Satgen126   Jupiter's Listening Post   by GM4IHJ        26th Aug 91

SARA Satellite Amateur Radio Astronomy was one of the microsats launched
by Ariane along with the prime payload Earth Resources Satellite ERS-1 .
UO5 was also on the same launch. SARA is a complete change from the normal
Amateur radio satellite. It is downlink only and its main job is to keep
watch on the natural radio transmissions from the planet Jupiter.

It has been known for 35 years that Jupiter has three bands of powerful
radio transmissions. 1 to 1000 kHz , 2 to 40 MHz, and 75 to 15000 MHz. The
first LF set appear to come from a spot on Jupiter and from the plasma
link between Jupiter and its volcanic moon Io. The second and more
interesting shortwave emmissions are known to come from the plasma in the
magnetic donut torus which Jupiters massive magnetic field throws around
the little moon Io. Io's volcanoes are throwing out sulphur oxygen and
several other atoms and molecules at a prodigeous rate and this material
is magnetically " bottled " by Jupiters magnetic field and then , ionised.
So great is the magnetic field and ionisation that the natural gyro
frequency of the electrons in this torus can reach 40 MHz and it is very
strong at around 20 MHz.

Because of the planetary link between Jupiter and Io, and the natural
beaming of the signal out into space, the signal burst keep sidereal time
appearing roughly 4 minutes earlier each successive day, and it takes
about 2 hours for the beam to swing across the earth. So this shortwave
activity is not continuous, but if Jupiter is above your horizon and the
ionosphere is thin,(say at night),when, the burst reaches earth space ,
the signal can get down through the ionosphere and be heard on the ground
using a quite simple indoor single loop horizontal antenna rigged around
the shack ceiling. SARA will with luck hear much more, high above the
ionosphere, and provided SARA's orbit stays in sidereal step with Jupiter
it should give uninterrupted observation of Jupiter over many months. If
however SARA slips out of sidereal synchronism ,the earth will get between
it and Jupiter,causing breaks in observation of up to 40 minutes/orbit

SARA's downlink has been reported by several observers on 145.955 MHz
using 300 baud ASCII 1200/2200Hz. For more information contact ON1KVE @
ON1TRC or, BELAMSAT asbl, Thier des Crichions 2 , B - 4032 CHENEE ,BELGE

As G3ZCZ has already pointed out, there may initially have been some
confusion as to just which sat was which ,on the Keplerian elements NASA
published for this 21575U 91 50 launch of Ariane. Only careful monitoring
of SARA in range windows on 145.955 MHz, will clear this up and only then
will it be possible to see if SARA has a sidereal synchronous orbit which
will last for a few years. 73 de GM4IHJ @ GB7SAN