(ORDO NEWS) — While SpaceX fans enthusiastically follow the company’s achievements, astronomers sadly watch as their work becomes more difficult with each launch of Starlink satellites.
Progress does not come without sacrifice. Therefore, various scientific associations are looking for ways to reduce the negative impact of many new man-made objects in near-Earth space on the quality of data obtained by telescopes.
Some solutions look extreme from the outside – for example, now lasers for adjusting adaptive optics can not be turned off if there is a Starlink satellite in the field of view. And this is tens of watts of radiation!
Many modern optical telescopes (since around the mid-2010s), as well as upgraded systems from earlier builds, rely on adaptive optics.
It allows you to correct the perturbations that the earth’s atmosphere introduces into the flow of light.
This radically increases the resolution of the instruments, but at the same time requires the most complex technical solutions. And not only special deformable mirrors.
To determine how turbulent air flows in the atmosphere change the wavefront, you need a light source with constant and well-known characteristics.
For example, a bright star – then, by analyzing the flux of its radiation, you can determine the distortion parameters and make adjustments.
But there are few suitable stars, so the fields of view for telescopes using such a landmark are limited. There is a solution – not to look for natural bright stars, but to create them manually. This is called a “laser reference star”.
The principle is simple: a laser shines in the “field of view” of the telescope, which excites atoms scattered in the upper atmosphere and makes them glow brightly.
The radiation wavelength is chosen based on the required height of the appearance of such a reference star.
Most modern systems use yellow lasers (589.2 nanometers) to excite sodium atoms, which are relatively abundant at an altitude of 80 to 105 kilometers (mesosphere) – well above the most turbulent layers.
The power of the emitters is measured in tens of watts, so they will automatically turn off if the beam can meet an aircraft or satellite.
In the case of aviation, everything is simple: most aircraft are equipped with ADS-B transponders . Automation just has to track traffic through open channels.
Moreover, observatories are located in regions where air traffic is not very busy anyway. Satellites are a little more complicated: their orbital parameters are constantly changing, and you need to update the ephemeris regularly.
The database for monitoring objects in the near-Earth space that are better not to illuminate with a laser is called Laser ClearingHouse ( LCH ).
It is used not only by astronomers, but also by the military: they also sometimes shoot powerful lasers somewhere there.
And if a satellite that is not included in the catalog appears on the path of the beam, then these are its problems.
Therefore, it is in the interests of their owners to bring satellites into LCH . But contrary to this logic, SpaceX will now remove all Starlink constellation vehicles from there.
This is part of an agreement between Elon Musk‘s space company and the US National Science Foundation ( NSF ).
Now astronomers from all over the world will have the opportunity not to interrupt their observations several times a night.
A powerful tool and an important precedent for other companies that are about to or are already deploying large-scale “constellations” of satellites in low Earth orbit.
In addition to this permission to “shoot” at their devices with a laser, SpaceX has taken on several other obligations.
For example, satellites will turn off their radio transmission when they are over areas where radio telescopes are located.
In addition, the second generation of Starlink devices, despite the increased size, will retain a low albedo (reflectivity).
The goal is for satellites to have an apparent magnitude greater than 7 (the smaller, the brighter), that is, they should not be visible to the naked eye.
Given the height of the orbit, this would give astronomers at least three hours of continuous observations per night.
Recall that these commitments are almost entirely in line with the wishes of the International Astronomical Union (IAU) and the International Dark Sky Association (IDA).
That is, SpaceX cooperates with astronomical organizations and fulfills their requests.
The claim of the International Dark Sky Association to the regulator is that the agency did not conduct an environmental review of the updated devices.
Moreover, a very free interpretation of the laws is used, equating the near-Earth space with the terrestrial environment. In other words, the prospects for a lawsuit are extremely vague.
Earlier, another satellite communications provider tried to delay the launch of the first generation of Starlink and appealed to the fact that an environmental review of their impact on the atmosphere was not carried out.
The court dismissed the claim as literally far-fetched. And the new litigation will be based on even more shaky foundations.
The FCC approval was published last December, the regulator allowed SpaceX to launch 7,500 second-generation vehicles into orbit out of almost 30,000 planned.
With the rest, Elon Musk’s company was asked to wait – they say, we need to think about other companies that also need radio frequency spectra and a safe space between orbits.
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