distributed space platform - unsam · 2017-06-09 · distributed space platform for lateral sar...
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1st IAA Latin American Symposium on Small Satellites: Advanced Technologies and Distributed Systems
IAA-LA-05-01
Distributed Space Platformfor
Lateral SAR Swath Revisit: Geometry, Guidance and Control
3/8/2017 1
Claus M. Rosito – Martín Españ[email protected] - [email protected]
March 7–10, 2017, Buenos Aires, Argentina
Objetive
To Co-Observe the lateral SAR Swath of SAOCOM
(Using a Distributed Space Platform)• Assess Overall Feasibility• Find Geometry and Constraints• Guidance & Control Implications
3/8/2017 2Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Background
SAOCOMBACKGROUND
3/8/2017 3Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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J. Medina, et al, “Saocom Mission Overview,” CEOS SAR C&V Workshop, Fairbanks, Alaska, USA, 2011.
Objetive
To Co-Observe the lateral SAR Swath of SAOCOM
(Using a Distributed Space Platform)• Assess Overall Feasibility• Find Geometry and Constraints• Guidance & Control Implications
3/8/2017 4Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Problem Formulation3/8/2017 5
• SAR points OFF-NADIR
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Problem Formulation3/8/2017 6
• SAR points OFF-NADIR• Lambert’s Cosine Law
degrades optical OFF-NADIR performance
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Problem Formulation3/8/2017 7
• SAR points OFF-NADIR• Lambert’s cosine Law degrades optical
OFF-NADIR performance
There is noÞ CENTRAL ORBIT
coincident with the SWATH
Solution: a DISTRIBUTED PLATFORM consisting of several satellites taking turns passing over
SAOCOM SWATH
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Orbits for Co-Observation3/8/2017 8
Working Hypothesis (First Approximation)1. Spherical Earth (Relaxed to WGS-84 Ellipsoid later on)2. J2: Only Kinematics3. Platform members share inclination and semi-major axis with SAOCOM
Tools:1. Observation Targets are given in (lat, long) 2. Sun synchronous orbits3.=> ECEF
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Co-Observing Orbits3/8/2017 9
Procedure:1. Obtain the points on the SWATH analytically.2. Find an orbit passing over a set of points on the SWATH3. Asses CO-OBSERVATION PERFORMANCE
THEN: Assess Guidance and Control Strategies & Challenges
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Co-Observing Orbits3/8/2017 10
SAR pointing parameters are translated to
parameters useful for NAVIGATION
CentralAngle
1. Find Points on Swath
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Co-Observing Orbits3/8/2017 11
Intersection:
SAR pointing parameters are translated to
parameters useful for NAVIGATION
1. Find Points on Swath
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Co-Observing Orbits3/8/2017 12
By Hypothesis:Semi-major Axis, Inclination y Eccentricity
are fixed
3 Parameters define the Orbit
Geometry
1. Target Latitude2. Target Longitude3. Target Co-Observation Time
(or Time Difference after Main Satellite observation)
2. Find Orbit passing over Target
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Co-Observing Orbits3/8/2017 13
Co-Observing Orbit is defined by:1. Longitude of the 1st Ascending Node2. Time of Passage over the 1st Ascending Node
2. Find Orbit passing over Target
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Co-Observing Orbits3/8/2017 14
Sub Satellite Point of Co-Observing Satellite (lat, long) in terms of:1. Longitude of the 1st Ascending Node2. Time of Passage over the 1st Ascending Node3. Time
ThisisthepointonEarthbeingobservedbytheCo-ObservingSatellite
3. Co-Observation Performance
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Non-Spherical Earth Correction3/8/2017 15
Correction to account forWGS-84 Ellipsoid
C -> A
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Co-Observing Orbits3/8/2017 16
Example: Target is a point in Córdoba, Argentina, and Co-Observation Delay is set to 5 min:
3. Co-Observation Performance
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Co-Observing Orbits3/8/2017 17
Performance (Overlap Extents) Depend on Target Latitude:
3. Co-Observation Performance
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Co-Observing Orbits3/8/2017 18
Performance (Overlap Extents) Depend on Target Latitude:
3. Co-Observation Performance
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Overlap3/8/2017 19
Example over several passes. Ascending vs. Descending
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Formation Geometry Determination3/8/2017 20
Single Satellite may have low FOV
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Formation Geometry Determination3/8/2017 21
”Virtual Chief”:
1. Doesn’t need to be close to SAOCOM
2. A formation can improve FOV around a target
3. Introduce the “Virtual Chief” as a GUIDANCE strategy
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Formation Geometry Determination3/8/2017 22
Co-Observing orbit found,
Þ Obtain transformation:
Coordinates ofpoints near -> Relative Orbital ElementsTARGET
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Formation Geometry Determination3/8/2017 23
Co-Observing orbit found,
Þ Obtain transformation:
Coordinates ofpoints near -> Relative Orbital ElementsTARGET
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Formation Geometry Determination3/8/2017 24
”Virtual Chief”:
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Formation Geometry Determination3/8/2017 25
”Virtual Chief”:
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Virtual Chief3/8/2017 26
Tools developed for Formation Flying …
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Virtual Chief3/8/2017 27
Tools developed for Formation Flying … can be used for AOK!
