A_Novel_Concept_for_Stratospheric_Communications_and_Surveillance_StarLight.pdf

7/28/2019 A_Novel_Concept_for_Stratospheric_Communications_and_Surveillance_StarLight.pdf

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American Institute of Aeronautics and Astronautics

1

A Novel Concept for Stratospheric Communications and

Surveillance: StarLightAdam Chu1, Mo Blackmore2, and Ronald G. Oholendt3

Near Space Systems Inc., Colorado Springs, CO, 80919, USA

Joseph V. Welch4, Gil Baird5, David P. Cadogan6, and Stephen E. Scarborough7

ILC Dover LP, Frederica, DE, 19946, USA

StarLight is a first-ever, persistent, maneuverable, high-altitude, hybrid, lighter-than-air (LTA) vehicle designed to provide continuous communications and surveillance

capabilities over a wide geographical area. StarLight will operate at an altitude between70,000 and 100,000 feet mean sea level, for a minimum duration of 6 weeks, giving its

payloads an operational area of coverage exceeding 160,000 sq miles at maximum altitude.

In addition to its LTA capabilities, StarLight incorporates an innovative flight controlsystem to provide a maneuverable vehicle capable of station keeping and/or flying a specified

ground track. Control innovations include a mechanically -driven rotating lower stage toeasily change the direction of thrust (0-360), and an actuator control that changes the

pitch/roll attitude of the upper stage balloon envelope to accommodate vertical maneuvering

above neutral buoyancy. The associated concept of operations allows for remote operations

with minimum logistics and infrastructure. The total system design provides multi-

functionality to maximize platform utility and easily support defense, security,

communications, intelligence, earth sciences and other federal and commercial applications.

I. Introduction

ear space is the area of our atmosphere between 65,000 and 325,000 feet above the earth. It is a virtual no-

mans land, visited only occasionally by scientific ventures. Near space offers the strategic advantages of space

without having to leave our atmosphere while presenting better responsiveness, lower cost access, and higher sensor

performance than space. Near space avoids the air traffic and vulnerability found in commercial airspace byoperating in air that is too thin for normal combustion engine driven aircraft.

StarLight (formerly known as MaXflyer1), is a patent pending, lighter-than-air, unmanned, two-stage, hybrid

near space vehicle that is currently being developed by Near Space Systems, Inc. StarLight can operate in near

space for months at a time. The system is designed using innovative, vacuum infusion composite engineering for

light weighting vehicle structures and creating housing and support for photovoltaic cells, power storage, vehicle

control systems, communications, and sensor systems. StarLights design uses state-of-the-art, highly efficient

power generation and storage to provide power for a 24/7 duty cycle of the platform and payload. Micro-engineering

plays a significant role in light weighting and reducing power requirements of the vehicles sensing and control

systems.

The StarLight concept of operations allows for minimum logistics and infrastructure. The total system design

provides multi-functionality to maximize platform utility in supporting security operations. The StarLight design

minimizes manufacturing costs and risks. The vast majority of the system components are commercial-off-the-shelf

(COTS). The two major unique components are the upper stage balloon envelope and the lower stage compositestructures. The balloon envelope will be manufactured by ILC Dover (Frederica, DE) while Enfusion Technologies

1 Chief Scientist, Near Space Systems, 8610 Explorer Dr. Ste 140, Colorado Springs, CO, Non Member2 President and COO, Near Space Systems, Colorado Springs, CO, AIAA Member3 CEO, Near Space Systems, Colorado Springs, CO, Non Member4 Senior Analysis Engineer, ILC Dover, One Moonwalker Road, Frederica, DE 19946, AIAA Senior Member5 LTA Program Manager, ILC Dover, AIAA Member6 Director or Research and Technology, ILC Dover, AIAA Associate Fellow7 Senior R&D Engineer, ILC Dover, AIAA Senior Member


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(Colorado Springs, CO) will manufacture the lower stage composites. The vehicle will be produced as an assemble-

on-site product. Assembly of the product on site just prior to launch benefits the customer by reducing

infrastructure and logistic requirements. These benefits translate to lower customer costs. The StarLights modular

design permits continuous component improvements without the necessity of platform redesign. The lower stage

and payload boxes will be pre-configured and stored in their shipping containers until needed for employment. The

StarLight is shown in Figure 1.

