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starship-design: FW: SpaceViews -- 1999 June 1
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Subject: SpaceViews -- 1999 June 1
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S P A C E V I E W S
Issue 1999.06.01
1999 June 1
http://www.spaceviews.com/1999/06/
*** News ***
Shuttle Mission Proceeds Smoothly
Mir Likely to Remain in Orbit until 2000
Asteroid Poses Greater Future Threat
Hubble Measures Expansion and Age of Universe
Chandra Launch Preparations Resume
Lunar Prospector Mission Might End in Ban
New 3-D Map Reveals Martian Geography
Amateur Rocket Sets Record, Falls Short of Space
SpaceViews Event Horizon
Other News
*** Articles ***
The First Reusable Spaceship
*** Letters ***
More on RLVs and Financing
*** News ***
Shuttle Mission Proceeds Smoothly
Despite a nearly six-month gap since the previous shuttle
mission, flight STS-96 has gone smoothly from a trouble-free countdown
and launch to its mission to service the International Space Station.
The shuttle Discovery lifted off on schedule at 6:49 am EDT
(1049 UT) Thursday, May 27, after a nearly trouble-free countdown.
The launch was the first for the shuttle program since the STS-88
mission in early December of last year.
The shuttle successfully docked with the station at 12:24 am
EDT (0424 UT) Saturday, May 29. The shuttle is scheduled to remain
docked with the station until Thursday, June 3.
The first task after docking was a spacewalk to install
equipment to the exterior of the station. Astronauts Tamara Jernigan
and Daniel Barry spent nearly eight hours outside the shuttle on the
night of May 29-30, installing the American-built Orbital Transfer
Device to one side of the Unity module and pieces of the Russian
Strela ("Arrow") crane to another side of the module.
The cranes will be used during future assembly spacewalks to
more efficiently move spacewalkers and cargo around the exterior of
the module.
The spacewalkers also attached three tool and equipment bags
to the exterior of the station that will be used on future assembly
spacewalks, and conducted an inspection of the station.
The seven-person crew has since turned their attention to the
interior of the station, including hauling nearly two tons of
equipment -- ranging from food and clothes to computers -- into the
station.
The shuttle crew will also deal with repairs and workaround on
the new station. Astronauts will repair a balky American
communications system and investigate why some Russian batteries on
the station are having problems charging. While working in the
Russian-built Zarya control module, the crew will wear earplugs
because noise levels there reach 72 decibels, equivalent to a busy
highway and higher than NASA standards. Mufflers to be installed by
the astronauts should decrease noise levels there somewhat.
After Discovery undocks from ISS, the crew will release a
small satellite that will be used in educational programs. The
STARSHINE satellite will be visually tracked by students on the
ground. Even through the satellite is only slightly larger than a
basketball, the 900 mirrors on its surface will allow it to reflect
sunlight and be easily seen on the ground.
Commanding STS-96 is Kent Rominger, making his fourth shuttle
flight, while rookie astronaut Rick Husband is the pilot. Mission
specialists include Ellen Ochoa, Canadian astronaut Julie Payette, and
Russian cosmonaut Valery Tokarev, in addition to Jernigan and Barry.
Payette and Tokarev are making their first space flights, while
Jernigan is making her fifth.
If all goes well, the shuttle is scheduled to land at the
Kennedy Space Center at 1:59 am EDT (0559 UT) Sunday, June 6.
Mir Likely to Remain in Orbit until 2000
Even if no private investors can be found, Russia's Mir space
station is likely to remain in orbit until at least early 2000,
Russian officials said this week.
However, one controversial source of private funding, British
businessman Peter Llewellyn, will not be paying or raising money to
fly on the station, although the reasons for his leaving cosmonaut
training are unclear.
Speaking in Florida prior to the launch of the shuttle
Discovery, Boris Ostroumov, deputy director-general of the Russian
Space Agency, said Mir will remain in orbit until at least February
2000, even if no funding is found to keep the station operating beyond
August.
"We've got more than 10 tons of scientific hardware on board
the Mir station," Ostroumov said. "It simply does not make too much
sense to get rid of such a treasure."
He said that Mir's orbit is currently high enough to allow it
to remain in orbit until at least February 2000, even if no funding is
found to keep the station operating. If funding is not found the
station would stay in orbit but be unoccupied, he said.
Last week Russia President Boris Yeltsin signed a decree
allowing Mir to remain in orbit of Energia, the company that operates
Mir for the Russia Space Agency, can find the funding to keep
operating the station. The decree appears similar to one signed in
January by now-former Prime Minister Yevegny Primakov.
A "final" decision on the fate of Mir should come as soon as
early June, Russia Space Agency officials said late in the week, based
on the likelihood of private funding.
