How was the JWST’s orbit determined as it began its journey?
The NASA James Webb Space Telescope (JWST) mission successfully launched on December 25, 2021, at 12:20 UTC. This paper details several novel challenges encountered in the orbit determination (OD) of JWST during the launch and early orbit. The first OD solution used only 6.5 hours of tracking data, much less than the 24 hours of data usually required for libration orbiters on an outbound trajectory. In addition, the observatory area exposed to solar radiation pressure changed through a series of sunshield deployments while concurrent momentum unloads and attitude telemetry outages occurred. This paper covers how the Flight Dynamics Team (FDT) prepared for these challenges, how these challenges were handled on-orbit, and the performance of the resulting OD solutions.
The James Webb Space Telescope (JWST) is a NASA flagship observatory that will explore astronomical phenomena in the near to mid infrared spectrum in the exploration of dark matter, first light from galaxies, exoplanets, and other astronomy research topics. JWST is developed by the NASA Goddard Spaceflight Center in partnership with the Johns Hopkins Space Science Telescope Institute (STSci), the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA JWST mission successfully launched on Dec 25, 2021, at 12:20 UTC and inserted into its operational orbit about the second Lagrange point (L2) in the Sun-Earth-Moon (SEM) system on Jan 24, 2022, at 19:00 UTC.
The JWST Flight Dynamics Team (FDT) consists of engineers who have a long heritage of mission support for SEM libration orbits for both L1 (ACE, SOHO, and DSCOVR) and L2 (WMAP) missions. 1,2,3,4 JWST brings several novel orbit determination (OD) challenges to this heritage to enable the next generation of astrophysics research. The JWST mirror and sunshield, driven by science research requirements, resulted in a multi-stage deployment sequence that continually changed the JWST dynamical model. This transition can be seen in Figures 1 and 2.5 Additionally, the initial OD solution used to plan the critical first maneuver could only use a maximum of 6.5 hours of tracking data. This made estimating the outward-bound trajectory of JWST using only ground-based tracking a unique challenge.
Figure 1. The JWST Initial Launch Configuration.
Figure 2. JWST Final Deployed Configuration (Launch+28 days).
This paper will detail the challenges and design solutions from the JWST early mission OD operations. Each of the OD estimation arcs are described and the on-orbit results are listed.
This is a part of a series of papers on JWST flight dynamics operations, with this paper focused on OD for the early mission. The overall JWST flight dynamics support is detailed in Reference 6. The mid-course correction (MCC) maneuver design and execution are described in Reference 7, while the MCC real-time support is detailed in Reference 8. Earlier papers have explored the impact of the launch date on the JWST MCC maneuver design and the resultant long term dynamical systems libration orbit characterization, Monte Carlo simulation of nominal MCC burn designs, and MCC contingencies and designs.9,10,11 Finally, Reference 12 presents an OD analysis to assess if mission requirements could be met.
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AAS/AIAA Astrodynamics Specialist Conference, 2022.
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14 NASA GSFC, https://webb.nasa.gov/content/webbLaunch/deploymentExplorer.html, 2020.
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Webb Space Telescope,” AAS/AIAA Astrodynamics Specialist Conference, 2019.