Software patch is favoured as continued problems threaten Shuttle schedule again

The Space Shuttle Atlantis mission STS 104 to the International Space Station (ISS) is facing further delays while NASA managers decide how to resolve continued problems with the $600 million Canadian Space Station Remote Manipulator System (SSRMS).

STS 104 is due to be launched to the ISS no earlier than 7 July on a mission to deliver the US Airlock module, which will depend on a fully functioning SSRMS, or Canadarm 2. Atlantis' roll-out to the launch pad has been delayed as NASA considers repair options for the SSRMS. The mission has already been set back once due to problems with the robot arm.

The SSRMS has displayed several computer anomalies since its installation in April. A persistent problem with a backup computer unit on one of the shoulder joints could cause problems with transferring the Airlock module from Atlantis to the ISS. The fault appears to be a backup electronics unit on the shoulder joint which continually puts the arm into a "safe" mode.

Plans to develop a new shoulder joint and install it during an emergency EVA by the current ISS crew have been dropped and several repair options are being considered. The primary repair option is an attempt to develop a software patch to "mask" the problem. If the software patch can be developed and tested by 18 June, Atlantis will be rolled to the pad for a 12 July launch. If not, Atlantis will move aside for Discovery to fly in August on a crew exchange and logistics mission while the former's launch slips to September.

Another option is to deliver a new shoulder joint during a November shuttle mission, STS 107 Endeavour, pushing STS 104 to February 2002. "If we can't fix the arm then we are going to have to stop and get it fixed before we start installing more modules," says NASA flight director John Curry.

Two small cracks found in a 47m ( 154ft) tall Space Shuttle external tank (ET) under construction by Lockheed Martin could result in a detailed inspection of all ETs already built. The ET carries 2 million litres (527,700 US gal) of liquid oxygen and liquid hydrogen propellants for the Shuttle Orbiter's three main engines. The US Department of Defense is considering using the Space Shuttle and the ISS to operate experimental and operational payloads. It has issued a preliminary sources sought synopsis for market research purposes.

The USAF space and missiles systems centre seeks "sources that are qualified to provide operational engineering support for the DoD Shuttle/ISS human spaceflight payloads contract". The work includes the manifesting, integration and operation support of "designated DoD payloads" into space shuttle and ISS missions.

Source: Flight International