Orbital debris, not functional satellites, make up 95 percent of the objects in this computer-generated illustration of objects in low-Earth orbit. That veritable explosion of space junk is causing problems, and it's getting worse. NASA estimates that there are more than 500,000 pieces of hazardous space debris orbiting Earth.
And as time goes on, the bigger pieces of abandoned debris, such as satellites, begins to collide with other objects, or each other, resulting in the larger pieces of junk turning into more and more smaller pieces of junk, increasing the population of hazardous debris.
DARPA is so concerned with the problem that it's started what it calls the SpaceView program, which seeks to enlist amateur astronomers as sky watchers, helping to track all the debris floating above.
Aluminum oxide slag is a byproduct of solid rocket motor (SRM). Orbital SRMs used to boost satellites into higher orbits are potentially a significant source of the centimeter-sized orbital debris. This piece was recovered from a test firing of a Shuttle solid rocket booster.
A chart showing the monthly object in Earth orbit by type shows how the problem of space debris is getting worse.
There are many sources of debris. One source is discarded hardware. Launch vehicle upper stages have been left in orbit after they are spent. Satellites are abandoned at the end of useful life, while spacecraft and mission operations have released items such as separation bolts, lens caps, momentum flywheels, nuclear reactor cores, clamp bands, auxiliary motors, launch vehicle fairings, and adapter shrouds.
The Advance Electro-Optical System (AEOS) located at the Air Force Maui Optical and Supercomputing (AMOS) site on top of Haleakala volcano in Maui, Hawaii is one of the tools NASA uses to image satellites and measure the spectra of orbital debris.
The Air Force Maui Optical and Supercomputing (AMOS) site. This optical sensor suite includes the 3.67m Advance Electro-Optical System (AEOS) telescope, a 1.6m telescope, two 1.2m telescopes, and three 1m Ground Based Electro-Optical Deep Space Surveillance (GEODSS) telescope installations.
This is the main propellant tank of the second stage of a Delta 2 launch vehicle which landed near Georgetown, Texas, on January 22, 1997. This approximately 250kg tank is primarily a stainless steel structure and survived re-entry relatively intact.
The Michigan Orbital Debris Survey Telescope (MODEST) near La Serena, Chile at the Cerro Tololo Inter-American Observatory is used for observations of the geosynchronous orbit regime. Observations are taken in two-week segments surrounding the new moon.
Long Duration Exposure Facility (LDEF) was left in low Earth orbit (LEO) for 5.7 years before being retrieved by space shuttle Columbia in January 1990.
More than 20,000 impacts have been documented on LDEF, approximately 1,000 of which have been chemically analyzed in an attempt to determine the origin of the projectile. These measurements have provided NASA scientists important information not only on the micrometeoroid and orbital debris populations, but their orbital distributions as well.
Even objects we think of as incredibly small, such as the paint flakes captured by the Mir Environmental Effects Payload (MEEP), seen here, are hazardous when moving at thousands of miles per hour. The MEEP was an International Space Station Phase 1 Risk Mitigation Experiment that provided a materials assessment for the construction and operation of the ISS.
The Kiernan Re-entry Measurement Site located on the Kwajalein Atoll. Four radars are visible here, ALCOR (ARPA-Lincoln C-band Observables Radar), TRADEX (Target Resolution and Discrimination EXperiment), MMW (MilliMeter Wave), and ALTAIR (ARPA Long-range Tracking and and Instrumentation Radar).
On January 21, 2001, a Delta 2 third stage, known as a PAM-D (Payload Assist Module - Delta), re-entered the atmosphere over the Middle East. The titanium motor casing of the PAM-D, weighing about 70kg, landed in Saudi Arabia about 240km from the capital of Riyadh.
A secret Soviet-navy satellite called Cosmos 954, which was launched on September 18, 1977, was powered by a compact nuclear reactor, making its failure, breakup, and re-entry particularly frightening.
Two events in recent years have greatly increased the amount of debris on orbit. On February 10, 2009, the active Iridium 33 satellite collided with the defunct Cosmos 2251 satellite, and created about 2,000 tracked objects. On January 11, 2007, the Chinese deliberately destroyed the FY-1C satellite in a test of an anti-satellite weapon, creating more than 3,000 tracked objects. The tracked objects represent a small fraction of the debris objects created.
Space debris populations seen from outside geosynchronous orbit (GEO). Note the two primary debris fields, the ring of objects in GEO, and the cloud of objects in low Earth orbit (LEO).
The debris environment in low Earth orbit is expected to continue to grow over time, even if strict end-of-life disposal measures are followed. Removing large objects from orbit is no easy task. Almost no spacecraft are designed to be physically grappled once they are in orbit, and they may be tumbling or spinning, making them difficult to control. But active debris removal such as this is a first step to cleaning up the environment in space, and maintaining the low Earth orbit as a safe place to do business.