Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHODS AND SYSTEMS FOR REDUCING RISK OF AIR COLLISIONS
FIELD OF THE DISCLOSIIRE
[0001] The disclosure relates to methods and systems for identifying and
reducing the risk of air
collisions, specifically collisions between aircraft in the airspace and re-
entering space debris.
Aircraft can include any airplane, helicopter, launch vehicle, suborbital or
orbital spacecraft, drone,
high-altitude balloon, sport parachute or other machine capable of flight. Re-
entering space debris
might include spacecraft, satellites, launch vehicles, meteors, asteroids,
other space objects or
fragments of one or more of these objects.
RACKGROUND
[0002] Space debris represents a hazard for aircraft. Due to relative speed
and associated energy, a
collision with one or more fragments of reentering space debris can have
catastrophic consequences
including the loss of life. The likelihood of an individual aircraft
experiencing such a collision is
remote. However, the cumulative likelihood of occurrence is sufficient that
the hazard warrants
implementing protective measures to mitigate the risk. Current vulnerability
models show that an
impact anywhere on a commercial aviation transport with debris of mass above
300 grams would
produce a catastrophic failure, resulting in a loss of the aircraft and the
loss of life of all people on
board.
[0003] Both reentering meteorites and man-made space debris pose a threat
aircrafL Estimates of
the total of reentering debris entering annually is shown in Table 1.
Number of Objects and Total Mass Entering the Atmosphere Annually
Number/Year Total Mass
Object
> 100g (tons)
Metente 1368O 53
Man-Made Space 2,267 1 40
Debris
Table 1
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[0004] The number of reentering operating and inactive space objects is also
an important factor in
assessing risk. Available data is shown in Table 2. For the first seven months
of 2020, there were
approximately 145 such objects. These numbers of reentries include controlled
reentries, including
the return of SOyUZ manned capsules, These statistics do not include the
stages which have been
deorbited rapidly after their launch as part of normal procedures.
Number of Satellites entering the atmosphere
Object 2017 2018 2019 2020 (Jan-July)
(approx.)
--
Number of 200 248 323 145
1
Satellites
Table 2
[0005] Air traffic density is also an important variable in assessing aircraft
risk. Although there are
several methodologies and tools to assess the risk for the public on the
ground due to a reentering
space debris event, few studies have been performed. for quantifying the risk
for aviation. It is
important to understand and quantify the effect of space debris to the
population, both on the ground
and on aircraft.
[0006] Space debris are manmade objects in orbit around the Earth, which no
longer serve a useful
purpose. The U.S. Space Surveillance Network regularly tracks and maintains in
its catalog an
estimated 28,21.0 items in orbit (as of January, 2021). The decay duration of
the space debris
depends on the object's altitude, area-to-mass ratio and solar activity.
[0007] Number of debris objects estimated by statistical models to be in
orbit, according to the
European Space Agency, as of January 8, 2021 is shown in table 3.
Size of Objects Number of Objects
objects greater than 10 cm 34,000
objects from greater than 1 cm to 10 em 900,000
objects from greater than 1 ram to 1 cm 128 million
Table 3
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[0008] Table 4 below provides general statistics of tracked objects. Note,
what is called "payload"
here are satellites, including dead ones; it is the sum of active and debris
satellites
Number of tracked objects METHODS AND SYSTEMS FOR REDUCING RISK OF AIR
COLLISIONS
ks. ,
4'W 111:1
S64:4 2MS
astsc 1=55
Table 4
[0009] The disintegration of the Space Shuttle Columbia on February 1, 2003
identified the
seriousness and necessity of reentry safety. It highlighted the need to select
vehicle reentry
trajectories that minimize the risk to ground populations and the need to take
measures to keep air
traffic away from falling debris. The Columbia accident demonstrated the need
for a deliberate,
integrated, and international approach to public safety during reentry
operations, particularly for the
management of air traffic and space operations.
[0010] The breakup of the Space Shuttle Columbia began at an altitude of about
60 km and led to a
"progressive breakup" in which a primary structural failure resulted in large
pieces which were
followed by smaller pieces that continued to shed off the larger pieces during
their descent. Large
pieces (landing gear, turbo pumps, etc.) had high ballistic coefficients
(defined as the ratio of an
object's mass to its drag coefficient times reference area), making them less
susceptible to wind and
drag.
[0011] Thus, these large pieces fell quickly, reaching the wound within three
to five minutes. While
there was no protection from these fragments, they comprised a very small part
of the total debris
field. Smaller pieces (thermal tiles, fragments of the cargo bay doors, etc.)
had low ballistic
coefficients, and were carried by the wind as they fell. Some developed a
small amount of lift as
they fell. As a result, these pieces took as long as approximately 40 minutes
to reach the ground.
While small and light, some of these pieces were large enough to substantially
damage aircraft. Still
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smaller pieces (similar to confetti and assumed to be harmless to aircraft)
remained airborne for over
two hours.
