May 29, 2025

Dr. V. Narayanan, Chairman, ISRO/ Secretary, DOS, released the Indian Space Situational Assessment Report (ISSAR) for 2024 compiled by ISRO System for Safe and Sustainable Space Operations Management (IS4OM) on 22nd April 2025. An executive summary of the ISSAR is presented below.

Introduction

Indian Space Research Organisation (ISRO) performs Space Situational Awareness (SSA) activities to protect national space assets against various space environmental hazards, such as Resident Space Objects including space debris, natural objects like asteroids and meteoroids, energy and particle flux. ISRO System for Safe and Sustainable Operations Management (IS4OM) functions as the nodal entity to concert all space sustainability efforts, including SSA activities, and to improve compliance with internationally recognised guidelines on the long-term sustainability of outer space activities. The prime activities conducted are regular assessment of close approach risks posed by resident space objects to satellites and launch vehicles, predicting uncontrolled atmospheric re-entries, and studying the evolution of space object populations. As an integral part of SSA activities, an annual assessment of the prevailing space situation is compiled in the form of the Indian Space Situational Assessment Report (ISSAR) for dissemination to the relevant stakeholders. The highlights of the most recent space situational assessment are presented next.

Global Scenario

• The year 2024 witnessed the highest number of launches since the beginning of the space age. There were 261 launches attempts, out of which 254 launches were successful resulting in an addition of 2578 operational satellites. A total of 2963 objects were placed in orbit. This number was less than that of the previous year, which was 3135 objects from 212 launches in 2023.
• Five lunar missions were launched in 2024 indicative of the renewed interest in lunar exploration.
• There were three major on-orbit break-up events in 2024. One major fragmentation of a Long March rocket stage (CZ-6A) reportedly added around 650 catalogued objects. Some of these fragments decayed within the same year, resulting in a net addition of 702 fragmented objects to the population of space debris by the end of 2024.
• Since the number of debris originating from the fragmentation events was more (702 compared to 69 in the previous year), hence, a total of 3665 objects from 254 launches and on-orbit break-up events were added to the space object population.
• A total of 2095 catalogued objects re-entered the atmosphere, this is also the highest number of re-entries. Out of them, 335 objects were Starlink satellites, there was a deliberate, large-scale deorbit of early V1 satellites. The year also witnessed intense solar activities as the peak of the 11-year solar cycle (Solar Cycle 25) was approached. There were 18 strong (G3 class), 20 severe (G4 class), and 2 extreme (G5 class) geomagnetic storms which accelerated the orbital decay.
• Although number of satellites placed in orbit was relatively less and a greater number of objects re-entered the atmosphere compared to the previous year, the total number of objects added to the space object population was higher because of the fragmentation events. Consequently, the growing trend in the space object population continued in 2024.

Indian Scenario

Statistics of On-Orbit Indian Objects

• A total of 136 Indian spacecraft, including those from private operators/academic institutions, were launched in Earth-orbit till 31 Dec 2024.
• As of 31 Dec 2024, the number of operational satellites owned by Govt. of India is 22 in LEO (Low Earth Orbit) and 31 in GEO (Geo-synchronous Earth Orbit).
• In addition, two Indian deep space missions, namely, Chandrayaan-2 Orbiter (CH2O) and Aditya-L1 at Sun-Earth Lagrange’s point were also active. The propulsion module of Chandrayaan-3 spacecraft continued to operate in a high Earth orbit (more than 1 lakh km away) after being relocated from its lunar orbit since Nov 2023.
• There were five launches from Sriharikota, namely PSLV-C58/XPoSat, PSLV-C59/PROBA-3, PSLV-C60/SPADEX, GSLV-F14/INSAT-3DS, and SSLV-D3/EOS-08 mission, all of them successfully injected the payloads in their nominally designated orbits. ISRO's GSAT-20 was launched by Falcon-9 Block 5 of SpaceX from Cape Canaveral. TSAT-1A was also launched by Falcon-9. Consequently, a total of 8 Indian satellites, 1 foreign satellite, and 6 rocket bodies (including POEM-3 and POEM-4) were placed in their intended orbits.

#	Indian Launch Vehicle	Indian Satellites		Foreign Payloads
		ISRO/GOI	Private/ Academic
1	PSLV-C58 / XPoSat	XPoSat		-
2	GSLV-F14 / INSAT-3DS	INSAT-3DS	-	-
3			TSAT-1A (launched by Falcon-9 Bandwagon 1)
4	SSLV-D3 / EOS-08	EOS-08	SR-0 DemoSat	-
5	PSLV-C59 / PROBA-3	-	-	PROBA-3
6	PSLV-C60 / SPADEX	SPADEX-A (SDX01) SPADEX-B (SDX02)		-
7		GSAT-20/ GSAT-N2 (launched by Falcon-9 Block-5)	-

• The upper stage of PSLV-C3 underwent an accidental break-up in 2001 and generated 371 debris. While most of these fragments have re-entered the atmosphere, 41 PSLV-C3 debris were still in orbit by the end of 2024.

