SA2 Flexible Array 39.67 ft (12.1 m)

9.75 ft (3.3 m)

SA3 Rigid Array 24.75 ft (7.1 m)

8.0 ft (2.6 m)

Item Power Size Weight Comments

SA2 4600 W at 39.67 ft x 9.75 ft 339 lb Actual on-orbit performance Flexible Array 6 years (12.1 m x 3.3 m) per wing measured at Winter Solstice, (actual) December 2000

SA3 5270 W at 24.75 ft x 8.0 ft 640 lb increased capability for Rigid Array 6 years (7.1 m x 2.6 m) per wing planned science (predicted)

Less shadowing and blockage

K7444_528A

Fig. 5-25 Solar Array detail comparison S c i e n c e I n s t r u m e n t Components of the SI C&DH unit are: • NASA Standard Spacecraft Computer C o m m a n d a n d D a t a (NSCC-1) H a n d l i n g U n i t • Two standard interface circuit boards for the computer The SI C&DH unit keeps all science • Two control units/science data instrument systems synchronized. It formatter units (CU/SDF) works with the DMU to process, format • Two central processing unit (CPU) and temporarily store information on the modules data recorders or transmit science and • A PCU engineering data to the ground. • Two RIUs • Various memory, data and command communications lines (buses) con- Components nected by couplers. The SI C&DH unit is a collection of elec- tronic components attached to an Orbital These components are redundant so the Replacement Unit (ORU) tray mounted on system can recover from any single failure. the door of Bay 10 in the SSM Equipment Section (see Fig. 5-26). Small remote inter- NASA Computer. The NSSC-1 has one CPU face units (RIU), also part of the system, and eight memory modules, each holding provide the interface to individual sci- 8,192 eighteen-bit words. An embedded ence instruments. software program (the “executive”) runs Hubble Space Telescope Systems 5-25 Extravehicular Activity Handle Remote Two Central A118 Interface Unit Processor A118 Modules A118 Four Two Standard A118 Memories Interfaces A231 A109 A120 A300 A211 A117 Four A115 Memories A113 A230 A300 A111

A210

Remote Control Unit/ Interface Unit Science Data Formatter Control Unit/ Science Data Power Control Unit Formatter Bus Coupler Orbital Unit A240 Replacement Unit Tray K7444_529

Fig. 5-26 Science Instrument Control and Data Handling unit

the computer. It moves data, commands The CU/SDF receives ground commands, and operation programs (called applica- data requests, science and engineering tions) for individual science instruments data, and system signals. Two examples in and out of the processing unit. The of system signals are “time tags”—clock application programs monitor and con- signals that synchronize the entire space- trol specific instruments, and analyze and craft—and “processor interface tables”— manipulate the collected data. communications codes. The CU/SDF transmits commands and requests after The memory stores operational com- formatting them so that the specific mands for execution when the telescope destination unit can read them. For is not in contact with the ground. Each example, ground commands and SSM memory unit has five areas reserved for commands are transmitted with differ- commands and programs unique to each ent formats because ground commands science instrument. The computer can be use 27-bit words and SSM commands reprogrammed from the ground for use 16-bit words. The formatter translates future requests or for working around each command signal into a common failed equipment. format. The CU/SDF also reformats and sends engineering and science data. Standard Interface Board. The circuit Onboard analysis of the data is an board is the communications bridge NSSC-1 function. between the computer and the CU/SDF. Power Control Unit. The PCU distributes Control Unit/Science Data Formatter. and switches power among components The heart of the SI C&DH unit is the of the SI C&DH unit. It also conditions CU/SDF. It formats and sends all com- the power required by each unit. For mands and data to designated destina- example, the computer memory boards tions such as the DMU of the SSM, the typically need +5 volts, -5 volts and NASA computer and the science instru- +12 volts while the CU/SDF requires ments. The unit has a microprocessor for +28 volts. The PCU ensures that all control and formatting functions. voltage requirements are met.

5-26 Hubble Space Telescope Systems Remote Interface Unit. RIUs transmit System Monitoring. Engineering data tell commands, clock and other system the monitoring computer whether instru- signals, and engineering data between ment systems are functioning. At regular the science instruments and the SI C&DH intervals, varying from every 500 millisec- unit. However, the RIUs do not send onds to every 40 seconds, the SI C&DH science data. There are six RIUs in the unit scans all monitoring devices for telescope: five attached to the science engineering data and passes data to the instruments and one dedicated to the NSCC-1 or SSM computer. The comput- CU/SDF and PCUs in the SI C&DH unit. ers process or store the information. Any Each RIU can be coupled with up to two failure indicated by these constant tests expander units. could initiate a “safing hold” situation and thus a suspension of science opera- Communications Buses. The SI C&DH tions. Refer to page 5-14, Safing unit contains data bus lines that pass (Contingency) System. signals and data between the unit and the science instruments. Each bus is Command Processing. Figure 5-27 shows multiplexed: one line sends system mes- the flow of commands within the SI C&DH sages, commands and engineering data unit. Commands enter the CU/SDF requests to the module units, and a reply (bottom right in the drawing) through the line transmits requested information and SSM Command DIU (ground commands) science data back to the SI C&DH unit. A or the DIU (SSM commands). The CU/SDF coupler attaches the bus to each remote checks and reformats the commands, unit. This isolates the module if the RIU which then go either to the RIUs or to fails. The SI C&DH coupler unit is on the the NSCC-1 for storage. Time-tagged ORU tray. commands, stored in the computer’s memory (top right of drawing), also Operation follow this process. The SI C&DH unit handles science instru- ment system monitoring (such as timing Each command is interpreted as “real and system checks), command processing time,” as if the SI C&DH just received it. and data processing. Many commands actually are onboard

