1 GENERAL DESCRIPTION AND OBJECTIVES

This part is written as information for the spacecraft manufacturer and for the scientific user community.

Descriptions of the SUMER scientific objectives and the experiment are given in the SUMER EID-B, Sections B1.2 and B1.3, and will not be repeated here. Additional information can be found in the introduction of Volume 1 of this document. Details of the SUMER instrument are moreover contained in the SUMER Design and Performance Requirements and Verifications Specifications in its latest issue.

Chapter 1.1. closely follows the CDS Operations Handbook.

1.1 The Mission

1.1.1 SOHO

The Solar Heliospheric Observatory (SOHO) is dedicated to furthering our understanding of the solar interior, the solar atmosphere and the solar wind. To accomplish these goals, the spacecraft carries a set of instruments designed to make measurements throughout the electromagnetic spectrum as well as detecting solar particles at all energies.

SOHO will carry several instruments to measure surface oscillations using the Doppler effect together with intensity changes. These observations must be made during long uninterrupted time intervals; this requirement is met by placing the spacecraft at the inner Lagrangian point (L1).

The SOHO spacecraft is stabilized in three axes and pointed towards the Sun within an accuracy of 1 arcsec per 15 minutes time interval. The spacecraft consists of a payload module, accommodating the instruments, and a service module carrying the spacecraft sub-systems and the solar arrays. The total mass is 1350 kg, of which 650 kg is payload, consuming 350 W out of a total of 750 W.

The planned launch date is July 1995. SOHO will be injected into a halo orbit around L1, about 1.5 million kilometers sunward from the Earth. The halo orbit has a period of 180 days.

SOHO is designed for a lifetime of two years. The on-board consumables may suffice for an extension of four years.

1.1.2 Spacecraft Control

The spacecraft flight operations support activities will be centered on the SOHO Mission Operations Control Center (SMOCC) located at the NASA Goddard Space Flight Center (GSFC). Contact with the spacecraft is achieved by using the Deep Space Network (DSN) for three short (1.3 hours each) and one long (8 hours) passes per day on average. During these periods, data is transmitted in real time and the on-board tape recorder, containing stored data, is played back at the start of each of the short passes. For two months each year, there will be continuous real time contact with the spacecraft. All data is passed to the Goddard Data Capture Facility (GDCF) where it is processed for onward transmission to the Experiment Operations Facility (EOF). The operations of the payload will be controlled by the experiment teams through the SMOCC and will allow interactive operations as well as routine operations to be carried out in near real time.

1.1.3 Experiment Operations Facility (EOF)

The EOF will be the central facility for the coordination and control of instruments such as SUMER. Through workstations connected to the EOF Local Area Network, investigators will be able to receive data from, and send commands to, the SMOCC as well as communicate with other instrument teams. The instrument health will be monitored and corrective action taken as necessary. All the scientific operations will be planned and coordinated from the EOF and will also receive data for planning purposes from other spacecraft and ground observatories. To support the operations and coordination of joint observations, quick look data analysis will take place in the EOF.

1.2 The Instrument

1.2.1 General
The instrument will allow the observation of EUV emission lines in the wavelength range from 500 to 1600 on the solar disk and above the limb out to approximately 1.5 solar radii. The limitation is probably given by the line intensities in the lower corona. The high spatial, spectral, and temporal resolution capabilities of SUMER will require many experiment modes and sub-modes. It is the main goal of this volume to acquaint the potential user with the operation of SUMER in these various modes. As outlined in the introduction of Volume 1, we will first discuss operations that are not critical and thus can be called by the largest user group. In subsequent sections we will then outline operations of increasing complexity, which can only be initiated by restricted user groups.

1.2.2 SUMER Characteristics
The Telescope
  • Focal length 1302.47 mm
  • Equivalent f-number 10.67
  • Plate scale in slit plane 6.315 um/arcsec
  • Total dynamic field-of-view 64 x 64 arcmin2
  • Smallest step size (N-S and E-W) 0.38 arcsec

The Spectrometer

Slits
  • 1.0 x 300 arcsec2
  • 1.0 x 120 arcsec2
  • 0.3 x 120 arcsec2
  • 4.0 x 300 arcsec2

Wavelength range
  • 500- 800 (2nd order) (*)
  • 800-1600 (1st order)

Collimator focal length 399.60 mm
Grating radius 3200.78 mm
Grating ruling 3600 lines/mm

Magnification factor in detector plane

  • 4.0917 at 800
  • 4.4073 at 1600
The Detectors
Pixel size 25 x 25 um2
Array size 360(spatial) x 1024(spectral) pixels
Spatial scale
  • 692 km/px at 800
  • 642 km/px at 1600 (1 arcsec at L1 715 km on the Sun)
Spectral scale
  • 21.2 m/px at 400 (*)
  • 19.7 m/px at 800 (2nd order)
  • 42.4 m/px at 800 (1st order)
  • 39.4 m/px at 1600

(*) The range from 400 to 500 is not available.