Atmospheric re-entry

• Among the intact Indian upper stages, 34 rocket bodies re-entered the Earth's atmosphere till 2024 end, and 5 of such re-entries took place in 2024. All LVM3 rocket bodies have decayed, only the one from LVM3 M2 OneWeb india1 mission remain in orbit. Among GSLV rocket bodies, only GSLV-F12 and GSLV-F14 rocket bodies are in orbit.
• A total of 31 Indian satellites have re-entered the atmosphere till the end of 2024. In the year 2024 alone, 9 Indian satellites re-entered the atmosphere. Among them was Cartosat-2 which re-entered the atmosphere on 14 Feb 2024, the first-ever LEO satellite of ISRO to be de-orbited at end-of-life to reduce its post-mission orbital life from more than 30 to less than 4 years.

Close approach risk mitigation for Indian space assets in 2024

Space Object Proximity Analysis (SOPA) for Satellites

ISRO regularly carries out analyses to predict close approaches by other space objects to Indian space assets. In case of any critical close approach, collision avoidance manoeuvres (CAM) are carried out for the operational spacecraft to mitigate the collision risk. The highlights for the year 2024 are as follows:

• More than 53000 alerts issued by CSpOC of USSPACECOM for ISRO’s Earth orbiting satellites were analysed using more accurate orbital data from flight dynamics.
• The table below consolidates the CAM statistics.

Orbital Regime of Spacecraft	No. of CAMs	Remarks
LEO	6	Requirements for collision avoidance were incorporated in regular orbit manoeuvres wherever it was feasible
GEO	4
Total (LEO+ GEO)	10
Planetary (Chandryaaan-2)	1	An orbit maintenance manoeuvre was originally scheduled on 26 Nov 2024 but advanced to 11 Nov to mitigate conjunctions with LRO which were predicted to occur on 15-16 Nov

The graph below shows the total number of Collison Avoidance Manoeuvres (CAMs) carried out by ISRO for its Earth orbiting satellites over the last few years. The number of CAMs was less in 2024 compared to the previous year. This is because improved close approach analysis methodology with larger conjunction screening volume and usage of more accurate ephemerides helped to meet collision avoidance requirements by adjusting orbit maintenance manoeuvres on several occasions and avoiding exclusive CAMs.



Figure 2: Cumulative number of CAMs performed for Earth-orbiting satellites of ISRO till 2024

• The number of orbit manoeuvres (OM) executed for the ISRO satellites to maintain their orbits within the respective mission specified limits are consolidated in the table below:

Orbital Regime of Spacecraft	No. of Orbit Manoeuvres
LEO	681
GEO	504 (excluding 1222 pulsing manoeuvres)
Deep Space	21 (14 for Chandyaan-2 Orbiter , 5 for Aditya-L1)

• All manoeuvre plans, including those of the CAMs, were subjected to close approach risk analysis to rule out any potential close approach with other neighbouring space objects imminently after the manoeuvres, 89 manoeuvre plans were revised to avoid post-manoeuvre close approaches with other space objects for LEO satellites. Similarly, on two occasions manoeuvre plans had to be revised to avoid post manoeuvre conjunctions for GEO satellites.
• A similar methodology for conjunction assessment and collision risk mitigation was followed for deep-space missions. 14 OMs were carried out for the Chandrayaan-2 Orbiter (CH2O), the plans were adjusted on 8 occasions. On one occasion, a scheduled orbit maintenance manoeuvre was advanced to avoid a close conjunction with Lunar Reconnaissance Orbiter (LRO) of NASA.
• Currently only four other spacecraft operate in the vicinity of Aditya-L1 which are separated by more than 1 lakh km. Nevertheless, regular close approach assessment is carried out for this mission as well to maintain situational awareness.
• The required coordination for spaceflight safety was carried out for all operational satellites.

Collision Avoidance Analysis (COLA) for Launch Vehicles

COLA analyses for lift-off clearance of launch vehicles were carried out as part of the mandatory Launch Clearance Protocol of ISRO launch vehicles. The table below shows the COLA results for the launches in 2024.

The lift-off of PSLV-C60/SPADEX was delayed based on the COLA analysis. The figure below shows the so-called “black-out” zones within the launch window, over which the lift-off timings were prohibited for the PSLV-C60 launch to avoid potentially close approach risk with other space objects.

Nominal lift-off timings of all other launches (PSLV-C58, GSLV-F14, SSLV-D3, and PSLV-C59) were cleared by COLA. To resolve close approach situations with active satellites, the required spaceflight safety related coordination was carried out with the respective operators.

Spacecraft Decommissioning and Post Mission Disposal

At its end-of life, Scatsat-1 was de-orbited as part of post mission operations through 12 manoeuvres, completely depleting the left-over fuel. Electrical passivation was carried out before its decommissioning on 26 Sep 2024, exactly 8 years after its launch. Two more LEO satellites, INS-2B and EOS-7 were also decommissioned before they re-entered the atmosphere.

