Grace Halferty, University of Arizona; Vishnu Reddy, University of Arizona; Roberto Furfaro, University of Arizona; Adam Battle, University of Arizona; Tanner Campbell, University of Arizona
Keywords: Starlink,SpaceX,magnitude,SSA,TLEs,Stingray,University of Arizona,photometry
Abstract:
The SpaceX Starlink is a Low Earth Orbit (LEO) satellite constellation which aims to provide satellite internet access. As of June, 2021, SpaceX has deployed over 1,740 Starlink satellites in twenty-eight different launches. Although 12,000 satellites were filed for the initial constellation, it could be extended to 42,000 satellites in low earth orbit. Nominal schedule calls for two Starlink launches a month, each deploying 60 satellites per launch. The deployment of large satellite constellations has important implications for ground-based astronomical surveys. Those most at-risk of being adversely affected would include the Rubin Observatory whose detectors can saturate if a Starlink satellite passes through the field of view, ruining the exposure and potentially degrading scientific output. The brightness of Starlink satellites has primarily been derived from citizen scientists visual observations without using quantitative detectors. In response to concerns from the astronomy community, SpaceX has made some effort to mitigate the impact their satellites will have by painting one of the satellites, dubbed DarkSat, with a low albedo material with the hope that it will reduce its reflectivity. Other methods SpaceX has implemented to reduce brightness include VisorSat, which has deployable sun visors. In order to address these issues, this paper aims to answer the following questions: what is the apparent GAIA G magnitude of Starlink satellites? What is the apparent GAIA G magnitude of DarkSat and what does this imply about the effectiveness of painting the Starlink satellites? Additionally, what is the apparent GAIA G magnitude of VisorSat and how does this show the effectiveness of sun visors in reducing the satellites apparent brightness? Lastly, what is the accuracy of the TLEs in predicting the location of Starlink satellites? Data for this research was collected with the Stingray prototype telescope located in Tucson, Arizona. Stingray consists of a 16 megapixel CMOS camera coupled with a 135 mm F/1.8 lens yielding a field of view of 7.5° x 5.7° and pixel scale of 5.81/pixel. This wide field CMOS sensor enabled us to collect multiple 0.2 second sidereally-tracked exposures on a single Starlink pass without significant trailing. Images were calibrated using darks, flats and bias frames collected at the time of observation. Data analysis was carried out using a pipeline developed to reduce the images and measure the magnitude. Another code was developed to calculate the difference between the measured positions and the published TLEs. It was found that the average GAIA G magnitude across 97 observed Starlink satellites with 736 observations was 5.6 +/- 0.13, with a 1-sigma standard deviation of 1.09. The brightness of DarkSat was found to be 7.3 +/- 0.13 with a 1-sigma standard deviation of 0.78. This makes DarkSat 4.8 times fainter than regular Starlinks. The brightness of VisorSat was found to be 6.1 +/- 0.13 with a 1-sigma standard deviation of 0.78. This makes VisorSat 1.6 times fainter than regular Starlinks.The average difference in RA and Dec between position measurements and the published TLE at epoch in arcminutes was found to be 7.1 and 25.6, respectively, with a standard deviation of 5.41 and 23.06 arcminutes. The average time difference is 0.6 seconds with a standard deviation of 0.84 seconds. The time between launch date and observation seems to have little effect on positional uncertainty when observing more than two months after launch. The results show that although certain factors, such as sun visors on VisorSat, can reduce brightness, the satellites are still relatively bright especially for large ground-based telescope observations. The large number of satellites being deployed, as well as the concerns of each individual satellites brightness are issues extremely important for the astronomical community and observations of other objects. Additionally, knowing the accuracy of published TLEs is important for astronomical surveys if they choose to close the shutter mid-exposure to avoid a Starlink from degrading it. By addressing the above questions, we hope to better understand the impact the Starlink constellation has on the astronomical community.
Date of Conference: September 14-17, 2021
Track: Non-Resolved Object Characterization