[0012] The Columbia accident showed that a Space Shuttle Orbiter failure
during reentry could
produce risks to aircraft that exceed the threshold that was subsequently
established by NASA for
safety of the public by several orders of magnitude. Prior to this accident,
neither the FAA nor
NASA took active precautions to protect uninvolved aircraft from the potential
hazards of Space
Shuttle debris during a planned reentry.
[0013] Standard practices have been applied and showed that the probability of
one of the exposed
aircraft being struck by a piece of falling debris could have been as high as
0.003 to 0.1. This is a
range from one in 10 to three in 1,000. The standard practices at the time of
the study were
provided in the Range Commanders Council (RCC) Standards 321-07
[0014] In the 40 minutes required for the majority of the debris from the
Space Shuttle Columbia to
fall to the Earth's surface, as many as nine civil aircraft flew through the
falling debris. Fortunately,
no damage was reported to any of those aircraft, a study conducted by ACA,
Inc. (now .ARCTOS)
of Torrance, CA applied (what is now a standard) practices and showed that the
probability of one
of these aircraft being struck by a piece of falling debris could have been as
high as 0.003 to 0.1.
This is a range from one in 10 to three in 1,000. The standard practices at
the time of the study were
provided in the in .R.CC 321-07 "Common Risk Criteria for the National
Ranges," published by the
Range Commanders Council (RCC).
[0015] After FAA executives were briefed about the potential for aircraft
impacts from the
Columbia accident, the FAA established procedures to be used as a real-time
tactical tool in the
event of a Columbia-like accident to identify how to redirect aircraft around
space vehicle debris,
[0016] Although the Space Shuttle retired from service in 2011, there are new
government and
commercial space transportation systems that plan suborbital and orbital
operations. These
necessarily include launches, reentries and also on-orbit operations. Across
this range of vehicles,
the available reaction time between space vehicle breakup and entry of debris
into the National Air
Space can range from zero (if the vehicle is in the air traffic environment at
the time of the failure)
to upwards of 90 minutes (if the vehicle is nearly in space and at orbital
speed at the time of
failure).
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[0017] Air Traffic Operators will require dependable information and
procedures to cope with the
sudden onset of such an event and with the short lead-time that will be
available until debris enters
the airspace. To address those operational needs, FAA has been developing a
systematic,
standardized space vehicle debris threat management process that can be
applied to the variety of
space vehicles that will eventually operate in the NAS.
[0018] The procedures established after the Space Shuttle Columbia accident to
clear the airspace in
case of a space vehicle breakup are only feasible for controlled reentries
such as those typically
performed for crewed missions, or at the end of a mission by the cargo
vehicles that ferry spare
parts, consumables, and other items to the International Space Station. The
eventual disposal of the
International Space Station will require a plan to, potentially first
dismantle the structure, and then
d.eorbit the entire Station or each segment of the dismantled Station through
one or more
controlled reentries. In such cases specific maneuvers are planned either to
bring the vehicle intact to
a preplanned location, at sea or on ground, or to place the debris field,
following
fragmentation/explosion, away from inhabited areas, like into the SPOUA (South
Pacific Ocean
Uninhabited Area). Unfortunately, most reentries are uncontrolled.
[0019] Uncontrolled reentries occur as the atmosphere slowly drags an orbiting
object deeper into the
atmosphere. Moving at speeds greater than 7 km/sec, the object begins to heat
as it encounters
increasingly significant atmospheric density below the reentry inteiface
altitude of about 120 km.
The heating increases as gravity and drag lower the altitude, and eventually
low melting point
materials reach a condition where they fail. Heating on the primary object and
on released fragments
continues to increase, and aerodynamic deceleration loads also begin to build.
Aluminum structures
have been observed to fail consistently at approximately 78 km altitude,
causing a catastrophic
breakup of the object. This major breakup phenomenon near 78 km altitude is
remarkably
independent of vehicle attitude and rates, diameter, shape, and entry flight
path angle in between ¨
0.3 and ¨1.5 . High heating rates and aerodynamic forces that produce thermal
melting, thermal
fragmentation and mechanical fracture during reentry are the primary causes of
the various external
destruction events.
[0020] There are competing effects that complicate the prediction of whether a
given object will
survive to impact or demise. However, reentry heating rates are approximately
proportional to the
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velocity cubed and inversely related to the radius of curvature. Thus, small
objects released early
often demise, unless they have low enough density to slow down rapidly.
[0021] The "footprint" is the area where debris hazards are predicted to
"land" given a reentry
break-up. A typical footprint for a reentering spacecraft of 5,000 kg or more
is approximately 2,000
km long, contained within 35 km of the original ground track. For a reentering
launch stage, a
typical footprint length is between 100 and 400 km. The major reentry breakup
process takes place
over a period of approximately 5 min. Objects that survive the reentry
environment continue to
decelerate and most will approach a terminal velocity proportional to the
square root of their
ballistic coefficient at about 18 km. From this point, the surviving fragments
fall nearly vertically,
with their trajectory blown by winds and some additional dispersion
potentially due to lift.
