Key players in UK space environmental testing tell Jonathan Newell how the industry is meeting the challenges of future space technology requirements.
Space travel and exploration is a huge industry with exciting potential for UK technology suppliers. According to figures released by the UK space agency for 2018, the industry is worth nearly £15 billion in revenues and employs nearly 42,000 people. However, in 2018, the UK held just a 5% share of the global space economy and so there was clearly potential for a lot of growth.
Since then, the gaps in the industry that the UK could fill have been analysed and Government funding has been distributed through the UK Research and Innovation (UKRI) Industrial Strategy Challenge Fund to exploit the potential.
The UK National Satellite Test Facility
One of the biggest projects is the National Satellite Test Facility (NSTF), which is being built at the Harwell Campus and will be operated by the UK’s national space laboratory, RAL Space, part of the Science and Technology Facilities Council (STFC). The facility is being completed ahead of commissioning and will enter commercial service from the summer 2022.
Robert Elliott, the Head of Business Development at STFC RAL Space, explained to me that after the review of industrial and academic space test facilities by the UK Space Agency in 2017, two major gaps were discovered. One was the need for a single spacecraft level environmental test facility to reduce the need to transport equipment offshore for long periods of time and the other was a sustainable propulsion development and test facility.
“The result was the creation of the National Satellite Test Facility to support the assembly, integration and testing of space payloads and satellites as well as the National Space Propulsion Test Facility at the Westcott Space Cluster, including an open access vacuum facility to allow the simulation of high altitude testing of thrusters,” Elliott tells me.
The NSTF at STFC RAL Space is nearing completion and will house an array of specialised equipment to put spacecraft through their paces before launch.
The NSTF will offer EMC and antennae testing. This requires an electrically neutral space, built into the fabric of the building. Copper sheet has been laid into the floor of the chamber as well as copper wall and ceiling panels to create a shield through which electromagnetic waves cannot pass.
Inside this quiet zone, satellite manufacturers will be able to accurately measure the noise that satellite antennas produce, ensuring that we get a high quality signal back to Earth for our TVs, weather forecasts and science operations.
Part of the large STFC RAL premises is home to a 16m cubed vibration test facility with two Data Physics LE-5000-VH shakers providing 222kN sine force on a 3″ stroke. The two tables comprise a 230 tonne vertical shaker and a horizontal system with a 2.1×2.1m slip plate.
This is the scale of the environmental test facilities required for the industry but RAL Space isn’t alone in having such equipment. Surrey Satellite Technology in Guildford produces satellite systems of different sizes, all of which have to go through shock and vibration testing for pre-launch qualification.
According to David Costello, Head of Mechanical and Propulsion at the company, the space industry is different from other sectors such as automotive or electronics, where components are made in volume. In such cases, industry standard 1/2 sine impulse shock tests are the norm and replacement of failed components is possible. For the space industry, volumes are low, shock levels are typically higher and across a wider frequency range and component replacement is often not possible.
“Shock events can be caused by jettison of the rocket fairing, staging, satellite separation, release of deployable items etc. The designer needs to ensure that optics, moving parts, ceramic components and relays are protected from such events,” he says.
Shock testing is done in two stages, first at the satellite level to characterise the way the shock transmits to sub-systems and components. The second stage is the lower level qualification testing.
The characterisation stage is important in determining whether there are any alterations needed to design characteristics such as component selection, positioning or mounting. This is difficult to model and so physical testing is necessary.
Once the design assesment is done, pyrotechnic shock tests are carried out at spacecraft level using a spacecraft structural model. A representative shock (eg separation) is performed and the transmission of the shock is measured throughout the structure. This enables unit level tests to then be carried out to qualify each one individually.
According to Dr Brian Le Page, Materials and Testing Functional Manager at Surrey Satellite, the tests generate massive amounts of data with which response envelopes can be created. Shock response within the spacecraft can be affected by structureal damping, the use of mass dummies etc..
“A results envelope is the best way of visualising the data and giving some confidence in the results. This enables a test to be designed for component qualification outside the spacecraft,” he says.
The Surrey Satellite facility is very data intensive and the STFC RAL vibration testers are equipped with 500 data acquisition channels so there are vast amounts of data involved in performing these tests. Making sense of the data is always a challenge as it can be difficult to analyse.
According to Dr Richard Ahlfield, founder of Monolith AI, there is an increase in the use of machine learning or AI to help with the analysis. This is particularly pertinent to the space industry as it is much more iterative than industries such as automotive.
The example Ahlfield used was that a typical car manufacturer uses 1000 simulation iterations, occupying 20 test days over a six month period at a cost of a million dollars. In Aerospace engineering, this can grow to 100,000 simulations over 100 test days occupying 36 months at a cost of 100 million dollars.
Recognising that AI itself isn’t straightforward and has had a mixed reception amongst test engineers, Monolith AI has taken the step of simplifying and streamlining the use of AI to make it more accessible to a wider community.
Simulation provides ways of interpolating data to understand system behaviour outside of observed conditions. For simple physical systems, that can be achieved with an equation, statistical modelling or higher level data modelling. For more complex systems, some aspect of AI or machine learning is required.
The AI software takes experimental data from complex system tests and presents the user with a parametric dashboard. The AI makes predictions on performance when parameters are changed. Some predictions will have higher levels of confidence than others and the user can design physical experiments to verify output as required. This can reduce testing requirements by as much as 70-80%, according to Ahlfield.