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Questions/Comments to

Ed Kyle

titan2-x20.jpg (45547 bytes)TITAN:  NEVER-FLOWN VARIANTS
by Ed Kyle

Titan 2 would have launched X-20 glider on suborbital test flights to Saint Lucia or Fortaleza, Brazil.  The giant fins on this never-flown Titan would have provided stability during abort scenarios.


NASA listed an orbital Titan 1 possibility in its early LV Handbooks, but never provided a drawing of what it might have looked like. It would have used a small solid apogee kick motor (perhaps from the Vanguard program) and probably would have used a small diameter payload shroud. The base of the Mark 4 Rentry Vehicle was 48 inches diameter, which, coincidentally, was roughly the diameter of NASA's Juno II shroud.

Here, then, is a notional version of that notional Titan 1 orbital launch vehicle. Something like an Altair kick motor, used by Vanguard and Delta, would have fit nicely on top. The problem would have been keeping the Altair pointed in the right direction while coasting after Titan vernier motor burnout. The Titan second stage did not have 3-axis control once the verniers cut out. This problem was later solved for Atlas by creating the Burner stages, which added 3-axis control to solid kick motors.

Another possibility raised by the Army Ballistic Missile Agency in 1958 was to add a Polaris upper stage to Titan 1. Von Braun's team, in its March 1958 "A National Integrated Missile and Space Vehicle Development Program" proposal, suggested that a three-stage Titan (1)/Polaris would have been able to boost 1.36 to 2.26 tonnes to LEO. The smaller number appears consistent with use of a nearly-stock Polaris A-1 or A-2 second stage. The larger number would require a higher performing motor or motors. Newly-formed NASA was not interested in Titan/Polaris, so the idea was never pursued.

Titan 1 quickly fell by the wayside. After the Titan 2 program began in mid-1960, Martin focused its energies on the new, more powerful storable propellant missile, including all studies of future derivatives. The Cape Canaveral Titan 1 pads were converted to support Titan 2 or Titan 3, leaving only the VAFB Titan 1 elevator silo launch sites. Titan 1 ICBM operational test flights continued only until the ICBM was taken out of service in 1965. The missiles were then mostly either scrapped or put on display.


Titan was the Dyna-Soar (X-20) launch vehicle at that proram's beginning, but as the program restlessly shifted, so did the boosters. Boeing had the space glider contract. Martin had the launch vehicle contract.

In 1959, Titan A (later Titan 1) was the suborbital booster for planned unmanned and manned flights to Saint Lucia and Fortaleza, Brazil. A proposed "Titan C", powered by four Titan 1 engines at liftoff, was being considered for later orbital flights.

In late 1960 the suborbital work shifted to the newly authorized, yet-to-fly Titan 2 and studies began for a subsequent Titan 2/Centaur type launch vehicle for orbital flights. Within a few months the idea had shifted toward a new LH2 upper stage powered by an LR87 derived engine or by a J-2 engine, a concept named "Plan C" or, once again, "Titan C". The bigger upper stage allowed use of a standard Titan 2 first stage, unlike the Centaur concepts. Meanwhile, thought was given to using NASA's Saturn C-1 instead.

By the early Fall of 1961 a real breakthrough had occurred with the SOLTAN (Solid Titan) idea. Here was a way to create a capable orbital launcher without having to completely change the basic Titan 2 core stages. The early SOLTAN had three-segment, 100 inch diameter solids, but these were soon replaced by four-segment 120 inch diameter solids as the rocket was named "Titan 3". In 1962, Titan 3C was changed to its ultimate five-segment solids, but the change caused problems for Dyna-Soar/X-20. Designers were considering what to do about the problem when cancellation loomed. McNamara finally pulled the plug in December 1963.

With limited references, I've made educated guesses about both Titan C concepts and about Titan 2/Centaur.