One source of private funding, though, has apparently backed
out of plans to fly on Mir in August. Russian sources reported this
week that British businessman Peter Llewellyn left Russia this week
after arriving earlier in the month to begin cosmonaut training for a
August flight to Mir.
The reasons why Llewellyn, who was reportedly going to pay or
raise $100 million to fly on the station, left cosmonaut training are
uncertain. The Itar-Tass news agency reported May 26 quoted the
deputy head of the cosmonaut training center, who said Llewellyn
"turned out to be an unreliable partner."
The next day, however, Russian Space Agency officials said
Llewellyn was dropped from training because, at 188 cm (6 feet 2
inches) in height, he was too tall to fit safely in the Soyuz
spacecraft. While it is true that there is a maximum height of about
183 cm (6 feet) for Soyuz passengers, it is not clear why this became
a factor after training began.
Doubts about Llewellyn's ability to pay for the flight had
been met with skepticism, particularly by Western observers. While
working in the U.S., Llewellyn faced fraud charges in a Pittsburgh
court until he agreed to repay approximately $40,000 to a former
business partner. Local police there had considered him something of
a con artist.
A lack of private investment raises new concerns about the
fate of Mir. While Russian officials say the station can be left
unstaffed, others, such as Viktor Blagov, deputy head of Mir mission
control, have claimed that the station must be kept occupied at all
times, or else the attitude control computers, which require frequent
maintenance, will fail.
A failure of the attitude control systems on Mir could cause
it to start tumbling uncontrollably, which would make a controlled
deorbit of the station into the Earth's atmosphere impossible.
Asteroid Poses Greater Future Threat
A near-Earth asteroid which earlier this year was found to
have a one-in-a-billion chance of striking the Earth in 2039 may have
a larger -- but still very small -- chance of a collision five years
later, JPL astronomers said.
In an interview with MSNBC, Don Yeomans, head of NASA's
Near-Earth Object Program Office at JPL, said that asteroid 1999 AN10
has a 1-in-500,000 chance of hitting the Earth in 2044.
That probability is still less than that for a unknown
asteroid. Astronomers estimate a 1-in-100,000 chance that an
undiscovered asteroid one kilometer or larger in diameter will strike
the Earth in a given year.
However, that very small probability has raised interest among
astronomers. "I'm not worried in the least about this object, but I'm
not going to ignore it," Gareth Williams of the Minor Planets Center
told MSNBC. Yeomans said the asteroid's impact probability is at a
threshold above which it might warrant special attention.
The revised orbit for 1999 AN10 came after new observations of
the asteroid by an amateur astronomer in Australia. Those
observations were likely triggered by debate in April when a preprint
of a scientific paper, publicized on a mailing list used by near-Earth
asteroid researchers, showed that the asteroid had a one-in-a-billion
chance of colliding with the Earth in 2039.
The revised calculations based on the new data also increased
the probability of a 2039 impact to ten million to one, 100 times
higher than previously but still far smaller than the odds of an
impact from an unknown object.
The asteroid will also make a close flyby of Earth in 2027,
coming as close as 32,600 km (20,200 mi.) of the surface of the Earth
on August 7. The chance of an impact on that date is essentially
zero, but the close passage the asteroid, within the Earth's magnetic
field, might levitate dust off the surface of the asteroid through
electrostatic repulsion and create a dim "dust coma."
Astronomers earlier noted that the asteroid's orbit will bring
it close to Earth many times in the coming centuries. Further
observations of the asteroid are planned in coming weeks that should
refine its orbit and better determine any impact probabilities in
future close approaches.
Hubble Measures Expansion and Age of Universe
Astronomers, marking the completion of one of the Hubble Space
Telescope's major projects, have made the most precise measurement yet
of a key cosmological factor that governs the age of the universe and
its rate of expansion, NASA announced May 25.
A team of astronomers, having completed an eight-year study of
distant galaxies with Hubble, found that the Hubble constant, a
measure of the rate of expansion of the universe, is approximately 70
km/sec per megaparsec (Mpc, equal to 3.25 million light-years),
corresponding to an age of 12 billion years.
With an error of only 10 percent, the result is the most
precise measurement made to date of the Hubble constant (often
referred to as "H0" or "H-nought"), one of the key values in
astronomy. The factor, named after American astronomer Edwin Hubble,
had also been hotly debated by astronomers, with the field at one time
divided into two camps: one who believed H0 was 100 km/sec/Mpc, while
others believed H0 to be just 50.
H0 is important because it also provides a measure of the age
of the universe: simply inverting the result and adjusting the units
gives a rough estimate of the age of the universe. The age is then
adjusted by accounting for the density of the universe and other
effects.
"Before Hubble, astronomers could not decide if the universe
was 10 billion or 20 billion years old," said Wendy Freedman of the
Observatories of the Carnegie Institution of Washington, who led the
HST Key Project Team. "The size scale of the universe had a range so
vast that it didn't allow astronomers to confront with any certainty
many of the most basic questions about the origin and eventual fate of
the cosmos."
