U.S. patent application number 11/687970 was filed with the patent office on 2007-10-11 for lighter-than-air aircraft including a closed loop combustion generating system and related methods for powering the same.
This patent application is currently assigned to Harris Corporation. Invention is credited to William Robert PALMER.
Application Number | 20070235583 11/687970 |
Document ID | / |
Family ID | 38172352 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070235583 |
Kind Code |
A1 |
PALMER; William Robert |
October 11, 2007 |
LIGHTER-THAN-AIR AIRCRAFT INCLUDING A CLOSED LOOP COMBUSTION
GENERATING SYSTEM AND RELATED METHODS FOR POWERING THE SAME
Abstract
A lighter-than-air aircraft includes a gas envelope for
containing a buoyant gas, and a propulsion system is carried by the
gas envelope. A solar panel is carried by the gas envelope for
powering the propulsion system when generating sufficient power. A
closed loop combustion generating system is also carried by the gas
envelope for powering the propulsion system when the solar panel is
not generating sufficient power. The fuel for the closed loop
combustion generator is regenerated by the solar panel from its
exhaust when the solar panel is generating sufficient power.
Inventors: |
PALMER; William Robert;
(Melbourne, FL) |
Correspondence
Address: |
ALLEN, DYER, DOPPELT, MILBRATH & GILCHRIST P.A.
1401 CITRUS CENTER 255 SOUTH ORANGE AVENUE
P.O. BOX 3791
ORLANDO
FL
32802-3791
US
|
Assignee: |
Harris Corporation
Melbourne
FL
|
Family ID: |
38172352 |
Appl. No.: |
11/687970 |
Filed: |
March 19, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10977791 |
Oct 29, 2004 |
7249733 |
|
|
11687970 |
Mar 19, 2007 |
|
|
|
Current U.S.
Class: |
244/30 ; 136/244;
244/58; 244/61; 244/96; 429/414; 429/418; 429/436; 429/441;
60/671 |
Current CPC
Class: |
B64B 1/24 20130101; B64B
1/14 20130101; B64B 1/02 20130101 |
Class at
Publication: |
244/030 ;
136/244; 244/058; 244/061; 244/096; 429/017; 060/671 |
International
Class: |
B64B 1/00 20060101
B64B001/00; F01K 25/00 20060101 F01K025/00; H01M 8/18 20060101
H01M008/18; H02N 6/00 20060101 H02N006/00 |
Claims
1-19. (canceled)
20. A method for operating a lighter-than-air aircraft comprising a
gas envelope for containing a buoyant gas, a propulsion system
carried by the gas envelope, at least one solar panel carried by
the gas envelope, and a closed loop combustion generating system
carried by the gas envelope, the method comprising: powering the
propulsion system using the at least one solar panel when
generating sufficient power; powering the propulsion system using
the closed loop combustion generator when the at least one solar
panel is not generating sufficient power, and producing exhaust as
a result thereof; and regenerating fuel from the exhaust when the
at least one solar panel is generating sufficient power.
21. A method according to claim 20 wherein the closed loop
combustion generating system further comprises a combustion
generator for generating the power and producing the exhaust as a
result thereof, and a converter for regenerating the fuel from the
exhaust.
22. A method according to claim 21 wherein the closed loop
combustion generating system further comprises a condenser for
receiving the exhaust from the combustion generator; the method
further comprising using the condenser for condensing the exhaust
to a liquid before regenerating the fuel.
23. A method according to claim 22 wherein the condenser is
adjacent the at least one solar panel, with the at least one solar
panel functioning as a heat sink during the night.
24. A method according to claim 21 wherein the combustion generator
comprises at least one of a turbine generator and a piston
generator.
25. A method according to claim 21 wherein the fuel comprises
hydrogen gas and oxygen gas so that the exhaust comprises water;
and wherein the converter comprises an electrolyzer for
disassociating the hydrogen and oxygen gases from the exhaust.
26. A method according to claim 22 further comprising routing a
portion of the liquid from the condenser to the combustion
generator so that heat being generated by the combustion chamber
heats the liquid to a pressurized gas; and wherein the closed loop
combustion generating system further comprises a secondary
generator being driven by the pressurized gas.
27. A method according to claim 20 wherein the closed loop
combustion generating system further comprises a fuel cell for
generating electricity from the fuel.
28. A method according to claim 21 further comprising: using heat
from the combustion generator for heating a supplemental liquid to
a pressurized gas; generating power using a supplemental generator
being driven by the pressurized gas, and producing exhaust as a
result thereof; and condensing the exhaust from the supplemental
generator using a supplemental condenser.
29. A method according to claim 28 wherein the supplemental liquid
comprises at least one of propane and butane.
30. A method according to claim 28 wherein the supplemental
condenser is adjacent the at least one solar panel, with the at
least one solar panel functioning as a heat sink during the
night.
31. A method for operating a lighter-than-air aircraft comprising a
gas envelope for containing a buoyant gas, a propulsion system
carried by the gas envelope, at least one solar panel carried by
the gas envelope, and a closed loop fuel cell system carried by the
gas envelope and comprising a fuel cell, a generator and a
converter, the method comprising: powering the propulsion system
using the at least one solar panel when generating sufficient
power; powering the propulsion system using the closed loop fuel
cell system when the at least one solar panel is not generating
sufficient power, the powering comprising using the fuel cell for
generating power, and producing heat and a first exhaust as a
result thereof, heating a supplemental liquid to a pressurized gas
with the heat generated by the fuel cell, driving the generator
with the pressurized gas for generating power, and producing a
second exhaust as a result thereof, and using the converter for
converting the first exhaust from the fuel cell into fuel based
upon power input from the at least one solar panel.
