For 30 years, the Space Shuttle orbiters Columbia, Challenger, Discovery, Atlantis, and Endeavour wowed millions with their thunderous climbs to orbit, their graceful orbital dances with satellites, Hubble, MIR, and the International Space Station, and their tell-tale twin sonic booms that announced their landings back on Earth – landings that would not have been as smooth as they were if not for the help of their sister vehicle that never experienced space: OV-101 Enterprise.
OV-101 – A test vehicle for the next generation spaceship:
With NASA’s new direction set, the Space Shuttle Program (SSP) was ready to begin a new era of focus on science and understanding in Low Earth Orbit (LEO).
But before the first Space Shuttle mission could launch from the Kennedy Space Center, FL, a great deal of ground testing was needed to fully, and to the best possible degree, understand the flight performance of this radical new design: A reusable, winged space plane that would launch like a rocket and land as glider with no propulsive force.
For this glider-landing method, a series of practice landings were drawn up to thoroughly test the proposed vehicle’s low atmosphere, pre-landing handling.
By 4 June 1974, structural assembly of OV-101’s crew module was underway, followed on 26 August 1974 by the start of structural assembly of her aft fuselage.
The Grumman company (near New York City) delivered the first set of Space Shuttle wings to OV-101’s Palmdale construction facility on 23 May 1975. By 24 August, final assembly of OV-101 was underway – as was a massive storm with the public regarding the name of NASA’s first Space Shuttle orbiter.
Honoring the bicentennial of the United States’ Constitution, NASA chose the name Constitution for OV-101 – much to the dissatisfaction of a large science fiction community… a community that was anything but silent.
Already successful eight (8) years earlier in bombarding NBC with letters to renew and save their favorite show (a show that gained immense popularity after its eventual cancellation in 1969), fans of the television series Star Trek wrote letters in droves to NASA and the U.S. Federal government urging them to rename Space Shuttle Constitution to Space Shuttle Enterprise as no space fleet of exploration would be complete without an Enterprise.
Eventually, NASA and the Federal government agreed, and OV-101 was officially, and permanently, named Enterprise.
Final Assembly of Space Shuttle Enterprise was completed at Palmdale on 12 March 1976, and she was revealed to the world (including several cast members and the creator of Star Trek who were on hand to witness her rollout from Palmdale) on 17 September 1976.
Final outfitting of Enterprise occurred between late-September 1976 and January 1977.
Towed the newly-built Mate-Demate Device (MDD), Enterprise was connected to a hoisting sling, lifted off the ground, her landing gear retracted, and placed atop of newly-acquired and newly-modified 747 airliner – budded by NASA as the Shuttle Carrier Aircraft, or SCA.
On 15 February 1977, Enterprise and the SCA duo left the MDD and headed for the runway at Edwards Air Force Base, CA to begin the Approach and Landing Test (ALT) Program.
To begin, the SCA, with Enterprise mated on top, performed three runway taxi tests. The first taxi test achieved a mild speed of 89 mph, while the second attained a speed of 140 mph and the third 157 mph.
All three taxi tests demonstrated structural loads of the SCA-Shuttle mated pair as well as responses and ground handling and control characteristics of the combined vehicle through taxi and take-off speeds.
The taxi tests also validated the SCA’s steering and breaking control while carrying a Shuttle orbiter.
Two days later, on 18 February 1977, Space Shuttle Enterprise took to the skies for the first time for the first of five Captive-Inactive (attached to the SCA for the duration of the flight and configured in an unmanned, powered-down status) flights.
The five Captive-Inactive Flights of Enterprise occurred on 18 February, 22 February, 25 February, 28 February, and 2 March 1977 and assessed the take-off, in-flight, and landing aerodynamics, structural integrity, and handling/performance characteristics of the mated SCA-Shuttle orbiter aircraft (with the tailcone assembly attached over Enterprise’s aft engine area).
Following the final Captive-Inactive Flight, Enterprise spent three and a half months on the ground as her flight systems were activated, tested, and prepared for the manned, Captive-Active Flights.
For this first Captive-Active Flight, Enterprise remained firmly attached to the SCA as her test-pilot crew operated her Flight Control Systems.
