EUV photometers measure the emissions of the Earth’s ionosphere and geocorona in the Extreme UltraViolet range. Since it is sensitive in that spectral range, where the Sun doesn’t radiate regularly, it is able to see the emissions both on the nightside and the dayside of the Earth (in opposite to photometer for visible light) and provides the information that can’t be seen from the ground stations.

Information about excitation of the atoms and ions of the atmosphere is useful for correlation with other measurements or as a support for measurements that can be disturbed by EUV emissions. (In the case of spinning satellite is possible to get the whole picture of the emission distribution, eg. of Aurora borealis in EUV range.)

Two or three photometers are proposed. One to monitor the Lyman alpha emission with a narrow passband around 121.6 nm (oxygen cell used as narrow filter) and second with a wider passband , cca 130nm - 155nm. The third photometer can be added to monitor the direct solar input, the outbursts of Lyman alpha emissions on the Sun. This third photometer can be used also to study the attenuation of the atomosphere, when the satellite goes to eclipse.

Spectral range : Lyman alpha (121.6 nm)

MgF₂ window

Oxygen cell filter

Spectral range : 130nm - 155nm

CaF₂ window

Characteristics for EUV-1 and EUV-2 detectors :

Quantum efficiency : cca 0,3 counts/photon (KBr Photocathode)

Geometric factor : 4 10E-4 sq.cm sr

number of channels : 4

gain (multiplication factor) : 4 10E7

Field of view : (2 x 1) deg. each channel, (2 x 4) deg. total

Dark countrate : 0.05 Hz

Maximum countrate : 20 MHz

(Countrate proportional to incident radiation)

Life span : 3 10E12 pulses without any drop of efficiency

for Sun observation in Lyman alpha

Field of view : 40 deg.

other charakteristics similar to EUV -1

Placement : The detector has to be placed along the satellite - Earth direction in the case of geocentric attitude of the satellite (or perpendicular to spin axis in the case of spinning satellite, doubled detectors in oposite directions are in that case possible to make the time resolution higher).

Dimensions : diam. 25 mm x 330 mm (one detector )

Mass : 90 g

consists of High Voltage power supply, fast amplifier of pulses, pulse shaper, counter, digital control unit and telemetry interface.

The electronics is mechanically divided into two blocks. One block contains the amplifier, the other the rest.

Placement : The amplifier has to be placed as close to the detector as possible. The block of electronics has no special or strict requirements to the placement.

Dimensions of the blocks are the following (note that the dimensions are preliminary and can be tailored according to the requiments):

amplifier : 60 x 40 x 150 mm

block of electronics : 150 x 40 x 200 mm

Power supply : cca 1 W 

Total Mass (detectors and electronics) : cca 1.4 kg

Supply Voltage : 27 V (can be changed)

Telemetry requirements : variable, depending on the chosen sample rate (1Hz- 256Hz)

64 bit/s - 16kbit/s

Commands : digital .. 2 Byte

(Command and telemetry interface will be tailored according to the satellite system)

All detectors are ceramic channel electron multipliers designed and fabricated by Dr. Hans Lauche from the Max-Planck-Institute for Aeronomy in Katlenburg/Lindau, Germany. The detectors of this family have been used in the frame of the following missions : Freja, Astrid 1, Astrid 2 and Cassini.