Real Life Airlocks : so simple. No cool controls.

[SomeGuy123]

So, here's how the ISS airlocks actually work, per one of the mission control staff.

There's of course an inner and an outer door.  Both are actuated with cranks - no electrics, no control panel, no cool "emergency blow" button per several movies.

Both are designed where mechanically an air pressure differential prevents you from opening the hatches at all.  So you cannot crank on the inner hatch while there is pressure inside the station, and you cannot crank open the outer hatch while there is pressure inside the airlock chamber.  

So to use the airlock, you just crank open the inner hatch and get inside the chamber.  Crank closed the inner door.  Then, you activate the vacuum pump.  It just pumps the air inside the inner chamber back inside the station.  That's it.  I always figured there were compressed air tanks for holding that air, there aren't.  Just a pump and 2 hoses and 1 set of electrical wires to a switch.  

What if the vacuum pump has failed or there is no power?  There's a vent.  You open the vent, the air in the airlock leaks out to space.  You will die if you do not have a suit on, but the venting takes time, so you could close it if you somehow opened the vent by accident.

You then crank open the outer hatch.  Done.

To get back in, you get inside, crank the outer hatch closed, and open the inner vent.  Air leaks into the air lock from the station through that vent.  Then open the inner hatch.

What if you wanted to board the station and the inner door is open and the station is still pressurized?

You open the outer vent, accessible from the outside.  All the air in the station will eventually drain out that vent.  This is how attacking space marines would board the station by force.  Apparently, the air maintenance systems in the station will not automatically dump their gas contents to try to keep pressure up - there are obviously compressed oxygen tanks and compressed nitrogen tanks onboard, but the computer controls on them won't automatically dump their contents - so there's plenty of air left in the gas tanks so you can repressurize.

Once the station pressure is zero, you can open the outer door.  Then close it.  You can then access controls and try to re-pressurize - one problem is the vacuum may destroy some of the equipment from overheating, preventing you from doing this.  You may have to access the valves to do this manually.  

What if there's an attacking alien and you need to open the airlock doors to eject them to space?  You're screwed.

If you wanted to execute someone, per several movies and tv shows, you'd put them in the inner chamber, while restrained, and activate the vacuum pump.  Some time later the air pressure would get low enough and they'd peacefully pass out and die.  No eyeballs exploding, no sudden ejection to space.

This is how airlocks should be designed.  If I were designing a futuristic airlock, the only thing I'd change is add an electric motor to turn the crank.  I'd deliberately make the motor too weak to actuate the crank unless there is no pressure differential.  (I'd design the motor to safely stall without burning anything up when this happens).

I'd then add some cool looking illuminate touch screen controls explaining how to use the airlock, and I'd have all the key controls backed up by manual switches and manual cranks.  Actually, nix the touch screen manual - print pictograms into a plate set into the side of the airlock panel.

The 2 main crank handles would fold inwards, and there would be 2 red disks that rotate when driven by the servo motor.  You'd see them turning.  If there's a motor failure, you just grab the disk, pull out the fold out crank handle, and turn them yourselves.

 

 

Edited January 28, 2016 by SomeGuy123

[Xorth Tanovar]

25 minutes ago, SomeGuy123 said:

This is how attacking space marines would board the station by force.

Nope. Real Space Marines use boarding torpedoes. 

[tg626]

Now I wonder what the issue crew would do if ,say a shenzou pulled up and started mucking with the station...

[magnemoe]

i would be supriced if it was not an way to block the vents from inside. Number of valves and even blinds used in any industrial piping is impressive. 
My guess is two pipes one with main valve on outside and an spare default open on inside, the inner one probably have an spare on inside too.
Reason to be able to went from outside is twofold, its an fail safe mechanic also useful if station is evacuated and inoperative and someone left inner door open.
Why store the air, station is large enough that pumping the air from lock will not increase pressure much. for an airlock on an small ship, it would be smarter to pressurize the air.

else its an smart well thought out design. I guess its also sensors showing air pressure in lock other places and that its possible to start the pump from inside, setting where you want to send something either to astronaut or to the robot arm without suiting up. 

