Estonian CubeSat Flies on VV23 Mission
Estonian CubeSat Flies on VV23 Mission
Spacecraft Largely Designed by Undergraduate University Students
Estonia’s next satellite is scheduled to aboard Europe’s Vega VV23 launcher Friday evening. While largely designed and built by undergraduate students, the shoebox-sized ESTCube-2 has ambitious goals in mind, including surveys of Estonian vegetation and the first successful in-orbit demonstration of ‘plasma brake’ technology. Deployment of a charged microtether will slow the CubeSat’s orbit, proving the prospect of helping to keep space clear of dangerous debris in the future.
“The ESTCube-2 team has invested eight years of development work in order to have another chance of testing the revolutionary E-sail propulsion concept in orbit."
Andris Slavinskis, University of Tartu
If successful, ESTCube-2’s plasma braking would mark the first use of electric sail, or E-sail, technology, devised by Pekka Janhunen of the Finnish Meteorological Institute (FMI) as a propellant-free means of exploring the Solar System. Beyond Earth’s magnetic field, electrostatic charging of satellite tethers would cause them to repel protons of the solar wind, lending them momentum in the process.
Closer to Earth, the magnetosphere repels the solar wind. Instead an e-sail can perform the opposite function: the charged tether would repel the nearly stationary plasma making up our planet’s ionosphere – an electrically active outer layer of our atmosphere – and cause drag as a result, leading it to slow down and its orbit to decay accordingly.
Plasma brakes therefore offer a low-cost, low-mass method of quickly removing satellites from orbit after their mission ends, marketed commercially through Finland’s Aurora Propulsion Technologies. ESTCube-2’s plasma brake e-sail is a 50-m (≈165 foot) long interweaved aluminum tether line made up of wires each just 50 micrometers (0.05 mm) in thickness – around the diameter of the average human hair.
ESTCube-2 has been developed and built by a team from Tartu Observatory of the University of Tartu and student organization Tudengisatelliit. The miniature mission also carries student-built microcameras to survey Estonian vegetation, based on a design originally developed for ESA’s European Student Earth Orbiter mission. Their results will be compared to the full-size Copernicus Sentinel-2 mission, as well as a materials payload investigating the corrosive effects of ‘atomic oxygen’ found at the top of the atmosphere, plus a software defined radio for amateur radio tests.
A 3-unit ‘CubeSat’ – a low-cost satellite built up from standardized 10 cm boxes – ESTCube-2 launched on Vega’s Small Spacecraft Mission Service, a rideshare service for small satellites. It secured its place through the European Commission’s In-Orbit Demonstration/In-Orbit Validation program. Managed on behalf of the Commission by ESA’s Small Satellite Platform Unit, this program allows the early orbital testing of new technologies to make Europe’s space sector more competitive.
“As a volunteer student project, this IOD/IOV program is ideal,” explains ESTCube-2 project manager Hans Teras. “It fits nicely with our timeline, including the testing we needed to be sure of our performance. Well over 600 university students across all study levels have played some role in making ESTCube-2 happen, but the mission as a whole is very ambitious, pushing the boundaries of what students can do.”
ESTCube-2 launched a decade after its predecessor, ESTCube-1, which flew on a Vega in 2013. It too carried an E-sail payload from FMI, but a motor problem meant it failed to deploy. ESTCube-2 is equipped with a stronger, more robust deploying motor that has undergone extensive mechanical testing.
“The ESTCube-2 team has invested eight years of development work in order to have another chance of testing the revolutionary E-sail propulsion concept in orbit," said the University of Tartu associated professor Andris Slavinskis who led the transition from ESTCube-1 to ESTCube-2.
“Last time we could encourage students to join us by the challenge of being the first Estonian satellite," said Kristo Allaje, Principal Systems Engineer of ESTCube-2. "This time we have to motivate them in another way, by asking them to enable excellent science.”
Around a year into the mission ESTCube-2 will be spun up using its reaction wheels. The ensuing centrifugal force should help serve to deploy the E-sail in a sufficiently taut fashion. If successful, the E-sail is expected to lower the orbit of ESTCube-2 much more rapidly than normal.
A follow-up mission ESTCube-LuNa is being designed to test an E-sail beyond Earth orbit, to prove its usefulness as a method of deep space propulsion. ESA has recently studied E-sail technology as an economical means of prospecting asteroids.
ESTCube-2 pair of student-made microcameras designed have been optimized for the ‘Normalized Difference Vegetation’ index to reveal plant health. The camera pair will be tilted as needed to observe Estonian territory as often as possible, offering more frequent revisits than other Earth observation missions.
Tartu University spin-off company Captain Corrosion is supporting an experiment mounted on ESTCube-2’s hull. A set of 16 different materials will be evaluated for their resistance to ‘atomic oxygen’ – a variety of oxygen normally encountered only in low orbits, known to eat away at satellite surfaces.
ESTCube-2’s software defined radio will also be busy, including transmitting 8-second video clips pre-recorded by Estonian citizens, connecting to Estonian schools along its swath and performing ranging experiments with amateur radio enthusiasts.