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Apollo X was the designation given at various times during the Apollo program for follow-on versions of the spacecraft for extended earth-orbit operations (for a time, all follow-on projects using Apollo hardware were termed 'Apollo X'. Initial studies concentrated on extending the life of the basic Apollo CSM to accomodate missions of up to 100 days. A 1962 design used an adaptation of �existing� Apollo hardware to create a space laboratory. Later variants used various kinds of laboratories within or integrated into the Apollo SLA adapter. Apollo X also covered rather extensive work to give Apollo a land landing capability, using a parawing or retrorockets, so that the vast naval recovery fleet could be dispensed with.

Earliest lunar orbit rendezvous schemes involved use of one or more extremely lightweight, unpressurized lunar landers to take a single astronaut to the lunar service. This Langley design used storable propellants. Others using cryogenic propellants were as low as 1,460 kg - to be compared with the 15,000 kg / 2 man design that eventually was selected. Propellant load estimated.

Earliest lunar orbit rendezvous schemes involved use of one or more extremely lightweight, unpressurized lunar landers to take a single astronaut to the lunar service. This Langley design used cryogenic propellants. An even more marginal cryogenic design was estimated to gross 1,460 kg - to be compared with the 15,000 kg / 2 man design that eventually was selected. Propellant load estimated.

Earliest lunar orbit rendezvous schemes involved use of one or more extremely lightweight, unpressurized lunar landers to take a single astronaut to the lunar service. This Langley design is the absolute minimum considered. Others ranged from 3,284 kg to 4,372 kg - to be compared with the 15,000 kg design that eventually was selected.

The General Electric design for Apollo put all systems and space not necessary for re-entry and recovery into a separate jettisonable 'mission module', joined to the re-entry vehicle by a hatch. Every gram saved in this way saved two or more grams in overall spacecraft mass. The 2183 kg re-entry vehicle used a shape of the highest possible volumetric efficiency and was only 2.88 m in diameter and 2.40 m high. The end result was remarkable. In comparison with the NASA final Apollo design, the General Electric D-2 provided the crew with 50% more living space, an airlock, and a service module for the mass of the Apollo capsule alone. Fueled for the circumlunar mission, the entire 10.18 m-long spacecraft weighed only 7,470 kg. But in the end, NASA administrator James Webb examined the model of the D-2, thanked the contractor for its efforts, and announced that Apollo would use the NASA design without any consideration of alternatives. The Soviet Union used the General Electric design approach for their Soyuz spacecraft, still in service 40 years later. The NASA Apollo deign was retired after 8 years.

Martin's L-2C design was the basis for the Apollo spacecraft that ultimately emerged. The 2590 kg command module was a flat-bottomed cone, 3.91 m in diameter, 2.67 m high, with a rounded apex. A jettisonable tower was equipped with a tractor-rocket launch escape system. Behind the flat aft bulkhead were propulsion, equipment, and mission modules. The circumlunar version had a total length of 12.5 m and a fuelled mass of 6,466 kg. Flaps provided limited manoeuvrability (hypersonic L/D ratio of 0.75) on re-entry, with a parachute landing system being used for final recovery.

Convair/Astronautics alternate Lenticular Apollo was a unique flying saucer configuration with the highest hypersonic lift to drag ratio (4.4) of any proposed design. The lenticular shape, with deployable wings for final approach, had first been suggested by Alan B. Kehlet of STG's New Projects Panel in 1959. The saucer was 4.88 m in diameter but only 1.73 m deep, with a total mass of 2867 kg. The unique shape required reverse packaging at launch. Within a large conical shroud the propulsion module was at the top, followed by the saucer, then the pressurised mission module. The crew's seats were set back 90 degrees for launch, then brought upright for normal operations and landing. Access to the mission module was through a hatch in the bottom of the saucer. The compact circumlunar version of the spacecraft was only 9.76 m long but also the heaviest Apollo proposed at 8,778 kg.

The lunar "bus" was an early NASA Apollo logistics vehicle study. The spacecraft "bus" concept could be adapted for use first on the Saturn C-1B and later on the Saturn C-5 launch vehicles. It would deliver supplies to a manned lunar expedition.

