L7 - Introduction to the Problem of Space Debris

Question 1

Describe the space debris environment.

Answer 1

Approx. 4,800 launches led to about 38,000 catalogued objects.
Sources of space debris: spent satellites and upper stages (3500 objects (~22%)), mission related objects (1020 objects (~6%)), fragments from explosions and collisions (9400 objects (~60%)).
Also there are roughly 950 operational satellites (~6%).

Question 2

Describe the methods to observe and detect space debris.

Answer 2

Space Surveillance Network (SSN). A system of discovery and tracking radars and optical telescopes, including the TIRA radar, European Incoherent Scatter Radars and the ESA Space Debris Telescope.

Telescope versus radar:
• The use of radar for space debris detection is most efficient below 5,000km
• Above this altitude, especially for debris in GEO, optical methods are used.
• In-situ detectors can be flown everywhere, but cover only the orbit of the host satellite and are normally limited in sensitive area.

Question 3

Describe the risks presented by space debris based on historical data.

Answer 3

• Since Sputnik about 38 000 catalogued objects in orbit.
• 22 000 objects have re-entered in the atmosphere without causing damage.
• Re-entries with fragments reaching the ground:
– Kosmos-954 (1978).
– Skylab (11 July 1979).
– Kosmos-1402 (1984).
– Salyut-7 / Kosmos-1686 (7 Feb 1991).
– Numerous rocket bodies.
• Risk on ground can be minimised by controlled re-entry.

Question 4

Describe future plans to mitigate space debris risks.

Answer 4

BAU: Business-As-Usual.
DEORB: Remove 4 LEO objects per year.
NOEX: No more explosions.
AVOID: Implement Collision Avoidance for 90 % of the cases.