(An ELF-VLF advanced Signal Analyzer and Sampler)

The main goal is the investigation of the ELF-VLF electromagnetic signals propagating in the Earth’s magnetosphere. Some scientific indications exist that the parameters and existence of these signals have relations to the Earth’s seismic activity. Therefore, the SAS-2 can record arbitrary shape signals in these bands and whistler signals generated by tropospheric lighting.

The detailed analysis of the fine structure of these signals could clarify the relations between the magnetosphere ELF-VLF activity and e.g. the seismic activity. Beside these the measurements planned by the SAS-2 the equipment can investigate the antropogenic modifications of ionosphere-magnetosphere region from the point of view of ELF-VLF activity, and the structure of the magnetosphere by analyzing the fine structure of whistlers.

The background of this experiment is the successful and efficient SAS-equipment, which was on board of the Intercosmos-24 (ACTIVE) satellite. The SAS-2 is an advanced version of this earlier SAS SI.

The SAS-2 itself is a single unit SI.

However, it does not contain antennas and preamplifiers. Therefore the SAS-2 must be input signals in the band 20Hz…16kHz (or 20kHz) from as other SI.

In this case the SAS-2 must get the wide-band ELF-VLF input signal form the

• Ukrainian EXO-EM SI, or
• Polish PWP SI.

This is important for the interunit connections.

2. Interunit connections

3. Functional diagrams and the description of operation

This report describes the actual development state of the SAS-2 experiment in the frame of the WARNING project.

The EGSE is a real-time data simulator and data acquisition system. It is comprised of a general purpose and several dedicated application specific interface module. The system is able to establish all of the spacecraft hardware and data interfaces required by the experiment during the stand-alone testing and the integration of the satellite.

In the case the WARNING passive micro-satellite the SAS-2 has two power connection possibilities. We can carry out both version, and therefore we ask the chief-engineer to decide that the 0 or the 0 versions are the better for the micro-satellite.

SAS-2 can use the stabilized +/- 5V; +/- 12V from the central power supply unit of the satellite, instead of using the +27V power line of the satellite.

The SAS-2 uses an inner buffer memory of size 4Mbyte (=32Mbit). The measured data is collected into the inner buffer memory. When this memory is full, the collected data must be transmitted to the central TM of the (passive) micro-satellite. When the data transfer is finished the scientific data collection can be continued.

The analogue to digital (A/D) sampling rate is 40 kHz / channel. (In the case of ECHO-EM: 3 channels exist, in the case of PWP: 6 channels exist.)

The speed of the data transfer between SAS-2 and the satellite TM system is planned to be 20Kbit/sec. (The parameter can be modified not later than the first quarter of 1998.)

The required long range (>24 hours) data rate on satellite to Earth central TM channel:

• minimum: cca. 2 kbps
• desirable: > 5 kbps

The data mass: 20…40 MBit/orbit

The used mass of commands: cca. 48 bit/orbit

The SAS-2 can and will operate on every part of the orbit. Theoretically, the continuous operation would be the best, but the SC TM capacity limits the real data collection time. Therefore the SAS-2 has the following operational modes:

Operation MODE 1 and 2: Data collection starting at a given on-board time (see chapter 0. 3.3 Functional description of the experiment on page *).

Default operation: Data collection from reduced number of input channels starting at a given on-board time.

(For more details see chapter 0. 3.3 Functional description of the experiment on page *).

The general description of the control requirements is given in the points 0. and 0.

There are the followings:

• The general “switch on” command after the launch.
• The operational mode selecting commands.
• The inner test starting command.

SAS-2 does not need any adjustment before mounting to spacecraft.

From the beginning of the satellite integration:

1. Stand alone test
2. Mounting SAS-2 into SC
3. Stand alone test on SC
4. Connecting of SAS-2 to the power line of the SC
5. Test of SAS-2 using the SC’s power system and the other simulated signals of the EGSE
6. Connecting of SAS-2 to the TM system of SC
7. Test of SAS-2 using the systems of SC except the input signals
8. Connecting of SAS-2 to the SVIST or ECHO-EM (or PWP) preamplifiers
9. Test of SAS-2 using the SC systems and the self-test of the SI
10. Disconnecting of EGSE from SAS-2
11. Connecting EGSE to the general ground control of SC
12. Test of SAS-2 as an integrated part of SC, using the general ground control and command

The SAS-2 equipment does not contain antennas (see chapter 0. 2. Interunit connections on page *).

