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Ed Kyle

acxx-slv3xs.jpg (33341 bytes)ATLAS:  PROPOSED BUT NEVER FLOWN DSIGNS
by Ed Kyle

SLV-3X Centaur Concept Illustrated Here Never Flew

Convair studied and proposed numerous Atlas designs over the years that were never developed or flown.  Many of the concepts were compelling.  Several are presented here in "baseball card" format.  

1. Five-Engine Atlas

Early 1951-ish Atlas concepts called for seven engines (five boost and two sustainer) based on the 120 Klbf LOX/Alcohol Navaho G26 engine by Rocketdyne. This would have been a stage-and-a-half design 12 feet in diameter and 140 feet tall, able to boost an 8 Klb warhead. By 1954, the design (shown here) had been slimmed to five engines and only 110 feet tall, though still 12 feet in diameter. It would have used four 133.2 Klbf LOX/JP-4 (kerosene) boosters and one 123.3 Klbf LOX/JP-4 sustainer. The boosters would have been fixed and the sustainer would have gimballed. Two verniers hidden within the booster section would also have been used. This Atlas would have lifted warheads weighing 3 to 7 Klbf depending on range. The final Atlas D was topped by a warhead weighing about half as much.

Five-engine Atlas would have been the same diameter as today's Falcon 9.  The conical engine nozzles were essentially from the Navaho program. Some of the first Atlas A vehicles actually used conical nozzles like these.  Rocketdyne quickly moved on to bell shaped nozzles.

2. Atlas Vega

Soon after NASA was formed, it began development of both Atlas-Vega and Atlas-Centaur. Atlas-Vega would handle early unmanned missions to the Moon, to Mars, to Venus, and to Earth orbit. Planners even contemplated its use for launching an early concept for what became the Gemini two-man spacecraft. Atlas-Centaur would take over more missions as it entered service several years later.

Atlas-Vega would have flown in two-stage and three-stage versions. The first stage would have been essentially the same as the Atlas Centaur first stage. Atlas-Vega might even have flown from LC 36. The second stage would have been a LOX/RP stage powered by an upgraded Vanguard first stage engine, the GE 405H-2. The stage itself would have been a balloon tank design built by Convair.

The third stage would have been a pressure-fed Hydrazine/Nitrogen Tetroxide stage powered by a JPL "6K" restartable engine. JPL would also have built the stage. Development of this stage had begun during 1958 before NASA's formation as part of the von-Braun group's "Juno IV" program.

A guidance system from JPL's Sergeant missile would have been used at first, to be supplanted later by avionics developed for Centaur.

The Atlas-Vega program was initiated in March 1959. Prototype stages were built, engines were tested, and $28.2 million was spent, but NASA Administrator Glennan cancelled the project in December 1959 after the Agency became aware of the USAF Atlas-Agena B capabilities. Atlas-Vega could lift more to deep space than Atlas-Agena B, but the two were about equal to LEO. Most importantly, Atlas-Agena B development was paid for and its use could be shared with the Air Force.

The cancellation freed up NASA funding for Atlas-Centaur, which in the end needed every dime. It also ended GE's rocket engine work, JPLs upper stage efforts, and also ended U.S. LOX/RP orbital upper stage development until SpaceX created Falcon 1 and 9 more than 45 years  later.

3. Atlas-Vega Spacelab

Atlas-Vega was proposed for a variety of missions, including an early 2-man Mercury with a small attached spacelab. Other proposed missions included precursors for Ranger, Mariner, Lunar Orbiter, and weather and communications satellites. The plan was to fly up to six Atlas-Vega missions per year, beginning in 1960. Growth options including upper stage improvements and use of Atlas Centaur fairings, guidance, and eventually stretched Atlas stages.


4. Atlas "F" ICBM

In 1960, Convair studied an upgraded Atlas "F" ICBM that would have used two Rocketdyne "H-2" booster engines, each producing 250 Klbf thrust, together providing a good 200 Klbf more liftoff thrust than then-existing Atlas ICBMs. (These 560 Klbf liftoff thrust missiles would have been monsters!) The sustainer and vernier engines would have remained the same. Note that this was not the lower-thrust "Atlas F" that ultimately appeared. Convair probably used "F" for the study simply because it was the next available letter after the then-planned "E".

It appears to have been proposed around the same time that the USAF was defining Titan 2, so there is a chance that it was Convair's competing  big-warhead missile plan. It still would have used cryogenic oxidizer, however, which would have made it an unlikely contract winner at that point in time. This Atlas "F" would have stood a bit taller than Titan 2 and it would have weighed more and probably carried more payload. I would love to find more details ...


5. Atlas "F" Centaur (Jr)

Convair also examined Atlas "F" orbital launch vehicles with Centaur upper stages, both the planned Centaur and a proposed "Growth" Centaur. A 96 inch diameter "Centaur Jr." with one RL-10 engine was also studied. It could have landed on the Moon with nearly a tonne of payload - in theory.

