Reusable Launch Vehicle RLV

8/7/2019 Reusable Launch Vehicle RLV

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INTRODUCTION

A hundred years ago, on December 17, 1903, Wilbur and

Orville Wright successfully achieved a piloted, powered

flight. Though the Wright Flyer I flew only 10 ft off the

ground for 12 seconds, traveling a mere 120 ft, the

aeronautical technology it demonstrated paved the way for

passenger air transportation. Man had finally made it to

the air. The Wright brothers plane of 1903 led to the

development of aircrafts such as the WWII Spitfire, and

others. In 1926 the first passenger plane flew holiday

makersfrom American mainland to Havana and Bahamas. In 23years the world had moved from a plane that flew 120 ft and

similar planes that only a chosen few could fly, to one

that can carry many passengers. Today air travel is worth

billions. The military has produced planes for special

purposes like SR-71 for high speed and high altitude

flying, F-117 Nightbird the stealth fighter, and other

world class dogfighters like Russian Sukhoi 37, French

Mirage, British Harriers, and American F22 Raptor.

In October 1957, man entered the

space age. Russia sent the first satellite, the Sputnik,

and in April 1961, Yuri Gagarin became the first man on

space. In the years since Russia and United States has sent

many air force pilots and a fewer scientists, engineers and

others. But even after almost 50 years, the number of

people who has been to space is close to 500.


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The people are losing interest in

seeing a chosen few going to space and the budgets to space

research is diminishing. The space industry now makes money

by taking satellites to space. But a major factor here is

the cost. At present to put a single kg into orbit will

cost you between $10000 and $20000. This is clearly

prohibitively high and a major objective for the coming

years is to drop the cost to a fraction of today's value.

Despite the fact that the space shuttle has regularly goneinto orbit over the last two decades there is still no

tourist business. This is due to the fact that to build an

orbital hotel under present conditions will cost 100's of

billions of dollars (at least). It is clear why there has

been so little progress in orbital developments.

The development of a plane which

can fly to space at lower cost, which is reusable and can

take more payloads, is very much required for further

development of space industries. The Reusable Launch

Vehicle, usually called Spaceplane or Hyperplane which can

take crew and payload into orbit is being developed by

various space agencies and private companies. The

Spaceplane would make space travel cheap and will help in

increasing space tourism and just like in the aviation

industry, within a few decades, the space tourism

industries would be worth billions.


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The Advantages

The rockets which take satellites and other payloads have

to carry the fuel and oxidizer with them as it uses

conventional rocket engines. The combined weight of the

fuel and oxidizer is very large due to the fact that a lot

of energy is expended pushing the plane forwards. This is

why today's rockets launch vertically as it maximizes the

rocket's potential by allowing all the energy expended to

be focused in the direction we want to go - upwards. With

present technology it is the easiest and cheapest method of

reaching space.

Clearly then the way forward is to

utilize jet engines in some manner. The main advantages of

jet engines over rocket engines are that they do not need

to carry their own oxidizer; instead they suck in air and

use the oxygen present in the air as their oxidizer. This

will greatly remove the need to carry oxidizer, as it will

only be needed when at an altitude that the air contains

insufficient oxygen for jets to operate. At this point the

rocket engines will fire and burn the much smaller quantity

of onboard oxidizer. This will dramatically reduce the

take-off weight and also the cost of the craft. Reduction

in take-off weight means the payload can be increased.

Further to this the use of jet engines will make a

substantial saving on the expensive rocket fuel. As a

comparison to produce the same thrust, jet (air-breathing)

engines require less than one seventh the propellants (fuel

+ oxidizer) that rockets do. For example, the space shuttle
http://science.howstuffworks.com/space-shuttle.htmhttp://science.howstuffworks.com/space-shuttle.htm


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needs 143,000 gallons of liquid oxygen, which weighs

1,359,000 pounds (616,432 kg). Without the liquid oxygen,

the shuttle weighs a mere 165,000 pounds (74,842 kg).