[0022] Current forecasts of the time and location of such uncontrolled
reentries may have errors of
several thousand kilometers and arc available only minutes before reentry_
Consequently, air traffic
controllers cannot issue specific "Notice To Airmen" (NOTAMs) on impending
reentries.
NOTAMs are effective only when mission planners can provide a specific time
and location in
advance, as in the case of controlled reentries_ As such, air traffic is
subjected to an annual total flux
of reentering space debris and meteoroids whose collision risk is not
generally controllable.
[0023] in addition to large objects, there are several thousand smaller space
debris, resulting from
on-orbit fragmentations due to explosions or collisions that reenter annually.
[0024] Reentry of fragments from launch vehicle are also important to consider
as risk to the
airspace. Consider the May 5, 2020 launch of a Long March 5B rocket from the
Wenchang launch
site on China's southern Hainan island. Scientists tracking orbital debris
from the launch detected a
20-ton piece of debris from the Chinese rocket as it passed over New York City
and Los Angeles
before it crashed into the Atlantic Ocean. There were between 15 and 20
minutes of elapsed time
from the reentry into the atmosphere and reaching the ocean surface. In May 7-
8, 2021, another such
Long March 5B launch stage landed in the ocean, with associated debris
reaching inhabited villages
in Cote d'Ivoire, The core stage of the launch vehicle that is falling to
Earth weighs 23 tons and is 10
stories tall. Several large Composite-Overwrapped Pressure Vessels, or COPVs,
from SpaceX
rockets have landed in Washington State and off the coast of Oregon in the
2020-2021 time frame.
One such COPPV from the March 4, 2021 launch left a four inch dent in the
soil. The COPV in
Washington wasn't the only piece of debris to land on US soil in Sping, 201.
An absolute hellstorm
of debris rained over SpaceX's Boca Chica, Texas facilities on Tuesday when a
Starship prototype
exploded mid-air during its attempt to land, marking the fourth explosion of a
Mars rocket prototype
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in a row in Elon Musk's speedy Starship test campaign.
[0025] In the United States, there are many new commercial launch providers
which are
inexperienced in this field. Many foreign countries are developing government
and commercial
launch services, often with little experience and few regulations and
government oversight. As such,
the potential for such anomalous behavior will grow resulting in an increase
risk to aircraft.
[0026] One study that attempts to quantify the risk from reentering space
debris was performed by
The Aerospace Corporation and published in 2019. It considered the number of
satellites that would
reenter as a result of the proposed large constellations (or mega-
constellations) of satellites. Given
the cumulative risk from the seven publicly announced mega-constellations
(with a cumulative
number of satellites calculated to be 15,968), the probability of debris
striking a commercial aircraft
would be 0.001 per year (1 in 1,000), and without emergency action by pilots,
the maximum yearly
casualtyexpectation for re-entries of satellites disposed from a single large
constellation for people in
aircraft could be 0.3 per year (3 in 10). Those estimates would be higher if
commercial air traffic
were updated to include all worldwide flights. Since the time this study was
published, the number of
satellites in the proposed constellations has grown. On October 15, 2019, the
U.S. Federal
Communications Commission submitted filings to the International
Telecommunication Union on
SpaceX's behalf to arrange spectrum for 30,000 additional Starlink satellites
to supplement the
12,000 Starlink satellites already approved by the FCC. In April, 2021, the
China Satellite Network
Group was founded under state leadership to bundle all activities. According
to the plans known so far,
more than 20,000 Chinese satellites are to be brought into orbit.
[0027] To mitigate the hazards to users of the airspace, three critical steps
must be taken. First, the
breakup of the expected reentering debris must be determined in advance to
characterize the potential
airspace and ground "footprint" threatened in terms of space and time. Second,
it is necessary to
iteratively forecast the probable space debris reentry critical locations with
reference to (high) air
traffic density, taking also into account predicted weather conditions. Third,
the information must be
disseminated in real time to all users in the affected airspace together with
specific instructions for
avoiding the hazardous region (because the region threatened is usually much
shorter in one
direction, an informed course correction can greatly mitigate the risk to an
aircraft in the vicinity of
the falling debris).
[0028] Identifying the reentry of large objects is indeed a difficult task.
From the point of view of the
risk evaluation from the airspace to the ground, an uncontrolled satellite can
renter anywhere on a
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large portion of the Earth surface, putting all the locations within the
latitude band defined by the
orbit inclination into the risk zone. Considering that a reentering satellite
in nearly circular orbit
completes a full revolution around the Earth in just less than 90 min, even a
few days before orbital
decay a reentry window still includes many revolutions, overflying most of the
planet. Due to the
very fast velocity of a low Earth satellite, a relatively small uncertainty in
time translates into huge
along-track distance uncertainties.
