| Issue | 1 (draft) |
| Document ID | EIS-sys-eng-sysreq-1 |
| Document File | D:\Users\mwt\Projects\Solar-B\EIS\docs\sys\eng\sysreq1d.doc |
| Authors | Matthew Whyndham, MSSL
Véronique Gorel, UCL/MSSL |
| Date | 07/08/98 |
Contents
Introduction 2Scientific Requirements 3Table of scientific requirements 3Notes 41. Modes 42. Wavelength range 43. Temporal Resolution 44. Spatial Resolution 55. Spectral Resolution 56. Field of View 67. Sensitivity 68. Misalignment 79. Alignment Measurement 710. Pointing 7Other requirements 8Spacecraft characteristics table 8Notes 920. Radiation environment 921. Thermal environment 9System Interfaces 10Management 11Introduction
This document is part of the framework for systems engineering for EIS. This is described fully in the Management Plan (ref).
The User Needs document (ref) expresses the goals which the system's operation will achieve.
The System Requirements document (this document) is a functional and performance requirements document. It reflects a subset of the needs by stating the functional requirements of the system and measurable terms (what the system must do).
Requirements which come from the user needs are described in the scientific requirements section of this document. Other sets of requirements or constraints are in separate sections.
The System Specification document describes how the system will meet the requirements. This will refer to the technology to be employed (whereas the Requirements do not).
These values are related to the User Needs as laid
out in EIS-sys-eng-userneed-1, but should ideally be independent
of the technology of any solution.
| Requirement | Value | Origin | Priority | |
| 1 | Modes | Primary: Slit spectroscopySecondary: Monochromatic imaging | EIS-x-2 | |
| 2 | Wavelength Range | should meet the User Needs (q.v.). Baseline range is 250 Å - 290 Å | EIS-x-2: p. 60-61 | |
| 3 | Temporal Resolution | commensurate with evolution of features Control of exposure time is required | EIS-x-2 | |
| 4 | Spatial Resolution | < 2 arc sec | EIS-x-1 : § 4.3.3 | |
| 5 | Spectral Resolution | < 20 km/s per pixel= 0.0203 Å per pixel | EIS-x-1 : § 4.3.3;
EIS-x-3 EIS-x-6 : p 8,10; | |
| 6 | Field of View | Imaging: 4' × 2' × 2 fields Spectroscopy : 4' × 4' (scanned) | EIS-x-2 (Strawman)EIS-x-1: § 4.3.4 | |
| 7 | Sensitivity | effective area: 0.42 cm2 at 270 Å | EIS-x-1Table 4.11 | |
| 8 | FOV misalignment | ±1' | EIS-x-6 | |
| 9 | Alignment measurement | ~1"should be compatible with pixel size of EIS and XRT | ||
| 10 | Pointing (scanning) | TBD fraction of EIS pixel |
There are TBD other modes. These will consist of combination of these two modes and image selections.
There are many possible modes which can use selected regions of the full CCD image. The regions of interest could extract certain spectral lines from the image, from either the slit image (spectra) or the slot image (context) portions of the detector.
The number of necessary regions of interest will be related to the wavelength range.
Some examples of possible modes are given in Table 10, page 59 of the Science Definition Team Report (EIS-x-2).
The EUV wavelength range contains many emission lines suited to velocity diagnostic of the transition zone and corona. The range used by EIS is the subject of discussion in the Science Team. US proposals may suggest other ranges.
EIS-x-2 p 60-61.
Refer to discussion in EIS-x-2, Figure 17: characteristic time scales. The minimum meaningful cadence of exposures is likely to be of the order of a second. The minimum achievable exposure time (given the instrument's sensitivity and the other requirements) may be greater than this.
The time (e.g. start time) of any exposure should be known to within TBD absolutely, and to within TBD relative to other instruments on Solar-B.
Spatial resolution must be as small as possible (1"-2" range), appropriate for the smaller scale structure of the solar atmosphere.
Moreover :
The resolution which can be achieved is related to the Field of View, the detector resolution and the magnification of the system (plate scale).
EIS-x-1: § 4.3.3.
The phenomena we will look at have typical velocities between 10 km/s and several 100 km/s (CME).
For an integration time of several seconds we should expect, following suitable analysis (question : how? Under what conditions?) of the spectral line shapes:
If the pixel size corresponds to a velocity as small as 20 km/s, it allows the line width and Doppler velocity from profile of lines that emanate from the transition zone and corona to be obtained. The line should be oversampled by the detector, thereby giving an accuracy of the calculated velocity of TBD km/s.
This will depend in practice on the sensitivity and resolution of the optics and detector, as well as the strength of lines.
