The old ET, still mated to the Space Shuttle Atlantis inside NASA's Vehicle Assembly Building at the Kennedy Space Center (KSC) in Florida, has been repaired with respect to reapplication of foam insulation to the liquid hydrogen (LH2) tank. The LH2 tank is located on the bottom portion of the external tank.

Liquid hydrogen fuel, a commonly used liquid rocket fuel, consists of the element hydrogen (chemical symbol: H) in a liquid state. It is often abbreviated LH2 because hydrogen is commonly found naturally in the molecular H2 form.

The engineers, many who are based at the NASA New Orleans’ Michoud Assembly Facility, where the ETs are made, are now concentrating on repairs to the liquid oxygen (LO2) tank, which is located on the upper portion of the ET.

Liquid oxygen consists of the element oxygen (chemical symbol: O) in liquid form. Oxygen is found naturally in air. LO2, sometimes also abbreviated LOX, is a common liquid oxidizer propellant for rockets, and is often used in conjunction with liquid hydrogen (LH2) fuel. Molecular oxygen is often designated O2.

The LH2 fuel and LO2 oxidizer are used for the three Space Shuttle main engines (SSMEs) on the orbiter (in this case, Atlantis) during lift-off and ascent.

The Space Shuttle Atlantis, on mission STS-117, is scheduled for a lift off no earlier than mid-May 2007 (the launch window closes around May 21) if the current ET can be completely repaired. If not, a new ET will replace it, which will cause further delays. Such a switch over will delay the launch until June at the earliest (the launch window opens near June 8).

A new external fuel tank arrived at KSC in Cape Canaveral, Florida on Friday, April 6. It was towed by a barge through Port Canaveral from the Michoud Assembly Facility, New Orleans, Louisiana. The contractor for the ETs is Lockheed Martin, which manufactures them at the Michoud facility.

NASA officials are expected to meet on Tuesday, April 10th, to decide which of the two ETs to use for the Atlantis mission.

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