SPACE DEBRIS

Anybody who has ever gazed up into a clear nightsky knows the feeling of awe when we witness the incredible sea of stars. The vastness of space has inspired humans of every generation. We normally think of space as virgin, unspoiled, mysterious and, well, spacious!  Now, computer graphics from the European Space Operation Centre (ESOC) paint a different picture. ESOC has been proactive in creating forums to discuss the problem of space debris.[1]

It seems everywhere humans go, we litter and space is no exception. ESOC’s computer generated images is based on the best dataset available listing all spaceships and satellites humans have launched into space. This list also includes unplanned objects such as spent booster stages, nuts and bolts from International Space Station (ISS) construction, accidental discards such as spacesuit gloves and cameras, and fragments from orbit-exploded spacecraft. This cloud of floating debris is not only unsightly, but poses a real hazard to any future spaceflights and communication satellites.  European Space Agency, (ESA) reports that the number and mass of debris in the Earth’s orbit has kept growing – despite a decreasing annual launch rate.

 

Fig. 1: European Space Operation Centre  graphic of the trackable objects in orbit around Earth in 1)  low Earth orbit (LEO) – the fuzzy cloud around Earth, 2) geostationary Earth orbit (GEO) — farther out, about 35,786 km above Earth and 3) all points in between. Click on image for larger view. (Source: European Space Operation Centre (ESOC) )

 

Fig.2: Space Debris in Low Earth Orbit (Source ESOC)

 

Fig 3: Space Debris in Polar Orbit  Click on image for larger view. (Source: ESOC)

 

The Kessler Syndrome

Because of the threat of space debris, NASA has commissioned the National Research Council to perform an independent study on the risk of debris to future collisions entitled: Limiting Future Collision Risk to Spacecraft: An assessment of NASA’s meteroid and orbital debris program. Among the findings, a key one is that a space debris “tipping point” has already been reached and that NASA has not been able to keep pace with increasing hazards posed by abandoned equipment, spent rocket bodies, and other debris orbiting the Earth.

Kessler is retired head of NASA’s Orbital Debris Program Office. As early as 1978, Kessler began to explore the possibility that the increasing amount of space debris could eventually become so large and dense that it would make low earth orbit unusable for decades. This scenario in which debris would continually collide with one another, creating even more debris and causing a ripple effect of collisions became known as the Kessler Syndrome.

“The current space environment is growing increasingly hazardous to spacecraft and astronauts,” said Donald Kessler, chair of the committee that wrote the report.  “NASA needs to determine the best path forward for tackling the multifaceted problems caused by meteoroids and orbital debris that put human and robotic space operations at risk.” says Kessler.

According to the NRC report, the Kessler syndrome is not an abstraction, but is, in fact happening now. The amount of debris is now growing exponentially. Since January 2007, two recent collisions have doubled the total number of space debris fragments in Earth’s orbit.

Fifth European Conference on Space Debris
30 March – 2 April 2009
ESA/ESOC
Darmstadt, Germany

  1. Since 1957, more than 4,800 space launches have led to an on-orbit population today of approximately 13,200 trackable objects, with sizes larger than 10 cm.
  2. Less than 6% of these (800) are operational spacecraft
  3. The remaining 94% are space debris
  4. About 50% of the routinely tracked objects are fragments from explosions and breakups of satellites or rocket bodies.
  5. In addition, there is evidence of a much larger population of debris that cannot be tracked operationally.
  6. Almost 600,000 objects larger than 1 cm are expected to reside in terrestrial space.
  7. Relative orbital velocities can be up to 56,000 km/hr.
  8. Centimeter-sized debris can seriously damage or disable an operational spacecraft.
  9. Collisions with objects larger than 10 cm will lead to catastrophic fragmentations, releasing hazardous debris clouds.
  10. Spacecraft designers and mission operators should thus implement debris mitigation measures to avoid the release of debris, and to conserve the environment in the already densely populated low Earth and geostationary orbit regions.

Since there are accurate records of all space launches, the total amount of debris in space, in mass (kg) has a calculable upper limit. However, events ordinary to no-longer-operational space technology such as in-orbit explosions,  incomplete burn up during entry into the denser earth atmosphere and collisions between orbiting debris create a larger set of debris which cannot be predicted. Researchers may guess but they actually don’t have an exact idea of just how much “uncatalogued” debris is floating in space.

Explosions have been a source of Space Debris:

  • About 40% of ground-trackable space debris come from explosions (approximately averaging about 5 explosions a year)
  • In 1961, the first explosion tripled the amount of trackable space debris.
  • In the past decade, operators have begun to design out latent sources of energy related to batteries, fuel tanks, propulsion systems and pyrotechnics that could lead to explosions.
  • At present rates, in about 25 years, collisions will exceed explosions as a source of new debris.

The danger of orbiting debris objects:

  • Both the ERS-1 and SPOT 2 satellites had to perform evasive manoeuvres in the last few years to avoid colliding with what is essentially now considered “rubbish”.
  • Officials from the space shuttle program have reported that the space shuttle regularly takes hits from space junk. Over 80 windows had to be replaced over the years.
  • The ISS occasionally has to take evasive maneuvers to avoid collisions with space junk
  • The problem will be further aggravated by the ambitious plans of Teledesic (jointly owned by Craig McCaw and Bill Gates) to launch a massive network of 288 LEO satellites to extent the scope of the Internet.

 

Solutions?

DARPA’s “Phoenix” pilot program is effectively a space junk recycling program. It aims to develop technologies to harvest and re-use valuable components from retired, nonworking satellites in GEO “graveyard” orbits and demonstrate the practicality of building new space systems at greatly reduced cost.

New satellites have to be launched to replace old ones. They have a high cost due mostly to the expensive launch costs, which are dependent on the weight and volume of antennas. More than $ 300 billion worth of satellites are estimated to be in the geosynchronous orbit. Many have been “retired” because of normal end of useful life, obsolescence or failure; yet many still have valuable components, such as antennas, that could last much longer than the life of the satellite. When satellites in GEO are “retire,” they are put into a  “graveyard” orbit. The repurposing of existing, retired antennas from the graveyard can result in sig­nificant cost savings.

The Phoenix pilot project will be a highly multi-disciplinary one involving fields as diverse as remote controlled ground-based telemedicine robotics systems to advanced remote imaging systems used for offshore drilling . Such technologies, if re-engineered for zero gravity, high-vacuum and harsh radiation, could be used in space to allow the repurposing of valuable antennas from retired GEO satellites … “If this program is successful, space debris becomes space resource,” said DARPA Director, Regina E. Dugan.

 

 

REFERENCES:

[1] “Space debris is a problem, say world experts“, CORDIS RTD-NEWS, Record Control Number 13826, October 26, 1999. European Communities, 1999.