The Galileo spacecraft utilizes a deployable lattice boom to position three science instruments at remote distances from the spacecraft body. An improved structure and mechanism to precisely control deployment of the boom, and the unique deployment of an outer protective cover are described

Benton, M. D.

Packard, D. T.

English

NASA Technical Reports Server

N85-33513
!
THE GALILEO SPACECRAFT
MAGNETOMETER BOOM
Doug._as T. Packard and Fax D. Benton*
ABSTRACT
The Galileo sr-_cecraft utllizes a deployable lattice boom to position three
science instruments at remote distances from the spacecraft body. An improved
structdre and mechani'cm to precisely control deployment of the boom, and the
unique deployment cf an outer protective cover are described.
INTRODUCTION
The Galileo spacecraft contains an 8.2-meter deployable magnetometer boom
as shown in Figure i. The boom consists of two deployable ,masts, three instru-
ment mounts, and a launch canister. These mechanisms were developed Jointly
by the Jet Propulsion Laboratory, California Institute of Technology, Pasadena,
California and ACE-Able Engineering of Goleta, California.
MAST DESIGN
The masts are coilable, longaron-type, deployable structures. The main
structural elements are three continuous (single-piece) longeroas which are
shear-stlffened when erected. The longerons are elastically deformed (coiled)
and the battens buckled in order to stow the boom. They ano the shear-
stiffening diagonals are made of unidirectional, S-glass epo:.y materia,, and
are therefore hilly elastic. In effect, the structure i.* made up of spring
members which must be forcibly dtstorted during initial -.towage into th_ canis-
ter. This distortion stores strain energy, which is released to effect Oeploy-
merit. Without some means for controlling the deployment, however, substantial,
undesL-able accelerations would he imparted to the spacecraft, and the boom
itself could be damaged.
The stowed boom is contained in a 0.6-meter-long canister during Galileo
launch Into earth orbit. The boom then deploy_ to its full length.
The collable, lor_eron-type, de_lo)lble structure has been used on previous
spacecraft app)ications, including Voyager, _._c!ar-Max: U,_aF'g-_, a..d Oao_-l.
However, the C,altleo applicat4o_ '_= ,tntq_e ;Ith regard to five featuces:
: _Jet Propulsion Laboratory, California Iratltute of Technology, Pasadena,
California, U.S.A.; A(_Able EnElneerir_, G_leta, California, U.S.A.c_
The research described in this paper was carried out by the oct Propulsion
Laboratory, California Institute of Technology, under a contract with the
National Aeronautics and Space Administration.
r
I
k
i
1985025199-012
https://ntrs.nasa.gov/search.jsp?R=19850025200 2020-03-22T19:53:06+00:00Z
o The Galileo boom consists of t'_o independent, d_ployable sections, an
inboard mast and an outboard mast, as shown in Figu. e 2.
o As it deploys, the boom is attached to a highly maneuverable, spinning
spacecraft, and thus experiences loading due to vehicle spin dynamics such
as nutation, wobble, and translational acceleratigns.
o Achievement of a stable, spinning-spacecraft attitude requires predict-
able boom deployment in order to minimize the amount oe undesired accelera-
tion to the spacecraft and boom structure during deployment.
o The Jovian environment requires that the mast structure and electrical
cables be protected from electrostatic build-up and micrometeoroids. Pro-
tection is provided by the use of a stowable, pop-out cover which totally
encloses each mast and provides "first surface" micrometeoroid protection.
o The protective cover over the masts requires that the launch/stowage
canister be mounted around the masts after the masts are stowed.
DEPLOYMENT SEQUENCE CONTROL
The Galileo magnetometer boom contains a deployment-control system which
] [rovides a precisely controlled deployment rate and sequence without the use
of active or commandable elements. Once re_ _a_ed from its canister, the boom
I automatically deploys in a controlled manner wzth the erecting sequence pro-
ceeding as described Delow.
