NASA Johnson Space Center's Shuttle II (1988)

Image credit: NASA.

Although the fact is mostly forgotten today, NASA launched plans to augment or replace the Space Shuttle even before the first Shuttle reached orbit on 12 April 1981. Much — though by no means all — of this planning occurred as part of joint Department of Energy/NASA Solar Power Satellite studies.

In 1985, U.S. President Ronald Reagan signed a directive ordering the U.S. civilian space agency to develop a Space Shuttle successor. Notably, this occurred before the 28 January 1986 Challenger accident laid bare the Shuttle system's many frailties.

One proposed Shuttle successor was called Shuttle II. Most Shuttle II design work took place at NASA Langley Research Center (LaRC) in Hampton, Virginia. Shuttle II first achieved prominence in 1986 in the high-level National Commission On Space report Pioneering the Space Frontier.

LaRC's Shuttle II design evolved — for a time it was to have been a single-stage-to-orbit vehicle. The favored design included a winged manned Orbiter and a winged unmanned Booster, both of which would take off vertically and land horizontally on runways. Both the Booster and the Orbiter would be entirely reusable. LaRC's Shuttle II Orbiter fuselage was meant to be crammed full of propellant tanks, so would tote cargo in a sizable hump on its back.

NASA Langley Research Center's dumpy Shuttle II, 1987. Image credit: NASA.

Shuttle II was intended mainly as a crew transport complementing a "mixed fleet" of launchers that would have included unmanned heavy-lift rockets capable of placing from 50 to 100 tons into space. LaRC envisioned that its Shuttle II would transport a small amount of cargo — perhaps 10 tons — and up to 25 astronauts, of whom only three would be considered Shuttle II crew members. The remainder would be passengers bound for a large advanced Space Station or a Transportation Node station. There they would board Moon or Mars spacecraft.

Although a good case can be made for calling LaRC's Shuttle II the Shuttle II, it was in fact not the only proposed Shuttle II design. The Advanced Programs Office at NASA Johnson Space Center (JSC) in Houston, Texas, put forward the sleek Shuttle II design depicted in the last seven images of this post. They portray JSC's Shuttle II as it would appear over the course of a typical mission.

The LaRC design was favored by NASA Headquarters and is relatively well documented. Neither can be said for JSC's design.

In flight: the Evolved Shuttle climbs toward space, probably sometime in the 1990s. Image credit: Eagle Engineering/NASA.

Model of proposed Evolved Shuttle showing major components. Image credit: NASA.

Engineers in Houston envisioned that their Shuttle II might develop from an Evolved Space Shuttle. In the Evolved Shuttle, Liquid Replacement Boosters stood in for the Shuttle's twin Solid Rocket Boosters. The Evolved Shuttle would retain the Shuttle's expendable External Tank and, with minor modifications, the Shuttle Orbiter's Space Shuttle Main Engines (SSMEs). Like the Space Shuttle, the Evolved Shuttle stack would ride to its Launch Complex 39 pad atop a creeping crawler-transporter with its nose aimed at the sky.

Winglets on the tips of the Evolved Shuttle's modified delta wings would replace the Shuttle's single vertical tail fin. Redesigned Orbital Maneuvering System (OMS) engines based on the venerable RL-10 engine would draw liquid hydrogen/liquid oxygen propellants from insulated tanks built into the Evolved Shuttle Orbiter wings.

The most dramatic changes would, however, be reserved for the Evolved Shuttle crew compartment. JSC engineers designed it so that it could separate from the Evolved Shuttle in the event of catastrophic failure and operate as an independent spacecraft. Canard winglets meant to improve the Evolved Shuttle's aerodynamic characteristics would separate with the crew compartment and become its wings.

JSC gave no timeline for the evolution of Shuttle to Evolved Shuttle. If, however, JSC's Shuttle II was to become operational in the same timeframe as LaRC's Shuttle II (the early 21st century), then one may assume that the Evolved Shuttle would have made its debut in the 1990s.

