Drawing Number: 00014-PP02 Rev: D

1. Drawing Number: 00014-PP02 Rev: D SNAP Electrical Block Diagram Power Point Presentation Drawn by: H. Heetderks Cognizant Engineer: H. Heetderks Date: 2003-11-03

2. SNAP Electrical Block Diagram Henry Heetderks Space Sciences Laboratory, UCB

3. 3 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Introduction The following slides consist of a simplified block diagram for the SNAP instrument and spacecraft followed by a detailed block diagram (controlled as SNAP drawing number 00010-AC14, currently at Rev H) The drawing shows interfaces between major instrument subassemblies and between SNAP and the JDEM spacecraft, and also shows how redundancy is implemented and single point failures are eliminated (To see details of this drawing zoom to 400%) Following the discussion of architecture and redundancy is a block diagram showing the data flow for a single string from the visible imager CCD to the out put which modulates the spacecraft Ka band transmitter The final viewgraphs show the inputs and outputs and describe the operation of each block in the data chain

4. 4 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Overall View of the SNAP Observatory

5. 5 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks SNAP Simplified Electrical Block Diagram

6. 6 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Electrical System Features No single point failures Fully redundant and cross strapped spacecraft Redundant Observatory Control Units and Large Memories in instrument Instrument Detectors and Mechanisms modularized for failure tolerance Industry Standard 1553 interface between instrument and spacecraft Wide band downlink controlled directly by Instrument Memory Capability incorporated into the Instrument No SSR in spacecraft Spacecraft consists of 3 independent modules connected by a 1553 bus Power system ACS System C&DH System

7. 7 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Detailed Block Diagram [shows full redundancy plan]

8. 8 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks CCD to Transmitter � One String

9. 9 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Imager CCD Module One back illuminated CCD is mounted on an AlN2 circuit board which is mounted on an invar/ molybdenum module mounted to the focal plane Four video outputs from the CCD are CDS�ed and ADC�ed by a custom ASIC (the CRIC chip) mounted on the rear of the circuit board The interface lines to this module include CCD clocks, a number of DC bias voltages, and the digital and control lineS which operate the ASIC Module operates at 135 degrees Kelvin

10. 10 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks CCD Clock Module One Clock Module is dedicated to each CCD Module Connection to the CCD is made via a 50-60 pin connector at one end Circuit provides CCD clocking and control of the CRIC chip System includes one or more ASIC�s and a DC-DC converter A connector at the other end has a pair of independent Power and Data interfaces for connection to the prime and back-up ICU�s Controller multiplexes the 4 CRIC ADC outputs onto a single serial interface Circuit operates at 135 Kelvin

11. 11 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Guider CCD Clock Circuit This circuit is similar to that used for the Imager CCD�s except that its clock waveforms and timing are consistent with the video rate of the Guider CCD�s

12. 12 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks ICU Interface Board The primary function of this circuit is to reduce the wire count coming from the focal plane to the ICU while isolating the redundant ICU�s from each other Separate identical circuits are dedicated to the two redundant ICU�s A relay matrix allows power to be applied to any combination of the 9 CCD�s controlled by each of the four interface boards Clock and Strobe signals are buffered and fanned out to each CCD module Guider interface is separate from Imager CCD�s

13. 13 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Visible Detector Interface Board in ICU One such board or module in the ICU controls a block of 9 Imager CCD�s Provides common Clock and Strobe lines for the serial data interface and takes data from 9 CCD�s Board is set up by the ICU DPU via a CDI interface (a serial interface used on the last dozen or so SSL projects) Switched power is provided by the ICU DC-DC power system under DPU control Interleaved data from the four corners of each of the 9 CCD�s are output from a single high speed serial interface to the Mass Memory (I have called this �USB� as a place holder). Data are written in a quasi-CCSDS Source Packet format.

14. 14 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Guider System Interface Board in ICU The Guider Interface board has a dedicated 3 wire serial link to each of the 4 guider CCD�s The DPU sets up modes and supplies power in the same way as for the Imager interface This board: Locates bright spots on the Guider CCD�s Calculates centroids Prepares a CCSDS packet with centroid data, brightness, quality, time, (velocities?), etc. Packet is dumped onto 1553 bus and also put into Mass Memory

15. 15 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks NIR Detector Interface Board in ICU Circuit operation is TBD but similar to that of visible imager

16. 16 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks DPU Board in ICU DPU sets up all ICU and Mass Memory functions using the CDI interface System has a port to read and write to the Mass Memory for diagnostic functions, but does not normally process or transfer high speed science data The DPU receives ground commands from the spacecraft via the 1553 and processes and distributes them to other subsystems It also collects SOH data via the CDI and generates CCSDS engineering packets and delivers them to the spacecraft via 1553 The DPU controls a switch system routing science data to the various modules in the Mass Memory

17. 17 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Controller Board in Mass Memory Unit All Mass Memory functions are controlled by the DPU via CDI command A cross point switch in the controller routes the various science data streams to the desired memory module The controller is provided with hardware capability to: Perform block data transfers De-interleave science data and generate final CCSDS source packets Perform memory scrubs and EDAC Perform data compression on stored data

18. 18 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks 128 Gbit Mass Memory Board Live chip map transparently maps out bad memory locations Boards are separately powered and have provision on interface lines to prevent power scavenging SEU latch-up circuit breaker included on board if needed

19. 19 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Mass Memory Unit Power System DC-DC converter takes 28 volt power from the ICU and generates switched, limited, and monitored power for all memory subsystems System can be powered from either the prime or back-up ICU CDI command from Memory Controller board determines which services are powered