Convair/Astronautics preferred M-1 Apollo design was a three-module lunar-orbiting spacecraft. Command, mission, and propulsion modules were designed primarily for lunar orbit, with flexibility and growth potential built in for more advanced missions (such as a lunar landing) with the same basic vehicle design. The preferred command module was a flat-topped blunt half cone lifting-body concept, similar to the HL-10 shape developed by Alfred Eggers at Ames. The re-entry vehicle was 3.17 m long, 3.66 m across, had a total mass of 2,540 kg, and a hypersonic L/D ratio of 0.52. Earth landings would be by glidesail parachute near San Antonio, Texas. The command module, with an abort tower attached through launch, would nestle inside a large pressurised mission module (a similar approach would be used in Russia for the L3M lunar landing spacecraft of 1972-1974). The circumlunar version would have a total length of 14.1 m.

General Electric's Apollo horizontal-landing alternative to the ballistic D-2 capsule was the R-3 lifting body. This modified lenticular shape provided a lift-to-drag ratio of just 0.70 but eliminated the severe heating and weight problems inherent in the basic lenticular configuration. The 2935 kg space pod was 4.57 m long and 3.30 m across. The propulsion module was as in the baseline GE Apollo proposal, but with the lifting body mounted atop the launch vehicle, any mission module was placed aft of the glider and accessed via a long tunnel. The re-entry vehicle used both ablative and radiative heat shielding and had a cross-range capability of 1500 km.

An Apollo unmanned logistic system to aid astronauts on a lunar landing mission was studied. Space Technology Laboratories did a feasibility study of developing a general-purpose spacecraft into which varieties of payloads could be fitted. Northrop and Grumman studied the possible cargoes. NASA Centers studied lunar logistic: trajectories, launch vehicle adaptation, lunar landing touchdown dynamics, scheduling, and use of roving vehicles on the lunar surface.

Martin's W-1 design for the Apollo spacecraft was an alternative to the preferred L-2C configuration. The 2652 kg command module was a blunt cone lifting body re-entry vehicle, 3.45 m in diameter, 3.61 m long. The propulsion, equipment, and mission modules were identical with those proposed for the L-2C baseline. The RV shape was heavier than the W-1 but provided higher manoeuvrability (hypersonic L/D ratio of 0.75). Flaps and a parachute landing system being used for final recovery were used as in the L-2C. The circumlunar version had a total length of 11.4 m including a short launch escape tower and a fuelled mass of 6,677 kg.

Apollo A was a pre-moon landing version of the Apollo spacecraft specifically designed for long-duration operations in space. In the adapter between the Saturn second stage and the Apollo spacecraft, as an integral part, was a section to be used as an orbiting laboratory. Preliminary designs indicated this laboratory would be a cylindrical section about 3.9 m in diameter and 2.4 m in height.

The Apollo Command Service Module was the spacecraft developed by NASA for earth and lunar orbit missions. Block I command service modules, which lacked forward docking tunnels and hatches, never flew manned after the Apollo 204 fire killed its crew on the pad. Block II CSM's successfully ferried crews to the moon, to the Skylab space station, and to a joint docking with the Russian Soyuz. The Apollo was abandoned in favor of the shuttle to continue American manned spaceflight.

ALSEP (Apollo Lunar Surface Experiment Package) was the array of connected scientific instruments left behind on the lunar surface by each Apollo expedition. Powered by radioistope generators, they were turned off as a budget move when still operating. Apollo 11 deployed a simpler version called EASEP.

In support of Apollo, Langley Research Center put into operation a Lunar Landing Research Facility. The huge structure (76.2 m high and 121.9 m long) was used to explore techniques and to forecast various problems of landing on the moon. The facility enabled test vehicles to be operated under one-sixth g conditions.

Bell Aerosystems initially built two manned lunar landing research vehicles (LLRV) for NASA to assess the handling characteristics of Apollo LM-type vehicles on earth. A follow-on contract for three 'production' versions for astronaut training were referred to as LLTV 'lunar landing training vehicles'. The LLRV could take off and land under its own power, reaching an altitude of about 1,220 meters, hover, and fly horizontally. A fan turbojet engine provided a constant upward push of five-sixths the weight of the vehicle to simulate the one-sixth gravity of the lunar surface.

