The USAF Manned Orbiting Laboratory Test Flight

At the dawn of the Space Age, the various branches of the US military all had their own grandiose plans for dominating space. Although the founding of NASA in October 1958 and the policies of the Eisenhower and subsequent administrations transferred responsibility for most of the country’s space program to civilian control, the desire to find a useful role for the military in space never disappeared especially in the United States Air Force (USAF).

This is a mockup of the X-20 Dyna Soar aerospace plane. It was the first manned spacecraft studied by the USAF but was cancelled on December 10, 1963 – the same day the Manned Orbiting Laboratory was officially announced. (Boeing)

While the USAF sponsored a number of programs for the development of unmanned spacecraft to aid in the defense of the US, they also actively sought a role for astronauts in space. For the first few years of the Space Age, the USAF was busy developing the manned X-20 Dyna Soar aerospace plane. Unfortunately, the program was cancelled in December 1963 because of its expense and the lack of a clearly defined mission which could not be accomplished by less expensive means (see “The Future Which Never Came: The X-20 Dyna Soar Aerospace Plane”). But in the wake of the cancellation of the X-20 Dyna Soar project came a new USAF project known as the Manned Orbiting Laboratory or simply MOL.

The Test Flight Payloads

The MOL program was officially announced by the USAF on December 10, 1963 – the same day that the cancellation of the X-20 Dyna Soar was made public. The purpose of the MOL program, according to the original Defense Department announcement, was “to determine the military usefulness of a man in space”. MOL would consist of a modified version of the Gemini spacecraft originally developed and built by McDonnell for NASA called “Gemini B” mounted on top of an orbiting laboratory which would be launched together into orbit on a Titan III-class rocket. MOL would house a crew of two in a shirt-sleeve environment for a mission lasting about one month. Within a couple of years, the National Reconnaissance Office, which was responsible for the nation’s photographic reconnaissance satellite programs, became interested in MOL and eventually it included the highly classified KH-10 DORIAN telescopic camera to allow MOL to secure high resolution images from orbit with the assistance of its crew.

An early depiction of the configuration of the Manned Orbiting Laboratory (MOL). Click on image to enlarge. (USAF)

Although the configuration evolved significantly over time with many options available, MOL with its modified Gemini B spacecraft would be launched into orbit with its crew on board using a variant of the powerful Titan III rocket. The laboratory with its Gemini B would have a diameter of three meters, a very long length of up to about 22 meters and a launch mass of around 14 metric tons. A number of different methods were examined for the crew to gain access into the laboratory from their Gemini B spacecraft once safely in orbit. The preferred option was to enter the top of the laboratory via a transfer tunnel through the base of the Gemini reentry module. Unfortunately, this meant that there would be a hatch with an ablative coating in the heat shield at the base of the capsule instead of a solid, one-piece shield – something that had never been attempted before.

A recently declassified drawing of the Gemini B spacecraft showing the location of its crew transfer tunnel. Click on image to enlarge. (NRO)

In order to address some of the engineering challenges of MOL, a number of test flights were envisioned. The first one would tackle the issues relating to the dynamics of the rather long and narrow shape of the laboratory during launch as well as the transfer hatch in the heat shield at the base of Gemini B. On top of the stack for the first MOL test flight was the Gemini B test article for the HST (Heat Shield Test). On April 29, 1965, McDonnell received a $2.1 million cost-plus-incentive fee contract to refurbish the previously flown Gemini 2 reentry module for the HST. Gemini 2 originally flew unmanned on January 19, 1964 for an 18-minute suborbital test flight which landed 3,422 kilometers downrange after its Titan II launch vehicle had lofted it to a peak altitude of 171 kilometers (see “The Launch of Gemini 2”). Just as this flight had provided a test to certify the standard Gemini heat shield for crewed flight, the refurbished “Gemini 2R”, as it was now designated, would also test MOL’s heat shield with its 65.5-centimeter off-center crew transfer hatch. Along with a boilerplate adapter section which mated it to the top of the stack (which would normally carry retrorockets and other system required for Gemini B to return to Earth), Gemini 2R was 4.8 meters tall and had a mass of 2,900 kilograms. The Gemini 2R capsule would separate from the ascending payload before orbit had been achieved to perform its reentry test.

