Canada Seeks To Help ESA Deorbit Envisat Using Robot Arm
VICTORIA, British Columbia — Canada could play a prominent role in a deorbiting mission for the European Envisat Earth observation satellite, with robotic arm technology the most feasible method for such a job, according to industry and Canadian Space Agency officials.
The European Space Agency has yet to approve a mission although Canada expects one to develop between 2017 to 2021, with a potential launch in 2021, according to the Canadian Space Agency.
MDA Corp. of Richmond, British Columbia, recently finished an initial study that concluded that deorbiting Envisat could be accomplished using a robotic arm and capture tool.
“Given Canada’s leadership, experience and capabilities in on-orbit serving Canada could play a prominent role in deorbit,” the agency said in an Aug. 14, 2014, examination of the Envisat issue. That document was released through the federal Access to Information law.
Dan King, MDA’s director of business development for robotics and automation, said that by the end of the year ESA is expected to start a new phase in its study of a potential deorbiting mission.
“From our capability standpoint we are definitely planning to continue to be engaged,” he said in an interview with SpaceNews. “But as to how far we go in the future it’s TBD [to be determined] at the moment.”
Envisat is one of the largest Earth observation spacecraft ever built. It is 26 meters long and an estimated 8 metric tons. It was launched in 2002 in a sun-synchronous orbit but stopped communicating in April 2012.
The defunct satellite is considered one of the largest orbital debris threats in low Earth orbit. In addition to its size, the satellite is outfitted with a variety of antennas and other equipment, a concern since such devices could splinter if hit by debris. There is also concern that as Envisat ages in the harsh space environment, such hardware becomes increasingly brittle, increasing the likelihood that debris could be created.
Envisat will continue to orbit for 150 years if nothing is done.
King said the ESA has studied other capture options, including the use of a harpoon device or a net to snag the spacecraft. MDA looked at using a robotic arm to grab the launch adapter ring of the satellite.
“You capture the defunct satellite and then put it into a trajectory that it can then deorbit,” he said. “The option we studied is totally viable.”
King noted that Envisat is spinning, a situation that makes the robotic arm scenario a more favorable option.
“Part of the advantage of the robotic approach is that you can make sure your robotic arm is fast enough to track the spin rate and then capture it,” he said, “which is in a way, to a lesser extent, not unlike the techniques we have used, for example, on the space shuttle to capture a satellite with a relative rate of motion.”
Canadian Space Agency spokeswoman Émilie Dutil-Bruneau noted that while the deorbiting mission has yet to be approved by the ESA’s Council of Ministers, the ESA recently published an invitation to tender for the preliminary phase of the potential mission.
“Under the Canada-ESA Cooperation Agreement, Canadian industry could participate in this process,” Dutil-Bruneau said. “That said, final procurement decisions have not yet been determined.”
ESA has faced criticism from some space law specialists who complained that the agency could have done more to prevent Envisat from becoming such a debris threat.
In an October 2012 presentation in Naples, Italy, to the 63rd International Astronautical Congress, Martha Mejia-Kaiser, an International Institute of Space Law member from the Autonomous National University of Mexico, labeled Envisat a “ticking bomb,” adding that it posed an unusually large danger in its orbit at 780 kilometers in altitude.
Critics say ESA did not maintain sufficient fuel onboard the spacecraft to lower its orbit to the point where it could enter a destructive re-entry.
In October 2012, ESA countered such views; Envisat, the agency noted, was planned and designed in 1987-1990, a time when space debris was not considered to be a serious problem and before the existence of space debris mitigation guidelines, established by the United Nations in 2007.
ESA pointed out that those guidelines have now been adopted for all its projects.
The voluntary guidelines recommend that countries with low-orbiting satellites cease operations early enough so there is enough fuel to lower a spacecraft’s orbit to the point that atmospheric drag pulls it into destructive reentry within 25 years.
Lowering Envisat to an orbit that would allow re-entry within 25 years, however, was never an option because of its design and limited amount of fuel, ESA has stated.
Some space specialists argue that ESA could be held liable if Envisat or pieces of it collide with an operational satellite.