The Experiment 5 Antenna deployment problem onboard Helios A, the failure analysis, and changes in design, test, and operation which led to a successful deployment of both antennas during the early Helios B mission phase are described

Mueller, J. W.

English

NASA Technical Reports Server

]N76"28285
THE HELIOS EXPERIMENT 5 ANTENNA MECHANISM
by-_. J. W. Miiller, Dipl.-Ing.
DFVLR-BPT, Germany
SUMMARY I
This paper describes the Experiment 5 Antenna Deployment problem on
• ooard HELIOS A, the failure analysis, and changes in design, test, and
operation which led to a successful deployment of both antennas during the
early HELIOS B mission phase.
t
INTRODUCTION
The two Experiment 5 antennas are installed ncrmal to the axis of rotation
close to the equatorial plane. The antennas ferm a dipole which is used by
the Plasma and Radio Wave Experiment. It was planned to deploy both
antennas at once, about 3 hours after the launch of HELIOS A. However,
the observed anomalies:
- Only one of the motors was switched off automatically by the end
switch
The spacecraft spin rate change due to the change in the spacecraft
spin moments of inertia was from 52. 966 rpm to 51. 072- rpm ,'"
instead of 49.36 rpm
- One antenna element was grounded to the spacecraft structure
indicated that only one antenna was deployed to the full length of 14.75
meters.
Description of the Antenna Mechanism !
Figure 1 shows the simplified antenna drive system. Each antenna mecha-
nism is powered by an AC motor and inverter which drives the antenna
storage spool and the pinch drive rollers. The pinch drive rollers are ; ;
geared to deploy the antenna material at a rate faster than it can be
unwrapped from the driven spool. A slip clutch in the gear train makes this
possible. The intent is to keep any slack material from developing between _
the spool and the pinch drive rollers by keeping tension in the antenna mate-
rial. A one-way clutch permits the pinch rollers to free wheel during
antenna retraction. ., potentiometer wi.rha range of five volts is driven by _ '
the rotating storage spool. Micr=,switches with.arms riding against the
antenna material shut the motor off automatica',i_ at full extension or retrac-
tion. This shut-off is accomplished by having a elot cut near each end of ithe antenna material. As the slot passes under t},e microswitch arm, thearm drops through the slot and opens tile circuit to the motor. These
switches are located outboard of the pinch drive rollers in an area where i
• the antenna material is forming into a cylinder around a form; therefore, i,?
jPL Technical Memorandum 33-777 133
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ii i
the antenna exhibits some stiffness in this area--':t is not a flat ribbon. The ':
antenna itself is a 0. 0038 cm (0. 0015 inch) thick Be Cu strip heat-treated to
form a 0. 673 cm (0. 265 inch) diameter cylinder along the longitudinal axis
of the strip. After forming into a cyl.inder, the edges of the strip overlap
each other by approximately 90°; there is no interlocking feature. The out-
board of the mechanism housing contains an ion guard approximately two
meters long when fully deployed. This ion guard consists of a thin rubber
sleeve expanded around a relatively long, weak coil spring, i.e., a glorified
vacuum cleaner hose about 5. 1 cm (2.0 inches) in diameter. During and
prior to launch, the ion guard is compressed into a housing about 25.4 cm , -
(10 inches) long and held in place by a fitting on the end of the retracted
antenna. Upon deployment of the antenna, the free end of the ion guard fol- ,).
lows the antenna out until the ion guard has extended to its Cull length. The
inboard end of the ion guard remains fixed to the front end of the mechanism
housing. The antenna then continues to deploy throPgh the extended ion
guard until the antenna is fully deployed. The mechanism is enclosed in thin
sheet aluminum dust covers to provide an RF shield between the antenna and
noise origina.ing inside the spacecraft. The antenna itself is atsoisolated
electrically from the remainder of the mechanism.
Failure Analysis
The commands to deploy both Experiment 5 antennas were properly received
and executed by the spacecraft; however, due to a malfunction within unit
S/N006, the antenna element of this unit was not properly deployed. The
