Georgia Tech researchers are developing small satellites and advanced technology for the next generation of space exploration.
For three decades, the symbol of the U.S. space program was the mighty Space Shuttle, an 86-ton reusable spacecraft that hauled astronauts, equipment, and supplies into orbit 135 times before being retired in 2011.
Among candidates for the next symbol might be the shiny aluminum box located on a clean room assembly bench in Georgia Tech’s Engineering Science & Mechanics (ES&M) building. Made of space-grade metal, the 50 x 50 x 30 centimeter structure is rapidly being transformed into Prox-1, a micro satellite that will itself become a launcher for an even smaller satellite known as LightSail-B. Next fall, the two spacecraft will orbit the Earth together to study automated trajectory control required for close proximity flying in space.
Beyond studying control issues, Prox-1 will help its mostly student crew learn how to design, build, launch, and operate spacecraft. The 60-kilogram satellite will also be Georgia Tech’s first entry into the era of small spacecraft — a phenomenon made possible by the same miniaturization and capability enhancements that put smartphones into nearly everyone’s pockets.
And LightSail-B, designed and built by the Planetary Society, will highlight the role of CubeSats — tiny satellites just 10 centimeters square that can be constructed for as little as $20,000 apiece. These spacecraft, built in a standardized template to hitch rides on larger space vehicles, are giving universities and other organizations the kind of space access once reserved for NASA, the Department of Defense, and big corporations.
“Where the space sector once revolved around mammoth spacecraft taking decades and billions of dollars to build, we are now breaking complex space objectives into smaller chunks,” said Robert Braun, a professor in Georgia Tech’s Daniel Guggenheim School of Aerospace Engineering and director of its Center for Space Technology and Research (C-STAR). “Working together, a dozen small spacecraft might accomplish that same big objective at a fraction of the cost. These small spacecraft might be the size of a trash can or a night table, and they can be developed much more quickly, providing opportunities to utilize the latest technology.”
In all, Georgia Tech researchers expect to launch six small satellites into Earth orbit over the next five years. Beyond that, they’re thinking about planetary exploration, and are helping design the instruments aboard spacecraft that may visit Europa, a moon of Jupiter whose ocean may harbor life. Other researchers are looking toward Mars, with the idea that tiny spacecraft could hitch a ride on larger probes to explore that planet or its moons.
But designing and building small spacecraft and their instruments isn’t the whole story of Georgia Tech’s growing presence in space. Researchers are also improving the electric propulsion systems that will power both large and small spacecraft — and perhaps even help haul supplies to Mars. And in early 2016 on the International Space Station, they expect to begin testing what may be a future generation of photovoltaic cells to provide space power.
CUBESAT LAUNCHER AND TRACKER
In June, Bill Nye — better known as the “Science Guy” — told reporters what was happening in space aboard LightSail-A, a tiny craft that was unfurling a 32-square-meter Mylar sail designed to test the ability to move a spacecraft by capturing photons from the sun. Nye is CEO of the Planetary Society, which designed the CubeSat mission.
At about the same time, in a wood-beamed control room in the ES&M building, Dave Spencer and a group of Georgia Tech students were tracking LightSail-A — and cheering when a photograph confirmed the sail’s opening. The Georgia Tech role in LightSail-A encompassed mission planning, satellite tracking, and mission operations. Spencer and the student team are currently building the Georgia Tech Prox-1 spacecraft that will launch the follow-on mission to LightSail-A.
“The Prox-1 mission is to demonstrate automated trajectory control of one spacecraft relative to another spacecraft,” explained Spencer, a professor of the practice in the Georgia Tech School of Aerospace Engineering. “We are actually bringing that other spacecraft with us and deploying it from Prox-1.”
Georgia Tech’s first complete spacecraft, Prox-1 will be a fully functioning vehicle with a single cold-gas thruster for propulsion. Solar panels will provide power; faculty and students will operate it from the ES&M control room. But the real novelty is a small door on the side of Prox-1 that will release LightSail-B into space.
