Design The EDS used on the cancelled
Ares V would have been propelled by a single
J-2X main engine fuelled with
liquid oxygen (LOX) and
liquid hydrogen (LH2), and was to have been designed at
NASA's
Marshall Space Flight Center in
Huntsville, Alabama as part of
Project Constellation. Originally, the stage would have been based on the
Space Shuttle's
external tank, and would have used two J-2X engines, while the
Ares V core booster would have used five
RS-25 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)
RS-68B rocket engines used on the
Delta IV Heavy as of 2019, the EDS was then redesigned using only a single J-2X engine and a common bulkhead, thus in its final design, the EDS resembled 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 would not have become active until the six RS-68 engines cut off, and the Ares V core was jettisoned to burn up in Earth's atmosphere. Upon separation using the on-board staging and
ullage motors, the single J-2X engine would then have fired at full thrust to place itself and the Altair into a
low Earth orbit until it was retrieved, via a separate launch on an
Ares I, by the
Orion MPCV and its four-person astronaut crew. Once the Orion was docked with the Altair and its systems were checked out, the crew was to 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 would have fired with the crew
facing the EDS. This "eyeballs out" type of flying would be similar to the flight profile of the proposed, but never flown
Manned Venus Flyby, from the cancelled
Apollo Applications Program of the late 1960s. When TLI was completed and the EDS was shut down for the last time, it would then have been 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 have been deliberately crashed into the lunar surface to help scientists calibrate sensitive seismometers placed on the lunar surface by either astronauts on
lunar sortie flights or by uncrewed robotic probes. ==Space Launch System==