A two-position (0 deg and 180 deg) actuating mechanism (flipper) driven by alternately-heated wax motors (pellets) will be used to rotate the low field triaxial fluxgate magnetometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 deg and 180 deg positions. The magnetic field, power requirements, weight and volume of this device are very restrictive. The problems encountered in design and development of this mechanism are presented

Stange, W. C.

English

NASA Technical Reports Server

N79-21382
THE MJS-77 MAGNETOMETER ACTUATOR
By William C. Stange
NASA Goddard Space Flight Center
SUMMARY
A two-position (0 ° and 180 °) actuating mechanism (flipper) driven by alternately-
heated wax motors (pellets) will be used to rotate the low field triaxial fluxgate magnet-
ometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 ° and 180 °
positions. The magnetic field, power requirements, weight and volume of this device
are very restrictive. The problems encountered in design and development of this mech-
anism are presented.
INTRODUCTION
The purpose of this experiment is to provide precise, accurate, and rapid vector
measurements (from 0. 017 to 20 gauss, 1_/= 10 -s gauss) of the magnetic fields of Jupiter
and Saturn in interplanetary space to them and beyond. These data extend in situ studies
of the solar wind interaction with Jupiter and characteristics of its magnetic field and
yield first studies of Saturn's field and its interactions if the solar wind extends to 10AU.
Performing accurate measurements of magnetic fields on a spacecraft not fabricated
magnetically clean is a major problem. A moderately long boom will be used to place two •
low-field (_64007) triaxial fluxgate magnetometers at remote distances from the space-
craft. Simultaneous measurements will yield separate estimates of the spacecraft field
and the ambient field.
The purpose of this essentially nonmagnetic actuator is in-flight calibration of the
triaxial fluxgate magnetometers. This calibration, which determines the sensor zero
point, is accomplished by periodically flipping the magnetometers by 180 degrees.
The advantages of this mechanism are that it satisfies more than any other known
device, the constraints of volume, weight, nonmagnetic materials, and power in relation
to the requirements of high torque, fast cycling and long life in the hard vacuum of space
and exposure to intense radiation fields at Jupiter. These properties are derived solely
from the unique mechanical qualities of the pellet. This actuator will provide cyclical
bi-directional rotary motion under varying environmental temperatures (-45°C to +650C)
in a vacuum for periods up to five years.
This paper describes the mechanical and electrical functions of the design which
evolved, as well as the problems encountered. The objectives achieved are evaluated
and other possible applications are presented.
77
https://ntrs.nasa.gov/search.jsp?R=19790013211 2020-03-20T18:55:10+00:00Z
OBJECTIVE
Theobjectivewasto developanactuatorwhich wouldmeet the following requirements.
1. Rotate180degrees±15minutes of arc.
2. Remainat the indexingstopuntil againactuated.
3. Havea permanentmagneticfield (whennotbeingpowered}less than 0.1_ at 1.27cm
(1/2 in).
4. Havea minimum capability of 300cyclesduring a period of five years.
5. Require not more than 11watts of power.
6. Weighless than 0.227kg (0.5 Ib).
7. Fail-safe indexing, i.e., the actuatormust not stop in anyposition other than0 or
180degrees.
8. Operatewithin the temperaturerangeof -45°C to +65°C.
9. Operatein a vacuum.
10. Completethe rotational indexingwithin 4 minutes of initiation.
DESIGN
The selectionof a designapproachrequired the considerationof other feasible con-
cepts. Amongthose reviewedwere bimorphpiezoelectric devices, opposingcoil sole-
noids (withoutcores), nonmagneticelectric motors, Freon state conversionbellows, and
NITINOLactuators.
A conceptutilizing pellets was adoptedbecauseit appearsto most reliably meet the
abovedesignrequirements.
PELLET
In 1965, McCarthy, et al., of GoddardSpaceFlight Center developedanoscillating
magnetometeractuatorwhich initiated theutilization of thewax pellet as its powerele-
ment (seeReference1). Thepellet is a standardproductionline component*which is
usedin thermostatsproducedby the Harrison RadiatorDivision, GeneralMotors Corp.
It consists of a brass casewith a rubber boot, anexpansionmaterial, anda piston. Fig-
ure 1 represents thebasic configuration. The expansionmaterial is Epoleneandparaffin
wax to which a fine copperpowderhasbeenaddedto improve the heat conduction. The
*PartNo.3005031,HarrisonRadiatorDivision,GeneralMotorsCorporation
78
Epolene and paraffin proportions are adjusted to obtain the desired melting point. The
solid to liquid transition of this material yields a 14% volumetric increase. Thus when
the applied heat raises the material's temperature to the melting point, the material ex-
pands and presses the rubber boot against the conical tip of the piston, forcing it outward.
