The Inertial Upper Stage (IUS) is a two-stage booster used by NASA and the Defense Department to insert payloads into geosynchronous orbit from low-Earth orbit. The hydraulic mechanism discussed here was designed to perform a specific dynamic and static interface function within the Space Transportation System's Orbiter. Requirements, configuration, and application of the hydraulic mechanism with emphasis on performance and methods of achieving zero external hydraulic leakage are discussed. The hydraulic load-leveler mechanism meets the established design requirements for operation in a low-Earth orbit. Considerable testing was conducted to demonstrate system performance and verification that external leakage had been reduced to zero. Following each flight use of an ASE, all hydraulic mechanism components are carefully inspected for leakage. The ASE, including the hydraulic mechanism, has performed without any anomalies during all IUS flights

Farmer, James R.

English

NASA Technical Reports Server

N87- 16339
HYDRAULIC MECHANISM TO LIMIT TORSIONAL LOADS BETWEEN THE IUS AND
SPACE TRANSPORTATION SYSTEM ORBITER
James R. Farmer*
The Inertial Upper Stage (IUS) is a two-stage booster used by NASA and
The Defense Department to insert payloads into geosynchronous orbit from low-
Earth orbit. The hydraulic mechanism discussed in this paper was designed to
perform a specific dynamic and static interface function within the Space
Transportation System's Orbiter. This paper discusses requirements, config-
uration, and application of the hydraulic mechanism with emphasis on perfor-
mance and methods of achieving zero external hydraulic leakage. The work was
performed on Air Force Contract FO47Ol-TB-C-O040, Headquarters Space Division
(AFSC).
INTRODUCTION
The mechanisms discussed herein were designed to function in the natural
environments of space and induced environments associated with orbiter boost,
payload deployment, and reentry of the space shuttle Orbiter. The environ-
ments are severe and require design solutions unavailable in normal industrial
applications.
The IUS interface with the Orbiter cargo bay is the IUS Airborne Support
Equipment (ASE). The ASE structure consists of (1) an aft support frame that
provides support for IUS X, Y, Z, Mx, and Mz loads, and (2) a forward support
frame that provides support for IUS Y and Z loads during boost. A keel pin
between the forward ASE frame and IUS carries the Y loads. The aft frame
pivots during deployment to elevate the IUS to a position to clear the Orbiter
cargo bay. The hydraulic mechanism is an integral part of the forward ASE
frame. Figure l shows the Orbiter and its relationship to the forward and aft
ASE frames.
During Orbiter boost to low-Earth orbit, thehydraullc load-leveler
mechanism minimizes torsional loads applied to the IUS and absorbs part of the
dynamic energy being transmitted to it. If attempts to deploy the payload are
unsuccessful and an ASE Payload Retention Latch Actuator (PRLA) motor failure
occurs during abort restow, the hydraulic mechanism can displace one actuator
up and the opposite actuator down to restow the payload and maintain IUS to
Orbiter alignment.
The major problem and drawback of using hydraulic systems for space
applications is potential hydraulic oll leakage and contamination. Consider-
able test experience has established a design application, assembly technique,
and screening test program that meet zero external leakage requirements.
*Boeing Aerospace Company, Seattle, Washington.
253
PRECEDING PAGE Bb_;?!K r,._OT F:t_::;O
https://ntrs.nasa.gov/search.jsp?R=19870006906 2020-03-20T12:15:04+00:00Z
DESIGN REQUIREMENTS
Natural environments and Orblter-lnduced environments present design
requirements for all mechanisms used in the Orbiter, such as:
a.
b.
C.
d.
e.
f.
Complete a minimum of I00 IUS shuttle flights over a period of approxi-
mately lO years.
Operate in zero gravity.
Survive temperatures as low as -59 °C (-75 °F).
Have an operating temperature range of -23 to ÷ 52 °C (-lO to +125 °F).
Be contained within the allowable dynamic envelope.
Use materials and flni_hes that will not outgas.
Specific hydraulic mechanism design requirements are:
a,
b.
C.
d.
e.
Allow zero external leakage of hydraulic fluid.
Limit maximum operating pressure to 3000 Ibf/In. 2
Have an active llfe expectancy of 50,000 cycles without refurbishment.
Limit differential load due to friction to less than 450 lb.
Provide a damping coefficient of 225±50 Ib-sec2/In. 2, and limit
load-leveler piston velocity to 14.0 In./sec and the maximum differential
