![Page 1: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/1.jpg)
16 November 2001
Guidance & Control Bradley/Markley p1
SuperNova/Acceleration Probe
SNAP Fine Guidance
Art Bradley/Spacecraft System Engineering Services
Landis Markley/NASA/GSFC
Nov. 16, 2001
![Page 2: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/2.jpg)
16 November 2001
Guidance & Control Bradley/Markley p2
SuperNova/Acceleration Probe
• Observing strategy An acquisition strategy is proposed to conduct
field mapping and spectroscopy. Field mapping is performed with a dwell scan
algorithm— Simple flight code and command I/F
– Primary eigenvector– Secondary eigenvector– Number of dwell points– Jerk pulse width– Constant rate interval– Primary eigenvector jerk pulse magnitude– Secondary eigenvector jerk pulse magnitude– Dwell time
Fine guidance CCD damps drift rate during shutter closure.
![Page 3: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/3.jpg)
16 November 2001
Guidance & Control Bradley/Markley p3
SuperNova/Acceleration Probe
• Stellar distribution Star tables of candidate Guide Stars
provided for planning purposes only. Two 25 deg2 fields have been compiled
with centers at 16h25m +57º and 4h30m -52º
Started with HST GSC. Supplemented with latest Yale Bright Star
Catalog & removed duplicates. Supplemented with USNO A2.0 to get
beyond 18mv & removed duplicates.
![Page 4: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/4.jpg)
16 November 2001
Guidance & Control Bradley/Markley p4
SuperNova/Acceleration Probe
• Stellar distribution NEP histograms
![Page 5: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/5.jpg)
16 November 2001
Guidance & Control Bradley/Markley p5
SuperNova/Acceleration Probe
• Stellar distribution NEP histograms
![Page 6: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/6.jpg)
16 November 2001
Guidance & Control Bradley/Markley p6
SuperNova/Acceleration Probe
• Stellar distribution SEP histograms
![Page 7: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/7.jpg)
16 November 2001
Guidance & Control Bradley/Markley p7
SuperNova/Acceleration Probe
• Stellar distribution SEP histograms.GSC population from 15.5 to 16mv not strong, should have used A2.0 in that region.
![Page 8: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/8.jpg)
16 November 2001
Guidance & Control Bradley/Markley p8
SuperNova/Acceleration Probe
• FGS Design – Area 4 geometric arrangements were
examined— 200x200 arcsec - one CCD— 400x400 arcsec - four CCD’s— 200x400 arcsec - two CCD’s column
stacked in Declination
— 400x200 arcsec - two CCD’s row stacked in
Right Ascension
![Page 9: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/9.jpg)
16 November 2001
Guidance & Control Bradley/Markley p9
SuperNova/Acceleration Probe
• FGS Design – placement
![Page 10: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/10.jpg)
16 November 2001
Guidance & Control Bradley/Markley p10
SuperNova/Acceleration Probe
• FGS Design – Guide Star Probability Determined with 100 arcsec
increments in Right Ascension and Declination.
NEP mv range is 5.5 to 18.2
SEP mv range is 6.1 to 17.6NEP SEP
200x200 asec
95.77% 97%
400x400 asec
99.995% 100%
200x400 asec
99.8% 99.9%
400x200 asec
99.8% 99.3%
![Page 11: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/11.jpg)
16 November 2001
Guidance & Control Bradley/Markley p11
SuperNova/Acceleration Probe
• FGS Design – Guide Star Probability Metric will be reduced for near
neighbor’s and exclusion areas around CCD edge resulting from attitude Star Tracker error.
![Page 12: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/12.jpg)
16 November 2001
Guidance & Control Bradley/Markley p12
SuperNova/Acceleration Probe
• FGS Design – Histograms
![Page 13: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/13.jpg)
16 November 2001
Guidance & Control Bradley/Markley p13
SuperNova/Acceleration Probe
![Page 14: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/14.jpg)
16 November 2001
Guidance & Control Bradley/Markley p14
SuperNova/Acceleration Probe
![Page 15: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/15.jpg)
16 November 2001
Guidance & Control Bradley/Markley p15
SuperNova/Acceleration Probe
![Page 16: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/16.jpg)
16 November 2001
Guidance & Control Bradley/Markley p16
SuperNova/Acceleration Probe
![Page 17: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/17.jpg)
16 November 2001
Guidance & Control Bradley/Markley p17
SuperNova/Acceleration Probe
![Page 18: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/18.jpg)
16 November 2001
Guidance & Control Bradley/Markley p18
SuperNova/Acceleration Probe
![Page 19: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/19.jpg)
16 November 2001
Guidance & Control Bradley/Markley p19
SuperNova/Acceleration Probe
![Page 20: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/20.jpg)
16 November 2001
Guidance & Control Bradley/Markley p20
SuperNova/Acceleration Probe
• FGS Design – Roll Control CCD’s placed on opposite ends of the
focal plane can provide:— optional roll control— disturbance detection
– Small focal plane X-Y disturbances will be greatly magnified in the roll axis.
– This indicator (even if not used for control), could assist in post facto image analysis and on-board Loss-Of-Lock detection.
![Page 21: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/21.jpg)
16 November 2001
Guidance & Control Bradley/Markley p21
SuperNova/Acceleration Probe
• Recommendation 200x400 arcsec CCD’s on opposite
ends of the focal plane Redundancy Roll control 95% Guide Star probability after
star elimination.
![Page 22: SNAP Fine Guidance Art Bradley/ Spacecraft System Engineering Services](https://reader036.vdocuments.mx/reader036/viewer/2022070405/56813e21550346895da80236/html5/thumbnails/22.jpg)
16 November 2001
Guidance & Control Bradley/Markley p22
SuperNova/Acceleration Probe