Andrew Gray wrote


STS (Shuttle I)

Which neatly implies a Shuttle II... were there serious plans for a
second-generation shuttle floating around then?


This may apply in some way; it appears to have been lifted from
a now-vanished NASA paper:


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The Shuttle II study began as an Agency activity in January 1985.
Midway through the planned two-year effort, the Challenger accident
occurred which reshaped the effort. Emphasis was placed on more
immediate, near-term Shuttle replacements and a focus on safety
and reliability issues. The National Aerospace Plane (NASP) and
Advanced Launch System (ALS) studies were also underway. Thus,
Shuttle II became viewed as one element of an overall architecture
which included unmanned heavy-lift vehicles, a near-term expendable,
and far-term replacement of Shuttle II by NASP-derived vehicles.

In 1988, the Shuttle II study was superceded by The Next Manned
Transportation System Study (TNMTS).

Primary Requirements Determined During Study:

Requirements evolved during the course of the study. Meet civilian
government, commercial needs, Mutlti-mission, flexibility and
Low cost (Low investment, low dollars/lb, low dollars/flight).

Baseline missions:

20,000 lb (15'dia x 30' volume) Space Station delivery
270 nmi, 28.5° inc)

12,000 lb (15' dia x 30' volume) Polar Platform servicing
(150 nmi, 98° inc).

Initial Phase Vehicle Configurations:

In the initial phase of the Shuttle II study, a variety of
configuration options were examined. These included single-stage
and two-stage vertical takeoff rocket systems, an all-rocket
horizontal launch SSTO, and single-stage and two-stage horizontal
systems with mixed airbreathing and rocket stages. Preliminary
analyses demonstrated the air-breathing systems to have higher dry
weights than comparable all-rocket systems. The NASP studies were
also expected to define far-term Shuttle replacements beyond the
time-frame of the current study options. The focus of the study
shifted to trades between near-term single vs. two-stage all-
rocket systems.

The level of technology available at the time a new system begins
developed has a pronounced effect on the vehicle designs. Specifical
sets of Shuttle, near-term (1992), and far-term (NASP derived)
technologies were compiled and used to define single- and two-stage
vertical takeoff rocket systems. These system designs also reflected
a particular set of design assumptions, e.g. the use of dual-fuel
with separate LOX/LH2 and LOX/HC rocket engines, the use of
externally-mounted payload canisters, and double-bubble propellant
tank arrangements that provided a "flat-bed" area for canister
mounting.

The SSTO core configuration was designed to satisfy the baseline
space station mission (20 Klb). This SSTO had relatively little
payload capability to a 98° inclination orbit. To capture the polar
platform servicing mission would require a much larger SSTO vehicle.
The Shuttle II study demonstrated, however, that relatively small
levels of augmentation, in the form of expendable or reusable
rocket strap-ons, significantly boosted payload performance. Small
solids (approximately 11% by weight of the Shuttle Solid Rocket
Boosters) permitted the required polar platform servicing mission.

To capture the polar platform deployment mission (28 Klb to polar
orbit), a small reusable liquid (LOX/HC) booster was used to augment
the SSTO. This low-technology glideback booster also provided the
SSTO with a large space station payload delivery capability.

The augmentation approach used in the Shuttle II studies is not
unlike the Ariane 4 expendable launch vehicle which can be
launched without boosters or, for heavier payloads, can use 2 or
4 solid and/or liquid boosters, thus tailoring the launch system
to meet the payload delivery requirements. For Shuttle II, a large
percentage of the missions did not require strapon boosters. For
the less frequent heavier payloads, the solid or liquid boosters
could be utilized.

A brief look was made of the "Bimese" configuration, which
essentially mated two nearly identical SSTO vehicles with one of
the SSTO vehicles acting as a booster for the orbiter stage. This
performance analysis indicated very large payloads could be
orbited, well beyond the mission model requirements noted.

A two-stage, vertical takeoff rocket was sized to capture the
polar platform servicing mission and baseline space station
mission. The low-technology, reusable booster utilized LOX/
hydrocarbon (HC) propulsion, crossfed propellants to the orbiter
engines, and staged at Mach 3 to glide back to the launch site.
The orbiter utilized LOX/LH2 and LOX/HC separate engine propulsion.

