Failure is the only option that would force the so-called Zero Crew to go up in space to manually dock the latest module with the International Space Station (ISS).

Trying to predict the unpredictable, two Russian cosmonauts have prepared for this mission, with the primary goal of guaranteeing the mating of the International Space Station and its critical element -- the Zvezda service module -- scheduled to blast off from Baikonur Cosmodrome on July 12.

Under normal circumstances, Russian piloted spacecraft need no human presence on board to dock in space. But if an automatic docking between Zvezda and the ISS fails, cosmonauts Genadi Padalka and Nikolai Budarin will fly a Soyuz spacecraft and board Zvezda to assist in the module's docking with the ISS. The cosmonauts are known as the Zero Crew, or Expedition Zero, as opposed to the first scheduled resident crew -- Expedition 1.

If Zvezda lifts off as planned on July 12, the planned automatic docking should occur on July 25. Attempts to dock the spacecraft automatically can be repeated in the following days. If they all fail, a Soyuz spacecraft for Expedition Zero will be prepared for launch around August 10.

Under that scenario, cosmonauts will dock with Zvezda, automatically or manually, and then use radio commands to remotely maneuver the ISS toward an eventual docking. Oddly enough, the pilotless ISS will perform all the intricate maneuvers during the rendezvous, while the Zvezda is just expected to orient its docking ports toward the incoming Zarya control module of the ISS.

If the docking is successful, the crew will remain aboard the ISS until a Progress cargo ship arrives and refills the Zvezda's exhausted propellant tanks.

The cosmonauts are expected to land on August 28 after accomplishing their unlikely mission.