Last INSPIRE mission of MIR

In November 1999 we had the last INSPIRE operations, consisting in the emission of signals at 10 and 1000 Hz. The Russian space station MIR will probably re-enter the atmosphere by first quarter of 2000.
Two antennas have been used to monitor these emissions: a vertical, top-loaded Marconi 'Tee' for the vertical field and a large horizontal loop for the horizontal field.


The arrow on a map show the receiving station position (my QTH). On all passes, MIR moves from west to east (left to right). The ground track shown is 2 minutes long which corresponds to the actual firing time of ISTOCHNIK. The passes are numbered with the UT start time on the dare indicated on the top of the map. On the track maps, the start time appears near the western end of the track. All the european passes has been monitored.

The two instruments on MIR are Ariel and ISTOCHNIK. Ariel is a plasma generator and operates for 5 minutes, alternating between axes. ISTOCHNIK is a modulated electron gun that accelerates a beam of electrons and emits them into space. The electron beam is turned on and off at frequencies of either 10 Hz or 1000 Hz, which should cause the radiation of electromagnetic waves in the VLF range at those two frequencies. ISTOCHNIK operates for a total of 2 minutes on the following schedule:
10 seconds modulated at 10 Hz
10 seconds modulated at 1000 Hz
10 seconds modulated at 10 Hz
10 seconds modulated at 1000 Hz
repeat for 2 minutes of operation.
On each pass, Ariel was either operated first or last, whichever gives the most coverage over INTMINS observers. Since the signal from ISTOCHNIK is more powerful, it was the one most likely to be detected. For that reason the schedule emphasizes the operation of ISTOCHNIK.

For each session corresponding to a MIR pass four sonograms have been recorded, monitoring vertical and horizontal fields in the 0-86 Hz and 940-1122 Hz bands. The MIR emissions, lating two minutes, are approximately in the middle of each sonogram. All operations were automatic and pre-programmed to avoid operating errors.

Click to see the four spectrograms of each pass:
E20-1 (East Europe)
E20-2 (Russian)
E20-3 (North Europe)
E20-4 (north Europe)
E21-3 (Italy)
E21-4 (Russian)
E21-5 (East Europe)
E27-1 (Italy)
E27-2 (Russian)
E28-1 (Italy, in this pass above my QTH)
E28-2 (Russian)
E28-3 (East Europe)

The large antennas used (Marconi 'Tee' 11 m high, 45 m wide; 120 m circumference loop, three turns) allowed a great sensitivity, demonstrated by the evidence of Schumann resonances in the vertical records. However no emissions from MIR were detected, even in direct over-head passages. My conclusion is that using the current setup, in terms of power to the electron beam, the signal strenght is insufficient to allow reception at ground.
Probably the noise power present is by far too large, or the ionosphere screening factor is very high at those ULF/ELF frequencies.

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