ISS Status Report # 20 Wednesday, June 20, 2001 – 4 p.m. CDT

After an extensive engineering analysis, International Space Station
Program managers Tuesday gave the green light to proceed with the launch of
Atlantis no earlier than July 12 to deliver the 6.5-ton Joint Airlock to the
orbiting complex.

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. Oversight from the ground is handled by the Payload
Operations Center at NASA’s Marshall Space Flight Center in Huntsville, AL,
except for the Human Research Facility, which is monitored and controlled
from the Telescience Support Center (TSC) at the Johnson Space Center,
Houston. For details on ISS science, visit the following website:
http://www.scipoc.msfc.nasa.gov.

The International Space Station is orbiting at an altitude averaging 240
miles (385 km). The next ISS Status Report will be issued Wednesday, June
27, or as mission events warrant.