In early 1987, the two-stage, vertical takeoff rocket system was
selected as the baseline option for further, in-depth Shuttle II
studies. This selection was made for several reasons related to
anticipated cost, cost risk, and availability.

The desire to examine a near-term Shuttle replacement dictated
only those technologies that might reasonable be available by
1992, The significantly higher dry weight and gross weight of
this design SSTO, The higher risk (greater sensitivity) of this
design SSTO system to weight growth at this level of technology
advancement, The desire to include significant operational
features (e.g. full engine-out capability on each stage, full
launch escape capability for passengers and crew, payload
canister operations, switch from orbiter dual position nozzles
to single position nozzles) that would have smaller weight growth
impact on a two-stage system.

Shuttle II Overview - 1988

The reference manned, reusable Shuttle II booster-orbiter system
was designed to perform priority, or sortie-class missions
involving personnel transport, on-orbit servicing and repair,
and transportation to and from orbit of high-valued payloads and
supplies. Designing the booster-orbiter vehicle to carry 12,000-lb
to polar orbit provided a capability of 37,000-lb to a space
station in a 28.5° orbit.

As a result of various trade studies, this vehicle had a lift-off
thrust-to-weight if 1.3, and a thrust split of 60 percent booster
thrust and 40 percent orbiter thrust at liftoff. The system
utilized parallel burn with crossfeed, which means all engines
were firing at liftoff with the orbiter engines drawing its
propellants from the booster. Crossfeed was shown to have large
benefits in scale reduction over a non-crossfeed system. The
booster staged at Mach 3 to glide back to the launch site. The
orbiter, full of propellants at staging, then continued on to
orbit. Staging at Mach 3 with glideback was not optimum from a
dry weight point of view, but had the operational benefits of not
requiring a thermal protection system or cruise back systems
to return the vehicle to the launch site.

The rocket engines used in the Shuttle II study were based on the
results of the STME (Space Transportation Main Engine) and STBE
(Space Transportation Booster Engine) studies performed at Marshall
Space Flight Center. These studies examined operationally efficient
reusable propulsion systems for next-generation space
transportation systems. The Shuttle II booster used 6 methane fuel
STBE-type engines. Methane was cited by the STBE engine study
contractors as the fuel of choice since it was clean burning
without the combustion instabilities associated with RP-type fuels.
The orbiter used 5 hydrogen fuel STME-type engines.

Both the booster and orbiter had engine-out capability built in,
which meant that a booster engine and an orbiter engine could both
fail benignly at liftoff, and the vehicle could complete its
mission.

The orbiter carried a full crew escape system in the form of a
jettisonable crew cabin which would function as a recovery capsule
complete with stabilization fins and parachutes. Incorporating this
system into the design reduced the payload capability of the system
by 12 percent.

Phased Approach Architectu

During the later stages of the Shuttle II study, a scenario was
developed that suggested how a Shuttle II development could be
integrated within a space transportation architecture to satisfy
national needs. The scenario was referred to as a "phased approach
architecture" and included unmanned heavy-lift elements and an
"assured access to space" element. The intent was to integrate
systems into a common architecture and share launch sites,
operational facilities, and workforce to reduce life-cycle costs.

A heavy-lift core vehicle element would be developed first,
augmented by three solid rockets and providing up to 100 Klb to
low-Earth orbit in the mid 1990's.

The next step would be the Shuttle II glideback booster to replace
the solid boosters for the heavy lift giving 150 Klb orbit
capability by the late 1990's. The core stage would also
incorporate a recoverable propulsion/avionics module.

The Challenger accident in 1986 heightened awareness as to the
reliability issue in space transportation. The challenge was to
provide an assured human access to space if the Space Shuttle or
Shuttle II were unavailable for whatever reason. This led to the
inclusion of the Space Taxi and Recovery (STAR) vehicle launched
by the heavy-lift core vehicle and available in the late 1990's.
The small STAR vehicle could be configured in a variety of mission
roles including space station crew rotation and crew emergency
return vehicle (CERV).

Finally, shortly after the turn of the century, the fully reusable
booster-orbiter Shuttle II would have been introduced to gradually
replace an aging Space Shuttle fleet.

