The development of space shuttle separation devices is reviewed to illustrate the mechanisms involved in separating the orbiter from the Boeing 747 carrier aircraft and from the externally mounted propellant tank. Other aspects of the separation device development discussed include design evolution, operational experience during the orbiter approach and landing tests, and the work to be accomplished before an operational system becomes a reality

Rogers, W. F.

English

NASA Technical Reports Server

SPACE SBUTTLE SEPARATION MECHANISMS -_ 
By William F. Rogers 
NASA Johnson Space Center 
ABSTRACT 
The development of Space Shuttle separation devices is reviewed to illus- 
trate the mechanisms involved in separating the Orbiter from the Boeing 747 
carrier aircraft and from the externally mounted propellant tank. Other 
aspects of the separation device development to be discussed include design 
evolution, operational experience during the Orbiter approach and landing 
tests, and the work to be accomplished before an operational system becomes 
a reality. 
INTRODUCTION 
The separation of the Space Shuttle Orbiter from the Boeing 747 carrier 
aircraft and from the external tank (ET) will be reviewed in this presentation; 
however, several other crucial separation events occur during a typical Shuttle 
mission. These include the separation of the Shuttle vehicle from the launch 
platform at lift-off and separation of the two solid rocket boosters attached 
to the ET approximately 2 minutes into the flight (fig. 1). Actual structural 
separation of the Orbiter from the ET is preceded by the separation and retrac- 
tion of the fuel and oxidizer lines and of the electrical connections between 
the Orbiter and the ET. 
The Orbiter and the Boeing 747 carrier aircraft are shown before release 
in figure 2. The first separation occurred in 1977 during a series of test 
flights. The purpose of these test flights was to verify Orbiter handling 
capabilities and to verify the adequacy of all systems used in the approach 
and landing procedures. For both the earlier test flights and the actual 
orbital flights, the separation hardware provides structural attachment of the 
Orbiter until the time of release and then mechanical release within the 
system design constraints. 
The purpose of this paper is to summarize the development of the struc- 
tural separation system of the Orbiter for (1) launching the Orbiter from the 
747 aircraft during flight tests and-(2) releasing the Orbiter from the ET 
during orbital flight operations. 
Two particular developmental problems are discussed for the Orbiter/747 
aircraft separation system: (1) the development of the separation device, a 
pyrotechnic-actuated bolt, and (2) the requirement for lateral as well as fore 
and aft motion capability at separation. For the orbital flight separation 
system, a significant developmental problem is that of obtaining a sufficiently 
157 
https://ntrs.nasa.gov/search.jsp?R=19790013195 2020-03-20T18:32:48+00:00Z
smooth surface on.the Orbiter after release. The purpose of this requirement 
is to control the aerothermal heating on the spacecraft to prevent excessive 
structural temperatures during entry. 
DESIGN REQUIREMENTS 
The separation system design requirements may be divided into two general 
categories: structural and mechanical. The separation hardware is the primary 
structural load path between the Orbiter and the 747 and between the Orbiter 
and the ET; hence, the hardware must satisfy the spacecraft overall structural 
design requirements. For the separation event, the system acts as a mechanical 
device and must satisfy the design requirements to assure a safe separation. 
The importance of this system is evident. A structural failure before separa- 
tion, a failure to separate, or an improper separation could be catastrophic. 
The structural design requirement for the Orbiter/747 separation is to 
provide structural support of Orbiter/747 interfaces for flight environments. 
The mechanical design requirements for the Orbiter/747 separation are the 
following. 
1. To accommodate unrestrained horizontal motion at release 
2. To accommodate the load measurement system 
3. To accommodate ground adjustment of the Orbiter incidence angle 
4. To provide redundancy in the release device and initiation 
5. To separate without fragmenting 
The structural design requirement for the Orbiter/ET separation is to 
provide structural support at Orbiter/ET interfaces for prelaunch, launch, 
and boost environments. The mechanical design requirements for the 
Orbiter/ET tank are the following. 
1. To provide release of the Orbiter from the external tank for normal 
and abort separation 
2. To preclude degradation of Orbiter functional systems after operation 
3. To satisfy aerothermal smoothness criteria after separation 
4. To provide redundancy in the release device and initiation 
5. To separate without fragmenting 
The requirements for the Orbiter/747 and Orbiter/ET design systems are 
similar; however, the Orbiter/747 system requires the capability to accommodate 
horizontal relative motion at release in addition to the obvious requirement 
158 
I 
- 
for unrestrained vertical motion. The purpose of this requirement is to allow 
the Orbiter to move relative to the 747 at release without inducing additional 
forces or impulses that would complicate the separation dynamics. The horizon- 
tal motion capability would allow the Orbiter to move forward and aft because 
of differences in drag between the two vehicles. 
The requirement to measure interface attachments loads had a twofold 
purpose: to confirm the flight conditions for release and to monitor the 
structural loads during the various phases of mated flight. Representative 
design flight loads for the two separation systems are summarized as follows. 
1. Orbiter/747 
a. Forward attachment (combined loads) 
Tension = 154.8 kN (34 800 lbf) 