Sources EIS-x-1 : p 49;
EIS-x-3
EIS-x-6 : p 8,10;
In the baseline instrument (EIS-x-1 and EIS-x-2), there are two fields of view, one determined by dimensions of the slot, and another by the height of the slit and its scanning range. Refer to figure 1.
The field of view must be large enough to cover typical structures of the quiet sun and of active regions. Therefore the required field of view is TBD.
Some proposed values are :
Field of view : 4 arc minute.
Scan Range : 4 arcmin x 4 arcmin
The field of view will depend on the focal length of the primary mirror.
A minimum signal to noise ratio (number of signal photons / number of equivalent noise photons) is required for determination of velocities and other plasma diagnostics to the required accuracy.
The available signal is determined by the effective area of the instrument and the intensity of spectral lines in the selected waveband. The effective area is physical area of the primary mirror multiplied by the reflectivities of the optical components and the quantum efficiency of the detector.
The figure in the table is an estimate of the obtainable effective area.
EIS-x-1 : Table 4.11.
This refers to the maximum permissible misalignment between the different instruments FOV's. It is a mission requirement that the instrument should obtain correlated information. This alignment is a critical topic which is TBD.
EIS-x-6
Knowledge of the relative alignment of the instrument's telescopes will be required.
This measurement should be carried out at TBD intervals.
The accuracy (linearity, reproducibility etc.) of the scanning mechanism is referred to here.
A system alignment error budget should encompass
the requirements for Alignment Measurement and Pointing.
These are requirements of the system that do not emanate from the User Needs, or other constraints. Their origin may be external to the system (as in the case of system interfaces) or internal and may apply to the system as a whole or to individual subsystems. This document is only concerned with constraints that apply to the system as a whole. Subsystem constraints are detailed in the relevant subsystem requirements document.
The instrument must be accommodated on the Solar-B
spacecraft, which will have the launch, orbital and environmental
characteristics in Table 2.
| Characteristic | Value | Definition | |
| 11 | Launch vehicle | M-V | EIS-x-1 |
| 12 | Launch vibration | evaluated for spacecraft
TBD at subsystem (telescope) level | EIS-x-5 p 20 |
| 13 | Orbit altitude | 600 km | " |
| 14 | Type, inclination | sun-synchronous polar, 97.8 | " |
| 15 | Contact with base station | 4x24h, duration is TBD, downlink rate (KSC): 2.2 Mbps minimum (will increase to 5 Mbps if additional DSN sites are used) | p6 AO-98-OSS-05 |
| 16 | Mission life | Designed for 2 yearsFuel for 5 years | " |
| 17 | Attitude control | examples:stability X,Y
0.2" /s 0.4"/minuteAbsolute pointing accuracy, <1' | see full spectrum in EIS-x-5. |
| 18 | Doppler shift | Vary : 0.1 m/sAmplitude less than 100 mÅ | EIS-x-2 p62 |
| 19 | Eclipse | operation desirable during eclipse season (?). | EIS-x-2 p62, eclipse parameters given in EIS-x-5, p25 |
| 20 | Radiation | TBD | Note R |
| 21 | Thermal | TBD | Note T |
the radiation environment is relatively well known (e.g. TRACE and SMEI missions) although the detailed predictions have to be determined. The sun-synchronous orbit includes passages through the auroral zones as well as the South Atlantic Abnormally. It also exposes the spacecraft to infrequent but intense solar particle events. The total dosage and the frequency of Single Event Upset (SEU) are TBD.
This can also be deduced from the studies done for the TRACE mission. The constant spacecraft attitude with respect to the sun means that variations of the spacecraft thermal balance are relatively small. The most critical aspect is the barbecue effect due to the earth. This effect has to be evaluated and its impact on the instruments specified.
EMC : no specification is available and no testing is anticipated. It is assumed that best practices will be observed in the design and build and that EMC problems are dealt with after delivery to Japan.
Table 3 shows the values of spacecraft interface characteristics and allocations of spacecraft physical resources which will apply to the system.
| Characteristic | Value | Origin | |
| 22 | data rate | 64 kbps | proposal |
| 23 | Data volume | 384 Mbits/orbit | " |
| 24 | envelope | ~ 3000 x 550 x 550 mm | " |
| 25 | mass | < 60 kg | " |
| 26 | power | < 20 W | " |
| 27 | Vibration | 1st resonance frequency > 70 Hz | " |
A full matrix of all interfaces within the system can be found in xxx (for the baseline EIS).
Figure 1 is an extract of that matrix and shows the subsystems
which have spacecraft interfaces and the nature of those interfaces.
Then, relate the two (enter values in appropriate boxes...).
Other designs will have different interfaces with the spacecraft, and this analysis will be included here when their details become known.