Spacesuits - Your inflexible friend

Hello Everyone,

Chris Carr will be at the second annual Spacesuit Symposium at the 9th
Mars Society Conference held August 3-6, 2006 at L`Enfant Plaza Hotel
in Washington DC...--Chris Vancil

Spacesuits - Your inflexible friend

Jul 20th 2006
From The Economist print edition

Sometimes the old ways are the best

IF YOU want to conserve energy, walking rather than running is the best
plan. At least, on
Earth it is. However, Christopher Carr, a researcher at the
Massachusetts Institute of
Technology, has shown in his recent research that for astronauts
exploring places with
lower gravity than Earth, the reverse is true. If they run, rather than
walk, they can achieve
more in the limited time before their oxygen runs out. They can also
travel further from
their spacecraft because, in an emergency, they can get back faster.
This discovery calls
into question efforts to design new spacesuits for America's
much-vaunted plan to send
people back to the moon, and eventually to Mars.

NASAEr, which way now?

The instinct of engineers at NASA, America's space agency, is to
improve on the suits used
three and a half decades ago during the Apollo project by making them
less rigid. That
would make them easier to walk in. But pulling this redesign off is
tricky, because their
rigidity is a result of their internal pressurisation. In inflatable
spacecraft (see article)
rigidity is a good thing. In spacesuits, it has been thought of as bad.

Dr Carr, however, has been reviewing the performance of the Apollo
suits by looking at
footage shot on the moon and by studying the astronauts' own thoughts.
He thinks the
basic design of the suits-inflexibility and all-is far sounder than
any of the proposed
improvements.

After immersing himself in the lunar-landing films and journals, he
noticed that although
the inflexibility of the suits did indeed create difficulties for
astronauts when they bent
down to collect rock samples, they found the action of running in a
suit on the moon as
easy as running on Earth without one. Nor was this a mere personal
perception. By
matching recordings of astronauts' oxygen consumption with what the
films showed they
were doing at the time, Dr Carr was able to show that their rate of
oxygen use was indeed
lower during running than walking.

More at:
http://www.economist.com/science/dis...ory_id=7188806

The problem with the Economist article is that it assumes roughly a
copy of Apollo. Using only energy of movement as a metric for suit
usability ignores many tasks that will need to be performed in future
space missions. The source concept assumes that people will get out of
their spacecraft, gather a few awkward samples and go home. Instead, we
can expect maintenance on extended (month-plus) stays, extensive
geology (lots of bending/squatting) and base/hardware assembly.

I'm not aware of any spacesuit that currently exists meeting these
demands, never mind added pressure on suit designs: NASA wants to
operate in lunar polar craters. The "MkIII" is pretty impressive, but
not in production.

Josh


wrote:
Hello Everyone,

Chris Carr will be at the second annual Spacesuit Symposium at the 9th
Mars Society Conference held August 3-6, 2006 at L`Enfant Plaza Hotel
in Washington DC...--Chris Vancil

Spacesuits - Your inflexible friend

Jul 20th 2006
From The Economist print edition

Sometimes the old ways are the best

IF YOU want to conserve energy, walking rather than running is the best
plan. At least, on
Earth it is. However, Christopher Carr, a researcher at the
Massachusetts Institute of
Technology, has shown in his recent research that for astronauts
exploring places with
lower gravity than Earth, the reverse is true. If they run, rather than
walk, they can achieve
more in the limited time before their oxygen runs out. They can also
travel further from
their spacecraft because, in an emergency, they can get back faster.
This discovery calls
into question efforts to design new spacesuits for America's
much-vaunted plan to send
people back to the moon, and eventually to Mars.

NASAEr, which way now?

The instinct of engineers at NASA, America's space agency, is to
improve on the suits used
three and a half decades ago during the Apollo project by making them
less rigid. That
would make them easier to walk in. But pulling this redesign off is
tricky, because their
rigidity is a result of their internal pressurisation. In inflatable
spacecraft (see article)
rigidity is a good thing. In spacesuits, it has been thought of as bad.