II. Operational Applications

StarLight is designed as a common platform that provides communications, imaging, data collection, and

navigation from near space for the widest range of commercial and government applications. Near space provides

strategic area coverage similar to space-based assets, but for a fraction of the cost of launching and maintaining

satellites in orbit. Since near space is below orbital altitudes, a constellation of platforms (satellites) is not required,

further reducing costs. Near space platforms can remain overhead a large geographical area. Since near space is

closer to earth than space, resolution and sensor sensitivity result in higher operational performance.

Domestic and international customers need persistent, cost effective, wide field of regard communications,

remote sensing, and (for military customers) force applications capabilities. This is readily illustrated by the sums of

money government and commercial agencies from around the globe are currently spending to gain these

communications/remote sensing application capabilities from space. A single space communications satellite can

cost billions of dollars to launch and operate over its lifetime. Providing wide area coverage from space requires

multiple satellites or highly expensive individual satellites at higher orbital altitudes, multiplying the costs associated

with these space systems. Air vehicles operating at 65,000 ft and below, providing greatly reduced persistence and

field of regard comprise another multi-billion dollar world market. Simply put, StarLight provides cost effective

operational capabilities that cannot be duplicated by platforms at other altitudes/operating regimes. With the tailored

payloads that are part of the StarLight design, the vehicle provides users with persistent communications, remotesensing, and (for military users) force application capabilities at a small fraction of the cost required by lower

altitude air, or space-based platforms.

The expanse and applications for commercial and government uses are seemingly unlimited. In summary, a near

space platform can provide space based capability more effectively and for a fraction of the cost compared with

other current methods. The areas of commercial and government applications are summarized below:

Figure 1. StarLight


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A. Communications:

Extend ground-to-ground, ground-to-air, and

ground-to-space voice communications beyond

line-of-sight

Extend wireless, broadband communications

beyond line-of-sight

Provide digital communications

Provide data link gateways and extend range

beyond line-of-sight

Selective Jamming

B. Remote Sensing and Imaging:

Persistent Intelligence, Surveillance, and

Reconnaissance applications

Collection of intelligence (signal, images,

electronics, communications)

Security:

Communications and surveillance for United

States borders and strategic resources

Communications and surveillance for

significant strategic events such as inaugurations,

conventions, public events

Intelligence gathering for the Department of

Homeland Security

C. Disaster Response:

Providing communications, imaging, and

sensing support before, during and after naturaldisasters such as hurricanes, tornados, wildfires,

floods, etc.

Reconstitute lost telecommunications

D. Vehicle and Object Tracking and

Identification:

Trucking and other shipping companies, local

and interstate

Taxi, limousine service

Supply and supply chain services

E. News and Public Information Services:

Public Information Broadcast

Emergency service information

Local, state, and federal information where

coverage does not exist today

Supporting search and rescue

F. Navigation:

Backup to GPS capabilities

G. Sciences:

Monitoring of air and water quality

Monitoring of agriculture (moisture, soil

conditions, crop conditions)

Monitoring of infestations

Monitoring of habitat, endangered species

Monitoring weather

H. Research and Development, Testing

I. Mapping

III. Lower Stage

The innovative lower stage contains all the functionality of StarLight. All controls, power, and payloads are

located in the lower stage as illustrated in Figure 2. The highlights and unique features of the lower stage include:

Manufactured with space qualified, lightweight composite material

Redundant motors for propulsion and flight controls ensure operability

Solar arrays incorporated into the lower stage saves weight and eliminates thermal stress on the balloon

envelope; the solar arrays also ease assembly, launch, and recovery

Plug and play payload box is easily replaced for mission changes requiring different sensors

Other balloon envelope problems common to many designs, such as heat stress from photovoltaics on the surface

of the balloon envelope, drove positioning of the solar cells and all platform functionality in the lower stage. There

is a penalty to pay by losing some direct sunlight on the photovoltaics through the translucent balloon envelope, but

the performance gains significantly outweigh the disadvantages. The solar array is sized to provide sufficient power

with albedo light during periods of high sun angle. The environmental conditions of high altitude and the need to

control the pitch of the upper stage led to the requirement to suspend the lower stage at a prescribed distance below


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the upper stage. The design of the lower stage and associated functional systems evolved, as we sought to

continuously reduce weight and solve challenges arising from developing a feasible operational employment

concept. The end result being a configuration for the lower stage with a plug and play, pre-configured payload

system.