The went air function is probably in lock only as its an fallback. 
Benefit of using station air to fill airlock is that its fast, if you have problems you want to fill the airlock fast. 
 

[radonek]

Neat. I would also add some device on the inner door that would show if there is pressure on the other side, so you could discern leak from a stuck hinge. Also note this is low-traffic design - when you have somebody out outer doors stay open unless they cared to close them from outside. With people going in and out often, you'd  need a way to close outer door from inside.

[AngelLestat]

Yeah, that is a nice way to solve all manually..  but you will not get rid of technology so easy, all cars still had complex mechanism and sensors for their doors or windows because it's cheap and faster.
So that is a nice safe mode in case your power is off, but no sure how much you can save ignoring electronics. 

[cantab]

I seem to recall astronauts sleep in the airlock, held at a reduced pressure, before a spacewalk because the spacesuits operate at a lower pressure than the station. It's like altitude acclimation on Earth. Is that still the case on the ISS or was it only on older craft?

[shynung]

They still do oxygen acclimation, but the modern procedure only takes an hour, because they integrated some kind of low-load exercise regime to be done while prebreathing.

[Nibb31]

2 hours ago, tg626 said:

Now I wonder what the issue crew would do if ,say a shenzou pulled up and started mucking with the station...

There would be a pretty severe diplomatic problem several days before the shenzhou pulled up. 

Oh, and this is a nice little piece of airlock trivia for you guys. This is a picture of the hatch on the Skylab airlock module. Doesn't it remind you of something ?  

Yes, that's what you think it is. The Skylab design team had instructions to use as much off-the-shelf hardware as they could, so they ended up being forced to reuse a Gemini gullwing door as a hatch (despite the fact that the window had absolutely no purpose and was blanked out from the inside). This caused some uproar among the engineers, who complained that it was much more expensive to design the rest of the airlock to fit the Gemini hatch than it would have been to use a blank sheet design. But there it is.

In the same vein, the Apollo Telescope Mount (the part on top of Skylab) was based on a LM ascent stage, despite the fact that it wasn't even pressurized or accessible by the astronauts.

Edited January 28, 2016 by Nibb31

[Kerbart]

Very interesting. The all-mechanical approach will please many engineers; it's simple, there's very little to break, and most important, nobody has to worry about a software bug that will suddenly open both doors, despite claims of the software vendor that something like that could never, ever, happen. Because we all know that there's no such thing as “never, ever” in software.

[DerekL1963]

3 hours ago, Nibb31 said:

In the same vein, the Apollo Telescope Mount (the part on top of Skylab) was based on a LM ascent stage, despite the fact that it wasn't even pressurized or accessible by the astronauts.

Not quite, it was based (very, very loosely) on the LM descent stage.   It's called the Apollo Telescope Mount because it was a descendant of an Apollo Applications Program proposal which would replace the descent and lunar surface equipment in the descent stage with telescopes and scientific equipment that would be operated from within what used to be the ascent stage.   (Not that anything survived from the LM design in the flown ATM mind you, the name just stuck around out of inertia.)

[GeneCash]

I don't think a servo motor would happen, since it would be like having a motor on your car that unlatches (not just unlocks) the doors... the lawyers & engineers would think about someone getting dumped on the road at 60mph and say "hell no"

The current design is lighter and has fewer failure modes, so you'd have an uphill struggle getting the servos approved.

Also note that after opening and before closing any of the large doors, you examine the seals as closely as possible for damage and anything stuck to them. You take a lot of time and give them the really hairy eyeball because your life depends on those seals.

Plus you check for leaks about a dozen ways. You want to find out as soon as possible so you waste as little air and time as possible if you have to reopen and reseal a door.

Going out: When you drop the pressure inside the airlock, you only do it a couple pounds at first, then wait a while to see if it comes back up (i.e. is there a leak on the newly closed inner door)

Coming in: When you raise the pressure inside the airlock, you only do it a couple pounds at first, then wait a while to see if it goes back down (i.e. is there a leak on the newly closed outer door)

Docking: You pressurize the bit between the two docking doors and wait and see if the newly docked seals hold the pressure, and that the latches are holding.

