karn@mouton.UUCP (08/25/84)
**** UoSAT Bulletin-89 24th August 1984 ****
** General News **
* Future UoSAT Missions are being proposed and studied, varying
in scope from UO-9 & UO-11 orbits to Phase 111 and involvement
in Geosynchronous orbits. We would be very interested to hear
of any (reasonable!) suggestions or areas of interest that you
may have - please direct to G3YJO.
One such future mission possibility being considered is the use
of an ARIANE-4 launch to place a constellation of six (or maybe
cut down to three) small amateur satellites into geosynchronous
orbit. The spacecraft would be transferred into geosynchronous
orbit by a common 'carrier' module, ferrying the spacecraft
through the drift phase of the orbit and then depositing them,
two at a time, at positions around the equator. It is proposed
that each spacecraft carry at least a MODE-L transponder. A
project of this scale would clearly have to be undertaken by a
international AMSAT team , probably US/DL/UK and each group
would also furnish additional experiments in keeping with their
interests. This is an ambitious idea (and costly) but could
advance amateur radio communications by a further quantum leap,
however it is early days yet and this scale of mission may not
prove practicable or even desirable. What are YOUR thoughts?
* A Masters Degree in 'Satellite Communications Engineering',
based heavily around the experience gained through the UoSAT
Projects, will commence at the University of Surrey this
October - although welcome, this adds, however, to the already
overloaded UoSAT Team! Details again avaliable from G3YJO.
* Three Active Magnetospheric Particle Tracer Expt. (AMPTE)
spacecraft were launched successfully by NASA DELTA from Cape
Canaveral on Thursday 16th August - after three aborted launch
attempts following ground station computer malfunctions and the
discovery of debris in the vehicle. A small UK spacecraft,
contributed by the UK SERC, was mounted between the two large
US & DL spacecraft - UoSAT contributed to the Particle Wave
Experiment on this s/c. The spacecraft have been in orbit over
a week now and are reported to be functioning very well.
** UoSAT-Oscar-9 Schedule **
The Bulletin/Digitalker/Telemetry on UoSAT-1 will run through
to Wednesday 29 August due to a UK national holiday on Monday
and a UoS holiday on Tuesday! It is hoped that a more normal
service will resume soon on UoSAT-1. The preparation of the
Bulletin is being re-organised to spread the workload and items
of relevant interest for the Bulletin are always welcome - the
weekly deadline is 10.30 local time each Friday - and should be
sent to the UoSAT Team in writing.
We have received a suggestion that it might be useful to
include line numbers in the Bulletin. This would be useful for
those using comuters to gather the Bulletin as it would allow
them to assemble a complete Bulletin from noisy data on
multiple orbit passes without manual editing. This feature
would, however, reduce the space available for text - what are
YOUR thoughts please!
Special 'Notice Board' items for demonstrations/displays using
UoSAT are also welcome as they can add 'interest' to such
activities.
The H.F.Beacons Expt. will be in use this week.
** UoSAT-Oscar-11 Operations **
Harold Price, NK6K, is continuing his efforts to commission the
Digital Communications Experiment (DCE).
Several whole-orbit data formats have been gathered last week -
interspersed with telemetry - to support analysis of the GG
lock and libration. A daily account follows:
Saturday - #2479, channels 1,2,3,52 reset at 11:49:30
#2484, channels 1,2,3,52 reset at 19:46:45
Sunday - #2498, channels 1,2,3,52 reset at 18:49:30
Monday - #2507, channels 1,2,3,52 reset at 09:48:25
Tuesday - #2521, channels 1,2,3,52 reset at 08:47:40
#2522, channels 0,10,20,30,50,51 reset at 10:32:00
#2528, ODATA ran incorrectly - no data
#2529, channels 1,2,3,52 reset at 21:40:50
Wedneday - #2536, 1,2,3,52 reset at 09:29:48
#2537, channels 17,18,19,27,28,29 reset at 11:07:55
#2542, channels 40,50,51,52,53,57 reset at 18:59:31
Thursday - #2551, channels 40,50,51,52,53,57 reset at 10:11:25
#2552, channels 1,2,3,52 reset at 11:47:00
#2556, channels 1,2,3,11,38,49 reset at 18:04:55
Friday - #2565, channels 1,2,3,52 reset at 09:10:50
The frequent dumps of data from the ODATA whole-orbit telemetry
recording program indicate that the gravity-gradient lock is
stable, and analysis now indicates that the libration
(oscillation about the ideal downward-pointing direction) is
currently contained within a 20 degree cone and with a very
long period - of the order of hours. The simulations carried
out at UoS before GG boom deployment indicated that we might
expect about 38 to 42 degrees of libration, so this result is
particularly pleasing.