These powerful Atlas Centaurs would have stood as tall as the eventual Atlas 3 vehicles and would have been as capable as some of the Atlas 2 series rockets that appeared 30 years later.  They would have outlifted Atlas 2 if they would have been able to use the Atlas 2 era RL10 engines. Note that they even would have out-lifted Titan 3C/Transtage to GEO. The H-2 was, I believe, an engine then being considered for growth versions of von Braun's Saturn C series rockets.

Imagine how history might have differed if these more powerful Atlas boosters had been developed.


6. Atlas SLV-3X Centaur

"SLV-3X" was an identifier for several different proposed growth Atlas models over the years. In 1965, for example, it was used to describe a design that became SLV-3C/Centaur. In 1968-70, SLV-3X referred to a "fat" Atlas design that used a 12 foot 7 inch diameter tank and an H-1D engine in place of the MA-5 sustainer engine. This allowed a more capable rocket while standing the same height as the existing SLV-3C/Centaur, allowing use of existing infrastructure. SLV-3X would also have dispensed with the verniers in favor of a roll control system in the interstage.

SLV-3X/Centaur D would have lifted off on 550 Klbf thrust and would have boosted nearly 2.7 tonnes to GTO or 4.5 tonnes to sun synchronous orbit with a big fairing or 2 tonnes to escape velocity with a small fairing. It was considered for Intelsat launches and for NASA "Grand Tour" missions during the 1970s. Titan IIIE was used for Grand Tour instead, and looming Shuttle development stunted plans for growth Atlas/Centaurs like SLV-3X. Such capability would not actually be achieved by Atlas until the Atlas 2A(S) era more than two decades later. GD reconsidered the design after Challenger before deciding on the stretched Atlas 2 approach.


7.   SLV-3A Uprated, SLV-3X Agena

By 1969, Convair had a series of never-developed growth Atlas designs on hand, including ways to improve SLV-3A performance while using the existing Agena D second stage.

One design was an "Uprated" SLV-3A that would be stretched another 38 inches (SLV-3A had already been stretched 117 inches beyond SLV-3 length) while using slightly improved MA-5 engines to gain nearly 10% in payload. SLV-3A was already ridiculously long with its planned Aquacade fairing. An "Uprated" version would have been ludicrously long!

Another design was SLV-3XA/Agena D, which like SLV-3X/Centaur would have used an H-1D sustainer engine to provide a substantial thrust increase, allowing more propellant to be carried in "fat" 151 inch diameter tanks. Payload would be increased around 35-45%, but the Agena and payload would have remained at their SLV-3A heights.


8. Atlas SLV-3K Centaur "D-1"

Convair proposed five-engine Atlas designs several times over the years, beginning with the early ICBM concept. By 1969, the company had suggested an "Atlas SLV-3K/Centaur "D-1"" concept that appeared to mimic the performance of Titan IIIC and, for deep space, the future Titan IIIE. It would have used a 192 inch diameter Atlas SLV-3K powered by five H-1D engines at 220 Klbf thrust each (four on the booster and one on the sustainer). A 1970s-era Centaur would have topped the vehicle, which was shown in Convair drawings topped by a 168 inch diameter "Viking Shroud". LC 36A or B would have been reconfigured for SLV-3K, as would one of the 576 A pads at Vandenberg AFB.

This was a non-starter back then because Titan existed and because Shuttle soon snuffed out all alternatives, but it is interesting to contemplate whether such a launcher, which only used two stages (O.K., two-point-five stages) compared to the four stages (including zero-stage boosters) needed by Titan IIIC/E, might have been a less costly approach over the long run.

9. Atlas SLV-3A (Uprated) Burner 2

Convair proposed adding the Burner 2 (Star 37B) motor as an upper stage atop both the developed SLV-3A Atlas and the proposed Uprated SLV-3A. It also proposed using an upgraded "2300 Burner 2" motor atop both variants that appears to have been a Star 37E. None of these proposed designs ever flew. SLV-3A never gained a west coast launch pad. Perhaps Convair was competing against itself a bit, since the USAF was happily flying off its stock of Atlas E and F missiles converted with solid motor upper stages during the 1970s and 80s. SLV-3A/Burner 2 would also have bumped up against the emerging Straight-Eight Deltas of the same period. Of course Convair GD ended up developing another Atlas in this payload class - Atlas H - during the 1980s. I've provided an Atlas F/Burner 2 for size comparison.


10. Atlas SLV-3C/Delta (1970)

Around 1970 or so, General Dynamics proposed an Atlas SLV-3C/Delta combination to NASA. This "Atlas-Delta" would have used a Delta E (Improved Delta) second stage with an AJ10-118E engine. It was pitched, probably more than once, as a way to replace NASA's entire Thor/Delta program with Atlas. It would have allowed NASA to trim contractors and launch pads, etc., while increasing payload capability. It would have shared its SLV-3C first stage with the Atlas-Centaur program.