3.  TITAN 2A

During 1962-64, Martin and Aerojet performed an "Improved Titan Feasibility Study" on a concept named "Titan 2A" that would have doubled Titan 2 payload.  Titan 2A would have burned gelled "Alumazine" (aluminized (metalized) hydrazine) with N2O4. This was aluminum powder suspended in 56.7% hydrazine and 0.3% Carbopol 904 (a gelling agent). The tanks (mostly Stage 1) would have been stretched a bit to hold the denser, higher-energy propellant. Higher thrust engines would also have been developed. Though now up to 116.556 feet long, Titan 2A would still have fit within modified Titan 1 or Titan 2 silos.

Scaled engine testing took place on what would have been highly efficient engines, but chamber cooling proved to be a challenge. Extra Aerozine-50 tanks would have been needed to feed the gas generators, some of which might have been in four external cylindrical tanks attached to Stage 1. The effort ended in 1964.

Perhaps Titan 2A was briefly considered as the U.S. answer to the USSR's R-36 "Satan".

4.  TITAN 2.5

"Titan II-1/2" was the informal name given to the "Mercury Mark II" (Gemini) launch vehicle being studied by NASA and Martin during 1961. This would have been a stretched Titan 2 (I'm guessing a roughly 40 inch first stage stretch) that would have slightly improved payload performance to LEO. The idea was short-lived due to budget and schedule squeezes and to then-new plans to develop Titan III using non-stretched core stages. NASA relented (one of its best decisions ever) in December 1961 and chose to use standard Titan 2 stages with minimal modifications. Without the extra launch vehicle development effort, Gemini came in relatively on-time, if not on-budget.

5.  TITAN 3X

In January 1965, the U.S. Air Force and its contractors began studying "Titan 3X" concepts to launch what would become Hexagon, the "Big Bird" photorecon system. Initial plans considered Titans using two or three-segment, 120 inch diameter solid rocket motors. The two-segment version could lift 12,000 to 13,000 lbs to sun synchronous orbit from Vandenberg AFB. I've estimated 16,000 lbs for the three-segment version. At the time, Hexagon was expected to have only two SRVs (Satellite Recovery Vehicles) and would have been quite a bit smaller and lighter than the version that ultimately flew.

From the beginning, a contingent of designers wanted to used the already-developed Titan 3C five-segment boosters, which would allow four SRVs and many more miles of film. By May 1967, Titan 3X had been renamed "Titan 3D" and it had two five-segment boosters. Development began in earnest at the end of 1967.

I'm very much guesstimating the two and three-segment booster numbers here. I'm also guesstimating the shroud length by assuming a shorter Hexagon with two SRVs.


Astronautix lists a "Titan 3BAS2" design from a 1967 Martin marketing brochure. This was a Titan 3B with a Centaur third stage and an optional Burner 2 fourth stage that would have been boosted by two Algol 2 strap on solid motors. The concept was apparently studied for deep space mission use, but I have yet to see the source material. A Cape Canaveral pad - likely a modified LC 20, would have to have been developed. This rocket would generally have had Atlas SLV-3C/Centaur performance to GTO, but would have lifted more than SLV-3C to LEO.

7.  TITAN 3M

Titan 3M, designed to launch the U.S. Air Force Manned Orbiting Laboratory (MOL)/Dorian KH-10 reconnaissance system, was nearly ready to fly when the program was cancelled on June 10, 1969. The effort was not totally lost because Titan 3M's "-11" series core stage engines, stretched first stage, and 7-segment motors all flew on subsequent Titan variants. Many of MOLs USAF astronauts went on to fly Shuttle missions.

The new VAFB SLC 6 launch pad for Titan 3M was built, but never used for Titan. It was converted for Shuttle at a cost of several billion dollars but never used for Shuttle. Lockheed's Athena finally christened the site during the 1990s, but it has been Delta 4 that has come closest to realizing the site's original goals.

The first launch was probably 18 months away when the cancellation came, which would have placed the first launch at the end of 1970. The first SRM was tested before cancellation (April 26, 1969). Three more SRM tests were allowed to be performed during 1970 to essentially complete the effort.

The first two flights were to be Gemini-only unmanned without a real MOL or KH-10 (probably would have used simulators). The third flight would have had a MOL and two crew. (At the very end of the program, consideration was given to more unmanned flights, but with active Dorian reconnaissance systems.) Plans appear to have called for 30 day missions and a couple flights per year.