analysis performed was based on the following parameters"
- Telemetered antenna length readout
- Solar aspect angle infcrmation "
- Science data of Experiment 5
- Spacecraft spin rate information
The telemetered antenna length readout of S/N006 shows some unsteady
behaviour during the early deployment phase. But looking into all trans-
mitted data, it _s obvious that the motor and gear train of S/N006 started up
and opera=ec until the 10-turn potentiometer was driven against its mechani-
cal stop, which indicated an 18 cm longer antenna element. The nonessen-
tial bus current monitor provides information on the total current drawn by .
all consumers fed by this bus. Besides the experin .=nts, the E-5 antennas ;7
also are powered from this line. The current is sampled by the A/D con-
verter for short time intervals only. This, together with the current chop-
ping caused by the D3A 400 Hz inverter, provides a very unsteady current
reading.
From this information, it can be deduced that both units drew approximately
the _redicted current (0.4 A each) and that one unit automatically switched
off after a run time of 32.5 rain. These data also show clearly that the
second unit did not switch off automatically. Only when the power disable :_
command for the antenna units was executed did the current reading drop to
the value ithad prior to antenna deployment. The solar aspect angle
changed during the deployment by O.Z ", which also indicates a malfunction
of one antenna element because both antennas are mounted about I0 cm
134 JPL Technical Memorandum 33-777
)
1976021184-141
above the center of gravity plane. During deployment of the E-5 antennas :_
the experiment was collecting data. The noise spectrum obtained shows two :.
distinct changes: 3.4 minutes after the deploy initiation command the noise I
went down, while at 7.1 minutes after initiation the noise went up to approxi-
mately its original level. The spacecraft spin rate data turned out to be the
best tool for locating the f_ilure. Figure 2 shows the relative spin rate ,,
variation as a function of the deployed antenna length. The upper dashed ._
line shows the variation for a nominal simultaneous deployment of both _
antennas, the center line shows the variation in spin rate for deployment of
one antenna only, and the lower line indicates the actual measured spin rate
change as a function of the transmitted antenna 1 _ngth read out. As can be
seenbylooking at all observed anomalies, the iailure must have occurred in
the early deployment phase during the simultaneous deployment of the ion
guards with the antenna elements. In subsequent meetings, the possible
failure modes were discussed, and the following were seen as the most
probable failure modes:
A) Failures based on the interaction of ion guard and antenna element:
- The turns necessary to fold the ion guard affected the boom
element during the first phase of deployment when the ion
guard rotated back.
Ion guard jammed during element deployment; suddenly it
came free, hit the antenna tip mass, and damaged the antenna
element or tip mass.
B) Failed mechanism: "
Clutch on the drive roller failed, then antenna element bloomed
up between spool and drive roller device.
- Element damage caused high friction between moving element i
and ploy; again blooming up of the boom either between spool
and drive roller or between drive roller and plo_,.
- Loss of load on the pinch roller caused element blooming up
between spool and drive roller due to slippage between drive iroller and antenna element.
- Loss of alignment due to a bearing failure or misalignment e
after relubrication at Kennedy Space Center (KSC).
: - During lubrication at KSC, some lubricant (grease) was put on
°_ the drive roller, causing slippage between drive roller and
;_. antenna element.
- Wrong lubricant in the worm gears: silicon lubricants tend to
creep. Suggestion was made to change to the Krytox 243
grease for lubricating the worm gears.
JPL Technical Memorandum 33-777 135
1976021184-142
As the outcome of the discussions, a test sequence was set up to simulate
the possible failure modes. It was decided to perform the tests with speci-
mens S/N001 and 00Z. Units 003/004/005 were reserved as flight and spare
units. The following tests were performed at Fairchild in early March 1975:
1. Test sequence for S/N 001/00Z