Post payload injection, the upper stages of PSLV-C58 and PSLV-C60 were de-orbited to 350 km, the former re-entered the atmosphere within 3 months, while the re-entry of PS4 of PSLV-C60 took place on 4 April 2025.

PSLV Orbital Experimental Module (POEM)

Two PSLV Orbital Experimental Module (POEM) missions were flown for a wide array of technology demonstration on the PS4 of PSLV-C58 (POEM-3) and PSLV-C60 (POEM-4), hosting 9 and 24 payloads, respectively. In both the cases, the upper stages were de-orbited to circular orbits of nearly 350 km altitude and passivated before functioning as POEM, the de-orbiting limited their post-mission life to approximately 3 months. Usually a technology demonstration mission typically lasts for a short duration of a few months and proper PMD for such smaller, experimental missions are often not feasible due to on-orbit failure and hardware limitations. Therefore, POEM provides an innovative approach allowing an emergent space actor to test and qualify new technologies without requiring to fly individual satellites in space.

International Cooperation

International cooperation plays a crucial role in obtaining relevant data and information for safe and sustainable operations in outer space. Mitigating space environmental concerns like space debris requires collective efforts. ISRO participates actively in various international fora deliberating on space debris issues and the long-term sustainability of outer space activities, these include Inter-Agency Debris Coordination Committee (IADC), International Academy of Astronautics (IAA) space debris working group, International Astronautical Federation (IAF) space traffic management working group, International Organization for Standardization (ISO) space debris working group and UN-COPUOS Scientific & Technical Sub-Committee/ Legal Sub-Committee. India currently chairs the UN working group on the Long-term Sustainability of outer space activities. ISRO chaired the IADC for the period of 2023-24 and hosted the 42nd annual IADC meet in April, 2024 at Bengaluru, which was attended by nearly 75 foreign delegates from the leading space agencies. ISRO substantively contributed to the revision of IADC space debris mitigation guidelines, released in January 2025, and the ongoing task of exploring space debris mitigation options for lunar orbits. ISRO also participated in the annual re-entry prediction campaign conducted by IADC (Cluster II/SALSA, ERS-02) by submitting predictions.

Debris Free Space Mission

One of the major highlights of 2024 in the area of space sustainability was the declaration of India’s intent for Debris Free Space Mission (DFSM) in the plenary session of the 42nd IADC annual meet. DFSM aims for debris-free space missions by all Indian space actors, both governmental and non-governmental, by 2030, by adopting the necessary measures during design, operation, and disposal phase. One of the major requirements of DFSM is compliance with PMD of spent orbital stages and satellites with a success probability of more than 99%. Special emphasis is placed on PMD of Low Earth Orbit missions, being the most crowded orbital zone, with a target of limiting the post-mission residual lifetime to 5 years through either controlled re-entry or de-orbiting to a lower orbit. Mission extensions should be recommended based on assessments of sub-system health, including redundancy aspects so that the ability of PMD (post mission disposal) is not compromised. Another important consideration is to treat 400 km+/-30 km as an orbital band as exclusive for human space missions.

Summary and Way Forward

The consolidated data for 2024 indicates intensified space activities, as reflected by the maximum number of launches as well as maximum number of re-entering objects. The growing trend in the space object population continued. The sheer number of close approach alerts indicate the alarmingly rising congestion in space, especially low-Earth orbit. With the easier access to space through rideshare coupled with technological advancements, miniaturization, mass-production capabilities, multifaceted application of space-based technology, the future space traffic is not likely to show any signs of slowing down.

Based on the projected deployment of multiple large constellations, active satellites are likely to be outnumber space debris population within the current decade, making Space Traffic Management (STM) an indispensable part of spaceflight safety. As of now, there is no accepted framework for STM, hence on-orbit close approach between two active space assets needs to be resolved on case-by-case basis through inter-operator coordination, with non-trivial operational overheads. Consequently, spaceflight safety in future scenario is expected to involve more intensive coordination and cooperation between various spacefaring entities, it is desirable that a suitable collaborative framework evolves for meeting STM requirements.

Recognising that Space Situational Awareness (SSA) plays a pivotal role in ensuring safe and sustainable operation, NEtwork for space objects TRacking and Analysis (NETRA) project has been undertaken by ISRO. Establishment of a radar at Chandrapur, Assam, and an optical telescope at Hanle, Ladakh, are in progress under the scope of this project. After refurbishment, the Multi-Object Tracking Radar (MOTR) at Sriharikota also commenced tracking space objects, including the Indian rocket bodies and satellites during their last few orbits before atmospheric re-entry, wherever feasibility existed.

The declaration of the Intent of Debris Free Space Mission in 2024 is a testimony of ISRO’s long-standing commitment to preserving the long-term sustainability of outer space activities. In the coming years, ISRO will steadfastly pursue space object observational capacity building for SSA, share experiences, engage with the emergent space actors, and raise awareness on responsible, safe, and secure space activities through proactive implementation of the pertinent guidelines and best practices.