Author Topic: Crew limitations for ISS  (Read 25558 times)

Offline DarkenedOne

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Crew limitations for ISS
« on: 03/12/2011 06:24 pm »
Alright lets just assume for the moment that SpaceX succeeds with the Dragon with the ability to carry crew.  I remember it was stated somewhere that SpaceX believes it would be able to deliver 7 astronauts on the dragon for $20 million.  If that pans out than NASA will be able to send twice as many people to the ISS for less than what we pay the Russians right now. 

At the moment as I understand it we are largely limited by the crew carrying capacity of the Soyuz.  I remember the Russians saying that they would no longer be able to use the Soyuz for any tourism because all four of the Soyuz spacecraft produced every year need to be dedicated to sustaining the 6 man crew on the ISS. 

What I have been wondering is whether or not there are any other obstacles to maintaining a larger crew on the ISS.  Are the life support systems up to the task, and if not could they be upgraded to handle the additional capacity.

Also assuming long term crew capacity could be increased would it increase the productivity of the ISS.  Obviously with any faculty you reach a point where increasing the number of workers decreases productivity. 

Offline Jason1701

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Re: Crew limitations for ISS
« Reply #1 on: 03/12/2011 06:35 pm »
Russians have committed to producing a fifth Soyuz per year starting in 2013. Space Adventures will once again be sending up tourists. I think the US crew could be increased to four from 2015 onward, since most of the commercial crew vehicles under development would carry seven.

Others are better equipped to answer your life support questions.

Offline Space Pete

Re: Crew limitations for ISS
« Reply #2 on: 03/12/2011 06:37 pm »
There's a lot more to it than just Soyuz seats.

As you mentioned, ECLSS hardware would have to be upgraded (which wouldn't be easy). More consumables would need to be launched each year to support the crew, and we'd need more sleep stations.

ISS has been designed to support 6 crewmembers. It can support more (the record is 13), but only for short periods of time (~2 weeks max).

One way to increase ISS crewmembers would be to use one Soyuz to launch three Russians, and one commercial vehicle to launch three Americans per Increment. A second Soyuz could then be used for short-duration "taxi flights", as Russia used to do prior to Columbia.
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Offline apace

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Re: Crew limitations for ISS
« Reply #3 on: 03/12/2011 06:43 pm »
ISS has been designed to support 6 crewmembers.

Not 7?

Offline Dapholine

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Re: Crew limitations for ISS
« Reply #4 on: 03/12/2011 07:02 pm »
Not 7?

I believe that plan died with the cancellation of the CRV. After the CRV was canceled, Soyuz would be used as the emergency vehicle, thus it was reduced to 6.

Offline Space Pete

Re: Crew limitations for ISS
« Reply #5 on: 03/12/2011 07:07 pm »
ISS has been designed to support 6 crewmembers.

Not 7?

ISS was originally intended for 7 crewmembers, but it was decided a while ago to only support 6 crewmembers.
« Last Edit: 03/12/2011 07:08 pm by Space Pete »
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Offline hop

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Re: Crew limitations for ISS
« Reply #6 on: 03/12/2011 07:58 pm »
At the moment as I understand it we are largely limited by the crew carrying capacity of the Soyuz.
In addition to the problems mentioned by others, it doesn't matter how many you can produce if you can't park them. Each crew member needs to have a ride home available for their entire stay (CRV). There are only 4 compatible docking ports, and they need to support Progress and ATV. Parking 3 Soyuz for long durations would be impractical. I suppose in theory the Russians could start building APAS Soyuz again and park them on a PMA...

The ISS already went to "indirect" handovers (having the station drop to 3 during rotation instead of going up to 9), in part to help deal with traffic issues.

The math also doesn't work out very well with 3 Soyuz, because ISS might support 7 but 9 for any extended period would be pushing it. So you'd end up wasting seats.

To support 7 for long periods, you'd need US side CRV or a Russian vehicle with more than 3 seats.

I think the US crew could be increased to four from 2015 onward, since most of the commercial crew vehicles under development would carry seven.
Only if they have CRV capability, which isn't a given.