Radial = 90.3 kN (20 300 lbf) 
b. Aft attachment (combined loads) 
Tension = 425.7 kN (95 700 lbf) 
Forward = 206.0 kN (46 300 lbf) 
Side = 147.0 kN (33 000 lbf) 
2. Orbiter/ET 
a. Forward attachment 
Tension = 529.3 kN (119 100 lbf) 
Radial = 404.8 kN (91 000 lbf) 
b. Aft attachment 
Bolt tension = 1579.1 kN (355 000 lbf) 
The incidence angle between the Orbiter and the 747 was preset based on 
aerodynamic and separation dynamic analyses. However, the ability to change 
this angle based on updated analyses and flight test data was required for 
separation as well as for ferrying the Orbiter. For the approach and landing 
test (ALT) system, the design was also influenced by the goal of minimizing 
the development of different release devices for this specialized application. 
As previously mentioned, a very stringent requirement for aerothermal 
smoothness at the outer moldline has resulted in a difficult developmental 
problem for the release device at the Orbiter/ET forward attachment. Redun- 
dancy in the release system and separation without fragmentation are required 
for both systems. 
159 
CONFIGURATION DESCRIPTION 
Orbiter/747 Separation 
Figure 2 shows the Orbiter spacecraft attached to the 747 aircraft before 
release and figure 3 shows the combination just after separation. The one 
forward and the two aft structural attachments are represented in figure 4. 
At each attachment, a load cell measures the vertical and horizontal interface 
loads. To avoid the development of several different separation mechanisms 
for this very specialized test program, a single pyrotechnic bolt design 
(fig. 5) was selected for the three attachments. One separation bolt is used 
at the forward attachment and three bolts are used at each of the two aft 
attachments to carry the interface loads before separation. At each aft attach- 
ment, three electrical connectors carry pyrotechnic and communications wires 
and are designed to part immediately after structural release. 
It should be noted that the separation bolt (fig. 5) fractures in tension 
at the separation plane - an ideal situation for the Orbiter/747 system. How- 
ever, this device does not satisfy the stringent outer moldline smoothness cri- 
teria for entry from orbital flight, so a similar device, which fractures in 
shear internally, is being developed for that application. 
Orbiter/ET Separation 
Figure 6, illustrating the major components for separation of the Orbiter 
from the ET shows details of the forward and aft structural attachments. At the 
forward attachment, release is accomplished by the shear-type separation bolt 
previously mentioned. Figure 7 shows in detail the shear section of the bolt 
before and after separation. After the piston shears the bolt shank, it pushes 
the lower section of the shank free of the spherical bearing, and the bottom 
of the piston stops flush with the outer surface of the bearing. 
At the two aft attachments, a frangible nut is used as the release device. 
Once the Orbiter is safely separated from the ET, doors close over the cavities 
left at the point of structural, feedline, and electrical umbilical attachments. 
SEPARATION SYSTEM DEVELOPMENTAL PROBLEMS 
Of the problems encountered during the development of the separation 
system, the following examples illustrate a variety of mechanical design 
problems and their solutions. 
ALT Separation Bolt 
The pyrotechnic-actuated separation bolt used for the ALT flights failed 
to separate during a functional test of a production bolt, just before the 
160 
start of qualification testing. This failure occurred after several success- 
ful development tests of nearly the same configuration. The functional failure 
occurred using one production cartridge in the lower chamber at a temperature 
of 219 K (-65" F). Several additional tests incorporating various changes were 
attempted before a successful separation was achieved with a modified bolt. 
The failure could not be definitely attributed to any specific inadequacy in 
design, construction, or material during these-additional structural and func- 
tional tests. However, a series of cartridge tests indicated that output 
pressure was dependent on cartridge propellant loading pressures. In effect, 
the bolt was redesigned, resized, and underwent a new series of development 
tests. The principal modification consisted of reducing the fracture area to 
increase the ease of fracture, thereby reducing the structural margin. The 
pyrotechnic cartridge loading pressures were also modified to obtain more 
uniform chamber pressures. This particular hardware failure, which is dis- 
cussed in more.detail in reference 1, was never fully duplicated during the 
failure investigation. However, a combination of design changes and the 
additional developmental work resulted in the bolt successfully passing quali- 
fication tests and interface certification tests before the Orbiter/747 mated 
flight tests. This particular hardware problem illustrates a design compromise 
by decreasing the hardware structural margin to increase overall functional 
reliability. 
ALT Aft Attachment Redesign 
The original design concept for the Orbiter1747 aft attachments used 
linear-shaped charge explosive devices to sever the attachment structure at 
the separation plane (fig. 8(a)) to satisfy the design requirement for possible 
lateral motion at release. 
Two additional concepts are illustrated in figures 8(b) and 8(c). These 
concepts involve the use of frangible nuts like that used at the Orbiter/ET 
aft structural attachments (fig. 6). Although these concepts did incorporate 
a pyrotechnic device already under development, neither concept provided the 
degree of horizontal motion at release as that in the final design. Both 
concepts were undesirable in that bolt withdrawal was required for a clean 
separation and a momentary hangup could occur. However, because of the massive 
