karn@mouton.UUCP (07/28/84)
**** UoSAT Bulletin-85 27th July 1984 ****
** 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 over the last 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 1802 was given instructions to
terminate the magnetorquing routines and deploy the boom for 15
minutes taking the spacecraft out of range of UoS. Spacecraft
telemetry indicated reasonable boom motor current and correct
operation of the 1802. The 1802 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.
Gravity capture could, however, occur successfully WITHOUT
correct boom extension due to the excellent initial controlled
attitude of the spacecraft reliant solely on the asymmetric
body shape - any residual energy and the effect of perturbing
forces, however, would be likely to cause this condition to
deteriorate quite rapidly if the boom had not deployed to a
significant extent.
Data gathered over the following days confirmed, however, that
the spacecraft maintained successful gravity gradient
stabilisation and showed no evidence of severe libration.
The most obvious effect of gravity gradient capture is that the
spacecraft will now maintain the communication antennas and
camera pointing at the earth. Residual energy before boom
deployment will translate itself into subsequent libration
after GG-lock which will be monitored and minimised using
magnetorquing routines similar to those used during initial
attitude control manoeuvres. The digital sun and earth horizon
sensors will now be activated to determined the spacecraft's
attitude and degree of libration.
Once the spacecraft GG attitude behaviour has been analysed, it
is probable that the spacecraft will be spun very slowly around
the Z-axis in order to improve the internal temperatures -
currently running somewhat cool. Introducing a very slow
Z-spin does, of course, interact with the GG stabilising forces
but only to 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). A more
detailed account of the Attitude Control and GG activities will
be prepared in due course.
A day-by-day account follows:
Saturday 21/7/84
TORQUEH (the 1802 program which actively controls the
magnetorquers in conjunction with reading the navigation
magnetometer, records and replays whole orbit data and runs
command timing loops) was further exercised as well as
re-initialising its ODATA function at 21:29:40.
Sunday 22/7/84
TORQUEH was re-loaded following minor modifications. Yet
further confirmations of spacecraft attitude taken!
Monday 23/7/84
Morning - tests of final ground "deployment decision" software
were made by switching the magnetometer on permanently and
watching the fields changing. Residual oscillations of under
10 degrees were encouraging.
Evening - A full rehearsal of the boom deployment operation was
run over 3 passes. The boom deployment commands were
substituted by commands which were equally visible on the
telemetry status points but otherwise harmless! After the
ODATA was dumped, active magnetorquing was re-enabled.
Tuesday 24/7/84 - Boom deployment
Orbit 2112 - While holding the telemetry system in dwell mode
(which prevents ODATA from recording since all channels are not
found), the TORQUEH ODATA segment was reset, and active
magnetorquing resumed. The spacecraft was left until LOS
transmitting dwell telemetry to the ground analysis software.
Orbit 2113 - Sending one command told the 1802 to turn the
z-magnetorquer on continuously, to allow the ground software to
take a precise fix of the spacecraft attitude. After about 3
minutes of data, Stephen finally confirmed a suitable attitude,
and the telemetry system was switched out of dwell mode to
enable ODATA recording to start at 10:35:00 (approx). The
channels recorded were 1,2,3,41,61,67. The last two record
hexadecimal numbers - sorry if your ODATA program expired at
this new facility!
At 10:35:20, a command to the 1802 turned the boom motor on for
a 15.0 minute deployment and we watched the telemetry
anxiously. An anomaly on the 5v current sensor prevented us
seeing the true current, but the 14v bus was as expected and
the motor was left running as the spececraft disappeared below
our horizon.
Orbit 2114 - Telemetry at AOS looked good, with the boom motor
off and a good battery voltage. After taking the stored ODATA
dump, the magnetorquers were disarmed and ODATA was reset at
12:19:23 to record channels 1,2,3 and 52. The real-time dump
of the ODATA looked most encouraging.
By the evening, the next ODATA dump to be analysed confirmed a
stable gravity gradient lock. More rapid dumps (always using
channels 1,2,3,52) were made after resets at 18:37:53 and
20:09:45.
