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Faster Than a Speeding Bullet

Fifty years ago this month, USAF Major William J. “Pete” Knight piloted the fabled USAF/North American X-15A-2 hypersonic flight research aircraft to a record speed of 4,520 mph – roughly a mile and a quarter per second. This is about 50 percent faster than the highest speed ever attained by a “speeding bullet”.

North American’s original X-15 production run consisted of three (3) aircraft. The X-15A-2 was a rebuild of the 2nd airframe (S/N 56-6671) which had been severely damaged during an emergency landing at Mud Lake, Nevada in November of 1962.

The rebuilt aircraft was configured with a pair of droppable propellant tanks that allowed the type’s XLR-99 rocket engine to operate 60 seconds beyond the stock X-15’s 80-second burn time. Among other modifications, the aircraft also carried a pylon-mounted dummy ramjet in the ventral region of the aft fuselage.

With the addition of the external propellant tanks, the X-15A-2 was really a three-stage vehicle. The first stage was the NASA NB-52B mothership which launched the X-15 at Mach 0.82 and 45,000 feet. The second stage consisted of the propellant-laden external tanks which were jettisoned at Mach 2.0 and 70,000 feet. The third stage was the X-15A-2 with its entire internal propellant load.

Due to the increased speed of the X-15A-2, the aircraft was covered with Martin MA-25S ablator to protect it from the higher aerodynamic heating loads. The baseline ablator was pink in color and gave the X-15A-2 a rather odd appearance. Fortunately, application of a white wear/sealer over the ablator gave the aircraft a more dignified look.

On Tuesday, 03 October 1967, Pete Knight and the X-15A-2 dropped away from the NB-52B (S/N 52-008) at the start of the X-15 Program’s 188th mission. Knight ignited the XLR-99 rocket engine and executed a pull-up followed by a pushover to level flight at a little over 102,000 feet. Aircraft speed at XLR-99 burnout was 4,520 mph (Mach 6.7).

As the aircraft decelerated following burnout, Knight executed a series of pre-planned flight maneuvers to acquire vital aerodynamics data. However, passing through Mach 5.5, he received an indication in the cockpit that a high temperature condition existed in the XLR-99 engine bay.

Knight attempted to jettison the aircraft’s remaining propellants, but to no avail. The jettison tubes were welded shut by whatever was happening in the engine bay. This meant he would land heavier and faster than usual. Fortunately, Knight’s piloting skills allowed him to get the X-15A-2 on to Rogers Dry Lake in one piece.

As flight support personnel inspected the X-15A-2 airframe following Knight’s emergency landing, they were alarmed at what they found. The aft ventral region of the aircraft had incurred significant thermal damage. Further, the dummy ramjet was gone.

As reported in the classic NASA document, TM-X-1669, higher-than-expected aerodynamic heating levels were responsible for the damage to the X-15A-2.

First, shock wave/boundary layer interaction heating on the lower fuselage just ahead of the pylon (1) completely destroyed the ablator in that region and (2) penetrated the Inconel-X airframe structure. This introduced very high temperature air into the X-15 engine bay.

Second, impingement of the dummy ramjet nose shock on the detached bow shock coming off of the pylon produced a shear layer that focused on the pylon leading edge. The resulting heating rates were of sufficient magnitude and duration to both burn away the pylon ablator and burn through the pylon structure. The weakened pylon structural attachment eventually failed and the dummy ramjet departed the main airframe.

Pete Knight will forever hold the record for the fastest X-15 flight. However, the X-15A-2 never flew again. Only 11 more flights remained in the X-15 Program at the time. A lack of time and funding meant that little was to be gained by repairing the thermally-damaged aircraft.

As for the final disposition of the X-15A-2 (S/N 56-6671), the aircraft’s remaining ablator was removed with its external surface cleaned-up and original markings restored. The aircraft now resides in a place of honor at the National Museum of the United States Air Force located at Wright-Patterson AFB in Dayton, Ohio.

