6
$\begingroup$

Even if only one astronaut is needed for an EVA, it makes sense to have a second suited up and outside in case of an emergency. Was there ever any exception to this number (e.g. 1 or 3) for the space shuttle or ISS?

Gemini 4 & 9-12 and Apollo 15-17 had single-person EVAs, although with other crew suited inside the spacecraft. And of course, the moonwalks were always 2 astronauts. This question is for the shuttle and ISS.

$\endgroup$

2 Answers 2

12
$\begingroup$

No single-person EVAs were ever done on Shuttle and to date, have not been done from the US side of the ISS.

The only 3 person EVA in history was on STS-49.

It was unplanned and in response to difficulties encountered grappling the satellite they were attempting to repair.

There is a good, detailed writeup in Walking To Olympus starting on page 88. Here's part of it.

While controllers on the ground determined if Endeavour had enough propellant to carry out a third rendezvous, the crew proposed capturing the satellite using a three-person EVA (the first in history) and components of the ASEM experiment payload. The ASEM struts would be assembled into a triangular structure to which the three EVA astronauts could attach their feet. Endeavour would maneuver under Intelsat VI and the astronauts would grasp the satellite with their hands. Astronauts Story Musgrave, Richard Clifford, and James Voss used the WETF to test whether three astronauts could fit in the airlock at once and to determine positioning in the payload bay for the capture. Meanwhile, the Intelsat organization verified that the satellite’s surface temperature would not exceed the 160 deg C (320 deg F) glove touch temperature limit, and engineers from Hughes, the maker of the satellite, determined the best grab locations. At one point on May 12, seven EMUs were being used simultaneously: three in Endeavour’s airlock, three in the WETF, and one in a NASA JSC vacuum chamber. On this date, Kathy Thornton helped Akers, Hieb, and Thuot suit up, and the astronauts commenced the 100th EVA in history. By the time they were finished, it was also the longest EVA in history.

(Longest EVA was later claimed by STS-102)

enter image description here

Acronymology -

  • ASEM - Assembly of Station by EVA Methods
  • WETF - Weightless Environment Training Facility
$\endgroup$
2
$\begingroup$

Generally two crew members were required for EVA, but NASA Shuttle flight rules had a few very specific provisions for solo EVA:

A2-107 EVA GUIDELINES

A. EVA WILL NORMALLY BE PERFORMED BY TWO EVA CREWMEMBERS; HOWEVER, ONE MAN EVA MAY BE PERFORMED IN THESE CIRCUMSTANCES:

  1. CONTINGENCY EVA. [EVA required for safe re-entry] Two crewmembers are always required for EVA to ensure that, if one EVA crewmember should experience trouble, the other is available to provide assistance. For contingency EVA, this rule is waived since the safety of the orbiter is involved and the risk of a one man EVA is therefore acceptable.

  2. SCHEDULED EVA - A SCHEDULED EVA MAY BE PERFORMED BY A SINGLE CREWMEMBER IF:

    a. A SINGLE CREWMEMBER CAN EXECUTE THE TASK(S) ASSIGNED.

    b. THE SECOND CREWMEMBER IS ABLE TO GO TO VACUUM AND REMAIN ON THE SERVICE AND COOLING UMBILICAL (SCU) FOR POSSIBLE RESCUE.

    c. THE SCHEDULED EVA TASK(S) MUST BE CAPABLE OF BEING TERMINATED AT ANY POINT AND LEAVE THE PLB IN AN ENTRY COMPATIBLE CONFIGURATION.

  3. UNSCHEDULED EVA - AN UNSCHEDULED EVA TO MEET HIGH PRIORITY MISSION OBJECTIVES OR TO PREVENT JETTISON OF A PAYLOAD MAY BE ACCOMPLISHED BY A SINGLE CREWMEMBER IF THE FOLLOWING CRITERIA ARE MET:

    a. A SINGLE CREWMEMBER CAN EXECUTE THE TASK(S) ASSIGNED.

    b. THE SECOND CREWMEMBER MUST BE ABLE TO GO TO VACUUM AND REMAIN ON SERVICE AND COOLING UMBILICAL (SCU) FOR POSSIBLE RESCUE.

    c. THE UNSCHEDULED EVA TASK(S) MUST BE CAPABLE OF BEING TERMINATED AT ANY POINT AND LEAVE THE PLB IN AN ENTRY COMPATIBLE CONFIGURATION.

  4. AN EVA WILL BE DEFINED IN THE FLIGHT SPECIFIC ANNEX AS BEING CAPABLE OF BEING ACCOMPLISHED BY A SINGLE CREWMEMBER.

B. IF CONTINGENCY EVA SUCCESSFULLY RESTORES PLBD’S, LATCHES, ETC., TO NORMAL OPERATION (E.G., FOREIGN OBJECT REMOVED), THE EVA WILL BE TERMINATED AND THE FLIGHT COMPLETED AS PLANNED.

Source: Space Shuttle Operational Flight Rules

NASA ISS flight rules prohibit solo EVA. (I don't have access to the B Flight Rule book anymore, so unfortunately I can't check if there's a provision for contingency EVA in it.) Crew members must go out in pairs - basically the buddy system in case one of them runs into trouble. (Like Luca Parmitano's terrifying EVA with a water leak in his helmet where he lost the ability to see when his eyes were covered in water.)

As for three person EVA, the US crew airlock cannot fit more than two EMUs in it at a time.

So the ISS is limited to two astronauts per EVA, unless in the future NASA and Roscosmos find the need to coordinate a 3+ person EVA using both the US and Russian airlocks to perform a joint EMU/Orlan EVA.

$\endgroup$
3
  • 2
    $\begingroup$ This sounds like good info. Can you support it with references, especially the part about EMUs and the Russian airlock? As a former MCC person, you understand "In God we trust, all others bring data." $\endgroup$ Oct 12, 2022 at 0:13
  • $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$
    – Community Bot
    Oct 12, 2022 at 5:12
  • $\begingroup$ Unfortunately I can't support it with publicly available references since I don't have access to the ISS Flight Rule book or training materials anymore. $\endgroup$
    – Doresoom
    Oct 12, 2022 at 11:25

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.