Sep. 1, 2015

In our quest to understand the space that surrounds our home planet, better research often requires better instruments -- faster, smaller or with higher resolution. A new space instrument, the smallest of its kind, just returned its first data analyzing the composition of our dynamic neighborhood, demonstrating it to be a technology ready for use on future missions.
The Mini Ion and Neutral Mass Spectrometer, or Mini-INMS, launched on board an National Science Foundation-funded CubeSat – a miniaturized satellite – called ExoCube on Jan. 31, 2015. NASA's Goddard Space Flight Center in Greenbelt, Maryland built the Mini-INMS to measure the particles in space, while the CubeSat was built by the California Polytechnic State University in San Louis Obispo.
ExoCube's goal is to measure the densities of a variety of particles in the upper reaches of Earth's atmosphere and watch how these densities change in response to daily and seasonal cycles. These measurements include the first hydrogen measurements ever directly measured in the region by a mass spectrometer, and the first direct oxygen, helium and nitrogen, measurements since the early 1980s. Hydrogen is of particular interest as its presence can contribute substantially to the total electron population around Earth, which, in turn, is a crucial parameter in understanding and modeling our space environment and its effects on satellites.

"It was a real challenge, because there's never been an instrument like this made this small," said Nick Paschalidis, science lead for the Mini-INMS instrument at Goddard. "But we had a great team and we put it together in just one year."
The final instrument measured just 3.5 X 3.5 inches square and 5 inches tall. It weighed about 1 1/4 pounds and fit neatly into the CubeSat, which measured about 12 inches by 4 inches.
The Mini-INMS instrument is built with an opening to face the direction in which the satellite flies. Like a bulldozer scooping up dirt as it moves, this open mouth naturally catches particles as the satellite speeds along at almost five miles per second. Once inside the instrument, the particles are accelerated to about the same energy. Pulses of these energetically homogenous particles are allowed to zoom through a gate. Then they're timed like a horde of runners in a race. The lighter they are, the faster they'll go: At the finish line the hydrogen will cross first, then the helium, nitrogen, and finally oxygen. By counting each set at the final detector, researchers can easily calculate how many of each type is present. There are two of these gated systems, one to measure ions and one for the neutrals, which must be converted to ions before they enter the main instrument.

"We've found that this first version of the instrument has adequate sensitivity to separate hydrogen, helium, nitrogen and oxygen particles. We're seeing a good read of all the space particles," said Paschalidis. "It's even sensitive enough to detect a bit of carbon from a fingerprint left on the side of the CubeSat from when it was being built."
ExoCube flies in a low-Earth orbit that reaches 250 miles at its closest approach, and 420 miles at its farthest. The satellite circles Earth every 90 minutes. Eventually, the satellite will be oriented so that one direction always looks toward Earth. However, ExoCube remained in a state of free rotation after launch during a phase when the team focused on -- and succeeded in -- establishing communications with the satellite after the ExoCube communications antennae failed to extend. Now that the instrument's viability is established, the team will turn its attention to expanding the gravity booms that will stabilize the satellite.
Once stabilized, ExoCube will be ready to send down solid science data on the composition of the space it flies through. Such measurements will be compared with measurements from a variety of telescopes measuring space from the ground, offering a chance to calibrate and validate these ground-based observations.
Proof of the Mini-INMS capabilities also opens doors for a host of other flight possibilities. An improved version is already being incorporated into a new heliophysics CubeSat being built at NASA Goddard called Dellingr, a name derived from the god of the dawn in Norse mythology. Paschalidis also is also exploring sending a version into orbit around the moon.

Image:
(Left) The smallest space weather spectrometer ever built, measuring just 3.5 X 3.5 inches square and 5 inches tall, was launched on board the ExoCube CubeSat in January 2015. The Mini Ion-Neutron Mass Spectrometer, or Mini-INMS, has provided some of the first direct measurements of particles in the upper atmosphere since the 1980s.
(Right) The ExoCube CubeSat before its launch in January 2015. Measuring almost 12 in X 4 in (30 cm X 10 cm), such CubeSats are able to provide relatively inexpensive space research. ExoCube is characterizing what kind of particles exist in Earth's upper atmosphere to help understand how it changes in response to space weather.