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Final Flight: STS-51L

Thirty-two years ago this month, the seven member crew of STS-51L were killed when the Space Shuttle Challenger disintegrated 73 seconds after launch from LC-39B at Cape Canaveral, Florida. The tragedy was the first fatal in-flight mishap in the history of American manned spaceflight.

In remarks made at a memorial service held for the Challenger Seven in Houston, Texas on Friday, 31 January 1986, President Ronald Wilson Reagan expressed the following sentiments:

“The future is not free: the story of all human progress is one of a struggle against all odds. We learned again that this America, which Abraham Lincoln called the last, best hope of man on Earth, was built on heroism and noble sacrifice. It was built by men and women like our seven star voyagers, who answered a call beyond duty, who gave more than was expected or required and who gave it little thought of worldly reward.”

We take this opportunity to remember the noble fallen:

Francis R. (Dick) Scobee, Commander

Michael John Smith, Pilot

Ellison S. Onizuka, Mission Specialist One

Judith Arlene Resnik, Mission Specialist Two

Ronald Erwin McNair, Mission Specialist Three

S.Christa McAuliffe, Payload Specialist One

Gregory Bruce Jarvis, Payload Specialist Two

Speaking for grieving families and countrymen, President Reagan closed his eulogy with these words:

“Dick, Mike, Judy, El, Ron, Greg and Christa – your families and your country mourn your passing. We bid you goodbye. We will never forget you. For those who knew you well and loved you, the pain will be deep and enduring. A nation, too, will long feel the loss of her seven sons and daughters, her seven good friends. We can find consolation only in faith, for we know in our hearts that you who flew so high and so proud now make your home beyond the stars, safe in God’s promise of eternal life.”

Tuesday, 28 January 1986. We Remember.

Posted in Aerospace, Final Flight, History

A Matter of Honor

Sixty-nine years ago this month, the USAF/Bell XS-1 became the first aircraft of any type to achieve supersonic flight during a climb from a ground take-off. The daring feat took place at Muroc Air Force Base with famed USAF Captain Charles E. “Chuck” Yeager at the controls of the rocket-powered XS-1.

Rocket-powered X-aircraft such as the XS-1, X-1A, X-2 and X-15 were air-launched from a larger carrier aircraft. With the test aircraft as its payload, this “mother ship” would take-off and climb to drop altitude using its own fuel load. This capability permitted the experimental aircraft to dedicate its entire propellant load to the flight research mission proper.

The USAF/Bell XS-1 was the first X-aircraft. It was carried to altitude by a USAF/Boeing B-29 mother ship. XS-1 air-launch typically occurred at 220 mph and 22,000 feet. On Tuesday, 14 October 1947, the XS-1 first achieved supersonic flight. The XS-1 would ultimately fly as fast as Mach 1.45 and as high as 71,902 feet.

All but two (2) of the early X-aircraft were Air Force developments. The exceptions were products of the United States Navy flight research effort; the USN/Douglas D-558-I Sky Streak and USN/Douglas D-558-II Sky Rocket. The Sky Streak was a turbojet-powered, straight-winged, transonic aircraft. The Sky Rocket was supersonic-capable, swept-winged, and rocket-powered. Each aircraft was originally designed to be ground-launched.

In the best tradition of inter-service rivalry, the Navy claimed that the D-558-I at the time was the only true supersonic airplane since it took to the air under its own power. Interestingly, the Sky Streak was able fly beyond Mach 1 only in a steep dive. Nonetheless, the Air Force was indignant at the Navy’s insinuation that the XS-1 was somehow less of an X-aircraft because it was air-launched.

Motivated by the Navy’s afront to Air Force honor, the junior military service devised a scheme to ground-launch the XS-1 from Rogers Dry Lake at Muroc (now Edwards) Air Force Base. The aircraft would go supersonic in what was essentially a high performance take-off and climb. To boot, the feat was timed to occur just before the Navy was to fly its rocket-powered D-558-II Sky Rocket. Justice would indeed be righteously served!

XS-1 Ship No. 1 (S/N 46-062) was selected for the ground take-off mission. Captain Charles E. Yeager would pilot the sleek craft with Captain Jackie L. Ridley providing vital engineering support. Due to its somewhat fragile landing gear, the XS-1 propellant load was restricted to 50% of capacity. This provided approximately 100 seconds of rocket-powered flight.

