For the second German Spacelab Mission D-2 all activities related to operating, monitoring and controlling the experiments on board the Spacelab were conducted from the German Space Operations Control Center (GSOC) operated by the Deutsche Forschungsanstalt für Luft- und Raumfahrt (DLR) in Oberpfaffenhofen, Germany. The operational requirements imposed new concepts on the transfer of data between Germany and the NASA centers and the processing of data at the GSOC itself. Highlights were the upgrade of the Spacelab Data Processing Facility (SLDPF) to real time data processing, the introduction of packet telemetry and the development of the high-rate data handling front end, data processing and display systems at GSOC. For the first time, a robot on board the Spacelab was to be controlled from the ground in a closed loop environment. A dedicated forward channel was implemented to transfer the robot manipulation commands originating from the robotics experiment ground station to the Spacelab via the Orbiter's text and graphics system interface. The capability to perform telescience from an external user center was implemented. All interfaces proved successful during the course of the D-2 mission and are described in detail in this paper.
CCSDS Consultive Committee for Space Data Systems CAP Command Acceptance Patterns CDF Command Data File CMD Command DLR Deutsche Forschungsanstalt für Luft- und Raumfahrt DPS Data Processing System DTS Data Transfer System ECIO Experiment Computer Input/Output EGSE Experiment Ground Support Equipment GSFC Goddard Space Flight Center GSOC German Space Operations Control Center HDRR High Data Rate Recorder HRFL High Rate Forward Link HRM High Rate Multiplexer JSC Johnson Space Center KUSP Ku-Band Signal Processor LAN Local Area Network OD Operational Downllink PCM Pulse Code Modulation PPF Payload Parameter Frame SCIO Subsystem Computer Input/Output SIPS Spacelab Input Processing System SLDPF Spacelab Data Processing Facility SPARCS pacelab Realtime Packet Converter System STL Subtimeline TAGS Text and Graphics System TDM Time Division Multiplexer WAN Wide Area Network
(1) Transfer the complete Spacelab high rate telemetry to GSOC. Capture, store and distribute the data.
(2) Process the Spacelab Experiment Computer and Subsystem Computer Input/Output (ECIO/SCIO) as part of the high rate telemetry and make it available for "quick-look" display to allow the mission operations support team to monitor the progress of the mission, status and health of the experiment computer and facilities.
(3) Transfer, capture, process and display the Payload Parameter Frame (PPF) telemetry. The PPF consisted of 151 data words of the Spacelab operational downlink processed by the Johnson Space Center (JSC).
(4) Forward command data blocks originating from the GSOC Command System in order to remotely manipulate the Spacelab and experiment computers.
(5) Receive and distribute command acceptance and trajectory data blocks.
(6) Support robot experiment operations by forwarding manipulation commands with minimum delay.
(7) Support telescience operations from the Microgravity User Center in Cologne, Germany.
(8) Support the retrieval of data in chronological order from the data archive in order to facilitate troubleshooting and detailed evaluation of the progress of the experiment.
(9) The performance pertaining to the distribution, processing and display of telemetry data was required to maintain the original data rates which were in the order of one update/repetition per second for most data channels.
(10) Deliver the experiment-related high rate Spacelab telemetry to processing equipment provided by the experimenters. The computers installed and operated by the experimenters are hereafter referred to as Electrical Ground Support Equipment (EGSE)
(11) Offer services prior to the actual mission during the Spacelab integration phase and the "integrated" simulations. Interfaces were implemented to support data flow from the Spacelab integration facility and the Spacelab Training Assembly, both located in Northern Germany. These interfaces, along with the voice, video, fax and other communication services necessary for the overall operations, are not discussed in this paper.
Spacelab High Rate Telemetry
The Spacelab provided a high-rate data system for the transfer of the ECIO, SCIO and PCM-data generated by the experiment facilities. The ECIO and SCIO contained housekeeping, monitoring and low-rate science data. The experiment channels exclusively contained science data. 5 experiment data and the 2 computer output channels with an overall bitrate of 607.39 kbps were processed by the High Rate Multiplexer (HRM) and nominally down linked at 1 Mbps via the Ku-band signal processor (KUSP). During Ku-band loss of signal the data was recorded onto the High Data Rate Recorder (HDRR) from where it was regularly dumped at a rate of 24:1.
