NASA’s CubeSat Fleet Gives Fresh Perspective
CubeSat Launch Initiative challenges student engineers to revolutionize the industry.
In an effort to revitalize current technology, NASA recently launched an ongoing program called the CubeSat Launch Initiative (CSLI). The program invites engineering students and faculty from across the nation to compete in inventing CubeSats that will ultimately fly as auxiliary payloads onboard the Poly-Picosatellite Orbital Deployer (P-POD).
CubeSats are nanosatellites that owe their name to their small cube shape. Typical measurements are four inches on each side, with a volume of about one quart, and a weight of less than three pounds.
These nanosatellites are used to collect and transmit data for research purposes and in-orbit inspection of larger satellites.
The program is off to a promising start as various worthy CubeSat designs have already been chosen for future missions, including those of several notable student engineers in the PolySat program at California’s Polytechnic State University (Cal Poly).
Intelligent Payload Experiment
A recent Cal Poly CubeSat design was put to the test in December 2013. The Intelligent Payload Experiment (IPEX) was part of the Educational Launch of Nanosatellite (ELaNa) missions chosen by CSLI for the purpose of testing satellite automation and data reduction. What makes IPEX unique is its five cameras used by NASA’s JPL software. The system analyzes collected images and reports back to NASA on which items may be of particular interest and worth further analysis. “I’m particularly proud of the camera on the board that I built. Since the satellite launch in December, the camera on that board has produced amazing pictures of the Earth," says Jeff Weaver, electrical engineer undergrad student at Cal Poly. "Knowing that something I’ve designed and built is in space and taking pictures is a good feeling.”
With both a primary and secondary payload processor, the IPEX’s primary processor, along with all critical electrical components, are integrated onto a single system board. Weaver’s specific involvement was in the creation of the power system and signal breakouts from the primary processor, as well as an integral side panel attached to the main processor.
“This panel connects all of the solar power to the batteries, manages the data buses from external sensors, and includes one of the five cameras on the satellite,” explaines Weaver.
The highly condensed single panel board design posed a challenge in incorporating all the power and data signals branching out from the single system board. Five of IPEX’s six panels hold cameras, all of which feed into the system board through shared data lines. Furthermore, each of the six panels include solar cells.
Initial testing for the IPEX was imperative in the team’s ability to ensure the satellite would perform well in a remote environment, independent of the designers’ continued support. Testing was carried out with the aid of a high altitude balloon, which held a model of the original satellite to be used. The team was able to remotely operate the IPEX by radio as it took pictures 100 km above Earth.
Upon successful testing, the IPEX was launched from Vandenberg Air Force Base on December 6th, 2013.
“Seeing it launch and then immediately jumping back into the car to drive to campus was the most stressful point of the project," recalls Weaver. "If we couldn’t hear from the satellite on its first active pass over California, then we would know we had problems. Thankfully, everything worked out well."
Low Power Detection
Cal Poly’s engineering students have created a line of successful CubeSats used in the CSLI project, and IPEX served as an important predecessor for future design teams.
PolySat Program Manager, Nicholas Weiser notes, “IPEX was a crucial demonstration for our team, as the hardware used served as the basis for CP9 as well, so our fates were very much tied. IPEX continues to serve as a learning tool for our team members in how operating our satellites will go, as well as providing ideas on how to improve the systems.”
However, Cal Poly’s ninth satellite, CP9, has quite a different purpose than the IPEX. Its primary mission is to record important environmental data of other launch vehicles. Vibrations and thermal data are recorded in order to give scientists and engineers a clearer picture of what launch environments look like.
In cooperation with Florida’s Merrit Island High School, the team worked to develop a wireless interface to transmit and record such environmental data during the launch. The wireless transmission, along with the primary system, makes the CP9 unique from other satellites.
“Being [powered] on is one thing, but adding intentional transmitting in the risk-averse environment of launch services has presented some challenging aspects,” says Weiser. “Ultimately, what allowed us to have functional wireless communications within the deployer was toying with the spacing, power, and transmit format between the two antennas.”
