A Sat-to-Sat Inspection Demonstration with the AeroCube-10 1.5U CubeSats

In the summer of 2020, the pair of AeroCube-10 1.5U CubeSats completed a series of mutual proximity operations as close as 22 meters separation and captured several sets of satellite-to-satellite resolved imagery, inspecting all faces of a vehicle in each pass with a resolution less than 8 mm. AeroCube-10 was designed and built by The Aerospace Corporation with the primary missions of atmospheric science and the maturation of nanosatellite technologies, including a new star tracker design, warm-gas propulsion system, GPS receiver, and a low-noise focal plane. Investigating the possibility of using CubeSats for satellite inspection missions, the AeroCube-10 team designed an experiment using these technologies in ensemble to bring the vehicles close together and demonstrate the feasibility of inspection missions in a package as small as 1.5U. Starting from a separation of more than one thousand kilometers, over the course of several weeks maneuvers executed with the AeroCube-10 propulsion unit brought the vehicles closer together, using proven formation keeping techniques to ensure safety of flight as the range dropped below 100 meters. The first imagery while in a natural-motion circumnavigation (NMC) was performed at a range of 64 meters. Gaining confidence in AeroCube-10’s capabilities, the operations team decreased the size of the NMC several times, obtaining imagery at 30 meters and then 22 meters. AeroCube-10 completed roughly one fourth of an NMC during each imaging run, and the observing satellite collected images of all faces of the target as it orbited around. At such close range, the inspection images clearly show individual solar cells, patch antennas, the exposed atmospheric probe magazine payload, the satellite’s miniature radiation dosimeter, and other features. AeroCube-10\u27s activities have demonstrated for the first time the feasibility of prolonged inspection activities in a very small form factor and, by closing from great distance and then entering NMC, proved that the nanosatellite platform has the potential for multiple-target inspection, as may be necessary for space-debris removal or constellation-inspection missions

The DiskSat: A Two-Dimensional Containerized Satellite

A key factor in the remarkable expansion of the CubeSat class of spacecraft over the past two decades is launch containerization. The container protects the launch vehicle and primary payload from issues that might arise from the CubeSat (which is essential for rideshare), and the standardized and highly-simplified launch interface reduces integration cost for the launch provider and development cost for the CubeSat builder. The downside of containerization is that the size of the contained satellites is rigidly limited. While there are available designs for larger dispensers and CubeSats, very few CubeSats larger than 6U have flown, and none have been larger than 16U. Future space missions will benefit from more power and RF aperture, beyond what can be provided by conventional CubeSats, even with complex deployables. We propose here the DiskSat, a containerized, large-aperture, quasi-two-dimensional satellite bus architecture. A representative DiskSat structure is a composite flat panel, one meter in diameter and 2.5 cm thick, to which components are affixed in a flat pattern within the panel. The volume of the representative DiskSat is almost 20 liters, comparable to a hypothetical 20U CubeSat, while the structural mass can be less than 2.5 kg. The surface area of a single disk face is substantially larger than the total surface area of any conventional CubeSat, supporting over 200 W of peak solar power without the complexity of deployables, thereby improving mission assurance and reducing vehicle cost. Alternatively, a single fixed deployable panel can ensure that the vehicle has over 100 W orbit-average power while maintaining nadir pointing in any beta angle. For launch, multiple DiskSats are stacked in a fully-enclosed container/dispenser using a simple mechanical interface, and are released individually once in orbit. Stacking of 20 or more DiskSats is possible in small launch vehicles, making it ideal for building large constellations of small satellites in multiple discrete orbital planes. The 1-m-diameter DiskSat was developed with the Rocket Lab Electron in mind; the concept can be extended to larger diameters (1.2 m for the Virgin LauncherOne, for example), or to other flat shapes (square for an ESPA port, for example), and to greater thicknesses if the mission requires it. The DiskSat concept was developed as a cost-effective solution for a LEO constellation that required significant power and RF aperture. Since then we have explored the utility of the bus architecture for a broad range of missions including Earth observation and space science, among others. One particularly useful feature of the DiskSat is the high power-to-mass ratio, enabling high-delta-v electric propulsion missions, including deep-space applications. Another feature is the ability to fly in a low-drag orientation which, in combination with electric propulsion for drag makeup, enables flight at very low altitudes in LEO. This paper will detail the design of the DiskSat and its dispenser, will explore the range of missions enabled by the DiskSat, and will describe current development activities in support of a DiskSat demonstration flight

Analytical theory for orbits of electrostatically charged spacecraft and direct calculation of planet-to-planet transfers

The first three-quarters of this thesis reports on the results of the development of analytical theory to describe the motion of electrostatically charged spacecraft in a planetary magnetic field. The motion of an electrostatic charge in a magnetic field yields a Lorentz force, which, when applied to a spacecraft, produces a source of propellantless thrust that may be harnessed to alter the vehicle’s orbit. The equations of motion for electrostatically charged spacecraft are developed in two- and three-body regimes, and equilibria and the stability of orbits are investigated. An equilibrium solution identified in the three-body system produces a control law that permits propellantless, marginally stable stationkeeping orbits near Enceladus, a moon of Saturn. Notably, the feasibility of such a mission is primarily affected by the navigational accuracy, rather than the charge level. Next, Lagrange’s Planetary Equations are derived with the Lorentz force as the orbital perturbation. The orbital elements are coupled, but the coupling in equatorial orbits is independent of charge level and magnetic field strength. Analytical expressions that characterize this coupling demonstrate constraints on the Lorentz force’s ability to raise a Lorentz spacecraft’s orbital energy to escape, and a numerically integrated example of escape at Jupiter confirms the analytical results. A closed-form solution exists that constrains the set of equatorial orbits for which planetary escape is possible, and a sufficient condition is identified for escape from inclined orbits. Lastly, the analytical theory is extended to accommodate propellantless planetary capture with the Lorentz force. Analytical solutions are applied to a capture at Jupiter and compared to similar arrival scenarios with the Galileo and Juno spacecraft. The last quarter of the thesis, on a separate topic, identifies a new parameterization of the tour-design problem, dubbed “FastTour,” that permits direct calculation of planet-to-planet transfers without the need for solving Lambert’s problem or performing so-called “ v8-matching.” Solution for the roots of a single function on a finite domain yields the transfer orbit and all of its associated quantities (e.g. orbital elements and time of flight). This parameterization also enables calculation of launch windows, whereby entire ranges of the parameter space, such as departure date, can be disqualified from containing candidate trajectories, eschewing the need (as in traditional methods) to perform computationally costly function evaluations where no transfers exist. Compared against the traditional tour-design algorithm, FastTour calculates pork-chop plots 7–10 times faster