Impacts of Large Satellite Constellations on Astronomy

[edzieba]

https://twitter.com/nasaspaceflight/status/1650234052572585984

An interview with astrophysicist Dr. Jonathan McDowell (@planet4589) from the Harvard-Smithsonian Center for Astrophysics on the concerns about megaconstellations photobombing observations from ground-based telescopes.

By Ian Atkinson (@IanPineapple)

https://www.nasaspaceflight.com/2023/04/megaconstellations-effects-on-astronomy/

Second image caption:

A Starlink v1.5 satellite (left) compared to a Starlink v1.0 satellite (right). Note the comparably larger size of the solar panel, which causes significant reflections when not angled away from Earth. (Credit: SpaceX)

The 1.0 satellite in the image only looks like it has a smaller array because the source is an image that had the array cropped out from the start - note the distinctive stairstep aliasing in the shadow on the bus, and how the corner of one of the array panels is clipped off due to the partially rotated image.

[FutureSpaceTourist]

https://twitter.com/planet4589/status/1651312934763593730

Oh brilliant. Think you've discovered a binary star using spectroscopy? Guess again, the second component is just reflected light from a Starlink sat.
Another new way that constellations can cause bogus astronomy discoveries if you're not very careful.

twitter.com/johnbarentine/status/1651310932537245698

MNRAS preprint showing contamination of LAMOST medium-resolution object spectra with sunlight reflected from Starlink satellites.

https://www.lamost.org/publications/upload/2023/Mikhail%20Kovalev-MNRAS(2023).pdf

[edzieba]

That's certainly an interesting failure mode! They determined that operational Starlink and Oneweb satellites would have been far too dim for the spectrograph to even detect, so this would have had to have be from a brighter source. The HST and ISS are given as examples of sufficiently bright sources, but they also estimated a recently launched Starlink train could also have been bright enough, and may have been in the right place at the right time. From the preprint:

While the satellites on operational orbit will not be a major
concern for LAMOST, the compact trains of very low satellites can
affect the observations. The probability of such a train crossing a
telescope field of view is low, but considering that constellations
will need to be regularly replenished, new satellites will need to
be continuously launched. Considering 100 000 satellites with a
life-time of 5 years, this would result in about one launch per day
(each with 60 satellites). If the satellites stay one month in low
orbit, this would result in about 60 trains in orbit, at various stage
of dispersion. It is therefore important that the satellite operators
also keep the brightness of the satellites to the absolute minimum
possible during their stay on transit orbit. The changes of satellite
attitude implemented by Starlink illustrate the improvements than
can be made.

[Twark_Main]

Considering 100 000 satellites with a
life-time of 5 years, this would result in about one launch per day
(each with 60 satellites).

Considering Starlink 2.0, the 100k estimate is increasingly implausible.

[FutureSpaceTourist]

https://twitter.com/jeff_foust/status/1665799882354098176

At the NSF town hall during #AAS242, Debra Fischer says the NSF has signed a coordination agreement with OneWeb to mitigate satellite interference on astronomy, similar to an agreement with SpaceX announced in January. More details about the OneWeb agreement "soon."

[deltaV]

Has anyone made a quantitative estimate of how much reflections from large constellations will cost astronomy in lost productivity and in mitigations? From the little I know it seems astronomers should be able to work around the satellite reflections with measures such as taking many short exposures and discarding the bad pixels in each frame, not using telescopes near dawn and dusk when they may see sun-lit satellites, or using more space-based telescopes. These mitigations could be expensive (especially if they have to use space telescopes) but probably not expensive enough to justify making internet significantly more expensive for millions of people.

[Twark_Main]

Has anyone made a quantitative estimate of how much reflections from large constellations will cost astronomy in lost productivity and in mitigations?

Hard to say.

What's the cost (in money) of a scientific breakthrough you didn't make, you furthermore one you don't know you didn't make? 

These mitigations could be expensive (especially if they have to use space telescopes) but probably not expensive enough to justify making internet significantly more expensive for millions of people.

Reasonable brightness mitigations do not make satellite internet "significantly more expensive", as Starlink's trailblazing work has demonstrated.

[Robotbeat]

Has anyone made a quantitative estimate of how much reflections from large constellations will cost astronomy in lost productivity and in mitigations?

Hard to say.

What's the cost (in money) of a scientific breakthrough you didn't make, you furthermore one you don't know you didn't make? 

These mitigations could be expensive (especially if they have to use space telescopes) but probably not expensive enough to justify making internet significantly more expensive for millions of people.

Reasonable brightness mitigations do not make satellite internet "significantly more expensive", as Starlink's trailblazing work has demonstrated.

I think deltaV is referring to preventing Starlink expansion entirely as the “making internet more expensive” option.

Starlink and it’s ecosystem (including Starship) is most certainly ALSO going to lead to scientific breakthroughs. The goal for everyone is to make sure the net benefit to astronomy and science and humanity are positive.

[edzieba]

Preprint: Starlink Generation 2 Mini Satellites: Photometric Characterization

Starlink Generation 2 Mini satellites are fainter than Gen 1 spacecraft despite their larger size. The mean of apparent magnitudes for satellites in brightness mitigation mode is 7.06 +/- 0.10. When these magnitudes are adjusted to a uniform distance of 1,000 km that mean is 7.87 +/- 0.09. The brightness mitigation mode reduces distance-adjusted satellite luminosity by a factor of 12 relative to spacecraft that are not mitigated.

7 was the target magnitude recommended at SATCON 1 (Recommendation 5).

[FutureSpaceTourist]

Crosspost. SpaceX video (which first tweet below quotes) gives very clear view of the dielectric mirrors:

https://twitter.com/starlink/status/1703132933102649527

Developed in-house, the dielectric mirrors on the surface of the satellites and extremely dark black paint for angled surfaces or those not conducive to mirror adhesion help absorb and redirect light away from the ground

We firmly believe in the importance of protecting the night sky for all to enjoy, which is why the Starlink team has been working with leading astronomers around the world to reduce satellite brightness

https://twitter.com/starlink/status/1703135000206745949

The Starlink team continues to share best practices for brightness mitigation, and has made the dielectric mirror film available at cost to other satellite operators → https://api.starlink.com/public-files/BrightnessMitigationBestPracticesSatelliteOperators.pdf

[Twark_Main]

Has anyone made a quantitative estimate of how much reflections from large constellations will cost astronomy in lost productivity and in mitigations?

Hard to say.

What's the cost (in money) of a scientific breakthrough you didn't make, you furthermore one you don't know you didn't make? 

These mitigations could be expensive (especially if they have to use space telescopes) but probably not expensive enough to justify making internet significantly more expensive for millions of people.

Reasonable brightness mitigations do not make satellite internet "significantly more expensive", as Starlink's trailblazing work has demonstrated.

I think deltaV is referring to preventing Starlink expansion entirely as the “making internet more expensive” option.

If that's what they meant, then deltaV was constructing a false dichotomy.