Operations:

A statement of Shuttle II operational groundrules and goals drove
the system design and operational scenarios. Rocket system designs
of the past have generally been performance driven because of
restricted development budgets, the desire to maximize payload to
orbit, or the exceptional mission needs. These usually penalize
the operational characteristics of the systems with consequential
increased operational costs. For this study, a design-for-operations
approach was groundruled. Rather than designing the system for
maximum performance and lowest dry weight, technology advantages
were reinvested in designing the system for operations, reliability
and safety . Often, these operational features necessitated a dry
weight increase of the system - for the levels of technology
assumed and particular system design, this forced the selection of
a two-stage reusable system.

As an example, the orbiter stage was designed with tip fins and
"double-bubble" propellant tanks which provided a "flat-bed" area
for the mounting of a removable payload container system (PCS). The
PCS concept was originally proposed in the FSTS study, but examined
in detail in the Shuttle II study including a contractor study with
Teledyne Brown Engineering to define system designs for a number of
mission types -- deployment, delivery, personnel tranport and
servicing containers. A significant weight penalty was accepted for
each of these container systems (aerodynamic fairings, structures,
subsystems). The intent was to decouple the processing of vehicle
and payload elements with assembly of the PCS to the orbiter late
in the ground processing flow.

The ground processing concept for Shuttle II shows the horizontal
processing of the booster, orbiter and payload containers in low-
bay work facilities. The ground assembly procedure demonstrates the
mating procedures envisioned for the processing flow. The low dry
weights of the assembled vehicle allow it to be towed to the
launch area eliminating the need for a mobile launch platform. At
the launch pad a strongback system would raise the assembled
vehicle to the vertical position before fueling begins. Minimal
launch pad access and servicing are key factors in reducing ground
turnaround times for the vehicle fleet. The ground processing
timeline, based on an analysis of the turnaround workforce and
time requirements for the system elements, shows how the 12-day
turnaround goal is met. Following launch and mission completion
both the booster and orbiter elements land at a runway near the
processing facilities.

Technologies:

A number of technology needs were identified for the Shuttle II
baseline configuration:

- Reusable aluminum cryogenic tanks Composite structures

- Advanced durable thermal protection system (TPS)

- Advanced carbon-carbon for high temperature areas

- STME and STBE Main Propulsion Rocket Engines

- Common cryogenic propellant

- OMS and RCS systems with no hypergolic propellants

- Electromechanical actuators

- Fault-tolerant subystems with built-in test equipment (BITE)

- Autonomous flight systems with adaptive flight control

- Advanced avionics Control-configured design

The primary structural technology assumptions for the booster
and orbiter reflect the state-of-the-art of technologies that
could meet the 1992 technology availability requirement to support
an early 2000 initial operatioal capability for Shuttle II.

Transition to Advanced Manned Launch System Study:

In the spring of 1988, NASA began looking at Space Shuttle
evolution as an alternative to a new, "clean-sheet" system such as
Shuttle II. By the fall of 1988, the study was formalized as The
Next Manned Transportation System (TNMTS) Study. The Shuttle II
effort was renamed the Advanced Manned Launch System (AMLS). In
addition to AMLS and Shuttle evolution, a third option - initially
viewed as a "simple rugged people carrier" was included. It was
subsequently named the Personnel Launch System (PLS). This three-
pronged approach provided the opportunity to directly compare
significantly different development options in satisfying future
space transportation needs. During this study transition, the
Shuttle II effort was also broadened to examine other "clean
sheet" multi-stage design approaches. This included a smaller
Shuttle II glider launched by a reusable booster and expendable
core stage, the glider launched by a two-stage expendable, and a
two-stage airbreather/rocket system that took off horizontally
(a placeholder drawing of the vehicle was used until a system was
defined). The AMLS section describes these latter Shuttle II
studies as the study transition to AMLS.

Note: Although Langley through VAB was designated as lead for
Shuttle II and AMLS and shared the lead for PLS efforts with
Johnson Space Center, a multi-center team including Lewis, Kennedy,
Ames and Marshall Space Flight Center provided major contributions
in technology and operations aspects of these studies.

Reference:

http://vab02.larc.nasa.gov/Activitie...eII/STSII.html (Lost Link)