32. A method according to claim 31 wherein the supplemental liquid
comprises butane.
33. A method according to claim 31 wherein the supplemental liquid
comprises propane.
34. A method according to claim 31 wherein the closed loop fuel
cell system further comprises a condenser for condensing the second
exhaust to a liquid.
35. A method according to claim 34 wherein the condenser is carried
by the gas envelope and is adjacent the at least one solar panel,
with the at least one solar panel functioning as a heat sink during
the night.
36. A method according to claim 31 wherein the fuel received by the
closed loop fuel cell comprises hydrogen and oxygen gasses so that
the first exhaust comprises water; and wherein the converter
comprises an electrolyzer for disassociating the hydrogen and
oxygen gases from the water of the first exhaust.
37. A method according to claim 31 further comprising generating
additional power during a day cycle using the closed loop fuel cell
system, the generating comprising: heating the supplemental liquid
to a pressurized gas with the heat generated by the at least one
solar panel when generating sufficient power; driving the generator
with the pressurized gas for generating additional power, and
producing a third exhaust as a result thereof; and condensing the
third exhaust back into the supplemental liquid by ambient air.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of
lighter-than-air aircraft, and in particular, to a lighter-than-air
aircraft capable of remaining in the air at high altitudes for
extended periods of time.
BACKGROUND OF THE INVENTION
[0002] High altitude, long-duration solar powered aircraft have
been proposed for both commercial and military applications. For
example, lighter-than-air aircraft have been proposed for cellular
telephone applications. Military applications also include
telecommunication applications as well as providing
surveillance.
[0003] There is a domain in the upper stratosphere at 60,000 feet
where it is ideal to position a lighter-than-air aircraft. This
altitude allows on-board sensors to see over the horizon at least
350 miles in any direction. In most such applications, long
duration station keeping is essential. Consequently, the issue is
not in getting an aircraft to 60,000 feet, but in maintaining power
so that the on-board sensors and electronics are continuously
powered for extended periods of time, which may be from a few weeks
to several months to even longer.
[0004] Electrical energy generated using solar cells or
photovoltaic cells are typically used to power lighter-than-air
aircraft. For example, U.S. Patent Application No. 2002/0005457
discloses a lighter-than-air aircraft powered with flexible solar
cells integrated within the material covering the aircraft.
Although the energy provided by solar cells is adequate to power
lighter-than-air aircraft while in the sunlight, the challenge is
to repeatedly get through the night. To keep a large
lighter-than-air aircraft in a general location at 60,000 feet
requires a significant amount of power. The solar panels not only
need to take in enough solar energy to power the aircraft during
the day, but also needs to take in additional power to be stored in
batteries so that it can be used during the night.
[0005] In addition, extra power is needed to maintain position due
to the upper winds or air currents at 60,000 feet, and for
maintaining direction of the solar panels toward the sun as the
direction of the sun changes throughout the day. This puts a bigger
demand on the ability to store power for use during the night. One
approach is to place more solar panels on the aircraft for
collecting and storing the additional power, but this results in an
increase of the weight of the aircraft. The greater the weight, the
greater the volume of lift gas required, which increases the amount
of material necessary to contain the lift gas. These increases in
weight and volume impose additional power requirements.
[0006] As an alternative to placing more solar panels on the
aircraft, one approach is to maintain an optimum position of the
solar cells in relationship to the sun. For example, most all
spacecraft are solar powered. In such spacecraft, the solar panels
are rotatable so that an optimum angle can be maintained between
the solar panels and the sun. However, these systems are not
particularly advantageous on a lighter-than-air aircraft. In U.S.
Pat. No. 6,371,409, solar panels mounted on an outer surface of a
lighter-than-air aircraft are movable over a portion of the surface
thereof to adjust for changes in the direction of the sun, or if
maintained in a stationary position, for the inclination of the sun
throughout the day.
[0007] Another approach to providing the power needed throughout
the night is to use fuel cells. For example, the power requirements
for the high altitude airship (HAA) as designed by Lockheed Martin
Corp. are met by a combination of solar cells, fuel cells and
batteries, wherein the fuel cells provide electrical power during
the night. The fuel cells receive the gaseous elements of hydrogen
and oxygen for generating electrical power.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing background, it is therefore an
object of the present invention to increase the efficiency at which
energy is collected, stored and converted to power so that a
lighter-than-air aircraft can remain aloft at high altitudes for
extended periods of time without having to return to ground for
refueling.
[0009] This and other objects, features, and advantages in
accordance with the present invention are provided by a
lighter-than-air aircraft comprising a gas envelope for containing
a buoyant gas, a propulsion system carried by the gas envelope, and
at least one solar panel carried by the gas envelope for powering
the propulsion system when generating sufficient electricity. A
closed loop combustion generating system is carried by the gas
envelope for powering the propulsion system when the solar panel is
not generating sufficient power, and has its fuel regenerated by
the solar panel from its exhaust when the solar panel is generating
sufficient power.
[0010] The lighter-than-air aircraft is capable of high-altitude
station keeping within tight altitude and perimeter boundaries for
extended periods of time. The lighter-than-air aircraft is intended
to operate at an altitude of about 60,000 feet in the stratosphere,
where it is ideal to sit, look and listen from a strategic
perspective. This altitude allows on-board sensors to see at least
350 miles in any direction.
[0011] In one embodiment, the closed loop combustion generating
system comprises a combustion generator, and a converter for
converting exhaust from the combustion generator into fuel based
upon power input from the solar cell.
