Earth Departure Stage

The Ares V Earth Departure Stage (EDS) was a rocket stage which NASA planned to design at its Marshall Space Flight Center in Huntsville, Alabama as part of Project Constellation. The EDS would be propelled by a single J-2X main engine fueled with liquid oxygen (LOX) and liquid hydrogen (LH₂), and would fly in a manner similar to that of the S-IVB rocket stage used on the Saturn V rockets that propelled the three-man Apollo missions to the Moon between 1968 and 1972.

Design

Originally based on the Space Shuttle's External Tank, the EDS would have used two J-2X engines, while the Ares V core booster would have used five Space Shuttle Main Engines and two 5-segment Solid Rocket Boosters during the first eight minutes of flight.

When the Ares V was then redesigned around the use of five (later six^[1]) RS-68B rocket engines currently used on the Delta IV EELV family, the EDS was then redesigned using only a single J-2X engine and a common bulkhead, thus in its current design, the EDS now resembles an oversized S-IVB, but with the capability of on-site storage (using new propellant storage techniques along with a "loiter skirt" containing solar panels for electricity) for up to 4 days, something impossible with the old S-IVB.

Mission

Launched on the Ares V rocket, the EDS with its Altair payload does not become active until the six RS-68 engines cutoff and the Ares V core is jettisoned to burn up in Earth's atmosphere. Upon separation using the on-board staging and ullage motors, the single J-2X engine then fires at full thrust to place itself and the Altair into a Low-Earth orbit until it is then retrieved, via a separate launch, by the Orion spacecraft and its four-person astronaut crew.

Once the Orion is docked with the Altair and its systems are checked out, the crew will jettison the "loiter skirt" and then fire the J-2X engine for a second time, this time at 80% rated thrust, for Trans Lunar Injection (TLI). Unlike the S-IVB, which propelled the Apollo Spacecraft and its three-man crew in a forward-facing motion, the EDS will fire its onboard rocket with the crew facing the EDS. This "eyeballs out" type of flying will be similar to the flight profile of the proposed, but never flown Manned Venus Flyby, from the canceled Apollo Applications Program of the late 1960s.

When TLI is completed and the EDS is shutdown for the last time, it is jettisoned to fly into a heliocentric orbit, or in a manner similar to that employed by NASA from Apollo 13 to Apollo 17, it may be deliberately crashed into the lunar surface to help scientists calibrate sensitive seismometers placed on the lunar surface by either astronauts on lunar sortie flight or by unmanned robotic probes.^[2]

Other uses

While the EDS will primarily be used for Orion/Altair lunar sortie, and later lunar outpost flights to the lunar polar regions, the EDS would also be used for the proposed Orion Asteroid Mission to a Near-Earth Asteroid, and possibly be used for the launching of the proposed 8 to 16-meter Advanced Technology Large-Aperture Space Telescope (AT-LAST) to the Sun-Earth L₂ Lagrange Point. The EDS itself, or a derivative of the EDS may also be used for the eventual mission to Mars after 2030.

References