The decision to launch Atlantis in July came after several reviews in which teams of engineers from NASA, the Canadian Space Agency and its prime robotics contractor - MD Robotics - concluded that a communications error between the Canadarm2's shoulder pitch joint and the arm's main computer commanding unit was attributable to an intermittent problem with a computer chip in the joint's electronic system and not a problem with joint itself.
As a result, Canadian engineers are completing the development of a software patch to be uplinked to Canadarm2 which will "tell" the arm to ignore similar erroneous communications from the chip which might occur as the arm moves the Airlock from Atlantis' cargo bay for its installation onto the Unity module. The arm is, in reality, functioning perfectly in both its prime and redundant modes for all seven joints since the one and only communications dropout occurred several weeks ago in the shoulder pitch joint's redundant string of electronics.
Expedition Two Flight Engineers Jim Voss and Susan Helms are scheduled to complete a second dress rehearsal of the Airlock installation task Thursday using the arm in its prime mode. The arm performed perfectly in its backup mode last week during an initial dry run.
With the arm having been declared in good shape and ready to support Airlock installation operations, Shuttle Program managers ordered Atlantis to roll to Launch Pad 39-B at the Kennedy Space Center Thursday morning. The rollout today was postponed due to lightning in the area overnight. Managers will meet at KSC on June 28 in the traditional Flight Readiness Review to set a firm launch date for Atlantis.
Discovery, also in the Vehicle Assembly Building, remains on track to roll out to Launch Pad 39-A next week to support a launch no earlier than August 5 on the STS-105 mission to deliver the Expedition Three crew to the ISS and to bring food, clothing and logistical supplies to the outpost.
Expedition Two Commander Yury Usachev, Voss and Helms continued a variety of science investigations this with more than 17 hours of experiment work budgeted for the crew.
The International Space Station is orbiting at an altitude averaging 240 miles (385 km).