[0012] The closed loop combustion generating system further
comprises a condenser for condensing the exhaust from the
combustion chamber to a liquid. The condenser may be carried by the
gas envelope and is adjacent the solar panel. The solar panel
functions as a heat sink during the night, i.e., a large black
surface pointing toward a black sky becomes very cold at night,
which is then used for cooling the exhaust received by the
condenser. The closed loop combustion generating system
advantageously increases the efficiency at which fuel is stored and
converted to power so that the lighter-than-air aircraft can remain
aloft at high altitudes for extended periods of time without having
to return to ground for refueling.
[0013] The combustion generator may comprise a turbine or piston
generator, for example. The fuel may comprise hydrogen gas and
oxygen gas so that the exhaust comprises water, and the converter
may comprise an electrolyzer for disassociating the hydrogen and
oxygen gases from the water of the exhaust.
[0014] A portion of the liquid from the condenser may be routed to
the combustion generator so that heat therefrom heats the liquid to
a pressurized gas. The closed loop combustion generating system may
further comprise a secondary generator being driven by the
pressurized gas for generating power.
[0015] The closed loop combustion generating system may further
comprise a fuel cell for generating electricity from the fuel. In
addition, a supplemental liquid source may receive heat from the
combustion generator to heat the supplemental liquid to a
pressurized gas. The closed loop combustion generating system may
further comprise a supplemental generator being driven by the
pressurized gas, and producing exhaust as a result thereof. A
supplemental condenser condenses the exhaust from the supplemental
generator.
[0016] The supplemental liquid may comprise butane or propane, for
example. At 60,000 feet, for example, butane or propane exhibits
low vapor pressure at -60.degree. F. (which is the ambient
temperature) and high vapor pressure at 110.degree. F. The
supplemental condenser may be carried by the gas envelope and is
adjacent the at least one solar panel so that the solar panel
functions as a heat sink during the night. This large heat sink
potential is advantageously used to increase the overall efficiency
of the closed loop combustion generating system, and allows
negative work to be performed on a mass that would normally require
work.
[0017] Another aspect of the lighter-than-air aircraft is one in
which a combustion generator is not used. Instead, the
lighter-than-air aircraft comprises a closed loop fuel cell system
carried by the gas envelope and receives fuel for powering the
propulsion system when the solar panel is not generating sufficient
power, and produces a first exhaust as a result thereof.
[0018] The closed loop fuel cell system may comprise a fuel cell
for generating power, and producing heat and a first exhaust as a
result thereof. The heat may be used for heating a supplemental
liquid to a pressurized gas. A generator is driven by the
pressurized gas for generating power, and produces a second exhaust
as a result thereof. A converter converts the first exhaust from
the fuel cell into fuel based upon power input from the solar
cell.
[0019] Another aspect of the present invention is directed to a
method for operating a lighter-than-air aircraft comprising a gas
envelope for containing a buoyant gas, a propulsion system carried
by the gas envelope, at least one solar panel carried by the gas
envelope, and a closed loop combustion generating system carried by
the gas envelope. The method comprises powering the propulsion
system using the solar panel when generating sufficient power, and
powering the propulsion system using the closed loop combustion
generating system when the solar panel is not generating sufficient
power. The closed loop combustion generating system produces
exhaust when powering the propulsion system. The method further
comprises regenerating fuel from the exhaust when the solar panel
is generating sufficient power.
[0020] Yet another aspect of the present invention is directed to a
method for operating a lighter-than-air aircraft comprising a gas
envelope for containing a buoyant gas, a propulsion system carried
by the gas envelope, at least one solar panel carried by the gas
envelope, and a closed loop fuel cell system carried by the gas
envelope. The closed loop fuel cell system comprises a fuel cell, a
generator and a converter. The method comprises powering the
propulsion system using the at least one solar panel when
generating sufficient power, and powering the propulsion system
using the closed loop fuel cell system when the at least one solar
panel is not generating sufficient power. Powering the propulsion
system using the closed loop fuel cell system comprises using the
fuel cell for generating power, and producing heat and a first
exhaust as a result thereof. A supplemental liquid is heated to a
pressurized gas with the heat generated by the fuel cell. The
generator is driven with the pressurized gas for generating power,
and producing a second exhaust as a result thereof. The converter
is used for converting the first exhaust from the fuel cell into
fuel based upon power input from the solar cell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a perspective view of a lighter-than-air aircraft
at high altitude providing surveillance and communications about a
desired location on earth in accordance with the present
invention.
[0022] FIG. 2 is an enlarged perspective view of the underside of
the lighter-than-air aircraft as shown in FIG. 1 illustrating in
greater detail the gondola and fuel storage holders.
[0023] FIG. 3 is an enlarged view of the gondola as shown in FIG. 2
illustrating in greater detail the propulsion system for the
lighter-than-air aircraft.
[0024] FIGS. 4a-4e illustrate various positions of the propulsion
system resulting in a navigation vector that varies while the solar
panel is continuously pointed in the direction of the sun for the
lighter-than-air aircraft in accordance with the present
invention.
[0025] FIGS. 5a-5f illustrate various positions of the propulsion
system resulting in a navigation vector that remains constant while
the position of the solar panel varies for tracking the sun during
the day for the lighter-than-air aircraft in accordance with the
present invention.
[0026] FIG. 6 is a cross-sectional side view of the
lighter-than-air aircraft illustrating the support structure within
the gas envelope wherein the upper portion of the gas envelope is
in a retracted position in accordance with the present
invention.
