Two mechanism types are presented, a rigid boom system and a 'hold and release' mechanism for spherical sensors. Both mechanisms have been designed, developed and tested by Saab-Space AB, Linkoping, Sweden for the VIKING project under a contract from the Swedish Space Corporation

Eriksson, S.

English

NASA Technical Reports Server

24901
DEPLOYMENT AND RELEASE MECHANISMS
ON THE SWEDISH SATELLITE, VIKING
Stefan Ertksson, Saab-Space AB, Link_ping, Sweden
I. ABSTRACT
TWo mechanism types are presented, a rigid boom system and a "hold
and release" mechanism for spherical sensors. Both mechanisms have been
designed, developed and tested by Saab-Space AB, Ltnk_ping, Sweden for
the VIKING project under a contract from the Swedish Space Corporation.
2. INTRODUCTION (Ref. Flg. i)
VIKING is a Swedish scientific satellite to be launched together with
the SPOT remote sensing satellite by the Artane Launcher, presently sche-
duled for late 1984. Its aim is to study a number of physical parameters
in the auroral zones of the magnetosphere. The payload consists of five
main experiments. Par_lcipattng scientist groups come from Sweden,
Denmark, Norway, Canada, United States of America, West Germany, England
and France. TWo of the experiments require the spacecraft magnetic
influence to be minimized at their sensors. These two sensors are a three
axes magnetometer and a loop antenna, located at the tips of the two
radial stiff booms.
Two other experiments use six spherical probes (/¢_= fOrm), includ-
ing inner/outer tips, for electric field measurements. These probes are
mounted on four wire booms which can each be deployed to a length of 40 m
in the satellite's spin plane, and on two tubular-element booms which can
be deployed 4 m each, parallel to the spin axis. Until deployment is
called for, these probes are to be stowed by Hold and Release Mechanisms
(H_).
Below the requirements of the radial stiff booms and the HRMs are
summarized. Their design, performances and test programs are described in
detail.
3. STIFF RADIAL BOOMS
3.1 Summary of requirements
The design requirements can be summarized as follows:
Launch Mode (stowed)
Sine vibration, all three axes
Random vibration, all three axes
5 - 100 Hz
20 - 2000 Hz
8.0 g2max
0.3 g /Hz max
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Deployment Mode
Spin rate
Release
Deployment shock (on boom tip)
Temperature
8.5 to 14.5 rpm
pyrotechnic device
max 50 g
-30 ° to ÷80°C
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Deployed Mode
Boom lateral deflection
Boom torsional deflection
within a cone angle of 0. i°
0.2 ° torsional angle
Boom Design
3.2 Detailed description (Ref. Fig. 2 and Fig. 3)
The rigid boom system consists of two identical booms symmetrically
mounted. The deployable boom element is an aluminium tube O.D. 53 mm,
thickness 1.5 mm and a length of 1385 mm. The limited space available in
the launcher adapter and the fact that the boom has to be stowed along-
side the payload deck, have set the boom length. Aluminium is also used for
the tip sensor mounting flange and the hinge part, both welded to the
tube. The other hinge part is designed as a separate unit, fastened to a
tubular leveUlng beam which is mounted on the payload deck. A titanium
shaft in two flanged bushings forms the hinge. The bushings have a rein-
forced P.T.F.E. llner material as lubricant. The hinge also includes the
locking mechanism: two beryllium copper leaf springs latching independent-
ly on two conlcal titanium locking pins. These pins are designed with a
slope, giving a smooth latching. Between the two spring blades a titanium
bolt acts as a stop, taking the collision load at locking. The boom is
stowed alongside the payload deck on two supports having a delrln sole.
The support nearest to the hinge is elevated with reference to the outer
support. The boom is furthermore stowed by means of a "hold down" wire
tightening the boom on to the outer support. The boom is thus preloaded to
protect the bushings in the hinge from heavy vibration. The preloadlng
also aids in lifting the boom off the supports.
