The results of the analysis and the evaluation of flight data obtained from the horizon sensor test project are described. The rotary mechanism of the scanning earth sensor composed of direct drive motor and bearings using solid lubricant is operated satisfactorily. The transmitted flight data from Engineering Test Satellite IV was evaluated in comparison with the design value

Ikeuchi, M.

Ishigaki, T.

Kida, T.

Matsumoto, M.

Ohkami, Y.

Wakabayashi, Y.

English

NASA Technical Reports Server

N83 24890
EVAI//ATION OF SCANNING EARTH S_SOR MECHANISM
ON ENGINEERING TEST SATELLITE IV
Masami Ikeuchi*, Yasufumi Wakabayashi*, Yoshiaki Ohkami**
Takashi Kida**, Takeo Ishigaki***, and Mikio Matsttmoto***
ABSTRAET
This paper describes the results of the analysis and the e%_luation of
flight data obtained frcm the horizon sensor test project conducted jointly
by National Aerospace Laboratory and National Space Development Agency of
Japan and manufactured by Matsushita Research Institute,'Ibkyo,Inc.
The rotary _a .hanism of the sc.anning, earth.sensor composed of direct
drive motor and arLngs uslng solld lubrlcant is operated satisfactorily.
have _he_ transmitted.flight da.ta from Japanese _hgineering Test Satellite IV
u_, evaluateu in crmparlson with the design value and the rotary mech-
ani_n is forecasted to be used for a practical satellite.
INTRODUCTION
A scanning earth sensor (called HOST as abbreviation of HOrizon Sensor
with Turning head) was originally designed as a roll/pitch attltt_e sensor
of three-axis stabilized spacecraft. The HOST is one of the experimental
equipments mounted on the Engineering Test Satellite IV (ETS-IV or 'Kiku 3 ')
which was launched on February Ii, 1981 from Tanegashima Space Center of
National Space Development Agency of Japan into a transfer orbit with
initial apogee and perigee heights of 36000 km and 223 km respectively and
with inclination angle of 28.5 degrees.
In comparison with other earth sensors such as the radiation balance
type and edge-track type, this conical scanning earth sensor is considered
to be one of the main practical earth sensors for low and middle altitude
because of its wide acquisition range and little influence to attitude
change of spacecraft, but it is difficult to design its rotating mechanism,
control its quality, and assure its reliability in general.
The ETS-IV spacecraft is spin-stabilized with nominal spin rate of 60
rpm and the nominal spin axis direction is perpendicular to the earth equa-
torial plane. The HOST has been tested not only as a horizon crossing
indicator for spinning spacecraft, but also as a scanning earth sensor witch
the scanning axis parallel to the spinning axis.
* National Space Development Agency, Tsukuba Space Center, Ibaragi, Japan
** National Aerospace Laboratory, Tokyo, Japan
*** Matsushita Research Institute, Tokyo, Inc.,Kawasaki, Japan
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The experimental items of the HOST are as follows.
i. Performance change of rotating mechanism at space environment
2. Characteristic change of infrared optoelectronics in a space
environment
3. Data acquisition at infrared input energy
4. Function and performance of attitude angle measurement by the
HOST
The HOST has been operated during the primary mission term and the extended
mission terms.
This paper describes the rotating mechanism of this HOSq and the data
analysis and evaluation of the flight experiments in the operating duration.
DESCRIPTION OF THE HOST
The HOST consists of three major components which are two rotary heads
(HD1, HD2; Figure i) and one electronic package. Each rotary head is mounted
to both sides of the ETS-IV perpendicular to its spin axis direction. HDI is
on the spacecraft spin axis but HD2 is offset from its spin axis by 0.9 meters.
For this reason, h132 is affected by a cer!_ifugal force of approximately 3.5 G
towards the radial direction.
