A Smaller, Simpler Mass Spectrometer for Exploration

Measuring individual charged particles is no easy task, but a mass spectrometer being developed at Goddard may help identify a wide variety of particles present in Earth’s auroras, on the surface of the Moon or coming in from interstellar space.

The Ion Velocity Mass Spectrometer being developed by physicists Ed Sittler and Robert Michell requires less power and is easier to build and operate than traditional mass spectrometers, Sittler said. What it can do is provide a high angular resolution, enabling three-dimensional imaging of the local environment, whether that means in Earth orbit, on the Moon or beyond.

“We can track the solar wind and measure it’s interaction with the surface of the Moon,” Sittler said. “We can capture backscattered ions from the wind hitting the surface dust.”

The more common time of flight mass spectrometers accelerate incoming ions using a strong electric field with a known strength. It requires the complexity of using ultra-thin carbon foils, high voltages up to 15 kilovolts, and high speed synchronized electronics to measure the time between the accelerated ion passing through the carbon foil and striking the detector. The measured time is proportional to the ion mass and charge ratio which allows scientists to calculate its composition. They can be large and power-hungry, Sittler said. That makes them unsuitable for smaller missions.

An IVMS instrument can operate on a few watts of power. Instead of accelerating ions, it uses permanent magnets and a small electric field to allow ions to enter the instrument. It can resolve solar wind and minor ions by calculating their mass-per-charge ratio, Sittler said, but doesn’t resolve each particle’s charge state. It also can detune the major ions, but not the minor ions, so it can measure a wider range of particle intensities.

“This a strategic instrument to enable new missions,” Goddard’s heliophysics technology lead Nikolaos Paschalidis said of the project. “IVMS is a new generation, velocity analysis-based mass spectrometer which makes it low power and easier to incorporate into smaller spacecraft.”

Sittler said the instrument parts have been fabricated, and they are waiting on components to finish the control board before testing it with a calibrated ion beam. The instrument will then fly on the Ground Imaging to Rocket investigation of Auroral Fast Features (GIRAFF) sounding rocket mission out of Poker Flat Alaska, planned for early 2024.

Sittler and his team are looking for Oxygen and Hydrogen ions that they believe are responsible for certain electron pulsations visible in auroras. “If O+ is not there,” Sittler explained, “it could mean there’s something missing with our theory.”