Undocking: You vent the bit between the two docking doors, seal it, and wait and see if the pressure goes back up, to find out if the newly closed station & spacecraft doors leak.

[magnemoe]

1 hour ago, GeneCash said:

I don't think a servo motor would happen, since it would be like having a motor on your car that unlatches (not just unlocks) the doors... the lawyers & engineers would think about someone getting dumped on the road at 60mph and say "hell no"

The current design is lighter and has fewer failure modes, so you'd have an uphill struggle getting the servos approved.

Also note that after opening and before closing any of the large doors, you examine the seals as closely as possible for damage and anything stuck to them. You take a lot of time and give them the really hairy eyeball because your life depends on those seals.

Plus you check for leaks about a dozen ways. You want to find out as soon as possible so you waste as little air and time as possible if you have to reopen and reseal a door.

Going out: When you drop the pressure inside the airlock, you only do it a couple pounds at first, then wait a while to see if it comes back up (i.e. is there a leak on the newly closed inner door)

Coming in: When you raise the pressure inside the airlock, you only do it a couple pounds at first, then wait a while to see if it goes back down (i.e. is there a leak on the newly closed outer door)

Docking: You pressurize the bit between the two docking doors and wait and see if the newly docked seals hold the pressure, and that the latches are holding.

Undocking: You vent the bit between the two docking doors, seal it, and wait and see if the pressure goes back up, to find out if the newly closed station & spacecraft doors leak.

An automated door makes sense if you want open and close it remotely,
One use would be of you put stuff in the airlock with the robot arm, open inner door and inspected or repaired it, then had the arm take it out again without having an astronaut in the lock. 
In this setting you are likely to have another airlock, first as the large one was in use, also to fix stuff if something went wrong. 
As I understand the ISS has an small breadbox sized airlock for this.

Yes you could make an mechanism where turning the handle disengages the motor. an primitive clutch would work well and have extremely low chance of fail if designed right. 

[GeneCash]

40 minutes ago, magnemoe said:

An automated door makes sense if you want open and close it remotely,
One use would be of you put stuff in the airlock with the robot arm, open inner door and inspected or repaired it, then had the arm take it out again without having an astronaut in the lock. 
In this setting you are likely to have another airlock, first as the large one was in use, also to fix stuff if something went wrong. 
As I understand the ISS has an small breadbox sized airlock for this.

Yes, the experiments airlock in the Japanese Kibo lab works like this. It's pretty big too! See http://space.stackexchange.com/questions/9809/how-was-the-airlock-for-the-iss-minisat-launchers-installed and "The outer hatch can be opened and closed electrically, but the inner hatch is operated by hand" according to http://iss.jaxa.jp/iss/kibo/develop_status_07_e.html

There's actually a movie on that page showing how it's operated and it DOES have sound of people discussing things and giving commands in Japanese.

It looks really simple. You just move a lever about 20 degrees. A lot simpler than the mechanisms on the airlock hatches and hatches between the modules in the rest of ISS, and most US manned spacecraft I've seen.

[SomeGuy123]

5 hours ago, GeneCash said:

I don't think a servo motor would happen, since it would be like having a motor on your car that unlatches (not just unlocks) the doors... the lawyers & engineers would think about someone getting dumped on the road at 60mph and say "hell no"

As described, it's more like a servo that helps you open the door after you've turned a handle.

You could add considerable automation.

1.  When pressurizing, the computer could do what you are describing and add 2 psi and then check for pressure loss.  If this happens, it would put a CHECK OUTER DOOR alert on the display and refuse to continue unless someone presses override on the GUI.

2.  When depressurizing, the computer could reduce pressure in the inner chamber and check for pressure gain (leakage from the station into the inner lock).  If this happens, the computer could put a CHECK INNER DOOR alert on the display and again refuse to continue.

