Canada’s York University recently launched a CubeSat mission that will demonstrate deorbiting technology for space debris. The mission was funded by the Canadian Space Agency Flights and Fieldwork for the Advancement of Science and Technology (FAST) program.
The Cubesat-sized spacecraft is called DESCENT (DEorbiting SpaceCraft using ElectrodyNamic Tethers) and it flew into space on Oct. 3 aboard the Northrop Grumman NG-14 resupply launch to the International Space Station. DESCENT flew inside a Cygnus cargo spacecraft called Kalpana Chawla, named after one of the astronauts who died during the 2003 Columbia space shuttle fatal incident.
DESCENT arrived on the ISS Oct. 5 and was deployed into its own orbit Nov. 5 using the Nanoracks Cubesat launcher in the Japanese Kibo module aboard the space station. If the mission is successful, DESCENT will add a new technology to space deorbiting practices.
Deorbiting technology demonstration plan
In the coming months, the DESCENT team plans to do attitude control tests, collect data from its experiments and take Earth images using a $15 smart phone camera on the spacecraft. The descent test will then take place in January, if the mission holds to schedule. DESCENT is supposed to deorbit from 380 km to 250 km in altitude in a mere two days, compared with the typical 10 months it would take for the Earth’s atmosphere to accomplish the same thing.
Space entities (such as agencies and companies) prefer to deorbit old satellites to avoid the risk of collisions between dead pieces of debris in space. The current way to deorbit is to push the satellite into the atmosphere using a final burn. This procedure, of course, assumes there is still fuel on board the satellite and that the satellite can still be controlled, which limits the use of this descent procedure.
By contrast, DESCENT will use a technology known as propellantless electrodynamic tethering (EDT). These tethers are essentially long conducting wires that convert their kinetic energy to electric energy. EDTs have been tested before in space, such as during the TSS-1 and TSS-1R missions that flew during space shuttle missions in 1992 and 1996, respectively. But the potential of EDT is not yet realized due to the early stage of testing the technology.
“Compared with the current approach [of deorbiting], the main advantage of EDT is it is propellantless, lightweight, compact, easy to use, and [has] no need of an operating satellite,” principal investigator Zheng Hong (George) Zhu at York told SpaceQ.
Zhu said the EDT is a first-of-its kind space demonstration in Canada, and will aim to improve upon other demonstrations of EDT. Besides the two space shuttle missions, EDT has been tested more recently by the Japan Aerospace Exploration Agency (2003 after a sounding rocket deployment, and 2016 in space with a larger spacecraft), and the U.S. Naval Research Laboratory using another Cubesat in 2019.
Most of these past EDT missions did not meet with success, Zhu explained. Both EDT deployments during the space shuttle missions ran into trouble, with TSS-1 jamming during deployment and TSS-1R breaking during its own deployment. The two Japanese attempts to deploy tethers also did not go to plan, but the U.S. mission of 2019 was able to deploy a 1,000-metre tether successfully. “Our DESCENT mission was originally planned to launch in the early 2019 to beat the U.S., but no success,” Zhu added.
DESCENT is made up of two 1U Cubesats connected by an aluminum tape tether that is 100 metres long. The tether was folded up inside one of the Cubesats for launch, while the two Cubesats were tied together using a compressive spring made of fishing wires, Zhu explained.
“Once activated, the thermal resistors will burn the wires and the two Cubesats will be separated by the spring and pull the tether out,” Zhu continued. “The long and electrically conductive tether will generate a ‘Lorentz force’ against its motion as it moves in the Earth’s magnetic field. By this electromagnetic interference, the kinetic energy of satellite is converted to electric energy, and then to heat dissipating into space, resulting in an accelerated descent of spacecraft.”
York plans to test the technology even further if this demonstration mission works out. Their long-term aim is to make a stand-alone EDT unit that can be carried by a typical satellite during launch. Once the satellite’s mission is finished, it would deploy an EDT to accelerate its descent into the Earth’s atmosphere. Alternatively, Zhu said, future space robotics units built to clean up debris could bring EDT units to a dead satellite and attach the unit to the satellite, allowing the debris to descend safely.
As is typical of space missions, DESCENT has a long history of development. In 2011, Zhu proposed the idea for an international nanosatellite constellation mission idea contest in Japan. While the idea didn’t win the top award, the EDT concept was shortlisted in the top 5 of 79 submitted proposals.
Zhu then continued the theoretical study of the technology with support from the Natural Sciences and Engineering Research Council of Canada (NSERC). In 2015, the Canadian Space Agency awarded Zhu a grant under the FAST (Flights and Fieldwork for the Advancement of Science and Technology) program, which funded the space mission, he said.
The EDT technology tested aboard DESCENT will use a different electron-emitting technology than the U.S. mission of 2019, Zhu added. DESCENT will use the Spindt field effect array to emit electrons (charged particles) back into the ambient plasma (superheated gas) in space. DESCENT aims to be the first to test this kind of EDT in space.
The CubeSat also has two science payloads for secondary objectives. These payloads include a particle detector from the University of Sydney to measure solar storms, and a high-efficiency solar cell built by the Lassonde School of Engineering at York.