1.1 (S/N 002) Deploy element to 1.Z mark. At his point, release
ion guard instantaneously (element pointing down,
motor in operation).
1.Z (S/N 002) Store ion guard with "4-turntwist." During deploy-
ment, measure rotation of element tip and ion guard
tip.
1.3 (S/N 001) Twist element on stationary mechanism. Observe
reaction of element on ploy and microswitch travel.
1.4 (S/N 001) Stall element during extension. Observe buckling of
element between drive roller and ploy.
1.5 (S/N 001) Check pressure between drive and pinch roller.
1.6 (S/N 001) Determine torque range of clutch for proper deploy-
ment, with no pull force acting on element. When
clutch fails (at minimum torque setting), continue
mechanism operation for 80 sec minimum and record
status. Attempt "retract" of antenna element.
I. 7 (S/N 002.) Determine clutch setting and roller pressure.
1.8 (S/N 00Z) Run full extend/retract load cycles:
? cycles, room temperature, min/max load
4 cycles, -20°C, min/maxload
4 cycles, +50°C, rain/max load
Operation in air, load ±50% of nominal, retraction
under nominal load.
I. 9 (S/N 002.) Determine clutch setting and roller pressure.
Z. Component tests and other matters
2. I Measure torque versus temperature performance for a clutch set
at center of acceptable torque range. See test 1.6 (S/N 001) and
callout on respective drawing.
2.2 Regarding the intended deletion of the ion guards, it was clearly
stated that antenna deployment will be achieved.
136 JPL Technical Memorandum 33-7_7 :
}
./ t
1976021184-143
3. Test sequence for SiN 003/004/005 (spare unit)
3. I If deployable ion guards are deleted, remove detent spring.
3.2 Check torque setting of drive roller clutch and check pressure
between drive and pinch roller.
3. 3 Perform full-length element extension at ambient pressure and
-20°C and +50°C ambient temperature, respectively. (If wear-
out was shown to be a problem by test 1.8, only the cold cycle
deployment is to be performed.) Perform visual inspection of
element wk, en fully deployed.
Results of the Failure Investigation Tests
The most probable failure mode which could have caused the problem on
ttELIOS A was found in tests No. l.g and 1.3 when the effect of the ion guard
on the antenna element was determined. When the ion guard and the antenna
system are assembled for S/C integration, the ion guard is compressed to
about 30 cm for storage. During storage, it is additionally twisted axially
through two to four turns due to the normal rotation of the helical spring
inside the ion guard. When the ion guard deploys (simultaneously with the
antenna element), it imparts a torqu_ to the antenna element transmitted by
the friction between ion guard end flange and antenna tip mass. When the
direction of the ion guard torque is such that the antenna cross section tends
to open, the antenna element is caused to bind at the end of the ploy. As a
result, a blooming or buckle occurs between the drive roller and the ploy.
When this effect was detected at Fairchild, approximately 5 seconds had
elapsed between stall of element and power switch-off. The 5-second delay
was enough to damage the antenna element. A possible explanation was that
one antenna worked properly and that it was impossible to overcome the
failure on board HELIOS A by retracting and deploying maneuvers of the
S/N 006 unit. Figure 3 shows a close-up view of the failed mechanism
after test step 1.2.
M odific ati ons
A) Design Modifications
Based on S/C noise data obtained by Experiment 5a on board HELIOS A, the
experimenter requested the elimination of the foldable ion guard. It should
be replaced by a rigid electrically conducting tube of 10-cm diameter and
0.8-m length to provide electrostatic shielding of the antenna base from
noise originated by the spacecraft solar array. This modification completely
eliminated the interaction between ion guard and antenna element. Together
with the elimination of the foldable ion guard, the detent spring inside the
mechanism could be removed. This spring was necessary tohold the
antenna element in its stored position during vibration loads, because of the
pulling force of the ion guard on the antenna element.
P
L JPL Technical Memorandum 33-777 137
1976021184-144
B) Test Modifications
Two full extension/retraction tests were added on a system level: one prior