Following the decision to use the lunar orbit rendezvous method to get to the moon, Grumman received the contract to develop the lunar module, which would take the first men to the surface to the moon. If funding had been available, modified lunar modules would have been used to set up the first lunar bases.

The Apollo Experiments Pallet was a sophisticated instrument payload that would have been installed in the Apollo CSM for dedicated lunar or earth orbital resource assessment missions. Study contracts were let to Lockheed, Martin, McDonnell, and Northrop, but with cutbacks to Apollo the concept never proceeded to the hardware stage.

Bell Aerosystems designed a rocket-propelled Lunar Flying Vehicle (LFV) to aid Apollo astronauts in their exploration of the moon. This work was the result of a year-long study that the company had conducted for MSFC. The LFV, nicknamed "Hopper," would be able to travel about 80 km from the lunar module. The concept was abandoned in favor of the lunar rover.

In the early 1960's the USAF was studying various types of manned spacecraft for inspection and destruction of enemy satellites (such as SAINT II, X-20B Dynasoar, Blue Gemini). The Grumman Space Development Team studied use of the Apollo Lunar Module in a role of 'Covert Space Denial' (CSD). A 1964 report 'Military Utilization of LEM in Earth Orbit' set forth the reasons the LM was suited to this role. Its tandem descent and ascent engines gave it a huge manoeuvre capability, greater than that of any other manned spacecraft. This could be augmented further by simply stretching the tanks, a capability designed into the LM from the beginning. The lunar role had also fitted it with a complete autonomous guidance system. This combination meant the lunar module could make large orbital manoeuvres, rendezvousing with enemy satellites by surprise and in total radio silence. For inspection and destruction of the satellite the LM was to be equipped with a single remote controlled arm.

Use of the Apollo LM as an earth-orbiting laboratory was proposed for Apollo Applications Programme missions. The LM would have its engines and propellants removed, providing space for up to 10 tonnes of scientific equipment. A specific version of the LM lab was the Apollo Telescope Mount.

LM Descent stage adapted for unmanned delivery of payloads of up to 5,000 kg to lunar surface in support of Apollo-based lunar base. Added to descent stage: Navigation and guidance system (126 kg); stability and control system (49 kg); reaction control system (250 kg); communications (21 kg); ECS for equipment (58 kg). The LM Truck would make precision landings using radio landing beacons prepositioned by the lunar base staff. The Truck could be accompanied by an Apollo CSM on a purely lunar orbital mission. Alternatively two Trucks could be delivered in a single unmanned Saturn V mission, with a partially-fueled Apollo Service Module being used for the lunar orbit insertion maneuver.

Bell Aerosystems designed a Manned Flying System for Apollo as a tool for lunar surface exploration. The Manned Flying System would be able to transport an astronaut and about 136 kg of equipment (or two astronauts) for distances up to 24 km from the original landing site.

The Apollo Mapping and Survey System was a kit of photographic equipment that was at one time part of the basic Apollo Block II configuration. The actual hardware, which would be installed in the equipment bay of certain SMs, would weigh up to 680 kg. The system was abandoned when it became clear that Lunar Orbiter would provide all the necessary photographs needed for Apollo landing site selection.

The Apollo Telescope Mount began as a solar telescope built into the spaceframe of an Apollo lunar module. Initially it was to be either fre-flying (operated by a visitng crew in an Apollo CSM) or launched separately and docked to a Saturn S-IVB orbital workshop. Over many years it evolved into a piece of hardware unrelated to the Apollo LM and integrated into the Skylab space station.

Essentially an Apollo LM lunar module with ascent stage engine and fuel tanks removed and replaced with consumables, scientific equipment for 14 days extended lunar exploration. Requiring two Saturn V launches, LM shelter would be landed on one launch, with manned Apollo CSM accompanying it conducting lunar orbit surveying operations only. A second Saturn V launch would deliver another CSM and LM Taxi combination to lunar orbit. The crew would take the LM taxi to the surface, landing near the shelter. Work was planned to begin in 1966, with 1-2 missions per year beginning in 1970 after accomplishment of the manned lunar landing goal. In the event, only the Lunar Rover vehicle, used in the later Apollo missions, ever saw actual use.

