The effects of Starlink satellites on meteor observations

By dvida | December 31, 2019 | Comments 0 Comment

Effects on different systems

The effect of Starlink will vary depending on the observation method. For example, back scatter meteor radars such as CMOR will not be affected at all. All-sky fireball cameras which aim to record meteorite falls (e.g. the NASA fireball network, the Desert Fireball Network, etc.) should also not be affected much because their limiting magnitudes are quite bright (they aim to record meteors brighter than magnitude -3).

A bright meteor recorded by the NASA fireball network camera in Huntsville

In contrast, meteor orbit and flux cameras have much fainter limiting magnitudes. State of the art Global Meteor Network cameras have limiting magnitudes of about +7 at 25 frames per second, and they might record many more Starlink satellites.

Co-added image of all meteor detections from the night of Dec 30-31, 2019. BE0001 camera in Grapfontaine, Belgium.

How bright will they really be?

In this section a way to simulate the Starlink constellation in Stellarium is given. This website provides a way to generate a satellite orbit TLE file which can be loaded into Stellarium: http://howmanystarlinkswillfillyoursky.com/

I generated the TLE file with about 12,000 satellites (initially proposed configuration which has now been increased about 4 fold) and uploaded it to the GMN site: https://globalmeteornetwork.org//public/starlink_tle.txt

You can load it into Stellarium by following these steps:

Here is how the simulation looks like:

All in all, the situation doesn’t look too bad. The satellites are few and not entirely bright, but some might interfere with meteor observations. Note that the satellites may be 4 times as numerous in the final configuration.

Meteor detection algorithms

Meteor detection algorithms work by keeping a running mean image (usually an average of the last e.g. 256 video frames) which is subtracted from every video frame. The algorithm then detects straight lines propagating in time that are above some standard deviation above that mean (usually about 2.5). These algorithms do detect satellites even now, but they can be easily filtered out by using an angular velocity threshold (meteors have geocentric velocities between 11 and 71 km/s, which translates to an angular velocity range of about 2 – 52 deg/s). Issues might arise with processing times, as the streak will have to be detected and then rejected based on the angular velocity.

The impact is not entirely clear at this point, but if the satellite streaks intersect with meteors, there just isn’t a good way to do good astrometry and photometry measurements, which may force us to reject those observations.

Science loss

In an extremely conservative scenario assuming that there’s a 25% reduction in observation time (I’m assuming that 2 hours out of an average 8 hour night will be unusable) – how will that influence observations of meteor showers and the sporadic background?

Firstly, all optical observations won’t be able to measure meteor showers from the helion source anymore (such as the Daytime Arietids), which are exclusively seen just after sunset and are large contributors to the total yearly shower flux.

Next, we won’t be able to observe small meteoroids on low-eccentricity orbits, as their geocentric velocities are the highest in the morning (more kinetic energy equals more light production, which means a higher detection efficiency). In the last few years we’re just beginning to understand that these meteors seem to be larger, more numerous, and of entirely iron composition, which we still cannot explain. We need more data.

The good news is that observations of well-known annual meteor showers will not be affected much, as long as there’s a large longitudinal coverage, which the Global Meteor Network aims to achieve. But these showers are not very interesting as they are well observed. On the other hand, rare meteor shower outbursts which may last only for hours (or less) and may have a large activity might not be observed if they fall into a “Starlink gap”. These outbursts are the main source of uncertainty in spacecraft meteoroid hazard models, thus their observation is critical. I find it ironic that spacecraft meteoroid hazard models might be hindered by spacecraft.

In reality, the impact will probably be negligible, especially if SpaceX reduces the brightness 25 times. This translates to a ~3.5 magnitude decrease in brightness, which would bring these satellites below the sensitivity threshold of our cameras.

Orbital debris environment concerns

My concerns are mostly about the orbital debris environment. My single grave concern is that if one Starlink satellite is pulverized in a collision with another satellite, this might shred the whole constellation within hours (read more about the Kessler Syndrome), faster than anyone can react to bring them down. I might be wrong, but I still haven’t seen an analysis of what would happen to satellites that are packed so densely in one part of the LEO.

I’m going to finish this post with a quote from Don Kessler’s 2009 overview which was written before Starlink was proposed:

Aggressive space activities without adequate safeguards could significantly shorten the time between collisions and produce an intolerable hazard to future spacecraft. Some of the most environmentally dangerous activities in space include large constellations such as those initially proposed by the Strategic Defense Initiative in the mid-1980s, large structures such as those considered in the late-1970s for building solar power stations in Earth orbit, and anti-satellite warfare using systems tested by the USSR, the U.S., and China over the past 30 years. Such aggressive activities could set up a situation where a single satellite failure could lead to cascading failures of many satellites in a period much shorter than years.