Following this highly successful first crewed and powered flight of Enterprise (and any Space Shuttle orbiter), two more crewed Captive-Active Flights were conducted on 28 June and 26 July 1977.
All three Captive-Active Flights (with the tailcone assembly attached) exercised and evaluated Enterprise’s systems in the flight environment for the up-coming major ALT evaluations.
The three specific, major tests for the Captive-Active Flights included flutter tests at low and high speeds, SCA-Orbiter separation trajectory tests, and a dress rehearsal for the first free flight test.
On the morning of 12 August 1977, the first astronaut crew to board a Shuttle orbiter climbed into Enterprise. Fred Haise and Gordon Fullerton took their places in the Commander’s and Pilot’s seats.
After climbing to 20,000ft, all systems were go. In the seconds preceding release, the SCA’s engines revved to over 100% thrust to boost Enterprise to release altitude, and the SCA’s nose pitched down into a shallow dive.
This maneuver allowed Enterprise to generate as much lift over her wings as possible (aided by her 7-degree upward angular tilt on the back of the SCA).
At 0848 PDT, Fred Haise triggered Enterprise’s release from the SCA, and the explosive bolts on the three attach struts between Enterprise and the SCA fired.
Enterprise released from the SCA while the duo tracked north (the SCA/Enterprise duo were east of Edwards at this time), and Haise pulled up Enterprise’s nose immediately following her release from the SCA to test her handling at relatively low air speeds.
Haise then angled Enterprise into a dive and executed a 180-degree left-hand turn (a maneuver that would later be referred to as “rolling around the HAC [Heading Alignment Circle]” for operational Space Shuttle missions) to align Enterprise with the dry lakebed runway.
Four minutes after releasing from the SCA, Fullerton lowered Enterprise’s landing gear, and Enterprise touched down safely and successfully at 0852 PDT.
The first free flight and solo flight of a Space Shuttle orbiter had occurred.
The next two free flight test, like first, saw Enterprise lofted to 20,000ft, released from the back of the SCA, rolled around the HAC, and landed on the dry lakebed runway at Edwards – all with her tailcone assembly attached.
Haise and Fullerton also piloted Enterprise for ALT-3 on 23 September 1977.
On 12 October 1977, Engle and Truly boarded a tailcone-less Enterprise. For the final two ALT flights, Enterprise would fly in “orbital” configuration, with three mock Space Shuttle Main Engines and two mock OMS (Orbital Maneuvering System) pods.
Releasing from the back of the SCA at an altitude of 20,000ft directly north of Edwards, Engle and Truly flew Enterprise on a steep, straight line approach to Edwards’ dry lakebed runway.
There was no “roll around the HAC” maneuver on for ALT-4.
ALT-4 lasted two minutes with an average decent rate of 10,000ft per minute, or 166.6ft per second.
For ALT-5, Enterprise did not aim for a dry lakebed runway. She aimed for the concrete runway at Edwards.
Landing on concrete runway 04, as Haise flared Enterprise in preparation for touchdown, a pilot-induced oscillation occurred. This was later investigated by NASA’s Fly-by-Wire F-8 Crusader.
Nevertheless, Enterprise landed safely, performing the first concrete runway landing for the Space Shuttle Program.
With the completion of ALT-5, Enterprise’s flight career came to an end. With the mounting cost realizations of up-converting Enterprise from a ground and low atmosphere test article to a space-worthy Shuttle orbiter becoming clear, NASA quickly made the decision that Enterprise would not be converted to a space-worthy ship of exploration.
STA-099 thus became OV-099 and was given the name Challenger.
But for Enterprise in 1977, the ALT program was not yet complete.
Over the next two months, Enterprise was prepared for four (4) ferry flight tests with the SCA. This involved draining and purging her fluid systems, reinstalling her tailcone assembly, and locking her elevons in place.
For the SCA, this ferry flight preparation involved replacing the attachment struts (where it connected to the Shuttle orbiter) to lower the Shuttle orbiter’s cant from 6 degrees to 3 degrees to reduce drag on the mated pair during flight.
A series of ferry flight tests were conducted before Enterprise was demated from the SCA and towed to a hanger at Dryden where she was modified for her next role: vertical ground vibration tests at the Marshall Space Flight Center (MSFC) in Huntsville, AL.