The new value from Hubble greatly improves our knowledge of
the universe, say astronomers. "We used to disagree by a factor of
two; now we are just as passionate about ten percent," said Robert
Kirschner of Harvard University. "A factor of two is like being unsure
if you have one foot or two. Ten percent is like arguing about one
toe."
The Hubble results are in accordance with research by other
astronomers, who have found values of H0 ranging from the mid-sixties
into the low seventies in recent years, using different techniques.
"It's exciting to see the different methods of measuring galaxy
distances converge, calibrated by the Hubble Space Telescope," noted
team member Jeremy Mould of the Australian National University.
The Hubble team measured the variation in brightness of
Cepheid variables, a class of variable stars with a well-known
relationship between the period of variation and its absolute
brightness.
By measuring the period and apparent brightness of Cepheids in
distant galaxies with Hubble, astronomers are able to estimate the
distance to these galaxies. This distance, combined with information
about the redshift of the galaxies caused by the Doppler effect,
allows astronomers to compute the Hubble constant and hence the rate
of expansion.
Combining the new value of H0 with current estimates for the
density of the universe, Freedman and colleagues found the age of the
universe to be about 12 billion years. This is in accordance with
estimates for the age of the oldest stars of the universe, ending past
concerns where some globular star clusters appeared to be older than
the universe itself.
Not everyone is in agreement with the new value for H0. Allan
Sandage, a colleague of Freedman's at Carnegie, is still a proponent
for a value of H0 in the range of 50 to 60. "If NASA is giving the
impression that the problem is solved, then we would dispute that,"
Sandage said in a telephone interview with the Associated Press. "They
have announced a final number, and they are not correct."
More discussion about the new value of H0 is expected at the
next meeting of the American Astronomical Society, scheduled to take
place in Chicago in early June.
Chandra Launch Preparations Resume
NASA has resumed preparations for the launch of the Chandra
X-Ray Observatory after resolving issues with the upper stage that
will be used to boost the satellite, the space agency reported Friday,
May 28.
The resumed preparations will permit the launch of the shuttle
Columbia, which will place Chandra and its upper stage into orbit, no
sooner than July 22.
Project officials at NASA's Marshall Space Flight Center said
the Inertial Upper Stage (IUS) that will be used to boost Chandra will
be delivered to NASA on Tuesday, June 1, permitting launch
preparations to resume. The upper stage will be mated to the
spacecraft and, after mechanical and electrical tests, the whole
assembly will be placed in the shuttle's cargo bay.
The delivery of the IUS and its integration with Chandra was
scheduled to take place a month earlier, but was delayed when another
IUS failed to place an Air Force early-warning satellite into its
proper orbit after an April 9 Titan 4B launch.
NASA said in a press release that the space agency "has taken
all appropriate actions to mitigate any issues raised regarding the
Inertial Upper Stage."
Plans now call for the launch of STS-93, previously planned
for early July, to take place no sooner than July 22. Columbia will
deploy the satellite on a four-day mission commanded by Eileen
Collins, the first woman to command a shuttle mission.
Lunar Prospector Mission Might End in Bang
Lunar Prospector project managers are considering ending the
spacecraft's mission later this year by deliberately crashing the
spacecraft into a region of the Moon thought to harbor water ice,
Space News reported in its May 24 issue.
The crash would through up a cloud of debris which would
include any water ice in the region of impact, allowing for a direct
detection of ice from telescopes on the Earth.
Lunar Prospector is the second half of an extended mission
which is expected to conclude this summer when the spacecraft runs out
of maneuvering propellant. The Moon's irregular gravity field would
then cause Prospector to crash to the surface.
However, project officials are considering deliberately
crashing Prospector in the crater Mawson in the Moon's south polar
region. That crater has a 33-km (20.5-mi.) floor thought to be rich
in water ice.
The impact would throw up a plume of material that could be
observed from minutes to hours after impact from telescopes on Earth.
Those telescopes could spectroscopically detect the presence of any
water ice in the debris.
Prospector has already amassed considerable evidence for water
ice on the Moon from its neutron spectrometer, which has detected high
concentrations of hydrogen in permanently-shadowed regions of the
lunar poles. Water is the most likely source of the hydrogen detected
by Prospector, scientists believe.
A final decision for targeting Lunar Prospector will come from
NASA administrator Dan Goldin, project officials said. If given the
go-ahead, the impact procedure would begin July 29 or 30.
Because the limited amount of debris a Prospector impact would
be able to throw up, scientists note that the odds of actually being
able to observe any water ice in the plume would be slim. "Lunar
Prospector is going to crash somewhere" anyway, noted Mike Duke of the
Lunar and Planetary Institute. "So if you aim it at a place that you
think is in shadow, there are instruments and people that stand a
chance of actually seeing something."
