MEMS-Based Accelerometer to Measure Microgravity for In-Orbit Manufacturing

August 1, 2024

The ForgeStar® program, from U.K.-based Space Forge, aims to harness the unique environment of space to create ultra-pure materials that cannot be replicated on Earth. The key opportunities lie in producing high-performance semiconductors and super-alloys with fewer defects and superior properties, thanks to the low-gravity and vacuum conditions of space.

Space Forge’s ForgeStar satellites will be used to produce advanced materials such as alloys, proteins and semiconductors in the ultra-vacuum and microgravity conditions of space. Manufacturing in low Earth orbit (LEO) has huge potential across sectors from medicine to advanced electronics. Two examples — high frequency amplifiers and super alloys — that Space Forge is focused are described in the next two paragraphs.

High frequency amplifiers: Space Forge already produces wide and ultra-wide bandgap semiconductors, which are crucial for high-frequency amplifiers in cell towers. Earth-made semiconductors often suffer from defects due to atmospheric contamination and gravity-induced lattice rotations, leading to significant energy loss. By producing these materials in the “ultimate cleanroom” of space, there is the opportunity to create semiconductors with far fewer defects, significantly improving their thermal conductivity and overall efficiency. This improvement could halve the energy consumption of cell towers, leading to substantial CO₂ emissions savings.

Super alloys for aircraft turbines: Today’s jet engine efficiency is heavily dependent on the strength and quality of turbine blade materials. Space Forge aims to produce superior single crystal alloys and ceramics in space, free from the contamination and buoyancy effects present on Earth. These space-made materials could result in turbine blades that are 30-50 percent lighter, translating to a potential — and massive — 10 percent increase in aircraft efficiency, along with the substantial fuel and emissions savings that would bring over the aircraft’s lifetime.

The main technical challenge is ensuring the safe and reliable return of materials produced to Earth. Program goals include demonstrating the viability of this re-usable satellite technology and proving that space-made materials can significantly outperform their Earth-made counterparts. Space Forge aims to achieve these milestones within the next 12 to 24 months, with a critical test run planned within the next year.

In this LEO environment, accurate microgravity measurement is critical to the success of the process. The precise measurement of microgravity conditions within the satellite ensures that the materials are grown in an environment with minimal gravitational disturbances, which will enable the creation of ultra-pure crystals and alloys.

As Space Forge explains, “Silicon Sensing’s CAS291 accelerometer is a crucial component in the ForgeStar-1 avionics bay. Its small size, low weight, and high accuracy make it ideal for space applications, where every gram and millimetre of space matters. Accurate microgravity measurement is essential for linking the production environment to the quality of the space-made materials, ensuring they meet the highest standards for industrial and technological applications.”

Silicon Sensing began discussing Space Forge’s ambitions for the ForgeStar program in a meeting at one of the first events following the Covid pandemic in 2021 – Space-Comm Expo in Farnborough, U.K.. These early discussions with Andrew Bacon, founder of Space Forge, and his team lead to more detailed technical meetings as the potential of micro electro-mechanical systems (MEMS) technology for this challenging project was realized.

Traditionally MEMS technology had been perceived as compact and extremely reliable and rugged — but not able to offer the highest levels of precision performance seen in competitive technologies such as larger, heavier fiber optic gyro (FOG)-based sensors and systems. MEMS inertial sensors and systems have typically been used in industrial-grade applications, but recent advances have seen several companies in this field, including Silicon Sensing, bring products to market that can deliver far more precise ‘tactical-grade’ levels of performance.

Across many market sectors, including space, there are persistent imperatives to both extend operational endurance and to shrink platform size, impacting available space, weight, and power. In this environment the latest performance levels of these compact, low power consuming, MEMS products means there is an immense, and ever growing, range of applications across extraordinarily diverse sectors. Space, including LEO satellites such as the ForgeStar program, is one of many sectors that MEMS products can be used in.

In Space Forge’s ForgeStar program, the challenge is not simply motion sensing or platform stabilization. Instead, an ultra-precise MEMS-based accelerometer, the CAS291, will be used for the first time to measure the level of microgravity inside the LEO satellite. The data will be used to assess the impact of microgravity on the effective manufacture, in the ultra-vacuum conditions of space, of advanced materials such as alloys, proteins and semiconductors.

In LEO applications such as the ForgeStar program, space, weight, and power are critical constraints, given the compact size of the CubeSat which will require lower power, highly sensitive accelerometers to accurately measure low gravitational forces. The CAS291 is supplied as a small (10.4 × 6.7 × 2.7 mm), surface-mounted package in both flat and orthogonal variations, enabling acceleration to be measured on all required axis. It is able to measure linear acceleration by using a silicon MEMS detector, forming an orthogonal pair of sprung masses. Each mass provides the moving plate of a variable capacitor formed by an array of interlaced ‘fingers’. When linear acceleration occurs, it results in a change of capacitance which is measured by demodulation of the square wave excitation. This structure yields a robust design, enabling the CAS accelerometer series to measure a wide range of gravitational forces ranging from ±0.85g to ±96g.

Dr. Mark Marshall, Chief Engineer, Silicon Sensing concludes: “This is an ambitious research program to which our accelerometer will make a critical contribution. Over a relatively short term, we believe ForgeStar will bring about real progress towards successful manufacture in space – and to achieving the related performance and environmental benefits that will stem from that.”

As the ForgeStar program advances, the collaboration between Space Forge and Silicon Sensing stands as a testament to the transformative potential of MEMS technology. The successful integration of the CAS291 accelerometer into the CubeSat platform not only underscores the versatility and precision of modern MEMS devices but also paves the way for groundbreaking advancements in space manufacturing. The ability to produce high-quality materials in the microgravity environment of space could revolutionize various industries on Earth.

Looking ahead, the continued development of MEMS technology will likely unlock new possibilities for space exploration and utilization, ensuring that projects like ForgeStar remain at the forefront of scientific and technological progress. As the boundaries of what is achievable in space continue to expand, the role of precise, reliable, and compact sensors will be crucial in realizing the full potential of this environment.

This article was written by Dr. Mark Marshall, Chief Engineer, Silicon Sensing Systems Ltd., (Devon, U.K.). For more information, visit here  .

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