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During the lifetime of the Space Shuttle, Rockwell International and many other organizations studied various Space Shuttle designs. These involved different ways of increasing cargo and crew capacity, as well as investigating further reusability. A large focus of these designs were related to developing new shuttle boosters and improvements to the central tank, but also looked to expand NASA's ability to launch deep space missions and build modular space stations. Many of these concepts and studies would shape the concepts and programs of the 2000s such as the Constellation, Orbital Space Plane Program, and Artemis program. [1]
The Heavy Lift Launch Vehicle was a study by NASA to turn the Space Shuttle launch stack into a dedicated uncrewed cargo launcher. The external tank and Space Shuttle Solid Rocket Boosters (SRBs) would be combined with a cargo module that took the place of the shuttle orbiter and included the Space Shuttle Main Engines. A ballistic return pod would be used as the main engine structure and carry 2-4 SSMEs as well as mount the payload/booster stage. It would be recovered via parachutes in the Australian outback or northern Mexico. Small lifting wings were added to allow more accurate landings. Various Heavy Lift Launch Vehicle concepts were investigated between 1984 and 1995 and it would eventually become known as the Shuttle-C, which lacked reusable engines and ballistic return pods.
The Shuttle-C concept would theoretically cut development costs for a heavy launch vehicle by re-using technology developed for the Shuttle program. End-of-life and Space Shuttle hardware would also have been used. One proposal involved converting the Columbia or Enterprise into a single-use cargo launcher.
With the Shuttle-C, it was thought that the lower maintenance and safety requirements for the uncrewed vehicle would allow a higher flight rate. Before the loss of Space Shuttle Challenger, NASA had expected about 14 shuttle flights a year. In the aftermath of the Challenger incident, it became clear that this launch rate was not feasible for a variety of reasons.
The Shuttle-C would also launch an uncrewed lunar lander and propulsion module while a second vehicle would launch the Crew Exploration Vehicle to perform lunar missions. The Shuttle-C would additionally act as the crewed component of the International Lunar Resources Exploration Concept proposed in 1993.
In the early 1990s, NASA engineers planning a crewed mission to Mars included a Shuttle-C design to launch six non reusable 80-ton segments to create two Mars ships in Earth orbit. After President George W. Bush called for the end of the Space Shuttle by 2010, these proposed configurations were put aside. [2]
The Magnum was a large Super heavy-lift launch vehicle designed by NASA's Marshall Space Flight Center during the mid-1990s. The Magnum would have been a booster around 315 feet (96 m) tall, on the scale of the Saturn V, and was originally designed to carry a human mission to Mars. It was to have used two strap-on side boosters, similar to the Space Shuttle Solid Rocket Boosters (SRBs), but using liquid fuel instead. Some designs had strap-on boosters using wings and jet engines, which would enable them to fly back to the launch area after they were jettisoned in flight. The Magnum was designed to carry around 80 tons of payload into low Earth orbit (LEO). [3]
The National Launch System (or New Launch System) was a study authorized in 1991 by President George H. W. Bush to outline alternatives to the Space Shuttle for access to Earth orbit. Shortly thereafter, NASA asked Lockheed Missiles and Space, McDonnell Douglas, and TRW to perform a ten-month study.
A series of launch vehicles was proposed, based on the proposed Space Transportation Main Engine (STME) liquid-fuel rocket engine. The STME was to be a simplified, expendable version of the RS-25 engine. The NLS-1 was the largest of the three proposed vehicles and would have used a modified Space Shuttle external tank for its core stage. The tank would have fed liquid oxygen and liquid hydrogen to four STMEs attached to the bottom of the tank. A payload or second stage would have fit atop the core stage, and two detachable Space Shuttle Solid Rocket Boosters would have been mounted on the sides of the core stage as on the Shuttle. Period illustrations suggest that much larger rockets than NLS-1 were contemplated, using multiples of the NLS-1 core stage. [4]
Early studies looked at alternate booster and external tank configurations such as:
NASA had planned on replacing the post-Challenger SRBs with a new Advanced Solid Rocket Motor (ASRM) to be built by Aerojet. They would have been built at a new facility designed by a subcontractor, RUST International, on the location of a canceled Tennessee Valley Authority nuclear power plant in Yellow Creek, Mississippi. The ASRM would have produced additional thrust in order to increase the shuttle payload to carry modules and construction components to the ISS. The ASRM program was canceled in 1993, after robotic assembly systems and computers were on-site and approximately 2 billion dollars spent, after NASA opted to instead issue minor corrections to the existing SRBs. [6]
A large focus of the NASA/MSFC Shuttle Growth Study contract was upgraded Recoverable Liquid Boosters. The boosters would have a similar flight path to the solid rocket motors, separating and deploying a parachute for recovery in the Atlantic Ocean. They were to be water-recoverable and used clamshell doors to protect the engines from saltwater immersion.