New 3-D Map Reveals Martian Geography
A new three-dimensional map of the surface of Mars, released
by NASA Thursday, May 27, has provided new insights on the geology of
the Red Planet.
The map, generated from data collected by a laser altimeter on
the Mars Global Surveyor spacecraft, allows scientists to know the
topography of the Red Planet to a greater detail than some regions on
Earth, NASA officials said.
The topographic map shows a striking difference between the
planet's northern and southern hemisphere, with the southern
hemisphere an average of five kilometers (three miles) higher than the
northern. The southern hemisphere is also more rugged and
crater-pocked than the smoother northern hemisphere.
The depressed northern hemisphere is likely a result of
internal geologic processes on Mars early in its history, and not the
result of an impact, according to David Smith of the Goddard Space
Flight Center, lead author of a paper on Martian topography published
in the May 28 issue of the journal Science.
The high elevations in the southern hemisphere may have been
partially caused by an impact that created the Hellas basin, the
scientists said. The impact threw up enough material to cover an area
the size of the continental United States to a depth of 3.2 kilometers
(2 miles).
Overall, the difference in planetary elevations, from the top
of Olympus Mons to the bottom of the deepest basins, is 30 kilometers
(19 miles), one and a half times the difference between the highest
and lowest elevations on the Earth.
The new map has also provided new insights about the drainage
of water on the early Mars. Portions of the eastern end of the giant
Valles Marineris canyon is actually up to one kilometer (0.6 miles)
below the level of neighboring outflow channels, suggested that water
may have collected there.
Information about the poles collected from the topographic
data show that if the residual polar caps on Mars are composed
entirely of water ice, there is enough water on the planet to cover
the surface to a depth of 22 to 33 meters (66 to 100 feet). This is
estimated to be about one-third of the minimum amount of water to
account for a proposed ancient ocean, suggesting that Mars either lost
the rest of the water to space or it is stored deep underground.
"This incredible database means that we now know the
topography of Mars better than many continental regions on Earth,"
claimed Carl Pilcher, science director of NASA's solar system
exploration program. "The data will serve as a basic reference book
for Mars scientists for many years."
The laser altimeter will continue to collect data as Mars
Global Surveyor continues its mapping mission, including data on the
topography of the planned landing site of the Mars Polar Lander
spacecraft, scheduled to land in early December.
Amateur Rocket Sets Record, Falls Short of Space
An amateur rocket launched Sunday, May 23, set an unofficial
altitude record but weather conditions prevented the amateur group's
bid to be the first to launch a rocket into space.
The balloon-launched rocket reached a maximum altitude of at
least 21,885 meters (72,223 feet) according to JP Aerospace, the
California-based amateur group that built and launched the rocket.
The rocket likely traveled to a higher altitude, John Powell,
president of JP Aerospace, said. The maximum altitude reported by the
group was the highest they measured from the rocket's onboard GPS
receiver. At that time the rocket was still traveling upwards at 240
meters per second (800 feet per second).
Powell said the group has calculated the estimated maximum
altitude the rocket has reached, but has chosen only to report the
lower, but verified, altitude from the GPS measurement.
The group had hoped that the rocket would exceed an altitude
of 97 km (60 mi.) and become the first amateur vehicle to fly into
space. However, after delaying the launch one day because of winds,
the group concluded that the upper-level winds above the Black Rock
Desert, Nevada, launch site would blow the balloon and rocket out of
operational range before they reached their planned launch height of
30,300 meters (100,000 feet).
Instead of scrubbing the launch all together, the group
decided to launch the rocket from just 7,880 meters (26,000 feet).
"We learn nothing from a rocket on the ground so we decided to 'cycle
the system' and verify that the launch system works," Powell said.
The maximum verified altitude of the rocket would set a record
for an amateur rocket, breaking the record of 20,000 meters (66,000
feet) by Ky Michelson. Powell said Michelson was on hand for the
launch and "unofficially handed over the title."
Other launches have claimed higher altitudes, but those
altitudes were calculated based on the trajectory of the rocket and
other parameters, but not directly measured. Other amateur launches
have also had NASA involvement, Powell noted.
In May 1997 Project HALO, an effort by the Huntsville, Alabama
chapter of the National Space Society, also launched a rocket from a
balloon. They estimated a peak altitude of 55,200 to 66,300 meters
(182,300 to 218,700 feet). However, they had no direct measurement of
the altitude since they were unable to pick up transmission from the
rocket's GPS receiver beyond 9,100 meters (30,000 feet).
Powell said this his group's record could be questioned as
well, since the launch took place from a balloon and not from the
ground. "The situation [about the record] is such a mess that we're
staying away from it like the plague," he said. "We flew our rocket
to 72,223 feet as part of our spaceflight project and next time it
will be even higher."