On Wednesday, 05 January 1949, Yeager fired all four (4) barrels of his XLR-11 rocket motor. Behind 6,000 pounds of thrust, the XS-1 quickly accelerated along the smooth surface of the dry lake. After a take-off roll of only 1,500 feet and with the XS-1 at 200 mph, Yeager pulled back on the control yoke. The XS-1 virtually leapt into the desert air.

The aerodynamic loads were so high during gear retraction that the actuator rod broke and the wing flaps tore away. Unfazed, Yeager’s eager steed continued to climb rapidly. Eighty seconds after brake release, the XS-1 hit Mach 1.03 passing through 23,000 feet. Yeager then brought the XS-1 to a wings level flight attitude and shutdown his XLR-11 power plant.

Following a brief glide back to the dry lake, Yeager executed a smooth dead-stick landing. Total flight time from lift-off to touchdown was on the order of 150 seconds. While a little worst for wear, the plucky XS-1 had performed like a champ and successfully accomplished something that it was really not designed to do.

Yeager was so excited during the take-off roll and high performance climb that he forgot to put his oxygen mask on! Potentially, that was a problem since the XS-1 cockpit was inerted with nitrogen. Fortunately, late in the climb, Yeager got his mask in place just before he went night-night for good.

Suffice it to say that the United States Navy was not particularly fond of the display of bravado and airmanship exhibited on that long-ago January day. The Air Force had emerged victorious in a classic contest of one-upmanship. At a deeper level, Air Force honor had been upheld. And, as was often the case in the formative years of the United States Air Force, it was a test pilot named Chuck Yeager who brought victory home to the blue suiters.

Posted in Aerospace, History

Flight Without a Tail

Fifty-four years ago this week, a USAF/Boeing B-52H Stratofortress landed safely following structural failure of its vertical tail during an encounter with unusually severe clear air turbulence. The harrowing incident occurred as the aircraft was undergoing structural flight testing in the skies over East Spanish Peak, Colorado.

Turbulence is the unsteady, erratic motion of an atmospheric air mass. It is attributable to factors such as weather fronts, jet streams, thunder storms and mountain waves. Turbulence influences the motion of aircraft that are subjected to it. These effects range from slight, annoying disturbances to violent, uncontrollable motions which can structurally damage an aircraft.

Clear Air Turbulence (CAT) occurs in the absence of clouds. Its presence cannot be visually observed and is detectable only through the use of special sensing equipment. Hence, an aircraft can encounter CAT without warning. Interestingly, the majority of in-flight injuries to aircraft crew and passengers are due to CAT.

On Friday, 10 January 1964, USAF B-52H (S/N 61-023) took-off from Wichita, Kansas on a structural flight test mission. The all-Boeing air crew consisted of instructor pilot Charles Fisher, pilot Richard Curry, co-pilot Leo Coors, and navigator James Pittman. The aircraft was equipped with accelerometers and other sensors to record in-flight loads and stresses.

An 8-hour flight was scheduled on a route that from Wichita southwest to the Rocky Mountains and back. The mission called for 10-minutes runs of 280, 350 and 400 KCAS at 500-feet AGL using the low-level mode of the autopilot. The initial portion of the mission was nominal with only light turbulence encountered.

However, as the aircraft turned north near Wagon Mound, New Mexico and headed along a course parallel to the mountains, increasing turbulence and tail loads were encountered. The B-52H crew then elected to discontinue the low level portion of the flight. The aircraft was subsequently climbed to 14,300 feet AMSL preparatory to a run at 350 KCAS.

At approximately 345 KCAS, the Stratofortress and its crew experienced an extreme turbulence event that lasted roughly 9 seconds. In rapid sequence the aircraft pitched-up, yawed to the left, yawed back to the right and then rolled right. The flight crew desperately fought for control of their mighty behemoth. But the situation looked grim. The order was given to prepare to bailout.

Finally, the big bomber’s motion was arrested using 80% left wheel authority. However, rudder pedal displacement gave no response. Control inputs to the elevator produced very poor response as well. Directional stability was also greatly reduced. Nevertheless, the crew somehow kept the Stratofortress flying nose-first.

The B-52H crew informed Boeing Wichita of their plight. A team of Boeing engineering experts was quickly assembled to deal with the emergency. Meanwhile, a Boeing-bailed F-100C formed-up with the Stratofortress and announced to the crew that most of the aircraft’s vertical tail was missing! The stricken aircraft’s rear landing was then deployed to add back some directional stability.

