ASTROMETRIA

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ASTROMETRIA

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The SL-200 is divided into three units along the optical axis of the tube for the convenience of use and to provide a possibility of replacing the beam (spectral) splitting filter and CCD photo detecting device on the board of SM. The three units are: the block of mirror light filter – BOM1, the bock of photo detecting device – BOM2 and the basic block of solar limbograph including pointing and control systems – BOM3. BOM1 and BOM2 are installed on BOM3 by the means of joint pins and are fastened by reusable locks.

A general view of units BOM1, BOM2 and BOM3 (with the photoguide) of the complex of SL-200 solar limbograph.
The BOM of the measuring and research complex SL-200 includes the following functional elements:

Tube of the limbograph with the optical system (OS);
Collapsible heat-shielding lens cover with a drive;
Replaceable mirror light filter with a drive;
Fine tracking platform (FTP) for Sun tracking by the sight axis of the limbograph;
Caging device with a drive;
Heat-shielding cover of the limbograph tube with a drive;
Replaceable photo detecting CCD array Ø50 mm – the heliophotomicrometer;
Autonomic thermal-regime assuring system (ATRAS);
Image quality analyser (IQA);
Remote control sensors;
Photoguide with the field of view 6 degrees, co-axial to the sight axis of the OS;
Fine tracking system for the Sun tracking by the sight axis of the limbograph;
Automatic focusing system (AFS) and automatic control system (ACS).

Two-degree fine tracking platform (FTP):

Angle range – on the vertical axis ±175° and ±45° on the horizontal axis;
Discontinuity (error) of tracking – 2.0 arc seconds (±175°, ±45°);
A error of stabilisation of the sight axis of the limbograph in the direction of the solar disk center – no more than ±5 arc seconds;
Sensitivity of the pointing system (drive operation) to the angular displacement of the limbograph – ±0.05;
Stabilization speed (speed error of solar tracking) – less than 5 arc seconds per a second of time;
Tracking system frequency – 5 kHz;
Operational range of the tracking system – up to 25 Hz;
Maximal speed of rotation (scanning) of the limbograph on the suspension axes – 2 degrees per a second of time.

The necessary dynamics of FTP is assured by the fine tracking system and by moment engines directly affecting the limbograph (without a reduction gear).

Spectral range:

520 ÷ 580 nm for solar measurements;
180 ÷1100 nm for positional measurements of bright stars.

Integration time:

10^-4 seconds for solar measurements and for the solar fine tracking system (with the mirror light filter on the entrance pupil);
10^-2 seconds for the measurements of angular distances between bright +2,5 ≤ m_b < +6,5 stars (without the mirror light filter).

The block of electronics includes the following functional elements:

Power supply for the instruments of SL-200;
Processor for the instruments of SL-200;
Controller of the heliophotomicrometer;
Controller of the control system and solar fine tracking of the sight axis of the limbograph;
Controller of the sensors and automatic focusing system (AFS);
Controller of the ATRAS;
Controller of the heat-shielding covers, mirror light filter and caging device;
Controller of the photoguide;
Controller of the connection to the information and control system (ICS);
Hard drive containing software ensuring the operation, control and testing of the instruments both in automatic mode and manually;
Replaceable hard drive for the recording of experimental data;
A system to control the photo detecting device and record images.
Controller of the photoheliometer.

HELIOPHOTOMICROMETER (a special CCD detector Ø50 mm)

The photo detecting device (PDD) is an array of CCD chips Ø50 mm consisting of three groups of autonomic photo detecting blocks located on a single padding.

16 limb blocks 475x362 elements;

2 central blocks 150x300 elements;

4 separate linear blocks 475x1 located on the opposite edges of the limb at 90 degrees to each other;

Photo detecting area of each element of any block or group of the PDD is at least 10x10 micrometers.

Each group of photo detecting blocks works independently and is driven by its own control system CS1, CS2, CS3. Each group of photo detecting blocks has its own (common for each group) electronic shutter with adjustable integration time.
Photometric quality control system: the software periodically checks the quantity and coordinates of defective pixels in the CCD array, dark voltage values and sensitivity coefficients.

Thermal stabilization of the invar tube and optical units of BOM:

-10±1°C in measurements mode and in duty mode between the measurement sessions;

-20±10°C in idle mode between the series of measurement sessions.
Time of switching to measurement mode – 60 minutes.

Thermal stabilization of the CCD array:

-10±0.1°C in measurements mode and in duty mode between the measurement sessions;

-20±10°C in idle mode between the series of measurement sessions.
Time of switching to measurement mode – 60 minutes.

The experiment is conducted in two-day uninterrupted series consisting of subsequent sessions of coordinate and photometric measurements of the shape and diameter of the Sun and also of its separate regions during the adjacent circuits. The quantity of the above two-day series is at least 6 per month. The quantity of sessions is up to 6 per day, duration of a session is defined by the possibility of solar observations and is up to 30 minutes (see the mission profile of the sessions of solar observations and power consumption).

Mission profile of the solar observational sessions and power consumption.
The basic relative construction of the elements and instrumental blocks of the "Astrometria" space experiment is shown on the block diagram of units within the complex of SL-200 solar limbograph.

A block-diagram of units within the complex of SL-200 solar limbograph.

The whole mass of the BOM is 64 kg, of the BE (internal sub block with a computer inside the airtight compartment) – 15 kg, of the external sub block with a microprocessor – 7 kg. Dimensions of the BOM – 1090x490x550 mm, of the BE (internal sub block with a computer) – 180x400x270 mm and of the external sub block with a microprocessor – 200x200x80 mm.