SpaceViews Event Horizon
June 6 Shuttle Discovery landing at the Kennedy Space Center,
at 1:59 am EDT (0559 UT).
June 7 Long March 2C/SD launch of two Iridium satellites from
Taiyuan, China
June 8 Delta 2 launch of four Globalstar satellites from Cape
Canaveral, Florida at 10:22 am EDT (1422 UT)
June 11 (NET) Atlas 2A launch of the GOES-L weather satellite from
Cape Canaveral, Florida (under review)
June 12 Proton launch of Russian Raduga comsat (and initial
flight of the Breeze-M upper stage) from Baikonur,
Kazakhstan.
June 23-24 First U.S. Space Tourism Conference, Washington, DC
July 15-16 Lunar Base Development Symposium, League City, TX
Other News
SETI@home Overload: SETI@home, the project that allows users to
analyze data from a University of California Berkeley search for
extraterrestrial intelligence (SETI) project, may be a victim of its
own success. Over 300,000 users have downloaded the software and
started analyzing the data, some on multiple computers. The crush of
users has caused problems for the Berkeley computers that send out the
data and receive the analyzed results. Project officials say a new
server, to be donated by Sun Microsystems within the next month,
should alleviate problems, as well as planned bug fixes to the
SETI@home software.
India Commercial Launch: An Indian rocket launched three satellites
May 26 in what was billed as the first commercial launch for the
country. A Polar Satellite Launch Vehicle (PSLV) launched the Indian
Remote Sensing IRS-P4 satellite as well as two small experimental
satellites for Germany and South Korea. The foreign satellites were
launched under commercial agreements, marking the first time Indian
Space Research Organization (ISRO) had sold launch services. ISRO
plans to sell launches on both the PSLV and the more powerful
Geosynchronous Satellite Launch Vehicle (GSLV) under development.
Beal Seeks Alternative Site: Beal Aerospace is looking at a South
American alternative to its planned Caribbean launch site. Last month
company officials visited the nation of Guyana, in northern South
America, to check out a potential launch site in a swampy region along
the country's Caribbean coast. The site could be an alternative to
Sombrero Island, an uninhabited island 55 km (35 mi.) from the British
colony of Anguilla. That site has run into opposition from
environmentalists, who are concerned that a launch site could
adversely affect sea birds who use the island as a breeding ground.
Leonids No Big Worry: The heavy storm of Leonid meteors expected in
November 1999 should not be a major concern for satellite operators,
experts said at a conference last month. While the peak of the storm
is forecast to be up to four times the rate of the 1998 storm, it will
still be far below the extremely heavy rates seen in the last Leonids
storm in 1966. The 33-year cycle of heavy Leonids storms had caused
concern that satellites could be damaged by the flux of small meteors,
but no satellites were damaged in the 1998 storm.
Cosmic Call: For the first time since 1974, humans have sent a
deliberate signal into interstellar space with a May 24 transmission
from a Ukrainian radio observatory. The message, sponsored by
Houston-based company Encounter 2001, consisted of one part designed
by a team of scientists and a second part that included 30-word
messages from members of the general public, who paid $14.95 each for
the privilege. The message was beamed to four Sun-like stars 51 to 71
light-years away in the Summer Triangle.
Briefly: China may be accelerating plans to put a human into space.
A Chinese newspaper article last week, reported by Reuters, claimed
that a manned launch may occur before the 50th anniversary of the
People's Republic on October 1. Previously, Chinese officials had
reported plans to launch the spacecraft, based on the Russian Soyuz,
on an unmanned test flight in October... Russian mission control
director Vladimir Lobachev, in Florida for the STS-96 launch, was
arrested on assault charges May 23 when he attacked two paramedics who
were transporting him to a hospital after discovering the Russian
semiconscious near a Cocoa Beach, Florida, pier. Lobachev was later
released on a $1,000 bond and left the country immediately thereafter.
When taken to the hospital authorities found that his blood alcohol
level was more than three times the state limit for being declared
legally drunk... AT&T, which has engaged in a $100 billion spree of
mergers and acquisitions, may have its sights on something even
larger: NASA. A joke passing through AT&T's email network and
reported in the May 31 issue of Business Week claimed that the company
was going to purchase the space agency in excess of $100 billion.
AT&T would then string coax cable from "Cape Canaveral to Mars" before
rolling out a "10-planet trial of communications services." However,
the joke continues, a lack of identified extraterrestrial
intelligences could limit the market for the company's services, but
if any would be found, the company would win them over with free
subscriptions to the Showtime premium movie channel...