[0029] Usually, the final reentry forecasts issued during the last hour or
minutes preceding the actual
reentry are based state vector which is 2-3 hours old. Therefore, the
predictions issued immediately
before reentry maintain a typical along-track uncertainty of half an orbit.
However, even though the
final reentry uncertainty window is in practice quite spatially extended along-
track, the possible
impact time of the satellite fragments at a given critical location may be
computed with reasonable
accuracy. This allows, for any critical location included in the reentry
window, to define a risk time
window. In other words, for each critical location included in the reentry
window, the debris impact
is possible, but not certain; however, in each place, the possible impact may
occur only during a
specific risk time window, which can be therefore used to plan aircraft
trajectories to avoid a
collision.
[0030] Included in the New Space economy is the emergence of several companies
which track
space debris to provide commercial space traffic management services. There
are several competitors
in this market with different approaches to improve the precision of tracking
objects. The capability
to predict reentry from attributed objects will improve as new ground-based
and space-based
methods for tracking are deployed and integrated with the known catalog of
objects.
[0031] To provide actionable information to a user in the airspace, there
needs to he a procedural
mechanism to inform pilots to avoid airspace affected by the hazard of
entering space debris. One
method is to provide data to the air traffic controllers which can inform
airplane operators of the
present hazard and provide assistance in minimizing their time in the affected
airspace.
[0032] Another option to inform users of the airspace is to utilize real time
notification of airspace
pilots through an application on internet-connected mobile device. One such
service is provided by
the company, ForeFlight. This service was created in 2007 by general aviation
pilots for the limited
purpose of offering weather data for private pilots to assist with flight
planning. The platform was
expanded to automate flight planning and, today, offers a range of features
for recreational pilots,
business aviation, military services, and commercial airlines in the United
States and around the
world. Pilots receive real time updates 'pushed by the ForeFlight service to
their mobile phone or
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tablet' and can have their flight trajectory re-routed, as necessary, to avoid
hazards_ Today, this
service assists pilots to make real time decisions to respond to weather
anomalies and other changes
in the airspace. Adding a space debris reentry hazard zone could be a seamless
solution to provide
pilot notification for the hazard of reentering space debris. Such tools could
be in addition to
notifications to pilot through air traffic controllers. Such tools could also
be used to calculate
cumulative risks to aircraft for the hazard of reenteringspace debris. The
tools could also calculate
the risk to aircraft resulting from the end of life of individual or
cumulative risk of constellations of
satellites.
[0033] It would be desirable to provide methods and systems for further
reducing the risk to aircraft
in flight.
[0034] The disclosure relates to methods and systems for reducing the risk of
air collisions,
specifically collisions between aircraft and re-entering space debris.
SUMMARY
[0035] In a first aspect, the present disclosure relates to methods for
reducing the risk of air
collisions, specifically between objects in the airspace and re-entering space
debris by performing the
following steps: 1) identifying the presence or re-entry space debris entering
the airspace, 2)
determining the footprint for re-entering debris (representing the widest area
for which debris
fragments might pass through the airspace, and the respective time of
passage), and 3) notifying
users of the airspace by one or both of the following two methods. The
information can be provided
to air traffic control personnel, automated systems or offices. The air
traffic control may then notify
the aircraft and/or re-route the aircraft. The information may also be sent
directly to pilots operating
aircraft using an application on an internet-connected or other wireless-
connected mobile device.
[0036] Identifying the presence or re-entry of objects in the airspace may
include developing a
catalog of all space debris. The catalog may be maintained by taking available
data from ground and
space-based observatories to improve the precision of the orbital parameters
specifying the orbit
trajectory (position and velocity) and epoch time.
[0037] Each item will be separately cataloged and will be described by a two-
line element set (TLE),
or some other comparable description to uniquely specify the orbital
parameters. With modification,
the data in the Space Track website can be refined (or improved) to provide
meaningful predictions
to protect the airspace. As such, a database would be generated with updated
accuracy of position and
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velocity as specified by the TLE and its corresponding uncertainty (or
covariance). This identifying
may also feature routinely propagating the orbit of potential debris objects
that may result in a re-
entry. This identifying may also feature using orbital mechanics to propagate
the object trajectory for
the next few hours, the next day, or two days, etc. of one or more objects to
calculate the re-entry of
such objects.
[0038] The identifying may include identifying re-entry of known objects. This
may also include
monitoring launch activities around the world and tracking the trajectory of
all objects including
newly created objects. For example, a typical launch vehicle is comprised of
one or more rocket
stages and, when the final stage reaches orbit, it releases the fairing (which
covers the satellite).
