Paving the way to the Moon: Estonian CubeSat to test new technologies
Estonia plans to launch a CubeSat into space in early 2019 with the aim to test advanced technologies, including a plasma brake for deorbiting satellites and an electric sail propulsion system. The mission, named ESTCube-2, is expected to serve as a prototype for Estonia’s future Moon-orbiting spacecraft.
ESTCube-2 is a three-unit CubeSat developed mostly by the students of the University of Tartu in Estonia as well as other students worldwide in the ESTCube program. The satellite comprises the following subsystems: the electrical power system, communication subsystem, onboard computer, attitude and orbit control system, and structure.
All of the subsystems fit within 0.6 CubeSat units and will be integrated with the satellite’s bus built by the Estonian Student Satellite Foundation (ESTCube Foundation) in cooperation with Tartu Observatory and the University of Tartu.
Such integrated structure will have several important goals once it achieves Earth’s orbit. The spacecraft’s main objectives are to test plasma brake deorbiting capabilities and the electric solar wind sail (E-sail) propulsion. Moreover, the satellite will also take images of Earth, test a high-speed communication subsystem and test a corrosion resistant coating in space.
“The main goal of the mission is the test plasma brake deorbiting technology which is very similar to the electric solar wind sail,” Andris Slavinskis, ESTCube-2 Satellite Project Manager told Astrowatch.net.
Plasma brake deorbiting is based on the electrostatic Coulomb drag effect that results in momentum exchange between a negatively charged body and ion flow by using a long thin electrically charged tether. That is why ESTCube-2 will deploy and charge a 984-feet (300-meter) tether, which will be used to reduce the orbit altitude of the satellite. Such long tether could deorbit a satellite from the altitude of 435 miles (700 kilometers) to 310 miles (500 kilometers) in half a year.
“We expect to deorbit ESTCube-2 much faster than it would happen with the natural aero drag,” Slavinskis said. “It takes more than 20 years to deorbit from a 650-kilometer orbit. We estimate that [a] plasma brake with a 300-meter tether would do the job in less than a year. When tested, the plasma brake would be a strong component in space debris mitigation.”
The tether should have a mass of about 1.06 ounces (30 grams) according to estimates. Therefore, a plasma brake is seen as a lightweight, efficient, cost-effective, and scalable deorbiting system with a potential to address the space debris issue at critical altitudes of 560 miles (900 kilometers) and less.
E-sail is a propulsion technology based on extracting momentum from the solar wind plasma flow and uses a positively charged tether, while in the case of plasma brake, it is charged negatively. This first attempt to test this technology was made by ESTCube-2’s predecessor – the ESTCube-1, which was launched into space in May 2013.
However, that attempt was unsuccessful as the sail cable unwinding mechanics did not survive the rocket takeoff vibration. Hence, the Estonian scientists place great hopes on the ESTCube-2, expecting that it could successfully test this novel technology essential for future cheap and fast space exploration. Moreover, they see this CubeSat as a prototype of a more complex and difficult mission to the Moon.
“The main goal of ESTCube-2 is to test technologies for ESTCube-3 to avoid problems in much less forgiving and more expensive Moon orbit,” Slavinskis said. “The reason why we want to launch ESTCube-3 to the [Moon’s] orbit is that E-sail’s authentic environment is the solar wind which in the low-Earth orbit is blocked by the Earth’s magnetosphere.
“From [a] satellite design point of view, the lack of [a] magnetic field changes the way we can control the satellite’s attitude. Instead of electromagnetic coils and magnetometers, we have to use reaction wheel[s], [electric sail] propulsion, and [a] star tracker.”
Besides testing E-sail and plasma brake propulsion, ESTCube-2 will take images of our planet. It will be equipped with the Earth observation imager (EOI) – a small, lightweight, two-spectral imaging system. Near-infrared (650–680 nm) and infrared (855-875 nm) spectral bands of this instrument could be very helpful for vegetation monitoring purposes.
ESTCube-2 will be also used to conduct a corrosion protection experiment in order to test material corrosion resistance in space. Moreover, the satellite will test a high-speed communication system which uses a field-programmable gate array (FPGA), hence allowing “firmware-defined radio”.
Currently, the ESTCube-2 team is now testing prototypes and working toward engineering model which is scheduled to be ready in summer 2017. Then, they would like to have the flight model ready in summer of 2018, what will give the team about half a year to test it and hand it over at the end of 2018.
“We hope to launch the satellite early 2019,” Slavinskis said. “We are negotiating the launch now. If everything goes well with ESTCube-2, then ESTCube-3 could be launched early next decade, but we don’t know yet how difficult it is to get a launch to the [Moon’s] orbit.”
Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski's generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.