karn@eagle.UUCP (Phil Karn) (07/16/83)
Here's a followup to my previous article regarding the separation
anomaly on AMSAT Oscar-10 - Phil, KA9Q
-------------------------------
A visit to the Washington offices of the European Space Agency
today (July 15) produced the following document which many of
you have been patiently waiting to see. The text, produced
jointly by ESA, Arianespace, CNES and AMSAT, explains what
really happened to the AMSAT-OSCAR-10 spacecraft after the
separation from the Ariane L6 third stage. It is being posted
here with no further editorial comment (at this time).
73, Rich K1HTV
--------------------------------------------------------------
ESA/CNES 13 July, 1983
ARIANE LAUNCH L6
----------------
ORBIT INJECTION OF OSCAR 10 SATELLITE
-------------------------------------
The apogee motor firing of (AMSAT) OSCAR 10, the radio amateur
satellite launched on the 16th of July, took place during the
night of 11 to 12 July and injected the satellite successfully
into an intermediate orbit of approximately 3900 km perigee,
35,800 km apogee height and 26 degree inclination. A second
and final apogee motor firing is scheduled within the next
fortnight. All equipment on bord (sic) of the satellite checked
out so far including the main transponder with its antennas is
working perfectly.
The firing had been delayed by about three weeks since the
satellite's attitude and spin rate after separation were not
as expected.
Indeed, whilst separation and orbital injection of the ECS 1
satellite were perfect the first acquisition of telemetry from
the OSCAR 10 satellite five hours after launch indicated that
there were gross errors in attitude and spin rate.The satellite
authority took rapid and effective action to guarantee the
immediate survival of the satellite so that the situation could
be analysed and further corrective action taken.
During the past weeks the AMSAT project authority has
established full control of the satellite and brought it into
the correct attitude for a first firing of the restartable
liquid propellant apogee motor. In doing so the AMSAT project
authority has demonstrated the extraordinary operational
flexibility of the design of its satellite and of the people
who operate it.
Examination of the launcher telemetry has shown that the dual
launch system SYLDA had functioned nominally and that the
original separation parameters (including satellite attitude
and spin) had been correct. This fact has later been confirmed
by stored satellite telemetry data.
Detailed investigation of both launcher and satellite data
indicates with a high degree of probability, that 53 seconds
after separation the third stage caught up with the satellite ;
this would explain the attitude and spin rate anomalies
observed subsequent to separation. This supposition of a
physical contact is reinforced by observation of small shocks
registered at that time by launcher vibration sensors and by
indications that at least one of the satellite's antennas is
slightly damaged.
The most likely reason that the third stage caught up with the
satellite is that the thrust due to programmed venting of the
oxygen tank was significantly higher than predicted and
annulled the margins taken for setting up the sequence of
orientation manoeuvres.
Following separation of each satellite, the Ariane 3rd stage
performs an attitude and spin change programme which is then
followed by a lateral distancing manoeuvres of this stage.
This sequence includes opening and closing of the 3rd stage
oxygen vent valves to control residual tank pressure and to
provide thrust for the distancing manoeuvre.
For future launches the higher residual thrust level and
additional margins will be taken into account and the sequence
of operations will be adjusted accordingly so that this kind of
problem will not be encountered again.
---------------------------------------------------------------