15 February, 1999
Matthew Whyndham

Science goals and instrument configuration need urgent definition.

US partner (NRL) selected.
Consortium Meeting at NRL.
Science priorities now being discussed generally.
Visit to EEV.
Technology trade-offs (with NRL and BU) commenced.

The selection of the US partners for the Solar-B instrument teams has now been made. The partner for the EIS team is the group led by George Doschek of the US Naval Research Laboratory (with whom the consortium was associated prior to the pre-selection blackout period). The completion of this important phase means that it has been possible to make much more progress in instrument design.
A consortium meeting was held at NRL in Washington DC in late January with the principal aims of:
- Defining the optical configuration of the instrument
- Selection of a wavelength range or ranges for the spectrometer
In preparation for this meeting, the UK Science Team met to discuss the scientific objectives of the instrument. The possibility of using a wavelength range in the region of 400 Angstroms was felt to be worth pursuit, since some lines associated with the "transition region" conditions of the solar atmosphere would be usefully observed there. The wavelength ranges put forward up to now were seen as being weak in these respects. Cambridge and RAL prepared a study of the 400-Angstrom range in the same manner as for the established candidate ranges, see EIS-sci-notes.
It should be recognised though that the use of this wavelength range would depend on a multi-layer technology (based on Silicon/Scandium) that is, at present, relatively immature. It would be dependent moreover on the US team's ability to pursue its development.
It was agreed that the merits of telescope configurations and wavelength ranges could only be assessed if quantitative spectroscopic performance data was available. Therefore both NRL and MSSL produced lists of count-rate for the spectral lines in each of the four candidates ranges, and for each of the two telescope configurations, for quiet Sun, active region, and flare conditions.
In brief, the MSSL and NRL analyses were in partial agreement, with the main differences being due to the way in which solar conditions are modelled rather than to differences in understanding of the instrument technologies.
The two instrument concepts differ in the spatial resolution and throughput. They share the same grating layout and hence have equal spectral resolution. The (NRL) Cassegrain provides 1 arc second pixel images whereas the (NAOJ Baseline) off-axis paraboloid telescope provides approximately 2 arc second pixel images. However, the latter has of the order three times the effective area of the Cassegrain system by virtue of having two reflections on multi-layer surfaces (reflectivity ~30%) as opposed to the Cassegrain's three reflections.
The choice of telescope type and wavelength range is a question of balancing the apparently diverse needs of a range of possible uses for EIS, each having its particular requirements for spatial resolution, spectroscopic performance and wavelength coverage. The whole consortium, coordinated by MSSL (Louise Harra-Murnion) is conducting this scientific tradeoff.
The technologies of both concepts are being investigated to find if there are any technological drivers that will influence the choice. Although these feasibility studies are not complete, the main consequences of the choice for the UK hardware teams are clear.

Can build either type of structure but would prefer Cassegrain because the mass budget is more easily achievable. Symmetry and dynamic behaviour considerations also lead to a preference for the Cassegrain. The thermal control issues may be very different for the two telescope types -this needs further study.

If two wavelength ranges are selected, then the probable requirement will be for a larger format imaging device, which would most likely be met by providing two of the baseline CCD's in the focal plane assembly. Depending on the total number of devices delivered, this would increase the cost of the CCD procurement. There would also be a marginal cost increase in the readout electronics and data handling electronics, but the increase power consumption of these would likely be more significant.
The nature of the mechanisms in the Cassegrain and Baseline systems is different, which leads to some differences in the mechanism driver electronics. The impact of this on the MSSL electronics package is uncertain.

The telescope type choice will affect only the details of the FM AIV procedures. If two wavelength ranges are selected than the effort involved in the end to end calibration may be marginally increased.
The consortium meeting at NRL exposed a good deal of the thinking behind the two concepts but was unable to reach a decision. A PI-level teleconference between the parties is scheduled for 16^th February with a suggested date for a decision by 20^th February. It has been agreed that the final decision, at least on telescope type, must be made before or during the Solar-B mission kick-off meeting at ISAS in March.
The addition of the NRL group adds considerable systems engineering expertise to the consortium as a whole. The main focus of system engineering activities continues to be with the UK project manager and the system design team (SDT), which will now meet or teleconference regularly.
The SDT will shortly consider a draft interface list for each of the instrument configurations - this will identify each institute sharing that interface. Further details in the Management Plan.

Chris McFee has been active (in consultation with EEV) in determining the properties of the EEV range of CCDs that relate to radiation tolerance. The main factor here is that the value of charge-transfer efficiency is related to operating temperature, clocking rate and is a function of radiation dose. The temperature requirement will affect the instrument thermal design and the clocking rate will limit the cadence of observation.
A breadboard readout electronics system is under development. Use of the INTEGRAL engineering model should expedite this.
An RFQ should be prepared for EEV to respond formally to in the next few weeks.

Discussions of the data handling protocols between EIS and spacecraft electronics are continuing at more detailed levels. All specifications are currently tentative. A baseline protocol should be agreed during the March meeting in order to facilitate progress.

The addition of the NRL group adds considerable systems engineering expertise to the consortium as a whole. The main focus of system engineering activities continues to be with the UK project manager and the system design team (SDT), which will now meet or teleconference regularly.
The SDT will shortly consider a draft interface list for each of the instrument configurations - this will identify each institute sharing that interface.

25/2/99 PPARC Steering Comitee
8-12/3/99 Mission Kick-off meeting, ISAS

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