Dr Carr, however, has been reviewing the performance of the Apollo
suits by looking at
footage shot on the moon and by studying the astronauts' own thoughts.
He thinks the
basic design of the suits-inflexibility and all-is far sounder than
any of the proposed
improvements.

After immersing himself in the lunar-landing films and journals, he
noticed that although
the inflexibility of the suits did indeed create difficulties for
astronauts when they bent
down to collect rock samples, they found the action of running in a
suit on the moon as
easy as running on Earth without one. Nor was this a mere personal
perception. By
matching recordings of astronauts' oxygen consumption with what the
films showed they
were doing at the time, Dr Carr was able to show that their rate of
oxygen use was indeed
lower during running than walking.

More at:
http://www.economist.com/science/dis...ory_id=7188806

I tend to agree with you on the current suits ablities and Chris is
talking of traveling in the suits more than doing field geology. But
the springs physics and the use of the suits pressure colume need to be
integrated into a real suit to do real work over months on the Moon and
(hopeful) Mars.

And of coarse the Moon has it's own issue that we can't be sure are
Mars' issues till we get a little more data.

Part of the reason for the Spacesuit Symposium was to bring together
folks in a relaxed atmosphere to talk of the radiation and dust
problems and MCP over pressure bladders suits.

I to think the Mark III (and would add the I-Suit) are cool but weight
to much and have to many bearings (non of which seem field
serviceable).

BTW, Pop Sci of August has a short article on the North Dakota analog
low pressure suit, HS Haughton no pressure analog suit and MIT Biosuit
(MCP).

--Chris Vancil

Josh wrote:
The problem with the Economist article is that it assumes roughly a
copy of Apollo. Using only energy of movement as a metric for suit
usability ignores many tasks that will need to be performed in future
space missions. The source concept assumes that people will get out of
their spacecraft, gather a few awkward samples and go home. Instead, we
can expect maintenance on extended (month-plus) stays, extensive
geology (lots of bending/squatting) and base/hardware assembly.

I'm not aware of any spacesuit that currently exists meeting these
demands, never mind added pressure on suit designs: NASA wants to
operate in lunar polar craters. The "MkIII" is pretty impressive, but
not in production.

Josh


wrote:
Hello Everyone,

Chris Carr will be at the second annual Spacesuit Symposium at the 9th
Mars Society Conference held August 3-6, 2006 at L`Enfant Plaza Hotel
in Washington DC...--Chris Vancil

Spacesuits - Your inflexible friend

Jul 20th 2006
From The Economist print edition

Sometimes the old ways are the best

IF YOU want to conserve energy, walking rather than running is the best
plan. At least, on
Earth it is. However, Christopher Carr, a researcher at the
Massachusetts Institute of
Technology, has shown in his recent research that for astronauts
exploring places with
lower gravity than Earth, the reverse is true. If they run, rather than
walk, they can achieve
more in the limited time before their oxygen runs out. They can also
travel further from
their spacecraft because, in an emergency, they can get back faster.
This discovery calls
into question efforts to design new spacesuits for America's
much-vaunted plan to send
people back to the moon, and eventually to Mars.

NASAEr, which way now?

The instinct of engineers at NASA, America's space agency, is to
improve on the suits used
three and a half decades ago during the Apollo project by making them
less rigid. That
would make them easier to walk in. But pulling this redesign off is
tricky, because their
rigidity is a result of their internal pressurisation. In inflatable
spacecraft (see article)
rigidity is a good thing. In spacesuits, it has been thought of as bad.

Dr Carr, however, has been reviewing the performance of the Apollo
suits by looking at
footage shot on the moon and by studying the astronauts' own thoughts.
He thinks the
basic design of the suits-inflexibility and all-is far sounder than
any of the proposed
improvements.

After immersing himself in the lunar-landing films and journals, he
noticed that although
the inflexibility of the suits did indeed create difficulties for
astronauts when they bent
down to collect rock samples, they found the action of running in a
suit on the moon as
easy as running on Earth without one. Nor was this a mere personal
perception. By
matching recordings of astronauts' oxygen consumption with what the
films showed they
were doing at the time, Dr Carr was able to show that their rate of
oxygen use was indeed
lower during running than walking.