[0027] FIG. 7 is a cross-sectional side view of the
lighter-than-air aircraft illustrating the support structure within
the gas envelope wherein the upper portion of the gas envelope is
in an expanded position in accordance with the present
invention.
[0028] FIGS. 8a-8c are perspective views of the gas envelope
changing from a retracted position to an expanded position as the
altitude of the lighter-than-air aircraft increases in accordance
with the present invention.
[0029] FIG. 9 is a perspective view of the gas envelope
illustrating various angles of solar incidence for the solar panel
in accordance with the present invention.
[0030] FIG. 10 is a block diagram of a closed loop combustion
generator for generating electricity for the lighter-than-air
aircraft in accordance with the present invention.
[0031] FIG. 11 is a block diagram of another embodiment of the
closed loop combustion generator as shown in FIG. 11.
[0032] FIG. 12 is a block diagram of a closed loop fuel cell for
generating electricity for the lighter-than-air aircraft in
accordance with the present invention.
[0033] FIG. 13 is a block diagram illustrating the on-board
electronics carried by the lighter-than-air aircraft in accordance
with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout, and prime, and double prime notations are used
to indicate similar elements in alternative embodiments.
[0035] Referring initially to FIGS. 1-3, the lighter-than-air
aircraft 20 is capable of high-altitude station keeping within
altitude and perimeter boundaries for extended periods of time. The
illustrated lighter-than-air aircraft 20 is in the upper
stratosphere at 60,000 to 80,000 feet, for example, where it is
ideal to sit, look, listen and provide surveillance and
communications from a strategic perspective. This altitude allows
on-board sensors to see at least 350 miles in any direction. For
example, the lighter-than-air aircraft 20 may provide surveillance
21 about a location of interest 23 on the surface of the earth, and
provide this information to a command and control center 25 via a
communications link 27, as illustrated in FIG. 1. The
lighter-than-air aircraft 20 may also provide over the horizon
surveillance or communications 29.
[0036] The lighter-than-air aircraft 20 is unmanned, and
communications 27 is provided with the ground based command and
control center 25. Communications 27 may be directly between the
command and control center 25 and the lighter-than-air aircraft 20.
Alternatively, communications 27, 29 may be provided via a relay
satellite or other airborne platform.
[0037] The lighter-than-air aircraft 20 comprises a gas envelope 22
containing a buoyant gas, and at least one solar panel 24 is
carried by a predetermined portion of the gas envelope. The at
least one solar panel may be one large solar panel, or may be a
solar array comprising a plurality of smaller solar panels. For
purposes of discussion, the at least one solar panel 24 will simply
be referred to as the solar panel. The solar panel 24 may be
integrated into the skin of the gas envelope 22, or may be separate
from the skin, as readily appreciated by those skilled in the art.
The buoyant gas, for example, may be helium, hydrogen or
combinations thereof, or other combinations of lighter-than-air
gasses.
[0038] At least one solar sensor 26 determines a direction of the
sun based upon the incident light rays received from the sun. The
solar sensor 26 may be separate from the solar panel 24, as
illustrated. Alternatively, the solar sensor 26 may be integrated
within the solar panel 24 for determining the direction of the sun
based upon the incident light rays. The illustrated solar sensor 26
is located on top of the gas envelope 22. In another embodiment, a
plurality of solar sensors 24 are spaced around the gas envelope
22.
[0039] A propulsion system 28 orients the gas envelope 22 so that
the solar panel 24 is oriented in the direction of the sun based
upon the solar sensor 26. This advantageously allows the solar
panel 24 to be constantly pointing toward the sun. Since the
performance of the solar panel 24 is optimized, extra solar panels
do not need to be carried by the gas envelope 22, which reduces the
overall weight, complexity and cost of the lighter-than-air
aircraft 20.
[0040] A gondola 30 is carried by the gas envelope 22. As will be
discussed in greater detail below, power conversion, management
functions and the propulsion system 28 are an integral part of the
gondola 30. Many of these items are carried by the payload bay 31
of the gondola 30. In particular, the payload bay 31 carries the
electronics, communications and/or surveillance equipment. Fuel
storage is above the gondola 30 and is enclosed by the gas envelope
22. The fuel storage includes hydrogen and oxygen fuel holders 32,
34 for respectively storing the gaseous elements of hydrogen and
oxygen to be used for powering the propulsion system 28. The water
that is broken down into hydrogen and oxygen gases is carried in
the gondola 30.
[0041] The propulsion system 28 comprises a plurality of spaced
apart propellers 40 extending from the gondola 30. Each propeller
40 can be independently driven, or the propellers can all be driven
together. In the illustrated embodiment of the propulsion system
28, six booms 42 are attached to the gondola 30 for supporting six
independent drives 44, i.e., six electric motors. Each boom 42 thus
supports a respective electric motor 44 for driving the propeller
40 coupled thereto. The actual number of motors/propellers can vary
depending on their size and the size of the lighter-than-air
aircraft 20.
[0042] Each electric motor 44 is also coupled to a dual axis gimbal
46. The dual axis gimbals 46 advantageously allow the propellers 40
to be positioned so that the lighter-than-air aircraft 20 can move
in any direction, similar to a helicopter. An advantage of the
propulsion system 28 is that the lighter-than-air aircraft 20 can
move in any direction while the solar panel 24 is continuously
being pointed in the direction of the sun. In other words, the
navigation vector of the lighter-than-air aircraft 20 can vary
while the sun vector associated with the angle of the solar panel
24 pointed in the direction of the sun remains constant toward the
sun.
