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A Ride on the
Wild Side
An
aerospace engineer has designed an airplane that could
fly at ten times the speed of sound by skipping off the
top of the atmosphere. But will it ever
fly?
By: Beate Kittl
engines | NASA
Nearly all great
innovations seemingly must be preceded by prophets, men
for the most part ignored or ridiculed, who have the
vision to comprehend the implications inherent in a new
discovery or a new innovation. Stating something novel,
something that differs radically from what is currently
believed, is dangerous business. It used to be common
practice to feed such prophets a stout of hemlock brew,
or simply burn them at the stake. In any period the role
of the prophet is no life of joy.
- Stewart Holbrook, The Story of American
Railroads
(Crown Publishers, NY, 1947)
It is the year 2040. High-speed monorails cut through the
desolate Mojave Desert, carrying hurried travelers to and
from a remote airport. The heat is shimmering over a couple
of 10,000-foot-long runways. This is home base for a fleet
of Mach 10 HyperSoars, the fastest airplanes ever built.
A silvery, wingless airplane shaped like a spearhead
turns onto a two-mile runway for takeoff. Inside, business
executives in designer suits fasten their suspender
seatbelts and sit back. With an ear-splitting boom the
aircraft lifts off the ground. Strict noise regulations have
banned the noisy bird from airports near inhabited areas.
The acceleration presses the 500 passengers of the
200-foot-long aircraft into their seats. HyperSoar quickly
attains its cruising speed of 6,750 miles per hour &endash;
ten times the speed of sound &endash; and after only five
minutes reaches its maximum altitude at 200,000 feet, four
times higher than the old Boeing 747s could ever go.
Flying on the uppermost layer of the atmosphere,
HyperSoar shuts off its engines and starts a shallow,
free-falling glide. At a speed three times faster than that
of the old Concorde, the aircraft starts its characteristic
alternating boost and glide flight pattern. Like a rock on a
still lake surface, HyperSoar goes skipping along the
atmosphere, prompting Australians to call it the “Kangaroo.”
At two-minute intervals, the engines propel the aircraft out
of the atmosphere before shutting off, as there is no air to
burn fuel with anyway. The triangular aircraft, designed for
gliding, then dips back into the atmosphere in a parabolic
curve like a roller coaster in slow motion. By rising into
the dead cold space void of air molecules, HyperSoar avoids
serious damage from the heat created by friction with the
air at such a speed. The passengers alternate between
free-floating in zero gravity and, during the acceleration
phase of the hop, being pressed back into their seats like a
kid on a swing. Just 1 hour, 15 minutes and 24 hops after
takeoff, HyperSoar glides the last 1,000 miles of its
journey and touches ground in the Australian desert.
Although an actual operational HyperSoar airplane is
still decades away, if indeed it ever appears, the
imagination of one man is working tenaciously to make this
science fiction journey come true some day. Preston Carter,
42, has spent 10 years working late nights, and enduring
discouraging criticism and his own nagging doubts to design
the airplane that flies through his dreams at hypersonic
speed.
In the summer of 1998, the space systems engineer at the
Lawrence Livermore National
Laboratory, California, presented the world with a
concept that, in theory at least, overcomes all obstacles
that have kept super-fast travel out of mankind’s reach.
During the following months, the mass media eagerly took up
the futuristic idea, which Carter dubbed HyperSoar (see
breakout).
“HyperSoar catches people’s imagination,” Carter explains
the hype.
Aviation
Week, September 7, 1998;
Science News,
September 12, 1998;
Space News,
October 5, 1998;
Jane’s
Defense Weekly, October 21, 1998;
Science
News Online September 19, 1998
The numbers that flicker over Carter’s computer screen
tell him that his creation would be the first hypersonic
airliner that is both technically feasible and economically
viable. Hypersonic means flying faster than Mach 5, five
times the speed of sound. Everything between Mach 1 and Mach
5 is called supersonic. No airplane without rocket engines
has yet reached that speed. The fastest fighter plane flies
at Mach 3, and the Concorde manages just about Mach 2.
HyperSoar would not only be the fastest airplane ever,
but would also be more efficient than anything flying,
Carter claims. “It is truly efficient to go very fast,”
Carter says, although that may seem counterintuitive. The
supersonic Concorde’s fuel use per weight transported is
extremely inefficient, because its body consists mostly of
wings. Believe it or not, HyperSoar would not have wings,
but would instead be shaped like a wing. The spearhead
shape, a so-called “waverider” design, is excellent for
gliding even at low speeds of 120 mph during landing.