Offline DarkenedOne

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Re: Crew limitations for ISS
« Reply #7 on: 03/13/2011 12:25 am »
At the moment as I understand it we are largely limited by the crew carrying capacity of the Soyuz.
In addition to the problems mentioned by others, it doesn't matter how many you can produce if you can't park them. Each crew member needs to have a ride home available for their entire stay (CRV). There are only 4 compatible docking ports, and they need to support Progress and ATV. Parking 3 Soyuz for long durations would be impractical. I suppose in theory the Russians could start building APAS Soyuz again and park them on a PMA...

The ISS already went to "indirect" handovers (having the station drop to 3 during rotation instead of going up to 9), in part to help deal with traffic issues.

The math also doesn't work out very well with 3 Soyuz, because ISS might support 7 but 9 for any extended period would be pushing it. So you'd end up wasting seats.

To support 7 for long periods, you'd need US side CRV or a Russian vehicle with more than 3 seats.

I think the US crew could be increased to four from 2015 onward, since most of the commercial crew vehicles under development would carry seven.
Only if they have CRV capability, which isn't a given.

Well I understand about the limitations of the Soyuz, but future planned vehicles including the Dragon, the Dreamchaster, and the Boeing CST-100 all are designed for 7 people. 

Assuming we use just one of these vehicles with the Soyuz the ISS would have a crew return capability of 10 astronauts. 

Also we should consider whether permanent crew return capability is necessary. After all future missions to places like the Moon and Mars might not have this capability.

Offline Danderman

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Re: Crew limitations for ISS
« Reply #8 on: 03/13/2011 12:31 am »
Russians have committed to producing a fifth Soyuz per year starting in 2013. Space Adventures will once again be sending up tourists.

From what I have read, the reverse is true - Space Adventures would like a 5th Soyuz, but Roskosmos has not agreed.

Offline pathfinder_01

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Re: Crew limitations for ISS
« Reply #9 on: 03/13/2011 12:32 am »

Also we should consider whether permanent crew return capability is necessary. After all future missions to places like the Moon and Mars might not have this capability.

It would be foolish not to have this ability if possible. The ISS can hold 7 but lacks a lifeboat.  The CST100 can stay in orbit for 7 months, unsure about manned dragon's limit and NASA's Orion can stay for 6 months. The US only needs 4 seats min but more is preferable.

Return from the moon is possible. It is just that for the moon or mars having a dedicated lifeboat makes no sense. For the ISS the need arose because the shuttle could not stay in space for months. With commercail crew a provider might not want to tie their craft up the for the whole lenght of the expidition.
« Last Edit: 03/13/2011 12:53 am by pathfinder_01 »

Offline Danderman

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Re: Crew limitations for ISS
« Reply #10 on: 03/13/2011 12:34 am »
In a world where Dragon can support 4+ crew members as a transfer vehicle and as a lifeboat, so that ISS crew would increase to 7 or more, all of the above issues could be trivially resolved.  We, however, don't presently live in that world.

Dragon could easily bring up additional life support resources, consumables, sleeping facilities, there really isn't a show-stopper for ISS crew expansion, if there is a functional and reliable Dragon.



Offline pathfinder_01

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Re: Crew limitations for ISS
« Reply #11 on: 03/13/2011 12:41 am »
In a world where Dragon can support 4+ crew members as a transfer vehicle and as a lifeboat, so that ISS crew would increase to 7 or more, all of the above issues could be trivially resolved.  We, however, don't presently live in that world.

Dragon could easily bring up additional life support resources, consumables, sleeping facilities, there really isn't a show-stopper for ISS crew expansion, if there is a functional and reliable Dragon.


Ideally a lifeboat would hold 7. It would allow more space to manurve a sick or disabled crew memeber as well as allow the whole station to evacuted if for some reason the russians can't get to Soyuz. Additional seats could also come in handy if a commercail crew craft is unable to return to earth.

Offline hop

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Re: Crew limitations for ISS
« Reply #12 on: 03/13/2011 01:17 am »
Well I understand about the limitations of the Soyuz, but future planned vehicles including the Dragon, the Dreamchaster, and the Boeing CST-100 all are designed for 7 people. 
At least initially, I don't think any of these are planned to be able to stay at the station for a long time. "Orion CRV" is.

