Bright Satellites Are Disrupting Astronomy Summary: Astronomers spent a lot of time asking SpaceX and other large satellite operators to pretty please make their satellites fainter and/or use fewer satellites. And then BlueWalker 3 was launched by some tiny company and is one of the brightest things in the sky. Asking nicely isn't working: international regulation and pollution penalties are needed.
From the author: ...
This article required weeks of back-and-forth with the editor, the editor-in-chief, and Nature's lawyers, so I hope that means it's a good one.
During this process, I learned that satellite companies are so powerful and litigious that even giant publishers like Nature are terrified of getting sued. Which is...rather worrying.
"By comparison, state-of-the-art Li-ion batteries with an energy density of approximately 250 Wh/kg are 48 times less than jet fuels, which possess a staggering energy density of 12,000 Wh/kg <26>. However, according to Ã hman <47> and, Haung and Zhang <48>, the fuel-to-wheel efficiency of an internal combustion engine averages â¼28%, while electric motors are â¼90% efficient. This reduces the ratio of batteries to aviation fuels from 1:48 to 1:15. Considering an average improvement of 600 Wh/kg battery energy density, the ratio is further reduced to 1:6.2. In addition, it has been proven through research that efficient aerodynamic designs such as distributed propulsion and boundary layer injection which are much more practical with electric aviation can reduce the overall energy consumption during flight by a factor of 3 to 5 <49>. Using the mean value of 4 reduces the ratio of batteries to aviation fuel to 1:1.5. In summary, the development approaches towards electric propulsion can be described as a three-point approach predicated on: 1. battery chemistries of minimum 600 Wh/kg, 2. advancement in electric motor design for high power applications, and 3. efficient aerodynamic design."
There is obviously a lot of blind optimism behind those figures. For instance jet turbines display 50% fuel efficiency, not the 28% cited here, but the trend is looking better than it did a couple of years ago. The new Toyota battery is expected to have an energy density of 450 Wh/kg, which is still some way off the minimum 600 Wh/kg stated above, so the more realistic alternative for zero-carbon aviation will probably remain synthetic bio-fuels for some time to come.