This article is from WeChat public account: scientific compound (ID: kexuedayuan) , author: Lee Hui-chao, from the title figure: vision China
On November 11, 2019, SpaceX’s second batch of 60 “Star Chains” (Starlink) satellites by Falcon 9 The rocket was launched.
These satellites are a small part of Musk’s massive Space Internet Satellite program. According to Musk’s vision, the star chain will reach the scale of 12,000 in the mid-2020s. By then, many users in the world without high-speed fiber-optic Internet access will be able to obtain high-speed and reliable Internet services through an additional small satellite receiver. In addition to SpaceX, Amazon and OneWeb in the United States are advancing similar projects, but the scale is much smaller than StarChain, and the number of satellites after completion is about several thousand.
Star chain satellites during batch launch into orbit (Image source: SpaceX)
Some of these seem to benefit humanityThe project has caused anxiety among some astronomers. In order to get a pure night sky, they had to build the telescope to the inaccessible mountains of Chile, Amasones, Mauna Kea, and other places, and sometimes even sacred mountains to repair the telescope and the indigenous people Lawsuit. And Musk’s star chain may destroy this last piece of clean sky without light pollution.
Real-time images of atmospheric parameters measured by lasers at very large telescopes set up by Chile’s Southern Observatory in Chile (Image source: European Southern Observatory)
The reflection of the star chain may bring great trouble to optical sky surveys
Starchain and other Internet satellite systems to be deployed by companies are planning to communicate satellites in low earth orbit . Compared with communication satellites in synchronous orbit, communication satellites in low-Earth orbit can provide shorter communication delays and minimize the occurrence of “high-ping soldiers.”
Because satellites in low-Earth orbit are moving relative to the ground, a large number of satellites must be deployed to ensure that a sufficient number of satellites over a specific location can provide services to users. As a result, the number of satellites contained in satellite constellations is often very large, often thousands. At the same time, the rapid development of microsatellite technology over the past few years has greatly reduced the threshold for satellite release and made it possible to construct such satellite constellations.
Star Chain Satellite (Image Source: SpaceX)
Astronomers are no stranger to the twinkling satellites in the sky. The iridium star system, which had previously failed and was taken over by the US military, occasionally entered the telescope’s field of vision. However, as the number of iridium stars is only a few dozen, the probability of this situation is not high, and astronomers have not paid much attention to it.
An indicator parameter for astronomical telescopes is “field of view”. When we take a picture with a mobile phone, if you use the zoom function to zoom in and zoom in on the scene, the imaging field of view at this time is smaller. On the contrary, if you zoom out and zoom out the scene, the imaging The field of view is relatively large. When the field of view is small, a specific object can be more prominently displayed, and when the field of view is large, the entire scene can be captured. As for astronomical telescopes, there are also telescopes with a smaller field of view and a larger field of view. The former is generally used for more detailed observation of selected celestial bodies, while the latter is generally used for large-scale sky surveys, which is equivalent to Constantly taking pictures of the entire sky, conducting “censuses” of celestial bodies, so that astronomers get batch data on the changes of each celestial body.
The usefulness of sky surveys is manifold. For example, astronomers can use sky surveys to observe sea-selected celestial bodies, find potentially newly discovered celestial bodies, and use telescopes with smaller fields of view to obtain more detailed information. At the same time, a large amount of celestial body information can also enable scientists to reach some common conclusions, or select some abnormal celestial bodies from a large number of celestial bodies for research. In addition, the time interval between repeated observations of the same area by sky surveys will not be long, which can support the study of some fast-changing phenomena in time-domain astronomy.
When the constellation of communication satellites has increased the number of satellites in orbit by several orders of magnitude, perhaps the first to suffer from this type of optical telescope for sky surveying. According to the calculation results of Stanford University astronomer Bruce Macintosh, quoted by the National Geographic website, the United States established a large-scale integrated survey telescope in Chile (LSST) In the images taken in the next hour or two after dusk, each image may invade 1-4 star-chain satellites. After dusk, the sun has just fallen below the horizon. If the location is appropriate, the satellite can reflect all the sunlight shining on it to the ground, showing very bright spots in the sky. This phenomenon is particularly pronounced in summer in mid-latitude regions.
LSST under construction (Image source: lsst.org)
To the confusion and worry of astronomers, Starlink satellites seem to be more capable of reflecting sunlight than other satellites. After the launch of two batches of satellite satellites, many amateurs around the world have enjoyed chasing the flash of stars.
Examples of astronomical observations affected by the International Astronomical Union. The bright points in the picture are the celestial bodies that the Lowell Observatory is trying to observe. The bright lines in the picture are the traces left by the star chain satellite invading the telescope’s field of vision (Image source: International Astronomical Union)
LSST ’s main tasks include the observation and research of dark matter and dark energy phenomena, as well as the search for small celestial bodies that pose a potential collision threat to the earth. An astronomical device that provides protection for possible future human calamities. If its observation is severely disturbed by a star chain or other communication satellite constellation, it is not only the telescope’s gold owner, the US Department of Energy, and scientists who carry out related research. In addition to LSST, there are currently many sky surveying projects around the world, such as the Sloan Digital Sky Survey in the United States and the LAMOST Sky Survey Telescope in China. If the light pollution problem of star chains becomes serious, they will be potential victims as well as LSST.
