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Hub Leads: Siegfried Eggl (University of Illinois), Mike Peel (Instituto de Astrofísica de Canarias) & Meredith Rawls (University of Washington/Vera C. Rubin Observatory)

SatHub was initially proposed by the Observations group of SATCON 2, envisaged as “a new comprehensive, worldwide, coordinated, and public observing initiative”. The main components of SatHub are Astronomical Data Repositories, an Orbital Solution Portal, Software Tools, a Training Curriculum, and support for Real-Time Collaboration. Each of these encompasses several critical modules — everything from queryable image databases to a developer guide for software contributors, to quick-start recipes for observers equipped with various hardware, to a mechanism for submitting requests to observe satellites in a particular way. SatHub components and organisation are shown in the figure below.

This image of Venus and the Pleiades shows the tracks of Starlink satellites. Credit: Torsten Hansen/IAU OAE

SatHub’s functions.

Astronomical Data Repositories support upload, query, preview, and download of most FITS optical/NIR observations and include services like Trailblazer, an open data repository of astronomical images containing satellite trails, which should launch in 2022. They must also encompass wavelengths outside optical/NIR including radio, space-based observations from observatories in low Earth orbit, non-image data products including spectra, and other formats including visual sightings or digital SLR camera images. Broad participation in SatHub is critical to minimising duplicated effort and disseminating current impacts from a rapidly changing low-Earth-orbit satellite population.

The position of a satellite at a future time is forecast with a propagator algorithm that uses an orbital solution from the recent past. The SATCON1 Report concluded that it is essential for satellite operators to provide prompt, accurate, updated, and publicly available orbital solution data in a standardised way. To achieve this, operators must agree to publicly and regularly share their orbital solution data, with uncertainties and along with any other available metadata, in standard formats. The SATCON2 Observations Working Group Report proposed that satellite operators could pay for the hosting and upkeep of SatHub’s Orbital Solution Portal, which would be a public-facing website leveraging modern astronomical software tools (e.g., Astropy, Astroquery). The goal of the portal is to retain past orbital solutions and provide an easy lookup interface for data retrieval. It should also include an open source software tool that allows users to translate between ephemerides, general perturbations in our preferred Orbit Mean-Elements format, and old-style Two-Line Elements (TLEs).

The SATCON1 Report noted that new software tools will be critical to dealing with the challenge of observing in the era of satellite constellations. The SATCON2 Algorithms Working Group considered the specific approaches recommended by SATCON1 and developed them into specific high-level software requirements. Each of the proposed packages will take a great deal of time and effort to create, partly because of the complexity of the problem they need to solve, and partly because they must serve multiple communities with varying levels of software familiarity. The group emphasises that in the end no set of software tools will allow astronomers to fully recover the data affected by satellite trails. The Working Group recommends that a number of specific software efforts are needed, and while the entire community is expected to contribute, coordination is needed to provide interoperability, end-to-end functionality, documentation and long-term support; SatHub will provide a natural home for that effort. Some relevant software which already exists is noted in the report.

Examples of SatHub software tools yet to be built are: (1) test datasets that can be used to validate the software tools that are developed, (2) TrailMask for recognising and flagging satellite trails in optical/NIR image data, and (3) PassPredict, which should use a satellite ephemeris database to check when particular areas of sky will be affected by satellite passes. In addition, simulation tools will be needed to assess the overall impact, both current and future, of satellite trails on our science. We must therefore develop software that creates images with simulated satellite trails at various levels of fidelity, as well as software that automatically assesses collections of such images to quantify things like the percentage degradation in source detection efficiency as a function of brightness.

Sharing data products and establishing SatHub are critical, but we must also train observers of all kinds to contribute to the global low-Earth-orbit satellite monitoring campaign. To accomplish this, the SATCON2 Observations Working Group Report outlined a training curriculum that can be adapted to suit a variety of observers. It includes a core curriculum with an introductory module and modules on observing satellites, reporting/sharing observations, and image/data analyses. In addition, we outline advanced modules: software development, radio astronomy, and laws governing outer space. Finally, it should include appendices with Quick Start Recipes for astrophotographers, smaller telescope users, and larger research-grade telescope users, as well as links to related citizen science projects.