*** Articles ***
The First Reusable Spaceship
by Andrew J. LePage
Ask the typical space enthusiast to name the first reusable
piloted spaceship and the most likely answer would be the Space
Shuttle. While the Space Shuttle's external tank is discarded on each
mission, its pair of solid rocket boosters as well as the highly
complex and expensive orbiter (the actual "spaceship") are certainly
reusable. But the Space Shuttle was not the first piloted spacecraft
that could be flown over and over. Nor was some little known piece of
Soviet engineering genius. The honor belongs to the grandfather of
all modern aerospace planes, the X-15.
While the X-15 is certainly the most famous of all the
X-series aircraft, the fact that it flew into space on no less than 13
occasions while the Mercury and Gemini programs came and went is
frequently overlooked. Even in NASA's "official" count of American
manned space missions, the suborbital X-15 flights are notably absent.
This despite the fact that three NASA pilots (not to mention five USAF
pilots) earned their astronaut wings during the program including Joe
Engle who went on to fly NASA's Space Shuttle in the 1980s.
There are several possible reasons the X-15 spaceflight
accomplishments are often forgotten: First the majority of the X-15's
199 flights were never meant to fly high enough to qualify as an
"official" spaceflight. Extremely high altitude flights were only one
of this long running program's many objectives. Combined with the
almost routine nature of what was really a test program, X-15 flights
did not generate the media coverage afforded to the far less "routine"
space missions of the Mercury and Gemini programs. Finally, when the
X-15 passed the threshold into space, it barely did so and only
briefly - hardly newsworthy to some when men are spending days or
weeks in orbit in preparation for a manned lunar mission. But exactly
where is this threshold where one "officially" passes into space?
The Edge of Space
There really is not a clearly defined altitude where one
passes out of the sensible atmosphere and into the vacuum of space.
In the late 1950's the USAF decided to award astronaut wings to pilots
who flew over 50 statute miles (80.45 kilometers) above sea level.
Besides being a nice round number (at least in English measurement
units), 50 miles is higher than any balloon or conventional aircraft
has ever flown (about 30 miles or 50 kilometers) yet lower than the
lowest perigee of a marginally stable satellite orbit (about 55 miles
or 90 kilometers). Eventually flying as high as about 108 kilometers
(67 miles), the X-15 was the first craft capable of flying in the
transition region between the sensible atmosphere and space.
The need to explore this region as well as the effects of
hypersonic flight (i.e. at speeds exceeding five times the speed of
sound or Mach 5), had been recognized in the early 1950s. In the
years after the last World War, rocket-powered aircraft such as the
USAF's X-1 series and the X-2 as well as the US Navy sponsored D-558
series of test aircraft first broke the sound barrier and proceeded to
set a string of speed records up to Mach 3. In addition, these
aircraft also flew at increasingly greater altitudes eventually
reaching as high as 38 kilometers (24 miles) above sea level. But
military planners anticipated the need for future aircraft to fly
faster and higher still. In addition, since the prevailing view of
manned spaceflight at the time called for a pilot to fly his rocket
powered aircraft into orbit and back, there was an obvious need to
explore the issues associated with high altitude hypersonic flight.
After a meeting held by the Executive Committee of NACA
(NASA's pre-Space Age predecessor, the National Advisory Committee for
Aeronautics) it was recommended that NACA start research into the
problems of flight at speeds of Mach 4 to 10 and at altitudes from 12
to 50 miles (19 to 80 kilometers). What would become the X-15 was
designed to meet this goal. A further resolution on July 14 extended
NACA goals to speeds from Mach 10 to escape velocity and altitudes
from 50 miles (80 kilometers) to infinity. Meeting this latter goal
lead to the USAF X-20 "Dyna Soar" and NASA's Mercury program (see "The
Beginnings of America's Man in Space Program" in the October 1998
issue of SpaceViews).
During the coming months NACA engineers performed numerous
studies on hypersonic aircraft designs and soon the USAF took an
interest. They had been performing similar studies and, along with
NACA officials, knew that such a research program would be best
carried out by pooling the resources of several agencies. By July 9,
1954 a joint NACA/USAF/US Navy committee started meeting to discuss
the need for such a vehicle and its basic design. By late 1954 the
base design criteria were determined and on January 17, 1955 the USAF
officially assigned the new aircraft the "X-15" designation.
The Design
Four aircraft manufacturers responded to the joint
NACA/USAF/US Navy call for proposals. Bell (the builder of the X-1
series) submitted its D-171 design, Douglas its Model 684 D-558-3, and
Republic its Model AP-76. While every agency involved had its
favorite design, ultimately they agreed on the North American NA-240
proposal and a contract for three aircraft was signed on September 30,
1955. This design was chosen because of its simplicity and ease to
modify to meet the agencies' various specifications. The final design
that emerged from this long process became an aerospace classic.
The X-15 was designed to attain speeds of Mach 6 and altitudes
in excess of 250,000 feet (76 kilometers). It was 15.2 meters (50
feet) long and weighed 15,100 kilograms (33,300 pounds) at launch.