“Prox-1 will deploy LightSail-B, maneuver relative to it, and demonstrate automated station-keeping to keep the two spacecraft in a desired formation,” explained Spencer, who served as a mission designer and project manager for several Mars missions at the Jet Propulsion Laboratory (JPL) before joining Georgia Tech. “If all goes as planned, Prox-1 will provide on-orbit inspection of the LightSail-B solar sail deployment, returning visible and infrared images of the event.”
Launch of the $1.2 million spacecraft is scheduled for September 2016 aboard a Space-X Falcon Heavy rocket, which will also carry two main spacecraft and about a dozen small satellites.
“Prox-1 is an ambitious mission that, if done by industry or the Department of Defense, would have cost about $80 million,” Spencer said. “We have driven down the cost by much more than an order of magnitude by leveraging a lot of CubeSat technology, involving students, and also testing new capabilities that haven’t flown before in space.”
Prox-1 will space qualify a number of devices and instruments, including:
- A thermal infrared sensor provided by Arizona State University. Using an uncooled commercial-off-the-shelf sensor, the imager will help track LightSail-B.
- Control moment gyroscopes provided by Honeybee Robotics that will help control the spacecraft’s orientation.
- A 3-D printed thruster produced at the University of Texas at Austin.
In fall 2015, the team was conducting “Day-in-the-Life” testing to verify functionality of the spacecraft subsystems and flight software. Prox-1 will be fully integrated in early 2016, prior to shipment to the Air Force Research Laboratory for environmental testing and launch integration.
Significant funding for Prox-1 came from the Air Force Office of Scientific Research University Nanosatellite Program. More than 150 students have been involved in the project over the past four years.
CATALOGING SPACE DEBRIS
Space may be infinite, but some parts of it are getting crowded. NASA reports that there are a half-million pieces of space debris orbiting the Earth, and only objects larger than 10 centimeters — about the size of a softball — can be reliably tracked on radar. But smaller objects still pose a threat to spacecraft traveling at 17,500 miles per hour.
Georgia Tech’s RECONSO mission will help address that problem by testing new technologies for identifying these hazards. RECONSO’s wide field-of-view sensor will allow it to detect, track, and characterize objects, adding to the information available for collision avoidance.
“The relative velocity of these objects is typically between 5 and 12 kilometers per second,” said Marcus Holzinger, an assistant professor in the Georgia Tech School of Aerospace Engineering and RECONSO’s principal investigator. “That’s faster than any projectiles we shoot on Earth. Since the collision energy depends on the square of the velocity, even small objects can cause catastrophic failures.”
Should speeding space junk hit a large spacecraft, the collision could create thousands of additional pieces of debris, worsening the problem. The debris density is greatest in areas of space that are especially useful, such as polar orbits.
RECONSO will be a six-unit CubeSat carrying a six-megapixel CMOS imager with a field of view of 9 x 11 degrees. The imager should be able to detect even very faint objects.
As with most very small spacecraft, power will be a challenge. RECONSO’s solar panels will provide just 25 watts of power — less than most home lightbulbs. But Holzinger expects that will be enough to operate an onboard computer to analyze the images and reduce the amount of data that must be downlinked to Earth.
“When I set out to work in space situational awareness, I never thought I would end up helping clean up space,” said Holzinger. “With the number of space objects increasing and economics pointing toward more launches, the space situational awareness and space debris problems will need substantial attention and investment.”
RECONSO, also funded through the University Nanosatellite program, is expected to launch in 2017. About 40 students are currently involved in the program through the Space Systems Design Laboratory in the Georgia Tech School of Aerospace Engineering.
FORMATION FLYING IN SPACE
The sat phones that make calls from anywhere in the world depend on an array of 66 Iridium satellites orbiting around the globe. In the future, hundreds or even thousands of inexpensive satellites could similarly provide global Internet access or real-time Earth observations such as imagery, precipitation data, or climate change information.
Current large satellites often know their position in space with great precision, but future inexpensive arrays will need less costly ways to know where they are. The Ranging and Nanosatellite Guidance Experiment (RANGE), another planned Georgia Tech satellite mission, seeks to address this issue with a series of experiments involving two small CubeSats flying in a leader-follower formation. Each satellite will weigh less than 2 kilograms and will collect measurements of both their absolute and relative positions using a miniaturized inter-satellite laser ranging system, as well as an onboard GPS receiver. These measurements will be checked by a ground-based laser ranging system operated by the Naval Research Laboratory.
