An operational tethered aerostat system, which demonstrates utility of LTA systems, is described. It was made possible by development of a reliable tethered aerostat that is used to support broadcast equipment at an altitude of 10,000 feet. Two elements of the TCOM system, the aerostat and mooring station, are particularly relevant to the LTA Workshop. They demonstrate the feasibility of using LTA vehicles in real, operational, all-weather applications and, in addition, illustrate an advance in the overall technology base of LTA. The aerostat and the mooring station, including their technical design features and demonstrated performance characteristics, are described

Menke, J. A.

English

NASA Technical Reports Server

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N,'/6- 15 067 ;
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- A REVOLUTIONARYAND OPERATIONALTETHEREDAEROSTAT
SYSTEM ILLUSTRATING NEW LTA TECHNOLOGY
James A. Menke*
3"
ABSTRACT: A tethered aeros':at system, which demonstrates !
utility'of LTA systems, has been in operation for about i,
one year. It was made possble by development of a reli-
able tethered aerostat that is used to support b_oadcast
"" equipment at an altitude of 10,000 feet. Two elements of
the TCOM system, the aerostat and mooring station, both
designed and manufactured by Sheldahl, are particular1 7
relevant to the LTA Workshop. They demonstrate the
feasibility of using LTA vehicles in real, operational,
all-weathe;r applications and, in addition, illustrate an
advance in the overall technology base of LTA. This
paper presents a description _f the aerostat and the
mooring station including their technical design features •
and demonstrated performance characteristics.
_ INTRODUCTION
:_ A revolutionary new' telecommunications concept has been developed that
i utilizes a Lighter to broadcasting equipmentThan Air vehicle elevate
_r as shown in Figure 1 It is very likely the only operational I.TA
il._ system in service anywhere in the world today. '
':• Developmental work by Sheldahl over the past five years has produced
> certain technological breakthroughs which enable tethered buoyant
_' vehicles or aerostats to be employed in practical around the clock ;
_,_ operations. Heretofore, such vehicles have been limited to short
_ duration scientific experimental use
_ •
* Manager, Tethered Aerostat Systems, Sheldahl, Inc., Northfield,
Minnesota, U.S.A.
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The wo_'d need for a tethered aerostat which will float continuously i
over a fixed earth location with payload carrying capacity is quite
extensive. For example, developing countries around the world cannot
afford elaborate conventional communication networks such as are
employed in the United States that use a combination ol microwave
: broadcasting towers, telephone wiring networks and sate!lites. :
The advent of a practical aerostat (balloon) system enables such a
country to very economically acquire effectively a two-z_ile high
i broadcasting tower, or mini-satellite which can carry electronic _
broadcasting and relay equipment. Such electronic equipment suspend_J _o
from a single aerostat flying nearly two miles (IO,O00 feet) overhead,
.,7-".',', I
Figure 1
Tethered Communications System
can provide direct line of sight communications to an area coverinq
45,000 square miles, blultiple aerostat installation_ can extend th_s ;.
coverage indefinitely. 'I'hu_, a single aerostat installation can take
the place of about 15 conventional ,,icrowave towers and yet offer .'.
much broader communications :apability at 20 to 50 percent the cost _,
of conventional equipment. '_:
The 'room Corporation, a subsidiary of the _'estinghousc Electric "_;
Company, has been established to integrate and market this revolu-
tionary telecommunications system, called the 'l'CObl (for Tethered
C()Mmunications) system, on a worldwide basis. At the present tl,.e,
a complete demonstration system is in operation at 'l'CObl's (;rand
Bahama Island fa_llit)' and operational systeras are being in.stalleO ;;
in the Republic of South Korea and lran. ,_,_
,¢
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6x4 RIa_Itt)I;U('IBII,ITY OF TIlE
: ORIGIN.\LPAGI" kSPOOR#
1976007927-605
This paper will deal with the two major elements of the TCOMsystem
that are particular!y relevant to the LTA Workshop, that is, the
aerostat and its mooring system. They demonstrate the feasibility of
using LTA technology in real, operatiopal, all-weather applications
and, in addition, illustrate an advance in the overall technology
baze of LTA, parti, ularly in the areas of structural design, flexible -.
materials, and manufacturing operations.
