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Smooth, 6.5 Hour Spacewalk To Fix ISS Ammonia Pump
The ISS crew can breathe a little easier now; the NY Times reports that the ammonia pump repair that the station has needed has now been partly completed, and in less time than expected. More work is scheduled, but, says The Times:
"The astronauts, Col. Michael S. Hopkins of the Air Force and Richard A. Mastracchio, were far ahead of schedule throughout the spacewalk as they detached tubing and electrical connectors from the pump. They were able to remove the 780-pound module and move it to a temporary storage location, a task that had been scheduled for a second spacewalk on Monday. ... Colonel Hopkins and Mr. Mastracchio stepped out of an airlock at 7:01 a.m. Eastern time, and even though they accomplished more than they had set out to do, they were able to return at 12:29 p.m., an hour earlier than had been scheduled. The two encountered few complications."
Ars Technica has video, too.
As everyone knows, all projects involve several trips to Home Depot for the odd tool or bolt that was overlooked in the initial planning stage.
Have gnu, will travel.
I know it's a nitpick, but isn't 7:01 a.m. - 12:29 p.m. more like 5.5 hours? I understand that they were an hour faster than planned (meaning they planned 6.5 hours) but the title seems a bit off nonetheless...
I smell a conspiracy. No WAY government workers finish ahead of schedule, unless it's for breaks, lunch or end of day.
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....while in orbit, where they don't feel the effects of gravity?
They feel the effects of gravity, just not as much gravitational pull from the Earth. Oh, and they still feel the effects of mass -- equal and opposite reaction and all that. Basically means that they were unable to rely on gravitational pull or friction to move the module. Sounds tricky, and not something I'd want to try (in space, 780 pounds will 'fall' whichever direction it is moving, even if you're in the way).
If you were wondering how it could be 780 pounds, I presume that was measured at sea level at STP, and doesn't refer to how much it cost to build.
"ISS crew breathing easier with Ammonia freely flowing".
Well, funnier anyway.
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Why store it? Why not just give it a good push away from the station earthwards?
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First, the pound is a unit of mass as well as a unit of force, thanks to our archaic English unit system. You can keep them apart by using pounds-force (lbf) and pounds-mass (lbm).
Second, the effect of gravity at the height of the ISS is about 88% of what it is at sea level. If it has a mass of 780 lbm, the gravitational force on it will be 689 lbf.
This is low earth orbit, not the moon.
"Ammonia".... Howard f-ed up the space-loo again...
These guys are amazing. Well done! Working without gravity to help you is quite an amazing trick for Earth-based monkeys. I am always greatly impressed by the training and skills of all these people who actually climb out of their tin can into open space. More than anyone I think they fit the spirit of the 50s and 60s "astronaut" image. Excelsior!
They feel the effects of gravity
No they don't.
Gravity is certainly there, keeping the ISS in orbit (as opposed to it shooting off into space in a straight trajectory), but as the astronauts are constantly 'falling' they don't feel the effect of it. This is why there's no up or down, why their bones atrophy and why they feel nauseous when they first arrive.
If you're walking in space and its bumpy then you have a big problem
The space station travels at roughly 17,500 MPH. They're working in (this is per the folks that make the suits) anywhere from -100F to +235F. Good job guys. It really takes a lot of people to crunch numbers and possibilities of failure, what to do if failure occurs, and how to do all of this within certain time restrictions. If mankind can claim any sort of technical achievements (I know most here would like to boast their computer skillz), this, in my mind, is a fine example of folks working together at far distances, and through many challenges. Bravo guys and gals!
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They feel the effects of gravity
No they don't.
Gravity is certainly there, keeping the ISS in orbit (as opposed to it shooting off into space in a straight trajectory), but as the astronauts are constantly 'falling' they don't feel the effect of it. This is why there's no up or down, why their bones atrophy and why they feel nauseous when they first arrive.
Yes they do; they just don't feel the SAME effects. But they're still gravitationally attracted to the module and vice versa.
Unless you're specifically talking about the fact that they don't feel the same gravitational effects they feel when on earth, in which case you're completely correct. It's much more subtle.
I'm sure there are plenty of reasons, but why does the ISS use a complicated ammonia-based refrigeration system? I had always assumed they just dumped the waste heat into space with something akin to the heat sink in my computer.
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Adespoton is spot on. No gravitational force can be detected when in "free fall" which is what space orbit is. Even as gravity may grab you and accelerate you towards a large mass, there is no bodily sensation whatsoever. Every molecule of the bodily is (almost) identically effected. There is nothing to cue the brain that gravity is pulling you, even as you may change direction as a result of it. Very difficult for most people to understand this who are used to feeling earth under there feet, air against their skin, and visual references all around.
....while in orbit, where they don't feel the effects of gravity?
They don't feel the effects of gravity, but they very much feel the effects of inertia.
In this context (i.e., earth orbit) the 780 lbs of the module refers to mass rather than weight. If the module were drifting and they had to stop it by grabbing it while they were connected to the ISS, you can bet they'd feel the effects of inertia. For the two-dimensional analogy, imagine a refrigerator, sliding on a perfectly slippery ice rink.
If it weren't for deadlines, nothing would be late.
So subtle, in fact, that they don't feel it at all.
Stick to metric, it is much easier, a Kilogram is a unit of mass, and a Newton is a unit of force.
F = Ma
g = about 9.8 m/s^2
so if gravity is 88% of Earth sea level, then the force on a 1Kg mass is equal to 1 * 9.8 * 0.88 Newtons, which is about 8.6 Newtons. The imperial system is way to complicated to be useful!
Very definitely they are affected by gravity, or they would not stay in orbit but go off independently of Earth!