The magnetic requirements of the MJS-77 magnetometer experiment necessitated
some modifications to the basic production line pellet. A survey of pellet production line
components with a magnetometer allowed selective use of all components except the
piston, flange seal and expansion material. A simple substitution of different materials
eliminated the magnetic problem with the production line piston and flange seal; namely,
titanium for the stainless steel piston and beryllium copper for the brass flange seal.
The magnetic problem with the expansion material was found to be in the copper powder.
The production line copper powder is processed with steel balls which contaminated the
resulting product. After an exhaustive search and many trials, a magnetically clean
copper powder was obtained which was processed with ceramic balls.
The developmental nature of these extremely magnetically clean pellets required that
they be hand assembled and tested in a clean room environment with all components being
checked with a magnetometer during all stages of fabrication. The Harrison Radiator
Division of General Motors Corporation at Lockport, N.Y. in conjunction with NASA per-
sonnel successfully produced enough magnetically clean pellets to insure the ultimate suc-
cess of this effort.
The pellet which was finally developed weighs 26 grams with 750 milligrams of ex-
pansion material and will produce a maximum force of 15.88 kilograms (35 lbs) with a
stroke of 1.14 cm (0. 450 inches). A summary of the pellet characteristics is presented
in Table 1.
MECHANICAL OPERATION
The flight mechanism as shown in Figure 2 is simply an experiment container (tri-
axial fluxgate magnetomete r) which can be bi-directionally rotated by heating either of
two opposing pellets, whose indexing is biased by two over-center Flexator springs.
When commanded, the function of the flipper is to rotate the triaxial fluxgate magnetom-
eter 180 ° counter-clockwise from the position shown and then, when later commanded, to
rotate the magnetometer back 180 ° clockwise to the original position.
As shown in Figures 2 and 3 the crank arm holds the contact against the left position
stop, thus completing an electrical circuit. To rotate the magnetometer 180 ° counter-
clockwise, the right pellet (Fig. 4) is heated to 100°C by a heater which is bonded to its
cylindrical surface. The pellet is filled with a special wax and copper powder mixture,
which undergoes a 14% volumetric increase in changing from its initial solid state to a
liquid state. The internal pressure thus created squeezes a rubber boot (Fig. 4) which
forces the piston out of the rubber boot. The shoulder of this piston bears against the
right beam (Fig. 4) and causes the toggle to rotate counter-clockwise. The toggle is tied
79
to the shaft througha pin which travels in the toggleslot. As the toggle starts to rotate,
it bears against thepin (Figs. 4 and5A) androtates the shaft andall membersattached
to it. Whenthe crank arm rotates counter-clockwiseabout100° (Fig. 5B) the two Flex-
ator springs flip the shaft (magnetometer)the remaining 80° (Fig. 5C), whichthe slotted
toggleallows, thus completingthe 180° flip (Fig. 5D). This flip is sensedby theopening
of the left contactto position stop(Fig. 3) openingtheminiature switch (Fig. 3) andthe
closingof the right contact toposition stop(Fig. 3). Whenthe right piston extendedfrom
the pellet it compresseda springwhich, as the liquid waxagainsolidifies forces the
piston back into its pellet. Themagnetometercannowbe flipped 180° clockwise back to
the position as shown in Figures 2, 3 and 4 by heating the left pellet and repeating the
above process.
MATERIALS
The prime considerations in the selection of materials for this mechanism were low
magnetic permeability (<1. 001), volume and weight. The Flexator springs were made of
E lgiloy, the bushings, housing and experiment container from Delrin, and the shafts and
other hardware from titanium alloy, beryllium copper, aluminum and brass.
C ONC LUSION
The mechanism described in this paper provides positive, cyclical indexing for a
sensor rotating 180 degrees 4-15 minutes ; the permanent magnetic field is less than 0.1_,
at 1.27 cm (1/2 in), the power consumed is less than 33 watt-minutes, the weight is less
than 0.227 kg (8 oz), and the volume (less the experiment container) is less than 577 cubic
centimeters (35.2 cubic inches).