Midway down its fuselage were a pair of low aspect ratio, trapezoidal
shaped wings with a span of 6.7 meters (22 feet). Based on NACA
research, the X-15 used a pair of thick, wedge shaped vertical
stabilizers and thin, down sloping horizontal stabilizers to provide
directional control during flight. These also gave the aircraft its
classic arrow-like profile. A set of a dozen small hydrogen
peroxide-fueled jets located in the nose and wingtips with thrusts of
180 and 450 Newtons(40 and 100 pounds) provided attitude control when
the X-15 was too high and the air too rarefied for its aerodynamic
control surfaces to work. A similar system was later used by NASA's
Mercury space capsule.
The bulk of the X-15 airframe was made from titanium while
most of the outer skin was composed of the heat resistant and then
exotic nickel-based alloy, Iconel X. Such materials were needed to
withstand the anticipated 650 C (1,200 F) temperatures generated
during hypersonic flight. The air conditioned, climate controlled
cockpit provided enough room for a single pressure suit clad pilot.
It was equipped with an advanced ejection seat that would work safely
at speeds up to Mach 4 and an altitude 36.6 kilometers (120,000 feet
or 22.7 miles). It provided an extra safety margin for what was
recognized as a risky test program.
Most of the X-15 fuselage housed a set of tanks holding 8,540
kilograms (18,800 pounds) of propellant for the X-15's single rocket
engine. Ultimately the XLR-99 engine built by Reaction Motors, Inc.
(which later became a division of Thiokol) was chosen based on a bid
the company submitted in December of 1955. This engine produced 223
kilonewtons (50,000 pounds) of thrust at sea level and was intended to
be restartable and throttlable in flight. Initially the engine was to
be throttled from 30% to 100% of its maximum thrust. Early versions
of the engine would only throttle between 50% and 100% but even later
versions were limited to a minimum 40% rating to avoid running
problems found during test flights at low thrust settings.
The turbopump fed XLR-99 ran on an unusual combination of
liquid anhydrous ammonia and liquid oxygen (LOX). While there are
certainly rocket fuels more powerful than liquid ammonia available,
Reaction Motors did have much experience with this propellant
combination and knew that engines burning it were very forgiving
during restarts - a very important safety factor. This powerful
engine would easily allow the X-15 to exceed its speed and altitude
design goals. Ultimately the performance of the X-15 would be limited
by the heat generated during high speed flight or reentry and not by
its engine.
But as development of the X-15 and its XLR-99 engine proceeded
it became increasingly clear that the first X-15 airframes would be
available long before their innovative powerplants. By February 1958
it was decided that the first two X-15 aircraft would initially be
equipped with a pair of less powerful XLR-11 engines similar to the
ones that powered the Bell X-1 series and the Douglas D-558-II
aircraft. Each XLR-11 engine consisted of four thrust chambers that
could be fired independently allowing for an eight-step throttle
capability. With all eight chambers running, the pair of alcohol/LOX
fueled XLR-11 rocket engines produced a total of 71 kilonewtons
(16,000 pounds) of thrust. While this was only a third of the maximum
thrust generated by the XLR-99, it did allow the X-15 test program to
proceed with the previously planned low speed trials that would be
flown initially.
But even with the powerful XLR-99, the X-15 would waste far
too much propellant taking off directly from the ground. Like many
other rocket powered test aircraft, the X-15 would be carried by a
large carrier aircraft to altitude before being dropped for the
beginning of a test flight. But the B-29 and its sibling, the B-50,
bombers used by earlier X-series aircraft were too small to handle the
much larger X-15. After much debate a modified B-52 bomber, which was
just entering service, was selected to be the X-15 mother craft. The
X-15 would be mounted under the B-52's starboard wing on a special
pylon that provided a variety of support functions before the X-15 was
launched. B-52A serial number 52-003 and B-52B serial number 52-008
were sent to North American for their transformation into the NB-52A
and NB-52B carrier aircraft.
First Flights
By the time the first X-15 was rolled out on October 15, 1958
the Space Age was already a year old and there was a new sense of
urgency in the program. The X-15 was the first craft ever built that
was capable of sending a man into space and it had a good chance of
not only beating the Soviet Union but NASA's just announced ballistic
man-in-space initiative. Because of the advanced state of
development, North American even proposed using an X-15 variant called
the X-15B to be launched into orbit using Titan boosters. Since NASA
was committed even at this early date to using a ballistic capsule for
its first manned flights, the North American plan lost out to the
proposal submitted by the McDonnell Aircraft Company (see "America's
First Spaceship" in the April 15, 1999 issue of SpaceViews).