The lower stage employs a modular design. Individual components can easily be modified or replaced. This

modular approach simplifies shipping and assembly, as well as design changes. The lower stage components such

as batteries, photovoltaics, autopilots, etc., will be primarily COTS products provided by a number of vendors.

The payload box is preconfigured for each customer, allowing for plug and play integration into the lower stage.

Customers can have multiple payload packages to meet their operational requirements. This allows maximum

flexibility for employment and the opportunity to fly complimentary payloads together on different StarLights

while flying in formation.

The StarLight lower stage is engineered specifically for persistent, high altitude LTA operations. The lower

stage structural components are made from lightweight, high strength carbon cloth reinforced composite material

that is precisely manufactured using the vacuum infusion process. The composite material is infused with space-

qualified, ultraviolet radiation (UV)-resistant resin. The lower stage structural components include the solar arrays,

fuselage, payload box, propulsion motor braces, flight control functions, and landing structures. The lower stage is

recoverable and reusable, and features redundant control functions for mission success and safety. The fuselage

houses and supports all the functional operating systems of the vehicle to include the power collection and storage,

propulsion, flight controls, communications, command and control, and the recovery system.

The lower stage makes maximum use of COTS components to minimize development, acquisition, operations,

and maintenance costs. The lower stage ships and stores in boxes, simplifying logistics and lowering costs. At thelaunch site, the lower stage is assembled with hand tools, tested, and readied for flight. Lower stage maintenance

benefits from easy access panels for component removal and replacement.

IV. Upper Stage

The primacies of persistence, survivability and costs drove consideration of LTA concepts during analysis of

alternatives. In order to achieve the above performance and operating characteristics, the design has to minimize

drag and weight, while maximizing thrust. Historical and current airship design concepts were analyzed. Traditional

cylindrical and spherical designs were considered, but ultimately not selected. The high drag components of these

shapes for forward flight and turning require a propulsion system with very high power demand and weight

penalties. The result would be an undesirably large platform. Weight is also saved in the StarLight design as

compared to traditional cylindrical/spherical airships because the StarLight is a super-pressure system and thus

Figure 2. Lower Stage with Laterally Displaced Propulsion


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does not utilize a ballonet. The larger the airship platform, the more expensive it is to build, operate, and maintain.

Larger airships are also more vulnerable to attack, weather and structural failure. One other key aspect of the upper

stage is that it is a disposable, low cost envelope.

Our research drove us to an ellipsoidal design due to the shapes low drag characteristics and positive lift-to-drag

ratio throughout the range of anticipated pitch changes. The ellipsoidal shape minimizes frontal cross-sectional area

(Figure 3) and rear wake size, while maximizing maneuverability against changing winds. The ellipsoidal shape of

the upper stage is maintained at altitude by super-pressure of the helium gas and use of mass efficient internal shape

control spars/catenaries2-6. Extensive CFD analysis of the StarLight aerodynamics has been conducted, greatly

increasing confidence in the superiority of the StarLight design.

The StarLights positive lift to drag ratio with positive pitch enables platform climbs above neutral buoyancy

during high wind surges. The altitude gained in the climb is used to accelerate the StarLight in a dive to recover

the distance lost during the wind surge. The illustration in Figure 4 illustrates StarLights unique climb and dive

maneuver that allows it to station keep when winds exceed thrust capability.

Figure 3. Comparative Cross-Sectional Areas of Various Airship Shapes

0

200

400

600800

1000

1200

1400

1600

1800

2000

0 20000 40000 60000 80000 100000

Volume, m3

FrontalC

ross-Sectional

A

rea,m

2 Saucer

Blimp

Sphere


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A. Envelope Design

The StarLight upper stage consists of the super pressure balloon envelope with its attachment lines and

associated load patches. The upper stage performance is critical in meeting certain operational system goals.