Wednesday 25/7/84
Another ODATA dump was initialised at 09:35:30.
The DSR was powered up on orbit 2127 and a CCD image taken.
This was blank (following a day's analysis with
hastily-assembled test equipment!) due either to incorrect
pointing (we still have an unquantified amount of libration)
or incorrect exposure. More experiments will be scheduled as
soon as possible.
ODATA resets were initiated at 11:19:23 and 12:53:44 and
19:12:00.
Thursday 26/7/84
ODATA resets were at 10:12:00 (approx) and 11:58:18. Attempts
to power up the sun sensors were partially successful due to a
known problem with their current trips. During the evening,
the spacecraft was set to re-transmit audio from the 438MHz
uplink to test this uplink at the new attitude. Results were
most encouraging.
Friday 27/7/84
The 2.4GHz beacon was tested and found to be much improved in
the new attitude. This downlink should prove to be very useful
for engineering and high speed data for ground stations which
are well-equipped with good receiving and decoding equipment.
** 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 will be available shortly.
** UoSAT-Oscar-9 Schedule **
The 2.4GHz beacon will be in use this weekend.
Friday Load bulletin
Saturday Bulletin / 1200 bd telemetry / Digitalker
Sunday Bulletin / 1200 bd telemetry / Digitalker
Monday Whole-orbit radiation data
Tuesday Checksummed telemetry
Wednesday CCD image
Thursday Whole-orbit telemetry data
Friday Load bulletin
Based on the response to our questionnaire, we are considering
generating Digitalker for the educational 'market' on Mondays,
now that we have started transmitting CCD images on Wednesdays.
Radiation data will be scheduled occasionally.
** General News - UoSAT Newsletters **
The following information has been printed at UoS. The full
pack has been sent to all enquirers who have written to us
since February this year. It is available on request.
Newsletter - General status of UoSAT activities at June 1984
Datasheet 1 - UoSAT Project Summary
Datasheet 2 - UoSAT-1 Technical Data Summary
Datasheet 3 - UoSAT-1 Orbit Geometry, Tracking and
Groundstation details
Datasheet 4 - UoSAT-1 Telemetry
Datasheet 5 - UoSAT-2 Project Summary
Datasheet 6 - UoSAT-2 Technical Description
Datasheet 7 - UoSAT-2 Reception, Data formats
and Telemetry equations
Datasheet 8 - UoSAT-2 FSK demodulation using BBC Micro.
Questionnaire - As transmitted on this bulletin
Sheets describing the DSR data format and how to assemble this
data to make up CCD images are under preparation as time
allows.
** Weather Satellite Status **
* The NOAA-8 spacecraft is being decommissioned following a
failure of the primary oscillator which commands the timing of
the gyros and attitude control system. Engineers have not been
able to switch over to the redundant oscillator as the primary
oscillator has not yet failed completely.
* The NOAA-6 spacecraft has been re-activated to replace the
failed NOAA-8 data.
* NOAA-7 will complete its planned operational lifetime this
summer, but is continuing to perform well.
* The NOAA-9 spacecraft is currently scheduled for launch on 23
October 1984.
* METEOR-2-7 remains active on 137.3 MHz
* METEOR-2-9 has not been heard recently.
* METEOR-2-8 is now active on 137.85 MHz.
** Thanks for Reports & Questionnaire Returns **
ZL1MO, G6AAL, IV3TKI, ZL1AOX, G3WDI / Kessingland VCP School,
G4BZB, OZ1RO, HB9AYX, K1KSY, Sir William Turner's 6th Form
College, G3TKW, G3UVC / Southampton C.H.E., Birger Lindholm.
OZ1WN, G3FIJ, ON1BTH, JA2WO.
HB9RJV / HB9RKR, PY2NKW, KDX1A, G3VOM, DD2OJ / DB2OS.
This week: PE1HLB, VK2ZYE, I2KBD, VK2RX, VK2XPW, VK2AVH,
ON4HW.
** Keplerian Orbital Elements - from KA9Q **
see OPS bb!!