Forty years ago: Saving the first TDRS satellite

The Tracking and Data Relay Satellite (TDRS) riding its white upper stage floats away from STS-6/Challenger.


While the crew of STS-6, after and launch and deployment of the Tracking and Data Relay Satellite (TDRS), slept — Well, everyone but Story Musgrave slept.  He spent the night in the airlock tinkering the the EVA spacesuits that he and Don Peterson will use on the first spacewalk from the Shuttle later in the mission — the TDRS continued on its journey to higher orbit using the solid fueled Inertial Upper Stage (IUS).  

At 5:45 a.m. EST, April 5,  the IUS second stage fired to begin a 105-sec. burn.  Suddenly, 80 sec. into it, controllers lost all data from the satellite/IUS.  No one knows it, but the spacecraft has veered 180-degrees as it continued to fire.  All they know is they can’t get a signal up to the the satellite or the IUS which is controlling the stack.

At 5:52 a.m., the White Sands, New Mexico, ground station receive blips of erratic data.  Radio noise five minutes later indicates the TDRS/IUS stack is out of control, in a roll.  At 6 a.m., all data is lost.  In the next 15 min. data from the spacecraft is regained and lost again, as the control team discusses trying to cut loose from the IUS.  Commands are sent, but no one knows if they are received.

At 6:27 a.m. they pick up the signal again, data indicating the satellite is in a flat spin with little IUS battery power remaining, power needed to cut the spent stage loose.  NASA controllers confer with engineers from TRW, builder of the satellite, and decide try to stop the spin by firing the satellite’s thrusters, even if the dead weight of the IUS is still attached.  The large communications satellite is equipped with 24 small (1-lb. thrust) jets.  “We have no other choice.” 

White Sands commands sends the commands at 7 a.m.  At the same time, IUS engineers estimate longer than expected battery life.  At 7:19 a.m., the control team receives a solid lock on IUS transmissions, followed by a lock on TDRS.  Within a half hour, the spacecraft begins accepting commands.  Yet contact is lost yet again at 7:57 a.m.  “Our chances are poor for separation” from the IUS.

At 8:08 a.m., the controllers say the spacecraft appears in a flat spin and is receiving no commands.  It appears the $100-million TDRS has been lost.

Hold on:  At 8:20 a.m., contact is established.  “It’s slowed down; it’s stabilized.  The gyros have nulled out.”  Telemetry at 8:50 a.m. shows TDRS has separated from the IUS, is under control, sending and receiving commands.

The ordeal to save the satellite that will be used to relay communications with the future Shuttle flights lasted just two hours.   But what to do now?  TDRS is an orbit of 21,780 by 13,670 mi., far from its desired circular orbit.  The perigee — low point — must be raised 7,000 mi.  Quickly a plan is devised to do so using long burns of the 1-lb. thrusters in a series of small steps through 58 days.  Once circularized at 21,950 mi., the thrusters will then fine-tune the placement at 22,300 mi. geostationary altitude  

The satellite holds 1,300 lbs. of hydrazine fuel.  The maneuvers to circularize the orbit will consume, controllers estimate, 800-900 lbs. of fuel.  The remainder actually is enough to support the 10-year lifetime of the satellite.

When the Shuttle crew awakens, they are told, “It was definitely not a crew problem” — nothing they did during the deployment — “And you are to be congratulated on the outstanding job you all did.”

“It looks like we will have a good TDRS here for us for future missions.”  

Indeed, it will be in place and checked out in time to support the STS-9/Spacelab 1 science mission at the end of the year.

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