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SEMINAR

MEC 3890

BACHELOR OF MECHANICAL ENGINEERING (AERSOPACE)

INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA (IIUM)

TITLE

HYPERSONIC INFLATABLE RE-ENTRY VEHICLE (HIRV)

BY

NUR HAZWANI BINTI MAZALAN (1112654)

AFIQ FADHLI BIN MISKAM (1113771)

ADVISOR

ASST PROFESSOR DR SYED MUHAMMAD KASHIF

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CONTENT

1.0 ABSTRACT

2.0 HISTORY

2.1 Phases of Flight

2.2 Multiple Independently Targetable Reentry Vehicle (MIRV)

3.0 PRINCIPLE

3.1 Shape

3.2 Size

3.3 Thermal Protection System

4.0 MECHANISM

4.1 Reentry Path

4.2 Inflatable Reentry Vehicle Experiment 3 (IRVE 3)

4.3 Advantages of Inflatable Re-Entry Vehicle

5.0 FUTURE PLAN

6.0 REFERENCES

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1.0 ABSTRACT

Atmospheric entry is the movement of human-made objects as they enter the atmosphere of a

celestial body from outer space. Objects entering the atmosphere are not released from rest just

above it, but rather are entering at hypersonic speeds because they are on suborbital (ICBM reentry

vehicle), orbital (space shuttle) or unbounded (meteors) trajectories. Therefore, controlled

atmospheric entry often requires special method to protect against severe aerodynamic heating.

Various advanced technologies have been developed to enable atmospheric reentry and flight at

extreme high velocities.

The atmospheric entry vehicle was inspired by the invention of Intercontinental Ballistic Missiles

(ICBM) which uses the basic concept of a reentry vehicle. It is a ballistic missile with a maximum

range of more than 5500 km typically designed for nuclear weapons delivery. Most modern designs

support multiple independently targetable reentry vehicles (MIRV), allowing a single missile to carry

several warheads, each of which can strike a different target.

The concept of reentry vehicle comes from the nose of the ICBM where it use high thermal

resistance of materials which having abrasive behavior. This applied to recent days where it helps

the NASA to bring the astronauts, instruments and experiments specimens from the International

Space Station (ISS).

The first atmospheric entry used ballistic missiles that featured long nosecones with narrow tips.

That shape cut through the air easily but high speeds and low drag led to overheating and melting

of the rockets surfaces. To overcome the aerodynamic heating problem, Hypersonic Inflatable Re-

Entry Vehicle, which looks like a giant cone of inner tubes assembled. This HIRV would allow

spacecraft to carry larger, heavier scientific instruments and other tools for exploration. The

technology could also be used to return payloads to Earth from the ISS or other low Earth orbit

locations.

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2.0 HISTORY

The concept of the abrasive heat shield was described as early as 1920 by Robert Goddard,"In the

case of meteors, which enter the atmosphere with speeds as high as 30 miles per second, the

interior of the meteors remains cold, and the erosion is due to a large extent, to chipping or cracking

of the suddenly heated surface. For this reason, if the outer surface of the apparatus were to consist

of layers of a very infusible hard substance with layers of a poor heat conductor between the surface

would not be eroded to any considerable extent, especially as the velocity of the apparatus would

not be nearly so great as that of the average meteor."

Practical development of reentry systems began as the range and reentry velocity ofballistic missiles

increased. For early short-range missiles, like theV-2 (Figure 1), stabilization and aerodynamic stress

are important issues (many V-2s broke apart during reentry), but aerodynamics heating on the heat

shield was not a serious problem. Medium-range missiles like the Soviet R-5, with a 1200 km range,

required ceramic composite heat shielding on separable reentry vehicles (it was no longer possible

for the entire rocket structure to survive reentry). The firstICBMs,with ranges of 8000 to 12,000 km,

were only possible with the development of modern ablative heat shields and blunt-shaped vehicles.

In the USA, this technology was pioneered byH. Julian Allen at Ames Research. In the Soviet Union,

Yuri A. Dunaev developed similar technology at the Leningrad Physical-Technical Institute.