J The deplayment rate is controlled by a rotary, viscous damper located at
the base of the inboard mast, as indicated in Figures 2 and 4. A metallic lan-
yard connects the storage reel to the deployable structure. This arrangement
is similar to that of previous applications. However, the method used to
attach the end of the lanyard to the deployable structure is unique. The lan-
yard passes through the center of the mast, 2tom the base of the inboard mast
to the outer end of the outboard mast. On previous applications, the lanyard
was attached at the outboard support plate, but in this application the lanyard
is looped over a pulley at the outboard end and routed back upon itself to the
midsection structure, where it is secured. This arrangement produces a mechan-
ical advantage between the lanyard forces produced by the inboard mast on the
outboard mast.
As the inboard mast deploys, the elastic energy stored in the erection
springs and the masts produces a force of 89 newtons (20 pounds) on the l_n-
yard. That force is transmitted to the rotary damper (rate limiter) as the
lanyard pays out in a controlled manner. The 89-newton lanyard force acts
around the outboard pulley and back to the midsection structure, thereby pro-
ducing a force of 178 newtons (40 pounds) across the coiled outboard mast. The
178-newton load holds the outboard mast closed even though it has an 89-newton
deployment force of its own.
2
1985025199-013
Once deployed, the inboard mast can no longer tension the lanyard. At this
time the 89-newton force of the outboard mast and outboard erection springs
tensions the lanyard to 44.5 newtons (i0 pounds). Now, the outboard mast de-
ploys at a much slower rate than the inboard mast. The rate is slower because
the tension in the lanyard is now only half of what it was during inboard-mast
deployment, and twice as much lanyard must be deployed for each unit length of
mast deployed.
Figure 3 shows that the inboard mast first erects into a rigid structure
at its base, and then continues to deploy outward. This controlled erecting
sequence minimizes the dynamzc loading produced by Coriolis and otl%er forces
during deployment.
The inboard end of each mast is caused to erect first by means of a base
erecting spring (see Figure 4) at the inboard end of each of the mast longer-
ons. The springs produce a relatively uniform torque through the first 45 ° of
longerons rotation and guarantee that the erecting sequence will begin as shown
in Figure 3.
Full deployment of the base of the mast is guaranteed _i uslng batten mem-
bers with 14% smaller diamcters in the first and second batten frames or the
inboard end of each mast. This assures that the base of the mast will lock-up
into a fully erect structure before the remaining stowes portions of that mast
begin to deploy.
Completion of the deployment of a coilab!e, longeron-type mast results in
a large transient load condition resulting from the final release of stored
energy as the longerons rapidly rotate into their fully deployed state. This
peak load is as much as 20 times greater than the 89-newton deployment force.
It is necessary to provide a method for relieving the peak load in order to
prevent failure of the lanyard.
Figure 5 shows the method employed for this purpose. The body of the rate
itmiter is spring-loaded with a negator spring to the base plate of the canis-
ter. When the spring preload is exceeded by the peak deployment force, the
body of the rate l_miter rotates, allowing sufficient additional lanyard to pay
out, thereby reducing peak lanyard loads. By using this method, the peak lan-
yard loads are limited to approximately 200 newtons (45 pounds).
DEPLOI_4ENT RATE CONTROL
The mechanism to control the magnetometer deployment rate is a "shear-type"
rotary damper. The damping force is produced by the fluidshearlng action
across a gap between the stationary damper housing and the rotor contained
within the housing. Figure 5 shows the construction details of that unit.
A similar damper configuration was previously used for boom deployment con-
trol on the 3-axls-stabilized Voyager spacecraft (Ref. i). However, the Voy-
ager boom was smaller in cross section, and the required damping was corres-
pondingly less. Also, deployment _rom a 3-axis-stabilized platform ellmlnated
much of the need for precise control of the deployment rate.