The refurbished Gemini 2R and its attached boilerplate adapter shown being raised into position on top of its Titan IIIC launch vehicle at LC-40. (USAF)

Below the Gemini 2R was a simulated MOL payload officially designated “OV4-3” (“Orbital Vehicle series 4 – number 3”). It consisted of a modified oxidizer tank from the first stage of an obsolete Titan I ICBM with a diameter of 3.0 meters and a length of 11.7 meters, including the boilerplate Gemini B adapter which would remain after Gemini 2R had separated. Although it differed structurally from how MOL was to be constructed, the 9,660-kilogram test article still offered engineers valuable data on the aerodynamic environment encountered by this long shape during an ascent into orbit.

Titan IIIC number 3C-9 with a simulated MOL payload mounted on top during roll out from the Solid Motor Assembly Building (SMAB) towards the pad at LC-40. (USAF)

This mission also took advantage of unused payload capability available on this flight and carried nine engineering and scientific experiments collectively known as “Manifold” with a total mass of 390 kilograms. The ORBIS (Orbiting Radio Beacon Ionospheric Satellite) experiment sponsored by the Air Force Cambridge Research Laboratories (AFCRL) used a 10.7-meter antenna to obtain ionospheric sounding data. Also included on board was a biocell experiment which would study organism growth in zero-g, a zero-g propellant gauging experiment, a heat transfer experiment, a pair of micrometeorite detectors and a stack of fuel cells which used hydrogen and oxygen to produce 200 watts of electrical power. The exterior of OV4-3 also supported a number of investigations. A total of 18 corner reflectors were carried for optical measurements from the ground using collimated light sources. A series of stripes 0.14 to 1.29 meters wide were painted on the exterior for observations using an electro-optical telescope. The exterior also sported a proturbance simulating an attitude control nozzle and its fairing to study its aerodynamics and heating effects.

This diagram shows the arrangement of various experiments and piggyback satellites carried by the USAF OV4-3 MOL simulator with the Titan IIIC Transtage attached. Click on image to enlarge.

In addition to these experiments, three OV-series satellites were carried in the boilerplate adapter section for deployment once orbit had been achieved. The OV (Orbital Vehicle) satellite series was a joint program of the Air Force Space Command (AFSC) and Office of Aerospace Research (OAR) to provide low cost satellites to support USAF space research. The heaviest of the piggyback satellites carried on this mission was OV1-6. Originally designed to be launched on surplus Atlas ICBMs, General Dynamics’ OV1 satellites were of a standardized design consisting of a cylinder with hemispherical caps having a total length of 1.39 meters and a diameter of 0.69 meters with a mass typically less than 100 kilograms (see “Riding Piggyback on an ICBM”). Since OV1-6 would be deployed directly into orbit, it did not require the 354-kilogram OV1-PM propulsion module and its X-258 solid rocket motor like OV1 payloads launched from a suborbital Atlas missile. The 25-day mission of OV1-6 was classified but it was longer and heavier than the standard OV1 satellite with a length of 1.72 meters and a mass of 202 kilograms. It was rumored that OV1-6 carried a set of inflatable decoys that were expected to appear like satellites to ground radar.

The pair of OV4-1 satellites carried as piggyback payloads during the MOL test flight. (Raytheon)

The next pair of piggyback satellites carried on this mission were built by Raytheon for what was termed a “whispering gallery” communications experiment. This experiment would attempt to determine if satellites could communicate with each other using HF and VHF transmissions when they were not in sight of each other. This “over-the-horizon” communications test would have one satellite transmitting signals at 20.75, 34.3 and 46.8 MHz and use the ionosphere’s F-layers to reflect them to a second satellite carrying a receiver as well as distant ground stations. The receiver satellite, the 136-kilogram OV4-1R, was a 0.43-meter in diameter cylinder with one domed end for a total length of 1.4 meters. The transmitter satellite, OV4-1T, had identical exterior dimensions with a mass of 109 kilograms. This satellite, however, was fitted with a small solid motor which would be fired after deployment. The resulting 11 meter per second delta-v would quickly increase the separation between it and the receiver satellite for the experiment. Both satellites employed silver oxide-zinc batteries and had an estimated lifetime of 50 days.