With Boeing engineers on the ground working with the B-52H flight crew, additional measures were taken in an effort to get the Stratofortress safely back on the ground. These measures included a reduction in airspeed, controlling aircraft center-of-gravity via fuel transfer, judicious use of differential thrust, and selected application of speed brakes.

Due to high surface winds at Wichita, the B-52H was vectored to Eaker AFB in Blytheville, Arkansas. A USAF/Boeing KC-135 was dispatched to escort the still-flying B-52H to Eaker and to serve as an airborne control center as both aircraft proceeded to the base. Amazingly, after flying 6 hours sans a vertical tail, the Stratofortress and her crew landed safely.

Safe recovery of crew and aircraft brought additional benefits. There were lots of structural flight test data! It was found that at least one gust in the severe CAT encounter registered at nearly 100 mph. Not only were B-52 structural requirements revised as a result of this incident, but those of other existing and succeeding aircraft as well.

B-52H (61-023) was repaired and returned to the USAF inventory. It served long and well after its close brush with catastrophe in January 1964. The aircraft spent the latter part of its flying career as a member of the 2nd Bomb Wing at Barksdale AFB, Louisiana. The venerable bird was retired from active service in July of 2008.

Posted in Aerospace, History

The Birth of Flight

One-hundred and fourteen years ago this month, the Wright Flyer became the first aircraft in history to achieve powered flight. The site of this historic event was Kill Devil Hills located near Kitty Hawk, North Carolina.

Americans Wilbur and Orville Wright began their legendary aeronautical careers in 1899. In a matter of just four short years, the brothers would go from complete aeronautical novices to inventors and pilots of the world’s first successful powered aircraft. Neither man attended college nor received even a high school diploma.

The Wright Flyer measured roughly 21 feet in length and had a wing span of approximately 40 feet. The biplane aircraft had an empty weight of 605 lbs. Power was provided by a single 12 horsepower, 4-cylinder engine that drove twin 8.5 foot, two-blade propellers.

The Flyer made a powered take-off run along a 60-foot wooden guide rail. The aircraft was mounted on a two-wheel dolly that rode along the track and was jettisoned at lift-off. The Flyer pilot lay prone in the middle of the lower wing. Twin elevator and rudder surfaces provided pitch and yaw control, respectively. Roll control was via differential wing warping.

The Wright Brothers had come close to achieving a successful powered flight with the Wright Flyer on Monday, 14 December 1903. Wilbur, who had won the coin toss, was the pilot for the initial attempt. However, the Flyer stalled and hit the ground sharply just after take-off. Wilbur was unhurt, but repair of the damaged aircraft would take two days.

The next attempt flight took place on Thursday, 17 December 1903. The weather was terrible. Windy and rainy. Even after the rain abated, the wind continued to blow in excess of 20 mph. The Wrights decided to fly anyway. It was now Orville’s turn as command pilot.

Orville took his position on the Flyer and was quickly launched into the wind. Once airborne, the aircraft proved difficult to control as it porpoised up and down along the flight path. Nonetheless, Orville kept the Flyer in the air for 12 seconds before landing 120 feet from the take-off point. Other than a damaged skid, the aircraft was intact and the pilot unhurt. Powered flight was a reality!

Three more flights followed on that momentous occasion as the two brothers alternated piloting assignments. The fourth flight was the longest in both time aloft and distance flown. With Wilbur at the controls, the Wright Flyer flew for 59 seconds and landed 852 feet from the take-off point.

The Wright Brothers father, Milton, would soon learn of the epic events that December day in North Carolina. Orville’s verbatim Western Union telegram message sent to Dayton, Ohio read:

Success four flights thursday morning all against twenty one mile wind started from level with engine power alone average speed through air thirty one miles longest 57 [sic] seconds inform press home Christmas.

Posted in Aerospace, History

Apollo 8

Forty-nine years ago today, three American astronauts departed Earth to become the first men to orbit the Moon during the flight of Apollo 8. This epic mission also featured the first manned flight of the mighty Saturn V launch vehicle as well as history’s first super-orbital entry of a manned spacecraft.

Following the Apollo 1 tragedy in January of 1967, the United States would not fly another manned space mission until October 1968. That flight, Apollo 7, was a highly successful earth-orbital mission in which the new Block II Apollo Command Module was thoroughly flight-proven.

Notwithstanding Apollo 7’s accomplishments, only 14 months remained for the United States to meet the national goal of achieving a manned lunar landing before the end of the 20th century’s 7th decade. The view held by many in late 1968 was that an already daunting task was now unachievable in the narrow window of time that remained to accomplish it.