Shuttle II ready for a tow to its launch pad. A round panel covering an extendable docking adapter is visible just above the American flag on the fuselage. Image credit: NASA.

The JSC Shuttle II was meant to be towed horizontally on its tricycle landing gear from a hangar to its launch pad just four hours before planned launch. Unlike the Space Shuttle and Evolved Shuttle, JSC's Shuttle II would have no need of the Vehicle Assembly Building, the massive cuboid structure built at Kennedy Space Center in the 1960s for the assembly of Apollo Saturn V heavy-lift rockets.

Nor would it use the twin Launch Complex 39 pads, which were built in the 1960s to launch Saturn V rockets and rebuilt in the 1970s to launch the Space Shuttle. Shuttle II would instead lift off from a new-design pad, and Complex 39 would be given over once again to heavy-lift rocket launches. In fact, the JSC Shuttle II would make a complete break from the massive-scale Apollo-era infrastructure upon which the Space Shuttle relied.

JSC's Shuttle II in launch configuration. The round panel covering the extendible docking adapter is again visible; it leads to a crew access tunnel that runs the length of the spacecraft. Image credit: NASA.

At the launch pad, crew and passengers would board JSC's Shuttle II, then it would be tipped up to point its nose at the sky. Its landing gear doors would be closed, then its ground crew — small compared with the army of personnel that serviced the Space Shuttle — would load it with three kinds of propellants: liquid hydrogen fuel, liquid hydrocarbon (kerosene or propane) fuel, and liquid oxygen oxidizer.

For safety, most of the volatile fuels would be pumped into Shuttle II's four expendable over-wing tanks, while an integral, reusable tank within the spacecraft would carry most of the dense liquid oxygen. Fully loaded with propellants and payload, Shuttle II would weigh about 550 tons, or a little more than a quarter of the Shuttle's weight at SSME ignition.

JSC designers hoped to minimize Shuttle II weight in part by building it from advanced materials. The Space Shuttle Orbiter, with an empty mass of about 85 tons, had a more-or-less conventional load-bearing aluminum-titanium airframe clad in aluminum and lightweight thermal-protection materials. These included thousands of uniquely shaped ceramic tiles and Reinforced Carbon-Carbon (RCC) wing leading edges. Shuttle II, with an empty mass of 50 to 75 tons, would also rely on RCC, "but in larger, load-bearing, monolithic panels." The over-wing tanks would be made from lightweight welded aluminum-lithium alloy.

At launch, Shuttle II's single Space Transportation Main Engine (STME) and twin Space Transportation Boost Engines (STBEs) would ignite simultaneously. The former, designed to burn liquid hydrogen and liquid oxygen, was envisioned as a second-generation SSME. The latter, located between the STME and the Shuttle II body flap, would burn hydrocarbon fuel and liquid oxygen and employ liquid hydrogen as engine coolant. The STME and STBEs would together generate about 30% more thrust than the Space Shuttle's three SSMEs — between 1.3 and 1.6 million pounds.

Climb to orbit: JSC's Shuttle II following detachment of its outboard tanks and its twin STBEs. Image credit: NASA.

When it reached a velocity of between two and three kilometers per second, JSC's Shuttle II would shed its depleted outboard over-wing tanks and the STBEs. Dropping the STBEs would improve Shuttle II's flight performance by shifting its center of gravity forward. The tanks would break up and fall into the sea, but NASA would recover the twin engines for reuse. JSC engineers envisioned that they would descend in reentry shells, deploy maneuvering parachutes, and land in arresting nets aboard recovery ships.

The STME, meanwhile, would extend its telescoping exhaust nozzle to its full length and diameter to improve its performance in vacuum. Following separation of the outboard tanks and STBEs, the spacecraft would burn only liquid hydrogen/liquid oxygen propellants.

