Small satellite technical capabilities continue to grow and launch opportunities are rapidly expanding. Several commercial constellations of small satellites for Earth observation and communications are making their way onto orbit, increasing the need for high bandwidth data downlink. Laser communications (lasercom) has the potential to achieve high data rates with a reduction in power and size compared to radio frequency (RF) communications, while simultaneously avoiding the significant regulatory burden of RF spectrum allocation. Lasercom benefits from high carrier frequencies and narrow beamwidths, but the resulting challenge is to precisely point these beams between transmit and receive terminals. Arcsecond to sub-arcsecond pointing is required from both the space terminal and the ground station. While existing lasercom ground stations have primarily utilized professional telescopes at observatory-class facilities, making optical ground stations more affordable and transportable is a key enabler for expanding lasercom to small satellites and new applications, as well as establishing networks to mitigate the effects of weather. This thesis focuses on the development of a portable optical ground station utilizing a commercial off-the-shelf (COTS), low-cost telescope. The Portable Telescope for Lasercom (PorTeL) reduces mass and cost by at least 10× compared with existing optical ground stations. To enable the use of a low-cost telescope, several contributions are made to the state-of-the-art approach to optical ground station design, pointing, and tracking. A system architecture is proposed that enables rapid deployment in approximately 30 minutes and that is capable of tracking satellites in low-Earth orbit (LEO) to within arcseconds of accuracy. A novel telescope calibration algorithm is developed that is agnostic to initial mount/telescope orientation and utilizes a star tracker for rapid, automated alignment. This eliminates the need for manual pre-alignment (e.g., leveling of the mount) and provides a generic framework that extends to different mount types. An approach to tracking LEO objects to better than 5 arcseconds RMS using only two-line element sets (TLEs) and low-cost hardware is presented. Pointing and tracking algorithms and performance are validated by using a physical ground station setup to track LEO objects, including the International Space Station (ISS).

Portable optical ground stations for satellite communication

System Design and Implementation of the Virginia Tech Optical Satellite Tracking Telescope

In order to protect critical military and commercial space assets, the United States Space Surveillance Network must have the ability to positively identify and characterize all space objects. Unfortunately, positive identification and characterization of space objects is a manual and labor intensive process today since even large telescopes cannot provide resolved images of most space objects. Since resolved images of geosynchronous satellites are not technically feasible with current technology, another method of distinguishing space objects was explored that exploits the polarization signature from unresolved images. The objective of this study was to collect and analyze visible-spectrum polarization data from unresolved images of geosynchronous satellites taken over various solar phase angles. Different collection geometries were used to evaluate the polarization contribution of solar arrays, thermal control materials, antennas, and the satellite bus as the solar phase angle changed. Since materials on space objects age due to the space environment, it was postulated that their polarization signature may change enough to allow discrimination of identical satellites launched at different times. The instrumentation used in this experiment was a United States Air Force Academy (USAFA) Department of Physics system that consists of a 20-inch RitcheyChretien telescope and a dual focal plane optical train fed with a polarizing beam splitter.

/pdf/identification-of-geostationary-satellites-using-4fd4vs3emt.pdf

Identification of geostationary satellites using polarization data from unresolved images

The heavens above

. This paper presents a satellite tracking method based on optical celestial images. The proposed method is composed of two acquiring modes that are called Sidereal Stare Mode (SSM) and Track Rate Mode (TRM). To track the unknown satellites, first of all the entire of the sky is observed and the primary knowledge of the satellite location is predicted in SSM. Then, the measured pointing data is calculated and used by the telescope to acquire the satellite tracking images at the appropriate time. The framework of SSM contains main steps such as the image correction due to the noise and the image background by applying the iterative filtering methods, the star detection and removal using a double gate filter and PSF concepts, the star identification for image calibration based on a star catalogue, the streak detection of the satellite using the matched filter and finally, the extraction of the celestial coordinate of the satellite as a predicted position. In TRM, the group of star streaks should be identified in the free background image. Then, Fast Fourier Transformation (FFT) is applied and the characteristic of star streaks are extracted. Finally, the centroid of the satellite is estimated precisely by applying a binary mask and the right ascension and declination of it is calculated using astrometric transformation parameters. In this study, the searching and tracking algorithms is applied on the simulation images to detect and identify the satellite position in the sky. Therefore, a telescope along with a CCD camera is simulated to generate sequences images using the well-known star catalogues, the optical and orbital parameters. The precise celestial coordinate of a real satellite and two fictitious satellites are obtained from simulated images. The study results show that the accuracy of the satellite estimated position after star calibration is better than 5 arc seconds and the satellites tracking accuracy is around 1–3 arc seconds.

/pdf/the-design-and-implementation-of-an-optical-astronomical-n1ggzwdo1m.pdf

The design and implementation of an optical astronomical satellite tracking system

: A commercial off-the-shelf satellite tracking system is developed and utilized for determining satellite characteristics on a minimum budget A summary of the system components, developments, capabilities, and future improvements is addressed within this paper The system is divided into four main components: camera and lens, tracking mount tracking and data handling computer, and software The system is highly mobile and has provided usable research data through the imaging of unresolved satellites as dim as 6th magnitude Future plans for a permanent assembly with networked control and automated data collection is also described

https://apps.dtic.mil/sti/pdfs/ADA570268.pdf

An Optical Satellite Tracking System for Undergraduate Research

: While many governments attempt to obtain information about satellites passing overhead using expensive equipment such as radar or large telescopes, many characteristics of a satellite, its orbit, and possible mission type can be inferred through analysis of its light intensity variations as it passes overhead. Using off-the-shelf equipment, a satellite can be tracked and recorded with a camera during visible sightings. Images are normalized based on range, the amount of atmosphere the light travels through, and the percentage of satellite illumination. A plot of the intensity versus time is created from these images. Based on patterns displayed by the light intensity graph, a satellite s cross-sectional ratio, its orientation to the earth, and its movement in the orbit can be determined. This inexpensive and easily duplicated process is done with only light intensity analysis. The satellite itself need not actually be resolved in the images.

/pdf/determination-of-satellite-characteristics-through-visible-2s0ba8sdxs.pdf

Shane Bruski

Papers

An Optical Satellite Tracking System for Undergraduate Research

Determination of Satellite Characteristics through Visible Light Intensity Analysis