The Earth Departure Stage (EDS) is the name given to the proposed second stage of the Block 2 Space Launch System. The EDS is intended to boost the rocket's payload into a parking orbit around the Earth and from there send the payload out of low Earth orbit to its destination in a manner similar to that of the S-IVB rocket stage used on the Saturn V rockets that propelled the Apollo spacecraft to the Moon. Its development has been put on hold (though not abandoned) until stages capable of transferring heavy payloads to Mars are required (currently expected in the 2030s). Ares V 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 cutoff 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