Another advantage of jet-engine craft

is that as they rely on aerodynamic forces rather than on

rocket thrust, they have greater maneuverability, which in

turn provides better flexibility and safety, for example

missions can be aborted mid-flight if there is a problem.

This is not the case for staged vehicles, which typically

have complex "range safety" requirements as the stages

detach and fall back to earth. Range safety is one of the

main reasons that the US launches from Florida, where the

rocket's flight path takes it out over open water almost

immediately. The lack of such abort modes on the Shuttle

requires incredible failure avoidance costs and massive

overhauls.

The space shuttle used by NASA is partially

reusable. It still has to take off vertically with the helpof multistage rocket and solid boosters. The use of rockets

increases the cost of manufacturing parts for each launch

as some rocket parts are not reusable. Further more, using

rockets increases the amount of fuel and oxidizer required.

Some of the components of the rocket get added to the space

debris and continue orbiting the earth. This causes

unwanted collisions with other debris or satellites. Thus

using a jet-engine craft as a reusable launch vehicle is

faster, efficient, and has increased affordability,

flexibility and safety for ultra high-speed flights within

the atmosphere and into Earth orbit.


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The Different Proposals

Today three main concepts are being proposed. The

difference is in way the RLV is launched. This difference

results in differing levels of complexity in design. The

major concepts are

Two Stage To Orbit (TSTO)

This is the easiest method; firstly a large aeroplane takes

off carrying a smaller rocket engine craft (called the

orbiter) and reaches a fairly high altitude. Then the

smaller craft launches from the carrier and as it is

already at high altitude before firing its engines, the

need for fuel is minimized. It also means that the wings on

the orbiter can be made smaller. There is no doubt that

this option certainly creates less engineering problems.

This type of technology was around in the 1960's and was

used during the testing of the X-15.

One and a Half Stage To Orbit (OHSTO)

There are various 'One and a Half Stages' ideas that are

certainly innovative ideas and deserve mention. The most

promising is that of mid-air fuelling, taking on the fuel

and oxidizer for space once at a high altitude. These ideas

do not overcome the problems of commercially viability that

the 2-stage models suffer from; however it could be a good

temporary measure.


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Single Stage To Orbit (SSTO)

It is a reusable launch vehicle (RLV) that takes off and

lands horizontally like a conventional plane. It is

generally regarded that this method will be more efficient

and safer than the 2-stage model, though that is not to

belittle the 2-stage method which would be a considerable

improvement on the vertical take off craft of today. It is

also felt that while the 2-stage idea would be easier, the

1-stage would almost certainly be more commercially viable

and would achieve a higher level of success in the

objectives of a spaceplane.

What is required here is

further development of jet engines. The only possibility at

the moment is ramjet working together with scramjet

(Supersonic Combustion Ramjet). The major problem is that

the scramjets are far from fully developed, offering many

difficult aerodynamic problems. These, however, offer the

only current hope of sustained hypersonic flight.

Even with the advance of scramjet

development there are still many problems to be addressed

with horizontal take off of spaceplanes. This is because a

Scramjet will only function at hypersonic speeds and a

ramjet will only function at supersonic speeds. The designwill therefore require:


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1. A turbojet, once the air intake reaches to mach 1

(supersonic speed) the ramjet would fire.

2. The ramjet would accelerate the plane to about mach 4

(hypersonic speed) then the scramjet would fire.

3. The scramjet is expected to be able to reach speeds of

mach 15, when finally the rocket engine would fire.

4. The rocket engine would accelerate the plane to mach

25 (escape velocity) and would be used in space

operations.

While this sounds very good in theory, in practice it is

very doubtful whether such vehicles will have the

efficiency to reach orbit, due to the excessive weight and

complexity of such a system. Further to this such a design

will not solve the other problem of heat build-up.

These problems have not, however, removed the interest in

this system and several proposals are currently being

tested by NASA.

What we are really looking for isthe development of a combined jet engine that operates

across the range, with maybe a switch to a rocket engine

for the last stage and for space operations. The

difficulties of designing a jet engine to perform at these

levels are such that it can not even be seen how it could

be done with present technology. The differences between

the engines are how they physically take the air in.