Quote
Also we should consider whether permanent crew return capability is necessary. After all future missions to places like the Moon and Mars might not have this capability.
Discussed previously, see  http://forum.nasaspaceflight.com/index.php?topic=20833.0 and http://forum.nasaspaceflight.com/index.php?topic=20543.msg557374#msg557374 for example.

Bottom line:
1) Having a CRV adds significant safety benefits for marginal cost.
2) It would be stupid to discard these benefits on this mission just because it won't be available on some other mission.
3) The people who operate ISS are not in the habit of taking unnecessary risk.

If the ISS partners wanted to up the crew count (which AFAIK none of them are particularly clamoring for), the most likely way to do it would be to certify one or more of the new US vehicles for long stays. This should not be hugely expensive, my earlier comment was to point out that they aren't all currently planned to have this capability. A US CRV will probably happen at some point, and it will probably be capable of carrying more than 3.

If the Russians actually add all their planned modules, supporting larger crews will also get easier.

Offline pathfinder_01

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Re: Crew limitations for ISS
« Reply #13 on: 03/13/2011 01:34 am »

At least initially, I don't think any of these are planned to be able to stay at the station for a long time. "Orion CRV" is.

[

CST100 is designed for 7 months. 1 month longer than Orion. Dreamchaser and Dragon unknown but I would expect dragon to be storable for months in it's basic form and as a free flyer dragon has a 2 year life. It is just the different enviroment at the ISS that might limit it.

Offline PeterAlt

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Re: Crew limitations for ISS
« Reply #14 on: 03/18/2011 03:45 am »
The plan is to use commercial crewed (or Orion as backup) vehicles as liefboats as well as crew transportation, just as the Soyuz is now. Once crewed commercial (or Orion) vehicles are in service, the Russians will use a single Soyuz (not two at a time) for Expedition crews, freeing up a Russian docking port for short term Soyuz visits or more Progress vehicles. The additional crew capacity of commercial crew vehicles or Orion will allow at least one additional crew member. In fact, the Russian Space Agency a few months ago announced in a press release that ISS will have a crew size of seven once the new American vehicles enter service.

Offline Danderman

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Re: Crew limitations for ISS
« Reply #15 on: 03/18/2011 02:10 pm »
Well I understand about the limitations of the Soyuz, but future planned vehicles including the Dragon, the Dreamchaster, and the Boeing CST-100 all are designed for 7 people. 
At least initially, I don't think any of these are planned to be able to stay at the station for a long time. "Orion CRV" is.

Really?

What aspects of a crewed Dragon would preclude lengthy stays at ISS?

Offline erioladastra

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Re: Crew limitations for ISS
« Reply #16 on: 03/19/2011 08:16 pm »
Not 7?

I believe that plan died with the cancellation of the CRV. After the CRV was canceled, Soyuz would be used as the emergency vehicle, thus it was reduced to 6.

Nope still the plan.  Not sure of the timescale but that is our next major milestone.

Offline robertross

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Re: Crew limitations for ISS
« Reply #17 on: 03/19/2011 08:44 pm »
Not 7?

I believe that plan died with the cancellation of the CRV. After the CRV was canceled, Soyuz would be used as the emergency vehicle, thus it was reduced to 6.

Nope still the plan.  Not sure of the timescale but that is our next major milestone.

whoa....7?
I assume you mean based on commercial crew capabilities.

Offline Space Pete

Re: Crew limitations for ISS
« Reply #18 on: 03/19/2011 08:57 pm »
Not 7?

I believe that plan died with the cancellation of the CRV. After the CRV was canceled, Soyuz would be used as the emergency vehicle, thus it was reduced to 6.

Nope still the plan.  Not sure of the timescale but that is our next major milestone.

Woo! That will certainly enable more science to get done.

We need another Crew Quarters! :)
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Online The-Hammer

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Re: Crew limitations for ISS
« Reply #19 on: 03/19/2011 10:38 pm »
I understand that there's supposed to be a third Russian CQ in MLM when it launches.
Grant Imahara: Oxygen deficiency alarm? Is that something I should be worried about?
NASA worker: Only if it goes off.

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