Because it has more room for cargo, HyperSoar could carry
about twice as much weight as a Boeing 747. However, it also
gobbles up about twice as much fuel, something that would
not gain Carter support from environmental organizations.
Because HyperSoar would go so fast, it could fly between
opposite ends of the world about five times in the time it
takes a conventional airplane to make the trip once. In sum,
it could therefore transport about five times more cargo,
which translates into a fivefold profit for the carrier.
Following that reasoning, HyperSoar would also make space
access cheaper, Carter says. NASA’s space shuttles can only
carry cargo equivalent to 2 percent of their own weight.
HyperSoar could carry five times more, he claims. In
addition, HyperSoar could return with more cargo
immediately, whereas the Space Shuttle needs a few months of
preparation, he says.
Carter’s interest in space flight runs in the family. His
father was an aerospace engineer for the Apollo space
program at Boeing and for a hypersonic rocket airplane
project at NASA in the
1960’s. The plane, first called
DynaSoar,
was supposed to use the same skipping flight path as
HyperSoar, but the project &endash; later renamed Dinosaur
&endash; was killed before it was ever built.
As a kid, Carter lived in communities with space programs
all over the country. He remembers looking up into the night
sky, admiring everything that could fly through space.
“I passionately love doing this [designing
HyperSoar],” he says. “It’s what I wanted to do as a
kid.”
Besides working on the HyperSoar design, Carter is
engineering spacecraft technology at Lawrence Livermore
National Laboratory, a place that, among other things,
designs nuclear weapons. His work included co-founding a
lunar mission and designing heat-stable spacecraft coating.
Carter who used to race motorbikes in college, received
his master’s degree in aerospace engineering from the
University of Texas,
Austin. After graduate school he worked for the Mars lander
group at Lockheed Martin and for Space Industries in
Houston, where he designed heat-tolerant materials and space
experiments.
It takes Carter only a few minutes to drive his old army
Jeep to his home in Livermore, where he lives with his wife,
Nancy, and two children, Albert, 9, and Cathy, 6. Nancy is
also an engineer, which Carter says makes her more prepared
to put up with his working overtime.
Carter sometimes wonders whether he is going to waste his
life investing in this idea. But then he tells himself he’s
got to believe in it. He sees himself nurturing his
adventurous project for the next 10 years to make sure it
does not deteriorate into mediocrity, he says.
The idea of a hypersonic cruising airplane skipping along
the atmosphere came to life 11 years ago in a coffee room at
Lockheed’s headquarters in Houston. Sitting over steaming
cups of sweet, creamy coffee, Carter and his college friend
Ron Humble, now an aerospace engineer at the U.S. Air Force
Academy, discussed a question that bugged them: why was
space flight so expensive? They realized the answer was a
catch-22: It was expensive because there was no commercial
market, and there was no market because it was so expensive.
Carter and Humble thought the international fast freight
market would be the perfect candidate to profit from an
airplane that could deliver goods from Los Angeles to Tokyo
in two hours. In 1988, they calculated the performance of a
skipping hypersonic airplane and sent a letter to Federal
Express. Only a week later, the company’s CEO, Fred Smith,
called Carter back. He said Federal Express was “extremely
interested” in hypersonic airplanes for the small-package
business but had no funds for such a project just then.
FedEx had been negotiating to buy some surplus Concordes,
but the French government had informed the company that
hauling mail would besmirch the image of France’s national
flag. Smith encouraged Carter and Humble to keep working on
the hypersonic airplane idea.
Initially, Carter worked on the concept in his spare
time, resisting the temptation of his fishing rods on
weekends, while Humble went on to other projects. For the
first six years he had no idea if he would run into a dead
end, because it seemed too difficult to solve all the
technical problems hypersonic flight posed. But by 1994,
technologies such as hypersonic engines and heat-stable
materials had advanced to the point that the HyperSoar
concept might be possible. Carter’s boss at the Lawrence
Livermore National Laboratory, Mark Eckert, encouraged him
to keep working on it.