Figure 1

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2.1 PHASES OF FLIGHT

Missiles are self-guided munitions that travel through the air or outer space to their targets. A

ballistic missile travels along a suborbital trajectory. An intercontinental ballistic missile can travel a

substantial distance around the Earth to its target. Thee intercontinental ballistic missiles consists of

propellant-filled stages, a guidance system and a payload (warheads). Once launched, the missile

passes through three phases of flight: boost, ballistic, and reentry. Figure 2 shows the structure of

the missiles where the structure shows the division of its body when it is going through those three

phases of flight.

During the boost phase, the duration of the ICBM to be launched into the atmosphere is around

three to five minutes which is shorter for a solid rocket than for a liquid-propellant rocket. The

altitude at the end of this boost phase is typically 150 to 400 km depending on the trajectory chosen.

The typical burnout speed of the missile is 7km/s. After that, entering the ballistic phase, with the

approximation of 25 minutes, the sub-orbital spaceflight in an elliptical orbit; the orbit is a part of an

ellipse with a vertical major axis.

Figure 2

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The apogee, the halfway of the midcourse phase, is at an altitude of approximately 1200km; the

semi-major axis is between 3186kmm and 6372km; the projection of the orbit on Earths surface is

close to a great circle, which is slightly displaced due to earth rotation during the time of flight. The

missile may release several independent warheads, and the penetration aids such as metallic-coated

balloons, aluminum chaff, and full-scale warhead decoys. The final phase is the reentry phase, which

starting at an altitude of 100km. The impact speed is up to 4km/s, where for the early ICBMs is less

than 1km/s.

In flight, a booster pushes the warhead and then falls away. Most modern boosters are solid-fueled

rocket motors,which can be stored easily for long periods of time. Early missiles usedliquid-fueled

rocket motors. Many liquid-fueled ICBMs could not be kept fuelled all the time as the cryogenic

liquid oxygen boiled off and caused ice formation, and therefore fueling the rocket was necessary

before launch. This procedure was a source of significant operational delay, and might allow the

missiles to be destroyed by enemy counterparts before they could be used. To resolve this problem

the British invented themissile silo that protected the missile from afirst strike and also hid fuelling

operations underground.Once the booster falls away, the warhead continues on an unpowered ballistic trajectory, much like

an artillery shell or cannon ball. The warhead is encased in a cone-shaped reentry vehicle and is

difficult to detect in this phase of flight as there is no rocket exhaust or other emissions to mark its

position to defenders. The high speeds of the warheads make them difficult to intercept and allow

for little warning striking targets anywhere in the world within minutes. As the nuclear warhead

reenters the Earth's atmosphere its high speed causes friction with the air, leading to a dramatic rise

in temperature which would destroy it if it were not shielded in some way. As a result, warhead

components are contained within an aluminum honeycomb substructure, sheathed in pyrolytic

graphite-epoxy resin composite, with a heat-shield layer on top.

Figure 3

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These fourshadowgraph images, Figure 3, represent early reentry-vehicle concepts. A shadowgraph

is a process that makes visible the disturbances that occur in a fluid flow at high velocity, in which

light passing through a flowing fluid is refracted by the density gradients in the fluid resulting in

bright and dark areas on a screen placed behind the fluid.

A blunt shape (high drag) made the most effective heat shield (Refer to Figure 4). From simple

engineering principles, the heat load experienced by and entry vehicle was inversely proportional to

the drag coefficient, i.e. the greater drag, the less the heat load. Through making the reentry vehicle

blunt, air cant get out of the way quickly enough, and acts as an air cushion to push the shock wave

and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in

direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move

around the vehicle to later dissipate into the atmosphere.

2.2 MULTIPLE INDEPENDENTLY TARGETABLE REENTRY VEHICLES (MIRV)

Another thing which is inspiring the invention of the reentry vehicle is the multiple independently

targetable reentry vehicles (MIRV). MIRV is a ballistic missile payload containing several warheads,

each capable of hitting one of a group of targets. By contrast a unitary warhead is a single warhead

on a single missile. The mode of the operation of this MIRV is the main rocket pushes a bus into a

free-flight suborbital ballistic flight path. After the booth phase, the bus maneuvers using small on-

board rocket motors and a computerized inertial guidance system. It takes up a ballistic trajectory

that will deliver a reentry vehicle containing a warhead to a target, and the releases a warhead on

that trajectory. It then maneuvers to a different trajectory, releasing another warhead, and repeats

the process for all warheads.

