Enric Grustan Gutierrez studies propulsion so maybe it’s not surprising that he’s a force of nature himself. The high-energy mechanical and aerospace engineering doctoral candidate designs and microfabricates tiny arrays of electric-propelled thrusters that could change the way telecommunication satellites and other spacecraft are launched and navigated.
Miniscule propulsion systems – each only the width of a human hair – are arranged in tiny arrays small and lightweight enough to fit on a penny. Unlike the huge thrusters found on most rockets, which are chemically propelled and deliver enormous power but little control, the microfabricated arrays have the potential to provide far more efficient and more easily controlled thrust. In addition, the amount of thrust can be increased by building more units into the array, whose small dimensions effectively reduce a satellite’s weight as well as the resources required for propulsion.
The technology starts with a silicon wafer, microfabricated to form the equivalent of a hollow hypodermic needle 80 microns wide and 300 microns high. (Eighty microns is about 3/1000ths of an inch, approximately the width of a human hair.)
The needle is filled with ionic liquid, which can conduct electricity, and aimed at a flat silicon plate with a tiny hole in the middle. An electric field generated by a power supply (similar to a battery) causes the metal plate to attract the electrified liquid toward it at an extremely fast rate – 10 kilometers per second. As the liquid hurls through the hole in the metal, it creates thrust to provide spacecraft acceleration.
When multiple thrusters are grouped in an array, they are capable of delivering much more thrust than a single device could. And because the array can be regulated – one booster or 100 can be utilized depending on need – they are much more flexible than chemical propulsion boosters, which basically are either “on” or “off.”
“The idea is to have something where the minimum amount of force is very, very small, and the maximum is pretty big,” Grustan says. “We put a bunch of them together, and if we want very, very small propulsion, we only work with one, but if we want 100 times the force, we work with 100 [boosters].”
The 10 millimeter x10 millimeter array, the size of a thumbnail, currently contains 81 individual devices that Grustan is working to power and synchronize. Ultimately, he hopes to perfect 100-unit arrays, after which, he says, additional units can be easily added.
The technology will be a boon to satellite manufacturers as they build smaller and smaller models. Grustan says the future includes satellite swarms comprised of 10-20 mini-satellites that operate as a cluster; these petite booster systems can provide propulsion without added weight and with just the right amount of thrust and control.
Grustan, whose graduate work is supported by a Balsells Fellowship, does most of his work in the INRF and Calit2 cleanrooms, on the reactive ion and deep reactive ion etchers, mask aligners and the scanning electron microscope. Cleanroom maintenance and safety issues this summer have conspired to limit the availability of those instruments, and time is ticking. His DARPA grant expires at the end of September but Grustan needs another academic quarter to complete and test his microarrays. “I have succeeded with one single [unit] but haven’t yet accomplished that with an array,” he says.
His solution? Crowdsourcing. Taking a page from the book of Hollywood producers, technology startups, artists and politicians, Grustan is appealing to the public. He created a project page on Microryza, an online venue dedicated to funding scientific research. The site has helped attract funding for more than 1000 research projects since its launch last year.
Grustan’s goal is $4,000 – money he needs to pay for cleanroom time and materials. Microyza requires each project to have a self-imposed time limit; Grustan’s coincides with the end of his federal funding. As of today, only 49 days remain. According to the terms of the Website, if he doesn’t meet his goal, all of the committed funds will be forfeited.
“I’m almost there,” he says of his research progress, adding that he’s been “working like crazy” to make up for lost time. But a planned equipment upgrade this month will cost him another two weeks while a new machine is brought online. “That’s fine in theory because it will work better, but the timing is not the best,” he says good-naturedly.
Grustan’s sunny demeanor and optimistic outlook mask an underlying anxiety.
“I have until the end of September to collect money. If I don’t meet the goal I will have to find some other way,” he says. He could become a cleanroom “super-user,” entitling him to a certain amount of free lab time but that’s not ideal either. “At that point I won’t be working whenever I want, I’ll be working whenever I can.
“So additional funding will give me another quarter to finish things properly because we’re almost there. With another quarter I think we will be in a very good spot; we’ll have something really nice.”
-- Anna Lynn Spitzer