Thursday 5 October 2023

Paper in Nature on the high optical Brightness of the BlueWalker 3 satellite


Last Monday 2 October 2023,  a consortium paper initiated by the IAU-CPS was published in the high-impact Journal Nature. It is titled "The high optical brightness of the BlueWalker 3 satellite", and I am one of the co-authors of this paper. An Open Acces version of the paper is here.

The BlueWalker 3 satellite (2022-111AL), launched in September 2022 into a 500 km altitude Low Earth Orbit, is a prototype satellite from AST Space Mobile. It is meant to demonstrate the feasibility of making direct contact with normal cell phones through a satellite

Eventually, AST Space Mobile wants to create a constellation with large numbers of these satellites (it filed with the FCC for 243 of such satellites, although lower operational numbers are also floating about on the internet. AST Space Mobile has said that they need at least 110 operational satellites to provide world coverage). Launch of operational versions might start in 2024.

 BlueWalker 3 filmed on 3 April 2023

The paper provides the results of our monitoring of the brightness of the satellite, before and after deployment of its large 64 m2 Phased Array antenna. We show that the satellite is very bright, brighter than satellites generally are, shining as bright as some of the brightest stars in the sky. It reaches magnitude +0.5 to zero on well illuminated passes. 

We discuss what this means for the outlook of the night sky, it's impact on Astronomy, and point to the mitigation efforts astronomical Observatories might need to take if large numbers of such satellites will be launched. At the end of the paper, we make a call that the impact of such satellite constellations should be made an explicit part of launch permit assessments.

While BlueWalker 3 and the proposed constellation of similar satellites are the inspiration for our paper, the implications stemming from our paper are explicitly relevant to a wider issue of the rise of large satellite constellations, and the impact these will have on the night sky and users of the night sky (which, by the way, are not just astronomers).

More backgrounds on the topic and my involvement with the study are provided in this interview with me on the website of Delft Technical University.

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