Impact of and considerations about Low Earth Orbit Satellites

Let’s talk about LEOs. LSST has an official statement

And @Tony as presented these slides at the 2019 PCW

Here is a collection of statements about LEOs that appeared on the Web (compiled on Aug 1st 2019 by Ana Gabela and lightly updated by @fed on Aug 13-14)

The results @Tony presented were certainly raising eyebrows. Personally, I agree with his assessment that more simulations of the impact of such satellite constellations on the LSST survey are necessary, to have a clearer picture of their impact. We’re on it.

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@Tony had additional slides at the unconference. Could these be posted? These satellite constellations are a significant concern, and one hopes both LSST and the astronomical community in general can effectively influence international policy. But I am mostly concerned at LSST’s internal response to this issue and to future external challenges.

The (negative) discussion at the plenary about the proposed Twilight Near-Sun Survey and later at the unconference was extremely premature. At the latter there was even confusion between the North Ecliptic Spur and the Twilight Survey White Papers. Indeed it sounded like absent NASA funding SSSC science (or perhaps just NEOs) is being seen by some faction only as a “public service” LSST might pursue, rather than one of the four scientific pillars of the Survey.

Simulations responsive to the ensemble of White Papers should be completed before making dramatic public statements, negative or positive for that matter. And what should be simulated should be the Twilight Near-Sun Survey as described in the White Paper, i.e., with the shorter exposures requested and implementing (in the twilight) a NEO-friendly, immediately actionable quad cadence. NEO surveys already encounter frequent streaking from satellites, some quite bright. Moving object pipelines do quite well detecting on three out of four exposures (or out of five), and this is already required to handle chip gaps.

The sheer numbers involved in the new constellations are a concern, as well as the frequent reprovisioning launches that will be necessary. If these will present a unique challenge to LSST, it will likely not be only the Twilight Near-Sun Survey that will be impacted. And this most certainly has nothing to do with decisions related to the North Ecliptic Spur!

I prefer to stick to the facts. The short unconference on this LEOsat issue which we tacked on to the LSB discussion was to address a question I got after the plenary: what about programs that observe into the twilight. There the LEOsats are brighter and there will be more of them per solid angle. The only new fact which is not in the Science Book which I presented is an image of one LSST CCD in the lab with an artificial LEOsat trail blooming the segments. To lead into this I quoted the one driver for twilight observing which has caught the attention of Congress: PHAs. Indeed many think that this will be a public service. I also said there are several other twilight observing proposals but never mentioned them by name. I did say in the plenary and yesterday that SpaceX wants to help us. Armed with enough facts, the science collaborations impacted by LEOsat constellations should undertake full observing simulations. I mentioned that we designed the LSST camera (many highly segmented CCDs) to be maximally immune to bright stars. However ghosts from bright objects cover degree scales.

I took a quick look and was surprised that only 15% of LSST observations would get a satellite hit from a 40k constellation. If anyone wants to check my work to make sure I didn’t screw up a rotation:

1584 satellites:

40k constellation:

My understanding of @Tony’s research was that we’d have about ~4% of effective area loss in twilight (for potential NEO search programs). That is under somewhat pessimistic assumptions – i.e., everyone launches what they’ve announced, every CCD image crossed by a satellite is rendered unusable, and there’s no mitigation from SpaceX et al. That is a cause for concern, but looks like it wouldn’t be catastrophic.

It’s still prudent to work this out in more detail, and work proactively with the satellite companies to completely mitigate this risk. It’s great that @Tony is pushing this forward.