23 December 2022

Table of Content

The uncontrolled re­entries of satellites

GS-3: Awareness in the fields of IT, Space, Computers, robotics, Nano-technology, biotechnology and issues relating to intellectual property rights. 

• Recently, Outer Space Institute (OSI) published a letter addressing S. Somnath – chairman of the Indian Space Research Organization (ISRO) – among others, calling for national and multilateral efforts to restrict uncontrolled re-entries. 
• Uncontrolled reentries refers to the phenomenon of rocket debris returning to earth in uncontrolled manner after completion of mission.

Orbit 

• An orbit is the curved path that an object in space such as a star, planet, moon, asteroid, spacecraft, etc. takes around another object due to gravity. 

Types of Earth orbits

• Low Earth Orbit (LEO)

• Range: 160km – 1000km (near to the earth)
• Utility: for communication and remote sensing satellite systems, as well as the International Space Station (ISS) and Hubble Space Telescope.

• Medium Earth Orbit (MEO)

• Range: Anywhere between LEO and Geostationary Orbit (GEO)
• Utility: for navigation systems such as Global Positioning System (GPS)

• Geosynchronous Orbit (GSO)

• Range: at constant altitude of 35,786 km
• Objects in GSO have a same orbital speed as that of the Earth’s rotation, yielding a consistent position over a single longitude.
• Utility: for monitoring weather, communications and surveillance.

• Geostationary Orbit (GEO)

• GEO is a type of GSO.
• Satellites in GEO rotate Earth above the equator from west to east following Earth’s rotation – taking 23 hours 56 minutes and 4 seconds – by travelling at exactly the same rate as Earth.
• They appear in a fixed position in the sky.

• Polar Orbit

• Polar orbit is a type of LEO ranging 200km-100km.
• They have have an inclination within 30 degrees of the Earth’s poles, i.e. travel past Earth from north to south (but not exactly through pole).
• Used for satellites providing reconnaissance, weather tracking, measuring atmospheric conditions, and long-term Earth observation.

• Sun-Synchronous Orbit (SSO)

• SSO is a type of Polar orbit ranging 600-800km.
• SSO objects are synchronous with the sun such that they pass over an Earth region at the same local time every day.

• Highly Elliptical Orbit (HEO)

• HEO is a highly eccentrical orbit with a low perigee (the point of orbit closest to the Earth) altitude of under 1,000 km and a high apogee (the point farthest from the earth) altitude of over 35,756 km.
• Can be used for communications, satellite radio, remote sensing and other applications.

• These satellites obtain momentum from the rocket pulling in one direction. On the other side, Earth’s gravity pulls it in opposite direction. Thus, balance between gravity and momentum keeps the satellite orbiting around Earth.
• Near to earth => More Gravitational pull => requires more momentum for balancing => Travels at a faster speed. 

• Thus, satellite in lower orbits must travel faster than a satellite orbiting farther away.

Satellite Launching

• All satellites are launched into space by riding on a rocket. 
• A rocket carrying different types of Propellants, which give the rocket energy to travel against the gravitation force of the Earth.

• Large and heavy spacecraft needs large rockets and requires comparative more amount of propellant.

• Thrust: It is an upward force created by burning of propellants, which in result pushes out exhaust.
• Depending on amount of burning of propellants, when thrust pushing rocket up is greater than pulling gravitational force, the rocket begins to move upward.
• To ensure that rocket does not pull back to ground, a rocket, it needs to speed up to at least 17,800 miles per hour and fly above most of the atmosphere in a curved path around Earth. 
• When rocket gets to a specific distance from Earth, it launches the satellite.
• These rockets have multiple stages.

• Some rocket sheds particular stage after attaining altitude and speed derived by that stage.

• Thus, they scrap all their larger stages before reaching the destination orbit and only a smaller engine then moves the payload to its final orbit.

• While, some rocket carry the payload to the orbit, then perform a deorbit manoeuvre to begin their descent.

• In both cases, scrap of rocket returns to the Earth either in controlled manner or uncontrolled manner.

Uncontrolled re-entry

• When rocket stages simply falls, it is called uncontrolled re-entry.
• In uncontrolled re-entry, returning path is determined by shape of rocket stage, angle of descent, air currents and other characteristics.
• During the travel, it may burn or further disintegrate, which increases the potential radius of impact on the ground.
• Though, most parts of rocket have landed in ocean because it occupies 71% of earth’s surface but there are many incidents of dropping on land, too.

• Example, parts of a Russian rocket in 2018 and China’s Long March 5B rockets in 2020 and 2022 impacted parts of Indonesia, Peru, India and Ivory Coast.

Way Forward  

• Make sure re-entry happens in controlled manner.
• Aim oceans for re-entry of rocket debris in order to avoid human casualties.

• The Liability Convention 1972 requires countries to pay for damages, not prevent them.

• Build low weight small satellites using advanced electronics and fabrications so that they are likelier to burn up during re-entry.
• International Agreement on re-entry: At present, there is no international binding agreement to ensure rocket stages always perform controlled re-entries nor on the technologies with which to do so. 

• These technologies include wing-like attachments, de-orbiting brakes, and extra fuel on the re-entering body, and design changes that minimise debris formation.

Best practice

• ISRO plotted India’s 300-kg RISAT-2 satellite’s predicted paths using models in-house on its re-entry after 13 years in low-earth orbit.
• The ISRO tracked it with its system for safe and sustainable space operations management and the RISAT-2 eventually fell into the Indian Ocean on October 30.

[Ref- TH]

Fact File