load between the two load levelers to 14,000 lb.
HYDRAULIC LOAD-LEVELER MECHANISM
The load leveler mechanism on the forward ASE (fig. 2) is a closed loop
hydraulic system that limits torsional loads applied to the IUS while pro-
viding determinant support in static and dynamic environments. The forward
end of the IUS and spacecraft is supported and restrained by double-actlng
pistons within the two load-leveler actuators. The upper chambers of each
actuator are plumbed together and the lower chambers are plumbed together.
Any upward displacement of one actuator is matched by an equal but opposite
deflection of the opposite actuator to maintain positive engagement of the ASE
keel pin in the IUS socket. In the event the left hand and right hand PRLAs
do not open simultaneous during deployment or close simultaneously during
abort restow, mechanical stroke llmlters on the load-leveler actuator rods
limit the maximum possible height differential between the two PRLAs to
approximately 1.25 in. A hydraulic accumulator, with a metal bellows type
diaphragm, is connected to the upper chamber tubing to accommodate thermal
expansion and contraction of the hydraulic fluid. The pressurant side of the
accumulator is pressurized to I080 Ibf/In. 2 (nominal) wlth gaseous nitrogen.
The hydraulic tubing connecting the lower chambers of the load-levelers
has two orifices installed to provide a controlled damping coefficient of the
total system. The damping coefficient requirement of 225 Ib-sec2/In. 2
nominal optimizes a trade off between load-leveler system travel and dynamic
loads transmitted to the spacecraft. A reduction in damping coefficient
reduces transmitted loads but exceeds total load-leveler piston travel
available. Increasing the damping coefficient results in higher dynamic
loads being transmitted to the spacecraft.
254
HYDRAULICMECHANISMDAMPING
Adjustment of the load-leveler mechanismdamping coefficient and verifi-
cation that resultant maximumdifferential loads and piston velocities were
within required limits were demonstrated by test. A summaryof the results
is discussed herein.
The governing equation for summation of load-leveler system forces is
FD = FFvV'L_ ÷ CVlVl ÷ MA
where
FD differential force, Ib; 14,000 Ib maximum
FF static friction force, Ib; 450 Ib maximum (acceptance test data show
nominal friction force of 300 Ib)
V piston velocity, In./sec; 14.0 In./sec maximum
C damping coefficient, Ib-sec2/In.2; 225±50 Ib-sec2/In. 2
A piston acceleration, In./sec 2
M effective load leveler system mass, Ib mass
II absolute value
The effective load-leveler mechanism mass was calculated by externally
driving the load-leveler system at varying velocities and measuring the
applied force and the acceleration of the driven piston relative to its
housing. Measurements were taken at the time of maximum piston acceleration.
The tests were conducted with no Inllne orifices to minimize damping. The
results are summarized in table I. As shown, the average effective mass of
the load-leveler mechanism was I0,980 Ib mass; within 2% of the predicted
value of I0,750 Ib mass.
The load-leveler mechanism was tested with several orifices to establish
the required damping coefficient. Test data for the production configuration
are summarized in table II. The damping coefficient is calculated from
measurements of the force applied to the driven piston and the velocity of
the driven piston relative to the housing, calculated by differentiating the
relative displacement curves. Again, the measurements were taken at maximum
piston velocity. As shown, the average damplnq coefficient is 227 Ib-sec2/In. 2
The data scatter fall within the 225±50 Ib-sec2/In. 2 requirement.
The governing equation for the load leveler system forces becomes:
IVl
FD = 300 V ÷ 227 VlVl ÷ IO,98o A
255
Figure 3 presents a comparison of the analytical predlctlon of system
performance and actual test results. The analytical prediction was based on
the assumption that the relative velocity between the piston and housing is
slnusoldal and the maximum velocity amplitude is 5.8 In./sec (table II). As
shown, predicted and test results are consistent, and maximum differential
forces are approximately lO,O00 lb.
Moreover, increasing the static friction force, FF, and damping coef-
ficient, C, to their maximum design values increases the maximum calculated
value of FD less than 20%. The resultant maximum calculated value for
the differential force satisfies the 14,000 Ib maximum design requirement.
ZERO EXTERNAL LEAKAGE
The ASE hydraulic load-leveler mechanism meets all system design require-
