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.