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National Aeronautics and Space Administration
Andrew Abraham
Lehigh University
Kenny Getzandanner
NAVIGATION & MISSION DESIGN BRANCH
NASA GSFC
www.nasa.gov
code 595
Preliminary and Detailed Survey
Phase of the OSIRIS-REx Mission
OSIRIS-REx Background
OSIRIS-REx =
 Origins
 Spectral
Interpretation
 Resource
Identification
 Security
 Regolith Explorer
$800 Million New Frontiers class mission to study
asteroid Bennu (RQ36)
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Asteroid Bennu (RQ36)
About Bennu
 Type B Carbonaceous – rich in organics
 500m in diameter
 Eccentricity 0.204
 Rotates every 4.5hrs.
 Approaches Earth every 6 years
Mission Goals
 Measure Yarkovsky effect
 Return organic-rich regolith to Earth
 Characterize surface properties
Arecibo Observatory
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Mission Timeline
l
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Proximity Operations
Ratchet
Approach
Detailed
Diamond
Survey
Preliminary
Orbit &
TAG
Departure
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Preliminary Survey
Goal: To measure the mass of the asteroid to 1% via fly-by
North Pole
Equatorial
South Pole
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Preliminary Survey Details
8 cm/s
A
B
7 km
E
D
F
2 days
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Detailed Survey
 Segment A
B gets to correct RA
C
A
 Segment B C has fixed RA and
sweeps DEC from -40o to 40o
 Spacecraft over viewing station for 4.8
hrs. to map entire surface
Equator
Station
Overflight
 Map ±3o DEC, at 3.8km radius, at each
station’s particular RA
B
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Nested Targeters: Single Station
C
A
Vary Pt. B & C
Target Pt. B
Loop
Vary ΔV @ A
Target Pt. C
Loop
Vary ΔV @ A
B
Loop
Achieve Station Overflight?
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Nested Targeters: Multiple Stations
Iterate Over “n” Stations
Vary Pt. B & C
Target Pt. B
Loop
Target Pt. C
Loop
Loop
Loop
Achieve Station Overflight?
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Conclusion: GMAT; better than STK
 GMAT scripting ability is key
 STK GUI can’t script
 Save stations to file  change
file and re-run code quickly if
mission changes
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Thank You!
Acknowledgements:
Kenny Getzandanner
Joel Parker
Steve Huges
Baseball Diamond
 High latitude viewing angle
 Viewing geometry complements
Ratchet maneuver
 Points are 3.8km in radius and
±30o RA and ±30o DEC with 1 day
time of flight
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