Figure 4

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Figure 5 showing the MIRV launching sequence:

1. The missile launches out of its silo by firing its first stage boost motor (A).

2. A bout 60 seconds after launch, the 1st stage drops off and the second stage motor (B)

ignites. The missile shroud (E) is ejected.

3. About 120 seconds after launch, the third stage motor (C) ignites and separates from the

2nd stage.

4. About 180 seconds after launch, third stage thrust terminates and the Post-Boost Vehicle (D)

separates from the rocket.

5. The Post-Boost Vehicle maneuvers itself and prepares for reentry vehicle (RV) deployment.

6. While the Post-Boost Vehicle backs away, the RVs, decoys, and chaff are deployed (although

the figure shows this happening during descent, this may occur during ascent instead).

7. The RVs and chaff reenter the atmosphere at high speeds and are armed in flight.

8. The nuclear warheads detonate, either as air bursts or ground bursts.

Figure 5

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The precise technical details are closely guarded military secrets, to hinder any development of

enemy counter-measures. The bus' on-board propellant limits the distances between targets of

individual warheads to perhaps a few hundred kilometers.[2]

Some warheads may use small

hypersonic airfoils during the descent to gain additional cross-range distance. Additionally, some

buses (e.g. the British Chevaline system) can release decoys to confuse interception devices and

radars,such asaluminized balloons or electronic noisemakers.

The Trident system contains cameras which are able to photograph the stars which allows them to

have an accurate location system which is independent of radio communications. Therefore even

with radio communications out of action the individual missiles are able to guide themselves. Testing

of thePeacekeeper reentry vehicles, all eight (ten capable) fired from only one missile. Each line

represents the path of a warhead which, if it were live, would detonate with the explosive power of

twenty-fiveHiroshima-style weapons

Accuracy is crucial, because doubling the accuracy decreases the needed warhead energy by a factor

of four for radiation damage and by a factor of eight for blast damage. Navigation system accuracy

and the available geophysical information limit the warhead target accuracy. Some writers believe

that government-supported geophysical mapping initiatives and ocean satellite altitude systems

such asSeasat may have a covert purpose to map mass concentrations and determine local gravity

anomalies,in order to improve accuracies of ballistic missiles. Accuracy is expressed ascircular error

probable (CEP). This is simply the radius of the circle that the warhead has a 50 percent chance of

falling into when aimed at the center.

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3.0 PRINCIPLES

Some factors of capability in designing these vehicles have to be considered. They are being

launched by a variety of launch vehicles, operating in low earth orbit as a free-flying unmanned

laboratory, and an independent atmospheric re-entry with an air-snatch recovery or a soft landing at

a preselected site (land or water), providing the experimenter with rapid access to the payload.

3.1 SHAPE

However, there are some specific design considerations. First, the important one is shape. The

aerodynamic shape configuration (ballistic or lifting) of a re-entry vehicle determines the severity,

duration and flight path of re-entry experienced by the vehicle. This, in turn, affects the vehicle

systems complexity and the heating loads on the payloads. A lifting re-entry vehicle has many

operational advantages over a non-lifting vehicle. The vehicle has the ability to deviate its re-entry

trajectory to reach selected landing sites cross range from the orbital track, and to fine tune

deorbit propulsion system errors. Spherical and ballistic vehicles can only deorbit to the selected

sites which are on the orbital ground track.[1]

But, there is a disadvantage of the lifting shape over the non-lifting shape lies in the complexity and

high cost associated with guidance and control of the lifting vehicle. A failure of the guidance or

control system could render the vehicle uncontrollable and cause it to diverge a great distance off

course.

Discoverer Recovery Vehicle Design

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The simple, such inflatable shield and aero brake were designed for the penetrators ofMars

96 mission. Since the mission failed due the launcher malfunction, the NPO Lavochkin and DASA/ESA

have designed a mission for Earth orbit. The Inflatable Re-entry and Descent Technology (IRDT)

demonstrator have launched on Soyuz-Fregat on 8 February 2000. The inflatable shield was

designed as a cone with two stages of inflation. Although the second stage of the shield failed to

inflate, the demonstrator survived the re-entry and was recovered. NASA launched an inflatable

heat shield experimental spacecraft on 17 August 2009 with the successful first test flight of the

Inflatable Re-entry Vehicle Experiment (IRVE).

