Spaceflight Now: STS-106 Mission Report

Explanation of Atlantis' docking to space station

Posted: September 9, 2000

NASA animation shows Atlantis docked to space station. Photo: NASA TV/Spaceflight Now
Shuttle commander Terrence Wilcutt faces a daunting challenge early Sunday when he guides the 250,000-pound Atlantis to a gentle docking with the 130,000-pound international space station while both craft are streaking through space at five miles per second.

In a pre-flight NASA interview, Wilcutt said the procedure is "not a difficult thing, but it is very delicate. The (relative) closure rate has to be about an inch a second."

Atlantis' blastoff Friday on a space station outfitting and activation mission was timed to set up a docking early Sunday as the two spacecraft sail over Russian ground stations.

The terminal phase of the rendezvous will begin at 10:59 p.m. EDT (0259 GMT) this evening with the shuttle trailing the space station by about eight nautical miles.

See our detailed timeline of the docking.

For reference, the station's orbital path is known as the velocity vector, or V-bar. The imaginary line connecting the station with the center of the Earth is known as the radius vector, or R-bar.

By convention, points on the line below the station are considered positive while points above it are negative. Likewise, the +V-bar is directly in front of the station.

An illustration of the international space station. Photo: NASA
Early Saturday, lead flight director Phil Engelauf provided a blow-by-blow account of the terminal rendezvous sequence:

"We'll fly up underneath the station on the radius vector, what we call the plus R-bar, and as we cross the plus R-bar we'll brake almost to a stop and then initiate a manual fly around underneath the station, up and in front of it, up to a position directly radial out from the station. If you were looking up from the Earth, we would be on top of the station.

"As the crew approaches the (minus) radius vector, they'll stop the flyaround and come pretty much to a stop in terms of relative motion on the radius vector and let the velocity between the vehicles near zero as we start to fall down to about 170 feet above the station, in a relative motion sense.

"We'll stop at 170 feet and hold at that point until the timing is correct so that we arrive at the station over the Russian ground sites in order to provide for commanding to the Russian segment motion control system when we dock.

"Then we'll fly on in to about 30 feet at a predetermined time and measure the relative orientation between the two vehicles and make any minor corrections to the orbiter attitude to line it up with the station.

"And then we will press in from 30 feet such that we arrive at contact at a point about two minutes after acquisition of the target by the Russian ground sites."

Once docked, the astronauts will stage a spacewalk early Monday before actually entering the station for the first time Monday evening.

Video vault
NASA animation shows Atlantis approaching and docking to the international space station during the STS-106 mission.
  PLAY (243k, 34sec QuickTime file)
Atlantis undocks and makes a fly-around of the international space station before departing during the STS-106 mission as seen in NASA animation.
  PLAY (251k, 51sec QuickTime file)
Take an animated tour of the international space station in its current configuration, including the Unity, Zarya and Zvezda modules and Progress cargo freighter.
  PLAY (271k, 42sec QuickTime file)

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