[0043] An example of the solar panel 24 being continuously pointed
toward the sun while the navigation vector changes is illustrated
in FIGS. 4a-4e. The navigation vector 50 represents the direction
and motion of the lighter-than-air aircraft 20. Even if the
lighter-than-air aircraft 20 is not moving, the navigation vector
50 may vary to compensate for wind direction and speed. In FIG. 4a,
the propellers 40 are rotated so that the navigation vector 50 is
at -30 degrees while the sun vector 52 is at 90 degrees. The sun
vector 52 represents the direction the solar panel 24 is
pointing.
[0044] If the navigation vector 50 changes to 30 degree, the
propellers 40 carried by the gondola 30 are rotated accordingly
while the sun vector 52 remains constant at 90 degrees, as
illustrated in FIG. 4b. The same concept applies when the
navigation vector 50 changes to 20, 10 and 0 degrees, as
illustrated in FIGS. 4c, 4d and 4e.
[0045] An example of the navigation vector 50 being constant while
the sun vector 52 changes is illustrated in FIGS. 5a-5f. With the
lighter-than-air aircraft 20 holding a fixed position, the gas
envelop 22 needs to rotate as the sun rises and sets during the day
so that the solar panel 24 remains constantly pointed toward the
direction of the sun.
[0046] At 8 am, for example, the sun vector 52 is at 10 degrees, as
illustrated in FIG. 5a. At 10 am, the sun vector 52 is at 45
degrees, but this requires the propellers 40 that are carried by
the gondola 30 to be rotated so that the solar panel 24 follows the
direction of the sun while the navigation vector 50 remains
constant, as illustrated in FIG. 5b. The process is repeated
throughout the day as the sun changes position, as illustrated in
FIGS. 5c-5f.
[0047] In the illustrated lighter-than-air aircraft 20, the gas
envelope 22 and the gondola 30 are fixed. That is, when the gas
envelope 22 rotates, so does the gondola 30. This embodiment
requires the motors 44 to operate in a sequence with a stepwise
re-clocking of the propellers 40 when they have been rotated as far
as they can rotate for maintaining a constant pointing of the solar
panel 24 toward the direction of the sun. For example, when a first
motor in the sequence of motors reaches its maximum allowable
gimbal rotation, it simply slows and rotates approximately 180
degrees and becomes the last motor in the sequence of motors. The
sequence of the motors continues to change as necessary based upon
the desired navigation and/or solar vector. Also, the thrust
direction of each re-clocked propeller 40 is reversed.
[0048] In another embodiment, the gas envelope 22 and the gondola
30 rotate independently from one another, much like a turret on a
tank. The gondola 30 may rotate as necessary to maintain a desired
flight path vector while the solar panel 24 remains in the
direction of the sun.
[0049] Referring now to FIGS. 6 and 7, the gas envelope 22
comprises a support structure for moving THE gas envelope from a
retracted position (FIG. 6) to an expanded position (FIG. 7). The
support structure comprises a hoop-truss member 60 having a ring
shape. The hoop-truss member 60 is derived from hoop antennas that
are deployed in space, as readily appreciated by those skilled in
the art. The hoop-truss member 60 includes a number of compressive
members and stabilizing tension cords 62 for providing the
necessary support. Other internal design structures are acceptable
as readily appreciate by those skilled in the art, such as a radial
rib structure, for example.
[0050] The gondola 30 is attached to the hoop-truss member 60 via
attachments 64, and to a control member 66 via attachments 71. The
control member 66 is above the hoop-truss member 60. Fuel storage
holders for the applicable gases are above the gondola 30, and are
enclosed by the gas envelope 22. The fuel storage holders as noted
above include hydrogen and oxygen fuel holders 32, 34 for
respectively storing the gaseous elements of hydrogen and oxygen to
be used for powering the propulsion system 28 during the night.
[0051] The control member 66 enables volumetric control of the
upper portion of the gas envelope 22 during ascent and decent. As
the buoyant gas expands or contracts as a function of the altitude,
the volume of the gas envelope 22 changes accordingly. Although not
shown in the figures, a perimeter stabilized inflatable structure,
in concert with the more stable rigid members 60 and 66, may also
be used to provide support of the desired contour of the gas
envelope 22. An approach of using radial members within the cord
structure allows the creation of a substantially circular
shape.
[0052] Volumetric control of the gas envelope 22 may be performed
manually or automatically. Small electric motors 68 are positioned
around the control member 66, and retract or release tie-downs 70
attached to the upper surface of the gas envelope 22, and tie-downs
71 attached to the gondola 30. The electric motors 68 are not
limited to being located around the control member 66. They may be
located around the hoop-truss member 60, for example. The gondola
30 carries an altimeter 72 for determining the altitude of the
lighter-than-air aircraft 20, and provides the altitude to an
envelope controller 74 or measurement of barometric
pressure/relative pressure.
[0053] The altimeter 72 and the controller 74, as well as other
on-board electronics and sensors, will be discussed in greater
detail when reference is made to FIG. 13. The envelope controller
74 operates the small electric motors 68 so that the tension cords
or tie-downs 70, 71 are either retracted or released based upon the
altitude. This feature of the present invention advantageously
allows for the expansion of the buoyant gas as the lighter-than-air
aircraft 20 traverses the atmosphere to the desired station keeping
altitude.
[0054] The desired altitude of the lighter-than-air aircraft 20 is
preferably in the stratosphere, which corresponds to an altitude of
60,000 feet or higher. Of course, the lighter-than-air aircraft 20
may operate at lower altitudes depending on its intended
purpose.
