Creativity fuels TDRS-I recovery

A team of Boeing engineers simply would not give up

BY JOEL R. NELSON

Things looked bleak for NASA's TDRS-I satellite a few months ago when a propulsion system malfunctioned.

But now, thanks to an innovative solution from Boeing Satellite Systems employees, program managers believe prospects are good that the Tracking and Data Relay System satellite will fulfill its mission.

The Boeing 601 model's launch on March 8, 2002, went smoothly, but the initial jubilation that accompanied the spacecraft's separation from its Atlas IIA launch vehicle was soon dampened by the discovery of a propulsion system malfunction. (The satellite's other systems were, and are, functioning normally.)

Not only did the problem jeopardize TDRS, a critical link in NASA's space-based communications capabilities, it generated widespread media coverage that strongly implied a total satellite failure.

"Not so fast!" said a team of about 35 Boeing Satellite Systems engineers that crafted a solution to restore the satellite's health and place the TDRS-I in its proper orbit.

They found the lower-than-expected pressure in one of its two propulsion tanks was caused by an improperly closed valve at the top of one tank that impeded the flow of helium, used to push propellant out of the tank. This situation was found to be unique to TDRS-I and not an issue for the Boeing 601 fleet.

The team's solution: Since both tanks can't be emptied concurrently, the team will clear out the good tank over a two-week period, then access the propellant in the faulty tank from the bottom — normally an outlet, not an intake valve — by providing pressure via a fuel line from the first tank.

"The procedure is similar to a coronary bypass," said Jon Goodney, Boeing Satellite Systems' TDRS-I Program Manager. "One ‘artery' doesn't work, so we'll route the ‘blood' via another artery." He said the rough concept was in place early on, "but the devil is in the details. It's a very complicated problem that required a lot of simulations and tests using stand-in tanks and thrusters on the ground."

TDRS-I's placement into its final orbit is expected by early August, followed by a checkout procedure lasting about two months.