High Altitude Swarm-based Synthetic Aperture for Ground and Space Observation

The biggest challenge with the hypersonic re-entry studies is the varying atmospheric parameters from the sea level to the von Karman line, resulting in a broad range of flow fields. The re-entry location, date, and time of a de-orbiting object are all dictated by the launch time within a specified launch window. The ground stations are strategically located to monitor the health of the de-orbiting and demising spacecraft. While this cycle of events from launch to demise has been the norm since the inception of launch systems, there is room for improvement, especially with the tracking of space debris. We propose an architecture based on the Glitter Belt concept as a swarm platform for multispectral imaging for space and ground observation. The work entails a system architecture and feasibility study for tracking targeted re-entry objects. Tracking the targeted re-entry systems using a swarm of high-altitude flying platforms opens up future opportunities for meteorological studies, not limited to wildfire and hurricane warnings.

Our prior work presented at the AMS 2022 Poster Presentation categorically showed the attainable resolution for tracking a 1U CubeSat with a synthetic aperture of the size of a single Flying Leaflet (FLT as part of Glitter Belt). It also showed the viability of using the width of the Pacific Ocean from Japan’s coast to the western border of the contiguous US as a synthetic aperture. A single FLT flying at 11 km altitude can resolve a re-entering CubeSat with a resolution of 0.286 x 10-3 arcseconds, and an FLT swarm with a synthetic aperture of the size of the Pacific Ocean can resolve up to 0.0137x10-6 arcseconds. This is several orders of magnitude required to resolve the two faces of a 1U CubeSat, attributing to 0.23 arcseconds. The proposed work will build on these results, showing the required spatial and temporal viewing windows for targeted tracking of the re-entry systems. A statistical analysis will be shown for variations in flight trajectories within a flight envelope that terminates at Point Nemo, the graveyard for satellites. A tradeoff study will be presented for attainable magnification and light intensities. Specific meteorological applications like identifying wildfires from a high-altitude swarm will be explored.

One application of swarms of large slow-moving reflectors at high altitudes, is to perform imaging looking up into Space. Our initial interest is in Low Earth Orbit and vehicle surfaces at the start of re-entry, where signal to noise ratio can be quite high. Later, as positional accuracy of the reflectors is improved, we project application to study Space Weather phenomena, and perhaps even Deep Space imaging, using the clear, thin atmosphere and steady flight of the arrays to achieve satisfactory signal to noise ratio.

The initial application is to capture hypersonic boundary layer and wake characteristics of Low Earth Orbit vehicles immediately prior to and during re-entry over the southern Pacific and Indian ocean areas. The southern oceans, being remote with few shipping or airline routes, are the favored areas for disintegration and surface impact of orbital objects at end of life. Predicting the trajectories and impact zones of these objects is of increasing interest, as the number of satellites and launch vehicle parts is projected to increase by orders of magnitude. The Glitter Belt Flying Leaf vehicles provide a unique set of platforms to perform imaging of re-entering vehicles. Very light wires can be integrated with the structural supports of the ultralight sheets to form antenna grids. Thus, much of the required mass budget of the imaging array may be met by vehicle structural elements. By combining several such vehicles in a swarm of suitable geometry, it is possible to form a large, distributed telescope capable of responding to a broad spectrum of information from Space. The paper will consider the characteristics of the flow fields around vehicles as they first encounter the atmosphere, and at later stages of descent. These features are transferred to imaging requirements, and thence to the requirements to be integrated into the vehicle design and payloads. Specific determinations will be made on the demands on reflector surface geometry and positional coordination required to accomplish the modest objective of imaging objects in Low Earth Orbit.