[0055] When the lighter-than-air aircraft 20 is in the lower
atmosphere, the upper portion of the gas envelope 24 is retracted
toward the control member 66, and the gondola 30 is also retracted
toward the control member as illustrated in FIG. 6. This reduces
the cross-sectional area of the gas envelope 24, which results in a
low profile, i.e., a reduced drag. The winds in the denser air of
the lower atmosphere have a significant effect on large structures,
such as the lighter-than-air aircraft 20.
[0056] When the gas envelope 22 is fully collapsed, the height
h.sub.1 of the illustrated gas envelope is 80 feet, and the height
h.sub.2 including the gondola 30 is 97 feet. When the gas envelope
22 is fully expanded, as illustrated in FIG. 7, these dimensions
h.sub.1, h.sub.2 are respectively 96 feet, 148 feet. The width
w.sub.1 of the gondola 30 is 22 feet, and the overall width w.sub.2
of the lighter-than-air aircraft 20 is 215 feet. The height h.sub.3
of the hoop-truss member 60 is 24 feet, and the height h.sub.4
between the hoop-truss member and the top of the gas envelope 22 is
91 feet. The radius r.sub.1 of the upper portion of the gas
envelope 22 when fully expanded is 118 feet, whereas the radius
r.sub.2 of the lower portion of the gas envelope is 272 feet. The
inside diameter of the hoop-truss member 60 is 161 feet. These
numbers are for illustrative purposes only, and the actual size of
the lighter-than-air aircraft will vary depending on the intended
application.
[0057] FIGS. 8a-8c are perspective views of the gas envelope 22
changing from the retracted position to the expanded position as
the altitude of the lighter-than-air aircraft 20 increases. In the
retracted position, the gas envelope 22 has a low drag because of
its "flat top" and because the gondola 30 is pulled or held closer
position toward the gas envelope, as shown in FIG. 8a. Because of
the reduced cross section, this helps to reduce the effects of
winds at the lower altitudes. As the lighter-than-air aircraft 20
increases in altitude, the buoyant gas expands so that the volume
of the gas envelope 22 increases and the gondola 30 is lowered away
from the gas envelope, as shown in FIG. 8b. Once the
lighter-than-aircraft 20 reaches its desired altitude near or above
60,000 feet, the gas envelope 22 is fully expanded and the gondola
30 is in its resting position, as shown in FIG. 8c.
[0058] Another advantage of the "flat top" design is that it allows
for a significant reduction in the height of the facility
constructing the lighter-than-air aircraft 20. The lighter-than-air
aircraft 20 may be constructed at the reduced height, and then
moved outside for deployment.
[0059] The flexible material covering the hoop-truss member 60 and
the control member 66 is preferably a high strength material. This
material may be made from Kapton films, Tedlar, and Vectran, for
example. The material may also comprise a polyester film, and may
also be a combination of different materials. For example, Vectran
may be used for the load bearing fabric. Tedlar and polyester film
laminates may form the ultraviolet protection layer, and also
function as a gas barrier. These materials have a high resistance
to radiation and to cold temperatures.
[0060] An advantage of the present invention is that the gas
envelope 22 may be constantly pointed in the direction of the sun.
The gas envelope 22 is substantially symmetrical about its vertical
axis and comprises an upper portion having a partial spheroidal
shape. This shape advantageously provides for good solar incidence
360 degrees around the perimeter of the gas envelope 22, and at low
elevation angles.
[0061] The solar panel 24 is carried by a predetermined angular
segment of the partial spheroid. Out of a total angular segment of
360 degrees, the predetermined angular segment is within a range of
about 60 to 120 degrees, for example, with about 90 degrees being
illustrated in the figures. In contrast, the direct front or rear
of a blimp has little or no solar exposure due to its lack of
symmetry about a vertical axis. As a result of the spheroidal shape
of the gas envelope 22, the solar panel 24 may be placed on any
side thereof and still be optimized for collecting solar energy via
the solar panel facing the direction of the sun. Since the
effectiveness of the solar panel 24 is directly related to the
incidence angle of the sunlight, it becomes very important to
optimize these pointing angles.
[0062] Various example positions of the sun above the horizon and
its footprint on the solar panel 24 are shown in FIG. 9. For
example, reference 53 represents the sun 0.degree. above the
horizon with a +/-40' view angle, reference 54 represents the sun
14.degree. above the horizon with a +/-40.degree. view angle,
reference 55 represents the sun 28.degree. above the horizon with a
+/-35.degree. view angle, reference 56 represents the sun
42.degree. above the horizon with a +/-30' view angle, and
reference 57 represents the sun 56.degree. above the horizon with a
+/-25.degree. view angle. In addition, the solar panel 24 is
plumbed back to the gondola 30 using reinforced channels within the
solar surface and routing through portions of the inner support
structure. The solar panel 24 thus has an efficient overall
incident area when directed toward the sun. As a result of the
additional weight of the solar panel 24 on one side of the gas
envelope 22, the gondola 30 should be slightly off center or
internal elements should be adjusted to balance the center of
gravity.
[0063] As an alternative embodiment resulting from the gas envelope
22 being symmetrical about its vertical axis, solar panels 24 may
be placed all the way around so that it does not matter which
direction the gas envelope is pointing. Consequently, the use of
the solar sensor 26 is no longer necessary. This embodiment may be
particularly attractive if the technology for solar panels allows
for light weight solar panels, and the impact of placing them all
the way around the gas envelope 22 is not too detrimental to the
overall weight and performance of the lighter-than-air aircraft
20.
