Space station future adrift (Soyuz purchase crisis)

In article ,
Keith F. Lynch wrote:
For a crash program, it is important to distinguish between
requirements (which absolutely must be satisfied) and wishlist items
(which can be disregarded if they prove inconvenient). The ability
to separate, wait, retrofire, reenter, and land is requirement.

Instead of years of expensive new development, why not just build
some more Apollo command modules?

Unfortunately, there's no "just" about it -- we don't have production
capability for them any more, and it's not simple to rebuild it. We'd
have to retest and requalify a lot of the stuff, given that the tooling
would be new and the skilled people would be new and even some of the
materials probably aren't available exactly as they were then. (Even
programs which are *in production* sometimes have problems when materials
change due to small changes in the chemical processes.)

Moreover, there would be good reasons to redesign some of the subsystems.
You probably couldn't duplicate the original electronics today if you
wanted to, not at any reasonable price... and you wouldn't want to.

It sounds like they'd meet the (ISS lifeboat) requirements just fine.

Unfortunately, no, not so, not as designed. Most notably, Apollo was
a low-pressure pure-oxygen spacecraft, and you'd need prebreathing just
to enter it.

An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch. You don't get a
lot of benefit from starting with such an old design, and it constrains
you not to do things that could be helpful, like a less overbuilt
heatshield. (The CM heatshield was drastically overbuilt for a *lunar*
reentry, never mind a LEO one.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote:
An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch.

IMO, keeping the moldline is a minor win, and about the best you can
hope with a reasonable neo-Apollo.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

In article ,
Derek Lyons wrote:
An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch.

IMO, keeping the moldline is a minor win, and about the best you can
hope with a reasonable neo-Apollo.

Keeping the Apollo *shape* is definitely useful, because its reentry
aerodynamics are very thoroughly explored and documented. There's a
reason why both ESA's ARD and Japan's OREX looked like miniature Apollos
at first glance.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) wrote in :

Unfortunately, no, not so, not as designed. Most notably, Apollo was
a low-pressure pure-oxygen spacecraft, and you'd need prebreathing just
to enter it.



I understand your point, but this probably should be changed to read
"Apollo was *equipped to be* a low-pressure pure-oxygen spacecraft" since,
as you pointed out once*, the capsule could be (and was routinely) operated
using pure oxygen, oxygen/nitrogen (60%/40%), and air mixtures at 14.7psi.
In particular, there wasn't any restriction on the electronics to prevent
it from working at the higher pressure (if anything, heat transfer would be
better).

You'd have to add nitrogen tanks, a gas mixer, and appropriate monitoring
equipment to an "original" Apollo capsule but there's nothing inherently
"low-pressure pure-oxygen" about it.

* http://yarchive.net/space/apollo/apollo_1_fire.html#2

--
Reed

Henry Spencer wrote:
Derek Lyons wrote:
An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch.

IMO, keeping the moldline is a minor win, and about the best you can
hope with a reasonable neo-Apollo.

Keeping the Apollo *shape* is definitely useful, because its reentry
aerodynamics are very thoroughly explored and documented. There's a
reason why both ESA's ARD and Japan's OREX looked like miniature Apollos
at first glance.

However, there are several other shapes which are also well
explored in practice.

The blunt cones include the range from Apollo to Gemini/Mercury
to Soyuz, and the early blunt ICBM warhead shapes.

There are also several lifting body shapes, sphere-cone shapes,
(Discoverer photo return capsules), and sharp cones (ICBM RVs).
As well as spheres.

There are also blunter flatter cones, the shapes that have been
used for planetary entry shapes.

I think that manned spaceflight constraints pretty well rule
sharp cones out; they're only more useful if your objective is
to avoid losing velocity at high altitudes, which is exactly
opposite what manned craft want to do.

Spheres seem to be inefficient on several levels, and can't do
lifting re-entries. Spheres with some sort of drag modulator might
do well but that's outside proven shapes.


-george william herbert

Reed Snellenberger wrote:
(Henry Spencer) wrote in :
Unfortunately, no, not so, not as designed. Most notably, Apollo was
a low-pressure pure-oxygen spacecraft, and you'd need prebreathing just
to enter it.

I understand your point, but this probably should be changed to read
"Apollo was *equipped to be* a low-pressure pure-oxygen spacecraft" since,
as you pointed out once*, the capsule could be (and was routinely) operated
using pure oxygen, oxygen/nitrogen (60%/40%), and air mixtures at 14.7psi.

It operated at 14.7 PSIA (absolute), which was under those conditions
0 PSIG (relative to surroundings). In space, that goes to 14.7 PSIG,
which Apollo never flew or was tested for. It was flown and tested for
around 5 PSIG.