3
1985025199-014
Three specific characteristics of the Voyager damper were unacceptable for
the Galileo application:
o The Voyager deployment for_e was 38 newtons (8.5 pounds) versus 89
newtons (20 pounds) for Galileo. Therefore, more damping was required.
o The ambient temperature deployment rate for the Voyager boom varied
from 0.26 m/s (10.2 in/s) at the start of deployment to 0.006 m/s
(0.25 in/s) at completion of deployment. This large variation in the
deployment Pate was not aoc_.ptable fop Galileo applioatioP-_.
o Because of the hiah Iluid-shear rate associated with the 0.26-m/s Voy-
ager deployment, a thixotropio loop (._e Figure 6) o_casionally formed in
the damping fluid and this occurrence caused less than expected damping.
DAMPERPERFORMANCE
The performance of the shear_type damper is given by the approximate (but
acceptably acommte) equation
hD3
eC 1
T = Torque
h = Rotor width
• Dynamic visooslty
• Rotor speed
D • Mean diameter of the fluid gap
; O • Fluid &ap width
CI It Numerical constant depending on system of units used
This equation o._.be simplified using the following factors:
h • 1.11 om (same as Voya&or)
• Kinenmtio visooslty • 32.11 (V/C) 0"51b's/ft 2 (measured value
for 500,000 oSt fluid; see Ref. 2)
o • 0.128 mm (same as Voyager)
V • Velootty aoross the l'lutd Eap
VD • Deployment velocity
J
1985025199-015
R = Pulley radius
C2 = Numerical constant depending on system of units used
The damping equation then simplifies to the form:
2 R3
FD
VD - C2D5
This equation identifies the sensitivities of the controlling damping param-
eters, and shows that D and R greatly affect performance.
This analysis also clearly indicates that the increased deployment force
: associated with the Galileo boom would result in excessively rapid deployment
unless the Voyager damper were redesigned to provide increased damping control.
This was accomplished by increasing the mean rotor diameter (D) from the
3.20-cm diameter for Voyager to 7.62 cm for the Galileo damper. Also, the
Voyager lanyard pulley allowed a pulley-radium decrease, as the lanyard paid
out, from 3.56 cm at deployment initiation to 1.02 cm at deployment completion.
This difference of radius (R) allowed the excessive deployment rate variation
as previously discussed. For Galileo, the variation of R is minimized by using
a larger pulley and a thinner, metallic lanyard with R varying from 3.81 cm at
the start of deployment to 3.30 cm at the completion of deployment.
These damper modifications result in the performance indicated in F±gures 7
: and 8. A fluid viscosity of 50,000 cSt was selected for the Galileo damper,
and this resulted in deployment characteristics as shown in Figure 9. The max-
imum fluld-shear rate which occurred in the Voyager damper was 411/s. But,
for Galileo, this maximum value was reduced to 178/s, and, can be seen from
the slopes of the damping curves in Figures 7 and 8, the possibility of the
formal!on of a significant thixotropic loop is eliminated.
PROTECTIVE COVER
• The magnetometer boom cover provides: (i) a bla_, nonspecular surface to
minimize reflections from the spinning boom back to the science instruments
: located on the despun section of the spacecraft; (2) a conductive outer surface
to prevent build-up of electrostatic charges; and (3) a "first surface" against
micrometeorolds in the Jovian environment for protection of the mast structure
an_ the instrument's electrical cables.
The "pop-out" covers (Figure i0) are fabricated from a graphite-coated,
Kapton _hermal-blanket material. Each cover is spaced from the coilable struc-
tures by fiberglass, lenticular-shaped springs (standoffs) (Figure II) which
are attached to the mast at each batten frame. The cover and lattice masts are
folded together by manually collapsing all standoffs (Figure 12), and then
folding the colla_eed cover into the stowed masts (Figure 13).