[0064] Referring now to FIGS. 10-12, various embodiments for
generating electricity for the lighter-than-air aircraft 20 during
the night cycle will now be discussed. It is worth noting that
these different embodiments for generating electricity may also be
used on other types of aircraft, including those that are
heavier-than-air, as readily appreciated by those skilled in the
art.
[0065] The sun is generally available for about 8 hours during the
day in which extra electricity is generated beyond what is required
for powering the lighter-than-air aircraft 20. Availability of the
sun is highly dependent on location of the lighter-than-air
aircraft 20 relative to the equator and on the time of the year.
This extra electricity is used for regenerating fuel, which is then
used for generating electricity during the night cycle. There are
an additional 1.5 hours in the morning and 1.5 hours in the evening
where the sun provides enough solar energy for powering the
lighter-than-air aircraft 20, but does not generate any extra
electricity. The night cycle is about 13 hours where there is
effectively no sunlight available.
[0066] In the illustrated embodiment of the lighter-than-air
aircraft 20, it is estimated that about 750 W-hr/kg is required.
However, current battery technology offers about 150 W-hr/kg
storage potential. Consequently, these batteries are not efficient
enough, per unit of weight, for them to be a good choice for
powering the lighter-than-air aircraft 20 during the night.
[0067] In one embodiment, a closed loop combustion generating
system 80 powers the propulsion system 28 when the solar panel 24
is not generating sufficient electricity (i.e., during the night),
and has its fuel regenerated by the solar panel from its exhaust
when the solar panel is generating sufficient electricity (i.e.,
during the day). The closed loop combustion generating system 80
comprises a combustion generator 82 for receiving the fuel, and for
generating a pressurized gas based upon combustion of the fuel. The
combustion generator 82 may comprise a turbine generator or a
piston generator, for example, for generating electricity and
producing exhaust 90 as a result thereof.
[0068] The closed loop combustion generating system 80 comprises a
condenser 88 for condensing the exhaust 90 from the combustion
generator 82 to a liquid. The condenser 88 takes advantage of the
cold ambient night to remove heat from the exhaust. In the
illustrated embodiment, the condenser 88 is carried by the gas
envelope 22 adjacent the solar panel 24. The condenser 88 is spread
out adjacent the solar panel 24, which acts as a radiator for
removing heat, i.e., a large heat sink potential. With the ambient
air being about -70.degree. F. at 60,000 feet, and the heat sink
potential being about 18 W/ft.sup.2, the solar panel 24 can
effectively function as a radiator. In another embodiment, the
condenser 88 is carried by the gondola 30, and air may be forced
over the condenser to help condense the exhaust 90 to a liquid.
[0069] At least one converter 86 converts the liquid from the
condenser 88 back into fuel when electricity is being input from
the solar cell 24, i.e., during the day. The fuel comprises
hydrogen gas and oxygen gas so that the exhaust comprises water.
The converter 86 comprises an electrolyzer for breaking the water
down during the day into the hydrogen and oxygen gases, which are
stored in respective fuel storage holders 32, 34. This fuel is then
used during the night cycle for generating electricity. The water
is stored in a water storage holder 78 in the gondola 30.
Insulation and mini-heaters are used to keep the water from
freezing at the high operating altitudes of the lighter-than-air
aircraft 20.
[0070] If the water ever needs to be replenished while the
lighter-than-air aircraft 20 is in flight, the aircraft may drop
its altitude so that it is in the clouds. Once the lighter-than-air
aircraft 20 is in the clouds, water may be collected, as readily
appreciated by those skilled in the art. Along these same lines, if
the buoyant gas in the gas envelope 22 needs to be replenished,
then a portion of the hydrogen gas in the hydrogen gas storage
holder 32 may be added to the gas envelope.
[0071] A fuel cell 110 may also be used for combining the hydrogen
and oxygen gases for generating electricity. A by-product 112 of
combining the hydrogen and oxygen gases in the fuel cell 110 is
water 112, which is routed to the water storage holder 78.
[0072] The closed loop combustion generating system 80 may also
includes a second generator 100 for generating electricity. A
portion of the water 102 from the condenser 88 or a portion of the
water 112 from the fuel cell 110 may be routed to the combustion
generator 82. The combustion generator 82 can reach temperatures of
about 5800.degree. F., and the heat generated by the combustion
chamber is used to heat the water.
[0073] Once the water is heated to a pressurized gas, it is applied
to the second generator 100. The pressurized gas may drive a
turbine, as illustrated, or a piston, for example, for generating
electricity. The exhaust 104 exiting the second generator 100 is
then combined with the hydrogen and oxygen gases within the
combustion generator 82. Effectively, this is a reheat stage that
includes the addition of the new combustion gas products.
[0074] In another embodiment, the closed loop combustion generator
80' is based upon the use of a vaporization fluid such as butane or
propane for generating electricity, as shown in FIG. 11. The
elements having the same reference numerals as in FIG. 10 perform
the same function and will not be discussed.
[0075] Liquid butane or propane 130' is first routed from a
supplemental fuel holder 132' to the fuel cell 110'. The fuel cell
110' is about 50% efficient, which means the heat generated by the
fuel cell when generating electricity may be used for heating the
butane or propane. The butane or propane will also be referred to
as a supplemental liquid 130'.
