Apollo 1

[Bob B.]

It's 5 psia +/- a pound or so.  The hysteresis was broad.

In the concluding remarks, the report does say that 6.2 psia is "the maximum pressure that will be used in space flight."

[Bob B.]

The following announcement appeared in the March 1968 Aviation Week & Space Technology:

"Washington - Decision to use a two-gas atmosphere (60% oxygen, 40% nitrogen) during manned Apollo on-the-pad preparations and in pre-orbital flight reflects a basic inability to make the spacecraft flameproof after 14 months of redesign that cost more than $100 million and added about 2,000 lb. to the system."

One thing that caught my eye in this quote is the part about adding 2,000 lb. to the system.  I know that the Block II CSM incorporated weight reduction improvements that made it considerably lighter than the Block I CSM.  Of course, even though the Block II was lighter overall, it still could have ended up 2,000 lb. heavier than would have otherwise been.  I'm unaware of any post-Apollo I design changes that would have added that much weight.  Does anyone have any details about this?

[Luke Pemberton]

One thing that caught my eye in this quote is the part about adding 2,000 lb. to the system.  I know that the Block II CSM incorporated weight reduction improvements that made it considerably lighter than the Block I CSM.  Of course, even though the Block II was lighter overall, it still could have ended up 2,000 lb. heavier than would have otherwise been.  I'm unaware of any post-Apollo I design changes that would have added that much weight.  Does anyone have any details about this?

This space.com article:

http://www.space.com/14379-apollo1-fire-space-capsule-safety-improvements.html

It describes that the walls would have been made thicker.

Maybe marginal, but it would be interesting to know how much the whole rewire job would add to the weight. All the wires were coated with a fireproof insulation, and from what I can understand the wiring was so well insulated that it was possibly a contributing factor in saving the Apollo 13 crew from condensation shorting the CM switches. I defer to the experts, but I would imagine that such a wiring refit would add to the weight too. Not 2000 lbs, clearly.

[JayUtah]

No, electrical insulation alone would probably not add 900 kg to the vehicle mass.  My understanding was that some additional plumbing had to be added to the SM to accommodate the mixed-gas atmosphere prior to launch, but now some of the postings Bob and Ka9q have offered make me question that.  I've seen the difference in the hatches firsthand, and the Block II hatch is considerably more massive.

Kapton (Block I) is a wonderful electrical insulator.  Compared to Teflon (Block II), it's as much as half the mass density and has better insulating capacity per unit thickness.  Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass.  But you have to do it -- Kapton has horrible performance in a fire.  Teflon is self-extinguishing.  Kapton is self-sustaining:  once ignited it will produce its own fuel.  If I could find the specifics on the cable harness lengths I could work out fairly quickly how much heavier the Block II harnesses were.

[Glom]

Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass.

Heavier per unit mass? That doesn't make sense.

[Luke Pemberton]

I've seen the difference in the hatches firsthand, and the Block II hatch is considerably more massive.

This link (+253 pounds)

http://www.space1.com/pdf/news1296.pdf

[JayUtah]

Switching from Kapton to Teflon requires thicker insulation sheaths, and the material is heavier per unit mass thickness.

Heavier per unit mass? That doesn't make sense.

...per unit thickness (see inline correction).  I originally just wrote that it was "denser" but that sounded dorky.  Then I decided "unit thickness" was confusing.  Then I forgot what I was writing.

[Luke Pemberton]

...per unit thickness (see inline correction).  I originally just wrote that it was "denser" but that sounded dorky.  Then I decided "unit thickness" was confusing.

In context of what you were writing about, unit thickness was least confusing (IMHO).

Then I forgot what I was writing.

Do you ever walk into a room to get something and then forget what you went in for? I do that at work quite a lot. My clients find it hilarious. But then it is like working at a chimps tea party at times 

[raven]

I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.

[Echnaton]

Do you ever walk into a room to get something and then forget what you went in for? I do that at work quite a lot. My clients find it hilarious. But then it is like working at a chimps tea party at times 

My particular vice is to put something down right beside me than not be able to find it two minutes later.  I'd like to be able to say it is a symptom of being over fifty, but alas, it is a symptom of my life.

[Luke Pemberton]

I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.

I've hung my work pass around my neck and then 2 minutes later gone on a 20 minute hunt for it - several times may I add. 

[raven]

I <sarc>love</sarc> when I am writing, get distracted, then write the last word I wrote again before continuing the paragraph, leading to a lot of doubled words.

I've hung my work pass around my neck and then 2 minutes later gone on a 20 minute hunt for it - several times may I add. 

I admit, I laughed, but I could so do that.
I once spent a whole day frantically looking for my Core Rulebook for the Pathfinder RPG, not so much because I needed it for itself, I got the  core rules mostly memorized, but because it had my character sheet in it. It should be noted I have a huge stack of RPG books (it reaches up to mid chest height, and I am 5'8'')  beside my kitchen table because I literally have no other space for them.  I looked in the stack, but I didn't find it. Finally, my friends came to pick me up, and I had to leave without it, recreating my character sheet with reasonable accuracy. The fact  we were level 3 helped.
Anyway, got home after having a good time, looked a bit more, didn't find it, and went to bed,
The next day, I looked again, and, bless my soul and whiskers, there it was in that bloody stack of books.
My head got into a beautiful relationship with the desk. At the very least, they were very close.

[Bob B.]

Do you ever walk into a room to get something and then forget what you went in for?

I've done that plenty of times.  Very often if you return to the location where you first had the thought about what it was you wanted to do, the memory will come right back to you.  It's just something quirky in the way the brain works.

[ka9q]

The report keeps referring to the use of a 6.2-psia atmosphere in space but, from all other sources I've seen, the cabin pressure was actually 5-psia.

They might be referring to the pressure in the suit, which was slightly greater than cabin pressure. Most of the references give the relative suit pressure in inches of water rather than psig or kPa, and I didn't convert them.

I really wish we'd just go SI...

[Bob B.]

They might be referring to the pressure in the suit, which was slightly greater than cabin pressure.

Although the report mentions 6.2 psia in reference to the suit loop, it seems pretty clear that they are also talking about the cabin pressure.  For instance, the report states the following:

"A pressure of 6.2 psia was chosen for the spacecraft while in the vacuum of space for several reasons:  (1) the spacecraft structure would be lighter because of the small pressure differential; (2) for lower pressures, less oxygen would have to be stored on board the spacecraft; and (3) at a pressure of 6.2 psia, sufficient oxygen would be available to sustain human life with no adverse physiological effects."