Driving requirements for the upper stage are:

1) Balloon shape lift and drag properties

2) Inflated shape maintenance in all thermal environments

3) Float altitude

4) Structural integrity under maximum super-pressure

5) Low cost, disposable design

6) Materials durability and negation of pinholing (all flight phases)

The lift and drag properties directly relate to the station keeping and maneuvering system requirements. The

upper stage balloon envelope must maintain positive differential pressure in order to achieve this ideal shape. The

challenges for shape maintenance arise from the minimum cold state and the effect of leakage during operational

life. Float altitude is the traditional analysis trade for super pressure balloons. The maximum hot day at float

altitude determines maximum super pressure. This maximum super-pressure is used in the stress analysis of the

upper stage envelope material, which would verify the structural integrity.

There are several interactions and dependencies in the design calculations for super pressure balloons. In the

case of StarLight, the importance of the aerodynamic shape is added to these. In the performance of these analyses

a best in class tool set was used including high fidelity CFD, Abaqus FEA, Navajo Trajectory7, and ThermalDesktop.

The primary input to the patent pending envelope design was the discovery that ellipsoidal asymmetry plays a

significant role in overall aerodynamic performance. Parametric analysis of two primary functions, the envelope

height-to-width ratio and the ratio of envelope volume above and below the equatorial chord line, revealed that

asymmetry in both areas contributed to the lowest drag coefficient with the highest lift coefficient. Both factors

relate directly to performance in the upper atmosphere. A cross section plot of this ellipsoidal shape is shown in

Figure 5. The challenge was to develop low stress inflatable shapes that came close to the theoretical shape, while at

the same time had acceptable weight. Design trades were conducted to develop potential envelope concepts. As

1. StarLight can resistwinds up to 30 knots

2. For wind > 30 knots

StarLight pitches upto maximum Cl/Cd.

StarLight climbsabove neutral buoyancy

Wind Direction

Neutral Buoyancy Altitude

3. At max Altitude gain,

Lift=Gravity,

StarLight will driftdownwind until wind

surge passes

4. StarLight will pitchdown to dive and

accelerate recovering

ground distance lost in

drift

Direction

of acceler

ationdurin

gdive

Figure 4. StarLights vertical maneuver is enabled by the aerodynamics of theupper stage balloon shape and functionality of the vehicles flight control systems,

separating StarLight from other LTA concepts


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aerodynamic results were derived from CFD modeling, the trades were updated and advanced in an iterative

process.

A view of the upper stage shape selected in the trades is shown in Figure 6. The oblate shape is held under

pressure by spars that run forward to aft. This spar concept has been successfully used by ILC Dover in a number of

inflatable wing and aerostat fin designs. The spacing of the spars is a balance of matching the ideal aerodynamic

shape versus the added weight of each additional spar sub-assembly. Iterative analysis has shown that six spar sub-

assemblies are needed. In this concept, nominal skin stresses from pressurization are limited by the radius of

curvature in the center section which is much lower than that of the natural oblate ellipsoidal shape. To verify

patterning and manufacturing ability, a small scale model was fabricated at ILC Dover (Figure 7). Note that this

model was fabricated out of a thin polymeric film material (not the operational material) to verify the patterning

technique and the inflated shape dimensions.

Radius

Height

Radius

Height

Figure 5. Cross-Section Profile of the Ideal Upper Stage Shape

Figure 6. Selected Upper Stage Shape


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B. Aerodynamic Analysis

High fidelity analysis of the platform aerodynamics during development is critical to validating the design and

increasing the probability of successful achievement of performance requirements. For the aerodynamics of the

upper stage the lowest possible drag coefficient was sought while maintaining a positive lift to drag ratio throughoutthe flight regime. Near Space Systems conducted internal computational fluid dynamics (CFD) analysis on the upper

stage shape throughout the design process to validate or invalidate design characteristic and projected performance.

