The Outer Space Institute (OSI), a network of world-leading space experts advocating innovative, transdisciplinary research for space use and exploration, has urged both national and multilateral efforts to regulate the uncontrolled re-entries of satellites.
Stages of a Rocket Launch Explained
A rocket launch follows a series of stages. The primary stage refers to the initial thrust from the first rocket engine, which operates until its fuel depletes and then disengages, falling to the ground. Following this, the secondary stage begins, where the next rocket engine takes over, continuing the trajectory. This stage faces less workload due to the high speed already achieved and the reduced weight of the rocket after the first stage’s separation. Additional stages, if present, repeat this process until the rocket is successfully launched into space.
The payload, such as a satellite or spacecraft, comes into play once the rocket reaches orbit. With the final stage of the rocket discarded, the craft employs smaller rockets for maneuvering. Unlike the primary rockets, these secondary rockets are reusable and can be used multiple times.
Understanding Uncontrolled Re-entry
In the event of an uncontrolled re-entry, the rocket stage simply falls. The path of descent depends on the rocket’s shape, angle of descent, air currents, and other characteristics. Furthermore, the rocket disintegrates during its fall. Some of its pieces burn up entirely while others don’t but can cause deadly impacts due to their high speed.
According to a 2021 report by the International Space Safety Foundation, any debris weighing more than 300 grams could cause a catastrophic failure if it hits an airliner, potentially killing all people on board. While most rocket parts typically land in oceans because of the water-dominant surface of the earth, many have also fallen on land.
Concerns Associated with Uncontrollable Re-entries
Several past incidences of rockets striking parts of Earth have raised concerns about uncontrolled re-entries. For instance, parts of Russian rockets in 2018, China’s Long March 5B rockets in 2020 and 2022, and a SpaceX Falcon 9 in 2016 have ended up hitting parts of Indonesia, Peru, India, Ivory Coast, and other regions.
The leftover fuel from re-entering stages raises another risk, atmospheric and terrestrial chemical contamination. It’s estimated that in the coming decade, the casualty risk from uncontrolled rocket body re-entries could be around 10%. The threat is even higher for countries in the ‘Global South’.
The U.S. Orbital Debris Mitigation Standard Practices (ODMSP) necessitates a less than 0.01% chance of casualties from a re-entering body. However, no international binding agreement enforces controlled re-entries or specific technologies to do so. The Liability Convention 1972 merely requires countries to compensate for damages, not prevent them.
Minimizing Damages: Future Prospects
The foreseeable solutions need to consider not only satellite launches but also their re-entries. Technological advances have led to the development of smaller satellites, which are easier to manufacture and launch in larger numbers. Despite experiencing more atmospheric drag, these satellites are more likely to burn up during re-entry, reducing the risk of causing damage.
India’s 300-kg RISAT-2 satellite, for example, re-entered the earth’s atmosphere safely in October after 13 years in low-earth orbit. The Indian Space Research Organisation (ISRO) tracked it using its system for safe and sustainable space operations management a month before its re-entry and predicted its paths using in-house models.
Growth in the Satellite and Rocket Launches
Since the launch of the first artificial satellite by the Soviet Union in 1957, over 6,000 satellites have been placed in orbit through more than 5,000 launches. Most of these satellites are in low-earth (100-2,000 km) and geostationary (35,786 km) orbits. The advent of reusable rocket stages has further amplified the number of rocket launches.