These one or more stages, fairing and other components may become new space
objects. During
nominal and, especially, during launch anomalies (i.e. failures), there may be
many debris objects
which nearly reach orbit and create a hazard in the airspace. Usually, there
is no ability to control the
trajectory or disposal of such objects and they reenter when the natural decay
of the orbit results in
the object eventually falling through the atmosphere and landing on the ground
or in the ocean.
[0039] The determination of the location of the objects or the determination
of the footprint for re-
entering debris is performed in order to identify what part of the airspace
must be closed to aircraft
traffic and for what time period. For each re-entering object, a footprint may
be calculated. This
footprint may be calculated, for instance, by determining how the object will
break up as it re-enters
the atmosphere and then determining the dispersion of the surviving pieces of
the object. For re-
entering satellites of known design, it is possible to consider the separate
components and assess
them individually. For re-entering satellites of unknown specific design, it
is possible to estimate or
approximate them by size and type (e.g., communications, observation, etc.). A
few components
may have a high degree of survivability through re-entry that are common to
all spacecraft, for
instance, thrusters or engines, pressure vessels, batteries, etc. These may
each have a signature on
breakup. The footprint that is developed for each object may encompass the
potential flight path of
the object and, as the object breaks up on re-entry, the respective fragments.
It may also be possible
to determine the time period that these objects require to pass through the
atmosphere. For example,
if a small satellite will re-enter at time t=t0, then all debris objects may
for example pass through the
airspace between, for instance, t0+10 minutes to t0+25 minutes, and the
footprint may be, for
instance, 150 km long by 6 km wide in a certain direction from a fixed point.
[0040] The providing of the location or the footprint to air traffic control
personnel or offices allows
such personnel or offices to notify aircraft and/or re-route aircraft that
might otherwise encounter or
be impacted by one of the resulting fragments. Algorithms may be developed
that automatically
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calculate the risk of any given aircraft encountering or being impacted by the
object. The calculating
and the informing of the aircraft may be performed using automated systems.
[0041] In a second aspect, the present disclosure relates to a computer
operated online catalog of
objects in the atmosphere and their respective two line element, or some
comparable comprehensive
method to uniquely specify an object's trajectory in Earth orbit. The computer
operated online catalog
may also include the footprint for re-entering objects into the atmosphere and
the corresponding time
when objects pass through the atmosphere in this footprint. The orbit may
further feature trajectory of
motion of the objects and/or velocity of motion of the objects in the
atmosphere.
[0042] The computer operated online catalog may be useful for use in methods
for reducing the risk
of aircraft encounters or collisions with objects such as debris in airspace
featuring identifying the
presence or re-entry of objects in the airspace, determining the location of
the objects or determining
the footprint for re-entering debris, and providing the location or the
footprint to air traffic control
personnel or offices. The air traffic control may then notify the aircraft
and/or re-route the aircraft.
When there is a high flux of particles for a specified period of time, air
traffic may also issue a
Notice to An-men with the appropriate information to alert pilots and flight
planners. Alternatively,
the location or the footprint may be sent directly to pilots operating
aircraft using an application on
an internet-connected or other wireless-connected mobile device
[0043] The computer operated online catalog may be useful for aircraft
operations such as airlines or
other flight planners of aircraft, spacecraft or suborbital spaceflight
operators or launch vehicles.
Flight planning may be adjusted to reduce the risk of encounters or collisions
with objects such as
debris in airspace featuring identifying the presence or re-entry of objects
in the airspace,
determining the location of the objects or determining the footprint for re-
entering debris, and
providing the location or the footprint to air traffic control personnel or
offices. For example, if a
launch vehicle routinely sheds debris in a general vicinity, aircraft
operators may chose not to fly in
that area during times of launches.
[0044] The identifying the presence or re-entry of objects in the airspace may
include developing a
catalog of all space debris. The catalog may be maintained by taking available
data from ground and
space-based observatories to improve the precision of the orbit from publicly
available databases,
such as the website Space Track. The United States Air Force tracks all
detectable objects in Earth
orbit, creating a corresponding TLE for each object, and makes publicly
available TLEs for many of
the space objects on the website Space Track, holding back or obfuscating data
on many military or
classified objects. The TLE format is a de facto standard for distribution of
an Earth-orbiting object's
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orbital elements.
[0045] This identifying may include the position, trajectory (velocity) and
epoch time. This
identifying may also feature routinely propagating the orbit of potential
debris objects that may result
in a re-entry. This identifying may also feature orbital propagation using
orbital mechanics to
determine the trajectory for the next day, two days, etc. of one or more
objects to calculate the re-
entry of such objects.
[0046] The identifying may include identifying re-entry of known objects. This
may include
monitoring launch activities around the world and tracking the trajectory of
new objects which do
not appear in the existing on-orbit catalog. For example, a typical launch
vehicle is comprised of
many rocket stages, when the final stage reaches orbit, it releases the
fairing (which covers the
satellite). These stages, the fairing and other debris become new objects.
