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The Winged-Horse Delivers

Twenty-five years ago this month, the Orbital Sciences Corporation (OSC) orbited a PegSat satellite using the then-new Pegasus 3-stage launch vehicle. This historic event marked the first successful implementation of the air-launched satellite launcher concept.

The concept of air-launch dates back to the 1940’s and the early days of United States X-plane flight research. A multi-engine aircraft known as the mothership was employed to transport a smaller test aircraft to altitude. The test aircraft was subsequently dropped from the mothership and went on to conduct the flight research mission.

A clear benefit of air-launch was that all of the fuel and propulsion required to get to the drop point was provided by the mothership. Thus, the test aircraft was allowed to use all of its own fuel for the flight research mission proper. In that sense, the mothership-test aircraft combination functioned as a two-stage launch vehicle.

The value and efficacy of the air-launch concept was demonstrated on numerous X-plane programs. Flight research aircraft such as the Bell XS-1, Bell X-1A, Bell X-1E, Bell X-2, Douglas D-558-II, and North American X-15 were all air-launched. More recently, the X-43A and X-51A scramjet-powered flight research vehicles also employed the air-launch concept.

An added benefit of the air-launch technique is that the launch site is highly portable! This provides enhanced mission flexibility compared to fixed position launch sites. The associated operating costs are much lower for the air-launched concept as well.

Orbital Science’s original Pegasus launch vehicle configuration was designed to fit within the dimensional envelope of the X-15. The standard Pegasus configuration measured 50 feet in length and had a wingspan of 22 feet. The same dimensions as the baseline X-15 rocket airplane. Pegasus body diameter and launch weight were 50 inches and 41,000 pounds, respectively.

A key design feature of the Pegasus 3-stage launch vehicle configuration was the vehicle’s trapezodal-planform wing which provided the aerodynamic lift required to shape the endoatmospheric portion of the ascent flight path. This made Pegasus even more X-15-like.

The real difference between Pegasus and the X-15 was propulsion. The X-15 performed a sub-orbital mission using an XLR-99 liquid rocket engine rated at 57,000 pounds of sea level thrust. Pegasus used a combination of three (3) Hercules solid rocket motors to perform an orbital mission. The 1st, 2nd and 3rd stage rocket motors were rated at 109,000, 26,600 and 7,800 pounds of vacuum thrust, respectively.

On Thursday, 05 April 1990, the first Pegasus launch took place over the Pacific Ocean within an area known as the Point Arguello Western Air Drop Zone (WADZ). Pegasus 001 fell away from its NASA B-52B (S/N 52-0008) mothership at 19:10 UTC as the pair flew at Mach 0.8 and 43,000 feet. Pegasus first stage ignition took place 5 seconds after drop.

Following first stage ignition, the Pegasus executed a pull-up to begin the trip upstairs. The second and third stage rocket motors fired on time. The stage separation and payload fairing jettison events worked as planned. Roughly 10 minutes after drop, the 392-pound PegSat payload arrived in a 315 mile x 249 mile elliptical orbit.

Since that triumphant day in April 1990, both the Pegasus launch vehicle configuration and mission have grown and matured. Of a total of 42 official Pegasus missions to date, 39 have been flown successfully.

Posted in Aerospace, History

Ryan X-13 Vertijet

Fifty-eight years ago this month, the USAF/Ryan X-13 Vertijet completed history’s first vertical-to horizontal-back to vertical flight of a jet-powered Vertical Take-Off and Landing (VTOL) aircraft. This event took place at Edwards Air Force Base, California with Ryan Chief Test Pilot Peter F. Girard at the controls.

The X-13 Vertijet was an experimental flight vehicle designed to determine the feasibility of a jet-powered Vertical Take-Off and Landing (VTOL) aircraft. The initial idea for the type dates back to 1947 when the United States Navy (USN) put Ryan under contract to explore the viability of a jet-powered VTOL aircraft. At the time, the Navy was quite interested in exploiting the VTOL concept for tactical advantage. The service envisioned basing VTOL aircraft on submarines and small surface ships.

The USN-Ryan team worked the X-13 VTOL concept for over six (6) years to good effect. While no flight vehicle took to the skies during that time, a great deal of progress was made in the realm of hovering flight using ground-based vertical test rigs. Particular effort was focused on VTOL low-speed flight controls. However, Navy research and development funding was slashed in the aftermath of the Korean War and the X-13 project ran out of money in the summer of 1953.