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Virtual Chief3/8/2017 28
Tools developed for Formation Flying … can be used for AOK!
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Autonomous Orbit Keeping3/8/2017 29
Orbit Keeping with Ground in the Loop requires
1. Precise Orbit Determination (from Earth)2. Maneuver Planning (in Earth)3. Upload Maneuver (transmit from Earth to Spacecraft)
4. goto 1
Autonomous Orbit Keeping:
1. Reduces mission cost 2. Enhances co-observation precision but3. Enables larger scale deployments
Onboard Precise Orbit Determination is required
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Autonomous Orbit Keeping3/8/2017 30
The Dynamic Model of the Satellite
Can be separated as
CONSERVATIVE DISIPATIVE
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Autonomous Orbit Keeping3/8/2017 31
Force Separation
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Autonomous Orbit Keeping3/8/2017 32
1. “Virtual Chief” defines the Reference Trajectory
2. “Deputy” is subject to the full range of perturbations.
3. Virtual Chief is the set point for a Tracking Control Problem
CONSERVATIVE DISIPATIVE
VirtualChief
Deputy
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Autonomous Orbit Keeping3/8/2017 33
Relative Control Techniques can be used to drive the Deputy to follow the Virtual Chief
Compensates for Perturbation => Orbit Keeping
CONSERVATIVE DISIPATIVE
VirtualChief
Deputy
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Autonomous Orbit Keeping3/8/2017 34
Relative Control Techniques can be used to drive the Deputyto follow the Virtual Chief
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Autonomous Orbit Keeping3/8/2017 35
Relative Control Techniques can be used to drive the Deputy to follow the Virtual Chief
Error Dynamics:
Adequate choice of gain matrix elements K provide asymptotic stability.
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Autonomous Orbit Keeping3/8/2017 36
Relative Control Techniques can be used to drive the Deputy to follow the Virtual Chief
The Deputy is able to maintain a predetermined orbit Compensating for Perturbations
The strongest Hypothesis used is Continuous Control(Ground in the Loop is not needed)
ElectricPropulsion
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Current Work and Future Work3/8/2017 37
1. The Virtual Chief – Deputy system is being simulated to validate the Control Strategies and models.
2. Hybrid impulsive/continuous (Garulli, De Florio) control is beingtested.
3. These Control Strategies are being considered for Orbit Reconfiguration Maneuvers
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Further study must assess the implications of relaxing the hypothesis
1. Spherical Earth (up to which order. ?)
2. Eccentricity ( )
3. Inclination (while keeping Sun Synchronicity)
Current Work and Future Work3/8/2017 38Distributed Space Platform for Lateral SAR Swath Revisit:
Geometry, Guidance and Control1s
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Main Results3/8/2017 39
1. Orbits design methods to Co-Observe Lateral Swaths were obtained.
2. From Required Target Geometry to Distributed Platform Design.
3. Control Strategies for Autonomous Orbit Keeping were assessed.
Distributed Space Platform for Lateral SAR Swath Revisit: Geometry, Guidance and Control
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Conclusions3/8/2017 40
1. Tools to design and analyze missions of Distributed Space Platforms for Lateral Swath Co-Observation were developed.
2. All together such a mission seems feasible, challenges and lines of work have been identified and are being worked on…
3. Autonomous Obit Control requires highly reliable GNC SW (GNC Algorithms) and HW.
=> INTENSIVE ON GROUND VALIDATION IS NEEDED
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Questions3/8/2017 41
¿Questions?
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1st IAA Latin American Symposium on Small Satellites: Advanced Technologies and Distributed Systems
IAA-LA-05-01
Distributed Space Platformfor
Lateral SAR Swath Revisit: Geometry, Guidance and Control
3/8/2017 42
Claus M. Rosito – Martín Españ[email protected] - [email protected]
March 7–10, 2017, Buenos Aires, Argentina
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