Liquid Flyback Booster concepts date back to the early 1970s. Original Shuttle boosters were massive piloted fly-back boosters. The concept was studied throughout the 1980s but shelved after the Challenger disaster shut down most Shuttle upgrades. The Flyback booster concept reemerged in 1997 during the NASA Liquid Flyback Booster Study. The concept was abandoned due to the increased complexity and minor returns. The Shuttle Growth Study built on this background by developing design concepts in great detail for the liquid rocket boosters. [7]
Prior to the destruction of the Space Shuttle Columbia in 2003, NASA investigated the replacement of the current 4-segment SRBs with either a 5-segment SRB design or replacing them altogether with liquid "flyback" boosters using either Atlas V or Delta IV EELV technologies. The 5-segment SRB, which would have required little change to the current shuttle infrastructure, would have allowed the space shuttle to carry an additional 20,000 lb (9,100 kg) of payload in a 51.6°-inclination orbit, eliminate the dangerous "Return-to-Launch Site" (RTLS) and "Trans-Oceanic Abort" (TAL) modes, and, by using a so-called "dog-leg maneuver", fly south-to-north polar orbiting flights from Kennedy Space Center. After the destruction of Columbia, NASA shelved the five-segment SRB for the Shuttle Program, and the three surviving Orbiters, Discovery, Atlantis, and Endeavour were retired in 2011 after the completion of the International Space Station. One five-segment engineering test motor, ETM-03, was fired on October 23, 2003.
As part of the Constellation program, the first stage of the Ares I rocket was planned to use five-segment SRBs – in September 2009 a five-segment Space Shuttle SRB was static fired on the ground in ATK's desert testing area in Utah.
After the Constellation program was canceled in 2011, the new Space Launch System (SLS) was designated to use five-segment boosters. The first test of an SRB for SLS was completed in early 2015, and a second test was performed in mid-2016 at Orbital ATK's Promontory, Utah facility. [8]
DARPA studied modifying the current external tank design to be able to carry low-density payloads in a 25 or 35 ft (7.6 or 10.6 m) diameter fairing where the oxygen tank was currently. The Shuttle on average would only fly 66% of its payload capability but at nearly 100% of its payload volume. The external tank payload fairing would solve this problem. The oxygen tank would be redesigned as a cylindrical tank rather than conical and the clamshell payload fairing would be mounted directly on it. In this configuration, the orbiter would launch without any payload. These studies were eventually abandoned due to the fact that the new aerodynamic profile would make a Return to Launch Site (RTLS) maneuver impossible. The proposal was reconfigured as an Aft Cargo Carrier (ACC) to be positioned towards the bottom of the tank rather than on top. This idea made it far into development with Martin Marietta contracted to design and fabricate the container. The first flights of the ACC were expected in 1986. However, after the Challenger disaster, the ACC as well as most payload-related Shuttle upgrades were canceled. [9]
The following are all accounts mentioned or discussed by Carl F. Ehrlich, Jr. in Shuttle Variations And Derivatives That Never Happened - An Historical Review [1]
In anticipation of upgraded boosters for the Shuttle, a design for a stretched orbiter was made. It would have had a larger payload bay with an additional 15 feet (4.6 m) in length giving it a payload capacity of 75 feet (23 m) and expected to carry payloads of up to 100,000 lb (45,000 kg). A new wing root and carry-through structure were designed to handle the additional weight at landing, keeping the outboard section of the original wings and requiring minimal modification. The 15-foot (4.6 m) barrel section would be attached just forward of the 1305 bulkhead towards the rear of the vehicle.
An undefined need for more payload led to the idea of using the lee side section of the payload bay (at the entry angle of attack) as an expanded payload bay. This would result in a "humpback" outsize cargo vehicle similar to the Airbus Beluga or the Aero Spacelines Super Guppy. The hypersonic aerodynamic characteristics during re-entry would stay mostly the same however issues would have most likely occurred at subsonic speeds without a high angle of attack.
