British scientists are to send an experimental radiation shield made from a solid form of hydrogen fuel for testing on the International Space Station (ISS).
UK firm Cella Energy, a spinout of the government-funded Rutherford Appleton Laboratory, developed the material by combining solid hydrogen compounds with plastic fibres as a way of storing and transporting it more easily for use as fuel.
The researchers believe the material could make an effective radiation shield for satellite electronics because it absorbs high-energy radiation and is less likely than current aluminium shields to generate secondary particles that can disrupt equipment.
‘The hydrogen content solution is a good one but it’s not been proven in space yet.’
Samantha Rason, senior spacecraft radiation environment engineer, SSTL
‘NASA is looking at high-hydrogen content materials as their shields,’ said Prof Stephen Bennington, Cella Energy’s chief scientific officer and the inventor of the material.
‘On the International Space Station, all the sleeping quarters have ultra-high molecular weight polyethylene slabs … The amount of hydrogen in our material is, by weight, 30 to 40 per cent higher.’
Aluminium is commonly used to protect satellite electronics because it is lightweight, strong, relatively cheap and can protect against high-energy radiation that degrades equipment and shortens the lifetime of the satellite.
But the radiation can also knock protons and neutrons out of the aluminium atoms’ nuclei, which can disrupt the operation of the electronic systems.
Materials with a high hydrogen content can offer similar protection against high-energy radiation but are less likely to generate these secondary particles because hydrogen atoms contain only one proton and no neutrons.
Samantha Rason, senior spacecraft radiation environment engineer at Surrey Satellite Technology, said: ‘The hydrogen content solution is a good one but it’s not been proven in space yet.’
The Cella Energy team are now preparing to test their material onboard the ISS by the end of the year, after winning a competition run by the US state funding body Space Florida.
The material is made from solid compounds containing hydrogen (hydrides) attached to polymer fibres using a process called electrospinning.
It was developed as an alternative to the compressed or liquid hydrogen used to power hydrogen fuel cells, particularly in vehicles. It releases the hydrogen upon heating to leave a solid waste that can then be recycled and regenerated with more hydrogen.
Bennington said that with modification the material could be particularly suitable for small Earth observation satellites in long, elliptical orbits around the poles as these tend to pass through the belts of charged particle radiation that surround the planet.
‘Our materials were not ever designed for this purpose,’ said Bennington. ‘They were designed to release hydrogen and be a power source. So we’ve had to modify them so they don’t release hydrogen at any reasonable temperature but they’re still flammable so we have to package them in a way that removes those issues …
‘We’ve already put it through what we call a “shake and bake” test at the Rutherford Appleton Laboratory,’ he said. ‘They put it on a big vibration table to simulate the launch and then bake it out to see if it gives off any noxious gases that would kill off the electronics because it can get hot up there.’
The material is now undergoing even more rigorous testing by NASA in advanced of the trial onboard the ISS, where it will be used to encase a miniaturised radiation monitor based on technology developed by CERN for the Large Hadron Collider, and compared to a second monitor inside a polyethylene shield.
Bennington added that the material’s high energy density could potentially make it suitable as a backup power source onboard the ISS, although not for deep-space missions because of the need to recycle it.
Cella Energy is also applying for two Technology Strategy Board grants to support projects developing the equipment that delivers the material to fuel cells.
One is a system to pump pellets of the material into a vehicle in a similar way to how liquid petrol is delivered but with an additional vacuum cleaner-like mechanism to simultaneously suck used pellets out for recycling.
The second approach is to create cartridges of the material dispensed by magazines that can be easily transported, stored and slotted into a fuel cell system.
The company plans to remain a material supplier rather than a technology manufacturer but is working with partners to develop the delivery systems in order to create a market for its product.