Numerous alternatives and follow-ons to Titan 3M were studied during the life of the program.


While it was working on Titan 3M for MOL, Martin Company put a good deal of effort into studies of "Large Diameter Core" (LDC) Titans to handle heavier MOL payloads in the future. These would have used four engines on a 180 inch (15 foot) diameter first stage. Martin went as far as building an LDC fuel tank with four LR87-AJ11 engines for transport testing during 1966-67 (oxidizer and fuel tanks would have shipped separately to the launch site).

At least two core engines would have ignited at liftoff. All four would have burned during the mid-point of the stage's flight, when the SRMs would have jettisoned, before reverting to two engines before staging. In early 1967, Martin briefly lobbied for an LDC with five segment boosters ("Titan 3M/LDC-5") as an alternative to Titan 3M. The company also studied an ultimate LDC-3 version with 156 inch boosters that could have lifted more than 36 tonnes to near-polar orbit.

LDC was never picked up by the MOL program, though VAFB SLC 6 was set up to accept it if needed. LDC died with MOL's 1969 demise, but the 15 foot diameter Titan idea kept reappearing in Martin proposals for at least two decades.


Titan 3D7/Centaur, otherwise known as Titan 3C7/Centaur and Titan 3F/Centaur, was a proposed follow-on to the Titan 3M/MOL launch vehicle that would have added a Centaur third stage and, potentially, a small solid fuel fourth, kick stage. NASA studied the rocket for deep space missions such as Grand Tour and Comet Halley. The MOL and Titan 3M cancellation drove NASA toward the smaller Titan 3E.

Although similar, the Titan 4A that would finally fly using seven-segment motors during the 1990s would end up with longer first and second stages and a fatter payload fairing than Titan 3C7/Centaur.


Titan 3B Centaur was proposed during the late 1960s/early 1970s period as a growth option for the 1980s and 1990s. It appeared in a 1972 economic analysis of the proposed shuttle system as part of a potential expendable launch vehicle alternative fleet to the shuttle. The projected performance was a bit underwhelming. It barely matched its contemporary, Atlas-Centaur, although the big payload fairing may have reduced payload. It did outperform Titan 3B Ascent Agena. Perhaps it was considered as a follow-on to that launch vehicle for spook work.

This was essentially the core of the Titan 3E launch vehicle, though it never flew alone as proposed here.

11.  TITAN 3L2/3L4

Titan 3L2 and 3L4 were Large Diameter Core Titans studied during the 1970-73 years. They were extensions of the earlier "LDC" designs, with 180 inch diameter core stages. New was the 4 x Seven Segment booster concept. Launch Complex 37, the by-then ex-Saturn IB launch site, would have been reconfigured for 3L4. NASA studied the designs for deep space missions, but development was never seriously contemplated. Titan 3L4 would have been more capable than any U.S. launch vehicle except Saturn 5. With a Centaur upper stage it would have out-lifted even Falcon Heavy to solar orbit.


For the early-1970s Mathematica economic analysis of the proposed space shuttle system, The Aerospace Corporation proposed a family of potential space shuttle alternative expendable launch vehicles. Since it was Aerospace Corporation, the USAF systems engineering contractor for missiles and space, the family was largely based on Titan. An interesting proposal for a medium payload launch system was the "Five Segment Solid Rocket Motor/Core 2" system. These would have used a suitably modified UTC-1205 five-segment motor from Titan 3C/3D/3E as a first stage topped by a Titan 3-series second stage. (A second TVC tank would have been added to provide enough fluid for 3-axis control.) Agena or Centaur or a Burner 2 type kick stage could have topped the vehicles.

The idea seemed to be to replace every Atlas variant in the national fleet with Titan based launchers. SRM/Core 2/Centaur would have flown from a rebuilt Cape Canaveral LC 36. SRM/Core 2/Agena D and, presumably Centaur too, would have flown from VAFB SLC 4W. An SRM/Core 2 with a Star 37 type kick stage would have been relatively cheap. An SRM/Core 2/Centaur would have outmatched all Atlas Centaurs up to the 1980-s Atlas G/Centaur D1AR series. Growth versions using 7-segment SRMs were, of course, possible.