3.2 SIZE

Second, the size of a re-entry vehicle has depended, for the most part; on the capabilities of

available launch vehicles. In general, the government-funded vehicles have been designed for the

large (Delta II) class of expendable launch vehicles while commercial design has been targeted to a

smaller class.The re-entry vehicle user (government or commercial) has the option of using a fullydedicated launch vehicle, or riding "piggyback" as a secondary payload.

Deceleration for atmospheric re-entry, especially for higher-speed Mars-return missions, benefit

from maximizing the drag area of the entry system. The larger the diameter of the aero shell, thebigger the payload can be. An inflatable aero shell provides one alternative for enlarging the drag

area with a low-mass design. Furthermore, some of the subsystems have to be applying to a re-entry

vehicle such as:

1. Attitude and spin control subsystem that is normally composed of sensors, controlelectronics and several low thrust assemblies that perform a variety of functions. The

functions are to spin the re-entry vehicle to induce artificial gravity and to trim the deorbit

manoeuvre to null errors in the performance of the solid rocket burn.

2. Deorbit Propulsion Subsystem provides the required velocity decrement to deorbit the re-entry vehicle and place it on a trajectory that is aimed at the landing site. A typical change in

velocity requirement to do this may be approximately 290 m/sec for low-altitude satellites in

near-circular orbit and for landing sites in the orbital plane.

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3. A tracking aid, such as a transponder, is normally required in the re-entry vehicle as an aid inrecovery.

4. Re-entry Vehicle Parachute Subsystem (or other retardation system) is designed to retardthe re-entry vehicle's vertical velocity and provide a relatively soft touchdown. For systems

that have parachutes, two types could be used for this application: a conventional type and

a lifting parafoil. The advantages of a conventional parachute are reduced weight and less

complexity. The lifting parafoil has three advantages over the conventional type:

a. Be able to reduce the dispersions associated with the deorbit and re-entrytrajectories by using its manoeuvrability to glide to a predetermined point,

b. Having the capability of being manually controlled to minimize landing area impactdispersions and,

c. By flaring, to reduce the vehicle impact shock at touchdown.

5. Re-entry Thermal Protection Subsystem protects the re-entry vehicle from aero-thermodynamic heating during atmospheric entry. Ablative material such as phenolic nylon,elastomeric silicon material (ESM), and white oak have been used in the past to protect

against excessive heating. For protection against the considerably lower heating rates that

occur on the conical skirt of the vehicle, two types of thermal protection systems have been

used: the ablative type or a ceramic-based surface insulation type. Other methods have

been investigated, such as reusable heat shields.[2]

3.3 THERMAL PROTECTION SYSTEM (TPS)

A thermal protection system or TPS is the barrier that protects aspacecraft during the searing heat

of re-entry vehicle. A secondary goal may be to protect the spacecraft from theheatand cold of

space while on orbit. Multiple approaches for the thermal protection of spacecraft are in use, among

them ablative heat shields, passive cooling and active cooling of spacecraft surfaces.[3]

Theablative heat shield functions by lifting the hot shock layer gas away from the heat shield's outer

wall (creating a coolerboundary layer). The boundary layer comes from blowing of gaseous reaction

products from the heat shield material and provides protection against all forms of heat flux. The

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overall process of reducing the heat flux experienced by the heat shield's outer wall by way of a

boundary layer is called blockage. Ablation can a provide blockage against radiative heat flux by

introducing carbon into the shock layer thus making it optically opaque.

Radiative heat flux blockage was the primary thermal protection mechanism of the Galileo Probe

TPS material (carbon phenolic). Carbon phenolic was originally developed as a rocket nozzle throat

material (used in theSpace Shuttle Solid Rocket Booster)and for re-entry vehicle nose tips. Initial

experiments typically mounted a mock-up of the ablative material to be analyzed within

ahypersonic wind tunnel.

Thethermal conductivity of a TPS material is proportional to the material's density. Carbon phenolic

is a very effective ablative material, but also has high density which is undesirable. If the heat flux

experienced by an entry vehicle is insufficient to cause pyrolysis then the TPS material's conductivity

could allow heat flux conduction into the TPS bond line material thus leading to TPS failure.

Consequently for entry trajectories causing lower heat flux, carbon phenolic is sometimes

inappropriate and lower density TPS materials.

