A Day-in-the-Life...
This simulation shows a "day in the life" of the MARCO POLO constellation, providing a proof-of-concept by demonstrating capability to gather and store high-resolution Earth images and transmit those images to ground stations during communication passes, while maintaining charge on the satellite. All performance metrics (e.g. downlink rate, communication power draw, solar panel charge rate, etc.) are drawn from the constellation design parameters and can be found in corresponding component or discussion pages.
Visualization
The sub-satellite point of each satellite is nominally represented by a blue circle in the 3D orbit (top-left) and ground-track (bottom) visualizations. When the satellite is imaging, the corresponding marker fills in green, and when the satellite is communicating with a ground station, the marker turns red. In the ground-track view, the shaded area represents the "night" side of the Earth, crucial because the satellite cannot image the ground without adequate sunlight.
Additionally, time-series plots (top-right) show the battery charge (in Watt-hours) and accumulated image data (in gigabits) for a sample satellite from the constellation. The sample satellite marker is changed to a triangle so that it can be followed throughout the simulation to corroborate the data. The simulation begins after all satellites have been deployed and phased into their orbit slots, so each satellite is initialized with zero image data and a conservative assumed half-maximum-capacity battery charge.
Additionally, time-series plots (top-right) show the battery charge (in Watt-hours) and accumulated image data (in gigabits) for a sample satellite from the constellation. The sample satellite marker is changed to a triangle so that it can be followed throughout the simulation to corroborate the data. The simulation begins after all satellites have been deployed and phased into their orbit slots, so each satellite is initialized with zero image data and a conservative assumed half-maximum-capacity battery charge.
Dynamics
Due to the careful orbit design, many perturbing accelerations typically experienced in LEO can be ignored for this constellation. This allows the satellites to be propagated using purely Keplerian two-body motion with reasonable fidelity. During the simulation, each satellite sub-point is tracked to determine whether the satellite is in an eclipsed region, indicated by the shaded area on the ground track.
Imaging
When not in an eclipsed region, each satellite is taking and storing a new image every 3.02 seconds (see imaging system analysis), indicated by green-filled symbols. The (compressed) image data accumulated on the satellite is tracked alongside power depletion. The data storage required is never seen to rise above 60 gigabits (7.5 gigabytes), well within the 16 GB storage capacity on-board. Additional analysis (not depicted in this video) using the projected image size of 30.70 x 23.02 km shows that the entire Earth is covered at least once. Since the orbit planes converge in the extreme high- and low- latitudes, more overlaps occur further from the equator. This validates the image system trade study for the number of satellites required to fully image the Earth by ensuring full equatorial coverage.
Communication
In the simulation, two ground stations are positioned (indicated by magenta stars) to receive image data from the satellites. Each ground station has 4 X-band antennae for communication. If a satellite is visible to the ground station and the ground station has an antenna available, the satellite begins to downlink its data, depleting stored data as well as battery charge. If the satellite has downlinked all its data, it terminates its connection to the ground station to allow another satellite to communicate.
In the simulation, you can see that our sample satellite (the triangle marker) experiences 6 good (long duration) communication passes over the course of the day, as well as a number of small passes, validating our conservative communication time estimates.
In the simulation, you can see that our sample satellite (the triangle marker) experiences 6 good (long duration) communication passes over the course of the day, as well as a number of small passes, validating our conservative communication time estimates.