Spacewalkers always in pairs

[Shaylen]

Hi,

I'm curious as to why it seems space walks are always done with 2 astronauts? Seems that there is lots to be done and there are more than enough astronauts to train etc? What are the criteria for determining the number of space walkers? Seems like they could get a lot more done, I'm sure there is a reasonable reason, but never found one so far.

Thanks all!

 

[docm]

Not less than 2 since the 'old days' and one shuttle mission (and he was joined after a few hours) for the same reasons you do buddy SCUBA diving; someone to bring in a disabled astronaut and the extra hands are useful. Probably no more because of the infrastructure and monitoring required. IIRC there has only been one 3 person spacewalk and that was during Endeavour's maiden flight in 1992.

 

[MeteorWayne]

I think the complications of having 3 people out there are not worth the benefit of whatever might be gained by the extra hands. It's more communication issues, more people to manage in 3D space so they don't hit anything and damage themselves or the spacecraft. It's just not worth it.

 

[newsartist]

I suppose that they could use multiple airlocks, (at the cost of having extra sets or preparatory work,) but the airlock is pretty confining for two spacewalkers.

 

[JonClarke]

To other factors to consider are:

1) When the ISS supported three people the preference to have at least one person on duty inside while the other two were outside. This presumably goes back to operations on Skylab and three person crews on Mir and Salyut. The Russians were far less strict about this rule, there was some angst in NASA when the ISS crew briefly dropped to two after Columbia, neccessitating both crew being outside. NASA had not had every once outside since Apollo, whereas the Russians had done it frequently during the Salyut and Mir years.

2) EVAs are very physically demanding, and ideally should be done no more often than every other day. When daily EVAs are required then two two teams are needed. Since the Shuttle has 6-7 people and the ISS 6, and allowing for people on duty running the spacecraft this again means that realistically only two people are available for an EVA.

In theory I suspect could have four people on EVA from the ISS, two exiting from Pirs and two fropm Quest. There would still be two people inside of course. The circumstances under which this would needed are no obvious. Since EVAs are seen a risky activities, it certainly would not be done for the sake of a record.

The only three person EVA in history does seem to be a case where more hands were needed to handle Intelsat VI when two previosu attempts with two astronauts was not sufficient.

 

[Shaylen]

Excellent comments, yes, I figured it had to do with logistics but I wish someone from NASA would actually comment on this. It seems though it would be a logical extension to allow teams of astronauts to get things done that are not dependent on each other and thus accellerate any construction.

Of course safety is paramount and you don't both want to be on the outside looking in on an empty station trying to figure out how to break that "basement window" but we handle complex construction on earth and I'm sure the brain trust at NASA can figure out protocols and operational procedures to make it happen.

It will be needed at sometime, ie 4 workers on the moon (if and when that happens), etc so might as well pioneer it earlier.

Thanks for the examples of when more spacewalkers were used, I'd never heard of those instances.

Cheers!

 

[MeteorWayne]

I think if anyone from NASA ever would reply, you would find that their answer would pretty much reflect what has been said in this thread. Some pretty good brains here

Glad you appreciated the effort put into the responses. It was a very good question.

 

[halman]

Doing an EVA (Extra Vehicular Activity) is a major undertaking. Because air pressure in the suit tends to make the suit rigid, the lowest possible air pressure is utilized. Thus, the 'camping out' in the airlock overnight to acclimate to the lower pressure. Then there is the suiting up, which takes a couple of hours. Each EVA is carefully choreographed before hand, planned out in detail, so that every moment is used to the best advantage. Each cosmonaut has to be able to talk to his partner, the crew on the station, the crew on the shuttle, (when the shuttle is at the station,) and to ground control, without interference. A limited number of radio channels are available for this purpose. Have you ever noticed that only one person talks to the cosmonauts from the ground? That person must be briefed as to what the EVA entails, and follow along in a binder prepared in advance. So a 7 hour EVA is actually a 10 hour day.

Staying on task without getting disoriented, sightseeing, or sidetracked would be very difficult for one person, I believe, and having a partner also means that there is someone who can see your back. Brushing up against structure can result in damage to the suit, which would be impossible to see or repair for the wearer. Cosmonauts must be tethered to the vehicle at all times, which means that they must be aware of where each others tethers are. Because it is impossible to recognize someone in a space suit, the suits must be color coded for identification. Keeping track of multiple color codes can be confusing, in a situation where confusion must be avoided at all costs.

The day will come when someone can decide that they are going to step out for a bit and fix that flapping shutter, but that day is still many years in the future.