1.3On-Board Data Processing Unit - Technical Description

1.3.1 General

The SUMER On-Board Data Processing Unit (SUMER DPU) is the central computer unit of the SUMER instrument. As a space-borne controlling and computing system, it has to fulfill severe requirements concerning

The SUMER DPU interfaces to the following units:

The DPU has to perform the following basic tasks:

Based on the necessary interfaces and tasks stated above, the DPU consists of the following functional blocks:

Computer units 1 and 2 are connected by two redundant busses to the IIMs A and B, the I/O decoder, and the spacecraft interface. Each CU is able to control every board. The BCM is connected by the common control (CC) bus to the IIMs A and B, the I/O decoder, to CU1 and CU2, and to the S/C I/F.

1.3.2 Computer Units 1 and 2

The two CUs are used for controlling the SUMER instrument and for processing the data acquired. They are functionally interchangeable. Besides the nominal operation of the CUs as separate units performing the ECP and SPU functionalities, this allows for an emergency operating mode where a single CU is able to perform both its own tasks and those of the other CU. While this obviously leads to reduced performance, it nevertheless permits continuing the scientific investigation program even if one of the CUs is completely inoperational.

The software to be executed by these CUs consists of functional units in several layers:

The system configuration is performed by the boot controller module according to the boot controller software.

Each CU consist of two boards, a CPU board and a RAM board. Both boards communicate via an internal bus.

1.3.2.1 CPU Board

To achieve the performance in computing power, a floating point unit (FPU) is required. To fulfill the performance according to the calculating and controlling function of the DPU, the transputer T800, which has an integrated FPU, is used as CPU. The data bus is 32 bits wide. The two CUs and the BCM are coupled by transputer links using a data rate of 10 Mbit/s.

1.3.2.2 RAM Board

Each CU has a memory capacity of 4 MBytes. This memory consists of 4 banks of 1 MByte each. The data bus is 32 bits wide. The addresses of the banks are freely interchangeable so that the program code can be loaded correctly at any time.

The memory is built using DRAM chips; it is combined with an error detection and correction unit that is able to correct single bit errors and detect double bit errors. Because SEUs have to be considered, the memory contents are checked and, if necessary, corrected.

1.3.3 Image Integration Memory

The image integration memories are the data collection units of the XDL detectors. They accumulate the data stream coming from the detector. They operate as autoincrement buffers using First In First Out (FIFO) memory to obtain images at a high statistical data rate. The IIMs are accessed by CU1 and CU2 by a 16-bit data bus. The two IIM boards allow collecting input data signals without any time gaps: while one IIM unit is accumulating data, the other one can be read out.

The IIM can be operated in three read-out modes:

This allows the memory to be erased while the data are transferred to mass memory.

1.3.4 Boot Controller Module

The boot controller module tests its own memories, the CU1 and CU2 memories, and the transputer links, it distributes a 5 MHz clock on two separate lines within the DPU, it configures the CU1 and CU2 memories and the bus organization, and it loads the software into the memories of the CU1 and 2.

The BCM consists of two redundant units:

1.3.4.1 Boot Controller

The redundant boot controller is built with two transputers of the INMOS type T222. Each of them is connected to its own EPROM and RAM memory by an 8-bit data bus.

The boot controller is connected to the CUs and the second boot controller via transputer link using a data rate of 10 Mbit/s.

1.3.4.2 Clock Generator

All transputer CPUs are supplied with a clock signal frequency of 5 MHz by a single clock generator. The clock generator and the clock signal lines are redundant. Both oscillators are active.

1.3.5 Input/Output Decoder

The I/O decoder represents the interface unit between the peripheral units and the DPU. The decoder is connected to CU1 and 2 by two redundant CU busses. It has to establish the communication to the following units:

1.3.6 Spacecraft Interface Unit

The spacecraft interface unit represents the coupling block between the spacecraft and the DPU. It communicates all signals between both units. For safety reasons, all signal lines are redundant including the pulse command lines.

The spacecraft interface unit is connected to the CUs by the two CU busses. In addition, it is linked to the BCM by the CC bus. The CC bus performs the configuration of the CU busses of the spacecraft interface unit.

1.3.7 DPU DC/DC Converter

The DPU is supplied with 5 V by a DC/DC converter integrated in the DPU. As the converter is a critical part of the DPU, two converters linked by a coupling circuit are used. One converter is supplied by the main power bus, the other one by the redundant power bus.

1.3.8 DPU Backplane

The DPU consists of nine printed circuit boards (PCB) and one redundant converter board. These boards are connected by a multilayer backplane board which is located at the bottom of the E-Box.

1.3.9 Harness

The input and output lines of the DPU lead to the E-Box connectors located at the lower side of the E-Box. The connectors are linked by harness to the DPU backplane or, if necessary, to the power converter.

1.3.10 E-Box

The SUMER DPU E-Box contains nine PCB boards, a DC/DC converter mounted in one box side, and a backplane. The E-Box is both rugged and light-weight.

1.3.11 Link Concept

The DPU consists of four transputers, two on the BCM and one on each CU. Each transputer has four links. The link concept aims at creating a redundant computer system. The links perform the following functions:

The transputer links are placed so that each transputer is connected by more than one link. The faulty function of one link shall not lead to catastrophic errors of the DPU.

In this link concept, there is no switch logic between the important links of the two CUs. Each boot controller is linked to CU1 and to CU2. There is only one link connecting BC1 and BC2. CU1 and CU2 are connected by two links. One test link is available for each boot controller. Only one boot controller is active at the same time. Only the links of the active boot controller are usable.


Authors:

Last revised: March 20, 1997 Dietmar Germerott


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