“Some of the experiments we want to do with the mission, such as the inter-satellite laser ranging, haven’t been done with CubeSats before, so this presents some engineering challenges,” said Brian Gunter, an assistant professor in the Georgia Tech School of Aerospace Engineering who is the principal investigator for the project. “We’re asking these small satellites to do a number of complex tasks, so the details can get complicated, and there are a lot of things we have to get right.”
The two CubeSats will have no propulsion systems of their own, but by rotating one of the satellites so that the atmospheric drag on the solar panels is different, the relative distance between the satellites can be controlled. To do this, the researchers will use on-board magnetic torquers, which change the attitude of the spacecraft by interacting with the Earth’s magnetic field, as well as a reaction wheel that acts like a gyroscope to provide better attitude control about one axis.
“We want to better determine the absolute and relative positioning of the two satellites,” explained Gunter. “Once you have that, you can think about having constellations or large formations of satellites and coordinating where they are relative to the Earth and one another. This would open up a range of new possibilities for future CubeSat missions, to include missions beyond Earth.”
RANGE will require the use of miniaturized atomic clocks, GPS positioning systems, laser transmitters, and laser detectors. Because laser light travels at a known and constant speed, the satellites can determine how far apart they are by knowing how much time it takes a laser pulse to travel between them. The same timing systems can also be used to send binary communications, creating a combined laser ranging and communication system.
Using this system, researchers also hope to achieve another CubeSat first: using the satellites to complete a communications loop, with a data packet going up to one CubeSat, being transmitted to the other, and then back down to Earth. Though a date hasn’t been finalized, RANGE is expected to launch in late 2016.
Gunter is also working on proposals and initiatives to send CubeSats along with larger missions to planetary destinations such as Mars or Europa.
“CubeSats would be great for planetary exploration because they are so small,” he said. “They could rideshare with a larger dedicated spacecraft, requiring minimal extra resources. Their low cost makes them expendable, so they can be used to explore science objectives that are too risky or inaccessible to the primary mission.”
For example, the Martian moons Phobos and Deimos are not likely to be the target of a dedicated mission in the near future but could be excellent targets for CubeSats on one of the upcoming Mars missions.
INSTRUMENTS TO EUROPA
Europa, one of Jupiter’s moons, attracts special interest because its icy surface is believed to harbor an ocean of liquid water heated by expansion and contraction caused by Jupiter’s powerful gravity. That ocean is among the most likely locations for hosting life elsewhere in our solar system.
Associate Professor Carol Paty and Assistant Professor Britney Schmidt from the Georgia Tech School of Earth and Atmospheric Sciences (EAS) are among the scientists helping develop the science components for two CubeSat missions being planned for possible inclusion on the Europa flagship-class mission recently started as an official NASA flight project.
Schmidt led a study funded by the Jet Propulsion Laboratory (JPL) for the Europa Plume and Exosphere CubeSat (EPEC), which involved Aerospace Engineering Professor Glenn Lightsey and 16 student engineers and scientists collaborating with Baylor University to develop an end-to-end study of the CubeSat. Paty and Schmidt also served as science team members for the Jovian Particles and Fields Mission (JPF), another Europa CubeSat mission study, led by Aerospace Engineering’s Dave Spencer.
EPEC would fly a dust detector instrument and possibly a mass spectrometer to study particles in the moon’s exosphere that could have originated in plumes from its surface. JPF would include a magnetometer and radiation dosimeter to study the induction signal for Europa’s ocean as well as complete a study of the magnetic and particle field environment around Jupiter. Other Georgia Tech researchers who participated in the Europa proposals are James Wray, Sven Simon, Paul Steffes, Thomas Orlando, and Josef Dufek. While both CubeSat missions remain in the study phase, the researchers hope they’ll advance to the second phase — and, ultimately, that NASA will decide to launch CubeSats as part of the larger flagship mission.
