Manufacturing Bits: May 15

Space metrology
NASA is developing a mini-electron probe based on an array of carbon nanotube dots. The probe would be used in an instrument, which would analyze the chemical properties of rocks and soils on asteroids, moons and planets.

For years, NASA has been working with carbon nanotubes in various applications. Carbon nanotubes are hard, cylindrical nanostructures with good electrical properties.

The work for the mini-probe is being done at NASA’s Goddard Space Flight Center in Greenbelt, Md. The funding comes from NASA’s Planetary Instrument Concepts for the Advancement of Solar System Observations Program, better known as PICASSO.

To make the tiny probe, NASA researchers first place a silicon wafer inside a furnace. Then, they bathe the substrate with a carbon feedstock gas. This, in turn, applies a thin coating of carbon on the substrate. Using lithography and other techniques, the resulting wafer consists of tiny dots of carbon nanotubes in a grid pattern. Then, silicon wires are positioned above and below the grid of dots.

These images show the nanotubes that would operate as electron emitters in a new instrument now being developed for analyzing extraterrestrial samples. The right image is a close-up of one of the bumps. (Credits: NASA)

The patterned nanotubes would act as a probe and would fit into an instrument. In effect, the patterned nanotubes would operate as electron emitters in a new probe instrument.

Within the instrument, electron beams would pass through a stack of electrostatic lenses and through the carbon nanotube probe. “We would be able to choose which bump to activate,” said Lucy Lim, a scientist at NASA’s Goddard Space Flight Center. “We would be able to analyze different spots on the sample individually.”

Lim added: “We want to obtain compositional maps. Without the addressable emitter, we might not discover all the minerals contained within a sample, how big they are, or their relationship to each other.”

Tracking the changes on earth
NASA is preparing to a launch a pair of satellites using a promising technique called laser ranging interferometry.

The technology involves satellites as part of NASA’s Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) system. GRACE-FO is the follow-on to the previous satellite system, dubbed GRACE. Launched in 2002 and concluded in 2017, GRACE tracked the movement of the Earth’s mass. This was done by measuring changes in the distance between two satellites that flew one behind the other around the Earth.

For example, the satellites would track the changes of mountain ranges, oceans or other masses. Each month, the satellites would calculate these masses and detect the changes. To measure the masses, a satellite would transmit microwaves to another satellite more than 100 miles away. This in turn creates a microwave interferometer in space.

GRACE-FO is similar. Each spacecraft carries a microwave instrument. What’s different is that each craft will also carry a laser ranging interferometer (LRI). In addition to transmitting microwaves, the GRACE-FO satellites will shine lasers at each other.

GRACE-FO will measure monthly changes in gravitational pull resulting from changes in Earth’s mass below the orbiting satellites. As the satellites orbit Earth, one following the other, these moving masses alter the gravitational pull below them, changing the distance between them very slightly. (Credits: NASA/JPL-Caltech)

The wavelengths in a laser beam are shorter than microwaves, so the LRI will improve the tracking precision of separation changes in masses. In fact, it will detect changes in distance more than 10 times smaller than before. “With GRACE-FO, we’re taking something cutting-edge from the lab and making it ready for space flight,” said Kirk McKenzie, the LRI instrument manager at JPL. “The reason we spend decades working in the lab is to see our technology enable a new type of measurement and result in scientific discoveries.”

The LRI is managed by NASA and the Max Planck Institute for Gravitational Physics.