In May, 2006, the United States Air Force approved a project to independently analyze the flight characteristics of

StarLight. Based on current mission needs, the government wanted to validate that the StarLight design could

successfully operate in the cold, rarified environment of the earths stratosphere in a persistent manner. The

processing capability of the Major Shared Resource Center (MSRC) at Wright-Patterson Air Force Base in Dayton,

Ohio allows significantly higher fidelity CFD analysis of StarLight than the earlier lower fidelity CFD modeling

could provide. The MSRC is a computational science facility supporting DoD research, development, test, and

evaluation using high-performance computing and visualization. Critical aerodynamic performance factors were

used in the CFD modeling. Extensive resources in terms of CPU time have been devoted to this task. An example

output of the simulations on the chosen upper stage shape is shown in Figure 8. These results, along with the

manufacturing considerations, are the main reason that this particular shape concept was chosen. The results of

MSRC CFD analysis is a higher design confidence, an optimized balloon shape for maximum performance, andlower overall project risk.

The MSRC CFD analysis on the StarLight saucer shaped body is focused on how much drag and lift the

aerodynamic lifting body presents to the wind as a function of angle of attack or pitch angle, altitude and wind

velocity. Once these aerodynamic forces were calculated, codes were developed to estimate the flight profile for

maintaining loitering position relative to a fixed geographical location as a function of wind velocity and direction.

The results of the CFD codes are critical to the assumption of either a laminar or a turbulent flow. The laminar

Figure 8. CFD Analysis of the StarLight Upper Stage

Figure 7. Inflated Table Top Model of the StarLight


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assumption results in higher (optimistic) lift to drag ratios for the different pitch angles. For the StarLight design,

we used turbulent flow assumptions, the most conservative case. Using 3-D mesh models of the StarLight shape,

below are the outputs (Figures 9-11) from the CFD calculations assuming the turbulent flow methodology.

Figure 9 shows that pitch angles from zero degrees and higher results in positive lift. This means that the

StarLight can pitch up to climb above neutral buoyancy using aerodynamic lift. Altitude gained above neutral

buoyancy is energy that is used to accelerate the StarLight in a dive allowing it to recover ground distance lost in

high velocity wind surges. StarLights vertical maneuver is enabled by the aerodynamics of the upper stage

balloon shape and functionality of the vehicles flight control systems, separating StarLight from other LTA

concepts.

Figure 10 shows the drag component for pitch angles with 30 knots of head wind. Notice that the drag remains

lowest between minus 5 degrees nose low to 7 degrees nose high. This information helps to identify pitch changes

that provide the highest lift to drag ratio. The higher the CL-CD ratio, the greater the climb above neutral buoyancy.

Zero degrees of pitch provide the least amount of drag to maximize thrust.

Figure 10. Drag Force Vs. Pitch Angle at 30 knots

Total Drag Force

WindVelocity= 30knots

0

50

100

150

200

250

300

350

-10 -5 0 5 10 15 20

Pitch Angle (deg.)

DragForce(nts)

Total Lift Force

WindVelocity= 30knots

-1000

-500

0

500

1000

1500

-10 -5 0 5 10 15 20

Pitch Angle (deg.)

LiftForce(nts)

Figure 9. Lift Force vs. Pitch Angle at 30 Knots


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Figure 11 shows the lift-to-drag ratio curve. A positive lift to drag ratio occurs when pitch is at zero degrees or

higher. Positive pitch will allow StarLight to climb above neutral buoyancy. In comparison, the results of

calculations from a laminar assumption results in lift-to-drag ratios of higher than 5 for zero degrees of pitch angle,

going up to about 10 at pitch angle of greater than 8 degrees.