20. 20 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks DPU Power Converter & Control Board The power converter in the ICU provides switched, limited, and monitored power for all ICU subsystems The system can be powered from either the prime or back-up spacecraft C&DH CDI commands from the DPU determine which services are powered

21. 21 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks ICU Downlink Board This board combines CCSDS source packets into CCSDS transfer frames and inserts the final header information The data are output as complete transfer frames to the Ka band transmitter at a 300 Mhz rate The output may be sent via 1, 2 or 4 lines depending on the details of the transmitter design Input data from the Mass Memory may be transferred on as many as 4 pre-interleaved lines depending on the speed of the memory�s serial data interface

22. 22 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Calibration Source Controller Board This low data rate board has only power and CDI interfaces

23. 23 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Motor Controller Board The Cassegrain shutter drive electronics requires a somewhat elaborate feed back control system to take position data from a magnetic angle resolver and control current to the limited angle torque motor so as to follow a prescribed opening waveform with high precision Control of the motorized bipods is expected to be quite a bit easier Plain stepper motor?

24. 24 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Redundant Control of Mechanisms Separate motors on a common shaft actuate the same mechanism Separate position sensors for the prime and back-up interfaces Prime int�f connects to prime ICU; back-up int�f connects to back-up ICU I.e. no cross strapping

25. 25 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Structure Thermal Control System Thermal control board in OCU has 32 separately fused branches of two-wire interfaces consisting of a power line with superimposed data and status return A second level of fusing distributed in the harness drives 8 ASIC�s from each branch Connectors are inserted as needed to insure that structural elements are not captive by wiring Each ASIC contains four heater controllers Set point of each controller can be independently commanded by ICU IICU can read temperature of each sensor for inclusion in engineering telemetry Each heater consists of a prime and back-up element, one controlled by the prime thermal control system and the other controlled by the back-up system Overall, the system independently controls and monitors 1,024 heater elements

26. 26 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Thermal Control ASIC One ASIC controls four independent heater circuits A single 2 wire interface controls all four circuits Power with superimposed command data and status return ASIC�s are used in a pair of redundant circuits which control four heaters with redundant elements Redundant thermistors provide temperature sense for the prime and back-up ASIC�s

27. 27 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Thermal Control Board in ICU

28. 28 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Pyro Controller Board in ICU There is currently one mechanical deployment baselined on the SNAP observatory: the opening of the telescope front cover Options for effecting this include an EUVE type bolt cutter or a Frangibolt of the type used on THEMIS In either case a DPU controlled power switch is required to actuate the mechanism

29. 29 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft Power System

30. 30 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft Power System Notes System operates solar array, performs battery charge control, and supplies switched, limited, and monitored +28 volt +/-2% power to OCU�s and spacecraft systems Includes a pair redundant independent controllers, either of which can control all solar array elements and both batteries Each controller has a pair of redundant 1553 interfaces to provide full cross strapped redundancy to the spacecraft 1553 bus Every powered subsystem (ICU�s and S/C components) has a redundant set of protected power input interfaces I.e. failure on one side will not propagate to the other side The Power System is stand alone with a pair of dedicated control units which are independent mechanically and electrically from the spacecraft C&DH and ACS systems. The only connection between it and the other S/C systems is the 1553 interface and the power service lines. There shall be no aspect or feature of the system which limits the ability of the SNAP Project to procure the power system from a different vendor than those supplying the other two major spacecraft subsystems.

31. 31 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft C&DH System

32. 32 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft C&DH System Notes The C&DH system includes the C&DH controllers, the S-band transponders, S-band antennas, the Ka band transmitters, and fixed 120 cm Ka band gain antenna. Either of the redundant independent controllers can control either set of telemetry components Each controller has a pair of redundant 1553 interfaces to provide full cross strapped redundancy to the spacecraft 1553 bus. The C&DH controller is the bus master. The C&DH controller tasks include Command decoding S-band antenna switching S/C Engineering T/M collection and transmission Control of high gain antenna gimbal Modulation of the Ka band transmitters is done directly by the OCU The C&DH System is stand alone with a pair of dedicated control units which are independent mechanically and electrically from the spacecraft Power and ACS systems. The only connection between it and the other S/C systems is the 1553 interface and the power service lines.

33. 33 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft ACS / Propulsion System

34. 34 SNAP Electrical Block Diagram 2004 May 18 H. Heetderks Spacecraft ACS / Propulsion System Notes The ACS / Prop system includes the ACS controllers, Reaction Wheels, Coarse Star Trackers, IRU�s, Sun Sensors, Propellant Tanks, Thrusters, and propellant valves and lines The current baseline has 3 star trackers instead of the 2 shown Each controller has a pair of redundant 1553 interfaces to provide full cross strapped redundancy to the spacecraft 1553 bus Interface between the ACS subsystem components is done by a separate redundant 1553 bus All ACS components including Instrument Fine Guider interface via the 1553 bus Interface to propulsion components is done by a dedicated custom board in the controller The propellant system includes 6 redundant fuel tanks connected to a redundant pair of manifolds with a redundant set of thrusters The ACS / Prop system controller tasks include Implementation of Safe-Hold mode on initial power up Operation of the ACS control algorithms including: Coarse (~2 arcsec) pointing of the spacecraft Fine pointing using Fine Guider centroid data received from the ICU via the S/C 1553 bus Control of prop system for R/W dump Control of prop system for orbit injection and station keeping Control of prop system for S/C disposal The ACS / Prop System is stand alone with a pair of dedicated control units which are independent mechanically and electrically from the spacecraft Power and C&DH systems. The only connection between it and the other S/C systems is the 1553 interface and the power service lines.