Towards nano-g sensing for high precision orbital manoeuvres
Authors:   Innoseis Sensor Technologies, Amsterdam, Netherlands, Beker Mark , Bertolini Alessandro , Heeres Matthijs , Peters Tjitte-Jelte , Dokoupil Aran , van den Brand Johannes 
Published: January 2024

Inertial navigation is a widely used approach to autonomous positioning and navigation. When accurate enough, it allows (autonomous) vehicles or spacecraft to stay on track or maintain orbit autonomously while optimizing fuel consumption. The challenge with inertial navigation is that small sensor errors expand quickly into large positional inaccuracies. Therefore, the performance requirements are stringent and extremely difficult to achieve in a compact and affordable form factor. Today’s small and low-cost MEMS (micro-electrical mechanical systems)-based inertial measurement units (IMUs) typically can only navigate standalone for tens of seconds before accumulated errors exceed acceptable margins of error. As a result, the majority of precision navigation applications found in automotive and aerospace applications require the use of large and high-powered sensor units. Furthermore, satellite positioning often requires ground based ranging systems which are expensive and time consuming. Other applications forgo the ease of autonomy for lack of a solution with a small enough footprint in terms of size and cost.
The large gap between high-performance accelerometers and low-cost MEMS devices was the impetus for Innoseis Sensor Technologies to integrate the proven performance of anti-spring technology into a chip-scale silicon platform. The accelerometer concept arose during fundamental research into gravitational wave detectors. Here, anti-spring technology for large scale isolation and sensing apparatus was successfully miniaturised into the microscopic domain of MEMS devices. The latest prototypes of the accelerometers have noise levels below 20 ng/√Hz and stability below 0.5 𝜇g. This is in part due to the patented anti-spring technology which allows the accelerometers to be significantly more sensitive while maintaining low power consumption. It is a purely mechanical invention and relies on conventional production methods making it cost effective.
The aim within the aerospace segment is to significantly improve the navigational capabilities of spacecraft and reduce the need to use other systems for orbit determination. Orbit maintenance in constellations will benefit as manoeuvres can be performed more accurately. Reduced propellant consumption will make onboard resources last longer, resulting in extended operational lifetime and a more cost-effective deployment.
We present the latest developments of the ultra-sensitive accelerometer and introduce the concept of geometric anti-spring technology. The spring implementation is achieved by an on-chip mechanical preloading system comprising four sets of curved leaf springs that support a proof-mass. Using this preloading mechanism, stiffness reduction up to a factor of 26 in the sensing direction has been achieved. This increases the sensitivity to acceleration by the same factor. The stiffness reduction is independent of the proof-mass position, preserving the linear properties of the mechanics and, due to its purely mechanical realization, no power is consumed when the accelerometer is in its preloaded state. Equivalent acceleration noise levels below 20 ng/√Hz have been demonstrated in a 50 Hz bandwidth, using a closed loop capacitive half-bridge read-out. Stability measurements conducted at a low noise environment will be presented as well as preliminary results on thermal performance of the devices.