On 13 March 1978, Enterprise departed Edwards Air Force Base, CA for ferry flight delivery to MSFC. Once on the ground in Alabama, Enterprise was demated from the SCA and moved to her testing facility.
There, she was mated with an External Tank and Solid Rocket Booster stack.
Over the next year, Enterprise and her ET/SRB stack were vibrated and shook to assess the mated Shuttle flight stack’s “critical structural dynamic response modes” in the predicted and extreme in-flight ascent environments.
Data obtained during these tests were compared to the analytical models developed in the preceding years to validate model accuracy and further refine predicted ascent flight stack performance standards.
All ground vibration testing was completed in March 1979, and Enterprise was once again hoisted atop the SCA.
Departing Huntsville, AL, Enterprise was delivered to the Kennedy Space Center on 10 April 1979 where she was used to verify, test, and validate all KSC ground processing, stacking, pre-launch, and launch countdown operations in anticipation of the first operational Shuttle mission on Columbia (OV-102).
At KSC, Enterprise was used to verify and validate certain OPF (Orbiter Processing Facility) procedures before being towed to the VAB. There, she was used to verify and validate hoisting/mating sling attachment/detachment operations, lifting operations, mating operations, and integrated stack checkout procedures.
She was then rolled out to launch pad 39A on 1 May 1979. During rollout, Enterprise was driven at various speeds to measure and note the various vibration strains on the fully-mated Shuttle stack. This was used to determine an optimal rollout speed for operational Space Shuttle missions.
Once at the pad, Enterprise helped validate launch pad procedures – with her biggest test and benefit to the ground processing operations coming during the full-up Wet Countdown Dress Rehearsal when she helped simulate External Tank fueling operations for launch.
During the test, Enterprise’s ET was filled – through Enterprise’s mock Main Propulsion System – with hundreds of thousands of gallons of Liquid Hydrogen and Liquid Oxygen.
During this time, the venting capabilities of the gaseous hydrogen vent line/system were tested.
However, something quite disturbing was discovered during this test – ICE was building up at the top of the External Tank where the gaseous oxygen was being allowed to vent directly from the tank.
This posed a significant problem as ice was already understood to be a serious hazard to the Shuttle orbiter’s Thermal Protection System tiles and panels.
With the maiden voyage of the Shuttle just under two years away, NASA needed a solution to this newly-discovered problem.
The GOX vent arm would be tasked with safely venting gaseous oxygen away from the top of the External Tank and thus prevent the buildup of dangerous ice on the top of the Tank.
For STS-1, the GOX vent arm was retracted away from the Tank during the T-9min and holding mark, but ice liberation from the top of the Tank, observed in-flight by Columbia’s STS-1 Flight Crew, prompted a change to the GOX vent arm’s retraction time.
For STS-2, the retraction time was changed to T-2mins 55secs, making it the last major swing arm to move away from the Shuttle stack before liftoff. STS-2’s timing was a success, and for all remaining 133 Space Shuttle missions, the GOX vent arm began its retraction sequence at T-2mins 55secs and successfully latched up along the side of the launch pad.
In fact, the GOX vent arm was the LAST significant piece of hardware added to the launch pad and launch countdown procedures, and its necessity was only realized prior to flight operations thanks to Space Shuttle Enterprise.
In a somewhat ironic twist, 32 years after its creation as the last major piece of launch pad hardware for Shuttle, the GOX vent arm would be the LAST thing in the Shuttle Program to hold up and delay a launch when sensors on the pad failed to record its proper retraction on STS-135 (although it had fully retracted and latched against the pad) – resulting in a heart-stopping last-second hold at T-31secs for the final Space Shuttle mission in history.
For Enterprise, the contribution of the GOX vent arm would be her second-to-last major contribution to the Space Shuttle Program.
Rolled back from the pad and demated from her ET/SRB stack, Enterprise was mated to the SCA and ferried back to Edwards Air Force Base, CA on 16 August 1979.
On 30 October 1979, she was transported back to Palmdale, where components of her flight systems were removed and refurbished for use on the space-worthy Shuttle orbiters that were still under construction at Palmdale.