C. Envelope Material Selection and Sizing

Historically, one of the greatest technical challenges to LTA design is developing an acceptable hull material that

meets the programs mass, life, and cost constraints8. The envelope material must be able to withstand the day/night

and seasonal temperature changes at the operating altitude, in conjunction with the stresses and loads associated with

operation. It is also important to note that the material must be able to survive the dynamic effects of deployment,

launch and ascent. For these reasons, and considering the harsh space-like environment at the altitudes between

65,000 and 110,000 feet, our design approach is to use a commercially proven, multi-layered polyester

film/polyester fabric. Our team also chose to decline to use photovoltaics on any part of the balloon surface because

of the thermal impact on the material. The other driver for selecting a polyester film/fabric for the envelope material

is cost, since the upper stage is disposable. Higher tenacity fibers such as Vectran or UHMWPE are available for use

in the construction or lower mass materials, but at significantly higher cost. These higher cost fibers and laminates

are still in consideration, especially if they can provide a system level performance benefit such as longer endurance,

but at this time polyester is the baseline fiber in the laminate.

A parametric super-pressure hull sizing model was created for sensitivity studies. One important parametric

component of the sizing model is material selection. Model inputs include a table of potential material candidates

including their strengths and areal weight. The sizing model selects the best candidate material based on the

structural margin goals. An early investigation was to determine if commercial off the shelf (COTS) materials could

be used for the upper stage envelope. COTS material laminates with a polyester tenacity of 4.5 gm/denier were

evaluated versus modified COTS laminates with a higher polyester tenacity of 8.3 gm/denier. The Modified-COTS

material design points were superior in terms of envelope weight by a large margin. The 3 layer lay-up of the

baseline polyester laminate material is shown in Figure 12.

Figure 11. Lift to Drag Ratio Vs. Pitch Angle at 30 knots

Lift to DragRatioWind Velocity = 30 knots

-6

-4

-2

0

2

4

6

-10 -5 0 5 10 15 20

Pitch Angle (deg.)

Cl/Cd


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In addition to cost and strength considerations, the hull material has also been selected for its low areal weight,

low permeability, and its compatible with state-of-the-art airship envelope manufacturing processes. A polyester

fabric is used to provide strength in the warp and fill directions while a polyester film layer is bonded to the fabric

using an adhesive to create a barrier layer to contain the helium inflation gas. The baseline coated fabric hullmaterial has a tensile strength of 60-lbf/in in the warp direction and 120-lbf/in in the fill direction. Related UV

exposure testing indicates that this hull material will have the endurance to withstand the UV environment above

80,000 feet for the 6 week mission, as a similar material was originally selected as a candidate hull material for the

Alternate Ultra-Long Duration Balloon (AULDB) concept9. The AULDB program had an intended mission duration

of 100 days at 100,000 feet.

One immediate outcome of the initial sizing model sensitivity runs was the strong influence that the maximum

temperature increase has on the size and weight of the envelope. Accordingly, one of the main objectives for this

initial model was to estimate the maximum diurnal increase in temperature. The thermal analyses were run at vernal

equinox with latitudes between 0 and 45 degrees. The estimate for maximum temperature increase was

approximately 32C and came from a run with 0 degree latitude. A plot of the helium temperature for this case is

shown in Figure 13. This value of diurnal temperature increase was an important input for subsequent sizing and

stress analysis modeling. It was found that the temperature results from the thermal analysis were in good agreement

with those from the trajectory modeling. As part of the trajectory modeling, the diurnal temperature result was used

to calculate the pressure change in the balloon envelope as shown in Figure 14.

The sizing model contains a first order for maximum stress in the upper stage under a uniform inflation pressure.

A more detailed stress prediction is needed to support the design effort of the upper stage. A finite element model

was constructed for the upper stage with the intent of evaluating stresses due to maximum super pressure. A quarter

symmetry model was constructed for this task. The mesh for this model is shown in Figure 15 along with some

principle stress contour results. The results indicated that the first order calculation in the preliminary sizing model

was over predicting stress by a small margin. The sizing model for the upper stage was updated with this more

detailed stress prediction.

Figure 12. Baseline Envelope Material Lay-up

Adhesive

Fabric,

Polyes

ter

Poly

ester F

ilm, Cl

ear, 0.

5 mil

Adhesive

Fabric,

Polyes

ter

Poly

ester F

ilm, Cl

ear, 0.