More at:
http://www.economist.com/science/dis...ory_id=7188806

If one wants to poke holes in the original article you quoted, one would
just have to note that: when in an unfamiliar place, running is a good
way to trip and fall. When wearing a pressurized suit, running where
there are jagged rocks is a good way to make a hole in it.

The author still did have other good points. If making the suits more
flexible detracts from other positive properties that they have, caution
should be exercised. As I understand it, the way to make a spacesuit or
other pressure suit more flexible is to design joints that bend without
changing in volume.

Ah, here we are! Design a spacesuit so that a channel for air to flow
surrounds the astronaut everywhere. And have in *one* spot an
accordion-pleated cylinder that can shrink and expand easily - so that,
as the astronaut moves, it compensates for what happens at all the
joints.

But that doesn't work - the suit is pressurized, so if any part of the
suit can freely shrink or expand, it will just expand as much as
possible to lower pressure inside the suit.

Instead, have a rapid sensor monitoring suit pressure. As the astronaut
begins to make a move that expands his suit, have a motor compress the
compensating volume to keep the suit volume constant - as measured by
the suit pressure!

This has an inevitable time lag, so the conventional design of
constant-volume joints is better.

John Savard
http://www.quadibloc.com/index.html
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In article ,
lid (John Savard) wrote:

But that doesn't work - the suit is pressurized, so if any part of the
suit can freely shrink or expand, it will just expand as much as
possible to lower pressure inside the suit.

Instead, have a rapid sensor monitoring suit pressure. As the astronaut
begins to make a move that expands his suit, have a motor compress the
compensating volume to keep the suit volume constant - as measured by
the suit pressure!

I don't think that will work, for the very reason you state above. If
the knee is bent, air pressure is going to try to straighten it out,
just like in a balloon. So it takes constant work to keep it bent, even
when the astronaut is not making a move. Your compressor could
compensate for this only by draining the suit of air entirely (to which
your astronaut might object).

This has an inevitable time lag, so the conventional design of
constant-volume joints is better.

Yeah, the trouble with this is that it just doesn't work all that well.
Especially where there are small joints close together -- like in the
gloves -- it's very hard to make them constant volume.

Personally, I suspect that the next big step up in suit usability is
hard, powered suits. The Japanese have robotic exoskeletons that are
actually practical, though they only assist with the major joints. But
with a bit more development, they could form the basis for suits that
help you instead of constantly fighting you.

Best,
- Joe

Joe Strout writes:

This has an inevitable time lag, so the conventional design of
constant-volume joints is better.

Yeah, the trouble with this is that it just doesn't work all that well.
Especially where there are small joints close together -- like in the
gloves -- it's very hard to make them constant volume.

What about making that problem a bit smaller by enlarging the total
volume of the suit? The rising pressure when bending a joint is
proportional to the total volume of the suit and if you enlarge the
volume (maybe by attaching a not too small inflatable container to the
backpack, connected by hoses to the suit) the pressure rises much less
and the suit is more flexible. This of course has its limits, but it
might help to improve the situation enough to be useful.

How large is the free volume of existing suits? I guess not that large
(they have to be a quite tight fit) and just doubling the volume with no
other changes to the suit would double the flexibility. Or am I wrong
with that?


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery

"Mike Rhino" writes:

What about making that problem a bit smaller by enlarging the total
volume of the suit? The rising pressure when bending a joint is
proportional to the total volume of the suit and if you enlarge the
volume (maybe by attaching a not too small inflatable container to the
backpack, connected by hoses to the suit) the pressure rises much less
and the suit is more flexible. This of course has its limits, but it
might help to improve the situation enough to be useful.

How large is the free volume of existing suits? I guess not that large
(they have to be a quite tight fit) and just doubling the volume with no
other changes to the suit would double the flexibility. Or am I wrong
with that?

As a thought experiment, assume that there is a glass wall with a vacuum on
one side and all of Earth's atmosphere on the other. If a spacesuit arm is
attached, will you still have a flexibility problem? I'm inclined to think
that you would.

Hmm, intuitively I'd say you're right... But intuition is no replacement
for understanding ;-)

When you're arm is relaxed, the tensile strength of the suit counteracts the
air pressure. When you do a curl, you still have full tensile strength on
one side, but not the other side. You're muscles replace the tensile
strength and you have to fight the air pressure.