Eight mechanisms have been fabricated': four flight models, two prototype models,
and two engineering test units. These units have been environmentally qualified at
temperatures ranging from -35°C to +40°C in vacuum. The flip times varied from 225
seconds at -35°C to 110 seconds at +40°C. The flight and prototype models have been
shipped to the Jet Propulsion Laboratory for integration aboard the two MJS-77 space-
craft to be launched between August and October 1977. The two engineering test units
have been life tested for up to 750 flips each through the temperature ranges of -350C
to +40°C in vacuum with no apparent change in operating characteristics.
o
REFERENCE
McCarthy, Dennis K., "Nonmagnetic, Lightweight Oscillating Actuator." NASA/
GSFC X-723-70-166.
8O
HTable 1
Pellet Characteristics
Start to open temperature
Start to open tolerance
Piston travel
72°C
±1°C
1.14 cm (0.450 in)
Linear rate
Piston force
Force required to return piston
Temperature fully open
Time to open
Time to close
Life
Advantages
Disadvantages
0.95 cm (0. 375 in) minimum travel after
10,000 cycles
0. 023 cm/°C (0. 005 in/° F)
15.88 kilograms maximum (35 lbs)
3.62 to 4.54 kilograms (8 to 10 lbs)
92°C to 105°C depending on return
spring force
3 to 4 minutes, depending on initial temperature
1 to 1.5 minutes
10,000 cycles minimum
Compact, lightweight and forceful
Must allow for over travel. Requires a heat
source.
81
BRASS CASE
PARAFFIN MATERIAL
FLANGE SE
Go
RUBBER
BOOT
PISTON
Figure 1. Wax Pellet
O0
O3
TRIAXIAL FLUXGATE MAGNETOMETER
EXPERIMENT CONTAINER
SHAFT
iNC_ PISTON (2)
SPRING(PISTON) (2) _ ©
POSITION STOP (2)
SPOOL
CABLE
(MAGNETOMETER)
CONTACT
BASEPLATE
CRANK ARM
MINIATURE SWITCH
(POSITION)
FLEXAT(_;)SPRING
TRUNNION (2)
R.H.U. HOUSING
BLE (FLIPPER)
END SUPPORT
!RMAL
TRANSDUCER
TOGGLE
BEAM (2)
PIVOT ARM (2)
HOUSING
PELLET & HEATER ASSEMBLY (2)
Figure 2. MJS-77 Magnetometer Flipper Assembly
PISTON(2)
(3O
CRANK ARM
CONTACT (..22
I
MINIATURE"
SWITCH
PISTON STOP(2)
FLEXATOR
_ SPRING(2)
Figure 3. End View
oo
ol
TOGGLE
BEAM (2)
RUBBER i_ j
PELLET (2)
I
PARAFFIN
MATERIAL
t,
I]
I
I
I
I
PISTON
•HEATER
(2)
Figure 4. Flipper Section View
O0
TOGGLE
- SLOT _ 3
Figure 5. Toggle Section Views


The MJS-77 magnetometer actuator

A two-position (0 deg and 180 deg) actuating mechanism (flipper) driven by alternately-heated wax motors (pellets) used to rotate the low field triaxial fluxgate magnetometer experiment on the 1977 Mariner Jupiter-Saturn spacecraft to its 0 deg and 180 deg positions is described. The magnetic field, power requirements, weight and volume of this device are discussed. The problems encountered in design and development of this mechanism are presented

https://ntrs.nasa.gov/search.jsp?R=19780011091 2020-03-20T12:53:13+00:00Z
NTS:19034
THE MJS-77 MAGNETOMETER ACTUATOR
By William C. Stange
NASA Goddard Space Flight Center
SUMMARY
A two-position (0 ° and 180") actuating mechanism (flipper) driven by alternately-
heated wax motors (pellets) will be ,:sed to rotate the low field triaxial fluxgate magnet-
ometer experiment on the 1977 Mar, net Jupiter-Saturn sl:acecraft to its 00 and 180 °
positions. The magnetic field, power requirements, weight and volume of this device
are very restrictive. The problems encolmtered in design and development of this mech-
anism are presented.
INTRODUC TION
The purpo3e of this exveriment is to provide precise, accurate, and rapid vector
measurements (from 0.01_/to 20 gauss, 17 = 10 -_ gauss) of the magnetic fields of Jupiter
and Saturn in in'_erplanetary space to them and beyond. These data extend in situ studies
of the solar wind interaction with Jupiter _-,d characteristics of its magnetic field and
yield first studies of Saturn's field and its interactions if the solar wind extends to 10 AU.