[0076] In lieu of propane or butane, another liquid or gas having
similar properties may be used as the supplemental liquid. These
properties include low vapor pressure at temperatures between
-30.degree. F. and -70.degree. F., and a much higher vapor pressure
at temperatures between 110.degree. F. and 180.degree. F. For
example, the supplemental liquid has gas properties of 0 psig vapor
pressure at -60.degree. F. (in the condenser 140'), and between
150-200 psig at 110.degree. F. (at the fuel cell 110'). Propane or
butane, for example, condenses to a liquid at about -60.degree. F.,
which is the same temperature as the ambient atmosphere at 60,000
feet. Thermal removal rate is about 18 W/ft.sup.2.
[0077] The heat generated by the fuel cell 110' is used to pre-heat
the supplemental liquid 130'. When the supplemental liquid 130' is
heated, it vaporizes at a much lower temperature. As it heats, the
liquid butane or propane turns into a gas. The goal is to convert
from liquid to vapor within the fuel cell 110' which maximizes the
effective heat transfer associated with the latent heat of
vaporization. The gas is routed to the combustion generator 82'. As
the gas is heated even higher, it becomes more unstable and becomes
a pressurized gas which increases the volume that is maintained
near constant pressure.
[0078] The pressurized gas 103' is used to drive a second generator
100' for generating electricity. The exhaust 104' from the second
generator 100' is routed to a second condenser 140'. The condensed
supplemental exhaust 105' is routed to the supplemental liquid
holder 132'. In the illustrated embodiment, the second condenser
140' is also carried by the gas envelope 22' adjacent the solar
panel 24'. In another embodiment, the second condenser 140' is
carried by the gondola 30', and air may be forced over the
condenser to help condense the gas to liquid form. The exhaust 104'
will be in the form of an expanded gas. The ambient temperature
will cool the gas back to the supplemental liquid 130' (a point of
re-liquefaction/condensing). This process for the supplemental
liquid 130' does not occur naturally at or near the earth's
surface, for instance, below 20,000 feet altitude.
[0079] In yet another embodiment of generating electricity during
the night, a closed loop fuel cell 80'' is used, and the
supplemental liquid 130'' is heated by the fuel cell 110''. The
supplemental liquid 130'' is heated until it becomes a pressurized
gas 133''. The pressurized gas 133'' is used to drive a generator
84'' for generating electricity. The generator 84'' is a turbine
generator or a piston generator, for example.
[0080] The exhaust 90'' from the generator 84'' is routed to a
condenser 88''. The condensed supplemental exhaust 136'' is then
routed to the supplemental liquid holder 132''. As in the previous
embodiments, the condenser 88'' is also carried by the gas envelope
22'' adjacent the solar panel 24'' so that it operates as a heat
sink during the night. In another embodiment, the condenser 88'' is
carried by the gondola 30'', and air may be forced over the
condenser to help condense the gas to liquid form.
[0081] Another advantage of this particular embodiment is that the
system can be reversed during the day for generating electricity.
That is, the supplemental liquid is heated by the solar panel 24 so
that it becomes a pressurized gas for driving a generator for
generating electricity, as readily appreciated by those skilled in
the art. Further, the supplemental liquid is re-condensed in the
gondola 30 by ambient air forced over a heat exchanger, as readily
appreciated by those skilled in the art.
[0082] The on-board electronics carried by the lighter-than-air
aircraft 20 will now be discussed with reference to FIG. 13. The
avionics 150 required to support the lighter-than-air aircraft
includes a number of different type communications links. A first
communications link 152 is a two-way, line-of-sight system capable
of uploading commands for controlling the aircraft's 20 systems and
payloads, and downloading the status of all on-board systems and
mission payload data. This communications link may operate at the
Ku-band and is capable of providing uplink rates of at least 200
kbps and downlink rates from 2 Mbps to 274 Mbps.
[0083] A second communications link 154 includes one or more
satellite communication systems to be used for both vehicle and
payload control and monitoring as well as transmission of payload
data. A third communications link 156 includes VHF/UHF radios for
providing a direct communications path to air traffic controllers.
It also allows a remotely located "pilot" to communicate with a
controller, thus providing a standard interface to the world. The
avionics 150 also includes a radar 158 and a camera 159.
[0084] The navigation controller 160 cooperates with the propulsion
system 28 to move the lighter-than-air aircraft 20 along a desired
flight path while the solar panel 24 is oriented in the direction
of the sun. The navigation controller 160 receives information on
the location of the lighter-than-air aircraft 20 from a GPS
receiver 162. An altimeter 170 provides altitude information to an
envelope controller 172 for controlling the profile of the gas
envelope 22 based upon the altitude. As discussed above, the gas
envelope 22 may be in a retracted position at low altitudes, but as
the altitude increases and the buoyant gas expands within the gas
envelope, then the envelope controller 172 places the gas envelope
in the expanded position.
[0085] Flight controls/mission computer 180 interfaces with the
other electronic devices on-board for providing overall control of
the lighter-than-air aircraft 20. An aircraft condition analysis
and management system (ACAMS) 182 is also carried by the
lighter-than-air aircraft 20 for providing aircraft
diagnostics.
[0086] Many modifications and other embodiments of the invention
will come to the mind of one skilled in the art having the benefit
of the teachings presented in the foregoing descriptions and the
associated drawings. In addition, other features relating to the
lighter-than-air aircraft is disclosed in the copending patent
application filed concurrently herewith and assigned to the
assignee of the present invention and is entitled LIGHTER-THAN-AIR
AIRCRAFT AND RELATED METHODS FOR POWERING THE SAME, attorney docket
number GCSD-1597 (51404), the entire disclosure of which is
incorporated herein in its entirety by reference. Therefore, it is
understood that the invention is not to be limited to the specific
embodiments disclosed, and that modifications and embodiments are
intended to be included within the scope of the appended
claims.
* * * * *