The pessimism about reaching the Moon before the end of the decade was easy to understand. The Saturn V moon rocket had not been man-rated. The Lunar Module had not flown. Lunar Orbit Rendezvous (LOR) was untried. Men had not even so much as orbited the Moon. Yet, history would record that the United States would find a way to accomplish that which had never before been achieved.

George Low, manager of NASA’s Apollo Spacecraft Program Office, came up with the idea. Low proposed that the first manned flight of the Saturn V be a trip all the way to the Moon. It was something that Low referred to as the “All-Up Testing” concept. The newly-conceived mission would be flown in December 1968 near Christmas time.

While initially seen as too soon and too risky by many in NASA’s management hierarchy, Low’s bold proposal was ultimately accepted as the only way to meet the national lunar landing goal. Yes, there was additional risk. However, the key technologies were ready, the astronauts were willing, and the risk was acceptable.

Apollo 8 lifted-off from LC-39A at the Kennedy Space Center in Florida on Saturday, 21 December 1968 at 12:51 hours UTC. The crew consisted of NASA astronauts Frank Borman, James A. Lovell, Jr. and William A. Anders. Their target – the Moon – was 220,000 miles away.

After a 69-hour outbound journey, Apollo 8 entered lunar orbit on Tuesday, 24 December 1968 – Christmas Eve. The Apollo 8 crew photographed the lunar surface, studied the geologic features of its terrain, and made other observations from a 60-nautical mile circular orbit. The spacecraft circled the Moon 10 times in slightly over 20 hours.

For many, the most poignant and memorable event in Apollo 8’s historic journey occurred on Christmas Eve night when each of the flight crew took turns reading from the Book of Genesis in the Holy Bible. The solemnity of the moment was evident in the voices of the astronauts. They had seen both the Moon and the Earth from a perspective that none before them had. Fittingly, they expressed humble reverence for the Creator of the Universe on the anniversary of the birth of the Redeemer of mankind.

Apollo 8 departed lunar orbit a little over 89 hours into the mission. Following a nearly 58-hour inbound trip, Apollo 8 reentered the earth’s atmosphere at 36, 221 feet per second on Friday, 27 December 1968. The first manned super-orbital reentry was performed in total darkness. It was entirely successful as Apollo 8 landed less than 1 nautical mile from its target in the Pacific Ocean. The USS YORKTOWN effected recovery of the weary astronauts and their trustworthy spacecraft. Mission total elapsed time was 147 hours and 42 seconds.

The year 1968 was a tumultuous one for the United States of America. Martin Luther King and Robert Kennedy had been assassinated. American military blood flowed on the battlefields of Vietnam and civilian blood was let in countless demonstrations taking place in the nation’s cities. The ill-posed sexual revolution continued to eat away at the country’s moral moorings.

But, as is so often the case, an event from the realm of flight, now newly extended to lunar space, reminded us of our higher nature and potential. For a too brief moment, Apollo 8 put our collective purpose for being here into sharp focus. Perhaps a short phrase in a telegram sent to Frank Borman from someone he had never met said it best: “You saved 1968!”

However, looking through the lens of history, we now know that Apollo 8 did much more than end the penultimate year of the 1960’s on a positive note. Indeed, it may be said that Apollo 8 saved the entire Apollo Program.

Posted in Aerospace, History

World Altitude Record

Fifty-eight years ago this week, USAF Captain Joe B. Jordan zoomed a modified USAF/Lockheed F-104C Starfighter to a world altitude record of 103,395.5 feet above mean sea level. The flight originated from and recovered to the Air Force Flight Test Center (AFFTC) at Edwards Air Force Base, California.

On Tuesday, 14 July 1959, the USSR established a world altitude record for turbojet-powered aircraft when Soviet test pilot Vladimir S. Ilyushin zoomed the Sukhoi T-43-1 (a prototype of the Su-9) to an absolute altitude of 94,661 feet. By year’s end, the Soviet achievement would be topped by several American aircraft.

FAI rules stipulate that an existing absolute altitude record be surpassed by at least 3 percent for a new mark to be established. In the case of the Soviet’s 1959 altitude record, this meant that an altitude of at least 97,501 feet would need to be achieved in a record attempt.

On Sunday, 06 December 1959, USN Commander Lawrence E. Flint wrested the months-old absolute altitude record from the Soviets by zooming to 98,561 feet. Flint piloted the second USN/McDonnell Douglas YF4H-1 (F4 Phantom II prototype) in accomplishing the feat. In a show of inter-service cooperation, the record flight was made from the AFFTC at Edwards Air Force Base.