5 mil


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Time (days)

Temperature(C)

0 0.5 1 1.5 2

-5 0

-4 0

-3 0

-2 0

Figure 13. Hot Case Helium Temperature from Thermal Desktop Model

2750

3000

3250

3500

3750

0 0.5 1 1.5 2

Time (days)

Pressure

(Pa)

Figure 14. Hot Case Gas Pressure @ Float


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V. Launch and Deployment

StarLight is launched using an out-of-the-box technique. The upper stage and the lower stage would be

delivered to the launch site in two separate containers via ground, sea, or air transportation. The upper stage is

packed in an umbrella / Z-folded configuration that allows the top center of the envelope to remain at the top of the

shipping container. The top center of the envelope is where the helium valves are located and this will also be the

location where the helium will be introduced into the vehicle. The payload lines are located at the bottom of the

container, but can be attached to the lower stage. The payload lines are attached to the upper stage at a specified

distance from the outer edge of the envelope in twelve locations. Once the upper stage and the lower stage are

attached, a support net or a crane is used to control the motion of the upper stage as helium is introduced into the

envelope. Three sleeves, are wrapped around the envelope in various locations (and are later released by remote

actuation) during packing are used to control the

helium bubble and limit loose material exposure to the

wind during inflation. In this manner only the top

center of the envelope is filled with helium. Once the

charging is complete and the upper tethering net/crane

are removed and the helium filling tube is detached.

The partially inflated envelope will be tethered using

three guy lines attached to the upper collar, similar to

that used in the logging balloon application in Figure16. This will provide control of the inflated system

until ready for release, and facilitate operations in low

wind conditions. Once the upper stage is extended

over the lower stage and the system is checked, the

collars are released and ascent begins

The system will ascend as a zero pressure balloon

and would not reach the fully evolved aerodynamic

shape until it reaches an altitude near the float altitude.

As the system ascends, the deployment is analogous to

that of a parachute and any extra helium gas is vented

on the way up. Suspension line attachments to the

outboard location of the envelope provide natural

balance and stability to the system during shapeevolution. Launch and deployment of the system are

considered risk areas of any balloon launch and a

detailed test plan has been developed utilizing the

launch of various sub-scale models to validate these processes for the StarLight.

For vehicle recovery at the end of a mission, lifting gas is vented at a controlled rate for controlled descent of the

entire vehicle. At the appropriate descent altitude, the upper and lower stages are disconnected and a GPS-guided

parachute is deployed from the lower stage for controlled landing in a designated location. The gas depleted upper

stage lands in a designated area in the vicinity of the lower stage.

Figure 15. Finite Element Model Mesh and Sample Principle Stress Contours

Figure 16. ILC Dover Manufactured Logging

Balloon Supported by Ground Tethers


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VI. Conclusion

The StarLight hybrid LTA vehicle can provide continuous communications and surveillance capabilities at

70,000 to 100,000 feet at a significantly lower total cost than comparable space-based platforms. The concept is

unique from other high altitude LTA vehicles because it utilizes a two stage design where the upper stage is a lifting

body. This two stage design provides a number of performance benefits including: separating the solar cells from the

envelope hull and payload modularity. Also, the upper stage envelope is a low cost disposable balloon, while thelower stage is recovered. The lifting body shape of the upper stage allows the system to fly above the neutral

buoyancy point during wind gusts and dash back to the target area after the wind gusts have subsided. The system

design is also unique because a great majority of the materials are commercial-off-the-shelf, thereby reducing

development time and costs. The development of the StarLight has been advanced significantly recently through

envelope material selection as well as detailed thermal, aerodynamic, trajectory, and sizing analysis.

Acknowledgments

The authors thank Dr. Hugh Thornburg of MSRC at Wright-Patterson AFB AFRL for all of his support

conducting the CFD analysis during the past year.

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Balloon Performance Simulation, AIAA 2005-7411, AIAA 5 th Aviation, Technology, Integration, and Operations Conference

(ATIO), Arlington, VA, September 26-28, 2005.8Miller, T., and Mandel, M. Airship Envelopes: Requirements, Materials, and Test Methods, ILC Dover Publication, 2002.9Welch, J.V., Wang, S., Blandino, J. R., McEvoy, K., Super Pressure Balloon Non-Linear Structural Analysis and

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