Nanotechnology could solve the problem by allowing the

engine to reshape itself in flight, whether it could be

shaped fast enough remains to be seen.


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Working

The working of a RLV can be divided into 4 stages

1. First stage subsonic and supersonic stage:

The RLV with its payload takes off from the runway and

climbs to about 100,000 feet or 30km using

conventional jet-engines, or using a combination of

conventional jet-engine and ramjet engine, or using

another plane to carry or pull the plane to a lower

height and using a booster rocket.

A ramjet operates by subsonic

combustion of fuel in a stream of air compressed by

the forward speed of the aircraft. It doesnt have or

use very less moving parts compared to a conventionaljet-engine with thousands of moving parts. The

compression of air before burning of fuel is done in

the ramjet by the addition of a diffuser at the inlet,

while it is done by the turbine in conventional jet-

engine. The flow of air is subsonic.

The plane is accelerated to a speed of mach 4

or mach 5 and the flow inside the engine becomessupersonic. Then the scramjet is powered up.


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2. Second stage - Hypersonic stage: When the

spaceplane is at an altitude of about 100,000 ft and

at a velocity of about mach 4, the scramjets are fired.

Scramjets are basically ramjets. They introduce fuel and

mix it with oxygen obtained from the air which compressed

for combustion. The air is naturally compressed by the

forward speed of the vehicle and the shape of the inlet,

similar to what turbines or pistons do in slower-moving

airplanes and cars. Rather than using a rotating

compressor, like a turbojet engine does, the forward

velocity and aerodynamics compress the air into the engine.

Hydrogen fuel is then injected into the air stream, and the

expanding hot gases from combustion accelerate the exhaust

air to create tremendous thrust. While the concept is

simple, proving the concept has not been simple. At

operational speeds, flow through the scramjet engine is

supersonic - or faster than the speed of sound. At that

speed, ignition and combustion take place in a matter of

milliseconds. This is one reason it has taken researchers

decades to demonstrate scramjet technologies, first in wind

tunnels and computer simulations, and only recently in

experimental flight tests.

The Scramjet engine takes the RLV to even

greater heights and to speeds of up to Mach 15. This is the

fastest speed an air breathing plane can go using current

technologies. At Mach 15, the RLV is at a great height that

there isnt enough oxygen to sustain the scramjet engine.

At this point the rocket engine fires up.


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3. Third stage - Space stage: When the rocket engine

fires by mixing oxygen from the onboard storage tanks

into the scramjet engine, thereby replacing the

supersonic airflow. The rocket engine is capable of

accelerating the RLV to speeds of about Mach 25, which

is the escape

velocity. It takes the RLV into orbit. The rocket engine

takes the RLV to the payload release site and the

required operations are done. Once this is over it

enters its last stage the re-entry stage.


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4. Fourth stage Re-entry stage: Once the RLV

finishes its mission in space, It performs de-orbit

operations, including firing its thrusters to slow

itself down, thereby dropping to a lower orbit and

eventually entering the upper layers of the

atmosphere. As the vehicle encounters denser air, the

temperature of the ceramic skin builds to over 1,000

degrees C, and is also cooled by using any remaining

liquid hydrogen fuel. It is here that the structure of

the plane undergoes heavy thermal stress. If the heat

shields do not protect the plane, it would simply burn

off to the ground, just like the space shuttle

Columbia. It enters a radio silence zone as due to the

heat, radio contact is lost. Once it reaches dense

air, it can use its aerodynamics to glide down to the

landing strip. It can also use any remaining fuel to

fire the ramjet or conventional jet (depends on the

design) and change its course. Once on the landing

strip it engages it slows down using a series of

parachutes and engages the brake.

CONSTRUCTION

The construction of a true RLV that can take a payload to

space is still in the design stage. It will sure have lot

of designs taken from the space shuttle. Here are the main

construction details.