Deployment
Deployment of the booms is initiated by ordinance cutting of the
hold down wires. The cuttings are effectuated by electro explosive
guillotines through which the hold down wires pass. Nominal spin rate for
boom deployment Is 11.5 rpm but the boom system has been tested in the
required spin rate range from 8.5 rpm to 14.5 rpm. The centrifugal force
306
generated by the satellite 8pln provides the booms with deployment ener-
gy. At nominal spin rate, deployment takes 2.0-2.2 seconds. When the boom
has locked into the deployed position the titanium stop bolt takes the
load and the boom is deflected. At the return bending the two leaf
springs transfer the load via the two locking pins. Since no damping
device is used and the deployment only uses a discrete amount of energy
the boom will oscillate until the whole energy is dissipated. The oscil-
lation has a frequency of _7 Hz. During this oscillation the two leaf
springs work their way down further on to the locking pins as the locking
pin angle acting against the leaf spring is set below the friction angle
for the mating surfaces.
Wiring
The power and slgnal cables are routed inside the boom and tied down
to the tube with brass wires at 15 cm spacings. Through the hinge a flat
cable is fed with a free loop length of 14 cm in order to lower
the wiring torque. The two boom cables contain:
magnetometer
loop antenna boom
5 coaxial cables RG 178
2
I twisted pair 0.25 mm
I coaxial cable RG 178
2
5 single cables 0.25 mm
Mathematical Model
A mathematical model for boom deployment was developed. It was used
for design purposes to estimate the deployment loads. The model is sim-
plified to two identical booms deployed symmetrically. Counter torques
from friction, cabling and latching were considered. The available energy
for boom deployment is the energy dissipated when the spinning satellite
changes its moment of inertia during boom deployment. This energy is
Zp _2p (Z)
-Ip x(z- i_a)x 2Tdlss
where Tdlss is dissipated energy
I
P
I a
W
P
moment of inertia prior to boom deployment
moment of inertia after boom deployment
satellite spin prior to boom deployment
307
t
3.3 Boos Tests
Four types of tests were carried out to evaluate the boom system
performance. Firstly, deployment tests have been conducted on a spin-
ning table. Secondly, the hinge has been tested separately in a vacuum
chamber. A third test has been conducted to determine the boom wiring
performance with regard to torque loss changes due to storage and extreme
temperatures. Finally, vibration tests have been performed.
Deployment tests
Deployment tests were performed with the booms mounted on a spinning
table, with a mounting plate having the same moment of inertia as the
sateUite itself, and with the spin table drive decoupled Just before
deployment. Thus the boon deployment was adequately simulated and the
interaction of the bodies at locking was not disturbed. To minimize spin
rate decrease caused by friction, the spin table bearings were axially
off-loaded by means of two support wires from the ceiling. The two booms
were also supported at CG location to unload their weight in the g-field.
All data acquisition equipment was placed on the rotating table to avoid
slip ring arrangements. The main parameters recorded were: the bending
moment at the boom root, the tip mounted experiment acceleration, the
deployment angle, the latch spring movement and the spin rate. The tests
were performed at three spin rates: 11.5 rpm which is the nominal spin
rate, 8.5 rpm and 14.5 rpm. After each functional test an alignment check
was performed.
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Separate hinge test
_uring the development phase a detached hinge was tested in a vacuum
chamber. Deployment was effectuated _y means of a pendulum stroke outside
the chamber. The counter torque from friction and latching was measured
in the axis from the pendulum to the hinge inside the chamber. As the
hinge was cooled and heated, the effects of different temperatures and
temperature gradients over the bushings were studied.
Wiring test
A test rig for the study of the wiring through the hinge was manufac-
tured. It consisted of an electric motor for simulated deployment with
means of measuring deployment angle and counter torque with hinge equiva-
lent wiring. The counter torque changes due to storage of the boom in
stowed position and due to the extreme wiring temperatures anticipated
were also studied.
