Ty Stromberg, US Air Force Academy; Kody Wilson, US Air Force Academy; Timothy Bate, US Air Force Academy; Francis Chun, US Air Force Academy; David Strong, Strong EO Imaging, Inc.; Darren McKnight, LeoLabs
Keywords: Photometry, Rocket Body, Rate of Tumble, Space Situational Awareness, Space Domain Awareness, Low Earth Orbit, LEO
Abstract:
Space Domain Awareness (SDA) helps the Air and Space Forces monitor and respond to potential threats to U.S. space assets, such as orbital debris, space launches, and space traffic. By clearly understanding the space domain, the Air and Space Forces can ensure the continued ability to operate in and through space, supporting military and national objectives. An increasing amount of space objects enter the Earth’s orbit each year and it is necessary to track these objects to ensure the safety and success of United States space operations. By characterizing the dynamic state (i.e., tumble rate) of abandoned rocket bodies and comparing to radar-derived positional uncertainties, the LeoLabs global network of radars can improve the custody (i.e., persistent, accurate knowledge of position in space over time) of these objects that pose the greatest debris-generating potential in low Earth orbit (LEO). This helps to reduce the probability of a collision with operational spacecraft by enabling more accurate conjunction data messages and more precisely quantifies the possibility of a collision with other derelict objects. This fusion exercise of optical and radar data exemplifies the type of coordinated effort required to enhance space domain awareness in this rapidly growing LEO space environment.
The United States Air Force Academy (USAFA), the University of Warwick, Sapienza University of Rome, and the University of Bern are participating with LeoLabs to help maintain Space Domain Awareness by monitoring 5 different types of rocket bodies in low-earth orbit. These 5 types include: SL-14, CZ-4C, SL-8, SL-16, and Delta 2. These rocket bodies will be observed using the USAFA 0.4-meter telescope. The USAFA campus telescope is a DFM Engineering f/8.2, 0.4-meter Ritchey-Chrétien telescope with B, V, R, and linear polarization filters. Using the R-filter, images of each rocket body were taken and processed using cadet-generated software that uses aperture photometry techniques to produce the instrument and calibrated magnitudes of the light signatures received from each image. Observations were conducted during dusk periods on 08 November 2022, 02 December 2022, 09 December 2022, 01-02 February 2023, and 10 February 2023, when the rocket bodies are illuminated by the sun while the telescope is in darkness. Images of a rocket body that is suspected to be spinning are put into a three-step analysis. First, photometric standard stars (usually Landolt calibration stars) are processed in order to create the extinction coefficient for the R filter each night. Second, aperture photometry is again applied to the rocket body images to produce its temporal photometric light curve. Finally, once a calibrated magnitude light curve is created, we categorize the type of motion of each rocket body and determine the rocket body’s rate of tumble.
The goal of this project is to provide an estimation of the rocket bodies’ dynamics with two measures. The first will be the type of motion which will be categorized as a stable body with no abnormal rotation, end-over-end tumbling which consists of rotation about the lateral axis, flat spin which is rotation about the vertical axis, gravity-gradient stabilization, or others. The second measurement will be the rate of tumble.
Additional goals of this project are to support the following hypotheses presented by LeoLabs: (1) It is anticipated that rocket bodies with no tumble or very fast tumble rates will have smaller positional uncertainties as determined by LeoLabs versus rocket bodies with moderate tumble rates (e.g., ~ 1 deg/min).
(2) The apparent rate of tumble of each rocket body will not change over the course of time. To support this, observations taken at the USAFA observatory in 2011 will be compared to observations of the same rocket bodies in the academic year 2022-23.
(3) LeoLabs believes that rocket bodies at higher altitudes are more likely to be gravity-gradient stabilized than similar ones at lower altitudes, the rotation category of rocket bodies at different altitudes will be compared.
Date of Conference: September 19-22, 2023
Track: Satellite Characterization