“I have chosen to focus on Europa because of its potential to have what other places may not have: a stable source of energy from the tides that can power geological cycles of the lifetime of the solar system,” said Schmidt. “We hope to be able to one day characterize the subsurface of Europa using radar sounding, landed seismology, or, perhaps, roving submersibles.”
Paty focuses on understanding the dynamics of planetary magnetospheres using space-based instruments such as the Cassini and Galileo spacecraft and the Hubble Space Telescope. Being able to obtain data on Europa from a small spacecraft could add significantly to her understanding of how these systems operate.
“I’m thrilled to be involved in planning instrumentation that would provide more information on Europa,” said Paty, whose research has focused on the icy moons of Jupiter and Saturn. “I’m interested in bridging the gap between magnetospheric and atmospheric sciences in these strange worlds.”
Their involvement demonstrates another key aspect of Georgia Tech’s growth in the space sector: multi-disciplinary involvement. Beyond aerospace engineers, the program involves electrical and mechanical engineers, computer scientists, planetary scientists, chemists, physicists, policy experts, and researchers from the Georgia Tech Research Institute (GTRI).
ELECTRICALLY POWERED SPACE THRUSTERS
In space, there are no fueling stations to replenish supplies for spacecraft propelled by chemical rocket engines. When they lift off the ground, they’re carrying all the energy they’ll ever have. But spacecraft using electrically powered thrusters replenish their energy through photovoltaic panels. Though electric thrusters lack the power to hurl spacecraft into orbit, they’re perfect for keeping them in the right location or changing orbits over time while in space.
With funding from NASA, Department of Defense agencies, and industrial companies, Mitchell Walker and his students are working to improve electric thrusters using a towering silvery vacuum chamber in the High-Power Electric Propulsion Laboratory housed at Georgia Tech’s North Avenue Research Area.
About the size of a coffee can, electric thrusters must often operate for thousands of hours, compared to just a few minutes for the more powerful chemical rocket engines that launch vehicles into space. The vacuum chamber allows Walker to test the thrusters long-term under conditions approximating space. It also allows him to understand the physics required to improve their performance, lifetime, and integration with spacecraft.
Walker’s thrusters use electricity to ionize a propellant gas: xenon, which is inert, easy to ionize, and of sufficient mass. Once ionized, atoms of the gas fly out of the thruster, applying the same Newton’s Law as chemical engines. Electric thrusters are already used in satellites that provide DirecTV and SiriusXM Radio, and they can also move spacecraft into higher orbits — even to other planets.
Beyond their ability to obtain additional energy in space, electric thrusters reduce launch mass by requiring an order of magnitude less propellant and utilizing the spacecraft’s existing electrical system instead of a separate chemical system.
Walker is interested in small satellites and even CubeSat arrays that might be assembled on orbit to make spacecraft large enough to produce hundreds of watts of power to operate revenue-producing sensors and obtain significant data transfer rates — as well as switch on electric thrusters. New classes of flexible photovoltaic arrays designed to be unfurled in space, in concert with lightweight deployable structures, could help provide the necessary power.
“When people talk about going to Mars, electric propulsion will probably take their supplies there because the reduced propellant mass enabled by electric thrusters would allow a significant increase in the supplies delivered by each launch vehicle.
That would reduce the total number of launches required,” said Walker, who’s an associate professor in the Georgia Tech School of Aerospace Engineering. “Based on our current technology, people will probably ride in a chemically powered spacecraft because these provide shorter trip times.”
Beyond boosting power levels, Walker expects to see other signs of maturity in small spacecraft: insurance on even the smaller satellites and a growing role for industry.
TESTING PV ON THE SPACE STATION
Most spacecraft today depend on electricity from photovoltaic systems. Boosting the amount of electricity produced by these systems could help address the critical problem of power management in small satellites. These small spacecraft can’t afford mechanical systems that align solar panels to catch the most sunlight.
That’s where three-dimensional solar cells developed in the Georgia Tech Research Institute (GTRI) could help. Built with miniature carbon nanotube “towers” that capture sunlight from all angles, the cells developed in Jud Ready’s lab could boost the amount of power obtained from the small surface areas many satellites have.