structure involved at the aft attachment to satisfy the Orbiter/747 load 
requirements and because of the additional pyrotechnic device that would have 
to be developed for this concept, it was decided that a separation concept 
using the existing separation bolt design was desirable and would be cost- 
effective. The baseline design that resulted (fig. 4) incorporates three 
separation bolts at each aft attachment. These bolts react the tensile loads 
at the interface, and a shear surface approximately 1.3 cm (0.5 in.) deep 
reacts the forward and side loads. It was judged that this shear surface 
*Jould not significantly affect the vehicle dynamics at release. Interface 
certification tests and flight tests have confirmed this to be the case. This 
design was a logical approach to satisfy the design requirements as well as to 
rlinimize the development of pyrotechnic devices. 
161 
Orbiter Outer Moldline Criteria 
For the Orbiter/ET forward structural attachment, a stringent design 
requirement exists to maintain a smooth outer surface after separation to 
minimize the aerodynamic heating on the lower surface of the Orbiter during 
entry. The aerothermal requirement is a maximum step of kO.043 cm (kO.017 in.) 
and a gap no greater than 0.089 cm (0.035 in.). Many developmental approaches 
have been considered, including various combinations of release devices, close- 
out mechanisms, and doors, 
Early design concepts for the Orbiter/ET structural attachments used 
electrical/mechanical release devices (.fig. 9). These devices were soon 
discarded in favor of pyrotechnic-actuated release devices because of the 
positive structural attachment before release and the highly reliable pyrotech- 
nic function at release. A preliminary design goal during the early phases of 
the Space Shuttle Program was to use completely reusable separation devices 
(primarily because of the Orbiter's quick-turnaround requirement) rather than 
pyrotechnic devices that had to be replaced after each flight. Figure 10 
shows the initial pyrotechnic devices chosen for the forward attachment. 
Because of the smoothness requirement for the outer moldline, the reusable 
devices were soon replaced by the pyrotechnic separation bolt design. 
The tension-type separation bolt was originally intended for this appli- 
cation; however, because the fracture plane was not within the aerothermal 
requirement and because of increased loads at this attachment, the shear-type 
separation bolt (fig. 7) was adopted, The shear bolt has the advantage of an 
internal fracture surface and a slight disadvantage in that the sheared bolt 
shank must be ejected from the monoball fitting for separation to be complete. 
It should be noted that the shear bolt has one pressure chamber with two 
pyrotechnic cartridges to satisfy the Space Shuttle redundancy requirements. 
This developmental problem illustrates a very difficult detail design challenge 
because of a combination of specific design requirements. 
FLIGHT PERFORMANCE RESULTS 
Before the first flight of the Orbiter/747 combination, the structural 
adequacy and functional operation of the separation system were demonstrated 
by analysis and by extensive ground tests. To date, the ALT separation system 
has been used for five Orbiter free flight tests and it has also served as an 
emergency system for Orbiter jettison on mated flight tests, both manned and 
unmanned. The ALT system operated successfully during the first free flight 
test on August 12, 1977, and has performed well during all other flight tests. 
In all tests, the pyrotechnics have functioned and the bolts have broken 
cleanly. The Orbiter and 747 crews have reported only a moderate "thump" as 
the bolts have separated. In all cases, onboard and chase plane photography 
have verified a normal release and separation. 
162 
After each flight test, the separation interfaces were thoroughly in- 
spected during buildup of hardware for the next flight, Only minor problems 
associated with the pyrotechnic and umbilical electrical connectors were 
encountered. Because pyrotechnic connectors have a tendency to gall at the 
initiator interface (presumably because of pyrotechnic shock), they have had to 
be replaced periodically. These connectors were lockwired to the initiator 
bodies during the later flights to preclude any possibility of the connectors 
becoming disengaged. 
The load measurement system functioned well during flight tests, Before 
the free flight tests, the system provided data to verify loads and aerodynamic 
predictions. During the free flight tests, the system provided backup data to 
verify the Orbiter/747 separation conditions for Orbiter launch. 
CONCLUDING REMARRS 
The approach and landing test phase of the Space Shuttle Orbiter flight 
test program has been successfully concluded. The developmental problems have 
been solved in a variety of ways without compromising the operational capa- 
bilities of the vehicle. A significant amount of testing and analysis remains 
to be accomplished before the actual orbital flight separation system is 
operational. However, developmental testing has already confirmed the ade- 
quacy of the basic design approach for these separation devices, For orbital 
flight separation, other types of pyrotechnic devices could be used and may be 
adopted in the future. Changes may occur to increase the Orbiter operational 
capabilities, to reduce operational costs by using refurbishable components, 
or to minimize the pyrotechnic mechanical shock by devices that operate at 
lower energy levels. 
REFERENCE 
1. Ritchie, Robert S.: Space Shuttle Orbiter Separation Bolts. Paper presented 
at the 12th Aerospace Mechanisms Symposium, April 27-28, 1978. 
163 
t h 
M 
%a. 
SOLID 
3KET BOOSTER 
BURNOW 
SOL,0 ROCKET BOOSTER 
JETTISON 
EXTERNAL TANK JETTISON 
ABORT MODE 
MZR 
Figure 1. - Orbital flight separation 
mission profile. 
764 
. . 
‘_
 