3.  There could be sensors inside the inner airlock that detect if anyone is in there.  (motion sensors).  If no one is there, you could remotely cycle the airlock from remote controls for it.

4.  The motor as I've described it will not work if there's a pressure differential.  So it's more like a motor on your car that can only open the doors if your car is stopped and the engine is off.

[WestAir]

If I was really dead-set on spacing somebody in Hollywood fashion, could I bypass all of the safety features by docking my ship, making sure both doors were open, then undocking so the sudden vacuum launches my victim out the airlock like a scene from Star Trek?

[Nibb31]

6 minutes ago, WestAir said:

If I was really dead-set on spacing somebody in Hollywood fashion, could I bypass all of the safety features by docking my ship, making sure both doors were open, then undocking so the sudden vacuum launches my victim out the airlock like a scene from Star Trek?

I'm pretty sure that docking systems have the same sort of mechanical failsafes to prevent you from undocking with the hatch open.

[fredinno]

15 hours ago, SomeGuy123 said:

So, here's how the ISS airlocks actually work, per one of the mission control staff.

There's of course an inner and an outer door.  Both are actuated with cranks - no electrics, no control panel, no cool "emergency blow" button per several movies.

Both are designed where mechanically an air pressure differential prevents you from opening the hatches at all.  So you cannot crank on the inner hatch while there is pressure inside the station, and you cannot crank open the outer hatch while there is pressure inside the airlock chamber.  

So to use the airlock, you just crank open the inner hatch and get inside the chamber.  Crank closed the inner door.  Then, you activate the vacuum pump.  It just pumps the air inside the inner chamber back inside the station.  That's it.  I always figured there were compressed air tanks for holding that air, there aren't.  Just a pump and 2 hoses and 1 set of electrical wires to a switch.  

What if the vacuum pump has failed or there is no power?  There's a vent.  You open the vent, the air in the airlock leaks out to space.  You will die if you do not have a suit on, but the venting takes time, so you could close it if you somehow opened the vent by accident.

You then crank open the outer hatch.  Done.

To get back in, you get inside, crank the outer hatch closed, and open the inner vent.  Air leaks into the air lock from the station through that vent.  Then open the inner hatch.

What if you wanted to board the station and the inner door is open and the station is still pressurized?

You open the outer vent, accessible from the outside.  All the air in the station will eventually drain out that vent.  This is how attacking space marines would board the station by force.  Apparently, the air maintenance systems in the station will not automatically dump their gas contents to try to keep pressure up - there are obviously compressed oxygen tanks and compressed nitrogen tanks onboard, but the computer controls on them won't automatically dump their contents - so there's plenty of air left in the gas tanks so you can repressurize.

Once the station pressure is zero, you can open the outer door.  Then close it.  You can then access controls and try to re-pressurize - one problem is the vacuum may destroy some of the equipment from overheating, preventing you from doing this.  You may have to access the valves to do this manually.  

What if there's an attacking alien and you need to open the airlock doors to eject them to space?  You're screwed.

If you wanted to execute someone, per several movies and tv shows, you'd put them in the inner chamber, while restrained, and activate the vacuum pump.  Some time later the air pressure would get low enough and they'd peacefully pass out and die.  No eyeballs exploding, no sudden ejection to space.

This is how airlocks should be designed.  If I were designing a futuristic airlock, the only thing I'd change is add an electric motor to turn the crank.  I'd deliberately make the motor too weak to actuate the crank unless there is no pressure differential.  (I'd design the motor to safely stall without burning anything up when this happens).

I'd then add some cool looking illuminate touch screen controls explaining how to use the airlock, and I'd have all the key controls backed up by manual switches and manual cranks.  Actually, nix the touch screen manual - print pictograms into a plate set into the side of the airlock panel.

The 2 main crank handles would fold inwards, and there would be 2 red disks that rotate when driven by the servo motor.  You'd see them turning.  If there's a motor failure, you just grab the disk, pull out the fold out crank handle, and turn them yourselves.

 

 

Simple is better .