Immediately following STME cutoff, the engine's nozzle would retract and the inboard over-wing tanks would be cast off. Upon reaching apogee (the highest point in its orbit about the Earth), Shuttle II's twin OMS engines would ignite to raise its perigee (the lowest point in its orbit) out of the atmosphere. This would place it into a circular "Space Station rendezvous orbit" 485 kilometers high and inclined 28.5° relative to Earth's equator. The inboard tanks, meanwhile, would intersect Earth's atmosphere as they reached perigee and be destroyed.

The Shuttle II OMS would comprise a pair of new-design Advanced Space Engines or RL-10-derived engines. RL-10 had the advantage of a long flight history; derivatives of that engine have propelled upper stages and spacecraft since the 1960s. Liquid hydrogen and liquid oxygen for Shuttle II's OMS and the Reaction Control System (RCS) thrusters would be stored in double-walled, heavily insulated tanks in its tail section. Some propellants from the tail section would be combined in next-generation fuel cells to generate electricity and water for the spacecraft.

A crew access tunnel would run aft from the forward crew compartment for most of the length of the fuselage. Midway along the tunnel, on its left side, Shuttle II's docking adapter for linking up with the Space Station would be stowed behind a streamlined panel. The round panel is visible near the American flag in images that display the left side of the Shuttle II model. Prior to rendezvous with the Space Station, the panel would hinge out of the way, then the crew would extend the cylindrical docking adapter.

The image above shows Shuttle II in its orbital configuration with inboard tanks in place; this is apparently a photographer's error, since image captions make plain that the inboard tanks would separate immediately after STME cutoff, before the crew opened the payload bay. Image credit: NASA.

JSC engineers chose a novel method for exposing Shuttle II payloads to space: the crew would disable the OMS engines, vent and disconnect hoses that had linked the over-wing tanks to the STME, disengage locks, and hinge the tail section downward using electric motors. RCS thrusters in the tail would continue to operate; to minimize flexible wiring links between the main fuselage and the tail section, engineers proposed that the astronauts control the RCS thrusters via a short-range radio link.

Hinging the tail section down would expose a large round window and the open aft end of the 15-foot-wide-by-30-foot-long cylindrical payload bay. Astronauts at an aft workstation would look out through the window as they extended the cradle bearing their mission's payload. The photo captions do not name specific Shuttle II payloads, but it is logical to assume that these would include experiment packages for mounting on the Space Station and reusable Station logistics modules packed full of supplies and equipment. The payload bay would include an airlock for spacewalks and a pair of robot arms.

Unlike the Space Shuttle and Evolved Shuttle payload bays, the Shuttle II bay would normally not include radiators for dissipating heat generated by onboard equipment and astronaut exertions. Instead, Shuttle II's radiators would be built into the top surface of its wings. Supplemental radiators would be mounted on the payload cradle before flight only if "special purpose, high heat load conditions" were expected.

Before return to Earth, the astronauts would retract the payload cradle, then hinge shut the tail section. Shuttle II would include triple-redundant electric motors and a mechanical backup system for closing the payload bay "to assure that the vehicle configuration for entry [would] not have paths for hot plasma to enter the vehicle interior." During the first few Shuttle II flights, an astronaut would exit through the docking adapter and clamber over the fuselage to inspect the hinge area and seam between the tail section and the rest of the spacecraft. He or she might carry a repair kit "to fill any voids."

Reentry would occur as in the Space Shuttle Program; that is, Shuttle II would turn so that its aft end pointed in its direction of flight, then its OMS engines would ignite to reduce its orbital velocity. The spacecraft would then flip to point its nose forward as it fell toward the atmosphere. Following reentry, Shuttle II would glide to a runway landing.

JSC's Shuttle II in landing configuration. Image credit: NASA.

Unlike the Space Shuttle, which even after the Challenger accident included few realistic options for crew escape in the event of catastrophic failure, Shuttle II could in theory protect its crew through all phases of its mission. Like the Evolved Shuttle, Shuttle II would include a separable crew compartment; after separation, Shuttle II's canard fins — proportionately larger than those of the Evolved Shuttle — would become the crew compartment's wings.