The changing volume of the joint is not the actual problem then? Or
better said, the changing volume of the whole system is not the problem
and this is a local problem instead? Your explanation sounds quite
convincing, but I've still trouble to understand how constant-volume
joints fit in here. Or is this just a misnomer and "constant-volume
joints" do the trick not by their constant volume but by a configuration
that keeps the area where pressure is applied constant when bent
(balancing the forces) and the constant volume is just a side effect
that follows from that?

Maybe it's just too hot here right now to think straight and I should
gulp down some water and take a nap...


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery

In article , John Savard
wrote:

The author still did have other good points. If making the suits more
flexible detracts from other positive properties that they have, caution
should be exercised. As I understand it, the way to make a spacesuit or
other pressure suit more flexible is to design joints that bend without
changing in volume.

This is true in a sense. However, your schemes to add a passive or
active system (with a bellows or pump) that automatically changes the
volume of the rest of the suit when you flex a joint would not make it
easier to bend the joints.

When you have a joint that maintains constant volume, it means that you
are not doing any work by compressing the gas. If the joint does
change the volume, then work is being done (negative work if the volume
increases). (Work done by the gas on the suit and thence on the
astronaut is pressure times the change in volume, work done by the
astronaut to the suit on the gas is the negative of that.)

If you have a separate system to maintain constant volume, then that
means that the astronaut is still doing work or having work done to
him, it is just that another system is also independently participating
in work.

You could have a system that works directly on the joints, such as
rubber bands that pull the joint bent with exactly the same amount of
force as the internal pressure is trying to straighten it. This would
work, but is hard to arrange mechanically.

Your intuition on this is probably working on the bicycle pump
paradigm: if you force the plunger down to pump air into a low-pressure
bladder it inflates, causing no change in volume and the pumping is
very easy. If you stop up the valve so that the air is all trapped in
the plunger, it is harder. This is different case because you are
working in an atmosphere, where the air behind the plunger is open to
ambient pressure, and the only change you are making is in where the
bladder is relative to the air, which all stays at about the same
pressure.

--
David M. Palmer (formerly @clark.net, @ematic.com)

"John Savard" wrote in message
...

Ah, here we are! Design a spacesuit so that a channel for air to flow
surrounds the astronaut everywhere. And have in *one* spot an
accordion-pleated cylinder that can shrink and expand easily - so that,
as the astronaut moves, it compensates for what happens at all the
joints.

But that doesn't work - the suit is pressurized, so if any part of the
suit can freely shrink or expand, it will just expand as much as
possible to lower pressure inside the suit.

Instead, have a rapid sensor monitoring suit pressure. As the astronaut
begins to make a move that expands his suit, have a motor compress the
compensating volume to keep the suit volume constant - as measured by
the suit pressure!

This has an inevitable time lag, so the conventional design of
constant-volume joints is better.

I don't think either solution will completely work. If you don't make the
joints constant volume, the air pressure will always put pressure on the
*joint* to rotate back to *its* maximum volume. You can't solve this
without making all the joints constant volume.

Think of this as a pneumatic cylinder pressurized to 5 psi when extended.
If you compress the cylinder, the force required will increase the further
you push, since the decreasing volume increases the pressure. If the
pressure increases to 5.5 psi, the force required to hold that cylinder in
that position is 5.5 psi times the cross sectional area of the cylinder.

Now, add to the cylinder a pipe running to a fancy regulator (the design of
which beyond the scope of this thought experiment) that will keep the
pressure to 5 psi. Now compress the cylinder. The force to hold the
compressed position is still 5 psi times the cross sectional area of the
cylinder.

By adding your pressure compensating regulator, you've just reduced the
force required by about 10%. Not a big savings, right? What you really
need to do is figure out a way to keep the volume constant.

One way to do this would be to use a pneumatic cylinder that has separate
ports for each side of its plunger and run a pressure line between the two
ports and pressurize that to 5 psi. Now there is zero force required to
hold the cylinder in any position. It's now a constant pressure joint.

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)