308
Vibration test
For mounting the booms on the vibrator, a fixture shaped as a seg-
ment of the payload deck was used.This fixture was also used for mounting
on the spin table. Thus the boom could be moved back to the spin table in
stowed position for a functional test.
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3.4 Test Results
During the functional tests the boom bending moment at the boom root
was recorded. The results are presented in fig 4. The maximum recorded
bending moment at 14.5 rpm deployment spin rate was 378 Nm. The designed
ultimate load was set at 1100 Nm, which resulted in a safety factor of
2.9. The bending moment, 378 Nm, corresponds to an experimental acceleration
of 24 g. At nominal spin rate deployment the acceleration was 18 g. A
typical interaction of the booms after locking is shown in fig 5.
An alignment check was also performed after each test and the deflec-
tions were as follows:
Boom lateral deflection
Boom torsional deflection
within a cone angle of 0.05 °
max 0.05 °
From the hinge vacuum test and the wiring rig test an energy budget
is deduced as follows. The values presented are the maximum obtained.
(Ref fig 6)
Energy consumed (J)
Pre-locking
Action phase
Locking Temp./Temp.gradlent
phase (°C)
- Bearing/shaft friction
- Harness work
- Latch work
- Latch-locklng pins friction
O. 60
0.05
0.05 -30/10
-30
0.40 NIA
0.40 N/A
Total Energy Consumed 1.5J
309
The figures represent one boom; thus a total energy of 3.0 J is
needed for the boom system. The equation (i) given in 3.2 yields the lowest
spin rate limit for a feasible latching, which is 5.9 rpm. The safety
factor on energy to the predicted lowest deployment spin rate, 8.5 rpm, is
2.1.
During vibration tests the experiment unit experienced an overall RMS
level of 6 g. The magnetometer boom configuration resonance frequency at
35 Hz showed a peak value of 46 g at the magnetometer location.
3.5 Problems encountered
Since the vibration level at the magnetometer boom resonance fre-
quency during the preliminary tests was quite high, a 1.5 mm rubber
isolator was inserted at the mounting flange. This measure reduced the
peak value by a factor of 1.7.
After the preliminary tests a larger safety factor on energy loss was
requested. Measures were taken to minimize the energy dissipation during
deployment and latching. Decreased width of the leaf springs and adjust-
ment of the locking pins slope resulted in a smoother latching.
A change in the payload deck was found necessary after the deployment
tests, because the boom vibrated after release and bounced against a HRM.
For protection of the HRM a L-profile with a plastic material on the edge
was introduced. The boom now bounces against the profile and the vibra-
tion is damped.
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6'
4. HOLD AND RELEASE MECHANISM
Stowed Condition
4.1 Summary of requlrements
Sine vibration, all three axes
Random vibration, all three axes
Resonance frequency
No sensor movement
5 - 100 Hz
20 - 2000 Hz
I00 Hz mln
I0.0 g max
18.1 g__MS
0.3 gZ/Hz max
310
Release Mode
Temperature -30 ° to +80°C
Swing of sensor at release within a cone angle of I0°
Switch indication at completed armpair deployment
4.2 Detailed description (Ref. Fig. 7)
The Hold and Release Mechanism (HRM) is used to hold the sensor in
stowed position until the wire boom and axial boom deployment is initia-
ted. Ten seconds before boom deployment starts, sensor release is effec-
tuated. The HRM consists of a mounting bracket and two moveable arm-
pairs. The mounting bracket is designed as a flat beam reaching out over
the edge of the payload deck. The axes of the two armpalrs rotate in
bearings similar to those used in the stiff boom hinges. Armpalr
deployment is effectuated by means of preloaded torsion springs. A wire
is used for tightening the armpairs around the sensor rods. The wire is
fastened in the armpalrs and passing through an electro explosive guillo-
tine in its housing. The holding force is set when the guillotine housing
is pulled towards the bracket.