Remote Modules Science Science Instrument Instrument Unique Memory Unique Memory

Remote Stored Modules Stored Science Command Instrument Command Output Buffer Memory Unique Memory Remote Modules Science Science Instrument Instrument Commands Unique Memory Unique Memory Remote To Science Instruments 1 – 5 To Modules NASA Standard Spacecraft Computer Model-I and Standard Remote Interface Modules Unit 1 Commands Units 6 and 7 Time Tags and Tags Time Units 4 and 5 Data Management Data Management Data Management

Support Systems Computer Commands Module Processor Interface Table Words Word Order, Time Tag and Parity Checks From Command Supervisory Bus Data Interface Parity and Type Reformat Code Checks 27-bit Commands

CU/SDF Remote To CU/SDF Parity and Word Modules Command Control Order Checks 16-bit Commands Processing Logic Science Instrument From Data Unique Memory Interface Unit To Power Control Unit/Science Data Formatter (CU/SDF) Control Unit

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Fig. 5-27 Command flow for Science Instrument Control and Data Handling unit

Hubble Space Telescope Systems 5-27 stored commands activated by certain S p a c e S u p p o r t situations. For example, when the tele- scope is positioned for a programmed E q u i p m e n t observation using the Cosmic Origins Spectrograph, that program is activated. Hubble was designed to be maintained, The SI C&DH can issue certain requests repaired and enhanced while in orbit, to the SSM, such as to execute a limited extending its life and usefulness. For number of pointing control functions to servicing, the Shuttle will capture and make small telescope maneuvers. position the telescope vertically in the aft end of the cargo bay, then the crew Science Data Processing. Science data will perform maintenance and replace- can come from all science instruments ment tasks. The Space Support at once. The CU/SDF transfers incom- Equipment (SSE) provides a mainte- ing data through computer memory nance platform to hold the telescope, locations called packet buffers. It fills electrical support of the telescope dur- each buffer in order, switching among ing servicing and storage for Orbital them as the buffers fill and empty. Replacement Instruments (ORI) and ORUs. Each data packet goes from the buffer to the NSCC-1 for further processing, The major SSE items to be used for or directly to the SSM for storage in SM4 are the Flight Support System the data recorders or transmission to (FSS) and the Super Lightweight the ground. Data return to the Interchangeable Carrier (SLIC), Orbital CU/SDF after computer processing. Replacement Unit Carrier (ORUC) and When transmitting, the CU/SDF must Multi-Use Lightweight Equipment (MULE) send a continuous stream of data, Carrier. Crew aids and tools also will be either full packet buffers or empty used during servicing. Section 2 of this buffers called filler packets, to main- guide describes details specific to SM4. tain a synchronized link with the SSM. Special checking codes (Reed-Solomon and pseudo-random noise) can be Orbital Replacement Unit Carrier added to the data as options. Figure An ORUC is a pallet outfitted with shelves 5-28 shows the flow of science data in and/or enclosures that is used to carry the telescope. replacements into orbit and to return replaced units to Earth.

NASA Standard Spacecraft Computer Model-I and Standard Interfaces Access 8 Access 3 Science Data Bit Stream Control Words Control Words Direct Memory Direct Memory

From End of Period Control Commands Central Unit/ Control Science Data Logic Formatter NASA Model-I Computer

Direct Memory Access 3 Direct Memory To Data

Direct Memory Access 14 Direct Memory Command Processing Management Unit Data Logs and Processed Science Control Control Unit/Science Data Formatter Logic PN Code Direct Memory Access 5 Direct Memory

Packet Raw Science Data Control Buffer 1 Switch Raw or Packetized Data Encoding Selected) Raw Time Tag (Only if Reed-Solomon (Only if PN Encoding Selected) Science Data Packet Segments Science Reed-Solomon Checkbit Segments Control Unit/ Reed- Format RAM Science Data Control Solomon Pseudorandom Noise Data Science Data and ROM Formatter Timer Switch Encoder Code Generator Input Selection Logic Ancillary Data Science Instruments Destination Time Tag Switch Packet (1 Per Science Filler Buffer 2 Instrument) Packets Control Unit/Science Data Formatter Logic

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Fig. 5-28 Flow of science data in the Hubble Space Telescope

5-28 Hubble Space Telescope Systems