DESCRIPTION
The aerostat and mooring station as shown in Figure 2 constitute a
single system. During all phases of operation, inc!uding launch and ¢
retrieval, the aerostat and mooring station are joined and function
as an inseparable system. The aerostat is flown directly from _he
mooring station. Both the aerostat and mooring station automhtlcally
rotate so that they are aligned wit_ respect to the wind.
|
_'_ Figure 2
Moored Aerostat
l'wo features of the system that make the TCOM telecommunicatio,s
concept economically feasible are the small crew size needed ,rid Its
all-weather operating capability. Since this concept requires that
the "Jerostat remain aloft for weeks or months at a time, a large full-
time ground crew is cost prohibitive. The _/stem, both mooring
station and aerostat, also had to be designed to withstand worldwide
environments, primarily winds and temperature, without hangar
facilities.
.
Aerostat
The aerostat described herein and illustrated in Figure 3 i_ the
Sheldahl Model CBV-250A. Speciflcation:_ are presented in F:"_rc 4.
It is capable of supporting sizeable payload, at altitudes _.p to
15,000 feet above mean sea level. Nomin:,l operatlag altLtuJe Ls
lO,O00 feet.
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:. MODEL NUMBER 4"
CBV-250A CBV-350A .(.
" WEIGHT 5,100 ibs 5,500 Ibs ;
,j
DIMENSIONS
-! Hull Volume 267,000 cuft 380,000 cuft 2
OveraI1 Length 175 ft 215 ft ,2.
tqO',
Hull Length 148 ft 188 ft ,;
,f
Hull Diameter 56.8 ft 56.8 ft i'
) ¢
Fin Spap 81.5 ft 81.5 ft 4.
Payload Enclosure Width 25 ft 25 ft :
' _i Payload Enclosure tleight 15 ft 15 ft !
OPERATIONAl, PERFORMANCE _
r;;
• ._ Wind Speed @ blSL 90 knots 90 knots ,"3 ';
Wind ',peed @ 10,000 ft 100 knots 100 knots ;
: _' Ceiling Altitude above MSL 1_,00 nft 15,000 ft
{_ I '
7 _ LOAD CAPACITY (PA___YLOAD,POWER PLANT, FUEL)
i? @ 5,000 ft 7,000 lbs 12,000 lbs
,.'.' ,? 10,000 ft 4,0./0 lt)_ 8,000 lbs
_ _a 15,000 it 1,000 lbs 4,000 lb._
Figure 4 ',
Ae:'o_tat Specificat ion_
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1976007927-608
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•; The aerostat is controlled or "flown" from the _round control station.
It is unmanned and can maintain its position in the immediate vicinity
of the launch site for continuous flight durations approximating one
week Retrieval to ground level for refueling, helium replenishment
and other maintenance can asually be accomplished within a few hours
and the mission resumed. The aerostat is a highly reliable, rugged
' vehicle constructed to withstand ve;y severe weather conditions. It f
;" is designed and constructed to operate safely in 85 knot winds and
carry a 4,000 pound load at an altitude of 10,000 feet.
ilu11 pressure is maintained by a conventional ballonet design. Fans
. and valves are automatically cycled to force air into or out of the
' batlonet thereby controlling pressure to within prescribed limits. ,e
The hull nose structur_ is made from a high strength aluminum alloy
,_.! and is provided for docking the vehicle to the mooring station.
, ¢?
The main payload attachment point en the aerostat hull within the
c payload enclosure is capable of supporting a package weighing up to
e
1,500 pounds. The volume availabIe for the payload ins;de the enclo-
sure is that of a 25 foot diameter hemisphere. In addition to tileI
main payload support structure, he underside of the aerostat has
provisions for attaching other hardware such as the airborne power ..
generator, fuel and fuel tanks. This load attachment provision
extends 113 feet fore and aft on the underside of the aerostat.