Posted in Aerospace, History

Joining the Fleet

Thirty-two years ago this month, the Space Shuttle Atlantis was launched on its maiden spaceflight. Known as Mission STS-51J, the flight made Atlantis the fourth member of the Space Shuttle Orbiter fleet to reach Earth orbit.

Mission STS-51J marked the twenty-first orbital flight of the Space Shuttle Program. The primary objective of Atlantis’ first mission was to deploy a Department of Defense (DoD) satellite payload to geostationary orbit. The all-military crew included Commander Karol J. Bobko, Pilot Ronald J. Grabe, Mission Specialists David C. Hilmers and Robert L. Stewart, and Payload Specialist William A. Pailes.

Although classified at the time, the STS-51J payload is suspected to have consisted of a pair of Defense Satellite Communications System (DSCS) satellites. The function of these Lockheed-developed spacecraft was to provide a secure communications capability in support of vital military installations situated across the globe.

Atlantis was launched from LC-39A at Cape Canaveral, Florida on Thursday, 03 October 1985. Lift-off time occurred at 15:15:30 UTC. The new orbiter was successfully inserted into a near-circular orbit having a mean altitude of 219-nm. Orbital inclination and period were 28.5-deg and 94.2 minutes, respectively.

Following deployment from Atlantis’ payload bay, a single Boeing Inertial Upper Stage (IUS) successfully propelled the pair of DSCS satellites into geostationary orbit. With each satellite weighing 5,760 lbs, the total DSCS-IUS stack tipped the scales at 44,020 lbs.

Atlantis orbited the globe 64 times before returning to Earth on Monday, 07 October 1985. The Orbiter touched-down on Rogers Dry Lake at Edwards Air Force Base, California at 17:00:08 UTC. Total mission time was 97 hours, 44 minutes and 38 seconds. From lift-off to landing, Atlantis and her crew flew a total distance of 1,462,203 nm.

History records that Atlantis flew 33 (24.4%) of the 135 missions flown over the life of the Space Shuttle Program. During an “operational” flight career spanning 1985 to 2011, Atlantis and her crews contributed immensely to American spaceflight. Key among many accomplishments were helping to build the International Space Station (ISS), refurbishing the Hubble Space Telescope (HST), launching of the Magellan Probe to Venus, and launching the Galileo Probe to Jupiter.

Like her other stable mates, Atlantis no longer graces the heavens with her presence. She had the honor (?) of flying the final Space Shuttle mission (STS-135) in July of 2011. Now eternally rooted to the ground, Atlantis resides on public display at NASA’s Kennedy Space Center (KSC) in Florida.

Posted in Aerospace, History

Through the Sonic Barrier

Seventy years ago this week, the rocket-powered USAF/Bell XS-1 experimental aircraft exceeded the speed of sound when it reached a maximum speed of 700 mph (Mach 1.06) at 45,000 feet.

Bell Aircraft Corporation of Buffalo, New York built three copies of the XS-1 under contract to the United States Army Air Forces (USAAF). The aircraft were designed to approach and then fly beyond the speed of sound.

The Bell XS-1 was 31-feet in length and had a wing span of 28 feet. Gross take-off weight was around 12,500 lbs. The aircraft had an empty weight of about 7,000 lbs. Propulsion was provided by a Reaction Motors XLR-11 rocket motor capable of generating a maximum thrust of 6,000 lbs.

On the morning of Tuesday, 14 October 1947, the XS-1 (S/N 46-062) dropped away from its B-29 mothership (S/N 45-21800) as the pair flew at 220 mph and 20,000 feet. In the XS-1 cockpit was USAAF Captain and World War II ace Charles E. Yeager. The young test pilot had named the aircraft Glamorous Glennis in honor of his wife.

Following drop, Yeager sequentially-lit all four XLR-11 rocket chambers during a climb and push-over that ultimately brought him to level flight around 45,000 feet. The resulting acceleration profile propelled the XS-1 slightly beyond Mach 1 for about 20 seconds. Yeager then shutdown the rocket, decelerated to subsonic speeds, and landed the XS-1 on Muroc Dry Lake at Muroc Army Airfield, California.

