Satellite constellations are a cluster of similar artificial satellites, by type and function, designed to operate in similar and complementary orbits for a shared purpose, under shared control. 

How are Satellites used in Astronomy?

These constellations are used for a variety of purposes like navigation and geodesy, satellite telephony, or Earth Observation. A mega-constellation is a group of large constellations, with hundreds or thousands of satellites.

A list of satellite constellations used for navigation is as follows: GPS (Global Positioning System), GLONASS, Galileo, BeiDou, NAVIC and QZSS. Of these, Global Positioning System or GPS, originally called the Navstar GPS is a popularly known satellite-based radionavigation system owned by the United States government. The navigation services of this satellite constellation are widely used by all of us. 

Some other systems from the list of satellite constellations used for communication are: 

• Sirius Satellite Radio, 
• XM Satellite Radio, 
• Othernet, 
• Globalstar, 
• Iridium NEXT, 
• O3b, 
• Orbcomm, 

among others. 

A list of some other observational satellite constellations includes RapidEye, Disaster Monitoring Constellation, Spire, A-train, SPOT 6 and SPOT 7. 

These satellites, besides serving their primary purpose of navigation, communication, broadcasting etc., also help in the research and studies about space, astronomy and other celestial bodies. 

For instance, the latest generation of low-cost small satellites, especially CubeSats have already proven to be very useful for scientific research as well as for remote sensing and communication. The obvious question is why satellite mega constellations are a threat to the future of space, if they are so helpful.

Do Constellations of Mini Satellites pose a Threat to Astronomy?

To understand why satellite mega constellations are a threat to the future of space, it is important to understand how constellations relate to astronomy. In recent times, the rapid increase in satellite constellations is a simmering crisis. 

We consider space as a shared community resource for all people on Earth. It is held in trust for future generations, like air, water and other land resources on Earth. It contains the heritage and future of humanity’s scientific and cultural practices, including information and evidence for further research. The presence of satellite constellations in space, help us conduct studies and experiments, while serving us on Earth as well. 

However, they also threaten our age-old ability to observe, discover and analyze space from the surface of the Earth. 

It is ironic that devices and technology designed and deployed to study orbits, electromagnetic waves and samples from outer space can now prevent us permanently from further exploration of the Universe. Moreover, astronomical research and its various institutions on Earth are now jeopardized by colonization of space by the satellite industry. 

The Vera C. Rubin Observatory describes that if this is unchecked, the observatory’s future as well as any other campaign will be now a risk to observe the universe in visible light. In 2019, the International Astronomical Union had also expressed concern that the planned mega-constellations of communication satellites may have an adverse effect on the pristine appearance of the night sky when observed from a dark region and, thus, on the astronomical observations.

Issues Posed by Satellite Constellations

One of the primary issues of satellite constellations is how visible they are from the ground, especially at dawn and dusk, or soon after launch, because of the solar panels and other reflective surfaces. 

The biggest factor in light pollution from satellite constellations is the size of these satellites, which is on the order of a meter. Thus, the obvious solution to mitigate this problem is to reduce the size of these satellites. Other solutions include measures to darken the satellites as well as, to calculate satellite positions to understand observational ‘avoidance zones’ by time or location. This would enable the observatories on Earth to make the necessary studies without obstructions. 

In November 2019, a group of 19 satellites, exemplified by California-based SpaceX’s Starlink network, passed over the Cerro Tololo Inter-American Observatory, disrupting astronomical observations and hindering the research. The vast groups of thousands of these Starlink satellites are designed to provide global Internet coverage from space. However, such a huge cluster of these satellites reflects sunlight to the ground, thus obstructing views from Earth. They could also cause optical–infrared spectrum interference.

Low-Earth orbit satellites (LEOsats) have a negative impact on the ground-based optical and infrared astronomy. Due to the thousands of the LEOsats, there is a fear of a disastrously altered night sky. This is due to a phenomenon called “Kessler syndrome” in which a cascading series of high-speed collisions could reduce thousands of satellites to an orbiting rubble pile in an impenetrable shell around the Earth. This debris could be a hazard to the atmosphere and the Earth’s surface. 

The NASA Orbital Debris Program Office, in partnership with the US Department of Defense, tracks over 500,000 objects in orbit with sizes over a certain threshold. Moreover, all US satellite operators are required to file detailed collision avoidance plans before launching the satellites as a precautionary plan.

Another issue caused due to satellite constellations is that of the solar heating effects i.e. the surfaces of these numerous satellites are often made of highly reflective metal. Thus, the reflections from the Sun in the hours after sunset and before sunrise make these satellites appear as dots moving in the night sky. 

Although many of these reflections may be too faint to see with the naked eye, they can still cause harm to the sensitive optical instruments and lenses of large ground-based astronomical telescopes due to the solar heating effects. Moreover, the aggregated radio signals emitted from the satellite constellations can still threaten astronomical observations at radio wavelengths, thus having detrimental effects on radio astronomy frequencies. 

It is also important to note that the most prominent trains of satellites that are recorded in images and videos, are observed immediately after launch and during the orbit-raising phase when they are considerably brighter than they are at their operational altitude and orientation. 

Thus the global effects of these satellites depend on how long the satellites are in this phase and on the frequency of launches. Hence, while it is impractical to expect the launch of satellites to stop completely, one way of mitigating the harmful effects is by coordinating and spacing out the launch of satellites so as to reduce the obstruction.

Conclusion

A lot of discussions are being conducted for the protection of the uncontaminated view of the night sky from dark places. There are detailed studies and reports being conducted by the astronomical organizations across the world to investigate how constellations relate to astronomy and how constellations of mini satellites pose a threat to astronomy. 

The American Astronomical Society (AAS), in collaboration with the International Astronomical Union, will continue to discuss with space agencies and private companies that are planning to launch and operate currently planned and future satellite constellations. 

These discussions and collaborative efforts will support the progress of fundamental science such as astronomy, celestial mechanics, orbital dynamics and relativity, while enabling the satellites to operate with maximum efficiency.