A strain gauge, which is used to measure the holding force, is glued
to a beam on one of the armpalrs. Each arm is set with 50 N against the
sensor tip. The pads (made of delrln) holding the rods have cylindrical
grooves for position of the sensor rods. On the sensor outer rod a cy-
lindric pin ( W ffi I mm) is used to prevent the sensor from radial and
rotational movements. The pin is placed in a track in one of the outer
pads. TWo micro switches are mounted on top of the bracket for indication
of full armpair deployment. The HRM for the two axial tubular element
booms is not described in detail but is similar to the unit presented
above.
4.3 HRM tests
Release test
The release test was conducted in a vacuum chamber (ix 10 -6 tort)
with a heatlng/coollng arrangement. Three release tests, with a lO°C
temperature gradient over the bearings at -30°C, +25°C and +80°C, were
performed on each unit. The effect of temperature was studied by compar-
ing the deployment time for each release test. During the test the HRM
was vertically mounted such that the sensor dummy used could be studied
with regards to side forces. The parameters recorded in these tests were:
release initiation (strain gauge voltage drop), armpalr deployment angles
(potentiometers), switch indication at fully deployed armpairs and the
sensor dummy movement. The sensor dummy movement was recorded by the use
of a small pick up roll mounted on the rod tip of the dummy. A larger
311
sending coll induced a voltage variation proportional to the swing of the
dummy.
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Vibration test
The HRM was
sensor mass dummy
performed.
tested to the levels specified. During these tests a
was attached. After vibration test, a release test was
4.4 Test Results
No significant changes due to bearing temperatures of -30°C to +80°C,
or 10°C temperature gradients over bearings, were found during the release
tests. The deployment times for all tests stayed within the interval 50-
60 ms. At release,the sensor swing stayed within a cone angle of 5° for
four units. Larger swings were recorded for the last unit due to an unin-
tentional torsional preloading of the wire boom cable, caused by the test
set up.
4.5 Problems encountered
During the preliminary test two major problems were dealt with. One,
the resonance frequency of the mounting bracket was 60 Hz for the first
HRM design. By adding a box shaped stiffener the resonance frequency was
increased to 130 Hz. Two, a number of different designs of the pads hold-
ing the sensor from rotational and radial movements were tested in vi-
bration. The design chosen is such that the wear inthe delrin pads during
vibration is low. This will minimize the sensor swing after release.
5. CONCLUS ION
The two mechanisms described above have successfully passed their
qualification and flight acceptance tests and meet the requirements. They
are presently being integrated with the VIKING satellite.
312
O_,GII';,L T:":_'-'F3"
OF POOR Q'jALI","V !
Fig. 1 Viking flight configuration
Spherical sensor /
|m
I
Fig. 2 Stiff booms in stowed position
©
÷t . .
Fig. 3 Stiff boom hinge and latching mechanism
f:
313
ORIGINAL PAGE 111
OF POOR QUALIFY
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zm--._ _a,. 9 mo,,_t
O_oymnteng,/"/'//_
/
s
hm
_)"._,.i .i ._;i, .7.8i 1'.0 _s z'0 i ;. i csJ;_
Fig. 5
1104I"" Uiham)e [o4d .....................
N4I
lW_r4
o iuD Omhlema Ii_lm o
Qi
-t
I
a
o
o
o
Boom interaction after locking
bV/_ng
0moy,,_t toru
(x1_ZNm Temp (°C)
...... 3o
7 "... _+2S
6 .... +110
5_
3 ,, :-
I- %%_'%
OIIDioylnenf (_'_1 e
::\
-3 .. %
Fig. 4 Max boom bending moment
at locking
Fig. 6 Boom wiring torque (Temp. 25°C)
/, t / Z
HH
Fig. 7 The HRM with the peds holdinq the sensor in place
I
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314


Deployment and release mechanisms on the Swedish satellite, VIKING

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