Analytical low-thrust satellite maneuvers for rapid ground target revisit

This paper presents an analytical solution for a low-thrust maneuver to reduce the flyover time of a given terrestrial target. The work extends the general solution previously developed by the authors for a 3-phase spiral transfer that results in a change in the relative right ascension of the ascending node and argument of latitude of satellites in a constellation, by varying the orbital period and the J2 effect experienced by each satellite. This work improves the accuracy of the existing method by including the periodic effects of J2 in the analytical solution. Using these improved equations, a calculation of the flyover time of a given latitude can be determined, and the passes for which the target longitude is in view identified. Validation against a numerical orbit propagator shows the analytical method to accurately predict the sub-satellite point of the satellite to within ±1° of longitude after 15 days. A case study is performed showing that the method can successfully be used to reduce the time of flyover of Los Angeles from 14 days to just 1.97 days, with a change of velocity (ΔV) of 63m/s. The full exploration of the solution space shows the problem to be highly complex, such that an increase in the ΔV used for a maneuver will not necessarily reduce the time of flyover, potentially making optimization using a numerical solution challenging. It also shows that very similar flyover times can be achieved with very different ΔV usage. As such, an overview of the solution space is extremely valuable in allowing an informed trade-off between the time of flyover and maneuver ΔV

NEMO-HD: High-Resolution Microsatellite for Earth Monitoring and Observation

The Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies, in collaboration with the Slovenian Centre of Excellence for Space Sciences and Technologies (SPACE-SI), is developing a 40 kg microsatellite for earth monitoring and observation that is capable of resolving a Ground Sampling Distance (GSD) of 2.8 m from a design altitude of 600 km. NEMO-HD (Nanosatellite for Earth Monitoring and Observation - High Definition) is the second spacecraft that is based on SFL\u27s high-performance NEMO bus and builds upon the heritage of SFL\u27s flight-proven Generic Nanosatellite Bus (GNB). NEMO-HD will carry two optical instruments: a narrow-field instrument as well as a wide-field instrument. The narrow-field instrument will be capable of resolving 2.8 m GSD in four channels corresponding to Landsat-1, 2, 3, and 4 spectral channels (450-520 nm, 520-600 nm, 630-690 nm, and 760-900 nm). The wide-field instrument will be capable of resolving 75 m GSD or better. Both instruments are capable of recording High-Definition video at 1920 by 1080 pixels. The spacecraft will be capable of performing global imaging and real-time video streaming over Slovenia and other regions where it will be in view of the ground station. In addition, the spacecraft will also be capable of performing remote observations. NEMOHD will include the standard complement of subsystems, sensors and actuators that make up a three-axis stabilized NEMO bus. NEMO-HD will be enhanced to include a 50 Mbps X-band downlink, 128 GB of on-board storage, a high-performance instrument computer, and a power system generating 31 W at end-of-life with a 130 W-h Li-ion battery. The paper provides an overview of the NEMO-HD system design