On course – sending composites into space
Professor Ian Hamerton, at the University of Bristol, UK, on testing advanced polymer matrix systems for Earth’s low orbit.
The approximate distance from Earth to our Moon is almost 400,000km. The journey to our nearest planetary neighbour, Venus, is some 40mln km, while Pluto, at the periphery of our solar system, is a lonely 7.5bln km distant. With such vast distances to cover, fuel efficiency is key and, in manned space flights, excess weight reduces payloads essential for survival.
Launching spacecraft into Earth’s orbit and beyond has also been phenomenally expensive – in 2016, it cost £4,095/kg to deliver a payload (or cargo) into Low Earth Orbit (LEO) aboard the Atlas V 551 rocket. Although the activity is becoming more affordable – £1,362/kg to deliver a similar payload in 2017 on Falcon 9 and £685/kg in 2020 on the Falcon Heavy – minimising the mass of a space vehicle is crucial.
In parallel with the physical demonstrators, we are developing a ‘digital demonstrator’ as a data analysis and simulation platform and a data visualisation tool for the space structure demonstrator. The tool is based on the material characterisation output from the physical – thermal, optical and spectral – and mechanical analyses.
The ‘digital twin’ approach, first proposed by NASA, has been used for well over a decade – a computational model of a functional object or system to understand and predict the physical counterpart’s performance. This often employs multi-physics simulation, data analytics and machine learning capabilities to give early warning of system failure and support intervention decisions. The key to producing a successful digital twin is to ingress a large body of high quality physical and mechanical data into the model, so the damaging effects of environmental exposure can be better understood. Ultimately, the model will incorporate the AO flux and temperature, etc. from the ISS into a real-time numerical model.
Over the last three years, our composite specimens have been subjected to a battery of physical tests in our laboratories to determine their softening and thermal degradation temperatures, their porosity and their resistance to an oxygen plasma, but until a digital twin is in place, it must be complemented with data from LEO tests.
The Bristol team has received financial support from the UK Space Agency to prepare and test the carbon-fibre-reinforced polymer (CFRP) samples prior to the space trials. In July 2021, 16 CFRP specimens – each 3mm x 25mm x 25mm, prepared at the National Composites Centre (NCC) with a V shaped machined groove to the surface – were delivered in sealed anti-static bags to the European Space Technology and Research Centre.
Located at the southern tip of Noordwijk in the Netherlands, the facility houses some 2,500 members of staff and is packed with state-of-the-art analytical equipment. Before they can be exposed to the high vacuum of the zero-gravity environment on the ISS, all the samples must be tested to determine how much mass they might lose under these conditions, described as ‘outgassing’.
The team, headed by Dr Sebastien Vincent-Bonnieu and assisted by Dr Agnieszka Suliga and Dr Johanna Wessing, have performed a series of exposures to low pressure and measured the mass lost, before giving the green light for integration into the SESAME module. The samples will be launched into space in 2022 and will be placed on the exposed outer surface of the ISS for at least six months to measure their performance, including their mass losses.
All of our composite matrix formulations are designed with the space environment in mind, for use as structural materials with thicknesses of several millimetres and in deployable composite boom structures constructed from ultra-thin laminates of less than 0.5mm.
However, with their attractive balance of engineering properties, high-performance polymers of this kind often have multiple uses, such as coatings and adhesives. In the shorter term, the cyanate ester resin formulation has been the subject of a recent patent application and is chemically related to another family of patented advanced composite materials that other members of my team have developed to enable composite components to be fabricated by a third party.
Components made from these materials are critical to the capability of the 2.5MW (3,400h.p.) Power Generation System 1 (PGS1) demonstrator programme for future regional aircraft. PGS1 is currently being tested in Trondheim, Norway, and Filton, UK, and forms an important element of Rolls-Royce’s sustainability strategy, which includes developing electrical power and propulsion systems. The work is supported by the UK Aerospace Technology Institute’s MegaFlight project, while the 2.5MW electrical generator, motor and power electronics design, make and testing in Trondheim has been supported by the EU Clean Sky 2 Programme.
The benzoxazine formulations are at a slightly lower level of maturity, but discussions are currently underway with a leading international resin manufacturer about their commercial development.
Both of these composite materials have already been designed to protect themselves in response to exposure to AO, but in their proposed use, the repeated swelling and contraction of the materials as they are thermally cycled will inevitably result in the formation of microcracks. Combined with the risk of impact with micrometeoroids or high velocity dust particles, the composites need to be resilient. Our longer-term plan, through a new PhD project, is focused on improving the ability of the polymer matrices to undergo self-healing in response to mechanical damage.
Having delivered the specimens to the ESA’s European Space Research and Technology Centre, the team can do nothing more with those samples until they are returned in 2023, but plans are already afoot to employ the cyanate ester resin system in an unmanned lunar mission. The structural component will again be manufactured in partnership with the NCC.
As the team looks ahead with excitement to the launch of the samples to the ISS, I recall the inspirational words of the late and incomparable Douglas Adams, 'Let’s think the unthinkable, let’s do the undoable. Let us prepare to grapple with the ineffable itself, and see if we may not eff it after all'.
In this project, Professor Ian Hamerton is supported by a team comprising: Dr Mark Schenk, Professor Fabrizio Scarpa, Professor Kate Robson-Brown, Professor Ian Bond, Dr Joseph Gargiuli, Ms Mayra Rivera Lopez, Dr Yanjun Desmond He, Mr George Worden and Mr Zac James of the University of Bristol, UK, and Mr Sean Cooper and Mr Stuart Donovan-Holmes at the National Composites Centre, UK.