Each rotary head consists of an antireflection coated Ge lens, a pyro-
electric infrared detector with an optical bandpass filter, a signal pre-
amplifier and a motor for a rotating metal mirror. This rotary mechanism is
composed of bearings using solid lubricant (Rulon C) and three phase direct
drive motor (DD motor) using phase locked loop (PLL) control. The rotor
magnet material of the DD motor is an anisotropic strontium ferrite.
The horizon crossing period of the instantaneous field of view (I_OV) is
determined by detecting infrared radiation fram the 14 to 16 um CO 2 band using
a narrow IFOV (about i. 4 degrees) conical scan with a cone angle of 120 degrees
and rotating rate of 60 rpm. Pitch and roll angles are measured by using two
conical scanning rotary heads.
The motors of either head can be turned on and off separately. When the
motor is on, the total scanning speed is approximately (60+60) rpm at nominal
spin rate and when it is off, it reduces to about 60 rpm, which is spacecraft
spin rate.
The dimension and the weight of each rotary head are 160 mmx 230 ram, 3.2
kg respectively.
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ROTARY _C_ANISM
Figure 3 shows the structure of the HOST rotary head. The scanning
mirror and the hollow shaft are driven Dy a three pDase DD motor with a
quartz stabilized PLL control which is to be at a constant rotation speed.
Bearing mechanism
A bearing mechanism has a preload structure to inner ring as shown in Fig-
ure 2 and has two angular ball bearings using a solid lubricant (Rulon C)
retainer. This mechanism's merits are that it is small, easy to assemble and
provides a wide distance of work points between two bearings. In order to
minimize the precession caused by the HOST head rotation, clearance fit
around two bearings was to be as small as possible.
Lubrication
An angular contact ball bearing is adopted and polymer composites }_vir_ self
lubrication are used witha retainer (Table i). Lubrication is performed
when a lubricant is transferred to a ball surface from a retainer by rotating
bearings and is then transferred to a raceway of inner and outer rings from
the ball surface. T}_ most powerful reason why oil is not used is because
the infrared optical system wouldbe contaminated by the oil evaporation
and adhesion. The reason why solid lubricant is used is because it is less
volatile and less influenced by the large temperature changes and radio-
activity of a space environment; this is important because of the HOST's
rotating parts which are exposed. _$2 is a good lubricant in vacuum, but
the ground test data in the air indicates it is not good because of weakness
to moisture. Rulon C is a composite type lubricant of fiber reinforced
PTFE (teflon) containing lead oxide (Pb304) and has been used in the .Apollo
Project of NASA.
This solid lubricant is characterized as follows.
i. Less contamination to the infrared optical system by means of low
vapor pressure
2. Radiation resistivity
3. Fitness for use on the ground in the air
4. Comparative high load resistivity
GROUND TEST
An EngineeringModel (EM), Protoflight 5kx_el (PM_ and Flight Model
(FM) of the HOST have been developed in turn, and the test levels of PM
and FMareQualified Test level (QT) and Acceptance Test level (AT) re-
spectively (Table 2 ). Both HDl and HD2 of the HOST-FMhave been operated
20 hours in air and ii0 hours in vacuum in the test at the factory, the
acceptance test for _- zh head and the inspection at the launching site.
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It is confirmed that the measured data _are of no difference between in the
air and in vacuum of 10-5 Pa.
At higher temperature, the average motor torque will be. larger, but the
torque fluctuation will still be the same level. At larger acceleration,
both the average motor torque and the torque fluctuation have larger values
