The brightness of AST SpaceMobile’s BlueWalker 3 satellite in low Earth orbit is causing concern among astronomers due to its potential impact on night sky observations. Here are some key points about this situation:
- Bright Satellite: BlueWalker 3, a prototype satellite launched by AST SpaceMobile in September 2022, has been observed to be exceptionally bright in the night sky. After deploying a large 64-square-meter antenna to support direct-to-device communications, the satellite’s brightness increased substantially, making it one of the brightest objects in the night sky.
- Magnitude Measurements: Astronomers use a magnitude scale to measure the brightness of celestial objects. BlueWalker 3’s brightness increased from magnitude 6, which is the limit of naked-eye observations in dark areas, to magnitude 0.4. This made the satellite as bright as certain prominent stars like Procyon and Achernar.
- Concern for Astronomy: The increase in brightness of commercial satellites like BlueWalker 3 poses challenges for astronomers. It can interfere with observations of celestial objects and impact the quality of astronomical research. Larger and brighter commercial satellites, particularly those in planned constellations, are of particular concern.
- Ongoing Trend: The study highlights an ongoing trend of launching larger and brighter commercial satellites. Given the plans to launch many more such satellites in the future, the potential impact on astronomy is a growing concern.
- Mitigation Efforts: Astronomical organizations, such as the International Astronomical Union Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS), are actively studying the impact of satellite constellations on astronomy and working on methods to mitigate these impacts.
- Balancing Space Activities: The situation underscores the need for a balance between space activities, including satellite deployments, and the preservation of the pristine and dark night sky that astronomers rely on for their research.
As more commercial satellites are launched into orbit, addressing their impact on ground-based astronomy remains a challenge that requires cooperation between space operators and the astronomical community to find workable solutions.
AST SpaceMobile’s response to concerns about the brightness of its satellites and their impact on astronomy involves several measures and collaboration with space and astronomy organizations:
- Collaboration with NASA and Astronomy Working Groups: AST SpaceMobile is collaborating with NASA and certain astronomy working groups to develop advanced industry solutions to address concerns related to the brightness of its satellites. While not directly addressing the observations in the paper, the company is actively engaging with experts in the field to find solutions.
- Brightness Reduction Measures: The company is working on practical methods to reduce the brightness of its satellites. This includes “roll-tilting flight maneuvers” to minimize sunlight reflection to the ground. Additionally, AST SpaceMobile plans to incorporate anti-reflective materials on its future satellites to further mitigate the issue.
- Comparatively Smaller Constellation: AST SpaceMobile emphasizes that its satellite constellation will be smaller in terms of the number of satellites. The company estimates that it will require only about 90 satellites to achieve substantial global coverage. In contrast, larger constellations, such as OneWeb and SpaceX, have significantly more satellites in orbit.
- Cooperation with Astronomical Community: Other satellite operators, like SpaceX, have also worked with astronomers to address concerns about satellite brightness. SpaceX, for instance, has taken steps to reduce the brightness of its Starlink satellites and signed coordination agreements with organizations like the National Science Foundation (NSF). The NSF is working on similar agreements with other satellite constellation operators, including Amazon and OneWeb, to ensure cooperation in mitigating the impact on astronomy.
As satellite constellations continue to expand, these efforts reflect the increasing recognition of the importance of balancing the benefits of satellite technology with the preservation of dark skies for astronomical research. Collaboration between space operators and the astronomical community is essential in finding effective solutions to this issue.
Astronomers have raised concerns not only about the optical brightness of AST SpaceMobile’s satellites but also the potential for radio astronomy interference:
- Radio Astronomy Interference: AST SpaceMobile’s satellites operate in frequencies allocated for terrestrial communications, which are in close proximity to the frequencies used for radio astronomy. Radio telescopes are typically situated in “radio-quiet zones” to avoid interference from terrestrial sources. However, satellite transmissions in these frequencies could potentially interfere with radio astronomy observations, even within designated radio-quiet zones.
- Coordination Measures: AST SpaceMobile has stated its intent to avoid broadcasting from its satellites into or near the U.S. National Radio-Quiet Zone in Virginia and West Virginia. The company also plans to avoid other radio astronomy locations as required, even if they are not officially recognized. This proactive measure is designed to minimize the potential interference with radio astronomy.
- Balancing Progress and Impact: Astronomers acknowledge the need for improved connectivity and internet access, especially in rural and underserved areas. However, they emphasize the importance of balancing this progress with the negative impact of bright satellites on the night sky and radio astronomy observations.
In summary, the coexistence of satellite constellations and astronomical research presents challenges, particularly in addressing issues related to optical brightness and radio frequency interference. Collaboration between satellite operators, astronomy organizations, and regulatory bodies is crucial to finding solutions that ensure both progress in satellite technology and the preservation of dark skies for astronomical research.