Satgen 476   Ao10 and Phase3D  by GM4IHJ   (BID SGEN476)   1998-05-09

Ao10 - This satellite continues to cling to life. Its house keeping
computer has refused commands for years, so it can no longer be
controlled. Recently it has gradually stopped spinning - a feature
which kept it pointing in space in a stable configuration. So it is
now tumbling slowly in an unpredictable manner and about a week ago,
it seems to have tumbled back into a position where its solar panels
are now seeing much more sunlight than they did in April 98. Since the
begining of May beacon signals have been quite strong. There are deep
fades roughly evey 75 seconds and the signal pattern on a digital
spectrum analyser suggests that it is making one complete cycle every
225 seconds. In step with this FMing is down to about 60Hz max against
the previous swings of up to 120 Hz.

Whether it is useful for communications depends on the patience and
guile of the operator . Certainly signals uplinked to it are being
transponded back to earth if you can synchronise your call with the
times when the beacon is heard loudly on a second receiver. But what
is clear is that the recent ( up to 6 April 98 ) situation where it
was possible to roughly forecast periods of weeks when it might be
useful for communications, is no longer relevant. Change when it
occurs as it has done between late April and early May, appears to be
unpredictable and likely to be of short duration.

Equally evident , the Ao10 downlink signal is coming to earth from the
satellites hi gain antenna . It is by no means certain however , which
antenna is connected to the satellites 70cm receiver.

Phase3D - In February 98 ESA 03-98 reported that Ariane 503 would be
fitted with a second attitude control system , in order to counter the
then unexplained 900 Nm torque experienced by the Vulcain engine,
which caused premature shut down of Ariane 502. In February the source
of the torque was postulated as either :-
 A broken turbo pump outlet rod, damaged by debris . 
 Or , a product of the "roughness of the inside of the rocket exhaust
cone" , whereby the inside of the cone carries a gradually widening
spiral of piping ,passing through which, fuel is pre heated before
being used for combustion.

Since February static test of 3 Vulcain engines have all shown
evidence of this torque. So it is now accepted that the problem is
being caused by "the roughness of the spiral of piping inside the
engine divergent". Such that the boundary layer of the main jet is
spiralling and creating the torque. In which cause they suggest the
second attitude controller will prevent a repeat of the problem which
upset Ariane 502.

As a result of this activity the suggested launch date for Ariane 503
of late May 98, is no longer tenable and has probably slipped at least
2 months. ESA bulletins have so far given no details of the target
launch date or indicated the likely payload.