The composite HRM signal was captured, processed and transferred to the GSOC by the Data Transfer System (DTS) implemented at the Spacelab Data Processing Facility (SLDPF), Goddard Space Flight Center (GSFC). The DTS incorporated the enhanced Spacelab Input Processing System (SIPS) and the newly developed Spacelab Realtime Packet Converter System (SPARCS).
The DTS consisted of a triple redundant system that provided real time processing and performed the following tasks:
(1) Captured the composite HRM onto tapes and monitored its data quality (2) Extracted 7 HRM data, the HDRR dump, voice and time channels and monitored their quality (3) Captured the extracted HDRR dump on tapes and played back the data at the nominal data rate upon request in parallel to the real-time data transmissions (4) Processed the HRM data by the SIPS which output data records containing a number of HRM minor frames for each data channel (5) Packetized the data records into Transfer Frames according to CCSDS recommendations by the SPARCS and output the frames at a rate of 1024 kbps (6) Replayed data from the tapes upon request in parallel to the real-time data transmissions. All minor frames of the HRM data, output by the SLDPF, were frame synchronized and tagged with Spacelab time and downlink quality.
Figure 1 Telemetry Data Flow Schematic
Auxiliary Data
Auxiliary data to support the mission was exchanged between the Johnson Space Center (JSC) and the GSOC. This included the PPF data set which was downlinked as part of the Orbiter Downlink data stream using either channel 1 of the KUSP or S-band propagation, processed and output by JSC at the rate of 1 block per second.
Command data blocks generated by the GSOC command system were forwarded to JSC at the maximum rate of 1 command data block per 3 seconds.
The robot experiment remote manipulation commands which were generated by the robot ground station were forwarded by GSOC to JSC using a dedicated link (HRFL). A new interface was implemented at JSC to validate and merge the commands into the Text and Graphic System channel (TAGS) for high speed uplink.
JSC periodically output trajectory messages (TRAJ) and generated acceptance data blocks (CAP) in response to the GSOC commands.
Time Division Multiplexers and Satellite Links
A triple redundant Time Division Multiplexer (TDM) system was set up both at GSFC and GSOC and provided the gateway to the communication links across the Atlantic. The TDM operated at an aggregate rate of 2048 kbps and incorporated 3 data, 22 voice, 2 FAX and 1 WAN channel. Two diverse satellite paths via two different Intelsat satellites transported the TDM aggregate. Ground stations were installed at GSFC and GSOC. Nominally one satellite link was dedicated for real-time data transfer and the other for the transfer of playback and replay data.
Figure 2 GSOC Functional Block Diagram
Front End Processing System
All incoming and outgoing telemetry data were transported to and from the GSOC Front End System via the Time Division Multiplexer system (refer to Figures 2/ 2).
(1) Redundant APTEC high speed input/output processors were implemented to process the Transfer Frames and embedded data. Nominally the APTEC eal time and hot backup systems were operated in parallel. In detail the high-rate front end system performed the following tasks.
(a) Two frame synchronizers received the Transfer Frames from two different satellite links in parallel at 1024 kbps each and forwarded both data streams to the processor which performed all operations in parallel.
(b) The 5 HRM data channels were restored from the Transfer Frames and synchronized on major-frame level (optional).
(c) Quality monitor information of the Transfer Frames and the embedded Spacelab minor frames was generated and displayed for on-line evaluation.
(d) Subsets from the ECIO and SCIO were generated and transferred to the Data Processing System via a special backplane interface at the rate of 80 kbps.
(e) HRM data frames and ECIO subsets were packaged into standard GSOC network record blocks providing time-tags and data quality information and transferred to the EGSEs via a dedicated LAN at the rate of 550 kbps.
(f) All Transfer Frames containing payload data and the restored HRM data frames were stored in the high-rate data archive which was based on a video tape storage device. Major-frame data could be retrieved from the archive and transferred to the EGSE. After the mission the high-rate data archive was reduced by building data records arranged in chronological order and made available on different media for post-mission evaluation by the experimenters.
(2) A set of redundant processors was implemented to handle all incoming and outgoing auxiliary data in NASCOM block-format via two 19.2 kbps lines. The NASCOM line handlers
(a) demultiplexed the NASCOM data blocks and routed the PPF, command acceptance and trajectory data blocks to the DPS, the Command System and the Orbit/Big Screen System respectively
(b) monitored the data quality using the established GSOC NASCOM block monitoring
(c) received commands from the Command System (ECOS CMD) and the robot EGSE (HRFL) and routed the data to the respective TDM channel.