ments. The hydraulic mechanism was selected during the design phase because
it provided the desired stiffness characteristics and load paths for a mechan-
ical system, and met limited envelope requirements. In addition, flow llmlter
(orifices) were easily changed-out during system tests to obtain desired damp-
ing coefficients.
The major drawback of a hydraulic system for space application is exter-
nal leakage. Small amounts of hydraulic oll discharged into a vacuum rapidly
expand and are attracted to cold surrounding structures. A film of oll on
critical hardware, such as star scanner, can potentially impact an entire
mission.
The ASE hydraulic system was designed to limit the number of potential
leakage paths. All tubing is welded, wlth seals (redundant) used only at
tubing to load-leveler Joints. The load leveler, shown in cross section in
figure 4, includes redundant, primary and secondary, seals at all static and
dynamic seal locations. In addition, storage cavities for primary seal leak-
age are used at all dynamic seal positions. Primary seal leakage of one drop
per day at dynamic seals is allowed. Storage cavities are periodically
drained through vent vent port plugs.
The O-rlngs used in the load leveler are fluorosillcone wlth a 70 to 80
durometer. Fluoroslllcone was selected because of the extreme low-
temperature survival requirements (-59 °C). The production configuration had
nominal O-ring squeezes of I0% for dynamic seals and 15% for static seals
consistent wlth standard O-rlng design practices.
Following delivery of all production units, numerous leakage problems
occurred during ground storage at ambient conditions. Intensive review by
BAC* Engineering, Customer Representatives, and Parker Seal** design engl-
neers, in addition to an extensive test program, identified five key elements
of the design, which, if controlled carefully, result in zero external
leakage.
*Boeing Aerospace Company.
**Parker Seal Group O-rlng Division, Lexington, Kentucky.
256
TABLEI. - TEST DATA USED TO DETERMINE EFFECTIVE LOAD-LEVELER
MECHAN
Forcing
function
2 kip at 4 Hz
4 kip at 4 Hz
6 kip at 4 Hz
8 kip at 4 Hz
lO kip at 4 Hz
12 kip at 4 Hz
14 kip at 4 Hz
6 kip at 6 Hz
8 kip at 6 Hz
lO kip at 6 Hz
4 kip at 7 Hz
8 kip at 7 Hz
Force at V = O,
kips
l .55
3.63
5.30
6.9
9.1
I0.25
II .5
5.5
7.3
9.0
3.5
7.0
ESM MASS
Relative
acceleration*,
g's
0.15
.39
.51
.6
.79
.90
.95
.46
.68
.83
.35
.60
Effective mass,
LMB x lO3
(M = F/A)
I0.3
9.3
I0.4
II .5
ll .5
II .4
12.1
12.0
I0.7
10.8
lO.O
II .7
*Relative acceleration of load-leveler piston to housing. Results
(based on geometry and fluid mass considerations): (1) MAV G
= 10,980 Ib mass; (2) Predicted MAVG = I0,759 Ib mass.
TABLE II. - TEST DATA USED TO DETERMINE DAMPING COEFFICIENT
OF LOAD-LEVELER MECHANISM
Forcing
function
2 kip at 4 Hz
4 kip at 4 Hz
6 kip at 4 Hz
8 kip at 4 Hz
lO kip at 4 Hz
2 kip at l Hz
4 kip at 1 Hz
Force at maximum
velocity,
F, kips
VMAX*,
In./sec
1.2
2.3
4.5
6.2
8.6
1.7
3.7
2.0
3.2
4.3
5.2
5.8
2.4
3.8
Damping coefficient,
Ib(In./sec)2
225
195
227
218
247
243
235
*VMA x obtained by differentiating deflection data. Results:
(1) C = (F - FF)/V_AxFF = 300 Ib**; (2) CAV G = Ib_sec2/In.2;227
(3) Tolerance C = (l + O.20)CAv G.
**Average of friction force measured for each ASE at ambient
(launch) conditions.
PRECEDING PAGE BLANK NOT FILMED
259
/, Hydraulic
_,_) f PR.LA - Mechanism
7_-Keel Pin
Forward ASE
IUS _ad Envelope
Crew Compartment
Control Station
Flgure 1. - IUS Airborne Support Equipment.
26O
Payload Retention
Latch Actuator (PRLA)
Piston
\
PRLA Track Fitting
Load Leveler Stroke
Limiter
Upper Lent Vent Plug
(Lower Plug Not Shown)
Load Leveler
Actuator
Orifice
Hydraulic Lines
Keel Pin
_- Hydraulic Accumulator
(1080 PSIG GN 2)
View Looking Forward
Forward Frame
Figure 2. - Forward ASE 10ad-leveler system.
261
I0000
Force
8000
6OOO
4O00
2000
-2000
-4000
-6000
-8000
-1000G
0.00
I
I
I
I
I
I
I
I
i
.20
Time
m
.30
\
\
\
\
m
.40
Solid curve _ Analytical
Dashed curve --.. u. Test Data
(_)=4 Hz
MEF F = 100980
VMAX = 5.8 measured
FDAMP = 227 V 2 + 300
Figure 3. - Comparison of analytical and test piston loads.
262
Dynamic Seals
Piston
Dynamic Seals
Hydraulic Tubing
Attachment (2 PIcs)
2.25 - 12 UNJ-3A
Rolled Thread
Housing
Port (Reservoir) (2 Plcs)
End Plug
Bleed-Fill Valve 2 Places (Not Shown)
Located 90 ° From HYD, PORTS.
Flgure 4. - Load
Seals Per MIL-R-25988/1 Dynamic
Seals Per MIL-R-25988/4 Static
leveler actuator.
263


Hydraulic mechanism to limit torsional loads between the IUS and space transportation system orbiter

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server