As an internal response to the Soviets' engineless Buran orbiter, an unpowered Orbiter was designed at Marshall Space Flight Center. A payload bay segment would be added to the rear of the spacecraft and look very similar to the Space Shuttle Enterprise albeit with a few differences. Most of the equipment was stored in the rear of the craft to make up for lost weight and compensate for a lack of engines.
From the late 1980s to the early 2000s NASA, in one form or another, pursued the Crew Return Vehicle; a small spaceplane/capsule capable of returning crew from a space station in the event of an emergency. Candidates evaluated included an Apollo-derived capsule, NASA's HL-20, HL-10, and M2F2, and the Air Force's X-24A. A sub-scale variant of the shuttle was proposed based on the ballistic return pod that was studied for the HLLV. The pressurized crew section would be modified into a lifting body. The main advantage of this design would be the proven technology and re-entry profile of the Shuttle.
A conceptual design for a high-capacity orbiter was drawn up. The concept used a series of canisters mounted in the payload bay that would carry 68 to 74 passengers in a double-deck configuration similar to a Boeing 747. This moved the center of mass forward requiring minor changes to the wing structure adding more canard-like surfaces to allow more lifting surfaces. The design would be used for a Von Braun-style space station that would need crew capacity in the hundreds.
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program name was Space Transportation System (STS), taken from the 1969 plan led by U.S. Vice President Spiro Agnew for a system of reusable spacecraft where it was the only item funded for development.
A booster is a rocket used either in the first stage of a multistage launch vehicle or in parallel with longer-burning sustainer rockets to augment the space vehicle's takeoff thrust and payload capability. Boosters are traditionally necessary to launch spacecraft into low Earth orbit, and are especially important for a space vehicle to go beyond Earth orbit. The booster is dropped to fall back to Earth once its fuel is expended, a point known as booster engine cut-off (BECO).
The Constellation program was a crewed spaceflight program developed by NASA, the space agency of the United States, from 2005 to 2009. The major goals of the program were "completion of the International Space Station" and a "return to the Moon no later than 2020" with a crewed flight to the planet Mars as the ultimate goal. The program's logo reflected the three stages of the program: the Earth (ISS), the Moon, and finally Mars—while the Mars goal also found expression in the name given to the program's booster rockets: Ares. The technological aims of the program included the regaining of significant astronaut experience beyond low Earth orbit and the development of technologies necessary to enable sustained human presence on other planetary bodies.
The Space Shuttle Solid Rocket Booster (SRB) was the first solid-propellant rocket to be used for primary propulsion on a vehicle used for human spaceflight. A pair of these provided 85% of the Space Shuttle's thrust at liftoff and for the first two minutes of ascent. After burnout, they were jettisoned and parachuted into the Atlantic Ocean where they were recovered, examined, refurbished, and reused.
A solid rocket booster (SRB) is a large solid propellant motor used to provide thrust in spacecraft launches from initial launch through the first ascent. Many launch vehicles, including the Atlas V, SLS and Space Shuttle, have used SRBs to give launch vehicles much of the thrust required to place the vehicle into orbit. The Space Shuttle used two Space Shuttle SRBs, which were the largest solid propellant motors ever built and the first designed for recovery and reuse. The propellant for each solid rocket motor on the Space Shuttle weighed approximately 500,000 kilograms.
The Space Shuttle external tank (ET) was the component of the Space Shuttle launch vehicle that contained the liquid hydrogen fuel and liquid oxygen oxidizer. During lift-off and ascent it supplied the fuel and oxidizer under pressure to the three RS-25 main engines in the orbiter. The ET was jettisoned just over 10 seconds after main engine cut-off (MECO) and it re-entered the Earth's atmosphere. Unlike the Solid Rocket Boosters, external tanks were not re-used. They broke up before impact in the Indian Ocean, away from shipping lanes and were not recovered.
The Shuttle-C was a study by NASA to turn the Space Shuttle launch stack into a dedicated uncrewed cargo launcher. The Space Shuttle external tank and Space Shuttle Solid Rocket Boosters (SRBs) would be combined with a cargo module to take the place of the Shuttle orbiter and include the main engines. Various Shuttle-C concepts were investigated between 1984 and 1995.
Shuttle-derived vehicles (SDV) are space launch vehicles and spacecraft that use components, technology, and infrastructure originally developed for the Space Shuttle program.
