전영역 이상 해결국(AARO): 위성 플레어링 페이퍼 508 최종 04222025

Correlations of Starlink Satellite Flaring with UAP Observations

All-domain Anomaly Resolution Office (AARO)
An AARO Information Paper
Correlations of Starlink1 Satellite Flaring with UAP
Observations
December 2024
Introduction
With the advent of satellite communication mega-constellations including the SpaceX Starlink,
Eutelsat OneWeb, Amazon Kuiper, and Chinese G60 constellations, there are currently thousands
of artificial satellites in Low Earth Orbit (LEO)2 and tens of thousands more planned for launch
over the next decade [1]. Satellite flaring is an optical phenomenon which occurs when sunlight
reflects off a satellite's surfaces, such as antennas or solar panels. This paper discusses specular
and diffuse reflection of sunlight from man-made satellites and how these effects can be interpreted
as unidentified anomalous phenomena (UAP). It also provides a method for observers to determine
whether observations may be attributable to satellite flaring.
Background
Using reflected sunlight from man-made satellites to observe and track their movement goes back
to the earliest days of space exploration [2]. As noted above, several companies develop and launch
mega-constellations, providing internet access to most of the globe. Currently, there are nearly
10,000 artificial satellites in LEO and this number is expected to grow several-fold over the next
decade [1]. Figure 1 illustrates the location of Starlink satellites in orbit as of December 2, 2024,
at 11:00 AM Eastern Standard Time. As of the end of November 2024, there were over 6,700
Starlink satellites in orbit.
Figure 2 illustrates the concepts of diffuse and specular reflections, which describe how light
bounces off objects. Figure 3 shows how sunlight reflected in these two ways is directed toward
an observer on the surface of the Earth. As seen in the left side of Figure 2, diffuse reflection occurs
when light reflects from a rough or irregular surface. Light impinging upon a rough surface reflects
in many directions, which spreads the light over a large range of angles from the reflecting surface,
as illustrated by the gray colored "light cone” in the Figure 3(a). From a single observation point,
this cone of light can be visible for up to several minutes as the satellite moves in its orbit across
the sky. Additionally, the intensity of reflected light significantly decreases the further away the
observer is from the reflecting surface. At the Earth’s surface, the intensity of diffusely reflected
light from a satellite in LEO will typically have diminished to the point that the brightness is
1 Any reference to a non-federal entity is for informational purposes only and does not constitute an express or implied
endorsement of any commercial service, from AARO, the Department of Defense, or the Executive Branch. This
report focuses on Starlink satellites, but its principles are applicable for any analogous satellite constellation.
2 Altitude for Low Earth Orbit (LEO) ranges from 300km to 2,000km.
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All-domain Anomaly Resolution Office (AARO)
comparable to starlight. Due to their construction and orientation, many man-made satellites in
LEO diffusely reflect sunlight and can appear as stars that move across the night sky.
Figure 1: Graphic of Starlink satellites in orbit. Ref: https://www.heavens-
above.com/StarLink.aspx
Specular reflection, also known as glint, occurs from a very smooth, mirror-like surface as
illustrated on the right side of Figure 2. Unlike diffusely reflected light, the light striking a smooth
surface reflects light at the same, or nearly the same, angle as the incident light. Therefore, the
reflected light cone from a satellite in LEO is much narrower for specular reflection as compared
to diffuse reflection, as illustrated in Figure 3(b). This dramatically increases its observed
brightness by several orders of magnitude, but greatly decreases its observation time as the cone
passes over the observer.
Figure 2: Image illustrating the difference between diffuse reflection (left) and specular
reflection (right).
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All-domain Anomaly Resolution Office (AARO)
These very bright, short lived flashes of light are called “satellite flares” or “satellite glint.” The
design, launch, and operation of SpaceX Starlink mega-constellations has led to a significant
increase in the sighting of satellite flares, dubbed “Starlink flares,” noted by scientists and non-
scientists alike.
Figure 3: Illustration of (a) diffuse reflection of sunlight from a satellite and (b) specular
reflection of sunlight from a satellite as viewed by an observer on the surface of the Earth.
