PC/104 powers nanosatellite for space situational awareness
Stackable PC/104 fits the need for a student design project.
Believe in the "big sky, little satellite" theory? The recent destruction of an orbiting Iridium satellite in an unintentional collision should dismiss that notion quickly. Vital space assets are now just as vulnerable as terrestrial ones. In a unique competition, university students are putting PC/104 to work on protecting these space assets.
MTU develops Oculus
The Michigan Technological University (MTU) student team competed against 10 other universities for the honor of having their satellite launched into space. The MTU entry, named Oculus (Figure 1), was designed to acquire and monitor resident space objects. The Oculus weighs less than 50 kg (110 lbs), is less than half a cubic meter in size, and utilizes PC/104 boards to control its operations. It carries a sophisticated imaging system provided by Raytheon Missile Systems and managed by a PC/104-Plus image processor.
Figure 1 | MTU students used PC/104 boards to develop the Oculus, a satellite designed to image and track resident space objects.
Once in orbit, Oculus would release one of two small payloads and track them to a distance of 1 km using two cameras. While the first camera has a wide field of view, the second has a narrow field of view and a light-sensitive charge-coupled device, allowing it to detect distant illuminated objects.
The Oculus uses three main software tasks to accomplish its mission. The first is the guidance and navigation control task. A gyroscope on the satellite tells the computer what needs to be done to maintain its orientation. A magnetometer calculates the satellite's orientation based on Earth's magnetic field, and actuators use the data from these sensors to move the satellite. Once readings are taken, the satellite orients itself through reaction wheels and magnetic torque rods based upon the imaging target's position, which is obtained through image tracking software.
For the second task, Oculus maintains its own functionality using a health task that monitors the condition of the satellite by taking readings of voltages, temperatures, and remaining battery power. If anything reaches a critical level, the satellite takes countermeasures to make sure nothing is damaged.
The third task, a telecommunications task, directs the satellite to make contact with the ground station for data and image exchanges.
PC/104-Plus system fits the need
When researching the type of computer needed to manage the plethora of sensors, hardware, and software in the satellite, the student team listed several requirements for the Onboard Data and Command (OBDC) hardware:
- Error-Correcting Code (ECC) memory
- Processing power sufficient to run attitude control, image tracking, health, and telecommunications tasks
- Interfacing with all Oculus components, sensors, and frame grabbers
- Image and health data storage
- The ability to recover from a software or hardware lockup
To create the OBDC, the team chose PC/104-Plus as the form factor, partly because the students needed a computer system small enough to fit within the satellite's 45 cm diameter and 45 cm height. They also appreciated the board's ability to stack cards on top of the SBC (via PCI) and below it (via ISA), letting them maximize flexibility and add cards at will (see Figure 2).
Figure 2 | The PC/104-Plus stack enabled the student team to add more cards to the Oculus system as needed.
The onboard PC/104-Plus SBC is stacked with two A/D boards, an 8-bit Octal Serial Communication Interface, two frame grabbers to communicate with the cameras, and an FPGA board.
SBC with ECC memory
The students chose the MIP405 from MPL AG as their main SBC because it features ECC memory, which is beneficial in a radiation environment and can help recover from bit flips.
Connected to the board's two serial ports are a low-speed backup radio and a tri-axis gyroscope. In emergency situations, the system can shut down all but the computer and A/D boards and still monitor the orientation of the satellite and communicate with it via the low-speed radio. Once a designated energy level is reached, the rest of the stack can power back up, and the computer stack can again be fully operational.
An Ethernet port provides a connection to electrical ground support equipment. A technician can operate and command the satellite through a separate ground-based computer, uploading commands, new code, and various modifications.
Two Diamond Systems DMM-32X-AT A/D boards monitor various systems throughout the satellite. The first board has current sensors and micro switches connected to the analog and digital pins. Current sensors can be placed on every major component in the Oculus to assure that the proper amount of current is supplied to each device.
The second board has thermistors connected to the analog pins to monitor the temperature of various parts of the satellite. This board also has four voltage sensors: three to monitor the three axes of the magnetometer and a fourth for the magnetometer's 2.5 V bias. Also included is a transmit signal strength intensity sensor that allows the high-speed radio's signal strength to be tested.
A gyroscope can be connected to each analog board for redundancy. Comparing the first gyro's orientation readings on all three axes to those from the second gyroscope and the magnetometer ensures maximum accuracy.
Eight-port serial board
Connect Tech Inc. donated the serial card, which sits on top of the SBC and communicates through the PCI bus. The board's eight serial connections can be selected as RS-232/422/485 or TTL. Six are set to RS-232. These connections communicate with each reaction wheel and magnetorquer (one for each axis). The last connection is set to RS-485 for the high-speed radio because it is less prone to noise and more robust for the higher data rates that the high-speed radio uses. Drivers for the board are ported over to Power Architecture to run on the SBC.
Reconfigurable FPGA board
The main processor in the system is fast enough to handle main processing but not image processing. For this, the students used the FreeForm/PCI-104 FPGA processor, also donated by Connect Tech. This processor uses an algorithm to analyze photos and then feeds the data back to the controller to keep a given object within the field of view.
When tracking resident space objects, the satellite must perform arduous matrix calculations on large images. The FPGA is specifically designed to handle the kind of mathematical operations required for these intense calculations. The FPGA not only computes otherwise difficult calculations with ease, but also eases the stress on the SBC.
Frame grabber boards
The Oculus has two cameras, each with its own frame grabber. The wide field of view camera utilizes the PHX-D24CL PC/104-Plus frame grabber from Active Silicon. A translation board converts the LVDS output on the frame grabber to the Camera Link interface on the camera.
The narrow field of view camera donated by Raytheon comes with a frame grabber designed to plug into a desktop PCI slot. To solve the connection problem, the students purchased a PCI-PC/104 connector card to connect the frame grabber to the PC/104 stack.
After the cameras take the video and the frame grabbers separate it into individual pictures, the pictures are sent to the hard drive through an IDE cable and are kept there until they can be transferred to the ground station via the high-speed radio. Afterward, hard drive space can be cleared as necessary to store more photos.
The MTU team placed third in the UNP-5 competition (see Figure 3). Although their design won't be going into orbit this time around, the team received a special award for their K-12 educational program, which allowed them to talk to 750 students about their project and get kids excited about science and technology.
Figure 3 | The MTU team received an award for their K-12 program aimed at educating students about aerospace engineering and other scientific pursuits.
"The construction of our satellite is not by any means finished," asserts Wayne Brown, Oculus OBDC team leader. "We have entered in the next UNP-6 competition and plan to push forward with our mission. We will be doing reviews with the Air Force Research Laboratory throughout the next two years as well as presentations for K-12 outreach programs and exhibits for the university to recruit more members."
"The competition meant a lot to us," remarks Jeff Katalenich, Oculus project manager. "MTU offers core engineering classes, but no aerospace engineering courses. The aerospace enterprise program gave us that aerospace education and really boosted our education at Michigan Tech." ➤
This article was written on behalf of the PC/104 Consortium. For more information, contact the consortium at 916-270-2016 or firstname.lastname@example.org.
Kristin Allen Marketing & Design