In the mean time the X-15 was put through its paces in
anticipation of its first powered flight. The first captive flight
with the first X-15 attached to the NB-52 carrier took place on March
10, 1959. After several more captive flights, the X-15 flew its first
unpowered glide flight on June 8, 1959. At the controls of this and
most early flights was North American's test pilot Scott Crossfield -
a former NACA pilot who had flown the X-1, D-558-I and D-558-II and
had been the first man to fly faster than Mach 2 on November 20, 1953.
The first XLR-11 powered flight took place using X-15 #2 on September
17, 1959 with Crossfield easily reaching a speed of Mach 2.11 and an
altitude of 15.95 kilometers (9.91 miles).
A near repeat was accomplished a month later but the fourth
flight on November 5 was almost catastrophic. An engine fire forced
an emergency landing which resulted in a structural failure with the
X-15 almost breaking in two between the cockpit and propellant tank.
Fortunately Crossfield was not injured. The structural design defect
that lead to the failure was corrected and the aircraft was repaired.
Over the coming months the X-15 performance envelope was gradually
increased and new USAF, US Navy, and NASA pilots began flying this
manned bullet. After 29 flights with the XLR-11 engines, the X-15
made its first XLR-99 powered flight on March 7, 1961. While the
delay in the delivery of the XLR-99 powerplant meant that the X-15
would not make the first manned spaceflight, it did mark the beginning
of an unprecedented test program that blazed the trail for future
aerospace planes.
Bibliography
Ben Guenther, Jay Miller, and Terry Panopalis, North American
X-15/X-15A-2, Aerofax, Inc., 1985
Robert S. Houston, Richard P. Hallion, Ronald G. Boston, "Transiting
from Air to Space: The North American X-15", from The Hypersonic
Revolution Case Studies in the History of Hypersonic Technology Air
Force History and Museums Program, 1998
Jay Miller, The X-Planes: X-1 to X-29, Specialty Press, 1983
Milton O. Thompson, At the Edge of Space: The X-15 Flight Program,
Smithsonian Institute, 1992
Author
Drew LePage is a physicist and freelance writer specializing in
astronomy and the history of spaceflight. He can be reached at
lepage@visidyne.com.
*** Letters ***
More on RLVs and Financing
[Editor's Note: These letters are in response to one published in the
May 22 issue of SpaceViews, available at
http://www.spaceviews.com/1999/05/letters2.html. Letters can be sent
to letters@spaceviews.com.]
While there are seeming dark clouds on the horizon for RLVs,
the situation is not as bad as some would paint it. The development
cost for privatized RLVs today is comparable to the cost of a single
ELV failure. If the Delta III program had been run by a start-up
venture rather than by the biggest aerospace company in the world, it
would have gone broke by now. Kistler and Roton haven't made any
money yet, but they'll never lose as much as the Delta III program
already has.
And there have been a lot of ELV failures of late. The
venerable Delta and Titan are having their share of problems, and the
vaunted Zenit doesn't make satellite customers comfortable, either.
Based on actual events, it's rather unrealistic to claim that ELV
technology is "proven" and "highly reliable." And if it's not proven
and highly reliable by now, when will it be?
The small first-generation RLVs are not necessarily excluded
from the heavy-lift market as the ELV proponents assert. The Kistler
K-1 and Roton can both boost fairly large payloads into LEO. From
there, a teleoperated vehicle -- a space tug -- can rendezvous with
the payload, join it with fuel tanks, and transfer it into GEO. My
company, Astrotug (http://astrotug.com) is developing a reusable space
tug for this purpose.
When teleoperated space operations become commonplace,
megasatellite builders will begin to think about redesigning their
payloads as snap-together to-be-assembled-in-orbit modules that could
be shipped up in multiple small-lift missions -- rather than a single
"'all the eggs in one basket" heavy-lift mission. We don't even need
this to recognize that if an RLV engine fails, the craft may yet abort
safely -- but if an ELV engine fails, your $100 million payload sleeps
with the fishes.
In the long run -- that is, about five years from now -- small
RLVs could be in competition with heavy-lift ELVs, and seen as both
the less expensive and less risky alternative. The ELV, like the
socialist utopia which conceived of it, is an idea whose time has
gone.
Joe Schembrie
Robert Clements' letter in the May 22 issue of SpaceViews also
forgets one additional and important point. Interest in developing
RLV's will remain low while it is cheaper to buy insurance for your
spacecraft launch rather than try and develop new, more reliable,
launch capabilities.
The failure of nearly every launcher in the US arsenal in the
past few weeks is going to have a significant impact on the space
insurance market and cause rates to rise. Like the oil shortages in
the 1970s -- which led to the development of lean-burn engines and an
increase interest in new sources of energy -- higher insurance rates
may lead to a new interest in developing new launch capabilities.
Over 36,000 people have involved in prepping the Space Shuttle
for launch, if you can get this down to the same number that look
after Concorde for example (148), significant cost savings could be
made.
Paul Guinnessy
========
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