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Early Lunar Access
Early Lunar Access
Early Lunar Access
Credit: NASA
American manned lunar base. Study 1993. Early Lunar Access (ELA) was a "cheaperfasterbetter" manned lunar mission study, carried out by General Dynamics in 1992-93.

Status: Study 1993.

It was intended as a joint US-European pathfinder for NASA's more capable 4-man First Lunar Outpost (FLO). The project tried to reduce total costs by a factor of ten compared with Apollo, by utilizing existing launch vehicles rather than developing a large Saturn V-class rocket.

This would be feasible since modern electronics, rocket engines and materials were more capable and weigh less than their Apollo-era counterparts. Hence a modern manned lunar spacecraft need not be as heavy as the Apollo Lunar Module. General Dynamics also claimed that an ELA-type program would have major scientific merit. It would offer major improvements beyond what was accomplished with Apollo, since ELA would enable 2-3 week crew stays on the Moon. Politically, it would encourage cooperation between NASA and ESA (or other foreign space agencies) which would make it appealing to US politicians.

To reach the main goals (low development cost and improved scientific return compared with Apollo), General Dynamics identified the following system and mission requirements.

Mission Objectives included:

Early Lunar Access would use the Space Shuttle and a large expendable launch vehicle such as the Ariane-5 or Titan IV. The former would carry a manned Lunar Exploration Vehicle spacecraft while the latter launched a wide-body Centaur G' rocket stage. Both payloads would rendezvous and dock in low Earth orbit. The Centaur then fired its engine to accelerate the complex toward the Moon and would then be jettisoned.

In a typical mission travel time to the Moon would be about three days. To save fuel, the LEV made a direct landing rather than enter an intermediate lunar parking orbit as Apollo did. The vehicle retained sufficient propellant to perform a later ascent burn to return the crew to Earth. For unmanned cargo missions, the LEV carried a heavier payload and used up all its fuel for landing.

The launch vehicles (Shuttle plus Titan IV or Ariane-5) would have required some upgrades. The Shuttle would have needed either a lightweight Al-Li External Tank or Advanced Solid Rocket Motors to carry 25,720 kg payloads to a 300 km orbit. The new ET later became available but the ASRMs were cancelled in 1994. The ELVs would have been uprated to carry a 27 t payload into Earth orbit. Proposed modifications included new aluminum-lithium tanks for the Titan IV plus a pair of additional solid rocket boosters for the Ariane-5.

The Centaur G' would have been modified for missions lasting up to ten days rather than a few hours. A single uprated RL-10 engine (since developed for the Delta III project) would have replaced the previous twin-engine configuration to save weight and improve reliability. The propellant tanks would have been enlarged and additional thermal insulation, power and reaction control propellant would have increased the in-orbit lifetime.

The crew capsule would be derived from the Apollo Command Module that last flew in 1975. It retained the external size and shape of the original Apollo CM design to take advantage of the existing aero- and thermodynamic databases developed during that program. The interior had however been scaled down since it only supported a crew of two instead of three, and the capsule would be lighter since its design would be based on modern materials, lightweight electronics and construction methods.

The lunar habitat (where the crew would live during their 21-day stay) would also be derived from previously developed hardware; in this case the Space Station Freedom mini-pressurized logistics module built by Italy's Alenia Spazio for NASA. The MPLM was later replaced with a larger module that presumably would be too heavy for Early Lunar Access. However, a scaled down version could still be taken from ESA's Ariane Transfer Vehicle which utilizes the same basic Alenia-built module.

Entirely new systems included a multiple payload adapter plus lunar science equipment and surface elements carried on the first unmanned ELA mission. The major new element was the Lunar Transfer Vehicle itself. It features an advanced high performance four-engine liquid oxygen/hydrogen propulsion system that throttled to enable soft landings on the Moon. The engines would be based on the RS-44 or similar systems. Redundancy was achieved through the capability to shut down a diametrically opposed pair in the event of a failure. The LEV system weights were summarized as follows:

The payload mass exceeded the Shuttle's landing limits in the event of an abort, so a mechanism that dumped the LEV propellant in case of emergency would have to be incorporated. NASA safety requirements probably required that the propellants be carried outside the Shuttle cargo bay during ascent as well. Fortunately, Boeing had studied a system that would transfer excess propellant from the Shuttle External Tank in orbit.