Figure 3 D-2 GSOC Data Processing User Interfaces
Data Processing System (DPS)
The Data Processing System was designed to process the Spacelab computer input/output channel data and the Payload Parameter Frame data sets as received from the front end system. For that purpose VAX 6320 processors were operated in a cluster environment. High-speed line printers and laser printers were available to generate computer printouts.
About 3200 parameters were computed as standard Spacelab data types, e.g. engineering unit, character, string and time conversion and up to 4th order polynomial calculations. About 600 parameters were derived from the standard data types and required special processing. These included complex shuttle attitude calculations, ring buffer rearrangements and value sensitive calculations. The software further flagged the out-of-limit conditions of selected parameters and allowed for the change of the out-of-limit values on-line. The computed telemetry was distributed to the display processing system over a dedicated local area network (LAN) using a "broadcast" data transfer method. The total amount of telemetry parameters to be transferred was in the order of 4000 including system parameters.
Telemetry data was stored within the data processing system computers. The storage contained the converted and calibrated telemetry parameters for both real time and playback transmissions in chronological order. The contents of the storage were made available as computer printouts to the experimenters and mission operations support personnel on request.
Display Processing System
At the tail end of the processing chain the telemetry output by the DPS could be observed on "quick-look" displays incorporated in a display processing system. The system consisted of 60 independent computer workstations picking up the "broadcast" parameters from the dedicated LAN. In this configuration each workstation was independent and did not influence the network or other workstations in case of failure.
Each workstation comprised a 19" color monitor, an ink-jet printer, a keyboard and a mouse. Provisions were made for attaching a second monitor. Data was presented as display pages in windows on the display workstation screen. Pages were selected from the display page directory. Graphics and alphanumeric representations and limit violation color coding were supported. The contents of each display page could be printed on the attached printer. The printer supported color printouts. The mouse provided all user interface functions, such as format selection, window manipulation and print initiation. Additionally an auxiliary timing unit allowed the setting of alarms in GMT and MET.
EGSE Services
The control center only distributed the experiment high rate data. Provisions were made for the experimenters to bring in their own computer equipment and plug it into the network. The requirement for experimenters to operate independent of the control center was supported for the telescience experiment.
The EGSE's ranged from single PC-type computers to whole computer networks. The EGSE's were physically connected to a dedicated LAN, a thick-wire ETHERNET with transceivers as the interface and had to comply to the DECnet protocol standard or the DEC Pathworks standard for DOS/Macintosh. User data connections did not differentiate between inside and outside users. Figure 4 provides an overview of typical EGSE connections to the LAN.
Data transfer mechanisms were established for
(a) continuous data, i.e. high-rate telemetry, robot manipulation commands and telescience data, by establishing logical links using the DECnet task-to-task protocol services or non-handshake transfer mechanisms for higher data rates which would otherwise pose network throughput problems
(b) non-continuous data, i.e. transfer of experimenter generated Command Data Files (CDF) and ECOS Subtimeline Files (STL), by using the file transfer services provided by the VMS/DECnet/DEC Pathworks operating systems.
High-rate data was distributed to the EGSE in real-time providing the respective data channel was active. Provisions were made to transfer HDRR dump playback data in parallel. The control center also retrieved and replayed data from the high-rate data archive upon request. ECIO subsets were distributed to the EGSE in real- time. There was no option to retrieve and distribute ECIO subsets from the HRM data archive.
Experiment operational support data, such as command data strings (Command Data Files-CDF) and ECOS Subtimeline files (STL) were generated locally by the experimenters and forwarded to the control center's Command System for validation, packaging and transfer. The need for almost instantaneous experimenter interaction in the flow of the experiment further called for the implementation of a telescience command interface from an external user center to the Command System. The robot manipulation commands generated by the robot ground station fall into the same category. The data was, however, routed directly to the control center's front end at the rate of two NASCOM blocks per second. Special configuration was introduced to cater for the stringent requirements of the robot experiment in respect to data jitter and delay.
Figure 4 Overview of EGSE Connections to the EGSE LAN
The data delay times inherent in the data transfer concept from the Spacelab to the control center displays were empirically observed and were about 3.5 s for ECIO and SCIO telemetry, 7 s for PPF telemetry, between 5 and 7 s for the robot experiment closed loop (forward and return link delays).
Conclusion
The success of the D-2 mission validated the concept for transferring high rate data as well as processing and distributing the telemetry at GSOC and effectively operating a Payload Operations Control Center in Europe.