Optionally: In a special test mode, the SAS-2 can generate external and / or internal whistler signal. For the external test signal, a small ferrite antenna must be installed on outside of the box.

SAS-2 will be mounted to the spacecraft by 4 screws (see chapter 0. 10. Outline drawing on page *). Size and position of the bore may be modified in a small compass.

Electric sockets of SAS-2 will be connected to the source of input channels, to power system, telemetry channel and control channel of spacecraft (see chapter 0. 2. Interunit connections on page *). The position of these sockets is given in chapter 0. 10. Outline drawing on page *.

The SAS-2 SI is built purely from electronic components, and does not contain any moving part or decrescendo material. In the SAS-2, no “dangerous circuits” are present.

The planned lifetime is about 5 years.

The scientific goals of the SAS-2 experiment and the scientific possibilities guaranteed by the SAS-2 equipment are at the front line of the actual research. The possible relation between ELF-VLF magnetospheric phenomena and the seismic activity of the Earth is not clear today, and this is a very important open question in science.

The technological level of the SAS-2 equipment is an advanced one. The conceptual and electrical construction of SAS-2 equipment is a middle-level version of high-tech solutions.

The KFKI Research Institute for Particle and Nuclear Physics (RIPNP) is ready to examine the possibility of preparing the onboard data acquisition and control computer for the passive subsatellite of the WARNING project. The real design and development can be started after the exact definition of the tasks and requirements. The estimated development time is two years.

A possible data acquisition and control computer (DACC) for the passive subsatellite will have the following preliminary main parameters.

1. The architecture of the DACC will have a redundant cold structure, as it is a part of the service system and have to have high reliability. The DACC consists of the following functional subunits: Processor Unit (PU), Mass Memory (MM), Radio Interface (RIF), and Instrument Interface (IIF). Each subunit will have the same redundant units and they will work in cold redundant mode.

2. Each Processor Unit consist of

- Microprocessor (16 bit),

- Fuse PROM, 4 k word (1 w = 16 bits),

- EEPROM for program (32 kword),

- RAM for temporary data (32 kword).

All memory types contain an Error Detection and Correction Circuit, so they are protected for the random failure with Hamming Code.

3. The Mass Memory is the temporary science data storage unit, which has no Error Correction Circuit. The baseline capacity is 16 MBit TBC. It has latch-up protection.

4. The Radio Interface will have a hardware decoder to handle a limited number (8) direct uplink commands. The expected downlink telemetry speed is 1 MBit/sec.

5. The DACC will have Central Interface Unit (CIU) for the communication with the Instruments. Each Instrument will have Remote Interface Unit (RIU) for the communication through the serial Interface.

6. The estimated mass is 2.5 kg and the estimated power consumption is 3 W of the DACC.

7. The DACC fulfills the following tasks:

- Telecommand (TC) decoding, verification and distribution,

- Storage and execution of time tagged TC sequences,

- Distribute the onboard time,

- Acquisition of science and housekeeping data from the instruments,

- Temporary storage of the instruments data stream in MM,

- General purpose data compression,

- Transmit TM frames.

8. The core of the onboard software will be a dedicated real-time multitasking system. It will have two operation modes: ground test mode with debugging possibilities and the real onboard mode.

The previous parameters are predicted on the base of the earlier mission's experience, where the KFKI RIPNP participated in the realization of the central data acquisition and control computer development. In the Phobos mission was developed the redundant central computer for the Lander: it weighted 2 kg, power consumption was 1 W, the mass memory had 96 Kbytes, the TM speed was 32 bit/sec, and microprocessor was 8-bit type. The central computer of the Spectr-X-Gamma mission has a double redundancy and it has a separate MM, it has 16-bit type microprocessor, redundant data acquisition bus, and galvanicaly isolated subunit architecture.