5
L
1985025199-016
Figures 3B, lO, and 13 show the cover as being loosely formed and not in
the triangular shape shown in Figure ii° The extra material in the cover is
to allow for differential thermal shrinkage between the boom and cover. It is
desired that the cover be untensioned when cold (approximately -223°C) to pre-
vent it from affecting the mast shape and thus changing the alignment of the
ins truments.
LAUNCH CANISTER AND RELEASE MECHANISM
The magnetometer outboard support plate and canister are shown in Figure
14. The canister consists of three curved, honeycomb panels joined at three
longitudinal joints along the panel edges, and attached to the magnetometer
boom base plate by a circumferential bolt pattern on the inboard end of the
canister. This structural arrangement is necessary to allow access to the
sides of the mast while it is being sto_:ed. Access is required to align the
protective cover's "pop-out" brackets and to fold in the deployable protective
cover. Once the masts are fully stowed, the canister segments are assembled
around them and secured to each other and to the base plate.
Spring-loaded latch pins are located at six places on the canister. These
pins en_age a set of three slots in the magnetometer boom cuter plate and three
_dditional slots in the magnetometer boom midsection structure. Three wire-
rope cables (Figure 14) are tensioned to push the spring-loaded pins into the
appropriate slots in the magnetometer boom. A single pyrotechnic pin-puller
mounted to the side of the canister (Figure 14) releases all of the cables and
allows deployment to start.
SUMMARY
The Galileo magnetometer boom development program began in late 1978 and
, .._flight boom was delivered to the Galileo space,raft in May 1984. Magneto-
meter boom formal testing included: sine and random vibration, hot and cold
deployments, magnetic cleanliness checks, and electrical bonding/grounding
checks.
The Galileo magnetometer boom design relied heavily upon the experience
gained during the earlier Voyager program. Many potential problems were
avoided and the Galileo development effort was mainly problem-free.
For the Galileo magnetometer boom, the use of a larger, less delicate,
coilable-mast structure than the one used for Voyager grea'ly reduced the hand-
ling damage which was a contir:uing problem during the Voyager program. The
only significant, unresolved Galileo magnetometer boom problem relates to the
complexity of the boom-cover degign. Each cycle of operation (deployment/
stowage) causes some damage to the cover surface. This damage is repairable
< after each deployment; however, the cover is definitely life-limited. A total
of six deployments is considered to be a reasonable llfe limit. With the
exception of the cover design, and given the same set of design requirements,
no design change would be recommended for similar boom applications.
A
1985025199-017
REFERENCES
(i) "The Voyager Ma_etometer Boom," David C. Miller, 12th Aerospace Mechanisms
: Symposium, April 27-28, 1978, Moffett Field, California.
(2) "Mariner-IV Structural Dampers," Peter T. Lyman, Ist Aerospace Mechanisms
Symposium, May 19-20, 1966, Santa Clara, California, pp. 37-50.
7
• }
[ ..... A_.
"i
1985025199-018
ORiGiNAL PAGE IS
OF pOOR QUALITY
i
!
i
t
SPIN AXIS
INBOARD
MAGNETOMETER
ANDMIDSECTION
STRUCTURE
INBOARD
MAST
OUTBOARD
MAST
PWSANTENNA
OUTBOARD
MAGNETOM_ER
ii Figure I. GalileoSpacecraft
i
8
1
1985025199-019
r/---BATTENFRAMES
BASEERECTING; /-- _ /,--MIDSECTIONSTRUCTURE
/ SPRINuS(3) ,//_ BASEERECTING
/ /--CANISTER ///SPRING (3) PULLEY-7
,_---_ INBOARDMAST / i_,_x OUTBOARDMASTi/-- # __ ,x
y _/ _/ \,'\/ \/ \v_/_ -_V _C,"XV \/N/_/_C,"xE_..fF___
'--RATELIMITER LANYARD OUTBOARDSUPPORT_
THEBOOMDEPLOYMENTCONTROLSYSTEM
CONSISTSOFTHREEFUNCTIONALE ENIENTS:
