Automating Celestial Navigation: George H. Kaplan
Automating Celestial Navigation: George H. Kaplan
Automating Celestial Navigation: George H. Kaplan
Celestial Navigation
George H. Kaplan
gk@gkaplan.us or
george.kaplan@usno.navy.mil
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Celestial Nav − What We Usually Think of
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Outline of Talk
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Limitations/Concerns About GPS
• Relatively weak signal, easily jammable
Schwartz Warns Against
• GPS spoofing (civilian vulnerability) Dependence on GPS
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Modern Nav Solutions
• Strengthen GPS Note: Omega,
– alternative frequencies/signals Transit, and U.S.
– “spot beam” for M code (military signal) LORAN are gone
– directional antennas on user side
– better signal processing algorithms
• Combine GPS with inertial navigation systems (INS) to provide
a nav “flywheel” that can bridge GPS outages
• Use blended-nav solutions using a variety of sensors
– GPS – magnetic sensing
– INS – bathymetry
– celestial – altimetry
– automated visual systems – use of radio signals of opportunity
• iGPS: Reprogrammed Iridium satellites (ONR/Boeing project)
• Pseudolites
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Modern Nav Solutions
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Why Celestial?
• Passive
• World-wide
50
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2 or more stars ⇒ 3-axis attitude
w.r.t. stars (inertial system)
+ local vertical ⇒ attitude
w.r.t. horizon and
position along a line in space
Center of
the Earth
+ time ⇒ latitude and longitude
...assuming
star catalog data and
formulas for Earth orientation
as a function of time
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A Technical Challenge:
Determination of the Vertical
• An essential part of celestial navigation
based on stars
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Determination of the Vertical
Solutions:
1. Use external natural surrogates for the vertical
– Horizon
– Atmospheric refraction of star positions
– Local average sea surface
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Scheme 1
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Scheme 3
Eliminating the Vertical
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Automated Celestial Nav −− Beginnings
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Automated Celestial Nav −− on ICBMs
Continued with ICBM guidance systems:
Polaris, Trident, Minuteman, MX
(also Soviet
missiles)
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Automated Celestial Nav −− Experimental
Aircraft Systems (Never Deployed)
Northrop OWLS Northrop Mini-OWLS
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Automated Celestial −− Current Space
Applications
Commercial
star trackers
Used for
attitude sensors
for satellites
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Automated Celestial Technology
• Old • New
– Gimbaled – Strapdown (no moving
parts)
– Photomultipliers,
vidicons, or similar – CCD or CMOS detectors
detectors
– Multiple stars observed in
– Single-star observations each field
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Recent & Current Activity
• SSC Pacific (San Diego) − USNO partnership with California
contractors Microcosm, Inc., and Trex Enterprises Corporation
– Focus on <100 m accuracy, day + night operation at sea level
– Funded by ONR, SPAWAR, AF Research Lab, NGA, NAVAIR, BMD
– Resulted in several prototype instruments for fixed locations on land,
including one for NGA surveying
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End
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USNO Work in Automated Celestial Nav
SBIR I II
II+
Microcosm
NGA
STELLA
NAVSS
BMD
CNO req PC app
I
SPAWAR SSC San Diego
AF Res
Lab
ONR
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The Vertical as Defined by the Horizon
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Observation Geometry
An observation consists of:
• Observed direction of target wrt
stellar reference system
• 3-D geocentric coordinates of
target
at instant of observation
Observed direction
vector d
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GPS Satellites as Optical Targets
from Vrba
(2005)
PPT
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1.3-meter Telescope at USNO Flagstaff
• The “average sky” is not typical — star counts per unit area of
sky are highly variable
Continued…
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Lessons Learned (II)
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End
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