Fortunately, the United States Air Force (USAF) had become interested in the X-13 and the possibilities of VTOL flight prior to the Navy running out of money. The junior service assumed ownership of the X-13 effort after securing the funding required to continue the program. A pair of X-13 prototypes were subseqently built and flown by Ryan Aeronautical. These aircraft were assigned USAF serial numbers 54-1619 and 54-1620, respectively.

The X-13 measured 23.5 feet in length and had a wing span of 21 feet. The single-place aircraft featured a maximum take-off weight of approximately 7,300 pounds. Hovering flight control was provided via wing tip-mounted yaw and roll nozzles. The heart of the VTOL aircraft was its reliable Rolls-Royce Avon turbojet. The non-afterburning powerplant used standard JP-4 fuel and produced a maximum thrust of 10,000 pounds.

The X-13 was transported, launched and retrieved using a special flatbed trailer. Hinged at one end, the trailer was raised and lowered through the instrumentality of a pair of hydraulic rams. Once raised to a vertical position, the X-13 hung on its nose hook from a steel suspension cable stretched between two mechanical arms. Rather than landing gear, the aircraft sat on two non-retractable tubular bumpers positioned on the lower fuselage.

Flight testing of the No. 1 X-13 (S/N 54-1619) began on Saturday, 10 December 1955 at Edwards Air Force Base, California. The purpose of this initial flight was to test the X-13’s conventional flight characteristics. The aircraft was configured with tricycle landing to permit a runway take-off. Ryan Chief Test Pilot Peter F. “Pete” Girard flew a brief seven minute test hop in which he determined that the X-13 had serious control issues in all 3-axes. The subsequent installation of yaw and roll dampers fixed the problem.

The next phase of flight testing involved vertical hovering flight wherein aircraft handling and control characteristics were explored. For doing so, the X-13 was outfitted with a vertical landing gear system composed of a tubular support structure and a quartet of small caster-type wheels. Thus configured, the X-13 could take-off, hover and land in the vertical. As vertical flight testing progresed, important refinements were made to the aircraft’s turbojet throttling and reaction control systems.

The first vertical flight test was made on Monday, 28 May 1956 with the No. 1 aircraft. Pete Girard was again in the cockpit. Restricting maximum altitude to about 50 feet above ground level, Girard found the aircraft relatively easy to fly and land. Succeeding flight tests would ultimately include practice hook landings wherein a 1-inch thick manila rope suspended between a pair of 50-foot towers was engaged. A great deal of experience with and confidence in the X-13 system was accrued during these tests.

Prior to flying the X-13 all-up mission, an additional phase of flight testing was required which would culminate with the events of Monday, 28 November 1956. With the conventional landing gear installed on the No. 1 aircraft, Girard took-off from Edwards and climbed to 6,000 feet. He then slowly pitched the aircraft into the vertical and hovered for an extended period. Girard then executed a transition back to horizontal flight and landed. The first-ever horizontal-to vertical-back to horizontal flight transition was entirely successful.

The big day came on Thursday, 11 April 1957. Edwards Air Force Base again served as the test site. This time using the No. 2 X-13 (S/N 54-1620), Pete Girard took-off vertically, ascended in hovering flight and transitioned to conventional flight. Following a series of standard flight maneuevers, Girard transitioned the aircraft back into a vertical hover, descended and engaged the suspension cable on the support trailer with the aircraft’s nose hook. The first-ever vertical-to horizontal-back to vertical flight of a jet-propelled VTOL aircraft was history.

Both X-13 aircraft would go on to successfully conduct additional flight testing and stage numerous flight demonstrations during the remainder of 1957. However, innovative and impressive as it was, the X-13 did not garner the advocacy and backing required to proceed to production. A combination of bad timing, a risk averse military and combat performance limitations resulted in the aircraft and its technology quickly fading from the aviation scene.

Remarkably, both X-13 aircraft survived the type’s flight test program. The No. 1 aircraft (S/N 54-1619) is displayed at the San Diego Aerospace Museum in San Diego, California. The No. 2 X-13 aircraft (S/N 54-1620) is on display in the Research and Development Gallery of the United States Air Force Museum at Wright-Patterson Air Force Base in Dayton, Ohio.

Posted in Aerospace, History

STS-1: Hail Columbia!

Thirty-four years ago this month, the United States successfully launched the Space Shuttle Columbia into orbit about the Earth. It was the maiden flight of the Nation’s Space Transportation System (STS).

