Re: SATCON1 day 2

Hi all,

Let me add a bit to what Brad and Jonathan already shared. The goal of
the workshop was/is to 'discuss, understand and quantify the impacts
of large satellite constellations on astronomy and the human
experience of the night sky' (as taken from the website:
https://aas.org/satellite-constellations-1-workshop). Hence, the
participants covered a large range of expertise, and included at least
two representatives of SpaceX Starlink, as well as people with space
law backgrounds, and obviously astronomers. Prior to the meeting, four
working groups were formed to investigate present and future
observations of satellites from mega constellations, simulate the
impact of future constellations, explore mitigation of satellite
trails on astronomical observations, and one group to develop metrics
to protect optical/IR observations. Both Jonathan and I participated
in the simulations working group, which, for me, turned out to be an
interesting experience. Each working group will provide a report of
their analysis and conclusions, which will be collated into a white
paper.

The main thing I took away from the meeting is how deeply SpaceX is
invested to minimize the impact of Starlink on astronomical
observations. The recent Darksat, using darkened antennas, and
Visorsat, shadowing the reflective antennas, are the direct result of
astronomers and Starlink collaborating. This also includes the
operational changes of the Starlink orientation during the orbit
raising phase, of which we've already seen the decrease in brightness.
In this sense, SpaceX is setting a very clear example, and we can only
hope other satellite operators will be equally willing to minimize
their impact on astronomy and the night sky.

To test the effectiveness of these brightness reductions, observations
are needed. To date, the SeeSat-L produced magnitude measurements are
the best data around, but many more observations are required to
determine the phase angle dependence and obtain what is called a
bi-directional reflectance distribution function that describes the
reflective properties of all areas of the satellite. The required
observations should provide magnitude measurements good to 0.1 to 0.2
mag. There was quite some discussion on how to obtain such brightness
measurements, and the idea of a widely distributed network was
mentioned several times. This would require observatories (since most
of the attendees were astronomers they were thinking about ~1 m class
telescopes, which I mentioned would be overkill), as well as tools to
know where to point when. While 0.1 to 0.2 mag accuracy will be
challenging for us, we don't need to be taught where to look for a
particular satellite, so there likely is a role to play for us
hobbyist satellite observers.

Regards,
   Cees
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