The margins would probably hold, but you'd be way way underspec for
reasonable remaining operating margins for seals and structure once
you ran it in space at 14.7 PSI.

The problems are entirely NOT with running the equipment inside
at 14.7 PSI. Other than instruments that require a good vacuum
to operate, spacecraft components are specced to run fine either
in a vacuum or at 14.7 PSI, as they have to be assembled and
tested at something like sea level.


-george william herbert

In article ,
Reed Snellenberger wrote:
...In space, that goes to 14.7 PSIG,
which Apollo never flew or was tested for. It was flown and tested for
around 5 PSIG.

Yeah, you're right. Thanks...
Phillips also says "The Command Module is designed to withstand an internal
pressure of approximately 13 pounds per square inch above external pressure
without rupturing." (Part V.2)

Which means a structural safety factor of about 2.5, which is not bad --
I'd have guessed lower for a NASA product.

(Normal industrial practice is a safety factor of 5 for unheated pressure
vessels; that can be reduced to 4 if a number of precautions are taken.
Aerospace in general and NASA in particular are notorious for cutting
the safety margins much closer.)

Note that this means that the maximum safe *working* pressure, in vacuum,
is not much above 5psi. The safety factor is not growth margin; it's
strictly a hedge against unpleasant surprises, it has to be preserved.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Greg D. Moore \(Strider\) wrote:
"George William Herbert" wrote:
It operated at 14.7 PSIA (absolute), which was under those conditions
0 PSIG (relative to surroundings). In space, that goes to 14.7 PSIG,
which Apollo never flew or was tested for. It was flown and tested for
around 5 PSIG.

And in fact we have a decent estimate for what overpressure a production
craft can sustain: Apollo 1.

Right. From pp 5-7 of the Apollo 204 accident report:
(6) Cabin Presure Rise
The cabin pressure for the period from first report of
the fire through lost of signal is show in Enclosure 21.
First indication by either the cabin pressure or
battery compartment (open to the cabin) sensors of a pressure
increase occurred at approximately 23:21:11 GMT or about
6 seconds after the crew first reported the fire. The pressure
exceeded the range of those transducers, 17 pounds per square
inch absolute (psia) for the cabin and 21 psia for the
battery compartment transducers by 23:31:16. Data from
this time until loss of signal were derived from the response
of Guidance and Navigation equipment to the different
pressure changes. The cabin ruptured at a time of about
23:31:19 GMT and at a pressure of at least 29 psia.

http://ntrs.nasa.gov/archive/nasa/ca...1982066930.pdf

I believe that the first time mark of 23:21:11 is a typo but it's
clearly listed as that in the report scan PDF.

If we assume the rupture was at 29 psia, then the gage pressure
was around 14 psig, which is slightly higher than the design
target of 13 psig and 2.5 factor of safety specified from 5 psig
operating pressure in space.


-george william herbert

I wrote:
An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch. You don't get a
lot of benefit from starting with such an old design, and it constrains
you not to do things that could be helpful, like a less overbuilt
heatshield...

A friend points out, in private mail, that it does have an advantage I
didn't consider: while some of those constraints might be troublesome,
accepting them eliminates the need to spend several years and several
billion dollars studying, and arguing over, what the lifeboat should look
like.

The subsystems need redesigning anyway, since you mostly *can't* just
duplicate the old ones. The sort of strong leadership needed to end the
debates and quickly go for something that works well enough is more likely
to be found at the subsystem level, where fewer people are involved,
politics are less troublesome, and decisions can be made by people who
understand the technology.

Technically it may not be the best approach, but in today's bureaucratic
environment, the idea has its points.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Henry Spencer wrote:
I wrote:
An Apollo-based lifeboat is not a ridiculous idea, but it's not clear that
it's any cheaper or easier than starting from scratch. You don't get a
lot of benefit from starting with such an old design, and it constrains
you not to do things that could be helpful, like a less overbuilt
heatshield...

A friend points out, in private mail, that it does have an advantage I
didn't consider: while some of those constraints might be troublesome,
accepting them eliminates the need to spend several years and several
billion dollars studying, and arguing over, what the lifeboat should look
like.

It doesn't take several years or several billion dollars to study
or argue over the configuration unless you're a dinosaur.

The subsystems need redesigning anyway, since you mostly *can't* just
duplicate the old ones. The sort of strong leadership needed to end the
debates and quickly go for something that works well enough is more likely
to be found at the subsystem level, where fewer people are involved,
politics are less troublesome, and decisions can be made by people who
understand the technology.

You don't necessarily need such a large team that one person
can't make that decision at the vehicle level.


-george william herbert