Transcript Long base-line stereoscope for LEO surveillance

Long base-line stereoscope for Earth-bound orbits surveillance
experiments in Romania
Octavian CRISTEA, BITNET CCSS, ROMANIA
SCI 229 ET NATO SSA, DLR Bremen, 14-16 Dec. 2009
A. Short comments on sensors for space objects surveillance
B. The ground based stereoscope project for LEO
surveillance experiments
C. The ground-to-space stereoscope project for high orbit
object tracking experiments
This Presentation is Unclassified
SCI 229 ET NATO SSA, DLR Bremen 14-16 Dec. 2009
A. Sensors for space objects surveillance
SPACE OBJECTS SURVEILLANCE: The combined tasks of detection, characterization,
correlation, and orbit determination of space objects.
Typical GROUND
BASED SENSORS
PASSIVE
ACTIVE
OPTICAL
Tracking telescope
Satellite laser ranger
RADIO
Satellite broadcast monitoring station
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Radar
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SPACE BASED
SENSORS
PASSIVE
OPTICAL
ACTIVE
?
LEO telescope for GEO orbits surveillance
?
RADIO
?
Real-time surveillance of Earth neighborhood is a big challenge
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Sensor limitations
There is no instrument which can detect any object on any orbit …
Detection
principle / object
Electro-optical
Radio
(passive)
Radar
Active satellite
Any orbit
Any orbit
LEO (GEO?)
Debris
Any orbit
No
LEO (GEO?)
NEO
Any orbit (passive
detection only)
No
No
Remarks
Short time windows for
operation if ground based
Continuous
operation
Continuous
operation
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B. The ground based stereoscope project for LEO surveillance
MAIN TASKS:
1.
2.
3.
4.
Very wide area search and detection of LEO objects using electro-optical sensors
Robotic operation of sensors
Orbit depth recovery using parallax
LEO orbit determination.
THE ELECTRO-OPTICAL SENSOR
Can we use a “classical” setup (telescope + CCD + PC) for building the
stereoscope ?
The answer is YES but, the probability to detect a LEO
object with unknown orbital parameters is incredible small !
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In a wide search mission, an optical sensor collects
frames of data on consecutive directions in order to find
objects in its range of detection.
If FOV is the telescope Field of View, and we take 10 s
only for integration time, data transfer to PC and repointing the telescope to a new direction, it means that a
complete survey (all directions) takes:
T (seconds) = 10 x (360 x 180) / FOV
For FOV = 1 x 1 (a big one for a telescope)
Illustrating how small is the probability
to detect a space target with unknown
orbital parameters – roughly speaking,
it is like shooting a flying bird with
closed eyes.
SCI 229, DLR Bremen, 14-16 Dec. 2009
=> T = 180 hours while a LEO object visible
pass is few minutes only!
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Telescope
FOV (sq. degrees)
Probability to point the telescope to an
unknown target at a given moment
SDT (ESA)
0.7 x 0.7
7.5 x 10-6
TAROT (CNES)
2x2
6.2 x 10-5
STARBROOK (UK)
10 x 6
9,2 x 10-4
t1
t1 t
2
Several cooperating sensors can
increase this probability
t2
A sensor taking consecutive
snapshots of the sky within its FOV.
Cooperative sensors taking N
snapshots of the sky at any given
moment.
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The visibility
window is very
small
THE REAL PROBABILTY TO DETECT AN UNKNOWN TARGET IS
SIGNIFICANTLY SMALLER SINCE OTHER FACTORS HAVE TO BE
TAKEN INTO ACCOUNT:
•
•
•
•
The sky must be clear and dark 1
The sensor must be in the Earth’s shadow 2
The space object must be above the sensor’s horizon 3
The space object must be illuminated by the Sun 4
The good thing is that if we wait enough, sooner or later any Earth orbiting
object will enter the sensor FOV during the visibility window.
The bad thing is that it might take a very long time until the sensor will
detect the unknown object. This is the challenge of real-time surveillance
of space objects.
REMARKS: Requirement 1 does not apply to space-based optical sensors; 1, 2
& 4 do not apply to radars.
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The first option in the stereoscope design was to
integrate an “all sky” camera with big aperture and
small f-theta distortion.
Problems:
• such a lens is very expensive
• best COTS lens we could find has 2% f-theta
distortion
• small threshold detection magnitude
• the Moon will be in the FOV many times.