, 
‘.’
 
.:-
 
.:.
. 
Fi
gu
re
 
2 
- 
O
rb
ite
r/7
47
 
co
nf
ig
ur
at
io
n 
be
fo
re
 
re
le
as
e 
:, ,, 
, 
. 
Fi
gu
re
 
3a
 -
 
Vi
ew
 
of
 
th
e 
O
rb
ite
r/7
47
 
af
te
r 
re
le
as
e 
.?
i 
: 
.I 
I 
,..
 
,..
.’ 
:. 
-, 
;: 
, 
_:
; 
.A
>.
. 
..I
,. 
i 
_,
.,,
 
., 
:::
_.
: 
Fi
gu
re
 
3b
 -
 
Vi
ew
 
of
 
th
e 
O
rb
ite
r/7
47
 
af
te
r 
re
le
as
e 
I I I 
Figure 4 - Orbiter/747 separation system 
39.93 cm (15.72 IN.1 
Figure 5 - Orbiter/747 separation bolts 
168 
Figure 6.- Orbiter/ET separation Figure 7.- Shear flange separation 
system. bolt. 
(a) Linear-shaped charge separation 
device. 
(b) Multiple frangible nut 
configuration. 
(c) Single frangible nut configuration 
Figure 8.- ALT aft attachment. 
169 
Figure 9.- Orbiter/ET structural 
attachments CET request for 
proposal configuration). 
Figure lO.- Orbiter/ET forward attach- 
ment (frangible nut configuration). 
170 


Space Shuttle separation mechanisms

The development of space shuttle separation devices is reviewed to illustrate the mechanisms involved in separating the Orbiter from the Boeing 747 carrier aircraft and from the externally mounted propellant tank. Other aspects of the separation device development discussed include design evolution, operational experience during the orbiter approach and landing tests, and the work required to produce an operational system

Space Shuttle separation mechanisms

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server

NASA Technical Reports Server