Satellite Flares and Satellite Trains
Figure 4 shows a Starlink satellite in its operational configuration. Starlink satellites’ unique design
and orientation make them susceptible to both diffuse and specular reflection, which causes their
high visibility in the night sky. There are two key components to most satellites: (i) the solar panel,
and (ii) the satellite bus. The solar panel provides a power source for the satellite bus. The bus is
the primary body of the satellite that contains the electronics and systems to perform its designated
mission. The Starlink bus has multiple mirrored panels and flat antenna arrays on the bottom side
of the bus that faces the Earth in its operational configuration. Dependent on the generation of the
Starlink satellite, the reverse side of the large solar panel can be a very efficient diffuse reflector,
while the satellite bus is a very efficient specular reflector [3].
The phenomenon of satellite flaring is not new. This was well documented in the late 1990s and
early 2000s after the launch of the Iridium satellite constellation [4]. However, satellite trains, or
“Starlink trains,” are relatively new and result from the launch process SpaceX uses, which deploys
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All-domain Anomaly Resolution Office (AARO)
dozens of small satellites during a single launch event. Immediately following a launch, and for
several days afterward, these satellites form a distinctive line of bright objects before fading as
they ascend to their final orbital positions. Figure 5 below provides examples of each flare
scenario.
Figure 4: Rendering of Starlink satellite noting the satellite’s bus and solar panel components.
Adapted from [5].
Starlink satellites transition through three orbital phases on their way to their final orbit, with each
phase creating a different visual phenomenology to ground observers. During the launch phase,
dozens of satellites, with their solar panels folded, are loaded in large groups on the rocket delivery
vehicle. Once the delivery vehicle arrives to an initial position in LEO, the satellites separate and
unfold their solar panels.
Figure 5: (a) photo of a string of Starlink satellites called “Starlink trains” not long after launch
on 29 August 2022 [6]; and (b) photo taken by AARO personnel of a satellite flare at peak
intensity for a Starlink satellite, which illustrates how much brighter Starlink flares can be than
surrounding stars. Photo taken before sunrise on March 11, 2024 near Sidney, Nebraska.
Camera settings: [7]
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After the satellites have separated and traversed a specific distance from one another, they enter
the second phase known as orbital raise. During this phase, the satellites navigate from their initial
low orbit to their final orbital altitude, which is nominally 550km for the current generation of
Starlink satellites. During the ascent, drag arises due to skin friction along the satellites’ surfaces.
To reduce the effects of drag, the satellites orient into a streamlined profile by shifting their solar
panels parallel to the Earth, see Figure 6(a). It’s this phase that creates the satellite trains, as light
reflects off each solar panel of the ascending satellites. In the third phase, the satellites reach their
final position called their operational altitude. Here the satellites reorient to their operational
configuration with each satellite bus and its mirrored panels facing the ground and their solar
panels extended above to maximize capture of sunlight.
It is this operational orientation of the satellites, Figure 6(b), that leads to flares or glint when the
geometry of the Sun, satellite, and observer are properly aligned. These flares are orders of
magnitude brighter than starlight and appear in a small section of sky called the “flare window.” It
is possible to have simultaneous flares from multiple satellites moving in differing orbits. To an
observer on the ground, simultaneous flares might appear to be spinning lights, small glowing orbs
that disappear and reappear, or tracing out geometric shapes such as triangles, or other odd
morphologies that move quickly across this small section of the sky. To demonstrate how bright
satellites can appear from the ground, AARO personnel photographed Starlink flaring on March
11, 2024, near Sidney, Nebraska (NE). These photographs are shown in Figure 7 and Figure 8.
These images were taken using a 10 second exposure time which makes them appear as short
streaks in the images versus point sources.
Figure 6: (a) rendering of Starlink satellite in its configuration during orbital raise; and (b)
rendering of Starlink satellite in its final operational orbit. Adapted from [8].
Estimating When and Where to See Starlink Flares
The location and appearance of these flares is a function of the satellite’s location, the Sun’s
position, the time, the date, and the observer’s latitude. Many in the astronomy community are
concerned about the light pollution created by satellite flares from these mega-constellations and
their negative impact on scientific studies as well as the risks posed to the access and safety of
space [9] [10] [11] [12]. This has driven some groups to create software models that predict the
brightness of satellites based on their astronomical locations. Despite this, few publications exist
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that discuss how to the predict the azimuth and elevation angles of satellite flares to assist a ground-
based observer. The key to performing this prediction is to understand the position of the sun
relative to the satellite and the observer.