Body: The body of a RLV has to withstand very high

stresses including thermal stresses during re-entry. The

plane expands due to the high heat of nearly 1500C or

more. It also has to cope with the rapid change in


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temperatures once in space. It changes from -250 degrees in

the shade to 250 degrees in direct sunlight. This change in

temperature between two sides of the same plane will put a

lot of stress on its body. Titanium alloys are being used,

being very strong and light. To cope with the high

temperatures developed in parts of the wing and fuselage of

the spacecraft today, reinforced carbon-carbon composite

material is being added to the leading edges of the

vehicle's nose and wings to handle the higher temperatures.

Researches are being conducted to

find the best materials for different parts of the plane.

One of these materials, -TiAl (Titanium Aluminide), has

superior high-temperature material properties. Its low

density provides improved specific strength and creep

resistance in comparison to currently used titanium alloys.

However, it is inherently brittle, and long life durability

is a potential problem along with the materials

sensitivity to defects.

Wings: The wing of the spacecraft has to be designed so

that it provides enough lift to fly to space and also

reduce the friction during re-entry.

Cockpit: The cockpit is the place where the astronauts

will stay most of the time during the journey. It will have

many windows, which are special double-paned glass, and

each pane alone can withstand the pressure and force of

flight and the vacuum. This doubling up ensures that if

either window were to crack, the passengers would still be

safe.


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The air inside the cockpit is made

breathable by a three-part system. Breathable air is added

at a constant rate by oxygen bottles. The exhaled carbon

dioxide is removed from the cabin by an absorber system,

and humidity is controlled by an additional absorber

created to remove water vapor from the air. During the

entire flight, the cockpit remains comfortable, cool and

dry.

The avionics system and display unit for

navigating has to be computer controlled and free from

bugs. It should give the pilot all the necessary data to

make his choices. The avionics are very critical, and it

also needs to be very precise for the pilot to do what he

wants to do, and do it well.

Electric Power: The electrical power required for the

running of the spacecraft has to be taken from batteries.

These batteries could be charged, if needed by using solar

energy. Researches are being initiated to find better andreliable batteries, like the lithium-based (i.e., Li metal

or Li-ion intercalation compound as negative electrode),

polymer electrolyte regenerative battery system. Its

advantages include reduced battery weight and volume,

relative to conventional Ni-Cd and Ni-H2, which permits

greater payloads and greater cell voltage, 3.5 volts vs.

1.2 volts, which permits use of fewer cells and results in

reduced battery system complexity.

Controls: When we're out in space, all you need to do is

release a puff of air in a direction to give you a reaction

force to push you the other way. That is called a reaction


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control system. High-pressure air is stored in bottles on

the ship, and on the release of a little blast of air for

about one second, for example, with the right wing tip

pointing up. And that is enough when you're in space to

push that wingtip down. It effectively rolls the aircraft,

and that are the controls when it is out in space.

Fuels: Many challenges have been overcome recently by the

discovery and synthesis of propellants that can have higher

performance than traditional O2/H2, and aircraft fuels.

These propellants include high-density monopropellants for

sounding rockets and upper stages, and onboard propulsion

for small spacecraft. Higher energy fuels, such as N4, N6,

BH4, and others, have a longer range development time and

would be more applicable to future launch vehicles.

Reusable Launch Vehicles

The X-43 Hyper-X from NASA

Hyper-X, NASA's multi-year hypersonic flight research

program, seeks to overcome one of the greatest aeronautical


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research challenges - air-breathing hypersonic flight. Far

outpacing contemporary aircraft of supersonic capability,

three X-43A vehicles were built to fly at speeds of Mach 7

and 10. Ultimately, the revolutionary technologies exposed

by the Hyper-X Program promise to increase payload

capacities and reduce costs for future air and space

vehicles.

MicroCraft, Inc. of Tullahoma, Tenn., is the

industry partner chosen by NASA to construct the X-43

vehicles. The contract award announcement occurred on March

24, 1997, with construction of the vehicles beginning soon

thereafter. Orbital Sciences Corporation's Launch Vehicles

Division in Chandler, Ariz. will construct the Hyper-X

launch vehicles.

