MEMS Accelerometer

A MEMS accelerometer is a motion sensor smaller than a fingernail that tells a rocket or spacecraft how fast it is speeding up, slowing down, or changing direction. It is one of the quiet workhorses that lets a vehicle steer itself when no GPS or ground signal is available.

Quick facts

• MEMS stands for Micro-Electro-Mechanical Systems — tiny machines etched onto a silicon chip using the same fabrication processes that make computer chips.
• It measures linear acceleration: the rate at which a vehicle changes its velocity along one axis.
• It is almost always paired with MEMS gyroscopes (which measure rotation rate) inside an Inertial Measurement Unit, or IMU.
• Sensors are sorted by “grade”: consumer-grade (high drift, used in phones), tactical-grade (the aerospace workhorse), and navigation-grade (precision tier).
• It has no spinning or moving parts, making it smaller, lighter, cheaper, and more reliable than older inertial instruments.

How it works

Inside the chip sits a microscopic “proof mass” — a small block suspended on tiny silicon springs so it can move along one sensitive direction. When the vehicle accelerates, the mass lags behind and deflects, because objects resist changes in motion (Newton’s second law). The springs push back, and that spring force balances the mass (Hooke’s law), so the distance the mass moves is directly proportional to the acceleration.

That motion is read out “capacitively.” The proof mass acts as one plate of a microscopic capacitor — a pair of conductors that store electric charge — and as it slides toward or away from fixed electrodes, the stored charge changes. On-chip electronics convert that change into a calibrated acceleration signal.

Three single-axis sensors (or one three-axis device) measure acceleration in X, Y, and Z. Combined with three gyroscopes in an IMU, the avionics gets a full six-degrees-of-freedom picture of motion. The flight computer then integrates acceleration over time — once to get velocity, twice to get position — a method called a “strapdown” inertial navigation solution. Because this dead-reckoning slowly drifts, the inertial data is usually blended with GPS/GNSS, star trackers, or sun sensors using a Kalman filter, a piece of math that fuses noisy measurements into a best estimate.

Why it matters

Knowing acceleration is fundamental to flying. The guidance, navigation, and control (GNC) system cannot steer, throttle the engines, separate stages, or insert into the right orbit unless it knows how fast the vehicle is accelerating and which way it is pointing — and it must do this on its own during ascent, when ground links and GPS may be degraded or jammed.

MEMS technology made high-quality inertial sensing affordable and miniature. Its small size, low mass, low power, low cost, and lack of moving parts give it long life and high reliability — exactly what mass- and budget-constrained CubeSats and SmallSats need. Those advantages, often summarized as SWaP-C (size, weight, power, and cost), are now pushing MEMS into larger launch vehicles, drones, and reusable boosters too. The trade-off is that MEMS sensors have historically drifted more and are more vulnerable to radiation and single-event upsets — glitches caused by space radiation striking electronics — so the highest-precision crewed and heavy-lift vehicles have still used legacy fiber-optic or ring-laser instruments. That gap is closing: navigation-grade MEMS units have now matched fiber-optic-gyro performance in orbit.

Where it is used and notable examples

• Einstein Probe / Lobster-Eye X-ray Satellite (launched 25 July 2020) — the first navigation-grade MEMS gyro IMU proven in orbit, matching a fiber-optic-gyro reference at about half the mass. That unit reached a measured gyro precision better than 0.02 deg/hr, weighed under 210 g, and drew under 1.5 W.
• CubeSats and SmallSats (such as TUM’s MOVE-III and NASA SmallSat programs) — fly low-cost off-the-shelf MEMS IMUs, like the Bosch BNO055, for attitude determination because of strict mass, power, and cost limits.
• Honeywell HG3900 — a tactical-grade, all-silicon MEMS IMU for aerospace navigation and guidance: accelerometer bias repeatability of about 0.5 mg (500 micro-g), a 37 g operating range, under 2 lb, under 6 W, and factory-configurable output data rates.
• Silicon Designs Model 1527 — tactical-grade MEMS accelerometers in plus or minus 10, 25, and 50 g ranges, built for spacecraft and satellite electronics testing.
• NASA SLS Block 1 RINU — a counter-example: it uses ring-laser gyros and QA2000 accelerometers, not MEMS, showing where legacy precision instruments are still chosen. Its navigation is purely inertial, making it very sensitive to initial alignment accuracy.

An IMU is the accelerometer-plus-gyroscope package, while “MEMS” describes the sensing technology — so not every IMU is MEMS, and not every MEMS device is a full IMU.