This Titan-centric view of the future, of course, never materialized.


During the Phase B-Prime Studies for Space Shuttle in 1971 or thereabouts, Martin Marietta proposed a series-burn booster concept. It would have used four 7-segment Titan solid motors strapped to a 194 inch (4.88 meter) diameter core stage that itself would have had five LR87-AJ11 Titan 3M engines.

The Orbiter engines would have ignited after staging, allowing them to be optimized for vacuum. The LH2/LOX drop tank would have been smaller than the eventual External Tank as well. It is likely that something like Pratt & Whitney's XLR-129 was base-lined as the orbiter engine at the time.

It seems likely that the SRMs and core would have burned in parallel, making something like 6.7 million pounds of thrust at liftoff. The SRMs by themselves would have made 5.57 million pounds thrust. The SRMs would have jettisoned at T+126 seconds. The core would have burned out at perhaps 265 seconds.

This was only one of several designs, which included parallel stage alternatives and a non-LH2 orbiter option, studied by Martin.


On November 30, 1987, Aviation Week & Space Technology ran an article titled "SDI Considers Cluster Booster to Launch SDI Zenith Star Spacecraft".  This was one of the most memorable two-page reads that magazine ever printed. It had a drawing of the massive proposed Zenith Star chemical laser experiment satellite, and a story about President Reagan's speech about the project during his Martin Denver visit. It was apparent that work had been underway in secret for some time on this SDIO project.

The article revealed studies for two massive launch vehicles proposed to orbit the 100,000 lb, 80 foot long satellite. It said that McDonnell Douglas and Martin Marietta were each completing secret studies of proposed "Barbarian", or "Huey" (for humongous), launch vehicles cobbled together using existing propulsion systems. The rockets would have stood 250 feet and produced 8 to 10 million pounds of liftoff thrust. The selected design would have cost $400-500 million. Its "support frame" would have been assembled with the rocket "like a building" at Cape Canaveral's then abandoned LC 37. Barbarian, it seemed, would have been built once, to launch one big payload in a hurry.

Martin Marietta's design would have used a large diameter core powered by five LR-87-AJ11 engines, topped by a second stage powered by one of the engines. A total of five Titan 4A seven-segment SRMs would have surrounded the core. All of the core engines would have ignited at liftoff with the solids, creating over 8.1 million pounds of thrust!

I've never found definitive details of this proposal. I believe that the design suggested by Astronautix is too lightweight and likely based on earlier
Titan LDC proposals. AWST suggested that the core would be 19 feet in diameter, but that seems too fat given that even the Shuttle Titan 3L booster designs were only 200 inches in diameter. In addition, the 200 inch Titan 4 diameter shroud would have been used to house the payload. Nothing would surprise me, however. AWST stated that the core might be assembled at Michoud using ET tooling, but ET was 27.58 feet diameter.

The idea was soon dropped in favor of cutting Zenith Star in half and launching it on two Titan 4 vehicles. Then that idea died with the end of the Cold War. I do find it interesting that Falcon Heavy is being designed to lift a Barbarian-class payload. Coincidence?

Here's a modified view of Martin's Barbarian, with contemporary Titan 34D provided for a sense of scale. Someday, perhaps, we might learn how they planned to assemble this behemoth with little launch site infrastructure.

15.  TITAN 5

A 1986-88 era "Titan 5" study was simply a continuation of Martin's long-running Large Diameter Core proposals, re-presented during the post-Challenger scramble. (Barbarian, which may have been a type of "Titan V", was proposed about this same time.) USAF did not sponsor the study. It appears that Martin made a presentation to OTA for its 1988 "Launch Options for the Future Special Report", which included a "Titan V" option for a notional future national space launch fleet.

