Shaylah Mutschler, Space Environment Technologies; W. Kent Tobiska, Space Environment Technologies; Marcin Pilinski, University of Colorado at Boulder / Laboratory for Atmospheric and Space Physics; Sean Bruinsma, Centre National d’Études Spatiales; Eric Sutton, University of Colorado / SWx TREC; Delores Knipp, Smead Aerospace Engineering Sciences Dept, University of Colorado; Vishnuu Mallik, Planet Labs PBC; Bhavi Jagatia, Planet; Mike Siegers, Planet; Tzu-Wei Fang, NOAA Space Weather Prediction Center; Tim Fuller-Rowell, Department of Commerce (NOAA); Brandon diLorenzo, Space Environment Technologies; Steve Casali, Omitron Inc.; Christian Siemes, Delft University of Technology; Kaiya Wahl, Space Environment Technologies
Keywords: SDA, space weather, LEO, thermospheric density, drag, modeling, operations, HASDM, MSIS, JB2008, DTM, WAM-IPE, TIE-GCM
Abstract:
In Low Earth Orbit (LEO), atmospheric drag is the largest contributor to trajectory prediction error. The Combined Space Operations Center (CSpOC) is responsible for the detection, identification, and daily tracking of all human-made objects in space. CSpOC also provides a conjunction analysis (CA) service that alerts satellite operators if their satellite exceeds a specific collision probability threshold with another Resident Space Object (RSO). The current thermospheric density model used by CSpOC in operations, the High Accuracy Satellite Drag Model (HASDM), applies corrections to an empirical density model every three hours using observations of 80+ calibration satellites. Since HASDM is not available for use outside of CSpOC, satellite operators are left to determine what publicly available/open-source density model they should integrate into their internal operational software. This decision is nontrivial due to the number of available density models, each having variable performance dependent on several factors including space weather conditions and orbit altitude. This paper outlines current state-of-the-art operations-ready thermospheric density models, describing their performance, computation time, required operational space weather input parameters, and notes for implementation. We define an operations-ready density model as a model that is well-documented, has verified and quantified model performance, and provides publicly available model code for implementation on a user’s own system.
The LEO regime is becoming more congested as the number of satellites continues to grow with the rising popularity and establishment of SmallSat constellations. For example, SpaceX is in the process of creating a 12,000-satellite Starlink constellation in LEO, with more than 4,000 SmallSats in orbit currently. The growth in the number of LEO objects directly increases the probability of unintentional collisions between objects due to accumulating space debris. This is called the Kessler syndrome, where unavoidable cascading collisions occur, leading to a potentially unusable LEO orbital domain. In addition to a congested LEO space environment, the rapid rise of this solar cycle suggests that the predicted solar maximum between 2024-2027 could be higher than the previous solar maximum, thus causing higher perturbations due to drag from atmospheric density on LEO satellites. Given the evermore challenging nature of operations in LEO, it is imperative for satellite operators to update legacy density models to a state-of-the-art density model to provide improved trajectory predictions for collision risk assessment and vital day-to-day operational decisions.
Current state-of-the-art models utilize input parameters (either proxies or indices) to generate a global density field nowcast and forecast. The ISO International Standard 14222 on Earth’s upper atmosphere recommends using the US Naval Research Laboratory Mass Spectrometer and Incoherent Scatter radar 2.0 (MSIS 2.0) empirical model for relative constituent abundances and Jacchia-Bowman 2008 (JB2008) model for mass densities related to satellite drag. JB2008 is the background density model applied in HASDM. It is an empirical model that uses solar and geomagnetic indices and proxies as inputs to obtain a global thermospheric density nowcast and forecast. MSIS is also an empirical model, but it utilizes information from only two space weather indices: the Ap index and F10.7 proxy. Unlike MSIS, JB2008 utilizes multiple solar irradiance parameters, S10, M10, Y10 and F10.7, to identify the energy deposition in particular layers of the thermosphere. The inclusion of additional solar irradiance parameters improves JB2008 model performance compared to other empirical models. In JB2008, the 1?sigma density uncertainties at 400 km altitude for a given epoch are 8% compared to 15% with the MSIS model. All required input parameters to MSIS and JB2008 are available operationally.
Although empirical models have historically been applied in operations due to their faster and more efficient nature, as computation power becomes more accessible, the incorporation of physics-based models, like the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM), may also become tractable in operations. Current research efforts are exploring data assimilation with physics-based models.
An analysis of the operations-ready density models is also provided in which their performance is compared during calm and storm conditions and resulting LEO object trajectory prediction errors are quantified at various orbit altitudes. This will be accomplished via a simulation scenario in which satellites are propagated through each model’s density field during historical storm and calm conditions. Each model’s corresponding satellite trajectory is compared to the true satellite trajectory generated by propagating the satellite through the true density field. The Space Environment Technologies (SET) HASDM density database will represent the true global density field; true local densities are provided by the Gravity Recovery And Climate Experiment Follow-On (GRACE-FO) satellite accelerometer density data. Models for this analysis include but are not limited to the Drag Temperature Model (DTM), HASDM, JB2008, MSIS, TIE-GCM, and the Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamics (WAM-IPE) model. Although WAM-IPE does not strictly meet the criteria for an operations-ready density model, we include it in this paper due to the availability of its operational density output and its recent designation as one of the density models in the Department of Commerce’s new Space Traffic Management (STM) system currently being developed. In addition to LEO satellite operators, the results from this paper will also be informative for the transition of civilian space traffic coordination efforts out of CSpOC and into the Department of Commerce.
Date of Conference: September 19-22, 2023
Track: Atmospherics/Space Weather