The Magnum was a large super-heavy-lift rocket designed by NASA's Marshall Space Flight Center during the mid-1990s. The Magnum, which never made it past the preliminary design phase, would have been a launcher some 96 meters tall, on the scale of the Saturn V and was originally designed to carry a human expedition to Mars. It was to have used two strap-on side boosters, similar to the Space Shuttle Solid Rocket Boosters (SRBs), but using liquid fuel instead. Some designs had the strap-on boosters using wings and jet engines, which would enable them to fly back to the launch area after they were jettisoned in flight. The Magnum was designed to carry around 80 tons of payload into low Earth orbit (LEO).
The Exploration Systems Architecture Study (ESAS) is the official title of a large-scale, system level study released by the National Aeronautics and Space Administration (NASA) in November 2005 of his goal of returning astronauts to the Moon and eventually Mars—known as the Vision for Space Exploration. The Constellation Program was cancelled in 2010 by the Obama Administration and replaced with the Space Launch System, later renamed as the Artemis Program in 2017 under the Trump Administration.
Before the Apollo 11 Moon landing in 1969, NASA began studies of Space Shuttle designs as early as October 1968. The early studies were denoted "Phase A", and in June 1970, "Phase B", which were more detailed and specific. The primary intended use of the Phase A Space Shuttle was supporting the future space station, ferrying a minimum crew of four and about 20,000 pounds (9,100 kg) of cargo, and being able to be rapidly turned around for future flights, with larger payloads like space station modules being lifted by the Saturn V.
The Ares V was the planned cargo launch component of the cancelled NASA Constellation program, which was to have replaced the Space Shuttle after its retirement in 2011. Ares V was also planned to carry supplies for a human presence on Mars. Ares V and the smaller Ares I were named after Ares, the Greek god of war.
Ares I was the crew launch vehicle that was being developed by NASA as part of the Constellation program. The name "Ares" refers to the Greek deity Ares, who is identified with the Roman god Mars. Ares I was originally known as the "Crew Launch Vehicle" (CLV).
The Space Shuttle orbiter is the spaceplane component of the Space Shuttle, a partially reusable orbital spacecraft system that was part of the discontinued Space Shuttle program. Operated from 1981 to 2011 by NASA, the U.S. space agency, this vehicle could carry astronauts and payloads into low Earth orbit, perform in-space operations, then re-enter the atmosphere and land as a glider, returning its crew and any on-board payload to the Earth.
The Lockheed Star Clipper was a proposed Earth-to-orbit spaceplane based on a large lifting body spacecraft and a wrap-around drop tank. Originally proposed during a United States Air Force program in 1966, the basic Star Clipper concept lived on during the early years of the NASA Space Shuttle program, and as that project evolved, in a variety of new versions like the LS-200.
The Shuttle-Derived Heavy Lift Launch Vehicle ("HLV") was an alternate super heavy-lift launch vehicle proposal for the NASA Constellation program. It was first presented to the Augustine Commission on 17 June 2009.
DIRECT was a late-2000s proposed alternative super heavy lift launch vehicle architecture supporting NASA's Vision for Space Exploration that would replace the space agency's planned Ares I and Ares V rockets with a family of Shuttle-Derived Launch Vehicles named "Jupiter". It was intended to be the alternative to the Ares I and Ares V rockets which were under development for the Constellation program, intended to develop the Orion spacecraft for use in Earth orbit, the Moon, and Mars.
OmegA was a medium-lift to heavy-lift launch vehicle concept that spent several years in development by Northrop Grumman during 2016–2020, with that development substantially funded by the U.S. government. OmegA was intended for launching U.S. national security satellites, as part of the U.S. Department of the Air Force National Security Space Launch (NSSL) replacement program.
The International Lunar Resources Exploration Concept (ILREC) was a proposed mission architecture under President George H. W. Bush's Space Exploration Initiative (SEI) by Kent Joosten, an engineer at Johnson Space Center. The plan would have used the help of international partners, mainly the Soviet Union, to assemble a lunar base and sustainable lunar transportation service.
First Lunar Outpost was a proposal for a crewed lunar mission that would have launched sometime in the 2010s. It was part of George H. W. Bush's Space Exploration Initiative. The main purpose of the proposal was to offer a much less expensive alternative to NASA's 90-day study from 1989 by a factor of US$30 billion. Although it did not gather much mainstream attention, NASA dedicated much time to assembling a detailed and thorough proposal. However, the entire Space Exploration Initiative was cancelled soon after the proposal's completion, and NASA closed the Office of Space Exploration in March 1993.