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## Astronauts Begin Final Spacewalk To Repair Hubble94

An anonymous reader writes "Astronauts John Grunsfield and Andrew Feustel began the fifth and final spacewalk of their Hubble Space Telescope repair mission this morning at 8:20AM. During their spacewalk the two will install the second battery group replacement in an equipment bay above the Wide Field Camera 2 and next to the compartment where the first battery set was installed on the second spacewalk. Each of the battery module weighs 460 pounds and contains three batteries. The batteries provide electrical power to support Hubble's operations during the night when there's no sun to power the solar arrays."
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## Astronauts Begin Final Spacewalk To Repair Hubble

• #### Watch it live (Score:5, Informative)

on Monday May 18, 2009 @11:41AM (#27997593)
Check it out on NASA TV [nasa.gov] if you haven't had the chance yet. Viewing Hubble the way the astronauts see it is a neat experience.
• #### