The space environment

Debris, radiation, space weather and what falls back to Earth.

1. What Is Space Debris? — Space debris, or space junk, is defunct human-made material left in orbit: dead satellites, spent rocket stages, and fragments from collisions and explosions.
2. What is Kessler syndrome? — Kessler syndrome is a chain reaction in which debris from one collision causes more collisions, so the junk in an orbit keeps growing even if launches stop.
3. How do satellites avoid collisions? — Operators predict close approaches from tracking data, work out the chance of a hit, and fire thrusters to shift the orbit when that chance is too high.
4. What is Project NETRA? — Project NETRA is ISRO's network of radars, telescopes and a control centre that tracks objects in space so Indian satellites can avoid collisions.
5. What are the Van Allen belts? — The Van Allen belts are two doughnut-shaped zones around Earth where its magnetic field traps fast charged particles that can damage satellites and harm astronauts.
6. What is the South Atlantic Anomaly? — The South Atlantic Anomaly is a weak patch in Earth's magnetic field over South America and the South Atlantic, where radiation reaches down to low-orbit satellites.
7. What is space weather? — Space weather is the changing conditions in space caused by the Sun — flares, particle storms and magnetic storms — that can disturb satellites, radio, GPS and power grids.
8. What are solar flares and coronal mass ejections? — A solar flare is a sudden burst of light and X-rays from the Sun; a coronal mass ejection is a giant cloud of magnetised gas the Sun throws into space.
9. How do solar storms harm satellites? — Solar storms heat and puff up the upper atmosphere, dragging low satellites down, and their fast particles can charge, glitch or damage satellite electronics.
10. How do satellites survive the vacuum and temperature of space? — Satellites use special materials, lubricants, coatings and heaters because space has almost no air, harsh sunlight and swings from searing heat to deep cold every orbit.
11. What are micrometeoroids and how do satellites survive them? — Micrometeoroids are tiny natural particles that hit spacecraft at tens of kilometres per second; satellites survive them with spaced, layered shields and careful design.
12. What happens when satellites fall back to Earth? — Most satellites and rocket stages that fall back burn up in the atmosphere, but large ones can drop surviving pieces, usually into the ocean.
13. What is a controlled de-orbit? — A controlled de-orbit is when operators fire a satellite's engines to bring it down at a chosen time and place, usually over an empty stretch of ocean.