(Table 3). Stability of the operation is ccmparatively good for a short
term (several tens of hours ), but variations cf the average motor torque
and the phase jitter are 2.5 x 10-6 N-m, e0.076 deg.D_ p (+1.2 x 10 -6 N.m
_nen converted to torque ), respectively, for a long %ehn (several months ).
OPERATING TEST ON THE SPACECRAFT
The operating test periods of the rotary mechanism on the ETS-IV are
as follows.
I. Mission term ( February 1981 ~ May 1981 )
o Continuous operating test ( several tens of hours )
o Function test
2. Extended mission term ( May 1981 ~ Febn_ry 1982 )
o Continuous operating test ( several hundreds of hours )
o Eclipse test
3. Extended mission term ( second ) ( February 1982 ~ August 1982 )
o Continuous operating test ( several thousands of hours )
o Test in maneuvers of the spac_raft
The accumulated operating hours amount to about 4,500 hours for HDI, and
_h_ut 4,000 hours for HD2 till August 1982. The orbital total hours includ-
ing nonoperating ti_ _,L_nt to about 18 _ont]Ls. _"_t_h_st is continuing.
DATA ACQUISITION
The data acquisition from the ETS-IV spacecraft is transmitted to the
ground station by t/_e PCM telemetry. The data of the motor coil current
and jitter output are acquired once about 2 seconds and once about 32 sec-
onds respectively. The variation within a short time can not be therefore
observed.
Average motor torq_._,
The hTJ1 has been o_rated through about 4,500 hours in the temperature range
fzum -34°C to 20°C _m_ its average motor torque is stable at the value of
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4 '_ 8 x 10 -6 N.m (including iron loss ). The HD2 has been operated through
about 4,000 hours in the temperature range from -32°C to 25°C and its aver-
age motor torque varied from i.i0 x 10-5 to 2.65 x 10 -5 N.m but these per-
formance values were well wit/]in the limit value of 5 x 10-5 N-m (Figure 4).
As HD2 is under stationary acceleration of about 3.5 G, its average motor
torque is considered to be increased especially at high temperature in
addition to the acceleration.
M_tor torque fluctuation
Themotor torque fluctuations for HDI in the periodof 20 _ 30 min. were
observed a few times at the beginning of this test schedule, but these
phenomena were _nall and stabilized during the extended mission term.
The fluctuations of the motor coil current are coincident with the_ data
from the jitter (AC cc_nponent) (Figure 5). There were no periodic motor
torque fluctuations for HD2. A slight increase of its motor torque
fluctuation was found at the middle of this test schedule, but this fluc-
tL_tion was stable from that time on. The variations of these data are
shown in Figure 5.
ANALYSIS AND EVALUATION OF BEARINGS
Table 4 shows the evaluation results of the average motor torque and
themotor torque fluctuation including the ground test data. The iron loss
is excepted frcrnthe averagemotor torque. The data of the motor torque
fluctuation are obtained from the motor coil current output (AC component).
The average motor torque for HDI varied once or twice from the ground
test data, and the periodic variations were observed in themotor torque
fluctuation for HDI which was not found in the ground test data. The
average motor torque and the motor torque fluctuation for HD2 are the
proper values based on the ground test data.
Concerning the bearings using zolid lubricant, temperature and accel-
eration factors make these characteristics change mainly in the ground
test and loading test on the spacecraft. Adhesion that is doubtful espe-
cially in high vacuum (10-6 _ i0-ii Pa ), is not a dominant factor to the
solid lubrication in case of slow revolution and light load such as the
HOST, but mechanical scratch on the raceway is considered to be a dominant
factor mainly due to friction.
As for the motor torque fluctuation, ripple variations occurred, then
subsided. This was not abnormal and was observed during the function test
