The sky’s the limit? The UK's role in space exploration

Materials World magazine
,
3 Mar 2011
Space satellite

Perceptions that the UK is lagging behind or is non-existent in the field of space exploration could not be more wrong. Guy Richards is on a mission to find out more.

For a child, a natural history museum is almost always a treat for two reasons – the dinosaur exhibit and the physical replica of our solar system. The fascination with these forms that seem so unreal, but were, or are, in existence, is unparalleled. But while the dinosaurs are a step back into history, the planetary system, it seems, will figure heavily in our future.

David Willets, UK Minister for Universities and Science, has noted that ‘one of the great strengths of the space sector is [that] it is one of the most effective ways of getting young people interested in science’. It could also be a key employer going forward.

As mixed messages about the state of the UK’s economy continue to emerge, it is encouraging to find that the space industry has remained blissfully unaware of the recession.

The sector has grown by 10% a year over the last two years, according to a report released in November 2010, by consultancy Oxford Economics, on behalf of the UK Space Agency (UKSA). The 260 companies actively involved in the UK space industry are generating a turnover of about £7.5bln per annum, and employing about 25,000 people, a figure rising by about 15% a year.

To exploit this potential, a Government and industry-sponsored Space Innovation and Growth Strategy (SIGS) has set out a 20-year vision to increase the UK’s share of the world’s space market from six per cent in 2007 to 10%, providing 100,000 new jobs and increasing revenues to £40bln per annum. It notes that, currently, satellite manufacturing in the UK is worth £800m, around 14% of the UK’s space sector.

Among the recommendations are the need for a national space technology programme. This will reduce reliance on R&D funding from the European Space Agency (ESA), but also improve the UK’s visibility in the field. The SIGS’ first report notes, that under the Lisbon treaty, the ESA will become an executive agency for EU Space policy, and so ‘there will be increasing opportunities to compete for a share of European programmes on a more commercial basis’.

Knowledge transfer

What might surprise an industry outsider, however, is that very little of the materials science R&D that underpins the industry is space-specific. A spokesman for Guildford-based Surrey Satellite Technology Ltd (SSTL), which has been building and launching satellites for more than 25 years, explains, ‘We keep a watching brief on the R&D going on in wider industry, cherry-picking suitable high-end terrestrial technologies’.

The R&D effort is therefore fragmented. But that is about to change. In April 2010, the UKSA in Swindon went live, bringing together all national civil space activities under a single management strategy. Simultaneously, the UK Government announced the launch of the International Space Innovation Centre (ISIC) and the opening of a European Space Agency (ESA) facility at Harwell Science and Innovation Campus, also home to the Science and Technology Facilities Council (STFC).

Professor Keith Mason, CEO of the STFC and Chairman of the ISIC establishment board, notes, ‘There are various distributed capabilities that need to be brought together. Space is a broad category – there are materials for craft construction, solar arrays and so on, much of which is not in a space context but where we still want to draw on those capabilities’.

Locating the ISIC at the STFC’s Rutherford Appleton Laboratory (RAL) is complementary, as the RAL already has a range of facilities available to conduct materials research. The Diamond Light Source, for example, is the UK’s national synchrotron science facility and is split into ‘beamlines’.

On the materials and magnetism beamline, scientists are collaborating with their counterparts at Leicester and Cardiff universities to investigate new materials for varying fixed-wavelength polarisation measurements of astronomical sources using X-ray telescopes.

Dr Nigel Bannister, of the Space Research Centre at the University of Leicester, explains, ‘X-ray polarimetric measurements of astronomical sources is an area that has lagged far behind techniques like high-resolution imaging and spectroscopy, because of the low-photon fluxes received from these sources and the limitations of existing instrumentation.

‘We need to produce [X-ray] dichroism in a specific range of energies – 0.5-8.0keV. We are particularly keen to produce materials that offer dichroism at approximately 0.5-1.0keV and also around 4keV.’

The work stems from research carried out by the beamline’s Principal Scientist, Professor Steve Collins. He investigated polymers doped with bromine that act as fixed-wavelength X-ray polarisers. Collins suggests that other possible solutions are matrices containing iodine and perhaps chlorine molecules.

Bannister adds, ‘We have obtained promising results from [using] a host matrix (urea and thiourea) to confine guest molecules. Dichroic materials based on metallo-porphyrins have also been produced and successfully demonstrated, and both of these approaches could lead to a practical filter’.

He notes that the motivation for this collaborative project was exclusively the space application, but work being carried out at Diamond Light’s neighbour, the ISIS neutron-scattering facility, is a good example of how a terrestrial technology could be adapted for space.

Radiation shielding

A team at ISIS is working with RAL-located spin-off company Cella Energy on hydrogen storage materials for various terrestrial power and transport applications. Recently, though, ISIS has attracted interest from the space industry regarding the potential for long manned flights and possible radiation shielding solutions for crew members.

There is a need for alternative materials, as conventional radiation shielding made from aluminium could do more harm than good. The heavy nuclei in aluminium causes high-energy primary cosmic particles to shatter into a ‘cascade’ of secondary particles. These can damage human tissue in a way analogous to a dum-dum bullet. Making the shielding thick enough to stop the primary particles completely, however, would incur such a mass penalty as to make the spacecraft impractical.