 

8 hours ago, DerekL1963 said:

Not quite, it was based (very, very loosely) on the LM descent stage.   It's called the Apollo Telescope Mount because it was a descendant of an Apollo Applications Program proposal which would replace the descent and lunar surface equipment in the descent stage with telescopes and scientific equipment that would be operated from within what used to be the ascent stage.   (Not that anything survived from the LM design in the flown ATM mind you, the name just stuck around out of inertia.)

Why did they bother with basing it off the descent stage? I get the ascent stage, so that they could reuse the control spaces for the telescope, but what doe the descent stage have that can make a Telescope Mount cheaper? I thought they just had the thing controlled from the ascent stage, and the descent stage was just replaced by the scientific payload?

[DerekL1963]

9 hours ago, fredinno said:

18 hours ago, DerekL1963 said:

Not quite, it was based (very, very loosely) on the LM descent stage.   It's called the Apollo Telescope Mount because it was a descendant of an Apollo Applications Program proposal which would replace the descent and lunar surface equipment in the descent stage with telescopes and scientific equipment that would be operated from within what used to be the ascent stage.   (Not that anything survived from the LM design in the flown ATM mind you, the name just stuck around out of inertia.)

Why did they bother with basing it off the descent stage? I get the ascent stage, so that they could reuse the control spaces for the telescope, but what doe the descent stage have that can make a Telescope Mount cheaper? I thought they just had the thing controlled from the ascent stage, and the descent stage was just replaced by the scientific payload?

The LM descent stage structure carried all the structural loads and transferred them to the SLA (Saturn Launch Adapter) via the landing gear.   (If you look at the diagrams in the link above, you can see where they retained a small portion of the landing gear for this purpose.)  Up until the S-IVB was jettisoned, all the telemetry for the LM went through an umbilical that ran from the descent stage to the SLA.  (After that, the crew had to enter the LM and power up the communications system before Mission Control could receive data from the LM.)  On it's own the ascent stage had a very limited lifetime, and the descent stage contained the lion's share of the LM's consumables (batteries, O2, and water for the evaporative cooler).*  

So they could modify the ascent stage and/or modify the CSM while also having to engineer a scientific package from scratch (that would still have to carry out most if not all the functions of the descent stage), or they could just re-use the existing systems (already flight qualified and for which a production chain already existed) to the maximum extent.  This is a bigger consideration than it looks on the surface, because by the time significant work started on the LM Lab in 1966 NASA and Apollo's budget had already been cut** and the medium term future of Apollo Applications and the Apollo Program was in some doubt.

* The ascent stage was so weight critical (partly for normal ascent but also for aborts) and so cramped that on the later (long stay) missions food, LiOH cannisters for the cabin, and supplies for the PLSS were stored in the MESA on the exterior of the descent stage and had to be retrieved while they were moonwalking.

** Contrary to popular belief and urban legend, not only did Apollo not have a blank check - it wasn't Nixon that killed it.  The Apollo program was essentially capped due to the budget cuts of '65-'67.   The only bits of Apollo Applications that survived were the long stay LM's, the Lunar Rover, and a very financially constrained Skylab.

[fredinno]

10 hours ago, DerekL1963 said:

The LM descent stage structure carried all the structural loads and transferred them to the SLA (Saturn Launch Adapter) via the landing gear.   (If you look at the diagrams in the link above, you can see where they retained a small portion of the landing gear for this purpose.)  Up until the S-IVB was jettisoned, all the telemetry for the LM went through an umbilical that ran from the descent stage to the SLA.  (After that, the crew had to enter the LM and power up the communications system before Mission Control could receive data from the LM.)  On it's own the ascent stage had a very limited lifetime, and the descent stage contained the lion's share of the LM's consumables (batteries, O2, and water for the evaporative cooler).*  

So they could modify the ascent stage and/or modify the CSM while also having to engineer a scientific package from scratch (that would still have to carry out most if not all the functions of the descent stage), or they could just re-use the existing systems (already flight qualified and for which a production chain already existed) to the maximum extent.  This is a bigger consideration than it looks on the surface, because by the time significant work started on the LM Lab in 1966 NASA and Apollo's budget had already been cut** and the medium term future of Apollo Applications and the Apollo Program was in some doubt.