During nominal and
especially during launch anomalies (i.e. failures) there may be many debris
objects which nearly
reach orbit or reach and orbit and subsequently reenter. These objects create
a hazard for users in the
airspace.
[0047] The determination of the location of the objects or determination of
the footprint for re-
entering debris is performed in order to identify the part of the airspace to
close to aircraft traffic and
for what time period. For each re-entering object, a footprint may be
calculated. This footprint may
be calculated, for instance, by determining how the object will break up as it
re-enters the
atmosphere and then the dispersion of the surviving pieces of the object. For
re-entering satellites of
known design, it is possible to consider the separate components and assess
them individually. For re-
entering satellites of unknown specific design, it is possible to estimate or
approximate them by size
and type (e.g., communications, observatory, etc.). A few components may have
a high degree of
survivability through re-entry that are common to all spacecraft, for
instance, thrusters or engines,
pressure vessels, batteries, reaction wheels or command moment gyroscopes,
etc. These may each
have a distinct signature on breakup. The footprint that is developed for each
object may encompass
the potential flight path of the object and, as the object breaks up on re-
entry, the respective
fragments. It may also be possible to determine the time period that these
objects require to pass
through the atmosphere. For example, if a small satellite will re-enter at
time t=t0, then all debris
objects may for example pass through the airspace between, for instance, t0+10
minutes to to-F25
minutes, and the footprint may be, for instance, 100 miles long by 4 miles
wide in a certain direction
from a fixed point.
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[0048] Thc providing thc location or thc footprint to air traffic control
personnel or officcs allows
such personnel or offices to notify aircraft and/or re-route aircraft that
might otherwise potentially
encounter or be impacted by the object. Alternatively, the location or the
footprint may be sent
directly to pilots operating aircraft using an application on an internet-
connected or other wireless-
connected mobile device. Algorithms may he developed that automatically
calculate the risk of any
given aircraft encountering or being impacted by the object. The calculating
and informing the
aircraft may be performed using automated systems.
[0049] In a third aspect the present disclosure relates to a computer operated
algorithm for describing
the location of the objects in the atmosphere and/or the footprint for re-
entering objects into the
atmosphere which may be in communications contact directly to pilots operating
aircraft using an
application on an internet-connected or other wireless-connected mobile
device. The location may be
described in terms of position, velocity and epoch time, and may further
feature trajectory of motion
of the objects and/or velocity of motion of the objects in the atmosphere.
Likewise, the footprint for
re-entering objects may be described in terms of position and may further
feature trajectory of motion
and/or velocity of motion of the re-entering objects in the atmosphere.
[0050] The computer operated algorithm for describing the location of the
objects in the atmosphere
and/or the footprint for re-entering objects into the atmosphere, which may be
in communications
contact directly to pilots operating aircraft using an application on an
internet-connected or other
wireless-connected mobile device, may be useful for methods for reducing the
risk of aircraft
encounters or collisions with objects such as debris in airspace featuring
identifying the presence or
re-entry of objects in the airspace, determining the location of the objects
or determining the footprint
for re-entering debris, and providing the location or the footprint to air
traffic control personnel or
offices. The air traffic control may then notify the aircraft and/or re-route
the aircraft.
[00511 The identifying may include identifying re-entry of known objects. This
may include
monitoring launch activities around the world and tracking the trajectory of
new objects to the on-
orbit catalog. For example, a typical launch vehicle is comprised of many
rocket stages, when the
final stage reaches orbit, it releases the fairing (which covers the
satellite). These stages and fairing
and other debris become new objects. During nominal and especially during
launch anomalies (i.e.
screwups) there may be many debris objects which nearly reach orbit and can
create a hazard for the
airspace.
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[0052] Thc determining thc location of thc objccts or determining thc
footprint for rc-cntcring dcbris
is performed in order to determine the part of the airspace to close to
aircraft traffic and for what
time period. For each re-entering object, a footprint may be calculated. This
footprint may be
calculated, for instance, by determining how the object will break up as it re-
enters the atmosphere
and then the dispersion of the surviving pieces of the object. For re-entering
satellites of known
design, it is possible to consider the separate components and assess them
individually. For re-
entering satellites of unknown specific design, it is possible to estimate or
approximate them by size
and type (e.g., communications, observatory, etc.). A few components may have
a high degree of
survivability through re-entry that are common to all spacecraft, for
instance, thrusters or engines,
pressure vessels, batteries, etc. These may each have a signature on breakup.
The footprint that is
developed for each object may encompass the potential flight path of the
object and, as the object
breaks up on re-entry, the respective fragments. It may also be possible to
determine the time period
that these objects require to pass through the atmosphere. For example, if a
small satellite will re-
enter at time t=t0, then all debris objects may for example pass through the
airspace between, for
instance, t0+10 minutes to t0+25 minutes, and the footprint may be, for
instance, 100 miles long by 4
miles wide in a certain direction from a fixed point.