UO-11 is now spinning about once every 4 minutes around the
z-axis in order to minimise the temperature gradients across
the spacecraft. The spin has not affected the GG lock but has
introduced some more complex motions which are currently being
analysed. The spacecraft spin rate will be increased slowly to
evaluate the interaction with GG lock and to study thermal
effects. The effect of the z-spin can be seen clearly in the
whole-orbit navigation magnetometer data ('wrinkles' on the
z-data & modulated oscillations on the x,y-data) and also quite
easily by observing the solar array currents on real-time
telemetry.
The CCD Imager tests carried out (Thurs & Fri last week) are
still being analysed - the results will take some time to
process, but will be announced a.s.a.p.!
** UOSAT-OSCAR-11 Gravity Gradient Boom Deployment **
Following several days final preparation and rehearsals, the
UO-11 gravity gradient boom was deployed under on-board 1802
computer control at 10:35 gmt during orbit 2113 on 24th July.
The automatic magnetorquing manoeuvres, continuously executed
by the 1802 OBC over the previous few weeks, had aligned the
spacecraft closely to the geomagnetic field vector and reduced
residual motions (wobble) to a very low value. Following final
confirmation of auspicious deployment conditions at AOS at
Surrey on orbit 2113, the OBC was given instructions to
terminate the magnetorquing routines and deploy the boom for 15
minutes taking the spacecraft out of range of UoS. The OBC
simultaneously recorded X,Y,Z, +5V current and boom & computer
status channels automatically throughout the operation whilst
the boom was being deployed and during the following orbit, to
monitor gravity gradient capture and spacecraft operations.
The stored data was dumped at UoS on the next orbit (2114) and
examination confirmed the correct operation of the deployment
routine and preliminary analysis of the stored Navigation
Magnetometer data indicated successful gravity gradient
capture.
Data gathered regularly since then has confirmed that the
spacecraft has maintained successful gravity gradient
stabilisation and showed no evidence of severe libration.
Residual energy before boom deployment translated itself into
libration following GG-lock - which has been monitored and will
be minimised using magnetorquing routines similar to those used
during initial attitude control manoeuvres. The spacecraft has
now been spun slowly around the Z-axis in order to improve the
internal temperatures - previously running somewhat cool.
Introducing a slow Z-spin does, of course, interact with the GG
stabilising forces but should only impart a small forward or
backward 'tilt' of a few degrees dependent on spin rate.
Gravity gradient stabilisation of UO-11 is the culmination of
many months of preparation and many weeks of spacecraft
activities - most of which has not been visible to the outside
world! It has been very demanding and has necessitated the use
of considerable facilities and required a particular, dedicated
effort from the UOSAT Team - particularly Stephen (Attitude,
Stabilisation & Navigation Analysis), Roger G8NEF (Spacecraft
Software) and Neville G8NOB (Ground Station Software).
** UO-11 Mission Plan **
Gravity gradient stabilisation marks the end of the major
spacecraft commissioning phase of UO-11 and now allows us to
progress with the commissioning of the experiments. This will
commence with evaluation of the DCE and CCD Camera, however a
more detailed Plan is being prepared.
** NOAA Spacecraft Update **
* NOAA-8, the first in a series of Advanced TIROS-N spacecraft,
began exhibiting problems on June 12 when it experienced a
'clock interrupt' that caused the spacecraft's gyros to loose
synchronism. Continued clock perturbations interfered with the
meteorological instruments on June 13th. Over the weekend of
June 30/July 1, the situation deteriorated to the extent that
the spacecraft's attitude control systems were affected and
NOAA-8 began tumbling. The spacecraft has no nitrogen attitude
control fuel left after remedial manoeuvres following launch on
March 28, 1983 aboard an ATLAS-E launcher. NOAA-8 weighes
3,775 lbs and carries six environmental monitoring instruments
and a search-and-rescue experiment. Although the
search-and-rescue facility will be lost if NOAA-8 cannot be
recovered, much of the environmental monitoring is being
conducted by NOAA-6, still operational since launch on 27 June
1979.
Engineers are working to resolve the problem before the launch
of NOAA-F, currently scheduled for 23 October 1984.
* NOAA-7 will complete its planned operational lifetime this
summer, but is continuing to perform well.
** Thanks for Reports & Questionnaire Returns **
PE1HLB, VK2ZYE, I2KBD, VK2RX, VK2XPW, VK2AVH, ON4HW.
W2RS, M.D.Oslender, G8DGR, WB9ANQ, G8KTM, G4PSO, G6TRR, G8JUB.
ON4AWV, OZ1IWS, G4ILN, G4SAQ, ON5EX, GM4CUX, G4MAB, G8AVH,
I2KBD, G6FPX G3MBN, VK5HI, ON6RL, G1BUY, G5TU, G3SLI, Steve
Hodson.
This week: G2DBT, K1KSY, N4NY, OZ2LW, JA1WO
** Keplerian Orbital Elements - from KA9Q **
etc....