Meanwhile, USAF was feverishly working on its own record attempt. The aircraft of choice was the Lockheed F-104C Starfighter. However, with the record now held by the Navy, the Starfighter would have to achieve an absolute altitude of at least 101,518 feet to set a new mark. (Per the FAI 3 percent rule.)

On Tuesday, 24 November 1959, the AFFTC accepted delivery of the record attempt aircraft, F-104C (S/N 56-0885), from the Air Force Special Weapons Center at Kirtland AFB in New Mexico. This aircraft was configured with a J79-GE-7 turbojet capable of generating nearly 18,000 pounds of sea level thrust in afterburner.

Modifications were made to the J79 to maximize the aircraft’s zoom kinematic performance. The primary enhancements included increasing afterburner fuel flow rate by 10 percent and maximum RPM from 100 to 103.5 percent. Top reset RPM was rated at 104.5 percent. Both the ‘A’ and ‘B’ engine flow bypass flaps were operated in the open position as well. These changes provided for increased thrust and stall margin.

An additional engine mod involved reducing the minimum engine fuel flow rate from 500 to 250 pounds per hour. Doing so increased the altitude at which the engine needed to be shut down to prevent over-speed or over-temperature conditions. Another change included increasing the maximum allowable compressor face temperature from 250 F to 390 F.

The F-104C external airframe was modified for the maximum altitude mission as well. The compression cones were lengthened on the bifurcated inlets to allow optimal pressure recovery at the higher Mach number expected during the record attempt. High Mach number directional stability was improved by swapping out the F-104C empennage with the larger F-104B tail assembly.

USAF Captain Joe B. Jordan was assigned as the altitude record attempt Project Pilot. USAF 1st Lt and future AFFTC icon Johnny G. Armstrong was assigned as the Project Engineer. Following an 8-flight test series to shake out the bugs on the modified aircraft, the record attempt proper started on Thursday, 10 December 1959.

On Monday, 14 December 1959, F-104C (S/N 56-0885) broke the existing absolute altitude record for turbojet-powered aircraft on its 5th attempt. Jordan did so by accelerating the aircraft to Mach 2.36 at 39,600 feet. He then executed a 3.15-g pull to an inertial climb angle of 49.5 degrees. Jordan came out of afterburner at 70,000 feet and stop-cocked the J79 turbojet at 81,700 feet.

Roughly 105 seconds from initiation of the pull-up, Joe Jordan reached the top of the zoom. The official altitude achieved was 103,395.5 feet above mean sea level based on range radar and Askania camera tracking. True airspeed over the top was on the order of 455 knots. Jordan started the pull-up to level flight at 60,000 feet; completing the recovery at 25,000 feet. Landing was entirely uneventful.

Jordan’s piloting achievement in setting the new altitude record was truly remarkable. His conversion of kinetic energy to altitude (potential energy) during the zoom was extremely efficient; realizing only a 2.5 percent energy loss from pull-up to apex. Jordan also exhibited exceptional piloting skill in controlling the aircraft over the top of the zoom where the dynamic pressure was a mere 14 psf. He did so using aerodynamic controls only. The aircraft did not have a reaction control system ala the X-15.

Armstrong’s contributions to shattering the existing altitude record were equally substantial. Skillful flight planning and effective use of available resources (including time available for the record attempt) were pivotal to mission success. Armstrong significantly helped maximize aircraft zoom performance through proper selection of pull-up flight conditions and intelligent use of accurate day-of-flight meteorological information.

For his skillful piloting efforts in setting the world absolute altitude record for turbojet-powered aircraft in December of 1959, Joe Jordan received the 1959 Harmon Trophy.

Posted in Aerospace, History

Boom and Zoom

Fifty-four years ago today, USAF Major Robert W. Smith zoomed the rocket-powered Lockheed NF-104A to an unofficial world record altitude of 120,800 feet. This mark still stands as the highest altitude ever achieved by a United States aircraft from a runway take-off.

A zoom maneuver is one in which aircraft kinetic energy (speed) is traded for potential energy (altitude). In doing so, an aircraft can soar well beyond its maximum steady, level altitude (service ceiling). The zoom maneuver has both military and civilian flight operations value.