[0053] The providing the location or the footprint to air traffic control
personnel or offices allows
such personnel or offices to notify aircraft and/or re-route aircraft that
might otherwise potentially
encounter or be impacted by the object. Alternatively, the location or the
footprint may be sent
directly to pilots operating aircraft using an application on an internet-
connected or other wireless-
connected mobile device. Algorithms may be developed that automatically
calculate the risk of any
given aircraft encountering or being impacted by the object. The calculating
and informing the
aircraft may be performed using automated systems.
[0054] One option to inform users of the airspace is to utilize real time
notification of airspace pilots
through an application on internet-connected or other wireless-connected
mobile device. Mobile
application services enable pilots in flight to make real time decisions to
respond to weather
anomalies and other changes in the airspace. Adding a reentry hazard zone
could be a seamless
solution to provide pilot notification for the hazard of reentering space
debris.
[0055] The tool can be used to calculate cumulative risks to aircraft for the
hazard of reentering
space debris. The tools could also calculate the risk to aircraft resulting
from the end of life of
individual or cumulative risk of constellations of satellites.
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[0049] In a fourth aspcct thc prcscnt disclosure relates to a mcthod for
rcducing thc risk of aircraft,
sub-orbital spacecraft or launch vehicle encounters or collisions with objects
such as space debris in
airspace by a) identifying the presence or re-entry of objects in the
airspace, b) determining the
location of the objects or determining the footprint for re-entering debris,
and c) providing the
location or the footprint to one or more selected from the group consisting of
air traffic control
personnel or offices, suborbital flight operators, spaceflight launch site
operators, administrators
of internet-connected or other wireless-connected mobile device applications
that assist aircraft pilots
and operators with flight planning and avoiding real-time hazards, and
aircraft pilots. This aspect may
provide a method for reducing the risk of users of the airspace including any
airplane, helicopter,
launch vehicle, suborbital or orbital spacecraft, drone, high-altitude
balloon, sport parachute from
encounters or collisions from objects including fragments of reentering space
debris and/or launch
vehicles featuring a) identifying the presence or re-entry of space debris or
remnants of launch
vehicles in the airspace, b) determining the spatial (area and altitude)
dispersion as a function of time
for objects associated with space debris after it reenters the atmosphere or
objects associated with
launch vehicles, and c) disseminating the information to users of the airspace
in order to enable the
operators to take corrective action to avoid collision with the identified
objects, by doing one or more
of the following: notifying controllers (such as airlines, suborbital flight
operators, spaceflight launch
site operators, and/or others) of aircraft operating in the airspace,
notifying air traffic control
personnel or offices, and notifying aircraft directly, such as through a
wireless-connected device to
the operator of aircraft or to the autonomous navigation system controlling
aircraft. The notifying
may be through a phone, tablet or other mobile application connected through
with a cellular,
internet, or other wireless service that integrates aircraft flight planning
and real-time upgrades of
hazards in the airspace.
[0050] In a fifth aspect, the present disclosure relates to a method for
reducing the risk of aircraft, sub-
orbital spacecraft or launch vehicle encounters or collisions with objects
such as space debris in
airspace featuring a) identifying the presence or re-entry of objects in the
airspace, b) determining the
location of the objects or determining the footprint for re-entering debris,
and c) providing the
location or the footprint to one or more of air traffic control personnel or
offices, suborbital flight
operators, spaceflight launch site operators, administrators of internet-
connected or other wireless-
connected mobile device applications that assist aircraft pilots and operators
with flight planning and
avoiding real-time hazards, and aircraft pilots. In some instances, this
aspect features a method for
reducing the risk of users of the airspace including any airplane, helicopter,
launch vehicle, suborbital
or orbital spacecraft, drone, high-altitude balloon, sport parachute from
encounters or collisions from
objects including fragments of reentering space debris and/or launch vehicles
featuring a) identifying
the presence or re-entry of space debris or remnants of launch vehicles in the
airspace, b)
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determining the spatial including area and altitude dispersion as a function
of time for objects
associated with space debris after it reenters the atmosphere or objects
associated with launch vehicles,
and c) disseminating the information to users of the airspace in order to
enable the operators to take
corrective action to avoid collision with the identified objects, by doing one
or more of the
following: i) notifying controllers (such as airlines, suborbital flight
operators, spaceflight launch site
operators, andJor others) of aircraft operating in the airspace, ii) notifying
air traffic control personnel
or offices, and c) notifying aircraft directly, such as through a wireless-
connected device to the
operator of aircraft or to the autonomous navigation system controlling
aircraft. The notifying
aircraft directly may be performed through a phone, tablet or other mobile
application connected
through with a cellular, internet, or other wireless service that integrates
aircraft flight planning and
real-time upgrades of hazards in the airspace.