The world would not find out about the daring exploits of 14 October 1947 until December of the same year. As it was, the announcement came from a trade magazine that even today is sometimes referred to as “Aviation Leak”.

Today, Glamorous Glennis is prominently displayed in the Milestones of Flight hall of the National Air and Space Museum located in Washington, DC. For his intrepid piloting efforts in breaking the sound barrier, Chuck Yeager was a co-recipient of the 1948 Collier Trophy.

Posted in Aerospace, History

Back in the Saddle

Twenty-nine years ago today, the Space Shuttle Discovery and her five man crew landed on Rogers Dry Lake at Edwards Air Force Base to successfully complete the Return-to-Flight (RTF) mission of STS-26. The flight signaled a resumption of the Space Shuttle Program after a 32-month hiatus in manned spaceflight resulting from the Challenger disaster.

Well chronicled is the tragic loss of the Space Shuttle Challenger and its crew of seven on Tuesday, 28 January 1986. Following lift-off at 16:38 UTC from Cape Canaveral’s LC-39B, the launch vehicle disintegrated 73 seconds into flight. The presidentially-appointed Rogers Commission concluded that the primary cause was failure of an O-ring seal in a field joint of the right Solid Rocket Booster (SRB).

While the SRB O-ring failure was the physical cause of the Challenger mishap, the Rogers Commission brought to light a more fundamental and disturbing reason for the tragedy. Specifically, the very decision to launch Challenger on that unusually cold January morning in Florida was fundamentally flawed.

As masterfully delineated in Dianne Vaughan’s “The Challenger Launch Decision”, a culture of deviance with respect to Shuttle flight safety issues had slowly developed at NASA. Pressure to launch, scarce resources and organizational disconnects contributed to NASA management’s blind spot when it came to Shuttle flight safety. The SRB contractor was culpable as well and for the same reasons.

Following redesign and testing of the SRB field joints and the implementation of a myriad of other fixes, NASA prepared to return the Shuttle to flight. The mission was designated as STS-26. To the Space Shuttle Discovery would go the honor of and the responsibility for flying the RTF mission. STS-26 was to be a five day orbital mission.

A five-member crew was selected by NASA to fly STS-26. Each crew member had spaceflight experience. You remember their names. Mission Commander Frederick H. “Rick” Hauck, Pilot Richard O. Covey, and Mission Specialists John M. “Mike” Lounge, George D. “Pinky” Nelson and David C. Hilmers.

Discovery and her brave crew lifted-off from at 15:37 UTC on Thursday, 29 September 1988 from the very same location that Challenger did; LC-39B at Cape Canaveral, Florida. Millions watched that day. Some were in the big crowds that formed in and around the Cape complex. Most observed the event on television. Many prayed.

All who watched Discovery lift-off that day could not forget the previous Shuttle flight. Indeed, they remembered what happened just after the CAPCOM’s call: “Challenger, go at throttle-up.” (Ironically, Richard Covey was the CAPCOM who made that very call.) Today, they heard a similar call over the Shuttle communications network: “Discovery, go at throttle-up.” A collective breath was held. After throttle-up, Discovery continued all the way to orbit. YES!!!

In comparison with the launch, initial climbout, and ascent into space, the remainder of the mission seemed somewhat anti-climatic. A Tracking and Data Relay Satellite (TDRS) was deployed from Discovery’spayload bay to replace the one lost in the Challenger explosion. A multitude of space experiments was conducted by the crew. Fairly standard stuff. Only deboost, the rigors of reentry and the typical dead-stick landing lay ahead.

Discovery landed on Runway 17 at Edwards Air Force Base on Monday, 03 October 1988. Main gear touchdown occurred at 16:37 UTC. Approximately, 450,000 American’s witnessed Discovery’s landing in person. A few who did had witnessed its launch in person as well.

The emotion that attended Discovery’s landing in October 1988 was simply overwhelming. Indeed, the experience was an integral part of the healing process for a nation that still grieved the loss of Challenger and her crew. A TIME magazine cover page headline the following week excitedly read: “Whew! America Returns to Space” And indeed it had.

Posted in Aerospace, History