Space Systems Development Laboratory

Department of Aeronautics and Astronautics

Stanford University

Santa Clara Remote Extreme Environment Mechanism Laboratory

Department of Mechanical Engineering

Santa Clara University


The EMERALD Nanosatellite Project is part of the University Nanosatellite Program funded by the Air Force Office of Scientific Research (AFOSR) and the Defense Advanced Research Project Agency (DARPA). Ten universities were chosen to build ten 10-15kg nanosatellites and was given $50,000 per year per university for two years plus a Space Shuttle launch. The goal of this program is to use commercial and new technologies to perform creative low-cost experiments as a stepping stone for future space missions.


Stanford University's SSDL and Santa Clara University's SCREEM, having done a joint-project in the past (OPAL/Artemis microsatellite / picosatellite), are teaming up to do a two-satellite mission called EMERALD. SSDL is known for their Master's program in designing and building low-cost spacecraft that relies extensively on Commercial-Of-The-Shelf parts. SCREEM is known for their creative implementation of robotics systems to perform scientific studies, as part of their Undergraduate Senior Design Projects.


A number of experiments will be flying on this mission: Radiation Testbed, Colloid Micro-Thruster, VLF Atmospheric Science, GPS Receiver, Autonomous Operations and Navigation, and Formation Flying. Sponsors for these experiments includes external organizations such as NASA Goddard Space Flight Center, NASA Ames Research Center, Jet Propulsion Laboratory, Department of Defense, Boeing, Lockheed-Martin, Honeywell, etc., as well as university laboratories such as Stanford's Space Telecommunications and Radioscience Laboratory, Plasma Dynamic Laboratory, and Aerospace Robotics Laboratory.


The EMERALD mission will be demonstrating Robust Distributed Space Systems architecture. Distributed Space Systems means a space system (consisting of several satellites and ground stations) whose functionality is distributed throughout the entire system. Much like a network of computers, each of the satellites can perform their own experiments and communicate with one another sharing their data. The word "Robust" simply means an enhanced failure tolerance: if one of the satellites dies, the others will still be able to function as a system and continue the mission; using the communication link to bypass a malfunctioning main computer; and so on. Compared to the current one-satellite architecture, if that satellite develops a malfunction, then the whole mission will be terminated. All of the experiments mentioned above -- individually and / or collectively -- are designed to support and demonstrate Robust Distributed Space Systems architecture.


Within each of the spacecraft, the computing power is also distributed among the individual subsystem. Instead of having to rely on the main computer to control all of the functions, the individual subsystem will be smart enough to be able to handle its own tasks, communicating the results back-and-forth between them through an I2C™ link.


This approach is implemented by incorporating a PICmicro® microcontroller (MCU) on the individual subsystems. The PICmicros will be handling tasks such as reading solar panel current sensors and determining sun/earth angle; monitoring VLF receiver for interesting signals and sampling/storing it to a local memory; controlling the fuel flow and high-voltage power supplies on the Colloid Micro-Thruster; monitoring the intersatellite-crosslink or uplink communication for direct-commands that bypass the main computer; etc. The main computer on EMERALD will act as a mediator. Compare this to a traditional spacecraft that relies on a single central computer to control all of its function. This approach also simplifies the development and integration efforts because the individual experimenters can develop and test their units independently.


The EMERALD project is perhaps a one-of-a-kind implementation of PICmicro® microcontrollers. Stanford, Santa Clara and Microchip have formed a partnership to take advantage of this unique opportunity. Both laboratories at Stanford and Santa Clara are being equipped with development tools and PICmicros, and will share their findings -- such as on-orbit data on PICmicros and studies on robust distributed system -- to Microchip.