Essentially the basic Apollo LM modified for extended lunar surface stays. This was forseen to be the workhorse of both Apollo Applications Extended Lunar Surface Missions beginning in 1970 and still be used to shuttle crews to the surface to larger LESA (Lunar Exploration System for Apollo) in the mid- to late- 1970's. Changes included additional water, oxygen, LH2, and Lox tankage in the descent stage in the payload bays; fuel cells in the ascent stage; a redundance Lox tank in the ascent stage over the back of the LM; and additonal micrometeorite and radiation shielding. This would permit the LM to accomodate a crew of three with the capability for a 14-day quiescent (inactive) lunar stay time, in addition to 3 days (active) operational time. The LM Taxi would land near the previously-landed LM Shelter or LESA Shelter, where the crew would spend most of its time during surface explorations lasting from 14 days to three months.

Under the Apollo Applications Programme NASA began hardware and software procurement, development, and testing for a lunar mapping and survey system. The system would be mounted in an Apollo CSM. The crew would operate the sytem during a one month mission to map the lunar surface. Emphasis would be on identifying the most scientifically interesting areas on the lunar surface for the lunar base phase of AAP. It was planned for the system to be tested in earth orbit in a single launch mission unrelated to the Orbital Workshop. The mission would have the primary objective of conducting manned experiments in space sciences and advanced technology and engineering, including the Earth-orbital simulation of LM&SS lunar operations. The LM&SS would be jettisoned after completing its Earth-orbital test. Planned launch date for the earth orbit mission was 15 September 1968.

LESA (Lunar Exploration System for Apollo) was an advanced lunar surface shelter. It would provide the maximum Saturn V-launched lunar base module by using a high efficiency LLV Lunar Landing Vehicle which used RL10 Lox/LH2 engines for the direct landing on the lunar surface. The LESA consisted of a circular inner cabin and annular outer cabin with control stations, bunks, and an airlock. The LLV would deliver the LESA together with a Molab lunar rover on the surface of the moon. Crews to man the base would be landed in 3-man LM Taxis. The crews would use the LESA Shelter for quarters, and the pressurised Molab for mobility. Initially the shelter would be manned by 3 crew members for 90 days. Follow-on flights would build up the base to six residents for indefinite lunar operations.

The Aeronutronic Division of Philco Corp. proposed the unique Lunar Worm Planetary Roving Vehicle Concept in 1966. This was a bellows-concept mobile vehicle which could 'inch' its way across almost any kind of lunar surface. Design studies were made of the concept as applied to a small unmanned vehicle, a supply vehicle, a small lunar shelter, and a large lunar shelter.

In 1967 it was planned that Saturn IB-launched Orbital Workshops would be supplied by Apollo CSM spacecraft and Resupply Modules (RM) with up to three tonnes of supplies and instruments. Following launch by a Saturn IB, the Apollo would back away, transpose, and dock with the RM, just as with the Lunar Module for the lunar missions. These modules could be left docked to the Workshop docking module. Later the Orbital Workshop became Skylab, launched by a Saturn V, and the RM's were not needed. However a descendent of the RM flew in the form of the Apollo-Soyuz Test Project Docking Module.

The SLA mini-base would be delivered first by an unmanned shelter-logistics launch vehicle, followed by a personnel carrier launch which delivered two astronauts in an LM Taxi for the mini-base. Since it would not be practical to leave one astronaut in the CSM circling the moon for 100 days, the third astronaut flew the CSM back to Earth. Three months later, a third mission would be launched to return the lunar base crew to Earth.

This was one of 18 conceptual designs published 25 April 1968 for the Earth-orbital spacecraft lunar module adapter laboratory prepared by spacecraft design experts of the MSC Advanced Spacecraft Technology Division. The configuration was developed to illustrate the extent to which the building block philosophy could be carried. It would utilize both Gemini and Apollo spacecraft and would require 2 unmanned launches and 10 manned logistic launches. The report was published 25 April 1968.

