Darin C. Koblick, Raytheon Intelligence and Space; Joseph S. Choi, Raytheon Intelligence and Space
Keywords: Cislunar SSA, SDA, Moon Based Sensor, Orbit Determination
Abstract:
As an increasing number of future space missions are projected to transit the cislunar corridor, the United States and other partner nations do not have a dedicated space domain awareness (SDA) system to ensure their flight safety. Legacy near-earth SDA systems were not designed to detect, track, and propagate objects in cislunar space as major fundamental differences between cislunar and near-earth SDA include the gravitational impact of a third body (chaotic dynamics), an order of magnitude greater range losses, and three orders of magnitude greater search volumes. While requirements for cislunar SDA architectures remain ambiguous, the space community is beginning to analyze which sensor types, quantities, and locations are required to detect and track objects in this region. Previous community focus has been on Earth ground-based sensors, Earth orbiting sensors, Moon orbiting sensors, and cislunar space-based sensors, without consideration for Moon-based sensors.
The placement of several Moon-based sensors near the south pole is a reasonable starting point for cislunar SDA activities as they offer six potential advantages over space-based systems:
Access to constant near absolute zero temperatures. NASAs Lunar Reconnaissance Orbiter has identified permanently shadowed areas inside craters near the south pole where temperatures stay at a constant 33 Kelvin. While these findings may not be surprising, lunar craters are the coldest known places in the solar system. Lunar surface conditions are perfect for hosting sensitive EOIR sensor payloads and Superconducting quantum-interference devices (extremely sensitive magnetometers) that operate below 80 K.
Proximity to the planned lunar base camps. Easy sensor access simplifies equipment upgrades and maintenance activities, which in turn decrease lifetime costs. Sensors have the added benefit of doubling as an early debris warning system for neighboring outposts. Systems may be powered directly from surface reactors, eliminating solar panels, dedicated communications, and timing equipment.
Surface placement not over-constrained. Sensors have no weather, international, or water restrictions; they also have no collision avoidance / flight safety concerns. Orbital overcrowding and slot assignments are non-issues for ground systems. Radar and EOIR systems on the lunar surface do not have atmospheric attenuation or turbulence which increase measurement uncertainty and degrade target detection sensitivity.
Elimination of platform inertial positioning system requirements. The selenographic coordinates of a Moon-based sensor are constant. Therefore, no maneuvers are needed to measure the inertial position, velocity, and acceleration of the sensor platform. Inertial attitude knowledge may be calibrated below star-tracker level accuracy through camera geometry models (e.g. alignment, calibration, and plate models). Mount systems can restrict pointing to only two degrees of freedom (azimuth and elevation) eliminating boresight roll (a common source of uncertainty when using stars for attitude estimation).
No ?V requirements. Most trajectories in cislunar space are unstable, as the dynamics near the Moon are highly sensitive to perturbations. Typically, frequent and small maneuvers are required to stay in an orbit. These maintenance maneuvers are orders of magnitude smaller than GEO station keeping maneuvers and require precise GNC capabilities. However, none of this is necessary for surface-based sensors.
In this research, we analyze the track quality performance benefits of fusing Moon-based sensor measurements with a cislunar space-based sensor in a halo orbit around Earth-Moon Lagrange point 1. A dozen sensor architectures were postulated to quantify the trajectory estimation error of tracking different families of cislunar targets. We used a variety of geometric viewing angles as well as angles-only and range measurements. An unscented Kalman filter was used to process the metric observations with an underlying dynamics model consisting of the circular restricted three-body equations of motion. The overall track quality performance was expressed in terms of its mean and standard deviation of inertial position, velocity, and acceleration estimation errors. Results demonstrate that a Moon-based sensor architecture, consisting of four mid-latitude narrow field of view angles-only observers, can maintain 100% track custody. The average position RSS error was below 1 km against all cislunar targets. We found that adding a single space-based, angles-only observer reduced the average position estimation RSS error by a factor of five. Overall, the best architecture performance combinations contained both Moon-based and space-based angles and range observations.
Date of Conference: September 27-20, 2022
Track: Cislunar SSA