The Space Shuttle was unlike any manned space vehicle ever flown. A giant aircraft known as the Orbiter was side-mounted on a huge liquid-propellant stage called the External Tank (ET). Flanking opposing sides of the ET was a pair of Solid Rocket Boosters (SRB). The Orbiter, SRB’s and ET measured 122 feet, 149 feet and 154 feet in length, respectively.

The Space Shuttle system was conceived with an emphasis on reusability. Each Orbiter (Columbia, Challenger, Atlantis, Discovery and Endeavor) was designed to fly 100 missions. Each SRB was intended for multiple mission use as well. The only single-use element was the ET since it was more cost effective to use a new one for each flight than to recover and refurbish a reusable version.

NASA called STS-1 the boldest test flight in history. Indeed, the STS-1 mission marked the first time that astronauts would fly a space vehicle on its inaugural flight! STS-1 was also the first time that a manned booster system incorporated solid rocket propulsion. Unlike liquid propellant rocket systems, once ignited, the Shuttle’s solid rockets burned until fuel exhaustion.

And then there was the Orbiter element which had its own new and flight-unproven propulsion systems. Namely, the Space Shuttle Main Engines (SSME) and Orbital Maneuvering System (OMS). Each of the three (3) SSME’s generated 375,000 pounds of thrust at sea level. Thrust would increase to 475,000 pounds in vacuum. Each OMS rocket engine produced 6,000 pounds of thrust in vacuum.

The Orbiter was also configured with a reusable thermal protection system (TPS) which consisted of silica tiles and reinforced carbon-carbon material. The TPS for all previous manned space vehicles utilized single-use ablators. Would the new TPS work? How robust would it be in flight? What post-flight care would be needed? Answers would come only through flight.

To add to the “excitement” of first flight, the Orbiter was a winged vehicle and would therefore perform a hypersonic lifting entry. The vehicle energy state would have to be managed perfectly over the 5,000 mile reentry flight path from entry interface to runway touchdown. Since the Orbiter flew an unpowered entry, it would land dead-stick. There would only be one chance to land.

On Sunday,12 April 1981, the Space Shuttle Columbia lifted-off from Pad 39A at Cape Canaveral, Florida. Official launch time was 12:00:03 UTC. The flight crew consisted of Commander John W. Young and Pilot Robert L. Crippen. Their Columbia launch stack tipped the scales at 4.5 million pounds and thundered away from the pad on over 7 million pounds of thrust.

Columbia went through maximum dynamic pressure (606 psf) at Mach 1.06 and 26.5 KFT. SRB separation occurred 120 seconds into flight at Mach 3.88 and 174,000 feet; 10,000 feet higher than predicted. This lofting of the ascent trajectory was later attributed to unmodeled plume-induced aerodynamic effects in the Orbiter and ET base region.

Following separation, Columbia rode the ET to burnout at Mach 21 and 389.7 KFT. Following ET separation, Columbia’s OMS engines were fired minutes later to achieve a velocity of 17,500 mph and a 166-nautical mile orbit.

Young and Crippen would orbit the Earth 37 times before coming home on Tuesday, 14 April 1981. In doing so, they successfully flew the first hypersonic lifting reentry from orbit. Though unaware of it at the time, the crew came very close to catastrophe as the Orbiter’s body flap had to be deflected 8 degrees more than predicted to maintain hypersonic pitch control.

The reason for this hypersonic anomaly was that ground test and aero modeling had failed to accurately capture the effects of high temperature gas dynamics on Orbiter pitch aerodynamics. Specifically, the vehicle was more stable in hypersonic flight than had been predicted. This necessitated greater nose-down body flap deflections to trim the vehicle in pitch. It was a close-call. But Columbia and its crew lived to fly another day.

Columbia touched-down at 220 mph on Runway 23 at Edwards Air Force Base, California at 18:20:57 UTC. Young and Crippen were euphoric with the against-the-odds success of the Space Shuttle’s first mission.

NASA too reveled in the Shuttle’s accomplishment. And so did America. This was the country’s first manned space mission since 1975. The longest period of manned spaceflight inactivity ever in the Nation’s history.

Fittingly, a well-known national news magazine celebrated Columbia’s success with a headline which read: “America is Back!”

And while it flies no more, we remember that first Orbiter, its first flight and its many subsequent accomplishments. To which we say: Hail Columbia!