The goal of the Hyper-X program is to

flight validate key propulsion and related technologies for

air-breathing hypersonic aircraft. The first X-43 was

scheduled to fly at Mach 7. This is far faster than anyair-breathing aircraft have ever flown. The world's fastest

air-breathing aircraft, the SR-71, cruises slightly above

Mach 3. The highest speed attained by NASA's rocket-powered

X-15 was Mach 6.7, back in 1967.

Hyper-X research began with conceptual

design and wind tunnel work in 1996. Three unpiloted X- 43A

research aircraft were built. Each of the 12-feet long, 5-

feet-wide lifting body vehicles was designed to fly once.

They are identical in appearance, but engineered with

slight differences that simulate variable engine geometry,

generally a function of Mach number. The first and second

vehicles were designed to fly at Mach 7 and the third at


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Mach 10. At these speeds, the shape of the vehicle forebody

serves the same purpose as pistons in a car, compressing

the air as fuel is injected for combustion. Gaseous

hydrogen fuels the X-43A. The first flight attempt in June

2001 failed when the booster rocket went out of control and

the booster rocket and X-43A combinationwas destroyed by

ground controllers. The second attempt at Mach 7, in March

2004, was highly successful.

At Mach 6.8or almost seven times

the speed of soundthe X-43A research vehicle was traveling

nearly 5,000 mph during the March 2004 flight, easily

setting a world speed record for a jet-powered (air-

breathing) vehicle. Guinness World Records has recognized

the accomplishment

The tricky part in the development

of this technology is that as the air is in the tube

remains for mere milliseconds, getting such details as the

fuel-air mixture right, is still very difficult. And thefact that what is right is different at different

velocities makes the problem more complicated. The big

challenge of designing a variable geometry engine (as the

professionals call it), which will be able to accommodate

these differences, has not yet been still solved by

engineers. So, for simplicity, the flights of the X-43A

didnt have to accelerate under its own power. Instead, it

was carried by a booster rocket to the required speed and

altitude.

On 16 November, 2004, NASA's unmanned

Hyper-X (X-43A) aircraft reached Mach 9.6. The X-43A was

boosted to an altitude of 33,223 meters (109,000 feet) by a


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Pegasus rocket launched from beneath a B52-Bomber jet

aircraft, which had taken off from Edwards Air Force Base

in California in the U.S. Then the booster rocket lofted it

to a height of 33,223 meters (109,000 feet). Thereafter the

booster separated and the scramjet was ignited. Moments

later the scramjet fired for about 10 seconds and the craft

while flying on its own at about 7000 miles/hour (using its

own gaseous hydrogen fuel) conducted a series of high speed

maneuvers, before gliding away and crashing into the

Pacific Ocean.

The SpaceShipOne from SCALED COMPOSITES LLC

The SpaceShipOne is a RLV built by the company Scaled

Composites LLC for competing in the X Price. The Ansari X

Prize is a contest that promised a cash prize of $10

million to the first registered team to:

Build a spaceship able to carry three adults (height

up to 188 centimeters [6 feet, 2 inches] and weight up

to 90 kilograms [198 pounds] each).

Launch the spaceship with three soon-to-be astronauts

to a height of 100 kilometers (62.5 miles), the

internationally recognized altitude at which sub-

orbital space begins.

Return the spaceship to Earth safely -- no broken

bones on the astronaut, no severe damage to the ship,

etc.

Repeat the flight within two weeks using the same

ship, having replaced no more than 10 percent of the

ship's parts (with the exception of fuel), thus


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classifying the spacecraft as a Reusable Launch

Vehicle (RLV).

Do it all without any government funding, using only

private financing.

The company designed and built another jet

aircraft which would carry the SpaceShipOne to a height of

about 50,000 feet. This turbofan powered aircraft, called

the White knight takes off like a plane from a normal

airstrip, with SpaceShipOne attached to its belly. The two

ships fly together under White Knight's power to a

predetermined altitude. Then White Knight releases

SpaceShipOne and drifts away. Once clear of White Knight,

SpaceShipOne begins its journey to sub-orbital space. The

White Knight was designed with a high thrust-to-weight

ratio and powerful speed brakes. These features help to

simulate space flight maneuvers.