The crew compartment aft end would include launch escape/deorbit rocket engines, a crew hatch, and a deployable aerodynamic flap. Following separation in orbit, the crew compartment could support 11 astronauts for up to 24 hours. This endurance was meant to ensure that Earth's rotation could bring into range a suitable landing site on U.S. soil. The crew compartment would touch down and slide to a halt on extendable skids.

Crew cabin separation on the launch pad or during ascent. Image credit: NASA.

Crew cabin separation in orbit or during reentry. Image credit: NASA.

JSC engineers acknowledged that wind-tunnel testing might show that the Shuttle II crew compartment shape was not flight-worthy in all abort situations. They proposed that inflatable or extendable structures "be employed to obtain an acceptable configuration for hypersonic, supersonic, and subsonic controlled flight."

They also proposed that the Shuttle II crew compartment become the Space Station's Crew Emergency Rescue Vehicle (CERV). The CERV was conceived as a "lifeboat" for use if the Space Station had to be evacuated rapidly, if a crew member became seriously ill or injured and needed hospital treatment on Earth, or if Shuttle II became grounded due to malfunction or accident and could not retrieve a Space Station crew.

The JSC engineers noted that the Shuttle II crew compartment/CERV, like Shuttle II itself, would subject its occupants to no more than three gravities of acceleration or deceleration. This would help to ensure that, during return to Earth, it would not inflict additional harm on a sick or injured Space Station crewmember.

NASA continued to attempt to develop a Shuttle successor — a winged spacecraft that would enable it to apply the lessons learned from the Shuttle Program. Some proposed complex new vehicles employing scramjets; others, vehicles smaller and less capable than the Shuttle tailored mainly for Space Station crew rotation and crew escape. Unfortunately, the space agency's budget was not expanded to permit simultaneous ongoing Shuttle operations, Space Station development and assembly, and development of a Shuttle successor.

By the mid-1990s, many in the Shuttle Program had changed their tactics; they declared that the Shuttle should continue to fly at least until 2010. In 2001, Boeing proposed that the Shuttle should fly until 2030.

The 2003 Columbia accident ended such plans. When the Shuttle was retired in 2011, a new NASA Shuttle design was as far away as it had been during Shuttle II planning in the late 1980s.

Sources

Caption Sheet, NASA Photo S88 29029, Shuttle II Candidate Configuration, 1988.

Caption Sheet, NASA Photo S88 29035, Shuttle II Launch Configuration, 1988.

Caption Sheet, NASA Photo S88 29032, Shuttle II Post-Boost Flight Configuration, 1988.

Caption Sheet, NASA Photo S88 29028, Shuttle II Orbital Flight Configuration, 1988.

Caption Sheet, NASA Photo S88 29026, Shuttle II Entry and Landing Configuration, 1988.

Caption Sheet, NASA Photo S88 29024, Shuttle II Pad Abort Crew Escape, 1988.

Caption Sheet, NASA Photo S88 29030, Shuttle II Crew Escape System, 1988.

Caption Sheet, NASA Photo S89 34837, Evolved Shuttle, 1989.

"Shuttle II Progress Report," T. Talay, NASA Langley Research Center; paper presented at the 24th Space Congress, 21-24 April 1987, Cocoa Beach, Florida.

Pioneering the Space Frontier: the Report of the National Commission on Space, Bantam Books, 1986.

"At 15, A Safer, Cheaper Shuttle," J. Asker, Aviation Week & Space Technology, 8 April 1996, pp. 48-51.

"Boeing upgrade would keep Space Shuttle flying to 2030," G. Warwick, Flight International, 8-14 May 2001, p. 37.

More Information

Electricity from Space: The 1970s DOE/NASA Solar Power Satellite Studies

What If a Space Shuttle Orbiter Had to Ditch? (1975)

One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)