Communication between myriad stakeholders is key to addressing this very rapidly changing situation. SatHub will therefore incorporate a variety of real-time collaboration tools to enable stakeholders to communicate rapidly and effectively. Examples of these tools may include Slack, email listservs, and forums on the CPS website.

SatHub welcomes community participation to achieve goals in all of the areas described above. Some examples include, but are not limited to, the following:

  1. Astronomical data repositories
    1. Software developer and web design expertise to maintain and enhance Trailblazer (trailblazer.dirac.dev), an open source repository for satellite-streaked FITS images.
    2. A new data repository designed to identify and archive satellite-contaminated spectra, at optical and infrared wavelengths.
    3. A new data repository designed to identify and archive satellite-contaminated radio observations.
    4. A new data repository designed to collect amateur astronomer data products, all-sky camera images, and photographs of the sky affected by satellites.
    5. Advertising, front-end web development, documentation, and maintenance of any/all of the above.
    6. Coordinated observing campaigns to monitor the changing satellite population.
  2. Software tools
    1. Establishing and maintaining a SatHub GitHub organisation with a contributor guide and other best practice tooling.
    2. A survey of existing software tools applicable to simulating, mitigating, and quantifying how satellites affect the sky, with a mechanism to maintain and update the list.
    3. An effort to document existing software tools following, e.g., Numpydoc standards.
    4. Work to port existing software tools in proprietary or less-familiar languages, or inaccessible webpages, into open source tools that are more user-friendly and accessible to the global community.
    5. Creating standard test datasets for vetting new and existing software tools.
    6. Building, documenting, and testing generic versions of TrailMask and/or PassPredict as outlined in the SATCON2 Algorithms Working Group Report.
    7. Creating a SatHub Simulation Suite web tool that enables users to select from different possible satellite populations and see the impact at various locations and when observing with different instruments.
  3. Orbital solution portal
    1. Writing a friendly introduction to the public-facing Space-Track and Celestrak websites explaining how astronomers can access and use this data to plan observing runs.
    2. Studies to quantify the necessary accuracy of satellite positions and trajectories for avoiding various science impacts in greater detail.
    3. Assembling and maintaining a list of existing tools for adjusting observing schedules in an effort to “dodge” satellites.
    4. Maintaining dialogues with satellite operators and encouraging them to share orbital solution data publicly, in standard formats, with relevant metadata, uncertainties and frequent updates.
    5. Designing and building a public and free SatHub Ephemeris Database that acts as a primary orbital solution portal for astronomers worldwide, translating publicly available orbital solution data into readily queryable formats.
    6. Developing a tool to translate between different styles of orbital solutions using the best available data (ephemerides and general perturbations in either TLE or Orbit Mean-Elements format).
  4. Training curriculum
    1. Build out and pilot any of the curricula outlines from the SATCON2 Observations Working Group.
    2. Write guides for different observers who would like to get started with taking and analysing data that will be useful for SatHub.
    3. Develop tutorials and/or guides for using the tools collated in SatHub’s Software Tools to accomplish routine tasks.
    4. Develop assessment tools for how effective various tutorials and lessons are.
  5. Real-time collaboration
    1. Volunteer as a GitHub maintainer.
    2. Volunteer as a Slack moderator/admin.
    3. Volunteer as an instructor or helper for lessons developed in the training curriculum.
    4. Host occasional SatHub meetings on an as-needed basis.
    5. Solicit speakers and coordinate sharing information among SatHub contributors’ efforts such as funding proposals, presentation slides, etc.
    6. Maintain a live bibliography of SatHub-related publications.
    7. Establish and maintain a SatHub/CPS social media presence.


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