1. THEDEPLOYMENTLANYARD.
2. THEDEPLOYMENTRATELIMITER.
3. THEBASEERECTINGSPRINGS.
Figure 2. Galileo Magnetometer Boom
9
i
1985025199-020
,.3
i (TRANSITIONZONEMOVES
' OUTWARDANDERECTEDMAST
• IS SELF-SUPPORTING)
OUTBOARDMAST
REMAINSSTOWED \ _ RETRACTEDPORTIONROTATESAS BOOM
UNTIL INBOARD "" J-J DEPLOYS
MASTCOMPLETES
DEPLOYMENT m
.. STOWED _. MIDSECTION
MASI
j. / _, STRUCTURE
l m
f 2-" LONGERONS 4,
]
.!' TRANSITION ,_; BATTENS
:_ ZONE _
, \ _ DIAGONAI_S
RESTRAININC
, _ LANYARD
'i
f ,_f
-i ERECTED " _
1 [ _ 0 f- ,.,.NY._,_,__,,¥o,.,,
Figure 3A. Erecting Sequence
I0
1985025199-021
pr
ORIGINALPAGE IS
OF POOR QUALITY
Figure 3B. Galileo Magnetometer Boom at Deployment Midpoint
ORIGINALPAGE IS
OF POOR QUALITY
i
i Figure 4. Hagnetometer Boom Base Plate
, 12
A
1985025199-023
ORIGINAL P/_C,FIS
OF POOR QUALITY
TEMPERATURE/VOLUM LANYARB/I_EELCOMPENSATION
J
Flgure 5. Hagnetometer Boom Rate L/_iter
73
1985025199-024
Figure 6. The Thlxotropic Loop
,t
14
1985025199-025
AMBlENTTEMPERATURE
I I I l 1 1 1
15 - 6.0 - FLUID
VISCOSITY
IcSt)
OUTGASSEDFLUID
5.0- • 50K
[] 150K
500K
,.°I
0 4 8 12 16 20 24 28 32
DEPLOYMENTFORCE{Ibs)
L ..1 1 I I 1 1 I
0 20 40 60 80 100 120 140
DEPLOYMENTFORCE(N)
Figure 7. Galileo Magnetometer Boom-Rate-.Limtter Damping qharacteristtcs
15
1985025199-026
I I I I I I
+65°C
STD50,000cSt
(OUTGASSED)
. A 15- +40°C
E
_ C
I,.M
I..--
< +22°C
_ 10
+lO°C "
O
....1
" 5 C
0 _.I._I_.L_L_
0 20 40 60 80 100 120
MASTDEPLOYMENTFORCE(N)
Figure 8. Galileo Hagnetometer Boom Rate Limlter Performance at Temperature
i
16
|
1985025199-027
70 I I I I I I i I
50 - CORRECTEDFORDEPLOYRATE -
VARIATIONDURINGDEPLOYCYCLE
40-
-40 I I I I I I I I
2 4 6 8 I0 12 14 16 18
CALCULATEDDEPLOYMENTTIME{min)
Figure 9. Galileo 7-bleter Deploysble Mast Deployment Characteristic_ -,
17 ,_
,.
1985025199-028
ORIGINAL PAGE IS
OF POOR QUALITY
Figure I0. Galileo Magnetometer Boom (Fully Deployed) i
18
i
1985025199-029
I19
1985025199-030
i; ORiGiNAL PAGE iS
OF pOOR QUALITY
Figure 12. Magnetometer Boom Cover Stowing Procedure
2O
?
i "
1985025199-031
ORIGINAl..PAGE IS
OF POOR QUALITY
ORIGINAL PAGE 1'.3
OF POOR QUALITY
Figure ]4. Stowed Magnetometer Boom
22
1985025199-033


The Galeleo spacecraft magnetometer boom

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server