The USAF/Lockheed NF-104A was designed to provide spaceflight-like training experience for test pilots attending the Aerospace Research Pilot School (ARPS) at Edwards Air Force Base, California. The type was a modification of the basic F-104A Starfighter aircraft. Three copies of the NF-104A were produced (S/N’s 56-0756, 56-0760 and 56-0762). It was the ultimate zoom flight platform.

In addition to a stock General Electric J79-GE-3 turbojet, the NF-104A was powered by a Rocketdyne LR121-NA-1 rocket motor. The J79 generated 15,000 pounds of thrust in afterburner and burned JP-4. The LR-121 produced 6,000 pounds of thrust and burned a combination of JP-4 and 90% hydrogen peroxide. Rocket motor burn time was on the order of 90 seconds.

The NF-104A was kinematically capable of zooming to altitudes approaching 125,000 feet. As such, it was a combined aircraft, rocket, and spacecraft. The pilot had to blend aerodynamic and reaction controls in the low dynamic pressure environment near the zoom apex. He was also required to fly in a full pressure suit for survival at altitudes beyond the Armstrong Line.

On Friday, 06 December 1963, Bob Smith took-off from Edwards and headed west for the Pacific Ocean. Out over the sea, he changed heading by 180 degrees in preparation for the zoom run-in. At a point roughly 100 miles out, Smith then accelerated the NF-104A (S/N 56-0760) along a line that would take him just north of the base. Arriving at Mach 2.4 and 37,000 feet, Smith then initiated a 3.75-g pull to a 70-degree aircraft pitch angle. Turbojet and rocket were at full throttle.

Things happened very quickly now. Smith brought the turbojet out of afterburner at 65,000 feet and then moved the throttle to the idle detent at 80,000 feet. The rocket motor burned-out around 90,000 feet. Smith controlled the aircraft (now spacecraft) over the top of the zoom using 3-axis reaction controls. The NF-104A’s arcing parabolic trajectory subjected him to 73 seconds of weightlessness. Peak altitude achieved was 120,800 feet above mean sea level.

On the back side of the zoom profile, Bob Smith restarted the windmilling J79 turbojet and set-up for landing at Edwards. He touched down on the main runway and rolled out uneventfully. Total mission time from brake-release to wheels-stop was approximately 25 minutes.

Much more could be said about the NF-104A and its unique mission. Suffice it to say here that two of the aircraft ultimately went on to serve in the ARPS from 1968 to 1971. The only remaining aircraft today is 56-0760 which sits on a pole in front of the USAF Test Pilot School (TPS) at Edwards.

Bob Smith went on to make many other noteworthy contributions to aviation and his nation. Having flown the F-86 Sabre in Korea, he volunteered to fly combat in Viet Nam in his 40th year. Stationed at Korat AFB in Thailand, he commanded the 34th Fighter Squadron of the 388th Tactical Fighter Wing. Smith flew 100 combat missions in the fabled F-105D Thunderchief; many of which involved the infamous Pack VI route in North Viet Nam.

Bob Smith was a true American hero. Like so many of the airmen of his day, Smith was a man whose dedication, service, and courage went largely unnoticed and underappreciated by his fellow countrymen. Bob Smith’s final flight came just 3 months shy of his 82nd birthday on Thursday, 19 August 2010.

Posted in Aerospace, History

Earth Entry Milestone

Sixty years ago this month, the first ablative nose cone to survive entry into the Earth’s atmosphere was formally presented to the American public. President Dwight D. Eisenhower displayed the recovered nose cone during a national television broadcast from the Oval Office.

An object making a hypersonic entry into the the Earth’s atmosphere from space possesses a great deal of kinetic energy. This energy of motion is transformed to thermal energy as aerodynamic drag slows the vehicle during atmospheric flight. A portion of the entry thermal energy is absorbed by the vehicle structure in a process referred to as aerodynamic heating. This heat transfer process causes the temperature of the external surface of the vehicle to significantly increase.

From a vehicle survivability standpoint, three parameters are key; (1) maximum heat transfer rate, (2) maximum surface temperature and (3) total thermal energy absorbed by the vehicle during entry. The concern is that there is enough kinetic energy in the entry flight domain to vaporize any known material if that energy is completely absorbed by the vehicle.

One has only to look into the heavens at night to become convinced of the ferocity of the entry environment. The streaks of white, yellow, green, blue, or red light that dramatically flash into and out of existence are associated with the vaporization of meteors transiting the atmosphere. Few meteors have enough pre-entry mass to allow a minor portion thereof to reach the ground. Those that do are referred to as meteorites.