Lunar missions using low Earth Orbit Rendezvous (EOR) were constrained by critical launch window opportunities. The LEV would be deployed and checked one day after the Shuttle reached orbit. If there was a problem that could not be fixed in orbit, the LEV and its 2-crew would be retrieved and returned to Earth with the Shuttle. Under normal conditions, however, the expendable launch vehicle would then place the Centaur rocket stage in a co-orbit with the Shuttle. The LEV and Centaur would then dock (possibly assisted by the Shuttle) and depart from low Earth orbit a day later, when the launch window opened.

If the LEV/Centaur failed to depart on time (the launch window would be in the order of one minute), there would be another translunar injection opportunity on the next orbit 90 minutes later. The Moon, however, would no longer be at the same point as the spacecraft when it would be time to land three days later. A midcourse correction would be required to "catch up" with it. Consequently, the LEV would carry an additional 2% propellant for unplanned midcourse plane change maneuvers. This would provide a total delta-V or velocity change capability of 205 meters per second, sufficient for 13 lunar departure opportunities over 18 hours. In contrast, Apollo only had about four translunar injection opportunities, but of course there was an Earth orbit rendezvous requirement. If the departure window would be missed completely, there would be another series of 13 departure opportunities 3-11 days later. The Shuttle, Centaur and LEV could wait up to a week in Earth orbit so there would typically be two translunar injection opportunities per mission.

Mission 1 would be primarily science oriented and would offer immediate returns (geophysics, ultraviolet and optical telescopes) after the first landing. Mission 2 would land the habitat module, an environmental control and life-support system (ECLSS), fuel cells and other equipment. The first crewed mission then would occur with Mission 3. The total cost at this point would be $13 billion (1992 rates) over seven years for a "business as usual" all-NASA program. This figure included all costs (research and development, launch, production, operations, testing) apart from the scientific payloads associated with the missions. European cooperation (where ESA would provide three Ariane-5 launchers, the habitation module and participate in some development and production work on the LEV/crew capsule) would reduce this figure by about $4 billion. A "cheaper faster better" approach would reduce the US share further, to $6 billion and total program costs to $10 billion. The marginal cost of continuing the program after this would be $2 billion per mission. The fourth expedition (not rigorously investigated by General Dynamics) would land additional equipment, supplies and spares for an additional 2-3 piloted missions to the same site.

If it had been approved, the ELA project would have started in 1994 with a number of 1-year hardware definition studies. Hardware development would have started in 1995, leading to a first unmanned landing in mid-1999. General Dynamics assumed that at most two Shuttles and two expendable launchers would be available per year. Mission 2 would take place six months later, followed by the first manned landing six months after that. Early Lunar Access would then have given way to NASA's advanced First Lunar Outpost (FLO) program in 2002.

In some ways, Early Lunar Access was ahead of its time both technically and politically. The political basis quickly evaporated when the Clinton Administration ordered yet another Space Station redesign only months after General Dynamics unveiled the project in early 1993. The International Space Station and Shuttle commanded virtually all of NASA's shrinking manned spaceflight budget ever since. Technically, ELA also ran into problems when NASA subsequently discovered that General Dynamics had underestimated the weight of the Lunar Exploration Vehicle. Had the project been approved, it would have required further costly upgrades to the Shuttle (=Advanced Solid Rocket Motors in addition to the currently approved super-lightweight External Tank) and Titan IV (=stretched aluminum-lithium propellant tanks).

The design philosophy behind Early Lunar Access appeared solid, however. The major space powers (USA, Russia, ESA, Japan) continue to uprate their expendable rockets while new vehicles were on the drawing board. For example, the US Delta IV and Russian Angara boosters would provide the required lifting capability without any modifications. Spacecraft electronics kept getting cheaper and more capable while propulsion and materials advantages would make it possible to launch heavier payloads on smaller vehicles. This trend had continued for decades and the major design driver today would be economic in nature -- not political. Someday it would be possible to assemble a manned lunar spacecraft entirely from existing off-the-shelf "building blocks" already developed for the Space Station and commercial satellite programs. If Early Lunar Access was not technically feasible in 1994, it certainly would be in 2004 or 2014.

- Article by Marcus Lindroos

Country: USA.
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Credit: NASA
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