Space debris from Indian satellite: NASA’s worry, and why risk is low

Headline : Space debris from Indian satellite: NASA’s worry, and why risk is low

Details :

The News

  • 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

Findings

  • 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’s defense

  • 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

Definition

  • 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

Collisions

  • 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.

 

Ripple effect

  • 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.
Section : Science & Tech
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