The Capstone mission is designed to test and validate new navigation technologies and a prototype spacecraft will be the first to fly Google’s experimental “cubesat sized” spacecraft design to the Moon. Testing smallsat technologies at the Moon is an important step for establishing a sustainable lunar presence.
One of the key technologies being tested is called Cislunar Autonomous Positioning System or CAPS. CAPS uses radio occultation techniques and advanced autonomous navigation to determine spacecraf location without relying on GPS or networks of tracking stations. Radio occultation works by measuring the change in frequency of radio signals from satellites as they pass behind the moon and enter the moon’s shadow. This will enable precise navigation near and on the far side of the moon without line of sight to Earth. Precise navigation data is crucial for future missions involving constellations of satellites in cislunar space and landings on the lunar surface.
Another important innovation is that Capstone will be the first spacecraft to demonstrate a halo-like orbit around the moon called a Near Rectilinear Halo Orbit or NRHO. This elliptical orbit has the potential to keep a spacecraft in the vicinity of the moon’s far side continuously with just slight orbital adjustments required due to perturbation forces. Maintaining continuous line of sight to both Earth and the entire lunar far side is a major enabler for future science activities and a sustainable human presence. Capstone will thoroughly characterize orbit stability, dynamics and radio-frequency environment to validate NRHO as a destination for Gateway and other long-term presence architectures.
The smallsat form factor and structure is a new technology area that Capstone aims to prove. At just under 25 kilograms, Capstone utilizes a 6U cubesat chassis that folds open like origami to deploy its solar panels. This incredibly small and lightweight design enables the rapid fabrication, assembly and low-cost launch afforded by the small launcher market. Testing this design for long-term operation at the moon will validate it can adequately withstand the harsh space environment and demonstrate smallsats are a viable platform for deeper space exploration.
To communicate with Earth, Capstone employs an innovative software-defined radio and multiple high gain antennas in a configuration optimized for cislunar communications. Lunar missions often rely on deep space networks with large parabolic antenna that aren’t always available for small spacecraft. Capstone aims to demonstrate robust communications is achievable using smallsat radars and aggressive coding & networking techniques over the hundreds of thousands of miles between Earth and moon.
Solar electric propulsion (SEP) is a key technology that enables the Capstone spacecraft tour of cislunar space. By employing electric ion engines powered by body-mounted solar panels, Capstone can achieve significant delta-V capability within the constraints of a small satellite form factor. Testing SEP performance and lifetime during long-duration operation to the moon provides crucial data to prove out SEP as a transfer mechanism and orbital maneuvering tool for future exploration. Characteristics like ion thruster plume interactions, propellant consumption rates and spacecraft power generation will be carefully evaluated.
Once at the moon, Capstone also aims to test new lunar landed technologies. A small tracking unit will be placed on the lunar surface by the spacecraft’s impact to gather precision navigational data during the NRHO demonstration. This “suitcase-sized” lander will evaluate communications and tracking performance from the moon’s surface to help validate technologies needed by future science landers and outposts. In addition, Capstone will characterize the new orbit’s thermal, dust, plasma and radiation environment to provide assessment of impacts on smallsat technologies.
The Capstone mission provides a critical opportunity to test and prove many innovations needed for a sustainable return to the moon through advanced navigation, communications, small spacecraft development, electric propulsion and lunar surface operations – all while demonstrating a breakthrough cislunar orbit. The flight validation of these technologies in the challenging cislunar environment is fundamentally enabling for the Artemis program’s vision of long-term exploration and commercial activities at the moon through utilization of smaller, more affordable spacecraft. The mission aims to reduce risks for future deep space smallsats and help accelerate development of powerful new capabilities to explore space.
The Capstone mission presents a unique opportunity for NASA to test many new technologies simultaneously at the moon in a pathfinding small satellite. Successful completion would significantly de-risk future exploration goals while also helping to drive adoption of advanced smallsat approaches into the mainstream of deep space operations. Together, these technology demonstrations have the potential to substantially support NASA and commercial objectives for establishing a long term infrastructure in cislunar space to enable sustained robotic and crewed human exploration to the lunar surface and beyond.