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[13]

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4.0 MECHANISMS

Since the hypersonic inflatable re-entry vehicle is

still in the research, NASA has launched the

vehicle in many times to get the perfect result in

their experiment. A large inflatable heat shield

(Figure 6) developed by NASA's Space

Technology Program has successfully survived a

trip through Earth's atmosphere while travelling

at hypersonic speeds up to 7,600 mph.

The Inflatable Reentry Vehicle Experiment was

launched by sounding rocket from NASA's Wallops Flight Facility on Wallops Island, Va. The purpose

of the test was to show that a space capsule can use an inflatable outer shell to slow and protect

itself as it enters an atmosphere at hypersonic speed during planetary entry and descent, or as it

returns to Earth with cargo from the International Space Station.[4]

It was great to see the initial results indicate it was successful test of the hypersonic inflatable

aerodynamic decelerator. This demonstration flight goes a long way toward showing the value of

these technologies to serve as atmospheric entry heat shields for future space. A cone of inflated

high-tech rings covered by a thermal blanket of layers of heat resistant materials, launched from a

three-stage Black Brant rocket for its suborbital flight. About 6 minutes into the flight, as planned,

the 680-pound inflatable aero shell, or heat shield, and its payload separated from the launch

vehicle's 22-inch-diameter nose cone about 280 miles over the Atlantic Ocean.

Figure 6

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4.1 REENTRY PATH

An inflation system pumped nitrogen into the vehicle aero shell until it expanded to a mushroom

shape almost 10 feet in diameter. Then the aero shell plummeted at hypersonic speeds through

Earth's atmosphere. Engineers in the Wallops control room watched as four onboard cameras

confirmed the inflatable shield held its shape despite the force and high heat of reentry. Onboard

instruments provided temperature and pressure data.

After its flight, the vehicle fell into the Atlantic Ocean off the coast of North Carolina. From launch to

splashdown, the flight lasted about 20 minutes. A high-speed U.S. Navy Stiletto boat is in the area

with a crew that will attempt to retrieve it. The Stiletto is a maritime demonstration craft operatedby the Naval Surface Warfare Center Carderock, Combatant Craft Division, and is based at Joint

Expeditionary Base Little Creek-Ft Story.

The team of NASA engineers and technicians spent the last three years preparing for the vehicle

flight. They are pushing the boundaries with this flight and look forward to future test launches of

even bigger inflatable aero shells. This test was follow-on to the successful IRVE-2, which showed an

inflatable heat shield could survive intact after coming through Earth's atmosphere. IRVE-3 was the

same size as IRVE-2, but had a heavier payload and was subjected to a much higher re-entry heat,

more like what a heat shield might encounter in space.

Figure showing the reentry path of a reentry vehicle from the outer space.

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4.2 INFLATABLE REENTRY VEHICLE EXPERIMENT (IRVE-3)

Figure 7 shows that theInflatable Reentry Vehicle Experiment (IRVE-3),a large inflatable heat shield,

survived a fall through Earths atmosphere at hypersonic speeds up to 7,600 mph, reportsNASA.The

IRVE-3 was launched from Wallops Flight Facility in Virginia on July 23, 2012.

The IRVE-3 tested the inflatable air beam heat shield that will be used for spacecraft reentry through

the atmosphere. It is part of NASAsHypersonic Inflatable Aerodynamic Decelerator (HIAD) Project

and is designed to land at any destination with an atmosphere.

The test showed that the inflatable outer shell was able to slow and protect a space capsule as it

enters an atmosphere at hypersonic speeds. The 680 pound inflatable aero shell (heat shield), along

with its payload, separated from the launch vehicle 280 miles above the Atlantic Ocean. Nitrogen

was pumped into the aero shell as it expanded into a 10 foot wide mushroom shape.

Onboard cameras and instruments showed that the shield held its shape through the heat and force

of the 20 minute reentry. It then splashed down in the Atlantic Ocean off the coast of North

Carolina. The goal of theHIAD project is to land cargo and people on planets with an atmosphere

and return to Earth. It will also be able to return payloads to Earth from the International Space

Station (ISS).

Figure 7

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4.3 ADVANTAGES OF INFLATABLE RE-ENTRY VEHICLE

Inflatable aero shells offer several advantages over traditional rigid aero shells for atmospheric

entry. Inflatables offer increased payload volume fraction of the launch vehicle shroud and the

possibility to deliver more payload mass to the surface for equivalent trajectory constraints. An

inflatables diameter is not constrained by the launch vehicle shroud. The resultant larger drag area

can provide deceleration equivalent to a rigid system at higher atmospheric altitudes, thus offering

access to higher landing sites. When stowed for launch and cruise, inflatable aero shells allow access

to the payload after the vehicle is integrated for launch and offer direct access to vehicle structure

for structural attachment with the launch vehicle. They also offer an opportunity to eliminate system

duplication between the cruise stage and entry vehicle.

