Satellite bus derived out of launch vehicle upper stage
PSLV Orbital Experimental Module
Unmodified PSLV fourth stage for PSLV-C11 campaign.
Names
PS4 Orbital Platform
Mission type
Technology
Spacecraft properties
Dry mass
~920 kg
Payload mass
up to 30 kg
Dimensions
Length: 3 meter Diameter: 2 meter
Power
200 to 500 watts
PSLV Orbital Experiment Platform (POEM) also known as PSLV Stage 4 Orbital Platform (PS4-OP)[1] is an orbital micro-gravity test bed based on spent fourth stage of PSLV. By adding modular subsystems for power generation, communication and stabilization like 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.[2][3]
POEM or PS4-OP was conceived by 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.[2][3][4]
PSLV fourth stage or PS4 has often been used to carry non-separable payloads like AAM on PSLV-C8,[5]Rubin 9.1/Rubin 9.2 on PSLV-C14[6] and mRESINS on PSLV-C21[7] 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.[2][3][8]
In 2017 as an early demonstration on PSLV-C37/Cartosat-2D[9] and PSLV-C38/Cartosat-2E campaigns,[10] PS4 was kept operational and monitored for over ten orbits after completion of its primary mission of deploying spacecraft.[11][12] Fourth stage on PSLV-C38 hosted IDEA (Ionization Density and Electric field Analyzer) as a non-separable payload by Space Physics Laboratory of VSSC,[11][10] two other non-separable payloads were mAMP and 'Earth Pointing Platform'.[13]
In January 2019, 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.[14] It hosted a 1U cubesat called KalamSAT-V2 as a non-separable payload by Space Kidz India based on Interorbital Systems kit.[15][16][17] Later in April, the fourth stage on PSLV-C45/EMISAT[18] had its own power generation capaciity as it was augmented with an array of fixed solar cells wrapped around the propellant tank of PS4 generating about 200 watts of power.[19][20][21] Three payloads hosted on PS4-OP were, Advanced Retarding Potential Analyzer for Ionospheric Studies (ARIS 101F) by IIST,[22] experimental AIS payload by ISRO and AISAT by Satellize.[23] To function as an orbital platform, fourth stage was put in spin-stabilized mode using its RCS thrusters.[24] PS4-OP on this campaign had mission life of 3 months and AISAT payload onboard was operational for almost a year.[24][20]
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.[3] And in following years POEM-1 aboard PSLV-C53/DS-EO campaign in June 2022[25] and POEM-2 aboard PSLV-C55/TeLEOS-2 campaign in April 2023 were launched.[26] Both of these orbital platforms had mature configurations utilizing 3-axis stabilization and on-board power generation capacity.[27][28]
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.[4]
On 1 January 2024 , POEM-3 was launched along with 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.[29] POEM-3 re-entered atmosphere on 21 March 2024 over the Pacific Ocean after having accomplished it's objectives by February and thus leaving behind no space-debris from the launch.[30][31]
In June 2022, the PSLV-C53/DS-EO campaign had its PS4-OP referred as PSLV Orbital Experiment Module (POEM) and it was first PSLV fourth stage based orbital platform to be actively stabilized using eight Helium based cold gas thrusters after the primary mission and stage passivization.[33][27] POEM-1 (COSPAR ID:2022-072E, SATCAT no.:52939) had additional sensors and navigational aids (4 Sun sensors, Magnetometer, MRGPD and NavIC). It generated about 150 watts of power using non-deployable, fixed solar cells wrapped around PS4 tank.[20] Six non-separable payloads facilitated by NSIL and IN-SPACe were hosted aboard.
In April 2023, on PSLV-C55/TeLEOS-2 campaign, seven non separable payloads were hosted by POEM.[28][37][38] POEM-2 had flexible solar arrays wrapped around PS4 propellant tank that generated about 500 watts of power upon deployment.[20] POEM-2 was again 3-axis stabilized by eight Helium based 1N cold gas thrusters (OPACS) developed by LPSC that utilize left-over PS4 pressurant.[39][20] Expected mission life of POEM-2 (COSPAR ID:2023-057A, SATCAT no.:56308) was of one month.[40] Payloads hosted on POEM-2 are:
ARIS-2 (Advanced Retarding potential analyser for Ionosphere Studies) by IIST for ionosphere studies in Low Earth Orbit.[41][42][43]
On PSLV-C58/XPoSat campaign, POEM-3 hosted ten payloads weighing ~145 kg cumulatively.[52][53] PSLV fourth stage was lowered to 350 km orbit at 9.6° inclination after deploying XPoSat to reach the POEM-3 operational orbit. POEM-3 will nominally be operational for a period of one month.[54] For power generation and storage it will again have flexible solar panels in conjunction with 50Ah Li-ion battery and will be three-axis stabilized.[55] Payloads hosted on POEM-3 (COSPAR ID:2024-001A, SATCAT no.:58694) are following, seven of them facilitated by IN-SPACe and three are by ISRO,
Radiation Shielding Experimental Module (RSEM): Experimental payload by TakeMe2Space to evaluate effectiveness of Tantalum coating for radiation shielding.[56]
Women Engineered Satellite (WESAT): Payload by LBS Institute of Technology for Women to compare and measure UV radiation in space and on Earth's surface in real-time.
^"Isro's PSLV-C55 places two Singapore satellites in orbits; upper stage of rocket 'going to write a summer poem'". The Times of India. 22 April 2023. ISSN0971-8257. Archived from the original on 23 July 2023. Retrieved 23 July 2023. The upper stage of the rocket is going to write a summer poem. Seven payloads are mounted on top of the upper stage. If everything goes well, it will function for the next one month. It is for the first time that we are deploying a solar panel in PS4. We'll update on the performance of POEM through our social media handles
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