ann23038 — Announcement

Star Trails Over Gemini South
20 October 2023
NSF’s NOIRLab Seeks Reclassification of Astronomical Lasers due to Satellite Constellation Proliferation
US astronomical community urges for reclassification of laser guide stars

Following a workshop organized by NSF’s NOIRLab at Vandenberg Space Force Base, a new report has been released describing the complex relationship between astronomical observatories, constellation satellite operators, NASA, the US Space Command and the US Air Force. With the proliferation of commercial satellites, the Office of Space Commerce at the Department of Commerce is also likely to be taking an increasingly important role. The report calls for US astronomical lasers, including those operated by NOIRLab, to be considered for reclassification at a lower risk level under the Laser Deconfliction policy that protects satellites from being ‘blinded’ by lasers. The proposal is supported by the International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (CPS).

Plans from several companies around the world will potentially grow the number of constellation satellites to several hundred thousand if all internationally notified systems [1] are brought into use — a 100-fold increase. In addition to issues this will pose to radio astronomy facilities, this can pose a major problem for current and upcoming optical telescopes such as the Thirty Meter Telescope and the Giant Magellan Telescope — both part of the US Extremely Large Telescope Program — which will require the use of laser guide stars and adaptive optics to achieve their potential. A worst-case scenario would see these lasers shut down so often each night that observations by astronomical observatories will become critically disrupted.

Telescopes such as those at the International Gemini Observatory and Southern Astrophysical Research Telescope (SOAR), both operated by NOIRLab, rely on the use of lasers to gather precise data and achieve finely focused images. Laser beams propagated high into the atmosphere create ‘artificial stars’ that adaptive optics systems are able to lock onto so that, by monitoring the twinkling of the artificial stars, they can alter the shape of a telescope’s mirror in real time to compensate for atmospheric turbulence.

The US Department of Defense established and implemented the Laser Deconfliction policy to prevent damage to objects in all orbits (including those carrying humans in space). There is a categorization process to determine the potential harm a laser could have on a space object. Astronomical lasers are currently categorized as Category III, which is the highest-risk category. Though many objects are omitted from deconfliction, each time a space object that is susceptible to the laser's wavelength and power intersects the laser's spatial uncertainty zone, science observations have to be paused, interrupting data collection between 30 and 120 seconds.

In 2015 there were an estimated 1400 active satellites in low Earth orbit. As of August 2022 there were 5311, with that number growing consistently as satellite constellations such as SpaceX’s Starlink are placed in orbit. This increase has seen the number of times optical astronomy observatories have had to pause observations increase by a factor of at least two. SpaceX, working with the NSF, has already waived the Department of Defense Laser Clearinghouse protection which has reduced the number of closure windows. While this waiver does not extend to other satellite constellation operators, especially those that don't require approval from US regulation authorities, the Federal Communications Commission has recently added required coordination with NSF for optical astronomy to several satellite authorizations [2]. OneWeb recently signed a coordination agreement with NSF and has agreed to also consider requesting a waiver from the Laser Clearinghouse after an analysis of astronomical lasers on their system is completed.

To address this growing problem, representatives from US Space Command’s Laser Clearinghouse, the US Air Force’s Satellite Assessment Center, NSF, NOIRLab, NASA and the satellite industry including SpaceX, convened for a workshop at Vandenberg Space Force Base on 12–13 April 2023. The workshop concluded that the best solution would likely be to reclassify astronomical lasers from Category III to a lower category, although other potential avenues were also discussed. Category II requires the coordinates of the point of origin of the lasers, and the laser’s parameters including power and wavelength, to be made available to satellite constellation operators so they can request mitigation if necessary. Category I declares a laser to be safe and not to pose a threat to satellites.

To determine which category is appropriate for which laser, the workshop concluded that the best way forward was for a Probabilistic Risk Assessment to be conducted to determine the vulnerability of satellites from specific astronomical lasers. This risk assessment would then be submitted to the Laser Clearinghouse for coordination. 

To ensure that this process runs smoothly to the satisfaction of all parties, and to allow ground-based astronomy to continue to thrive, close collaboration between the NSF, satellite owner-operators, the Department of Defense, the Department of Commerce’s Office of Space Commerce, and current and future observatories is essential. The IAU CPS commends the work of NSF’s NOIRLab, SpaceX and all involved parties for the continuous collaboration to improve the coexistence between astronomical observations and large satellite constellations.


[1] See the website of the IAU Centre for the Protection of the Dark And Quiet Sky from Satellite Constellation Interference.

[2] Coordination with NSF for mitigating impact to optical astronomy is now required for SpaceX, Kuiper, OneWeb, Planet Labs, and ICEYE.

More information

NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory), the US center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on Iolkam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

The IAU is the international astronomical organization that brings together more than 12,000 active professional astronomers from more than 100 countries worldwide. Its mission is to promote and safeguard astronomy in all its aspects, including research, communication, education and development, through international cooperation. The IAU also serves as the internationally recognised authority for assigning designations to celestial bodies and the surface features on them. Founded in 1919, the IAU is the world's largest professional body for astronomers.

The International Astronomical Union’s Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) is a global organization co-hosted by the US-based NSF’s NOIRLab and the SKA Observatory (SKAO), under the auspices of the IAU. The CPS facilitates global coordination of efforts by the astronomical community in concert with observatories, space agencies, industry, regulators and other sectors to help mitigate the negative consequences of satellite constellations on astronomy.

The SKAO, formally known as the SKA Observatory, is an inter-governmental organization composed of Member States from five continents. Its mission is to build and operate cutting-edge radio telescopes to transform our understanding of the Universe, and deliver benefits to society through global collaboration and innovation. Headquartered in the UK, its two telescope arrays will be constructed in Australia and South Africa and be the two most advanced radio telescope networks on Earth. Through the development of innovative technologies and its contribution to addressing societal challenges, the SKAO will play its part to address the United Nations’ Sustainable Development Goals and deliver significant benefits across its membership and beyond. The SKAO recognises and acknowledges the Indigenous peoples and cultures that have traditionally lived on the lands on which the SKAO facilities are located.



Julian Christou
Phone: +1 520 307 4358

Lars Lindberg Christensen
IAU Director of Communications/NOIRLab Head of Communications, Education & Engagement
Cell: +1 520 461 0433/+49 173 38 72 621

Mathieu Isidro
IAU CPS Communications and Outreach Lead
Phone: +44 7824 016 126

Josie Fenske
NSF's NOIRLab Communications

About the Announcement



Star Trails Over Gemini South
Number of telescope closures due to satellites