Headline : Space debris from Indian satellite: NASA’s worry, and why risk is low
- A-SAT missile test of India has received some criticism from NASA over the potential impact of the space debris it has generated.
In focus: Space Debris from Mission Shakti
- NASA has identified that India’s A-SAT missile test has generated around 400 pieces of pace debris.
- 60 are larger than 10cm in size and 24 are identified by NASA as potential threat to International Space Station (ISS) orbiting at the height of 410 km.
NASA’s concern: Threat to ISS
- The A-SAT missile test produced 24 pieces of space debris that are larger than 24cm and going above the apogee (farthest point) of the International Space Station.
- This according to NASA has increased the risk of collision with ISS to by 44% in the 10-day interval post the test.
How is ISS protected?
- ISS is constantly at risk from space debris with over 23,000 of them moving in trajectories considered prone to collisions.
- If an object is assessed to have the potential to enter the area of size 25 km × 25 km × 4 km around the ISS, it is considered a potential threat.
- Every time space debris is around the aforesaid space, the ISS is maneuvered away from its normal trajectory in a process called Debris Avoidance Manoeuvres.
- Since 1999, the ISS has undergone 25 DAMs, the last time in 2015.
- India has justified its missile test saying that it chose the orbit above 300 km in order to reduce the impact of space debris.
- Further, the number of satellites at such heights is few reducing the probability of a collision.
- ISRO has estimated that the debris generated due to A-SAT test will decompose in a span of few weeks.
- This is because of 2 reasons
- Due to gravitational influence of the earth the space debris will fall on earth. Earth’s atmosphere albeit very feeble at such heights will decompose the space debris.
- Further, if the velocity of the space debris decreases for some reason, the object will fall back on earth and burn out in its re-entry to atmosphere because of air-friction.
In brief: Space Debris
- Inactive satellites that have passed their functional life, leftovers from a rocket or other small fragments form space debris often called as space junk.
Threat from space debris in general
- At low earth orbits the objects including satellites are moving at high velocity of 7.8 km/sec.
- High velocities are required for objects in order to be in orbit at such low heights due to gravitational influence of earth. (which is around 95-98% at heights of 300km as that on surface)
- At such high velocities, the kinetic energy released in case of collision is extremely high. (1/2 mv^2)
- As a result even objects with small sizes about 10cm can potentially damage functional satellites in low earth orbit.
- According to estimates by NASA, there are about 900000 pieces of debris of sizes above 1cm in space.
- About 34000 are larger than 10cm in size.
- A small collision can produce cloud of debris that can eventually trigger more collisions setting up a chain reaction of collisions.