The second (and actually) option is to integrate an “all
azimuth” sensor using few COTS wide FOV and big
aperture lenses.
This solution:
• decreases the angular distortion
• increases the angular resolution (1 to 3 arc min is the
target) for a designed FOV of 3600 x 520
• 6 to 7 threshold detection magnitude should be easy to
reach.
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Stereoscope setup. Pair cameras take simultaneous consecutive photos of the sky.
The stereoscope’s base-line is 37 Km, a compromise between simultaneous detection
of low altitude objects from two locations and triangulation accuracy. Pair cameras
synchronization is made through GPS.
Geometric calibration of the image is made by matching captured stars in the image
with an astronomical catalogue of stars. The recovery of orbital depth is made by
correlating matching feature points from pairs of simultaneous images.
The project is in the concept development phase. Contributing organizations: BITNET
CCSS (stereoscope setup and operation), the Technical University of Cluj (robotic
stereoscopy), the Astronomical Observatory of Cluj (astrometry), the Romanian Research
Authority (financial support). The project consortium is open for cooperation.
SCI 229, DLR Bremen, 14-16 Dec. 2009
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C. The ground-to-space stereoscope project idea
MAIN IDEA: a stereoscope made from
One LEO telescope
One (or several) ground based telescope (s)
which will take simultaneous photos of the same high
orbit space object.
NEOSSAT – Near Earth Object
Surveillance Satellite
Such a stereoscope has a very long,
time dependent base-line.
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NEOSSAT MISSION & SPACECRAFT
Spacecraft developed by the Canadian Space Agency (CSA) together
with Defense Research and Development Canada (DRDC).
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The Spacecraft
• Microsatellite platform
• Mass about 75 Kg, available power approximately 35 Watts, dimensions 1 x 0.8 x 0.4 m
• Pointing stability of 0.5 arcsec in pitch and yaw for extended periods
• Reaction wheels, no propulsion
• Sensors: sun sensor, star tracker, magnetometers, solar cells
Orbit: 500-850 km dawn-dusk sun-sync
The Science Payload
• Customized 15 cm aperture F/6 Maksutov telescope
• Filed of view is 0.85 deg
• CCD array 1k x 1k pixels, sensitivity range 310 to 1100 nm
• Limiting magnitude: approximately 20 v.mag with 100 sec exposure
• Pixel scale: 3 arcsec/pixel
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THE GROUND SEGMENT WHICH IS IN DEVELOPMENT AT BITNET
Rural area, 1200 m altitude, 55
Km far from Cluj-Napoca,
electromagnetic quiet zone, no
light pollution.
The testbed will host:
• a ground station to downlink data from the satellite
• a robotic telescope (probably 40 cm aperture) for acquisition of satellite or other
space object metric and signature data
• GPS for time synchronization
• VSAT for internet connectivity through a geostationary telecommunication satellite.
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EXAMPLES OF POSSIBLE JOINT EXPERIMENTS USING A SPACEBASED AND A GROUND-BASED TELESCOPE
Simultaneous space object signature and position information acquisition from Earth and
space
Comparison of ground spacecraft signature with on-orbit spacecraft signature for space
object identification tests. In addition, the spacecraft will be rapidly changing its
orientation with respect to the ground-based sensor, and “truth” knowledge of these
changes can be made available.
Evaluation of the roles played and value added by a space-based telescope.
Comparison of observation-based attitude and pose estimation with NEOSSat truth
data from telemetry
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Octavian Cristea is the founder and managing director of BITNET CCSS Ltd., a small
contract research company in Romania specializing in technology applications
development and/or demonstration (surveillance sensors, satellite communications,
software).
Since 2004 he is deeply involved in the development of the SofS activities in Romania
(consulting, space surveillance systems analysis and design, project proposals
development).
Before founding BITNET CCSS, he worked as scientist at the Romanian Institute of
Space Sciences and at the Babes-Bolyai University, being involved in gravitation and
space-time related research.
He is a diplomat physicists of the Babes-Bolyai University, specialized in several
technical areas over the years (sensors, space technology applications, commercial
satellite communications).
SCI 229, DLR Bremen, 14-16 Dec. 2009
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Thank You for Your Attention!
SCI 229, DLR Bremen, 14-16 Dec. 2009
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