The second generation of Starlink satellites being lobbed into orbit by SpaceX might not reflect as much sunlight as the old ones, yet astronomers say they're leaking up to 32 times the unintended radio waves instead.
In a paper published yesterday, a group of scientists reported that observations at the Netherlands Institute for Radio Astronomy (ASTRON)'s LOFAR radio telescope found massive amounts of unintended electromagnetic radiation (UEMR) leaking from Starlink V2 satellites - both the mini and direct-to-cell capable variants.
"Compared to the faintest astrophysical sources that we observe with LOFAR, UEMR from Starlink satellites is 10 million times brighter," ASTRON's Cees Bassa, lead author of the study, said.
"This difference is similar to the faintest stars visible to the naked eye and the brightness of the full Moon," Bassa added. "Since SpaceX is launching about 40 second-generation Starlink satellites every week, this problem is becoming increasingly worse."
In short, this is already a serious problem, and it's only going to get worse as more satellites get sent skyward.
The team behind the research is the same that published a study last year finding Starlink's first-generation satellites also leaked UEMR, but only a few microwatts. That's still enough to interfere with radio astronomy observations.
The radiation coming from the V2 Starlink satellites already in orbit isn't minuscule - as mentioned above, it's up to 32 times stronger, and the research indicates it's over a wider range of radio frequencies - including more frequencies used by astronomers.
In their previous study, the team found Starlink sats emitted UEMR in the 110 to 188 megahertz range, a portion of which is protected for radio astronomy uses. Here's where that 32x brighter UEMR figure comes from - it's in this range where V2 satellites are so much brighter.
At lower band frequencies between 10 and 88 MHz, the researchers said, 27 of 29 Starlink satellites observed for the study in July emitted "exceedingly bright" UEMR in a range where V1 satellites didn't.
On a positive note, the astronomers said V2 Starlink sats don't appear to be leaking UEMR at 125, 135 and 150 MHz frequencies like V1 did.
"While this is an improvement, it is completely negated by the stronger broadband UEMR, which affects a significantly larger part of the observed frequency range," the team noted. In addition, UEMR coming from V2 Starlink satellites appears to exceed thresholds set by the International Telecommunication Union's Radiocommunication sector.
Radio astronomy is likely to see a number of different effects due to this interference, the team said, with the most noticeable one being low-frequency radio telescopes losing sensitivity as more leaky sats come online.
As time goes on, more satellites will be in a radio telescope's field of view at any given time, meaning that eventually masking of satellite data won't be effective.
"This is the primary reason why broadband UEMR is particularly worrisome for radio astronomy," the researchers wrote. "It increases the risk that the entire observing bandwidth is affected by UEMR for the entire duration of the observation."
Additionally, interferometric telescope arrays that use closely-spaced elements like parabolic dishes or antenna stations may start seeing satellites appearing in the same sky location during observations. That means UEMR won't be decorrelated properly, potentially introducing "artifacts on large spatial scales."
As we noted alongside the previous study, there aren't any international regulations that control the emissions of UEMR from satellites. Without such a rule, it falls to astronomers to beg satellite companies to fulfill their promises of addressing satellite interference.
The team noted in their previous study that it was in discussions with Starlink's parent company SpaceX to mitigate some of the issues, and the company was negotiating changes in "good faith" which it hoped would make it into the second-generation satellites. SpaceX has talked up its fixes to negate light pollution from satellites, and the researchers told us the rocket maker was responsive to the previous research.
"After our initial paper last year, things indeed got better," Federico Di Vruno, astronomer at the Square Kilometer Array Observatory and a co-author on both papers, told The Register in response to emailed questions. "Last year, SpaceX fixed the issue in a matter of weeks. We're not sure why the V2 satellites now show much brighter radiation."
That said, the astronomers remain confident that SpaceX is willing to help. "We have spoken with [SpaceX] and urged them to look into this quickly," Di Vruno said. "Given how quickly they launch new satellites, this case is urgent."
The team doesn't think an in-situ fix is likely to be possible given how such leaks are usually related to the design of onboard electronics, but they're not sure that's the case. SpaceX hasn't responded to questions.
With astronomy-related problems cropping up in each generation of Starlink satellites, it's possible this back-and-forth will continue unless regulators step in and take action, paper co-author Benjamin Winkel told us.
"SpaceX is not the only operator and we expect the number of satellites to exceed 100,000 by the end of the decade," Winkel, an astronomer at the Max Planck Institute for Radio Astronomy, added. "Working on the regulation will take many years, if one can succeed with this at all."
In the meantime, we'll all have to just hope SpaceX continues to be gracious in its responses to astronomers. ®