The Apollo Lunar Roving Vehicle was one of those sweet pieces of hardware that NASA and its contractors seemed to be able to develop so effortlessly during the short maturity of the Apollo programme. The collapsible 208 kg battery-powered rover could take two astronauts, 55 kg of scientific equipment, and 27 kg of lunar samples over a cumulative distance of 92 kilometres during one lunar day. The Lunar Rover was the only piece of equipment from NASA's ambitious post-Apollo lunar exploration plans to actually fly in space.

NASA designed the MET lunar hand cart to help with problems such as the Apollo 12 astronauts had in carrying hand tools, sample boxes and bags, a stereo camera, and other equipment on the lunar surface. The MET would extend lunar surface activities to a greater distance from the lunar module prior to availability of the Apollo Lunar Rover vehicle. It was planned to use the MET on Apollo 13, 14, and 15. But the Apollo 13 landing was aborted, and the original Apollo 15 H class mission was cancelled. So the MET was only used on Apollo 14.

During Skylab 3, one of the thruster quads of the Apollo service module developed leaks. When the same problem developed with a second quad, the possibility existed that the spacecraft would not be maneuverable. Preparation work began to fit out a rescue CSM, and astronauts Vance Brand and Don Lind began preparations to rescue astronauts Bean, Garriott, and Lousma aboard the station. However the problem was localized, work arounds were developed, and the first space rescue mission was not necessary. The Skylab 3 crew returned successfully in their own Apollo CSM at the end of their 59 day mission.

The external solar/meteoroid shield ripped off during ascent, tearing away one solar panel wing and debris jamming the remaining panel. Without the shield internal temperatures soared to 52 deg C (126 deg F). Launch of the first crew was delayed for 10 days to develop procedures and crew training to make the workshop habitable. Repairs by subsequent crews led to virtually all mission objectives being met. It was intended that the station would be revisited and boosted to a higher orbit on the third flight of the space shuttle. But delays in the shuttle program and higher-than-anticipated atmospheric drag led to the station decaying from orbit well before the first shuttle launch. Skylab re-entered the earth's atmosphere amid worldwide hysteria on July 11, 1979, with chunks of the disintegrating space station crashing over a wide area of Australia.Payload: Imaging cameras. White-light coronagraph. Ultraviolet scanning polychromator- spectroheliometer. Extreme ultraviolet and X-ray telescope. Space manufacturing experiments. Externally mounted Earth resources instruments included a multispectral imaging camera, an Earth terrain camera, an infrared spectrometer, a multispectral scanner, a microwave radiometer/scatterometer and altimeter, and an L-band microwave radiometer. From fore to aft, Skylab was made up of the following modules, each with their own development history and heritage from the earlier Orbital Workshop and Apollo Applications Program: MDA Multiple Docking Adapter: 5.2 m x 3.05 ft diameter / ATM Apollo Telescope Mount: 3.96 m x 3.05 ft diameter / AM Airlock Module: 5.49 m x 3.05 ft diameter / IU Instrument Unit: 0.9 m x 2.04 m diameter / OWS Orbital Workshop: 14.6 m x 6.7 ft diameter.

The ASTP docking module was basically an airlock with docking facilities on each end to allow crew transfer between the Apollo and Soyuz spacecraft. The docking module was 3.15 m long, 1.4 m maximum diameter, and weighed 2,012 kg. Apollo's cabin atmosphere was 100 percent oxygen at 0.34 atmosphere pressure, while that of Soyuz was nitrogen/oxygen at 1.0 atmosphere. Transfer between these two atmospheres would require pre-breathing of pure oxygen to purge the blood of suspended nitrogen. This was avoided by lowering the Soyuz pressure to 0.68 atmospheres pressure. The docking module served mainly as an airlock to raise or lower the pressure between 0.34 and 0.68 atmospheres when moving from one spacecraft to the other. This was done through the use of pressure equalisation valves with both hatches closed.

Module developed for Shuttle to deliver to Skylab to boost it to a higher orbit for use during the Shuttle program. Due to Shuttle development delays, Skylab re-entered and burned up over Australia before the first Shuttle mission, and NASA would have to wait another twenty years for a space station.