The Accelerator Laboratory of the University of Jyväskylä’s Physics Department hosts the Radiation Effects Facility (RADEF), one of only a few such radiation effects facilities in the world. Here, electrical components for spacecraft are tested to see how they will perform when exposed to radiation in space, accurately simulated using precisely engineered ‘particle cocktails’.
Before launch into orbit, satellites, their on-board systems and even individual electronic components must be thoroughly tested. The harsh environmental conditions experienced during the launch and, later, in space pose many threats to satellite components. The only way to be sure that they can survive the shaking and vibrations during liftoff and the high and low temperatures, ultra-low vacuum, electromagnetic interference and energetic radiation in space is to test the components thoroughly before the launch.
The University of Jyväskylä’s RADEF is one of the three external radiation laboratories supported by ESA, the European Space Agency; the other two laboratories are in Belgium and Switzerland. Each is specialized; the Belgian lab uses neutrons while the Swiss add protons to their test palette. The Finns complement the offering with high-energy particles and electrons.
The RADEF facility serves mainly European companies, primarily for projects related to ESA missions, but it has also welcomed customers from the US and Japan.
Image: The component is placed inside the test chamber. During the test, a vacuum is created inside the chamber and ions from the accelerator are irradiated onto the component.
20 years of experience
“This laboratory was inaugurated in 1995 and we planned it from the beginning to accommodate applied research and commercial applications,” says Ari Virtanen, the current head and founder of RADEF.
For the facility, radiation testing of space components was one of ideas for supporting commercial activity. Virtanen had visited US and European facilities, and finally set up the first test campaign in the brand new laboratory for Daimler-Benz Aerospace in 1998. The Germans were happy and since then many other customers have followed.
In the early 1990’s, Finland wasn’t very well known in ESA as it was a newcomer and had relatively little experience in space. It took some time to persuade ESA to come and see the facility on a lakeside in central Finland – in the middle of nowhere when looked at from the ESA’s long-established technical centre ESTEC in the Netherlands. However, a contract with the agency was eventually signed in 2003 and the test facility was opened, with full ESA qualifications, in 2005.
“Nowadays, we devote about 20 percent of our ‘beam time’ for the radiation test campaigns and, on average, 20 companies come here for testing each year,” Virtanen says.
“We’re struggling with capacity, as this approximately 1 000 hours of annual test time is actually not enough. We’ve got a long waiting list.”
Image: The RADEF electron test facility is a modified electron-beam radiation therapy accelerator used in hospitals for cancer treatment.
When electronics go haywire
Radiation has very clear and well-known effect on electronics, so the Jyväskylä scientists and engineers can torture the components in very specific ways to obtain the needed results.
“Typically, components mounted on satellites are expected to work in the harsh environment of space for several years,” Virtanen states.
“We simply calculate how much and what kind of radiation any particular device will receive during that expected life time. Then we double or triple the dose. If the component endures that and continues functioning, it will surely work perfectly in space.”
“The first effects of radiation damage are just small functional errors. For instance, the information in memory circuits will be slightly damaged when radiation kicks some of the stored bits around, leading to corrupt data. When you rewrite the data, the component will still work fine – there’s no physical damage. The more you raise the amount of radiation, the more you encounter these errors, until you reach a level where the amount of errors no longer increases.”
These two radiation levels, when the errors start appearing and when they no longer correlate with increasing radiation bombardment, are the most interesting.
Then, at some level, the circuits will also suffer physical damage. The radiation particles will create short circuits and finally the component stops working.
“All this is a play with the probabilities. Even a component that has passed the pre-flight tests with flying colours may be hit in space by a very energetic cosmic ray on the first day and it’s dead right away. But by testing the components, we can still be very confident that that they can withstand the radiation very well in virtually all instances.”
Image: A particle ‘cocktail’ is produced in an ion source. These particles are then accelerated and the desired ions are selected before being fed into the test facility.
Creating real-space conditions
Reproducing the types and energies of radiation in space on Earth is hard, if not impossible. Therefore, testing at RADEF focuses on simulating the effects of space radiation as accurately as possible.
“There’s not just one, single space radiation model, since the radiation environment in space depends on the orbit the satellite is using,” explains Virtanen.
“The radiation a spacecraft encounters in low Earth orbit, where the satellite is protected by the Earth’s magnetosphere, is different than in higher orbits, where the Earth’s radiation belts add their spice to the ambient levels of radiation, and the levels additionally vary far away in interplanetary space.”
The trick for successful testing is bombarding the components with known radiation particles to achieve the same damaging effect. For instance, fast, highly energetic but smaller radiation particles are replaced with slower, but more massive ions, which are just normal atoms with some or all of their electrons stripped away. Almost all possible space radiation environments can be mimicked by selecting a tailor-made ‘cocktail’ of suitable ions.
The advantage of the RADEF facility is its ability to change the ions very rapidly. The Jyväskylä team can choose the ions one by one at the end of the acceleration process, making it possible to use up to seven different ions during one day of testing. A test taking seven days elsewhere can be made in a single day at RADEF.
In addition to ions, RADEF can test components by irradiating them with electrons. A new test facility, created for testing the electronics for ESA’s Jupiter-bound JUICE mission, is one of just a handful with this capability worldwide.
“These tests have been done previously with cancer treatment equipment used in hospitals, but they are not made for the kind of testing need for spacecraft and their components, and we can do the tests in a standardised way just as the other kinds of space radiation tests are done.”
Image: Ari Virtanen (right) and Arto Javanainen.
Next step: commercial test facility
At the moment RADEF, is a university laboratory providing a test facility and beam time for its customers. The clients come to Jyväskylä with their team and components, and the test itself is done by the client with assistance from the local RADEF team.
“In most of the cases, we could also do the testing, as we sometimes have even more experience than the customer has,” says Virtanen.
“Therefore, we’re gearing up to start offering commercial services. In this business model, the customer will ship the components to us, explain what kind of tests they need and then we would do the rest. They save money and time, and we can accommodate their test needs in a more flexible way to balance our over-subscribed timetable.”
Virtanen says commercial services would be offered through a joint venture with the university, and establishing this is already underway. However, final permissions and approvals are still pending, meaning that, so far, there have been only a few pilot tests and no firm funding decisions.
In addition to commercial testing, Finnish space radiation expertise could be used for developing new, better solutions for space-borne electronics. The University of Jyväskylä is already a partner in an EU-funded project developing radiation-proof memory circuits.
Text, photos, video: Jari Mäkinen