Yeah it is surprising how many people think there is no gravity in orbit.
Gravity is only reduced by roughly 10 percent at that distance from earth. The reason it seems like there is no gravity is you are always falling towards the earth. You just happen to keep missing !
Do a retrograde burn and you will stop missing quickly though.
It's easier to fight for one's principles than to live up to them.
pound is force to everyone who understands and uses it regularly. pounds is only mass to idiots on wikipedia with no idea what they're on about
But they're still gravitationally attracted to the module and vice versa.... It's much more subtle.
Yeah, about as subtle as the tidal forces I feel when the moon is overhead. No, actually, a quick back-of-envelope calculation shows it is infinitesimally smaller than that.
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...which is why I used the word "archaic". Yes, kg and newtons are much better units, although there are those who try to corrupt the setup by defining a "kilogram-force" as the weight of one kg.
Incidentally, all the Imperial units are now formally defined in terms of SI units; the pound-mass is defined as 0.45359237 kg. The kilogram is also the only SI unit still based on an actual physical object; there's a platinum cylinder in a vault outside Paris that by definition masses one kg. And even that is on the way out...within a few years the kilogram will be based on the Planck constant.
First, the pound is a unit of mass as well as a unit of force, thanks to our archaic English unit system. You can keep them apart by using pounds-force (lbf) and pounds-mass (lbm).
No it isn't. A pound is a unit of force only. Our archaic English unit system uses the slug as a unit of mass.
Pounds are a unit of weight, measured using a scale, not a balance. Slugs are a unit of mass. Pounds-mass is just retarded.
This is a US based website. People in the US understand pounds of weight. They typically do not understand kilograms, and definitely do not understand slugs, of mass. Using pounds is the most sensible way to report it.
In reference to the Earth at that altitude, it weighs around 700lbs. Space is not a "weightless environment". You cannot make such statements without specifying first that you're operating off the local space station reference frame.
yes "kilogram-force" is ugh!
Many years ago in NZ there where some US warplanes, and I saw the abomination 'Kg/cm^2" (the 2 was actually a superscript) - arghhhh!
also when NZ went metric, and at least a couple of years AFTER the inch was legally define as 25.4mm, cardboard converters were given out stating that an inch = 25.3999997 mm (don't remember the exact number of 9's!)!!!!!
http://www.engineeringtoolbox.com/mass-weight-d_589.html
"The English Engineering System - EE
In the English Engineering system of units the primary dimensions are force, mass, length, time and temperature. The units for force and mass are defined independently
the basic unit of mass is pound-mass (lbm)
the unit of force is the pound (lb) alternatively pound-force (lbf).
In the EE system 1 lb of force will give a mass of 1 lbm a standard acceleration of 32.17405 ft/s^2."
Very definitely they are affected by gravity, or they would not stay in orbit but go off independently of Earth!
Correct, but the point is that they don't feel the effect of gravity because they are in a constant state of free-fall. The orbital motion keeps them from hitting the earth while they're in that state.
If it weren't for deadlines, nothing would be late.
And yet, no self respecting engineer would use the pound-mass measure, as it complicates any calculations in the system by requiring the addition of a unitless gravitational constant term.
There is still the tidal effect.
If you have a non-conducting rod in orbit, it will try and align itself pointing towards the Earth's gravitational centre - so long as other forces do not prevent that.
But the key thing is, is not to propagate the myth that gravity does not apply in orbit - I know what _YOU_ mean (but, did you forget the tidal effect still applies?), but lay people will tend to take what you say at face value, hence my strenuous objection!
There is still the tidal effect.
If you have a non-conducting rod in orbit, it will try and align itself pointing towards the Earth's gravitational centre - so long as other forces do not prevent that.
Yes, correct again. However, the tidal effect takes a long time to synchronize an earth-orbiting object's rotation to the earth. I'm not up on the numbers, but surely it is much longer than a typical space mission -- perhaps even longer than humanity has been in space? I invite correction from those who know better.
In any case, the astronauts still would not feel tidal effects because they are too small. But if they were in orbit around an object with a very strong gravitational field, then they certainly would feel something unpleasant.
But the key thing is, is not to propagate the myth that gravity does not apply in orbit - I know what _YOU_ mean (but, did you forget the tidal effect still applies?), but lay people will tend to take what you say at face value, hence my strenuous objection!
The OP began a discussion about what the astronauts feel, and I was sticking to that topic. But thanks for the clarifications. I agree that one should disabuse lay people from the false notion that there is "no gravity" in earth orbit.
If it weren't for deadlines, nothing would be late.
Using the tidal force was an idea for stabilizing satellites I read about 45 years ago. I don't recall the time periods, but I suspect that it would be significantly less than a year. The longer the 'rod' the more pronounced the effect.
I suspect that they found using gyroscopes gave faster stabilization and a lot more control, while have a 'keel' would have a higher mass penalty and be far less effective than using gyroscopes!
Pounds are a unit of weight
There is also a unit of mass called the pound.
systemd is Roko's Basilisk.
Using pounds is the most sensible way to report it.
It may be the best way for the average American understand it, but that doesn't make it sensible.
systemd is Roko's Basilisk.
Using pounds as a unit of mass is not sensible, as it is a scaled unit that must carry an arbitrary factor along with it if it is to be used in calculations.
I never suggested using pounds as a unit of mass.
Using pounds (weight) as a measurement of something in a weightless environment makes just as little sense.
It would weigh that much if it wasn't in orbit, but it is, so it doesn't.
systemd is Roko's Basilisk.
I never suggested using pounds as a unit of mass.
http://slashdot.org/comments.pl?sid=4585781&cid=45765969
I never suggested using pounds as a unit of mass.
systemd is Roko's Basilisk.