RETAILED DESCRIPTION
[0051] In the description that follows, the terminology and phraseology used
herein is solely used
for descriptive purposes and should not be construed as limiting in scope.
Language such as
"including," "comprising," "having," "containing," or "involving," and
variations thereof, is intended
to be broad and encompass the subject matter listed thereafter, equivalents,
and additional subject
matter not recited, and is not intended to exclude other additives,
components, integers or steps.
Likewise, the term "comprising" is considered synonymous with the terms
"including" or
"containing" for applicable legal purposes. All numerical values in this
disclosure are understood as
being modified by "about." All singular forms of elements, or any other
components described
herein including without limitations components of the apparatus are
understood to include plural
forms thereof. By "aircraft" is meant any machine or device made by man and
designed for
movement or travel in theair, atmosphere, or space including, for example,
airplane, helicopter,
launch vehicle, suborbital or orbital spacecraft, drone, or other machine
capable of flight. By "space
debris" is meant as any suborbital or orbital spacecraft, satellite, launch
vehicle, meteor, asteroid, or
other space objects or fragments of one or more of these objects.
[0052] The US Air Force maintains a catalogue of objects in Earth orbit that
is publicly available
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through the wcbsitc Space Track. The maintenance of this database includes
updating the trajectory
when data is available. Because of uncertainties in the atmospheric density
and the orientation and
dynamics of the reentering body, reentry prediction using this tracking data
have an error of
approximately 10 percent in time; that is, if an object is observed and an
accurate orbit based on that
observation is computed one hour prior to reentry, there is a 6 minute error
in that prediction. Since
this object is traveling at orbital speed (-7.6 km/second), this error
translates to an uncertainty in the
reentry point of approximately 2740 km, (this is likely an optimistic
scenario¨ without special
tasking, good estimates of final orbits are generally not computed within one
hour of reentry).
[0053] The uncertainty in the impact zone can be reduced substantially if the
object is observed at
the primary breakup altitude. If an object is observed before breakup, no
major debris has yet been
released, so the predicted impact zone must include uncertainties in the
atmosphere, vehicle
dynamics, etc., for the remaining time before breakup.
[0054] After breakup, there is uncertainty as to whether the observed object
is at the toe or heel of
the debris footprint, and since the objective is to produce a ground impact
zone that will contain the
debris with a high level of confidence, the possible ground area affected is
larger than the actual
debris footprint. For these reasons, the observation altitude that produces an
affected area that is
closest to the actual debris footprint length is the altitude where the object
experiences the primary
breakup event. The best predictions of the airspace to be affected by debris
are made if the object is
observed during re-entry. Thus, the actual re-entry and the prediction is
based on trajectory data
obtained at the breakup altitude.
[0055] From the point of view of the risk evaluation from the airspace to the
ground, an
uncontrolled satellite can renter anywhere on a large portion of the Earth
surface, putting all the
locations within the latitude band defined by the orbit inclination into the
risk zone. Considering
that a reentering satellite in nearly circular orbit completes a full
revolution around the Earth in just
less than 90 min, even a few days before orbital decay a reentry window still
includes many
revolutions, overflying most of the planet. Due to the very fast velocity of a
low Earth satellite, a
relatively small uncertainty in time translates into huge along-track distance
uncertainties.
[0056] Usually, the final reentry forecasts issued during the last hour or
minutes preceding the
actual reentry are based on a state vector that is at least 2-3 hours old, due
to an unavoidable
communication and processing delay between the orbit determination epoch and
the release of the
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corresponding reentry prediction. Therefore, the predictions issued
immediately before reentry
maintain a typical along-track uncertainty of half an orbit. However, even
though the final reentry
uncertainty window is in practice quite spatially extended along the track,
the possible impact time
of the satellite fragments may be computed with reasonable accuracy. This
allows, for any sub-
satellite location included in the reentry window, to define a risk time
window. In other words, for
each sub-satellite location included in the reentry window, the debris impact
is possible, but not
certain; however, in each place, the possible impact may occur only during a
specific risk time
window, which can be therefore used to plan risk mitigation measures on the
ground and in the
airspace overhead. If the attention is focused on a quite compact and small
area of the planet, it is
possible to produce additional information useful for the civil protection
authorities.
[0057] Successively, the nominal impact times and ground tracks are integrated
with a small time
dispersion to account for initial conditions variability, a larger time
dispersion of tens of minutes to
account for the different flight times of fragments with distinct ballistic
properties (including small
particles not dangerous on the ground, but possibly representing a hazard for
aircraft crossing the
affected airspace), and a cross-track safety margin to account for the
expected dispersion of the
fragments and the trajectory residual uncertainties. Applying this method, the
ISTI-CNR (Italian
Council of Research) has found for the Italian territory, the "risk" time
windows typically have an
amplitude of about 30-40 minutes, including the airspace crossing from an
altitude around 10 km
from ground impact.
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