_Jo_ori_S t a ti___ o_
The mooring station is a permanent installation with primary fm,ctions
to a) serve as the ground anchor for the aerostat when tt is on
., station, and b) serve as a maintenance station for the aerostat
between missions. The mooring system is shown in Figure 5.
?' A reasonably level area approximately 500 feet in diameter is needed
to provide adequate ground clearance for the moored aerostat. A
concrete pedestaI is located at the center of this area to support
the main winch and enclosure as well as the mast. Concrete footings
are also t'rovided for the nonorail. These footings can either be a
full circle of era,crete or smaller footings at each rail an,:hor point.
The mooring area net i not be paved, llowever, gravel or some other
stable surt'acc is n cessary *o carry erection and maintenance
equipment.
The mooring _tation consists of a central macilinery enclosure and
masl mounted on a large central bearing, a horizontal boom COml,ression
member and a circular monorail which supports the outboard boon,, end,
flying :;heave and clo._e-huul winches that are mounted on rollers. \
mechanical lock with a remote electrical release is provided at the
top of the mast. Work surfaces are provided on tile top deck of the
machinery enclosure, on tile boom and at the locatton of the acrostat
payload when it is moored. A diesel powered main winch and an auxil-
iary power unit locat,,d within the mochinery enclosure furu!sh the
power req,ired to laur, ch and retrieve the aerostat and *o _,mo_ it in
the close-hauled mode. The main winch is used to control and st,. ....
the tether cable during fligl:t operations. Three smaller wi:_ch_:,,
one at the base of the mast and two on the circular rail, plovlde
the restrai_ ts and control during early stages of launch ap.l d_t" _,.,,.
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ORIGINAL t_AGE IS POOR
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1976007927-610
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final recovery. A completely enclosed operator's cab is located on
the forward side of the machinery enclosure, providing visibility to
all operational areas. The specifications for this system are pre- , '_
sented in Figure 6. -"
, The principle feature of this design is its ability to be rotation-
ally drive::, either by the forces generated by the aerostat or exter-
nally, to align: in azimuth, with the aerostat or its tether cable.
This allows a single operator to maintain the balloon in flight and
only a four member crew to launch and recover the aerostat. During
servicing and maintenance when moored, the crew rides with the t
system as it rotates into the wind thereby provi,ting improved acces- ,i:
" sibility and greater safety and again reducing "the crew size require- ,_._
ment.
SYSTEM PERFORbtANCL
z
¢
When moored the aerostat is mechanically locked to the mooring mast
._--' at tile nose and secured by its suspension lines to the _ervice plat-
form under tile aerostat payload. In this configuration, any changes
in wind direction will cause a rotation of the COh_.plete system and
maintain the balloon heading into the wind. It also allows the
field crew to "ride" the mooring system and work w_thout concern
for shifting winds and gusts. In relatively calm weather (winds less
than 15 knots}, the brakes can be engaged so that heavy loads, such
as the aerostat pa.vload, can be transferred from truck to work
plat form.
The entire system is designed to sustain 90 knot wind loads with the
aerostat in its moored mode. 'l'h,_ a critical componc,_t design was
that of the nose structure of the aerostat since it provides the
mechanical attachment of the flexible aerostat {q the rigid mooring
tower, blaximum loads anticipated in 90 knot wilds including dynamic
loads are 2o,000 pounds axial and 15,000 pound s:_de load. The
structure has been successfully tested to these w, lues.
When tile aerostat is moored, a 3 to 5 knot wind 10 degrees off the
aerostat heading will cause the mooring station to realign itself
into the new wind direction.
The maximum operating altitu,le for the aerostat is a function of
aerodynamic forces on the aerostat and tether cable, helium volume
at altitude, total weight aloft, and environmental factors, such as
temt_erature and baromc.tric pressure. The CIW-250A vehicle can attain
an altitude of 15,0t)0 feet; however, payload capability at thi.-
altitt,de is extremely limited. Typically, the t'IW-250A is flo_'n at
I0,000 feet with a ,1,000 pound load. Ascent and descent rates are
approximately 200 feet per minute.
