1. SuperNova / Acceleration Probe System Engineering Mike Roberto and Mike Amato November 16, 2001

2. SNAP System Engineering P2 Roberto/Amato ISAL Team Mike AmatoSystem Engineering Jeff BologneseStructural Analysis Art BradleyStar Field /Fine Guidance Jennifer BrackenISAL Team Lead Judy BrannenMechanical Design Mick CorreiaMechanical Design Paul EarleElectrical Dennis EvansOptics Rodger FarleyMechanical Systems Landis MarkleyGuidance, Navigation, and Control Wes OusleyThermal Mike RobertoISAL Systems Carl StahlDetectors John WoodISAL Science Liaison Eric YoungElectro-optical Systems

3. November 16, 2001 SNAP System Engineering P3 Roberto/Amato Summary 1.Requirements 2.Trades and Issues 3.Instrument Diagram 4.Orbit Parameters 5.Observation Strategy Summary 6.Optics 7.Detectors 8.Mass, Data Rate 9.Conclusions

4. November 16, 2001 SNAP System Engineering P4 Roberto/Amato Requirements

5. November 16, 2001 SNAP System Engineering P5 Roberto/Amato Trades and Issues 1.Baselining Hubble type structure rather than lower structure Hubble like and upper structure tripod. Metering structure is stiffer, less obscuration, and more thermally isolated. However, it has higher mass and more complicated baffle integration. 2. Converged on ‘two vane’ shutter design. Advantage is the same illumination time for each pixel, but feedback control is needed. Alternate shutter type did not need feedback control but required very rapid operation to minimize time differences in pixel illumination. 3. Baselining five degrees of freedom secondary mirror adjustment Based on flight design, because secondary mirror is the most sensitive to alignment errors. Tertiary mirror adjustment mechanism does not seem to be needed. 4. May not need thermal control of metering structure, but this could easily be added (approximately 150 W). Plan to use low coefficient of thermal expansion graphite epoxy materials.

6. November 16, 2001 SNAP System Engineering P6 Roberto/Amato Trades and Issues (continued) 5. Do not see unusual stray light problems, but careful baffling is necessary. 6. Baselining 16 bit analog to digital converters. Could also use 12 bit A/D converters with multiple gains. 7. Baselining fixed filters on focal plane which requires stepping across focal plane. Advantage is the reduction in the number of mechanisms (filter wheel not needed. 8. Future Trade – consider placements of spectrographs so behind focal plane to reduce stray light.

7. November 16, 2001 SNAP System Engineering P7 Roberto/Amato Instrument Diagram

8. November 16, 2001 SNAP System Engineering P8 Roberto/Amato Orbit Parameters Modified Chandra orbit for complete observation of ~ northern or southern ecliptic in one orbit and equalizing spectrograph and focal plane observation times. Radius of perigee3.0 Earth radii Radius of apogee24.5 Earth radii Period3.0 days Height for data collection=/> 60 x 10^3 km Time spent near perigee12 hours Time for focal plane observations29 hours Time using spectrograph31 hours

9. November 16, 2001 SNAP System Engineering P9 Roberto/Amato Observation Strategy Summary Art Bradley and Landis Markley provided the inputs. Inside electron belts, slew 180 degrees, download data, orbit maintenance, shutter closed 2.Outside electron belts, use ACS guide star CCDs on focal plane for fine pointing control when shutter is open 3.Observation time = 200 seconds 4.Focal plane shutter is then closed for 20 seconds while focal plane is read out, drift is fixed, and pointing is changed by ¼ of CCD position 5. Sky observations on focal plane are repeated for 480 steps in one direction, covering about 5 degrees in 29 hours

10. November 16, 2001 SNAP System Engineering P10 Roberto/Amato Optics

11. November 16, 2001 SNAP System Engineering P11 Roberto/Amato Detectors

12. November 16, 2001 SNAP System Engineering P12 Roberto/Amato Mass

13. November 16, 2001 SNAP System Engineering P13 Roberto/Amato Data Rate 1.Focal plane average data rate during an observation 40 M bits/sec (144 CCD arrays with 1600x1600 pixels, 44 HgCdTe arrays with 2000x2000 pixels,16 bits per pixel, 220 seconds to complete observation plus read out focal plane) 2.Average data rate during spectrograph observation 73 K bits/sec (one HgCdTe array with 1000 x 1000 pixels, 16 bits per pixel) 3.Data collected per orbit (assuming about half focal plane observations and half spectrograph observations, assume data compression by factor of 2) Focal plane telemetry per orbit2.1 T bits Spectrograph telemetry per orbit4.0 G bits Housekeeping telemetry per orbit47 M bits 4. If focal plane data taken all the time, and data compressed by factor or two, total data collected during orbit about 4.2 T bits.

14. November 16, 2001 SNAP System Engineering P14 Roberto/Amato Backup Slides

15. November 16, 2001 SNAP System Engineering P15 Roberto/Amato Orbit Parameters

16. November 16, 2001 SNAP System Engineering P16 Roberto/Amato Data Rate