She was returned to Edwards on 6 September 1981 where she remained in storage.
On 4 July 1982 she served as the backdrop for President Ronald Reagan as he announced the successful completion of Space Shuttle Columbia’s four (4) Developmental Flight Tests earlier that day and the full operational capability of the Space Shuttle fleet.
One year later, Enterprise was mated to the SCA again, but this time, she had a very different destination: Paris, France.
During the May-June 1983 tour, Enterprise was taken to Germany, Italy, and England before being flown back across the Atlantic to Canada and then eventually Edwards Air Force Base, California.
One year later, Enterprise was taken to Vandenberg Air Force Base for Open House display in April 1984. From there, she was ferried to Mobile, AL for public display.
From Mobile, she was demated from the SCA, rolled onto a barge, and shipped down the Gulf of Mexico cost to New Orleans, Louisiana for the United States’ 1984 World’s Fair.
After her display at the World’s Fair, Enterprise was ferried back to Vandenberg in November 1984 where she was used as the practice and fit-check vehicle to verify, test, and validate all ground receiving, processing, stacking, and pre-launch procedures/activities for the upcoming Air Force launches of Space Shuttle Discovery from Vandenberg’s SLC-6 facility.
This test series was completed in 1985, and in May, Enterprise was ferried back to Edwards Air Force Base where any remaining, sensitive government equipment was removed from her.
On 20 September 1985, Enterprise was ferried back across the country to the Kennedy Space Center for public display near the Vehicle Assembly Building.
After two months of display, Enterprise was mated to the SCA and flown out of the Kennedy and up the East Cost of the U.S. to Dulles International Airport near Washington, D.C.
In the months that followed, NASA and the U.S. Congress agreed that a fifth Space Shuttle orbiter was needed to replace the lost Challenger. For a time, consideration was again given to converting Enterprise into a space-worthy Shuttle orbiter.
However, it was not to be. Structural spares built during Discovery’s (OV-103) and Atlantis’s (OV-104) construction would be used to build a completely new Shuttle orbiter – a move that was both quicker and cheaper than converting Enterprise.
The new orbiter would be Endeavour, OV-105.
From 1985 to 2003, Enterprise sat in the Smithsonian’s hanger at Washington Dulles International Airport. During this time, a restoration project was undertaken on Enterprise to preserve her and prepare her for display as the rightful cornerstone of the Smithsonian’s newly constructed Udvar-Hazy center for the National Air and Space Museum.
It was in the wake of the Columbia accident that Enterprise gave her last contribution to the Space Shuttle Program: portions of her RCC wing leading edge TPS panels to aid in an investigation of how the RCC panels react to foam liberation strikes during launch.
Damage incurred to the panels during these tests is still visible on her to this day, a lasting mark of her help to return her sisters Discovery, Atlantis, and Endeavour to flight.
After this, Enterprise took her place as the centerpiece of the Smithsonian’s Air and Space Museum on 21 November 2003 – where she remained until Discovery kicked her out on 19 April 2012.
After the official handover ceremony of Discovery to the Smithsonian, Enterprise was transported to Apron W at Dulles International and mated to the SCA for one final time – the very same SCA that flew her on all of her ALT flights in 1977.
Now, Enterprise will take her place at another museum: the Intrepid Air and Sea Museum in New York City.
After arriving at John F. Kennedy International Airport late-morning, Enterprise, still mated to the top of the SCA, will be moved into a storage hanger while the gigantic cranes and machines needed to demate her are broken down at Dulles, transported to JFK International, reassembled, and readied for her.
In mid-June, Enterprise will be rolled out of storage and demated from the SCA. She will then be loaded on a barge and taken down the Hudson River to the Intrepid, where cranes will lift her onto the deck of the ship.
She will then be rolled into a temporary, climate-control enclosure on the deck of the Intrepid until her permanent facility can be built in the coming years.
To read about the orbiters – from birth, processing, every single mission, through to retirement, click here for the links:
(Images: Via L2 Historical (from 200-500mb of hi res images PER shuttle mission) and L2 content, Ron Smith, plus NASA and NASA TV)
(L2 and NSF are continuing to follow the orbiters through their transitional period. To join L2, click here: http://www.nasaspaceflight.com/l2/)