite web |title=PSLV-C55/TeLEOS-2 mission press kit |url=https://www.isro.gov.in/media_isro/pdf/Missions/PSLVC55/PSLVC55TeLEOS.pdf |archive-url=https://web.archive.org/web/20230528023203/https://www.isro.gov.in/media_isro/pdf/Missions/PSLVC55/PSLVC55TeLEOS.pdf |archive-date=28 May 2023}}</ref>

In July 2023, [[Indian National Space Promotion and Authorisation Centre]] (IN-SPACe) issued an announcement of opportunity inviting payloads to be hosted aboard upcoming POEM campaigns tentatively scheduled between November 2023 and June 2024.<ref name=":7">{{Cite web |title=IN-SPACe Announcement of Opportunity for hosting of payloads on POEM Page - IN-SPACe |url=https://www.inspace.gov.in/inspace?id=inspace_hosting_payloads_on_poem_page |access-date=2023-07-25 |website=www.inspace.gov.in |archive-date=26 July 2023 |archive-url= https://archive.today/20230726172619/https://www.inspace.gov.in/inspace?id=inspace_hosting_payloads_on_poem_page|url-status=live }}</ref>

On 1 January 2024, POEM-3 was launched along with [[XPoSat|XpoSat]] on [[PSLV-C58]] hosting ten payloads. The stage was lowered from a 650 km (circular) injection orbit of XpoSAT to a 350 km circular orbit for POEM-3 operations.<ref>{{Cite web |last=PTI |date=2024-01-01 |title=ISRO Fires Fourth Stage Of PSLV-C58 Twice To Hold Scientific Experiments |url=https://www.ndtvprofit.com/technology/isro-fires-fourth-stage-of-pslv-c58-twice-to-hold-scientific-experiments |access-date=2024-01-01 |website=NDTV Profit |language=en}}</ref> POEM-3 re-entered atmosphere on 21 March 2024 over the [[Pacific Ocean]] after having accomplished its objectives by February and thus leaving behind no [[Space debris|space-debris]] from the launch.<ref>{{Cite web |title=PSLV accomplishes zero orbital debris mission |url=https://www.isro.gov.in/PSLVC58_POEM3_accomplish_zero_orbital_debris_mission.html |archive-url=https://web.archive.org/web/20240325150554/https://www.isro.gov.in/PSLVC58_POEM3_accomplish_zero_orbital_debris_mission.html |archive-date=25 March 2024 |access-date=2024-03-26 |website=www.isro.gov.in}}</ref><ref>{{Cite web |title=POEM-3 Mission achieves all its Payload objectives |url=https://www.isro.gov.in/POEM-3_Mission_achieves_Payload_objectives.html |access-date=2024-03-26 |website=www.isro.gov.in}}</ref>

On 30 December 2024, POEM-4 was launched with 24 non-separable payloads as part of the [[PSLV-C60]]/[[SPADEX|SpaDeX]] mission.<ref>{{Cite web |title=PSLV-C60 SPADEX Mission Press-kit |url=https://www.isro.gov.in/media_isro/pdf/Missions/PSLVC60/PSLVC60-mission-brochure-english.pdf}}</ref><ref>{{Cite web |title=POEM-4 in PSLV-C60 / SpaDeX Mission |url=https://www.isro.gov.in/POEM_4_Payloads_spadex.html |access-date=2025-02-09 |website=www.isro.gov.in}}</ref> The PS4 stage was restarted twice to lower the orbit from 470 km to 350 km circular orbit for POEM-4 operations.<ref>{{Cite news |last=C.S |first=Hemanth |date=2024-12-31 |title=ISRO’s PSLV-C60 Mission: 10 payload from non-government entities successfully deployed on POEM-4 |url=https://www.thehindu.com/sci-tech/science/pslv-c60-mission-10-payload-from-non-government-entities-successfully-deployed-of-on-poem-4/article69046002.ece |access-date=2025-02-09 |work=The Hindu |language=en-IN |issn=0971-751X}}</ref>

== Platform capabilities ==

Specifications and capabilities of PSLV fourth stage based orbital platform which may improve over time.<ref name=":6" /><ref name="NSSS2022">{{Cite AV media |url=https://www.youtube.com/watch?v=J7XKKZMrkB4&t=475s |title=DAY 1 {{!}} PS 5 {{!}} SESSION A |date=31 Jan 2022 |time=8 minutes}}</ref><ref name=":7" />

* Mission life: Up to six months depending on left-over Helium pressurant in fourth stage.
* Maximum mass of payload: 30 kg
* Maximum size: About 3U, depends on spare area available for a particular mission and mounting location.
* Maximum power of payload: 200 to 500 watts
* Power bus: 28 Volts
* Maximum data rate: 1 Mbps
* Pointing accuracy:
** During sunlit period: within ±1°
** During eclipse: ±5°
** Slew rate within 0.5° per second during stabilized regime.
* Data storage: 1GB
* TT&C: S-band
* Downlink at ISRO ground station
* Suitable for experiments requiring large Inertia and structure.

== Missions ==
{{further|List of PSLV Orbital Experiment Module Flights}}
As of February 2025, the POEM module has been used on Four missions;

# [[PSLV-C53]]/[[List of PSLV Orbital Experiment Module Flights#POEM-1|POEM-1]]
# [[PSLV-C55]]/[[List of PSLV Orbital Experiment Module Flights#POEM-2|POEM-2]]
# [[PSLV-C58]]/[[Poem of Sidi Boushaki|POEM-3]]
# [[PSLV-C60]]/[[List of PSLV Orbital Experiment Module Flights#POEM-4|POEM-4]]

== Gallery ==
<gallery>
File:PSLV-C53, DS-EO - Render of PSLV Orbital Experimental Module (POEM) without DLA upper.png|PSLV-C53/POEM-1
File:PSLV-C55, TeLEOS-2 - Render of POEM with solar panels deployed.webp|PSLV-C55/POEM-2
File:PSLV-C58, XPoSat - Render of POEM-3 orbital platform.png|PSLV-C58/POEM-3
File:PSLV-C60, SpaDEx — Render of POEM-4.png|PSLV-C60/POEM-4
</gallery>

== See also ==
* [[RM-81 Agena]]
* [[Rocket Lab Photon]]
* [[Comparison of satellite buses]]
{{Commons category|PSLV Orbital Experiment Module}}

== References ==
{{reflist}}

{{Portal bar|Spaceflight}}
{{Orbital launch systems}}

[[Category:Polar Satellite Launch Vehicle]]
[[Category:Satellite buses]]

PSLV Orbital Experiment Module - Revision history

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