Performing accurate measurements of magnetic fields on a spacecraft not fabricated
magnetically clean is a major problem. A moderately long boom will be used to place two
low-field (_6400_) triaxial fluxgate magnetometers at remote distances from the space-
craft. Simultaneous measurements will yield separate estimates of the _,;pacecraft field
and the ambient field.
The purpose of this essentially nonmagnetic actuator is in-flight calibration of the
triaxial fluxgate magnetometers. This calibration, which determines tha sensor zero
point, is accomplished by periodically flipping the magnetometers by 180 degrees.
The advantages of this mechanism arc that it satisfies more than any other known
device, the constraints of volume, weight, nonmagnetic materials, and power in relation
to the requirements of high torque, fast cycling and long life in the hard vacuum of space
and exposure to intense radiation fields at Jupiter. These properties are derived solely
from the unique mechanical qualities of the pellet. This actuator will provide cyclical
bi-dircctional rotary motion under varying environmental temperatures <-45°C to +65"C)
in a vacuum for periods up to five years.
This paper describes the mechanical and electrical functions of the design which
evolved, as well as the problems encountered. The objectives achie_red are evalua'ed
and other possible applications are presented.
77
him.._ _
OBJECTIVE
The objectivewas to develop an actuator which would meet the following requirements.
1. Rotate 180 degree_ i15 minutes of arc.
2. Remain at the indexing stop until again actuated.
3. Have a permanent magnetic field (when not being powered) less than 0.17 at 1.27 cm
(1/2 in).
4. Have a minimum capability of 300 cycles during a period of five years.
5. Require not more than 11 watts of power.
6. Weigh less than 0.227 kg (0.5 lb).
7. Fail-safe indexing, i.e.. the actuator must not stop in any position other than 0 or
180 degrJes.
8. Operate within the temperature range of -45°C to +65°C.
9. Operate in a vacuum.
10. Complete the rotational indexing within 4 minutes of initiation.
DESIGN
The selection of a design approach required the consideration of other feasible con-
cepts. Among those reviewed weze bimorph piezoelectric devices, opposing coil solp-
noids (without cores), nonmagnetic electric motors, Freon state conversion bellows, and
NITINOL actuators.
A concept utilizing pellets was adopted because it appears to most reliably meet the
above design requirements.
PELLET
In 1965, McCarthy, et al., of Goddard Space Flight Center deveioped an oscillating
magnetometer actuvtor which initiated the utilization of the wax pellet as its power e_e-
ment (see Reference 1). The pellet is a standard production line comp,ment* which is
used in therraostats produced by the Harrison R_.diator Division, Ge:leral Ivlotors CorI:.
It consists 9f a brass case with a rubber boot, an expansion material, and a piston. Fig-
ure 1 represents *.he basic configuration. The expansion material is Epolene and pax: (lin
wax to which a fine copper powder has been added to improve the heat conduction. The
*Part No. 30(.)503I, llarrison RadiatorDivision,Ge,eral MotorsCorporation
7O
Epolene and paraffin proportions are adjusted to obtain the desired melting point. The
solid to liquid transition of this material yields a 14% volumetric increase. Thus when
the applied heat raises the materialls temperature to the melting point, the material ex-
pands and presses the rubber boot against the conical tip of the piston, forcing it outward.
The magnetic requirements of the MJS-77 magnetometer experiment necessitated
some modifications to the basic production line pellet. A survey of pellet production line
components with a magnetometer allowed selective use of all components except the
pistoa, flange seal and expansion material. A simple substitution of different materials
eliminated the magnetic problem with the production line piston and flange seal; namely,
titanium for the stainless steel piston and beryllium copper for the brass flange sea/.
The magnetic problem with the _xpausion material was found to be. in the copper powder.
The production line copper powder is processed with steel balls which contaminated the
resulting product. After an exhaustive search and many trials, a magnetically clean
copper powder was obtained which was processed with ceramic balls.
The developmental nature of these extremely magnetically clean pellets required that
they be hand assembled and tested in a clean room environment with all components being
che_.ed with a magnetometer during all stages of fabrication. The Harrison Radiator
Division of General Motors Corporation at Lockport, N.Y. in conjunction with NASA per-
sonnel successfully produced enough mr, gnetically clean pellets to insure the ultimate suc-
cess of this effort.