to the spacecraft vibration test and one after all mechanical system tests,
prior to encapsulation at Cape Kennedy.
C) Operational Modifications
A new operational procedure was worked out that makes it possible to stop
the deployment if any anomaly occurs. It was planned to deploy both antennas r
on board HELIOS A at once. The new procedure was the following.
Before starting antenna deployment, operations E5 and E4 shall be turned on
and S/C telemetry shall be in science data mode to monitor S/C spin rate for
possible antenna short to ground and indication of motor current flow. It
shall be monitored continuously, displaying nonessential bus current, antenna
potentiometer reading, antenna motor switch status, S/C spin rate, E5b
scientific data, and E4 scientific data. One operator shall continuously plot _2
the above parameters on a chart which has the predicted values plotted on it. :
Deviations from predicted values will be cause to stop antenna deployment
operations. A pre-arranged command shall be at the instant ready, stowed
in the command queue, to turn off the antenna motor current.
Sec_uence of E5 Antenna Deployment
Stevl
Deploythe +Y antenna element to a length of 1 m, where it is possible to
detect a change in the S/C spin rate and monitor all parameters.
?
Step 2
Deploy the -Y antenna element analogously to step I.
Step 3
Deploy the +Y antenna element from I m to 2.5 m.
Step 4
Deploy" the -Y antenna element from 1 m to 2.5 m.
Time for bow shock measurements.
Step 5
i
Deploy the +Y antenna element from 2.5 m to 14.4 m.
Step 6
Deploy the -Y antenna element from 2.5 m to 14.4 m.
D
i
138 JPL Technical Memorandum 33-777
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1976021184-145
Step 7
Deploy the +Y antenna element to the full length in steps of 50 to 60 ram,
which correspond to a running time of I0 to 12 seconds. Monitor all param-
eters and perform an impedance measurement after each step. Deployment
commands shall be terminated after a step increase of the impedance mea-
surement or closure of the end switch.
Step 8
Deploy the -Y antenna element analogously to step 7.
The Inflight Deployment of the HELIOS B Experiment 5 Antennas
Steps 1 to 6 of the deployment were performed successfully on the first day
of the HELIOS B mission. All above-mentioned parameters were monitored
and plotted and did not deviate from the predicted values. Figure 4 shows
the plot of the spacecraft spin rate and solar deviation angle as function of
deployed antenna length. Steps 7 and 8 were performed successfully during
the third Goldstone pass on the third day of the mission.
Ac knowled_ement
The author thanks Gordon Smith and Richard Kramer of Fairchild Industries
and Dr. Wunderer of Messerschmitt-B61kow-Blohm for the excellent coopera-
tion which made it possible to locate the problem and introduce, in a short
time, changes to prevent a similar failure on board HELIOS B.
t"
References
1 MBB Procurement Specification Extensible Antenna, HELIOS Spacecraft.
2 Dr. Wunderer (MBB), Failure Analysis D3A S/N 006.
3 E. Angulo/W. Sours (GSFC), Memorandum, "Summary of the HELIOS
Experiment 5 Antenna Problems. "
4 E. M_iller (GfW), E5 Antenna Problem Investigations.
5 ._airchild/MBB, Test procedure for failure investigation tests with
'.;/N 001/00_..
6 E. Mi_ller, Test report of failure investigation tests.
JPL Technical Memorandum 33-777 139 "
1976021184-146
CLUTCH-
BACK-
I
6
NOTE:GEARSNOTIDENTIFIEDARESPURGF.&RS
Fig. 1 Antenna drive system
' ' i I I IRELATIVE
.008 _SPIN RATE NUMINALL)I:PLUYM_.NT--. ,i ///VARIATION 2 ANTENNAS _J
007 1 l 1 1 I /'_/" i >"I/ ,:
• 006 -- AT THIS TIME - r "S" _'/" _/"
S/N . 006MAY ' /J _"
HAVE STALLED ,/ <"
.005 I s" P_ _ / _'ONE ELEMENTSTALLED
,J ..,., '"/' ,_ _ _'- AT END OF ION GUARD
.004 I ..-_ .--._i- t t t
j _,_.._"._ _" OBSERVEDSPIN RATEVARIATION
• 003 I _ • DATA ACCURACY -+10"4; SPIN RATE
17/r''- IS AVERAGEDOVER 40. 5--sINTERVAL
•002
'-- RECONSTRUCTION• 001-, OF ACTUALBEHAVIOR//l
0 I.e-.--J1 I 452 3 4 5 6 7 8 9 10 11 12 13• _ rain
Fig. Z Spin rate variation on board HELIOS A
! as function of time
140 JPL Technical Memorandum 33-777
1976021184-147

, T
Fig. 4 HELIOS B Experiment 5 antenna
deployTnent steps I to 6
J
14Z JPL Technical Memorandum 33-777
1976021184-149


The Helios experiment 5 antenna mechanism

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