‘One of the best substances for shielding radiation is hydrogen. Its low atomic mass means the atoms do not fragment in the same fashion when struck by the primary particles, and so don’t produce secondary radiations to the same degree,’ explains ISIS Director Dr Andrew Taylor. ‘Cella is developing technology to allow hydrogen to be stored at high densities but not high pressures, doing away with the need for strong and therefore heavy containment.

‘A prime hydrogen storage material is ammonia borane, NH3BH3. [It] has a high hydrogen density [19.6%] but is quite a nasty substance, so it is encapsulated in a polystyrene nanoscaffold using a process called coaxial electrospinning,’ he says.

The technology is still at R&D stage but it illustrates a crucial requirement of materials for use in space – multifunctionality. In this case, a material that stores hydrogen for fuel also has a low-mass form for radiation shielding.

Space for materials

Low mass and good dimensional stability are key parameters for space applications. The RAL Space facility focuses on the assembly, integration and verification of satellite and spacecraft instrumentation systems for NASA and the ESA. Project Manager Nigel Morris says ‘the most important materials’ to fulfil these requirements are metal-matrix and carbon fibre composites.

‘We are always looking for materials with a high Young’s modulus and low density, to allow us to build lightweight structures with a natural frequency above about 70Hz. Metal-matrix composites offer high specific stiffness and low, or even zero, coefficient of thermal expansion, but also high thermal conductivity’.

He continues, ‘Silicon carbides and other ceramics are important as well, especially in mirror technology. To get the high resolution required of these mirrors they have to be a few metres diameter – if they were made from traditional glass, they would be far too heavy.’

Researchers at Bristol University and Imperial College London are investigating other aspects of carbon-fibre reinforced composites and ceramics.

At Bristol, Dr Sameer Rahatekar is a member of the Advanced Composites Centre for Innovation and Science, and while his research is aimed at aerospace engineering, there is potential for it to be applied to space. ‘My research has three main strands – increasing the toughness of polymer matrix composites, improving their electrical conductivity and thermal performance, and developing self-healing [materials],’ he says.

Rahatekar is adding graphene and carbon nanoparticles to the resin, as well as sandwiching carbon nanotubes between the composite layers, to make the material tougher and improve conductivity. The nanotubes reinforce the composite while also acting as a radiator, improving thermal performance.

Although the concept is proven in the lab, Rahatekar concedes there are shortcomings. ‘If you have an electrically conductive resin, it could damage sensors built into the structure. [On the other hand], if a crack occurs in the composite, that upsets its conductivity, [this can be detected]’.

This leads logically to self-healing composites – useful in space, where repairs are usually impossible. Rahatekar’s approach is to use hollow glass fibres filled with resin that ‘leaks’ into a crack like blood platelets into a wound. This is at an early stage of development, he says. The challenge being that, at the moment, the leaks reduce the strength of the composite’s local area, so he is now looking at ways to overcome this.  

Thermal stability

At Imperial College London, Dr Finn Giuliani is a researcher at the Structural Ceramics Centre. He says, ‘Our main work here is in ultra-high temperature ceramics for reusable spacecraft, principally the successor to NASA’s Space Shuttle. The aim is to allow NASA to control where these craft land if there is bad weather at one landing site, or in an emergency. They will need heat-resistant control surfaces to allow them to fly more like a conventional aircraft’.

The team is investigating a range of ceramics, but the two prime candidates are zirconium diboride and hafnium diboride, which have good thermal stability. Giuliani outlines, ‘Hafnium diboride has a slightly higher melting point than zirconium diboride and is less reactive, but also has nearly twice the density. In general though, the heat resistance of ceramics outweighs any mass penalty, and, in any case, there are not many other materials suitable for this type of application – unless of course there’s a whole new class of materials out there that no-one’s discovered yet’.

In orbit

As well as structural and instrumentation applications, another vital aspect is propulsion and, as a corollary, orbit control. One approach is the use of electrochromic coatings, such as those made of tungsten oxide and applied in smart windows.

The Advanced Space Concepts Laboratory at the University of Strathclyde, in Glasgow, is exploring their use to control micro-satellites, about one cubic centimetre in size. By coating them in an electrochromic material, a current passed across the surface changes the reflectivity, and, in turn, the thrust on the craft using photon pressure. This controls ‘the “push” from sunlight, in effect,’ proposes Laboratory Director, Professor Colin McInnes.

Each micro-satellite will act as a sensor ‘node’ in a collaborative system of hundreds, possibly thousands, for telecoms and environmental monitoring.

The UK space industry is now a key part of the national economy, and opportunities to contribute in advances are unlimited. As Mason says, ‘The list of R&D strands here is endless’. But with the inauguration of the UKSA, the ISIC and the ESA’s Harwell facility, researchers and developers in Britain – whether they be in academia or industry – at last have a focus for their work.

Further information

www.ukspaceagency.bis.gov.uk
www.spaceigs.co.uk
www.stfc.ac.uk/isic/default.aspx
www.stfc.ac.uk/ralsp ace
www.isis.stfc.ac.uk  

 

In flight – smart R&D


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The ‘sysbrain’ makes use of natural language programming to read technical control documents, preventing vehicles from crashing into other objects and enabling them to adapt during missions. Professor Sandor Veres, who is leading the work, claims ‘this is the world’s first publishing system of technical knowledge for machines’.


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Discrete self-aligning flat antennae could resign bulky satellite dishes
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The research is funded by the European Space Agency.


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