* The ascent stage was so weight critical (partly for normal ascent but also for aborts) and so cramped that on the later (long stay) missions food, LiOH cannisters for the cabin, and supplies for the PLSS were stored in the MESA on the exterior of the descent stage and had to be retrieved while they were moonwalking.

** Contrary to popular belief and urban legend, not only did Apollo not have a blank check - it wasn't Nixon that killed it.  The Apollo program was essentially capped due to the budget cuts of '65-'67.   The only bits of Apollo Applications that survived were the long stay LM's, the Lunar Rover, and a very financially constrained Skylab.

But I thought the long duration LEMs and rovers were included in the original Apollo Program. And AAP was mainly axed b/c of Apollo 1.

[DerekL1963]

3 hours ago, fredinno said:

But I thought the long duration LEMs and rovers were included in the original Apollo Program. And AAP was mainly axed b/c of Apollo 1.

Not quite.   In particular, while rovers had been studied in early 60's the whole thing was mostly shelved by the mid 60's.  (Due to a mix of budget concerns and LM weight concerns.)  Development of the actual LRV didn't start until 11 July 1969.

What was cut after Apollo 1 was the originally planned sequence of test flights before proceeding with the moon landing.  In particular, the E mission, which would have been a test of the CSM and LM in high earth orbit.

And keep in mind, the original Apollo program wasn't a lunar landing program - it was a general purpose spacecraft that could have been used for a variety of missions.   In the midst of Mercury (which is when Apollo was born) NASA really wasn't sure where it was going next or when so they left their options open.  But the original general purpose Apollo was only around for a year or so before Kennedy's speech changed everything.

[fredinno]

21 minutes ago, DerekL1963 said:

Not quite.   In particular, while rovers had been studied in early 60's the whole thing was mostly shelved by the mid 60's.  (Due to a mix of budget concerns and LM weight concerns.)  Development of the actual LRV didn't start until 11 July 1969.

What was cut after Apollo 1 was the originally planned sequence of test flights before proceeding with the moon landing.  In particular, the E mission, which would have been a test of the CSM and LM in high earth orbit.

And keep in mind, the original Apollo program wasn't a lunar landing program - it was a general purpose spacecraft that could have been used for a variety of missions.   In the midst of Mercury (which is when Apollo was born) NASA really wasn't sure where it was going next or when so they left their options open.  But the original general purpose Apollo was only around for a year or so before Kennedy's speech changed everything.

Apollo 1 though, also significantly reduced AAP funding, so it was one of the primary factors to kill it.

[cantab]

On 29/01/2016 at 0:15 AM, GeneCash said:

I don't think a servo motor would happen, since it would be like having a motor on your car that unlatches (not just unlocks) the doors... the lawyers & engineers would think about someone getting dumped on the road at 60mph and say "hell no"

 

It's sometimes known as a "Door popper" and it's a fairly common modification, though I don't know any vehicles that factory fit it to the main doors. (Motorised boot lids on the other hand are super common).

Then again, if your door does open when you don't want it to that's not all that dangerous in a car really, not compared to on a space station.

[magnemoe]

29 minutes ago, cantab said:

 

It's sometimes known as a "Door popper" and it's a fairly common modification, though I don't know any vehicles that factory fit it to the main doors. (Motorised boot lids on the other hand are super common).

Then again, if your door does open when you don't want it to that's not all that dangerous in a car really, not compared to on a space station.

Doors and back lid of cars are kept close by air resistance. Remember one trip where we had to tie down the trunk as we had skies poking out. the rope came loose but we did not notice before we was slowing down and the trunk opened spilling content. 

 

[cantab]

Indeed. And as Someguy123 said at the very start, a similar thing goes for the space station - the airlocks are designed so that the pressure difference mechanically prevents the doors opening.