Musk responded, but still couldn’t dispel astronomy doubts
For the concerns of the astronomy community, Musk initially responded that there were so many satellites in the sky, and he could put in more. Moreover, the obvious point of light that people see is the state when the satellite chain satellite just entered orbit. As they gradually rise to the working track, the brightness will diminish to an unaffected level. However, astronomer Jonathan McDowell of the Harvard-Smithsonian Astrophysics Center found that the first satellite satellites launched in May this year, although the altitude has risen to about 550 kilometers, their brightness can still reach about 4 to 7 magnitudes. Magnitude not only can interfere with telescope observations, but even people can see with the naked eye.
Images of star-chain satellites drawn overnight by Dutch astronomy enthusiasts (Image source: Phys.org)
After finding that astronomers ’questions are getting louder and louder, and even the International Astronomical Union has officially issued a statement on this, Musk tweeted that they will take measures in the future to reduce satellite reflections, thereby reducing Interference from astronomical observations. But this did not dispel astronomers’ doubts. In addition to the promises posted on Twitter, SpaceX did not give details on how to reduce satellite reflections, and astronomers could not obtain information on future star chain orbits, and could not conduct systematic research to accurately assess the star chain’s impact on optical astronomy. The threat of observation.
Moving the ground telescope to space to solve the problem of light pollution?
Some people say that the Hubble Space Telescope in low-Earth orbit has achieved world-renowned success. The Webb Space Telescope, which will go to the sky in the future, will raise the observation capabilities of the space telescope in the visible light band to a new height. Why do you need to stay on the groundHow about building telescopes and astronomical observations?
In fact, although the space telescope does not need to consider the effects of the atmosphere and satellite flash on observations, its caliber is still not comparable to ground-based telescopes. The larger the aperture, the better the angular resolution of the telescope, and the more detailed the structure can be seen. At the same time, ground-based telescopes can continuously update and upgrade equipment to apply the latest technology to observations. Once the space telescope is in the sky, it means that the parameters of all instruments will be locked and cannot be updated.
Telescope for Sloan Digital Sky Survey (Image source: sdss.org)
In addition, for sky surveys, if you want to launch a telescope into space, you must consider the limitation of the amount of observation data on the bandwidth of celestial communications, but there is no such problem on the ground. In the end, getting anything into space can inflate capital costs and technological complexity. At present, the Webb Space Telescope has spent nearly $ 10 billion of NASA’s huge funds, and the sky is still in the air. Astronomers estimate that no gold master can be found and can move all existing astronomical observation capabilities into space.
Interfering with radio observation, potential space junk, star chain satellites have many problems
Even if the star chain really no longer flashes, eliminating the threat to optical astronomy, its threat to radio astronomy still exists. Radio astronomy observes by receiving radio signals emitted by celestial bodies, so the general radio telescope looks more like a huge satellite antenna, or a huge pot.
In recent years, with the increasing use of radio, radio astronomers have been dealing with other radio users such as satellite communications through organizations such as the International Telecommunications Association. interference. Once a large number of Internet communication satellites are deployed in low orbit, radio astronomy”Fighting” for frequency will become more difficult. At the same time, the diameter of radio telescopes is tens of meters, and the diameter of radio telescopes built according to terrain such as FAST has reached 500 meters. There is currently no concrete feasible solution for building such a radio telescope in space.
In addition to its impact on astronomical observations, Space junk is also a potential problem that star chains can cause. Of the first 60 StarChain satellites launched in May this year, 3 have lost contact with the ground and become potential space junk. Although the resistance of the upper atmosphere can make them fall naturally, it takes a long time from the loss of contact to the fall. According to a study by the NASA Space Debris Project Office, satellite constellations with a number of thousands can reach at least 99% of the satellites’ ability to actively control their de-orbit when they are nearing their end of life, and quickly fall into the atmosphere to burn and burn. The probability of a possible satellite collision in low earth orbit does not fall into a state of runaway. This study assumes that the satellite’s orbital altitude is about 1,000 kilometers, and the current orbital altitude of 550 kilometers planned for the satellite chain. As for the star chain, although the possibility of the outbreak of space garbage problems has been reduced due to the stronger orbital atmospheric resistance, SpaceX does not seem to conduct similar research to determine the relationship between the satellite chain system satellite reliability and the risk of space garbage.
Concept map of the satellite constellation of satellite chains, (Image source: technology.org /)
Conclusion
If you want to own a new car, you must first get the car purchase qualification, go through a series of formalities, pay related fees, and comply with traffic regulations in daily driving. All this is for the public resources to be effectively and appropriately allocated and used to maintain the sustainable and stable operation of the city. In space, there is still no coercive international law or convention to maintain the corresponding order. When SpaceX and other businesses prepare for ambitiousWhen occupying space, no international agency or organization can regulate their behavior and provide adequate protection for the night sky and orbits shared by human beings.
Different from automobile ships and planes, As long as the spacecraft is in orbit, it will turn around the whole earth and even fly away from the earth, using the world’s and all human resources. How to keep space from falling into the jungle can be a more important issue.
References:
1.Liou et. al., NASA ODPO’s Large Constellation Study, Orbital Debris Quarterly News, 22 (3), 2018
2.https: //www.nature.com/articles/d41586-019-03446-y
3.https: //www.iau.org/news/announcements/detail/ann19035/
4. https://www.space.com/spacex-starlink-astronomy-observations.html
5. https://www.space.com/astronomy-group-worries-about-starlink-science-interference.html
This article is from the WeChat public account: scientific compound (ID: kexuedayuan) , author: Lee willSuper