Figure 7: Image of Starlink flare taken by AARO personnel before sunrise on March 11, 2024
near Sidney, NE. Image was taken using a 10 second exposure time which led to the Starlink
flare appearing as a streak instead of a point source. [7]
Figure 8: Image of multiple Starlink flares taken by AARO personnel before sunrise on March
11, 2024 near Sidney, NE. Image was taken using a 10 second exposure time which led to the
Starlink flares appearing as streaks instead of point sources. [7]
The Sun’s position in the sky can be described using two measurements: (i) the Sun’s altitude
angle, and (ii) the Sun’s azimuth angle. The Sun’s altitude, or solar altitude, is the angle between
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the Sun and the Earth’s surface at the horizon as viewed from an observer’s position on the earth.
During the day, solar altitude is a positive number expressed in degrees above the horizon. Solar
altitude is negative at night, expressed in degrees below the horizon. Solar azimuth describes the
angle to the Sun as referenced from true North at the observer’s position, e.g., 90° being due East
and 270° being due West. Seasonal changes affect the measurement of solar azimuth because of
the Earth's 23.5° axial tilt. In the northern hemisphere, the Sun appears to rise and set further north
each day between the winter and summer solstices. After the summer solstice, this cycle reverses,
and the Sun rises and sets further south each day until the winter solstice. Thus, the specific
azimuths of the rising and setting Sun are also dependent on the observer’s latitude [13]. There are
many online resources that will calculate the Sun’s altitude and azimuth at a given time and date
for a specific observer’s location expressed in latitude and longitude [14] [15]. Similarly, the
satellite’s altitude with respect to an observer’s position can be represented by an angle above the
horizon. This look angle is the elevation angle from the horizon to the observation point in the sky,
i.e., the point in the sky to potentially see flares. These geometries are shown in Figure 9.
The following calculations provide a guide to help observers predict when and where they might
be able to view a satellite flare in the night sky. This is an approximate mathematical treatment
and meant to be a guideline good to within a few degrees to help the observer estimate the look
angles and times for Starlink flares.
Figure 9: Cartoon of Sun’s altitude and azimuth as referenced to the location of an observer on
the Earth. Also defined is the look angle to observation point in the sky.
Using equations (11), (1) and (5) in reference [16], we can calculate the look angle to the satellite,
e, as a function of the Sun’s altitude, .
𝑎𝑎 , (1)
𝜋𝜋 −1 𝑅𝑅𝐸𝐸 𝜋𝜋 −1 𝑅𝑅𝐸𝐸
𝑎𝑎(𝜀𝜀) = 2 −𝜀𝜀 −sin �𝑅𝑅𝐸𝐸+ℎsin�2 −𝜀𝜀��+cos �𝑅𝑅𝐸𝐸+ℎ�
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All-domain Anomaly Resolution Office (AARO)
where is satellite height above the Earth’s surface, is the Earth’s radius. As the zenith angle
is complementary angle of the look angle, , the substitution has been made in Equation
ℎ 𝑅𝑅𝐸𝐸
𝜋𝜋
(1).
𝜀𝜀 𝑧𝑧 = 2 −𝜀𝜀
Equation (1) is a transcendental equation, meaning that it must be solved numerically to find ε as
a function of , the sun’s altitude. Using the mathematical software package MATLAB®, a plot
was generated and is shown in Figure 10 for various Starlink satellite constellations, each of which
𝑎𝑎
have varying orbital altitudes between about 540km and 570km.
Figure 11 illustrates the geometry for a nominal Starlink orbital altitude of 550km. Simple
trigonometry is used to determine that and the angle . For
perfect specular reflection and a satellite bus with its bottom surface that is aligned exactly
θr ≅ θi ≅ 67° A ≡ |a|+ε ≅ 46°
perpendicular to its orbit, . In other words, the satellite and resultant flare are
directly at the horizon. Realistically, no surface is a perfect specular reflector and any small
A = 46° and ε = 0
deviations from exactly perpendicular will reflect light off-axis resulting in . Assuming the
light cone is reflected as much as ± 2° off axis, Starlink flares are then generally visible when the
ε ≠ 0
Sun’s altitude is roughly between -38° and -46° as illustrated in Figure 10. This is determined from
the inset in Figure 10, which shows that flares are visible somewhere between the horizon and
about 10° above the horizon for up to 2° off axis reflection, as indicated by the dashed green lines.
Figure 10: Plot of the Elevation Look Angle from the horizon to the satellite flare window as a
function of the Sun’s altitude below the horizon. Green lines indicate best set of Elevation Look
Angles for observing Starlink flares is up to about 10° above the horizon assuming off-axis
reflections up to 2°.
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Figure 11: Graphi