Lacking hard data, Carter did not publish any papers on
the technical feasibility of HyperSoar. In November 1998,
however, the respected Journal of Aircraft printed the first
of a series of papers on the performance of a hypersonic
airplane using a skipping trajectory that Carter had
submitted. These theoretical papers were well received,
according to Carter, but they assume that all the technology
would be available.
For now, HyperSoar is only flying through the circuits of
Carter’s office computer. According to his flight path
analysis, the aircraft would have to rise to the upper
atmosphere to an altitude of 40 miles. During a single
parabola, in which it would glide without engines, HyperSoar
would cover a distance of 250 miles and lose almost 20 miles
in height. It would then fire its engines and rise again. It
could reach Tokyo from LA in about 24 cycles.
Although Humble predicts that traveling on HyperSoar
“would be quite a wild ride,” Carter argues that the
skipping would be much smoother than a roller coaster ride.
He thinks many people would rather ride in a HyperSoar for
1_ hours than sit in a commercial airliner for 12 to 16
hours.
However, it may not be entirely harmless to be without
gravity for two minutes, as experiences with the “vomit
comet,” NASA’s zero gravity plane KC-135 that trains
astronauts have shown. One rider said in a CNN live report
that “it was kind of like being on a roller coaster going
over the top when your stomach jumps to the top... but on
the KC-135, it never came down.” To be fair, it must be said
that the KC-135 drops at the much steeper angle of 45
degrees instead of HyperSoar’s 2.8 degrees.
There are two big technical problems that a hypersonic
airplane would face. Hypersonic flight a hard nut to crack
for engineers because of the incredible heat that the
aircraft must face while cutting through the atmosphere at
this speed. At Mach 10, the air in front of the plane is
compressed by the travel speed and heats up to more than
1600° Celsius, a temperature that can melt iron.
HyperSoar would avoid excessive heating by bouncing into the
cold of space.
Although engineers know how to make materials that can
withstand the heat, some instruments or other parts of the
aircraft could fail. Until the first successful flight
tests, Carter is cautious about HyperSoar’s heat tolerance.
In early test flights of the fighter plane Blackbird, used
in the Gulf War, the hydraulic fluid started boiling and the
rubber tires melted at Mach 3. HyperSoar will profit from
lessons learned in such earlier attempts to fly fast.
The second big challenge is building engines that
function at hypersonic speed. A new generation of engines
combining rocket and air-breathing technology could solve
this problem. The so-called Rocket-Based Combined-Cycle
engine is a hollow tube that sucks in air and contains
mechanisms that can burn fuel at different
speeds.
A rocket accelerates the plane until it is flying at the
speed of sound. The engine then switches to a ramjet, an
air-breathing engine used by supersonic fighter planes,
which slows down the air enough to burn the fuel within the
tube. At hypersonic speed &endash; over Mach 5 &endash; the
air gets pressed so hard against the front of the airplane
that it heats up the oxygen particles to the point they
start falling apart. This is why until now only rockets
&endash; which carry their own oxygen in huge tanks &endash;
could reach this speed. The newest engine part, a so-called
air-breathing scramjet, will be able to burn fuel at
supersonic speed.
NASA will start testing such engines in flight next year
(see NASA’s
HyperX website).
The idea of a skipping airplane has been around since
World War II, when a German engineer had an idea for a
rocket-propelled bomber that could be boosted up to the
Earth’s orbit, fly hopping off the atmosphere, and drop
bombs on New York.
No airplane has yet used a skipping flight path, however.
Only the Apollo capsule bounced off the atmosphere once to
slow down before reentering the atmosphere. Carter was the
first to think about a hypersonic, cruising airplane with
jet engines that would use such a flight course.
But when he told his colleagues about a hopping plane,
they thought he was out of his mind. The concept of a
hypersonic cruising airplane was an old idea with a bad
track record. NASA sunk $160 million into such a project,
which proved too ambitious. After the project was cancelled
in 1994, a NASA
website called hypersonics “one of the greatest
aeronautic research challenges.”
But significant advances in aerodynamics, engine design,
and heat-stable materials make the HyperSoar idea now appear
technically feasible.
Aerospace engineering circles learned of HyperSoar last
summer, when a reporter discovered the HyperSoar design at
an air show and wrote about it in the in September issue of
the aeronautics journal
Aviation
Week & Space Technology. Many engineers slapped
their foreheads: this was the design that could make
hypersonic flight a reality &endash; given that none of the
other technology would fail.