Another challenge was that the satellite had to be able to begin recording the launch environment with utmost accuracy as soon as T+0.5 seconds. The team also had to prepare CP9 to be able to launch from various types of vehicles, while possibly waiting up to a year to detect the launch. Therefore, the team chose to develop a low power launch detection system, which would also account for false detections.
“[The low power system] was very challenging, but quite fun as well,” says Weiser. “It’s rare that you find yourself needing to use nano-ampere resolution scopes to verify power consumption.”
Set to launch from Vandenberg, CA in November 2014, the CP10, also known as the ExoCube, is a 3U CubeSat manifested on ELaNa 10. ExoCube’s mission is to measure in-situ densities of ions and neutrals in the upper ionosphere and lower exosphere, the first in decades. The project, in collaboration with the University of Illinois, the University of Wisconsin, Scientific Solutions, and the National Science Foundation, will also take measurements over various ground observatories, including Arecibo Observatory in Puerto Rico, and Pine Bluff Observatory in Great Plains, UT.
PolySat Mission Manager and Aerospace Engineering student, Chad Taylor, led the initial integration, testing, and verification of the gravity gradient attitude determination control system (ADCS) of the ExoCube.
In addition to successful implementation of the ADCS, the PolySat team also engineered a gravity gradient to fulfill pointing and stability requirements, as well as a satellite bus that housed a gated time-of-flight mass spectrometer, developed by the Goddard Space Flight Center.
Desiging the ExoCube wasn’t without its own set of challenges, as the team decided to change the scientific instruments nearly halfway through development in favor of a more accurate, robust design.
“Designing an individual component is already a challenge; but bringing hundreds of different things together to complete a satellite is the biggest challenge,” says Taylor. “This process isn’t black and white either; often it does require a vast amount of engineering and creativity at the same time.”
After a complete design overhaul, the PolySat team is back on schedule for its November launch.
“The fact that I can say I’m working to put a satellite in space that will have a heavy impact on the science community while I’m 21 years old is an amazing feeling,” reflects Taylor.
Secret to Success
The high level of talent and commitment required to design a CubeSat for NASA is a given. Fulfilling the technical requirements and necessary precision of such a prestigious line of satellites is one thing, but following through from design to implementation is another. However, the secret to complete success is a familiar one to most engineers, as many of the students agreed: Communication is key.
“When engineers don’t talk to each other, mistakes happen. Stay organized, use proper documentation, meet your deadlines, and the project will steadily move forward,” Taylor suggests to future contenders.
Weaver agrees, “If two people work independently, they often find they’re solving the same problem without knowing it.”
Not only did the students learn the importance of collaborating with fellow engineers, but others from outside the discipline as well. NASA’s CSLI has opened up the opportunity of a lifetime for students in all engineering disciplines to receive a proactive, rewarding experience unlike any other.
“I will receive my diploma from Cal Poly in June, but I have received my education through the PolySat lab,” says Weiser. “The experience that I have gained as an engineer has given me a wealth of hands-on experience from not just a design standpoint, but a general systems engineering standpoint as well. That cradle to grave design cycle has trained me to be ready for the workforce.”
So, what else does it take to design a NASA-worthy CubeSat?
“Testing, testing, and more testing,” says Weiser. “No amount of simulation and derivations will be as good as testing your system, something that we learned rather quickly when we decided to stick two antennas inside a mostly closed metal box.”
Perhaps the most valuable ingredient for designing the newest line of CubeSats comes from thinking outside the box.
“Even though our satellites are cubes or rectangles that get packaged into a rectangular deployer, it is still important to think outside the box. My team’s creativity is what enabled our system to accomplish its goals,” concludes Weiser.
By opening up the program to student engineers, NASA not only offers opportunities, but the students offer a fresh perspective for new technology and research. This approach is precisely what fosters the kind of novel technology needed to revitalize the industry.
This article originally appeared in the January/February print issue. Click here to read the full issue.