of the same type of bearings in the HOST. For the cases which used solid
lubrication, the motor torque could be attributed to the fine differences
in the adhesive state of the lubricant, mechanical contact state, mechani-
cal accuracy, and surface roughness. Therefore, it is necessary to under-
stand the lubrication properties and to choose the lubrication wisely.
147
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Regarding the motor revolution accuracy, the phase jitter has a slight-
ly large value of about 0.8 deg.p_p (max.) in contrast with the nominal
value of 0.2 deg.p_p.
Encoding necessary for obtaining the chord width is the time measure-
ment because the ETS-IV is a spinning spacecraft. This r_qn]irement is not
essential if an optical encoder is adopted for pract3cal use.
There were two unexpected events that occurred to the motors of }_DI and
HD2. First, both HDI and HD2 were stopped rotating three times by means
of operatiD_ the current limitter for hours in the continuous operatinq
test. Second, the motors were not driven in the long period eclipse test
when HDI and HD2 were exposed to low temperature below the designed value.
In both cases, the motors of HDI and HD2 were recovered and normally
operating after these events. These events were unaccountable by means of
no data acquisition when the events were occurred.
Long period eclipse test
A long period eclipse test has been performed during the extended mission
term to investigate the characteristics of the rotary mechanism at the
large temperature change. This test has been also performed to investigate
the temperature change rate dependence of the rotary mechanism by contin-
uously rotating the motor for the eclipse of 90 min. period over maximum
eclipse time on the geostationary orbit (about 72 min. ). It is shown that
HDI is hardly affected by the temperature change rate of 21°C/hr. and HD2
has large values of _/ne average motor torque of 1.3 4 2.2 x 10-5 N.m and
the motor torque fluctuation of i.3 x 10-5 N-m by the te_oerature change
rate of 13°C/hr., but a PLL cycle slip does not occur for HD2.
Test in maneuvers of the spacecraft
Maneuvers of the spacecraft have been carried out for the purpose of the
interference test by the Sun to the infrared optoelectronics. The motor for
HDlwas operating in these maneuversand the characteristics were observed
in case of vibrations. The motor characteristics did not change and had a
good operationbefore/in/after the maneuvers.
EVALUATION OF OI_ER LUBRICATION
The long life study of the HOST (HOST-LL) was performed in addition to
the lubrication results of the HOST. Several sorts of retainers were
attached to the same type bearings of the HOST (a part of bearings have a
raceway of inner and outer ring and balls sputtered with MoS2) and a life
test was performed with a revolution of 2,000 rpm and preload o_ 5 kg in
high vacuum (10 -6 _ 10-7 Pa) and atraospheric pressure. The results show
that the bearings using Rulon E have a s, all average friction torque and
are good for the life test over 1,000hours. Rulon E is composed of PTFE
and M_S 2. The bearings assembled along witha Rulon E retainer and a race-
way of inner and outer ring and balls sputtered by MoS 2 (0.5 _ 1.0 _m) are
148
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stable at small friction torque (4 _ 5 x 10 -6 N.m) and small friction loss
of retainer. So these bearings exceed the target total revolution of i.6
x 108, which Is equivalent to the life of the HOST-LL over 5 years.
It is concluded that about one-third of the HOST's average friction
torque will occur, given the structure of the HOST-LL and a preload of 2 kg(Table i ).
The friction torque contains dispersive fluctuation and ripple fluctu-
ation and so on. These fluctuation sources are mainly considered to be
retainers from the test described above (Figure 6). It is necessary to