On October 4th 2004, the SpaceShipOne

flew to take the $10 million price. It was timed partially

to coincide with the 47th anniversary of the Soviet launch

of Sputnik. When the SpaceShipOne is released, it glides

for about 10 seconds while the pilot sets up the aircraft

for the rocket boost and he throws the switch, and the

hybrid rocket motor in the SpaceShipOne accelerates the

aircraft. The hybrid rocket motor has combined elements

from both solid and liquid rocket motors. This makes for a

unique motor capable of accelerating SpaceShipOne to twice

the speed of sound. SpaceShipOne is propelled by a mixture

of hydroxy-terminated polybutadiene (tire rubber) and

nitrous oxide (laughing gas). The rubber acts as the fuel


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and the laughing gas as the oxidizer. The pilot immediately

commences a pullout maneuver to go straight up. The ship

continues to accelerate going straight out for a little

over a minute. It flies for about one minute, straight up

and then burn out about 150,000 feet, roughly. The motor

stop burning at that point, but now the ship is moving over

2,000 miles per hour, straight out, and so it coasts. From

there it coasts up another 150,000 feet roughly, up until

it reaches apogee (the point at which SpaceShipOne is

farthest from Earth). The pilot feels Zero g or

weightlessness for some time at the topmost point. Then it

falls back to earth. The pilot makes changes to theaerodynamics and the spacecraft slows down. It then glides

down to the landing strip.

In addition to meeting the

altitude requirement to win the X-Prize, pilot Brian Binnie

also broke the August 22, 1963 record by Joseph A. Walker,

who flew the X-15 to an unofficial world altitude record of

354,200 feet. Brian Binnie's SpaceShipOne flight carried

him all the way to 367,442 feet or 69.6 miles above the

Earth's surface.

Conclusion

The recent development in the field of scramjets,

hyperplanes, and truly Reusable Launch Vehicle will result

in the development of space tourism. This advancement of

technology helps us to understand more about science and

also helps us to improve our life.


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In 1927, hotel magnate

Raymond Orteig's announced an aviation contest, a price of

$25,000 to beawarded to the first man to build and fly an

airplane non-stop from New York to Paris. As a result of the

successful flight of Charles Lindbergh's, in the United

States:

The number of airline passengers increased by 167,623

between 1926 and 1929.

The number of pilot's license applications increased

by 300 percent in 1927.

The number of licensed aircraft increased by 400

percent.

The number of airports doubled within three years.

Once this technology will be common, people will

start their pursuit towards even better technologies. Only

time will tell if the Ansari X Prize will have a similar

effect on the burgeoning sub-orbital flight industry as the

1927 $25,000 Orteig's price did.

References

1.http://www.nasa.gov/missions/research/x43-main.html

Official site of NASA X-43 spaceplane.
http://science.howstuffworks.com/airplane.htmhttp://science.howstuffworks.com/airplane.htm


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2.http://www.thespacesite.com/space/future/spaceplane.php

Contains basic information about the Reusable Launch

Vehicles and current projects.

3.http://trc.dfrc.nasa.gov/Newsroom/FactSheets/FS-040-

DFRC.html

Contains facts about the NASA X-43 Hyper-X plane.

4.http://trc.dfrc.nasa.gov/Gallery/Movie/Hyper-

X/index.html

Contains motion pictures of the X-43 .

5.http://trc.dfrc.nasa.gov/Gallery/Photo/X-43A/index.html

Contains images of the X-43 spaceplane.

6.http://science.howstuffworks.com/x-prize.htm

For details about X-Price.

7.http://www.lerc.nasa.gov/WWW/RT1999/intro/contents.htmlFor advance papers on space research

8.http://www.scaled.com/index.htm

For information on SpaceShipOne.

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Reusable Launch Vehicle RLV