Posted in Aerospace, History

The Original Seven

Fifty-six years ago this week, NASA held a press conference in Washington, D.C. to introduce the seven men selected to be Project Mercury Astronauts. They would become known as the Mercury Seven or Original Seven.

Project Mercury was America’s first manned spaceflight program. The overall objective of Project Mercury was to place a manned spacecraft in Earth orbit and bring both man and machine safely home. Project Mercury ran from 1959 to 1963.

The men who would ultimately become Mercury Astronauts were among a group of 508 military test pilots originally considered by NASA for the new role of astronaut. The group of 508 candidates was then successively pared to 110, then 69 and finally to 32. These 32 volunteers were then subjected to exhaustive medical and psychological testing.

A total of 18 men were still under consideration for the astronaut role at the conclusion of the demanding test period. Now came the hard part for NASA. Each of the 18 finalists was truly outstanding and would be a worthy finalist. But there were only 7 spots on the team.

On Thursday, 09 April 1959, NASA publicly introduced the Mercury Seven in a special press conference held for this purpose at the Dolley Madison House in Washington, D.C. The men introduced to the Nation that day will forever hold the distinction of being the first official group of American astronauts. In the order in which they flew, the Mercury Seven were:

Alan Bartlett Shepard Jr., United States Navy. Shepard flew the first Mercury sub-orbital mission (MR-3) on Friday, 05 May 1961. He was also the only Mercury astronaut to walk on the Moon. Shepherd did so as Commander of Apollo 14 (AS-509) in February 1971. Alan Shepard died from leukemia on 21 July 1998 at the age of 74.

Vigil Ivan Grissom, United States Air Force. Grissom flew the second Mercury sub-orbital mission (MR-4) on Friday, 21 July 1961. He was also Commander of the first Gemini mission (GT-3) in March 1965. Gus Grissom might very well have been the first man to walk on the Moon. But he died in the Apollo 1 Fire, along with Astronauts Edward H. White II and Roger Chaffee, on Friday, 27 January 1967. Gus Grissom was 40 at the time of his death.

John Herschel Glenn Jr., United States Marines. Glenn was the first American to orbit the Earth (MA-6) on Thursday, 22 February 1962. He was also the only Mercury Astronaut to fly a Space Shuttle mission. He did so as a member of the STS-95 crew in October of 1998. Glenn was 77 at the time and still holds the distinction of being the oldest person to fly in space. John Glenn will be 94 in July 2015.

Malcolm Scott Carpenter, United States Navy. Carpenter became the second American to orbit the Earth (MA-7) on Thursday, 24 May 1962. This was his only mission in space. Carpenter subsequently turned his attention to under-sea exploration and was an aquanaut on the United States Navy SEALAB II project. Scott Carpenter died in October 2013 shortly after suffering a stroke. He was 88 at the time of his passing.

Walter Marty Schirra Jr., United States Navy. Schirra became the third American to orbit the Earth (MA-8) on Wednesday, 03 October 1962. He later served as Commander of Gemini 6A (GT-6) in December 1965 and Apollo 7 (AS-205) in October 1968. Schirra was the only Mercury Astronaut to fly Mercury, Gemini and Apollo space missions. Wally Schirra died from a heart attack in May 2007 at the age of 84.

Leroy Gordon Cooper Jr., United States Air Force. Cooper became the fourth American to orbit the Earth (MA-9) on Wednesday, 15 May 1963. In doing so, he flew the last and longest Mercury mission (22 orbits, 34 hours). Cooper was also Commander of Gemini 5 (GT-5), the first long-duration Gemini mission, in August 1965. Gordo Cooper died from heart failure in October 2004 at the age of 77.

Donald Kent Slayton, United States Air Force. Slayton was the only Mercury Astronaut to not fly a Mercury mission when he was grounded for heart arrythemia in 1962. He subsequently served many years on Gemini and Apollo as head of astronaut selection. He finally got his chance for spaceflight in July 1975 as a crew member of the Apollo-Soyuz mission (ASTP). Deke Slayton died from brain cancer in June of 1993 at the age of 69.

History records that the Mercury Seven was the only group of NASA astronauts that had a member that flew each of America’s manned spacecraft (i.e, Mercury, Gemini, Apollo and Shuttle). Though just men and imperfect mortals, we honor and remember them for their genuinely heroic deeds and unique contributions made to the advancement of American manned spaceflight.

Posted in Aerospace, History