investigate the following items more clearly.
i. Shape and size of retainers
2. Processing of retainers
3. Uneven materials of retainers
4. Roughness and shape of raceway and balls
It is also necessary to investigate bearings sufficiently for the limit
value and design life.
CONCLUSION
Some problems are left unsolved for now, but the rotary r_chanism
system of the HOST has reached the expected goal through the mission term
and the extended mission term. It is shown that the rotary mechanism
system using solid lubricant is adequate for space applications.
1. T. Kida et al.
REFERENCES
.
Proc. of the 13th International Symposi_n on
Space Technology and Science (1982)
Y. Wakabayashi et al. AIAA Guidance and Control Conference, San
Diego (1982)
149
OR4GINAL "___'_
OF POOR QUALITY
Table I. Bearings specifications and structure of the HOST and the HOST-LL
Structure
Bearings
Items
Method of preload
Preload
Clearance fit
(bet_en axis and
inner ring)
Clearance fit
(between housing
and outer rin_)
Grouping
Design
Ball materials
HOST
Preload to
inner rin@
1.5 k@
25 _m
10_m
HOST-LL
Preload to
outer ring
2 k@
5_m
5 _m
Angular contact bali bearings
using solid state lubricant
retainer
7204Cbase l
SUS 440CSUS 440C
Retainer materials Rulon C Rulon E + MoS2
Inner radius 35 mm
15°
15
Contact angle
The n_mber of balls
35 mm
15°
12
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Table 2. Test level of the HOST rotary head
Vibration test
Random
13.1 Grins
60 s.
Sine wave
5.3C__p
max.
13.1 Grins
60 s.
Thermal test
in vacuum
Acceleration
_M -20 ~ +50 °C 0 ~ 10 G
PM ( QT ) 5.3 Go- p 19.6 Grm s -30 ~ +50 °C 0 ~ 5 G
max. 90 s.
FM ( AT ) -20 ~ +40 °C 0 ~ 5 G
150
ORIGINAL "_ '-"-" r'_
OF POOR QUALITY
Test
Ground test results for the HOST-FM
Temperature
Acceleration e)
Table 3.
Average motor tor_de a)
Condition
-21 °C
+19 °C
+36 °C
I G
_i c)
1.75
2.5
3.0
HD2 d)
5.25
6.0
12.5
2.5 _3.0 c)
18 ~23.5 f)3.5G
Torque fluctuation b)
HDI c) HD2 d)
2.4 7.8
I .8 3.0
I.2 2.4
I.2c)
g6~I_ _f)
unit ; x 10-6 N.m
a) The data with the exception of iron loss ( 2 x 10-6 N.m )
b) The data f_mn the HOST jitter output
c) Thrust direction ( I G / earth o-ravit_v )
d) Radial direction ( I G / earth gravity )
e) Room temperature in the air
f) Radial direction
Q
. '
Table 4.
Ground test
Mission term
Long period test
Eclipse test
Long telnn
Evaluation data for the HOST bearings
Average motor torque a)
HDI
1.8-3.0
2.0 ~3.0
3.0~3.5
3.0
3.0 ~6.0
HD2 b)
18.0~ 23.5
9.0 ~ 15.0
13.0~!8.0
13.0 ~22.0
14.0 ~25.0
Torque fluctuation
u
HDI
1.0 ~ 3.0
2.0 -12.0
2.0- 7.0
5.0
HD2 b)
I0.0 ~14.0
2.0- 6.0
6.0 _ 9.0
13.0
unit ; x 10-6 N.m
a) The data with the exception of iron loss ( 2 x 10-6 N-m )
b) _%easured value at the stationary, acceleration ( 3.5 G )
151
ORIGINS.;. " + J
OF FOOR Q_;.:,LF._"!
Figure I. Rotary head of the HOST
Spring for _reload Outer rin_
Inner rincf
Figure 2. 5_thod of preload
Peta iner
Balls
Rulon C )
152
Stainless mirror
Hollc_ shaft
Rotor ( maonet )
Stator ( coil )
FG coil
FG maqnet
O0
O_
o
\
Infrared detector
Ce lens
( solid lubricant )
Fio_re 3. Structure of the HOST rotary_ head
40
o 20
v
_0
-20
-40
50
40
__0
20
-4
8
lO
o
Eclipse
OF. POOR QUALITY
Continuous operating test
• @
O
• HD2
o
O • •
S •
• |o • •o
i I ! , I
0 1000 2000 3000 4000
Vic_re 4.
Operating time ( hours )
Changes of the average motor torc_e
o
30 , , , 3 .w
4J _ _
o ,_-'.o_! I - 0
i!2 _1 05 1
;_ o o
0 I00 200 300 400
Operating time ( hours )
Figure 5. Chanqes of the motor torr_e fluctuation
( * mark shows the data of fluctuation)
154
ORIGINAL _,,.'-',-";:_': _
OF POOR QUALITY
|
A
O
t'-"
x
¢..)
o
15
I0
5
0
0
Preload 2 kg
16rpm
H24
Teflon + Glass fiber
5 10 15
TIME ( DAYS )
Figure 6. Bearing test of all sorts of retainers
( Equivalent parts of the HOST bearings )
155


Evaluation of scanning earth sensor mechanism on engineering test satellite 4

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