Those hurdles include more software testing and review, a requirement SpaceX CEO Elon Musk concedes has been one of the primary causes of delay since Dragon’s original November 2011 launch date. Musk stressed that while SpaceX and NASA are confident the Falcon and Dragon have proven themselves in action, “there’s no space station on the ground,” meaning final testing can only be simulated with software before the real thing is attempted in space.

Assuming final software checks pass, there will be no final FRR, and Dragon will be cleared to fly. SpaceX owns the last leg of testing responsibility, which includes a “hot fire” pad test. The Falcon will be fueled with propellant and have its nest of nine engines ignited while securely bolted to the launch pad. That test is expected to occur about a week before flight.

If the April 30 launch date slips, further attempts are set to be staggered every three days. Traditionally, a vehicle like the space shuttle has a daily launch window when aiming for the ISS, but as Musk explained, the optimum trajectory for low fuel consumption comes only once every three days. SpaceX clearly wants to ensure they have every drop of hydrazine available in the Dragon’s Draco thrusters as it performs its shakedown tests in orbit.

So, how will this unprecedented partnership between NASA and SpaceX work during the flight? NASA flight director Holly Ridings explained that SpaceX will be responsible for launching the Dragon getting it to the imaginary two-by-four kilometer ellipsoid safety zone surrounding the station. The Dragon will cruise through that zone two and a half kilometers under the station, establishing communication with the outpost to say hello. The craft will continue onward out to a distance of 200 kilometers and raise its altitude, reverse course and cruise back past -- this time, above the station -- continuing another 200 kilometers to trace out a large box.

During this time, the technologies originally required for the second Commercial Orbital Transportation Services demonstration flight will be carried out. This includes showing the ability to abort, using absolute and relative GPS tracking, entering free drift, and communicating with and receiving commands from the ISS.