The situation with Europe’s defunct Envisat Earth observation satellite, now a giant piece of space junk menacing other spacecraft in its orbital path, once again highlights the importance of adhering to international guidelines for mitigating debris that threatens critical satellite operations in a variety of orbits.
Envisat, built by the European Space Agency () and launched in 2002, was five years beyond its design life when it failed without warning this past April. The satellite, measuring 26 by 10 meters, weighing 8,000 kilograms, and bristling with instrumentation hardware, now poses a huge hazard in a polar orbit heavily populated by environmental and imaging spacecraft. A collision between Envisat and an operational satellite or inert piece of space junk — Envisat cannot make evasive maneuvers — could create tens of thousands of pieces of new debris, increasing the danger exponentially.
ESA began designing Envisat in the late 1980s, well before orbital debris was recognized as the problem it is today. ESA, like other responsible space agencies around the world, has adopted international debris mitigation guidelines that include preserving sufficient fuel at the end of a satellite’s life to either raise it to a relatively unused area of Earth orbit or lower it to an altitude where solar activity, atmospheric drag and other forces will eventually cause it to re-enter the atmosphere and disintegrate.
An international space law expert recently said ESA could be held liable if Envisat damages or destroys someone else’s satellite during the 100 or so years it is expected to remain on orbit. During a presentation at the 63rd International Astronautical Congress in Naples, Italy, Martha Mejia-Kaiser of the International Institute of Space Law said ESA chose to try and squeeze more time out of the $3 billion mission rather than use the satellite’s remaining fuel to lower it to an orbit from which it would re-enter the atmosphere within 25 years as specified by the debris guidelines.
ESA rose to its defense a short time later, asserting that lowering Envisat to the 600-kilometer altitude that the agency said would ensure the satellite’s re-entry within 25 years was never an option. Because of design decisions made early in its development, Envisat could not have been lowered to that altitude even if controllers began the procedure immediately after launch, ESA said.
Ms. Mejia-Kaiser said the satellite only needed to be lowered to 750 kilometers to effect re-entry within 25 years, but one would have to assume that ESA was in the best position to estimate the fuel reserves and model the orbital degradation of its own satellite. Notably, ESA didn’t wait until after Ms. Mejia-Kaiser raised the specter of legal liability to make its point: Agency officials said the very same thing two years ago, when they were preparing to lower Envisat’s orbit to an altitude that would enable it to conserve fuel during its last years.
ESA has a good track record of orbital citizenship. In 2011, for example, the agency lowered the orbit of its aging ERS-2 Earth radar observation satellite to an altitude that will ensure its re-entry within 25 years. ESA also is a member of the Inter-Agency Debris Coordination Committee, which drafted debris mitigation guidelines in 2002 that were embraced by the United Nations in 2007.
But if Ms. Mejia-Kaiser’s point about potential liability is questionable — never mind that there is no recognized international legal mechanism for establishing liability in orbital collision cases — she has forced the debris issue to the forefront again: Envisat is an orbital time bomb and a dramatic example of why countries must stay vigilant about protecting and preserving the orbital environment.
The United States and Europe can help lead the way by strongly encouraging other spacefaring nations, including those with fledgling programs, to adopt established best practices for debris mitigation. They also should continue to discourage their respective commercial space industries from buying products and services that are not up to standard — rockets that leave upper stages in orbit, for example.
An even bolder step would be to get serious about debris removal, which has been a focus of several proposed hardware programs — both government and commercial — that to date have gotten no real traction. Orbital garbage collection might not have the immediate urgency of operational missions like weather monitoring and navigation, or the sex appeal of exploration, but none of these applications will be possible in the future if Earth orbit continues to be a passive repository for hazardous waste.