“It’s unlike anything we’ve ever built before. It’s
pushing the limits of untested technology,” says Mark Lewis,
an aerospace engineer at the University of Maryland who used
to collaborate with Carter on earlier stages of the
HyperSoar concept.
Carter’s college friend Ron Humble says it’s nothing
magical. “But if it works, it’s a breakthrough.”
Space engineers cautioned that the technology was not
advanced enough yet, but they did not say that HyperSoar was
technically impossible, Carter said.
With one significant exception. NASA engineers working on
Hyper-X, the airplane to test the air-breathing combo
engines, did some tests and calculations of their own after
hearing about HyperSoar. They concluded that HyperSoar could
not work, Lewis says.
Lewis claims that NASA used a completely different
aircraft and the wrong trajectory for their tests. He has
published many theoretical papers on computer models that
test the properties of hypersonic vehicles. He used to work
for NASA, and says they may have a political interest in
debunking HyperSoar. The NASA engineers did not want to
comment on HyperSoar.
Carter would like to collaborate with NASA because they
have the most know-how about hypersonic airplanes. He says
they fight him because “the publicity of HyperSoar rains on
their parade.”
For Carter, the publicity &endash; and increasing
acceptance &endash; of his design means that funding for a
prototype may be within reach. If someone gave him $500
million right now, he could have a one-third-scale prototype
hopping on the atmosphere in only four or five years. The
first commercial freight carriers could be flying in eight
to 10 years.
This multibillion-dollar project is too big for one
agency to finance. Carter has considered asking Boeing,
Lockheed Martin, and Northrop Grumman to help fund his
research. Carter would also like to see a collaboration of
Livermore, NASA, and the U.S. Air Force. Together, these
three agencies combine state-of-the-art heat-stable
materials, aerodynamic expertise, and flight-testing
centers. Carter predicts that the military would be quite
interested in an ultra-fast airplane for reconnaissance or
as a bomber capable of dropping huge loads of bombs.
Private venture capitalists are also eager to tap into
the intercontinental express-transportation market. If
hypersonic flight came true, the value of the fast freight
market is expected to grow from today’s $12 billion to more
than $150 billion over the next decade, according to a
report about FedEx in Fortune Magazine in 1997.
As the HyperSoar idea is taking shape, Carter is not the
only one pondering the possibilities of affordable space
flight. A team of visionaries at NASA has thought up all
sorts of ideas on their
website.
In the future, you may be able to pick up a video from a
digital movie satellite, watch “Microgravity Games” held in
space, or deliver organs for transplantation all over the
world. We could dump our nuclear waste on the far side of
the moon, book a “zero-gravity” joyride, or exploit
extraterrestrial minerals.
But even if HyperSoar can overcome the substantial
technical difficulties, it may not catch on as an airliner.
Travelers might object to a roller-coaster type of
long-distance transportation in which they’re hanging over
their air-sickness bag for an hour and a half. Passengers
demand a high level of comfort on a flight—even today many
prefer regular airplanes over the fast but crammed and
uncomfortable Concorde, says Carter’s collaborator Mark
Lewis.
For adventurous people, however, it may be just the ride
they’ve been looking for. Carter imagines that they could
experiment with weightlessness in a zero-gravity lounge—a
large, padded room. Food and drink would arrive in special
containers via conveyor belt. In the weightlessness,
HyperSoar could unnoticeably turn upside down and reveal a
breathtaking view of the blue-green planet.
Engineers and visionaries alike have been intrigued by
hypersonic flight for more than 50 years. Their curiosity
may bring HyperSoar to life. For many decades to come, the
Mojave Desert will remain silent, the oven-dry air
shimmering over the gray dust. But someday, bulldozers may
move in and cut through the soil and the silence,
transforming the venerable wasteland into the runways of an
ultra-modern HyperSoar airport.
“HyperSoar is the next-century equivalent of the
airplane,” Carter muses.
engines | NASA
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- BIO
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- WRITER
Beate Kittl
- Diplom (B.A.),
University of Basel, Switzerland; M.A. equiv., Simon Fraser
University, Canada.
Internship: Discover magazine, New York.
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Text ©
1999 Beate Kittl
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