Titan IIIC number 3C-9 shown on the pad at LC-40 for the launch of the MOL test flight with a refurbished Gemini 2 reentry module. (NASA)

The launch vehicle for this mission was the Titan IIIC – the most powerful rocket then available to the USAF. The Titan IIIC consisted of a pair of three-meter in diameter solid rocket motors strapped to a set of liquid propellant core stages. This pair of five-segment motors generated a total of 10,500 kilonewtons of thrust at lift off giving the Titan IIIC half again the liftoff thrust of NASA’s Saturn IB. The first two stages of the core consisted of a modified Titan II ICBM that had been fitted with new engines and structurally reinforced to handle heavier payloads and extra stages. The final stage of the Titan IIIC was the restartable Transtage. The Transtage, which would remain attached to the OV4-3 MOL test article to provide attitude control and other support functions, would fire its pair of Aerojet AJ-10-138 engines three times to place its various payloads into the proper orbits. While MOL would use the larger Titan IIIM employing a pair of seven-segment motors and a stretched core fitted with improved engines to lift its payload into a polar orbit from Vandenberg Air Force Base in California, a Titan IIIC launched from Cape Kennedy, Florida would provide an adequate test of the MOL launch configuration for this mission (see “The First Missions of the Titan IIIC”).

The Mission

On July 19, 1966 the USAF announced the upcoming MOL test flight scheduled for launch on October 28. For this sixth development flight of the Titan IIIC, rocket number 3C-9 would be launched from LC-40 – just the second mission from this then brand new pad which today supports launches of SpaceX’s Falcon 9 rocket. Inevitable schedule slips delayed the launch to November 3 when the Titan IIIC successfully lifted off at 8:50:42 AM EST. The Titan’s solid rocket motors and the first two stages of the core operated as intended placing the Transtage and its payload into a trajectory with an apogee of 228 kilometers.

The launch of the MOL test flight with a Gemini B capsule on November 3, 1966. (NASA)

With the payload and the attached Transtage pitched nose down following apogee, the pair of AJ-10-138 engines ignited for the first time to place the Gemini 2R capsule into the proper trajectory for its heat shield test. At an altitude of 193 kilometers, the Transtage shutdown and released the Gemini B capsule for a reentry at a speed of 7,820 meters per second. The heat shield experienced temperatures of nearly 1,700° C during a punishing maximum lift-to-drag reentry and successfully protected the spacecraft despite the presence of the plug for the crew transfer hatch. After a 33-minute flight which covered 10,200 kilometers, the Gemini B capsule came down near Ascension Island only 13 kilometers from its recovery ship, the Raleigh-class amphibious transport vessel, the USS La Salle. With this recovery, Gemini 2R was dubbed by some as the first American spacecraft to fly into space twice, albeit on suborbital ballistic trajectories both times (not an entirely accurate claim since X-15 number 3 had already flown a suborbital trajectory above the 100-kilometer Karman line twice during 1963 with Joseph Walker in the cockpit – see “The First Reusable Spacecraft: The Flights of the X-15 Above the Karman Line“). Post flight inspections showed that the ablative coated plug for the transfer hatch in the heat shield had been welded shut during the reentry. The safety of the internal crew transfer tunnel via this hatch had been verified.