There are however several potential technical challenges for inflatable aero shells. First and

foremost is the fact that they are flexible structures. That flexibility could lead to unpredictable drag

performance or an aero structural dynamic instability. In addition, durability of large inflatable

structures may limit their application. They are susceptible to puncture, a potentially catastrophic

insult, from many possible sources. Finally, aero thermal heating during planetary entry poses a

significant challenge to a thin membrane. Structural integrity and structural response of the

inflatable will be verified with photogrammetric measurements of the back side of the aero shell in

flight. Aerodynamic stability as well as drag performance will be verified with on board inertialmeasurements and radar tracking from multiple ground radar stations.

[5]

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5.0 FUTURE PLANS

Re-entry vehicle demonstrated the stability and acceptable flight dynamics of inflatable

aerodynamics decelerators, corroborating methods and design principals used in the vehicle flight

dynamics and aero thermal analyses. Future flights will be needed to test the technology at higher

re-entry heat rates and at larger scales, for eventual use with re-entry and descent of larger

payloads.

The integrated re-entry vehicle is planned for launch on three stage sounding rocket, with the

mission objective of increasing the previous re-entry vehicle peak heat flux by a factor of five to ten.

Re-entry vehicle improvements envisioned for integrated re-entry vehicle span the range of on-

board systems. The aero shell structure and thermal protection will be improved using designs

developed and tested in parallel with the previous vehicle project. The inflation system will include a

reseal able control valve, to reduce the inflation gas lost through the pressure relief valves.[6]

An attitude control system will be added to remove the previous vehicles reliance on passive

aerodynamics, and the associated inertial measurement unit will provide more accurate trajectory

and attitude data. Additional thermal sensors will be used, heat flux gauges on the rigid nose of the

vehicle and thermocouples secured between the inflation aero shell, far from seams in the fabric.

Also, the integrated re-entry vehicle plan to continue thermal protection system development and

to manufacture a large scale development unit, working toward a future large scale flight.

8/12/2019 HIRV

20/20

6.0 REFERENCES

1.

http://www.faa.gov/about/office_org/headquarters_offices/ast/media/survey.pdf2. http://en.wikipedia.org/wiki/Atmospheric_entry3. http://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-

thermalprotectionsystem.html

4. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050182124_2005183200.pdf5. http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/S

ession6B/pr484.pdf

6. Introduction to Flight, 7thEdition, John D. Anderson, Jr., Mc Graw Hill International Edition2012

7. http://www.space.com/16695-nasa-launches-hypersonic-inflatable-heat-shield.html8. http://science.howstuffworks.com/spacecraft-reentry.htm9. http://www.faa.gov/other_visit/aviation_industry/designees_delegations/designee_types/a

me/media/Section%20III.4.1.7%20Returning%20from%20Space.pdf

10.http://www.ask.com/wiki/Multiple_independently_targetable_reentry_vehicle11.http://www.icas-proceedings.net/ICAS2008/PAPERS/146.PDF12.http://www.daviddarling.info/encyclopedia/R/reentry_vehicle.html13.http://www.space.com/19601-how-intercontinental-ballistic-missiles-work-infographic.html

http://www.faa.gov/about/office_org/headquarters_offices/ast/media/survey.pdfhttp://en.wikipedia.org/wiki/Atmospheric_entryhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050182124_2005183200.pdfhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://www.daviddarling.info/encyclopedia/R/reentry_vehicle.htmlhttp://www.daviddarling.info/encyclopedia/R/reentry_vehicle.htmlhttp://www.daviddarling.info/encyclopedia/R/reentry_vehicle.htmlhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Presentations/Session6B/pr484.pdfhttp://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050182124_2005183200.pdfhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://www.nasa.gov/centers/ames/research/humaninspace/humansinspace-thermalprotectionsystem.htmlhttp://en.wikipedia.org/wiki/Atmospheric_entryhttp://www.faa.gov/about/office_org/headquarters_offices/ast/media/survey.pdf