0 Comments A newly published study from researchers at the University of California (Department of Physics and Astronomy) has found that Starlink’s (SpaceX) second generation (v2) broadband satellites, which sit in a Low Earth Orbit (LEO), are darker than V1s despite being much larger (both bus and solar arrays). The results represent good news for astronomers. At present Starlink has around 8,000 satellites in Low Earth Orbit (c.4,300 are v2 / V2 Mini) – mostly at altitudes of c.500-600km – and they’ll add thousands more by the end of 2027. Residential customers in the UK usually pay from £75 a month, plus £299 for hardware (currently free for most areas) on the ‘Standard’ unlimited data plan (kit price may vary due to different offers), which promises UK latency times of 28-36ms, downloads of 103-258Mbps and uploads of 15-26Mbps. Cheaper and more restrictive options also exist for roaming users. NOTE: The International Astronomical Union (IAU) recommends that LEO satellites should have a maximum brightness of magnitude +7. On this scale, the brightest objects actually have the smallest numbers (e.g. brilliant Venus can reach up to -4.6, while the North Star is dimmer at +2). However, one of the biggest complaints about mega constellations like these is that they tend to be very bright, which can cause disruption to observational sciences like optical astronomy (i.e. LEOs showing up as multiple streaks in telescope images). This can make it much harder to picture the night sky and do other things, such as to spot dangerous asteroids or detect key celestial events. Advertisement In response, SpaceX has busy been making changes to their satellites, both physically (e.g. black paint) and orbitally speaking (e.g. changing the alignment of the craft and panels). Past studies have indicated that this work appears to be having a positive impact (here) and the new UC study reaches a similar conclusion (here), albeit limited by its focus on the Legacy Survey of Space and Time (LSST) at the new Vera C. Rubin Observatory in Chile. Summary In order to reduce the impact on ground-based optical astronomy, the new Starlink V2 satellites incorporate improvements to the chassis brightness through dielectric mirrors, off-pointing solar arrays, and black paint on exposed components. To assess the effectiveness of these mitigations for the general case in which the reflectivities are initially unknown, we simulate LSST operations and repeated photometry of every satellite in simulated model constellations. We derive a brightness model of the Starlink V2 satellite and study the simulated apparent brightness as a function of the satellite position relative to the observer and the sun. We find that the V2 Starlink satellites appear brightest at two distinct positions in the sky: when oriented toward the sun at low elevations where light is specularly reflected, and nearly overhead where the satellite is closest to the observer. A simulation of Starlink V2 satellites at 550 km height distributed across a series of Walker constellations (Walker, 1984), with varying inclinations was analyzed to study the impact on the LSST observations. The results of the V2 Starlink satellite trail simulation were compared to a similar simulation of V1.5 Starlink satellites. We find that some bright satellites will be visible in LSST observations. For every thousand V1.5 Starlink satellites imaged by LSST in the first hour of a summer night, we find 1.2 of them will appear brighter than 7 AB magnitude. By comparison, for every thousand V2 Starlink satellites observed, we find only 0.93 of them will appear this bright. The off-pointed solar array and reduced diffuse reflection of the chassis mitigate the brightness. Finally, we simulate lowering this Walker constellation to 350km. Only 0.56 V2 Starlink satellites per thousand brighter than 7 AB magnitude will be observed in the first hour at this height. This is a ∼40% reduction in number of bright satellites entering the focal plane compared to the constellation at 550km height. We find that a combination of factors yield an apparent surface brightness of these satellites for LSST operations only 5% brighter than at 550km orbit. The overall science impact on LSST will of course depend on the whole satellite population and not just Starlink’s latest platforms. For example, Starlink’s new global Direct to Cell (DtC) mobile roaming capable satellites still appear much brighter (here) and AST Space Mobile’s massive array has a similar issue. But the hope is that more operators will adopt measures to tackle this, just as SpaceX are doing. The real test will be whether SpaceX can continue to make improvements as their satellites get ever larger in the future (GEN3). At the same time, we shouldn’t forget that observational science is only one area of concern, with radio astronomers also having complaints (here), although there has been some progress on that too (here). Advertisement Not to mention the wider concerns over an increase in “space junk” around the earth and the risk from catastrophic collisions (Kessler Syndrome).