The Gemini 2R capsule shown on the deck of its recovery ship, the USS La Salle, following splashdown at the end of a 33-minute suborbital test flight. (USAF)

Meanwhile back in space, the Transtage and its attached simulated MOL payload pitched upwards following the separation of the Gemini B and the Transtage fired its engines for a second time to enter a 144 by 307-kilometer transfer orbit. A third burn of the pair of AJ-10-138 engines 38 minutes later placed OV4-3 and its piggyback payloads into a 301 by 302 kilometer orbit with an inclination of 32.8°. Shortly thereafter, OV1-6 was deployed into a nearly circular 290-kilometer orbit along with OV4-1R into a virtually identical orbit. OV4-1T was also deployed and fired its separation motor to enter its own 291 by 319 kilometer orbit. With its piggyback payloads deployed, the Transtage set itself and the attached OV4-3 simulated MOL into a slow tumble to even out solar heating on the spacecraft to begin its extended orbital mission.

An artist’s depiction of the Gemini B separating from the MOL laboratory. (USAF)

Although the simulated MOL OV4-3 satellite had an expected lifetime of 75 days, it ceased transmissions after only 30 days. Its low orbit decayed quickly and OV4-3 entered Earth’s atmosphere on January 9, 1967 (just 67 days after launch). This had been preceded by the decay of the classified OV1-6 on December 31, 1966 and OV4-1R five days later. The last payload from this flight to reenter the atmosphere was OV4-1T on January 11, 1967. Along with the recovery of Gemini 2R reentry module, the flight had met all of its objectives.

A view of the Gemini 2R reentry module on display at the Air Force Space & Missile Museum at Cape Canaveral. Note that a portion of the circular crew transfer hatch has been removed. (Wikipedia)

With this success under their belts, work continued on the MOL program with many of the people who had been working on NASA’s Gemini program transferring to the USAF project at the successful conclusion of NASA’s last Gemini mission later in November 1966 (see “The Grand Finale: The Mission of Gemini 12“). In addition to many pieces of Gemini program hardware, NASA transferred the previously flown Gemini 6 reentry module to the USAF in March of 1967 and there were plans for Gemini 9 and 10 hardware to be transferred as well for abort and additional flight testing following their refurbishing.

An artist’s depiction of an option with a pair of MOL laboratory modules docked tail-to-tail. (NRO)

Unfortunately, escalating costs for this increasingly ambitious program and schedule slips resulted in the cancellation of the other MOL test flights in the years that followed. Finally in June 1969, the USAF MOL program was cancelled after it became clear that the latest generation of automated reconnaissance satellites would be more cost effective than MOL. With the remaining largely unclassified objectives of the USAF program such as dealing with the long term effects of space travel on humans to be addressed by NASA’s Apollo Application Program (later known as Skylab), the expense of the MOL program at a time when US involvement in southeast Asia (and its costs) were escalating could no longer be justified. The November 3, 1966 flight of Gemini 2R and the simulated MOL would remain the only test flights of this USAF program.

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Related Video

Here is an excellent episode of the PBS series Nova called “Astrospies” which gives details about the USAF MOL program and the Soviet response – a space station called “Almaz” whose technology now serves as the basis of the Russian add-on modules to the earlier Mir space station as well as today’s International Space Station.

Related Reading

“The First Missions of the Titan IIIC”, Drew Ex Machina, June 18, 2015 [Post]

“The Launch of Gemini 2”, Drew Ex Machina, January 19, 2015 [Post]

“The Future Which Never Came: The X-20 Dyna Soar Aerospace Plane”, Drew Ex Machina, April 10, 2016 [Post]

General References

Dwayne A. Day, “All along the watchtower”, The Space Review, February 11, 2008 [Post]

Dwayne A. Day, “Heavy Glass: The KH-10 DORIAN reconnaissance system”, The Space Review, July 21, 2014 [Post]

Donald Pealer, “MOL Part I: Manned Orbiting Laboratory”, Quest, Vol. 4, No. 3, pp. 4-16 , Fall 1995

Donald Pealer, “MOL Part II”, Quest, Vol. 4, No. 4, pp. 28-35, Winter 1995

Donald Pealer, “Manned Orbiting Laboratory Part III”, Quest, Vol. 5, No. 2, pp. 16-23, 1996

“OV4 3, OV1 6, OV4 1T and OV4 1R”, TRW Space Log, Vol. 6, No. 4, pp. 17-20, Winter 1966-67