In early January 2016, an experimental module, including 20 photovoltaic cells, is scheduled to be launched to the International Space Station (ISS), where it will be installed on the exterior to study how well the 3-D cells operate and survive under space conditions. The module will include four types of PV devices: 3-D cells based on traditional cadmium telluride, 3-D cells based on less costly copper-zinc-tin-sulfide (CZTS) materials, traditional planar solar cells, and planar cells based on CZTS.
“We want to see both the light-trapping performance of our 3-D solar cells and how they are going to respond to the harshness of space,” said Ready, who is a GTRI principal research engineer and adjunct professor in Georgia Tech’s School of Materials Science and Engineering. “We will also measure performance against temperature, because temperature has a great influence on the performance of a solar cell.”
Ready knows firsthand the risks of small spacecraft. A CubeSat named ALICE, developed by the Air Force Institute of Technology, was to have provided the first test of his “cold cathodes” — another technology based on carbon nanotubes that could be useful in spacecraft. ALICE was successfully launched in December 2013 but never established contact and has not been heard from since. The 20-cell ISS payload has been scheduled — and then bumped — from three previous missions, fortuitously including one that later exploded on launch over Wallops Island, Virginia.
RISE OF THE SMALL SATELLITE
Through the Center for Space Technology and Research (C-STAR), Georgia Tech is helping create a future in which small satellites return significant scientific, economic, and national security benefits to the United States. While continuing to support traditional missions through NASA, Department of Defense agencies, and corporate partners, Georgia Tech’s initiative in small satellites offers an opportunity to get into space faster, at a lower cost, using cutting-edge technology — and in ways that can provide hands-on research experiences for more students.
“The small satellite culture is well aligned with Georgia Tech’s high-risk, high-reward research philosophy,” said Robert Braun, who is former chief technologist at NASA. “You don’t have to work for the government or a large company today to build a spacecraft. Universities and small companies all over the country are building spacecraft in rapid sequence, and the pace of innovation in this area has been remarkable.”
Glenn Lightsey is among Georgia Tech’s newest faculty members, but his background includes nearly 30 years of space experience, including development of a half-dozen small satellite projects during his time at the University of Texas at Austin. He sees small spacecraft making space exploration available to organizations that previously had been locked out by cost.
“There are only two ways to reduce cost,” he said. “One is to reduce the cost of the delivery vehicles, and a lot of new U.S. companies created in the last decade are doing that. The other way is to accomplish the same function in a smaller package. That has been enabled in the last 20 years by the miniaturization of components in the cellphone mass market. We’re taking advantage of that.”
Beyond miniaturization has been the standardization of the system used to launch CubeSats. Lightsey compares those to the cargo containers that revolutionized worldwide logistics by making it easier for goods to move from ships to trains and trucks. “Because we have that standard, we get an economy of scale we wouldn’t get otherwise,” he said.
And some missions can be improved by using multiple smaller vehicles, which reduces the risk related to losing a single large spacecraft. “You can have much more sophisticated missions with smaller satellites than you could even five years ago,” Lightsey said. “I’m riding that wave with many of my colleagues to see what we can do with these smaller satellites.”
Among the greatest beneficiaries of the small satellite revolution may be students.
“We used to teach space systems engineering from a textbook,” noted Braun. “It was entirely theoretical. While we still teach the fundamentals, now an individual student can help conceive a space mission, build a space structure, integrate it with an electronic system, do the necessary testing, and participate in space mission operations. These systems are going from concept to flight in a time frame that is consistent with a student’s academic degree milestones.”
In addition to NASA, Department of Defense agencies, and the large aerospace companies, space missions are now being performed by new companies like SpaceX, Planet Labs, Virgin Galactic, Google, and Sierra Nevada. Today, there is a broad range of opportunities across the growing civilian, military, and commercial space sectors for space systems engineers.
“There is a fundamental change taking place, and our students have the opportunity to get in on the ground floor and be part of that innovation,” Lightsey said. “This is really an exciting time to be starting a career in aerospace. We’ll see things happen in the next 50 years that we can’t even imagine right now.”