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@This answer describes two cases where astronauts performed space walks less than six days after arriving at the ISS;

  • Timothy Kopra (Expedition 46)
  • Andrew Feustel and Richard Arnold (Expedition 55)

Such a short turn-around time (in one door, out the other) seems to be unusual, as the ext shortest interval is given there as one month.

Were there special circumstances that lead to these astronauts performing space walks so soon after arrival? Did they have special experience necessary for the activity compared to the other astronauts available on the ISS at the these times?

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There were indeed special circumstances in each case.

For the Expedition 46 EVA, this was an unscheduled EVA. Scott Kelly had inadvertently engaged a brake on the Crew and Equipment Translation Aid (CETA) cart during a prior EVA.

This cart moves along the ISS "railway" used by the Mobile Base Servicer (MBS) (part of the station robotics system) and the immobile cart was blocking the motion of the MBS. This rendered planned robotics operations impossible until the brake was released.

It was desirable to rectify this situation as soon as practical.

This picture shows the MBS with the CETA carts on either side of it just right of center of the truss.

enter image description here

Source 1

Source 2

I also just read Kelly's memoir Endurance, which covers this situation in some detail.

For the Expedition 55 EVA, it seems to be simply a matter of taking advantage of a quiescent period. This article states

It will be one of the shortest intervals between the arrival of a new long-duration crew and a spacewalk in ISS Program history and is being conducted to take advantage of a break in visiting vehicle traffic, ahead of the launch of SpaceX’s CRS-14 Dragon in early April.

None of the EVA objectives seem particularly time-critical.

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  • $\begingroup$ Thanks for your answer! For the Expedition 55 EVA, the "special circumstances" are the quiescent period? $\endgroup$ – uhoh Apr 11 '18 at 9:33

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