The pellet which was finally developed weighs 26 grams with 750 milltgrarns of ex-
pansion material and will produce a maximum force of 15.88 kilograms (35 lbs) with a
stroke of 1.14 cm (0.450 inches). A summary of the pellet characteristics is presented
in Tab:e 1,
MECHANICAL OPERATION
The flight mechanism as shown in Figure 2 is simply an experiment container (tri-
axla; t'_te magnetometer) which can be bi-directionally rotated by heating either of
two cppostng pellets, whose indexing is biased by two over-center Flexator springs.
When commanded, the function of the flipper is t9 rotate the triaxial fluxgate magnetom-
eter 180" counter-clockwise from the position shown and then, when later commanded, to
rotate the magnetometer back 180" clockwise to the original pos)/ion.
As shown in Figures 2 _-_d 3 the crank arm holds the contact against the left position
stop, th,.ls corvpleting an electrical circuit. To rotate the magnetometer 180 ° counter-
clockwise, the right pellet (Fig. 4) is heated to 100°C by a heater which is bonded to its
cylindrical surface. The pellet is filled with a special w_x and copper powder mixture,
which u_dergoes a 14% volumetric increase in changing from its initial solid state to a
liquid state. The internal pressure thus created squeezes a rubber boot (Fig. 4) which
forces the piston out of the rubber boot. The shoulder of thiz_ piston b_ars against the
right beam (Fig. 4) and causes the toggle to rotate counter-clockwise. The toggle is tied
79
to the sb.aft through a pin which travels in the toggle slot. As the toggle starts to rotate,
it bears against the pin (Figs. 4 and 5A) and rotates the shaft and all members attached
to it. When the crank arm rotates counter-clockwise about 100" (Fig. 5B) the two Flex-
ator springs flip the shaft (magnetometer) the remaining 80" (Fig. 5C), which the slotted
toggle allows, thus completing the 180" flip (Fig. 5D). This flip is sensed by the opening
of the left contact to position stop (Fig. 3) opening the miniature switch (Fig. 3) and the
closing of the right contact to position stop (Fig. 3). When the right piston extended from
the pellet it compressed a spring which, as the liquid wax again solidifies forces the
piston back into its pellet. The magnetometer can now be flipped 180" clockwise back to
the position as shown in Figures 2, 3 and 4 by heating the left pellet and repeating the
above process.
MATERIALS
The prime considerations in the selection of materials for this mechanism were low
magnetic permeability (<_1. 001), volume and weight. The Flexator springs were made of
_.lgiloy, the bvshlngs, housing and e_periment container fr)rf: Delrin, and the shafts and
other hardware from titanium alloy, beryllium copper, aluminum and brass.
B
CONC LUSION
The mechanism described in rids paper provides positive, cyclical indexing for a
sensor rotating 180 degrees _15 minutes; the permanent magnetic field is tess than 0.1T
at 1.27 cm (1/2 in), the power consumed is less than 33 watt-minutes, the weight is less
than 0.227 kg (8oz), and the wLume (less the experiment container) is less than 577 cubic
centimeters (35.2 cubic inches).
Eight mechanisms have been fabricated: four flight models, t_,o prototype models,
and two engineering test units. These units have been envirorLmentully qualified at
temperatures ranging from -35"C to +40°C in vacuum. The flip times varied from 225
seconds at -35°C to 110 seconds at +40°C. The flight and prototype models have been
shipped to the Jet Propulsion Laboratory for integration aboard the two MJS-77 space-
craft to be launched between August and October 1977. The two engineering test units
have been life tested for up to 750 flips each through the temperature ranges of -35°C
to +40°C in vacuum with no apparent change In operating characteristics.
REFERENCE
1. McCarthy, Dennis K., "Nonmag_etlc, Lightweight Oscillating Actuator." NASA/
GSFC X-723-70-166.
80
Table 1
Pellet Characteristics
Start to open temperature
Start to open tolerance
Piston travel
Linear rate
Piston force
Force required to return piston
Temperature fully open
Time '_ open
Time t,) close
Di sa_ _:rantage s
72°C
=I°C
1.14 Cm (0.450 In)
O. 95 cm (0.375 in) minimum travel after
10,000 cycles
0. 023 cm/°C (0.005 in/° F)
15.88 kilograms maximum (35 lbs)
3.62 to 4.54 kilograms (8 to 10 lbs)
920C to 105°C depending on return
spring force
3 to 4 minutes, depend':ng on initial temperature
1 to 1.5 minutes
10,000 cycles minimum
Compact, lightweight and forceful
Must allow for over travel. Requires a heat
source.
81
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The MJS-77 magnetometer actuator

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