Aeronautics and astronautics – Aircraft – steering propulsion – Fluid
Reexamination Certificate
1997-02-07
2004-07-06
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Aircraft, steering propulsion
Fluid
C244S003220, C239S265350, C060S232000, C060S279000
Reexamination Certificate
active
06758437
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a nacelle for protecting a reusable rocket engine from the effects of its exhaust plume and, more particularly, to a nacelle which includes a rigid shroud enclosing and rotating with the rocket engine when the engine is rotated to vector its thrust.
The exhaust plume emananting from the nozzle of a reusable liquid propellant rocket engine creates a severe thermal and acoustic environment adjacent to the engine. More particularly, the temperature adjacent the nozzle's exhaust orifice may exceed two thousand degrees Fahrenheit (2,000° F.). At high altitudes, the exhaust plume expands laterally beyond the circumference of the nozzle's exhaust orifice. Thus, especially at high altitudes, the lateral sides of the engine, if left unprotected, would be exposed to an extremely high heat transfer rate due to convection and radiation from the expanded exhaust plume. Many of the essential components of a liquid propellant rocket engine, in particular, the lines communicating the liquid propellant, hydraulic fluid, and electrical current, could not withstand such a high heat transfer rate.
The exhaust gases expand downstream of the choke plane of the nozzle. A lattice of standing shock waves is created in the exhaust plume when those gases expand and accelerate to reach supersonic velocity. High amplitude acoustic waves are generated by the shock waves in the plume. When the flight vehicle is in subsonic flight, these acoustic waves travel upstream from the plume. If the rocket engine was left unprotected, these waves would impinge on the engine's sides. Due to the proximity of the rocket engine to the exhaust plume, the strength of these acoustic waves would be only minimally diminished upon impingement. Repeated exposure to such high intensity acoustic waves would cause fatigue in the operating parts and structure of the rocket engine, and deleteriously affect its reliability and structural integrity.
Furthermore, in a vertical launch the exhaust plume causes debris on the ground to be blown upwards. Absent a protective barrier, this debris could impinge on the sides of the rocket engine. This problem would also be present should a liquid propellant rocket engine be used on a flight vehicle designed to land vertically, that is, with the thrust vector oriented perpendicularly to the ground, as opposed to a conventional horizontal landing.
Designers of reusable rocket engines have used rigid covers to insulate the engines from the heat and acoustic waves generated by the exhaust plume, as well as to protect them from impinging debris blown upwards from the ground during launch. Since modern rocket engines rotate about at least one axis in order to vector thrust, the cover must allow for such rotation. In addition, since the rocket engine is reusable, the cover must provide for easy access to facilitate inspection, maintenance and repair of the engine.
As illustrated in
FIG. 1
, one approach has been to enclose rocket engine
11
with rigid cover
13
, and to attach cover
13
to flight vehicle
15
. In particular, rocket engine
11
includes gimbal
17
, propellant lines
19
communicating with powerhead
21
, exhaust nozzle
22
, and nozzle throat
23
. Nozzle
22
includes insulation
25
to protect its exterior sides from the acoustic waves and heat that will emanate from an expanded exhaust plume.
Gimbal
17
is attached to flight vehicle
15
and allows rocket engine
11
to rotate relative to flight vehicle
15
about pitch and yaw axes. Pitch actuator
27
is connected to engine
11
and rotates it about the pitch axis to vector its thrust. A second actuator for controlling yaw rotation is not shown. Powerhead
21
contains electrical, hydraulic, and liquid propellant lines.
Cover
13
is fixedly attached to flight vehicle
15
and is comprised of shroud
29
and eyeball shield
31
. Eyeball shield
31
includes annular opening
33
, which circumscribes nozzle throat
23
. Flexible annular seal
35
provides an airtight interface between shroud
29
and eyeball shield
31
. Eyeball shield
31
rotates with rocket engine
11
as the engine is rotated about gimbal
17
by pitch actuator
27
and the yaw actuator. Eyeball shield
31
thus rotates relative to flight vehicle
15
and shroud
29
, along with rocket engine
11
.
A second approach is shown in FIG.
2
. Rocket engine
37
includes gimbal
39
, propellant lines
41
communicating with powerhead
43
, exhaust nozzle
45
, and nozzle exhaust orifice
47
. Gimbal
39
is attached to flight vehicle
49
about pitch and yaw axes. Actuator
51
is connected to rocket engine
37
and rotates it about the pitch axis to vector its thrust. A second actuator for controlling rotation about the yaw axis is not shown.
Cover
53
is rigidly attached to flight vehicle
49
and is comprised of shroud
55
and eyeball shield
57
. Eyeball shield
57
includes annular opening
59
. In this case however, opening
59
circumscribes exhaust orifice
47
rather than the nozzle throat. Annular seal
61
provides an airtight interface between shroud
55
and eyeball shield
57
. Eyeball shield
57
thus rotates relative to vehicle
49
and shroud
55
, along with rocket engine
37
.
Annular seals
35
and
61
are comprised of a complex spring mechanism which presses a flexible material against the opposing surfaces of the shroud and the sliding eyeball shield. Due to their mechanical complexity and the effect of harsh operating conditions, the annular seals used in the engine covers of the prior art are expensive, unreliable, and require continual inspection, adjustment, and maintenance.
Furthermore, inspecting and performing repairs or routine maintenance on the rocket engine requires removing and reinstalling the annular seal of the prior art because the eyeball shield remains attached to the nozzle when the shroud is removed. Referring to rocket engine
37
in
FIG. 2
, eyeball shield
57
remains attached to exhaust orifice
47
when shroud
55
is removed from flight vehicle
49
. Removing shroud
55
pursuant to performing routine maintenance on engine
37
thus entails detaching shroud
55
from flight vehicle
49
and removing seal
61
. Reinstallation of shroud
55
requires reinstallation of seal
61
, which is a tedious, laborious and time consuming task.
Based on the foregoing, it can be appreciated that there presently exists a need in the art for a nacelle for a reusable rocket engine which overcomes the above-described disadvantages and shortcomings of the prior art. The present invention fulfills this need in the art.
SUMMARY OF THE INVENTION
Briefly, the present invention encompasses a nacelle for enclosing a reusable liquid propellant rocket engine. The nacelle is comprised of a rigid shroud and a support truss. The shroud encloses the truss and the rocket engine. The shroud is comprised of three sections, including a top section and two side sections. The top section has openings to permit the communication of lines for liquid propellant, electrical current, and hydraulic fluid between the flight vehicle and the engine. The two side sections are connected to each other by longitudinal field joints, and to the top section by a circumferential field joint.
The rocket engine is attached to the flight vehicle by a gimbal allowing the engine to rotate relative to the flight vehicle about pitch and yaw axes. A pair of actuators is located in the flight vehicle. One of the actuators controls the rotation of the engine about the pitch axis, while the other controls the rotation about the yaw axis. Each actuator is connected to the shroud at a hard point where the shroud is attached to the truss.
The shroud is also fastened to the rocket engine around the nozzle's exhaust orifice, and around an attachment cone located adjacent to the gimbal. The foregoing attachment configuration transmits almost all of the forces applied by the actuators through the truss to the engine. The shroud transmits very little of the actuator forces. Since the shroud is
Lane Jeffery G.
Magarro Richard B.
Alston & Bird LLP
Eldred J. Woodrow
McDonnell Douglas Corporation
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