This idea was a non-starter for a variety of reasons. Atlas-Delta would have likely cost more than Thor-Delta and would have had about the same performance as the already-existing, but soon to be phased-out, Atlas-Agena. The Delta E stage with its contractors would have still been needed. Delta was a Goddard program while Atlas-Centaur was a Glenn program, and so on. Still, it was a compelling proposal that likely garnered serious consideration at some point.

11. Atlas CELV

For the USAF Complementary Expendable Launch Vehicle (CELV) competition in 1984, General Dynamics proposed a formidable Atlas "II" Centaur G-Prime launch vehicle that would have lifted nearly 5 tonnes (metric tons) directly to GEO, more than 9 tonnes to GTO, or about 18 tonnes to LEO.

A new 200 inch diameter Atlas "II" stage (not to be confused with the Atlas II ultimately developed) would have been powered by five Rocketdyne H-1D engines that together would have produced more than 1 million pounds of liftoff thrust. This would have been a stage-and-a-half design, with the center engine remaining as a sustainer.  A Centaur G Prime from the Shuttle Centaur program would have served as the second stage. Four big 67 inch diameter solid rocket boosters would have augmented thrust at liftoff. These SRBs would have carried nearly as much propellant as the AJ-60A Atlas 5 SRBs.

Atlas "II" Centaur G Prime would have flown from a rebuilt Launch Complex 41, which at the time had been mothballed since the Titan 3E era. The design hints at future EELV design choices, because it has those Atlas 5 class SRBs, a Delta 4 tank diameter, and a Centaur similar in capability to today's Atlas 5 Centaur. With its "single-core" ability to handle the "heavy" missions of its era, it even aligns with today's Vulcan. 

Centaur G Prime had a fatter LH2 tank that the Atlas 5 Centaur (170 inches versus 120 inches), but the stage only held 20.7 metric tons (tonnes) of propellant versus 20.8 tonnes for the Atlas 5 Centaur stage. Centaur G Prime also had a larger dry mass due to the second RL10 and the less than optimum tank setup (and so had higher gross mass at 23.7 tonnes than the 22.8 tonne Atlas 5 Centaur). Shuttle payload bay limitations drove the decision to create the "fat" Centaur G' and its equally fat but shorter cousin Centaur G (for longer USAF payloads).


12. Atlas Centaur Super G

Soon after STS-51L made it apparent that national space launch plans would change, General Dynamics revealed its Atlas Centaur "Super G" proposal. This never-flown design provides insight into the design work that eventually led to Atlas 2, 2A, and 2AS. The proposal was to add four Star 31 solid motors (developed for the Scout third stage) to an Atlas G, to stretch Centaur about 24 inches (or so), to replace the jettisonable insulating panels with fixed foam, to add nozzle extensions to the RL-10 engines, to upgrade and lighten Centaur avionics, and to add a 4 meter Contraves payload fairing option.

The Star 31 motors would have ignited 3.5 seconds after liftoff, together adding 27.2 tonnes of thrust, and would have been jettisoned before Max-Q.

"Super G", a cool name for a rocket if ever there was one, would have lifted 6,000 lbs (2,722 kg) to GTO. Though not developed, many of its features later appeared in the Atlas 2 family.

I think the idea was to use solids small enough to attach to the booster package so that the Atlas G sustainer structure could remain unchanged. Also, the motors would have burned out and jettisoned before Max-Q, simplifying structural modifications. The Star 31 motors would have looked a bit like JATOs compared to the size of the rocket, but would have been substantially longer-burning than aircraft boosting motors.

13. Atlas K (1986)

After the Challenger failure, launch contractors scrambled to provide Shuttle launch alternatives. During August 1986, the USAF awarded four six-month "MLV" R&D contracts to develop plans for launching the GPS 2 constellation originally slated for Shuttle. McDonnell Douglas, Martin Marietta, General Dynamics and Hughes Aircraft were the awardees.

Requirements called for placing 930 kg satellites into 20,200 km circular orbits. General Dynamics apparently offered two possibilities. One was an Atlas G topped by what was essentially an AJ-10 powered Delta second stage (named SSPS). Another was an Atlas G stretched by 109 inches - apparently named "Atlas K" - topped by a PAM D2/Star 48A solid motor stack. These appeared designed to place GPS 2 satellites fitted with Star 37 AKMs into transfer orbits, as was ultimately done using Delta 2.

The McDonnell Douglas Delta 2 proposal won the MLV contract during January 1987. GD quickly focused on the subsequent "MLV-2" contract that it won with Altas 2(A)(S). Atlas 2 ended up being 6 inches longer than the proposed "Atlas K".

A final, related proposal, for an "Atlas K"/SSPS/PAM-D that could have handled much of the work ultimately done by Delta 2, was also made.  SSPS would have been powered by an AJ10-118F engine. There were hints in GD brochures that the stage might have been produced by or based on Japan's MHI-assembled N-2 second stage, which itself was a licensed Delta second stage. (Remember that the McDonnell Douglas Delta production line had shut down by then.) The rocket would have lifted more to GTO than Delta 2-6925.   It is apparent that substantial payload growth beyond this proposal would have been available.