The OTA report described three Titan V options, as follows:

Option 1: 4 meter diameter core with 3 core engines and 2-3 solid motors, 60-80 Klb to 100 nmi x 28.5 deg
Option 2: 5 meter diameter core with 4-5 core engines and 3-5 solid motors, 80-130 Klb to 100 nmi x 28.5 deg
Option 3: 6 meter diameter core with 5-6 core engines and 5-6 solid motors, 130-150 Klb to 100 nmi x 28.5 deg

The core stage would have used Titan 4 type engines burning N2O4/A-50. Development cost was estimated at $0.8 to $3.5 billion, depending on the option, over a 3.5 to 5 year time frame.

Note that the attached drawing from the OTA report shows Titan IV and V at the same height, which as we've seen would not have been the case. The large-core Titans would have towered over even Titan IV.

16.  TITAN 2S

Even as it began launching its first Titan 23G (refurbished ICBM) vehicles on orbital missions from VAFB SLC 4W beginning in 1988, Martin Marietta studied upgrades. The first obvious possibility was to add Delta 2 type Castor 4A or GEM-40 strap-on motors to create a "Titan 2S" (Titan 23S). This approach would have doubled Titan 23G payload, but a new aft skirt would have been needed to support the motors and to protect the first stage engine section. Four to ten SRMs could have been mounted. They would have burned in staggered sequence similar to the Delta 2 solids, though with three burn sets rather than only two.

Given the limited inventory of retired Titan 2 missiles, the cost to develop and fly the upgraded rocket, and the duplication of Delta 2 capability (once Delta 2 began flying from VAFB), "Titan 2S" was never developed. I'm not sure for what specific payload the launch vehicle was considered, but a 2,300 kg to 890 km x 99 deg "reference mission" was mentioned in a 1991 AIAA paper by Bruce French of Martin Marietta.

17.  TITAN 2L/3L

During 1988-90 Martin Marietta also proposed using retired Titan 2 first stages as liquid boosters for 2-stage Titan 2 core vehicles. The resulting "Titan 2L" ("L" this time standing for "Liquid" rather than "Large") would have lifted off with only one of the two core first stage engine "subassemblies" ignited to reign in acceleration forces. When the liquid boosters staged, the second core stage subassembly would have started to provide full thrust. Titan 2L would have been able to lift 7.5 tonnes or more to low sun synchronous orbit from Vandenberg AFB, more than 3.5 times more than Titan 23G and nearly twice as much as the proposed Titan 2S. In theory, Titan 2L could also have lifted more than 9 tonnes to LEO x 28.5 deg from Cape Canaveral.

Another variation was named "Titan 3L". This would have used two Titan 2 first stage liquid boosters strapped to a Commercial Titan 3 core. The minimal description I found in a JSC presentation said that the core stages would, oddly, also have been powered by Titan 2 engines. Although I've shown it this way on the card, this description makes little sense because it would likely have underperformed Titan 2L. All engines would had to have ignited on the ground to provide enough liftoff thrust unless propellant was offloaded from the boosters. Perhaps a Commercial Titan core with its Titan 4 type engines was the real plan.

Keep in mind that only 41 unassigned Titan 2's remained after the Titan 23G program began. If they were used up three at a time, only a dozen Titan 2L or 3L launches would have been possible. With the Cold War ending and with Delta 2 and Atlas 2(A)(S) soon offering comparable alternatives, we never got to see a "triple-barrel" all-liquid Titan launch.


In June 1991, AIAA's Journal of Spacecraft published a paper submitted in 1989 by James A. Martin of NASA Langley titled "Titan Improvement Study: Hydrogen Core Stages". The paper proposed replacing the hypergolic Titan stages and Centaur stage of Titan 3E/3A with two hydrogen fueled core stages powered by a new expander cycle engine. A 68 tonne thrust engine could power the second stage while three or more of the engines could power the first stage. The core stages would have been the same diameter as the Titan 4 type payload fairings, allowing the Titan 3C/D/E five-segment boosters to be used as "Stage Zero".

Though it would only have used two core stages, rather than Titan/Centaur's three, and would have only use existing five-segment boosters, rather than Titan 4's seven-segment boosters, its payload would have been Titan 4 class.

To my knowledge, Martin Marietta never made such a proposal, certainly not one named "Titan", but the study does offer a glimpse into the thinking of the time. Similar thinking was soon reflected in the Advanced Launch System trades, in which Martin was heavily involved.