The aerostat is de<igned to operate in wind ._peetls up to 90 knots at
sea level and higher speeds corre:;ponding to a dynamic pres, ure of
27 pounds per square feet at higher altitudes.
tilectrical power for vehicle and payload operation is _upplied by
either on-board rotary engines COUl',led to I_,oshless generator,; or
by using tl,e tether cable as a condt,ctor to transmit power from a
ground source,
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1976007927-611
MODEL NUMBER ,
18500 18600 :
APPLICATION CBV-250A Aerostat CBV-350A Aerostat • _.
" WEIGHT 95,600 lbs 99,600 lbs ,
DIMENSIONS ,_;
Rail Diameter 173 ft 203 ft ,e,.
Tower Height 47 ft 47 ft " :
Payload Service
Platform 16 ft x 22 ft 16 ft x 22 ft .}
Machinery
:._-" Enclosure 12' W x 9' H x 31' L 12' W x 9' H x 31' L :
STRUCTURAL CAPABILITY _
Wind Speed (With
_' Aerostat Moored) 90 knots 90 knots
.}_ Wind Speed (Without
¢_ Aerostat) 120 knots 120 knots
_'_' Operating Temperature -30°F to +120°F -30°F to +120°F
_, Design Criteria AISC Standards, AISC Standards,
_, 7th Edition 7th Edition
HYDRAULICS (Supplied by OECO)
, Main Winch
Tether Cable
Capacity 20,000 ft 20,000 ft
Maximum Pull 30,000 Ibs 30,000 lbs
Maximum Line Speed 200 fpm 200 fpm ,
Close Haul Winches (3) :
Maximum Pull 12,000 lbs 12,000 lbs
Maximum Line
Speed 140 fpm 140 fpm
Figure 6
Specification Summary, Sheldahl
Aerostat Mooring Sy';tem
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,. EXPERIENCE
A total of six aerostat systems have been built and three additional
t systems are presently under construction. One of these systems has
: been in operation on Grand Bahama Island for the past 14 months
providing television coverage for the outer islands.
,_ During this initial 14 month operating period many performance
features of the system have been demenstrated. For example, the
•; aerostat has flown in 85 knot winds, in electrical storms, and in
heavy rain. The aerostat has remained on station aloft continuously
for five days. Highest recorded superheat has been 25 degrees
Fahrenheit. Supercooling at night has been as low as 10 degrees
Fahrenheit. Tests of material samples removed from the hull after 12 ,,
months indicate no significant degradation. The aerostat has been
launched in ground winds gusting to 35 knots. Ease of servicing both
the aerostat and payload in variable direction ground winds has
._.. verified the functionalism of the autowatically rotating mooring '
system. Launch and recovery operations have been conducted with only
a four man crew.
FUTURE PLANS
At the present time a complete system is being installed in Korea.
It will be fully operational this year. Shortly thereafter, a system
will be installed in Iran.
A "stretched" version of the aerostat has been designed and is cur-
rently under construction. Its configuration will be identical to
the CBV-250A except that a 40 foot cylindrical section will be
added at the major diameter of the hull, thereby increasing hull
: volume by 100,000 cubic feet. Payload capacity will be increased
to 8,090 pounds at 10,000 feet altitude. The mooring system design
has also been modified to accept the larger vehicle. This larger
vehicle designated CBV-350A will undergo flight qualification tests
eariy in 1975.
SUMMARY
What is the significance of this new telecommunication system
development as it relates to airships? Materials and technology, of
course, are common to both. Further, based on experience with
tethered aerostats, it is the opinion of this author that airships
can be designed and constructed to operate as reliably as conventional
aircraft, ttowever, one of the more pertinent questions that must I,e
answered is: "Will the airship solve a problem or provide a service
more econoh, ically than other transportation systems?" There are,
of course many other issues and influences that must be considered,
such as energy consumption, government subsidies, etc.. but the key
issue should be one of economics. The telecommunication system is
viable mainly because the service it provides is done at a fraction
of what it would cost if provided by other more conventional means.
In like manner, if objective studies show that airships could sol'.'e
a problem or provide a service at lower cost_ when compared to other
solutions, then and only then would there be any merit in their
development.
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A revolutionary and operational tethered aerostat system illustrating new LTA technology

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