The problem of surviving atmospheric entry was a major research topic in the 1950’s. Attention focused on protecting the nuclear warhead carried by the reentry vehicle of an Intercontinental Ballistic Missile (ICBM). A pair of research scientists at the NACA Ames Research Center in California, H. Julian Allen and Alfred J. Eggers, are credited with solving the problem. The key was to hemispherically-blunt or round the nose of a reentry vehicle.

A blunted forebody disposes a detached, hyperbolic-shaped shock wave which slows the post-shock flow to subsonic speeds in the stagnation region. A byproduct of this flow deceleration is a significant increase in post-shock static pressure and temperature. While this dramatically increases vehicle wave drag, most of the high temperature air passes around the vehicle and thus never physically comes in contact with it. The result is that only a small fraction of the overall thermal energy of the freestream flow is convected to the vehicle surface.

In contrast to the above, a sharp-nosed vehicle nose disposes an attached, highly-swept shock wave. This flow topology results in a large fraction of the overall thermal energy being convected to the vehicle surface. The is because the degree of post-shock flow slowing in such a situation is small. Indeed, the post-shock flow has a high supersonic Mach number. Now, due to the “no-slip” condition caused by fluid viscosity, the flow velocity at the vehicle surface is zero. Thus, the bulk of the flow deceleration has to occur within the boundary layer. The huge shearing stresses and temperature gradients that result generate extreme heat flux rates at the vehicle surface.

On Thursday, 08 August 1957, a Jupiter-C launch vehicle carrying a one-third scale version of a Jupiter IRBM nose was launched from LC-6 at Cape Canaveral, Florida. The nose cone traveled 1,168 nautical miles, reaching nearly 9,000 mph and an altitude of 260 nautical miles in the process. During reentry an ablative heat shield was used to protect the nose cone from the aerodynamic heating environment. The vehicle parachuted into the Atlantic Ocean and was recovered by Navy swimmers within three hours of launch.

On Thursday, 07 November 1957, President Dwight D. Eisenhower displayed the recovered Jupiter IRBM scaled nose cone in a nationally televised broadcast from the Oval Office. The excellent condition of the recovered vehicle was a stark testament to the effectiveness of a blunted, ablative nose cone to weather the rigors of reentry heating. This historic breakthrough would forever change the science of atmospheric entry. Indeed, it would ultimately make possible successful entry of Apollo astronauts returning from the Moon at 25,000 mph.

Today, one can view the recovered Jupiter IRBM subscale nose cone at the Smithsonian’s National Air and Space Museum in Washington, DC. Specifically, it is on public display in the Space Race Exhibition at the National Mall Building.

Posted in Aerospace, History

First to Mach Two

Sixty-four years ago today, the USN/Douglas D-558-II Skyrocket became the first aircraft to fly at twice the speed of sound. This historic event took place in the skies over Edwards Air Force Base, California.

The D-558-II was a United States Navy (USN) X-aircraft and first flew in February of 1948. It was contemporaneous with the USAF/Bell XS-1. The aircraft measured 42 feet in length with a wing span of 25 feet. Maximum take-off weight was 15,266 pounds. Douglas manufactured a trio of D-558-II aircraft (Bureau Numbers 37973, 37974 and 37975).

The original version of the swept-wing D-558-II had both rocket and turbojet propulsion. The latter system providing a ground take-off capability. However, like other early X-aircraft such as the XS-1, X-1A, X-2 and X-15), the D-558-II achieved max performance through the use of a mothership and rocket power alone.

The record-setting day was Friday, 20 November 1953. On that occasion, the white D-558-II (Bureau No. 37974) was carried to the drop altitude of 32,000 feet by a USN P2B-1S (Bureau No. 84029). NACA test pilot A. Scott Crossfield was in the D-558-II cockpit. Although ailing with the stomach flu, Crossfield was not about to let a little urpiness force him to miss today’s historic aeronautical events!

Following a successful drop from the mothership, Crossfield ignited the Reaction Motors LR8-RM-6 (USN designation for the XLR-11) rocket motor and started uphill. After closely adhering to a carefully planned climb schedule, Crossfield initiated a pushover at 72,000 feet that resulted in a shallow dive. Passing through 62,000 feet, the D-558-II hit a speed of 1,291 mph; Mach 2.005.

The D-558-II reached Mach 2 due to a confluence of several factors. First, Crossfield flew the profile as briefed. Second, temperatures at altitude that day were unusually low. This lowered the speed of sound and thus increased Mach number. Third, the ground crew did an extraordinary job of optimizing the D-558-II for the maximum speed mission.

Expanding on the last point mentioned above, extension tubes were added to the LR8-RM-6 rocket motor. This increased thrust from 6,000 to 9,000 pounds. The aircraft was then cold-soaked overnight in an effort to maximize its propellant load. Finally, external airframe gaps and panel openings were taped over and the aircraft was waxed and polished in an effort to minimize aerodynamic drag.

Scott Crossfield received the 1954 Lawrence B. Sperry Award for his Mach 2 exploits. The record-setting aircraft (Bureau No. 37934) is currently displayed at the National Air and Space Museum in Washington, D.C. in tribute to its many contributions to aviation history.

Posted in Aerospace, History

First Reusable Space Vehicle

Thirty-six years ago this week, the Space Shuttle Columbia completed the second orbital space mission of the Space Shuttle Program. Designated STS-2, the mission marked the first reuse of a space vehicle for manned orbital flight.

America’s early manned spacecraft – Mercury, Gemini and Apollo – were single-flight vehicles. That is, a new spacecraft was required for each space mission. This was appropriate for meeting the aims of the early space program which concentrated on getting America to the moon before the end of the 1960’s.

The concept of space vehicle reusability came into vogue with the introduction of the Space Transportation System (STS). The original goal of the STS was to provide frequent and routine access to space via a fleet of Space Shuttle vehicles. For the STS to achieve economic viability, this meant flying a Space Shuttle once every two weeks. History records that this projected flight rate was much too optimistic.

The Space Shuttle vehicle was ultimately configured as a 3-element system consisting of (1) a winged orbiter, (2) a pair of solid rocket boosters (SRB’s) and (3) an external tank (ET). Both the orbiter and the SRB’s were designed to be reusable. The ET would be the only disposable element of the system since higher costs would be incurred in the recovery and refurbishment of this piece of flight hardware than in simply using a new one for each flight.

The Space Shuttle was designed to haul large payloads; on the order of 60,000 and 50,00 lbs into and out of orbit, respectively. With a maximum landing weight of 230,000 lbs, the Space Shuttle Orbiter needed wings to generate the required aerodynamic lift force. Wings were needed to satisfy the Orbiter’s 1,100-nm entry cross range requirement as well.

Following the successful first flight (STS-1) of the Space Shuttle Columbia in April of 1981, preparations began immediately to ready the Orbiter for its equally monumental second flight. The STS-2 flight crew would consist of Commander Joe Henry Engle and Pilot Richard Harrison Truly. STS-2 would be the first orbital spaceflight for both men.

On Thursday, 12 November 1981, the Space Shuttle Columbia lifted-off at 15:09:59 UTC from Cape Canaveral’s LC-39A. Ascent flight was nominal and Columbia was placed into a 125-nm x 120-nm orbit. At this point, Columbia became the first manned spacecraft to achieve Earth-orbit twice. It was an extra special occasion for Richard Truly inasmuch as it was his 44th birthday.

Engle and Truly anticipated 5-days in orbit with their celestial steed. However, one of Columbia’s three fuel cells failed early-on and the mission was reduced to just over two days. Nonetheless, the crew achieved 90 percent of the mission’s goals. They even remained awake during a scheduled sleep period to exercise the new Canadian Remote Manipulator System (RMS).

On Saturday, 14 November 1981, Columbia and her crew successfully completed STS-2 by landing on Rogers Dry Lake at Edwards Air Force Base, California. Main gear touchdown occurred at 21:23:11 UTC. Joe Engle flew the entire reentry manually. He holds the distinction of being the only pilot to manually fly a lifting space vehicle all the way from orbit to landing. Engle completed a total of 29 Programmed Test Input (PTI) aerodynamic maneuvers in the process.

STS-2 was a monumental success. Columbia became the first space vehicle to be reused for manned orbital space operations. Other Orbiters would follow including Challenger, Atlantis, Discovery, and Endeavor. The final mission of the Space Shuttle Program (STS-135) was flown by Atlantis in July 2011.

As a footnote, Joe Engle went on to command one more Space Shuttle mission in 1985 (STS-51I). He retired from the USAF in November of 1986. Richard Truly served as Commander of STS-8 in 1983. That mission featured the first night launch and landing of the Space Shuttle. Richard Truly also served as NASA Administrator from May of 1989 to May of 1992.

Posted in Aerospace, History
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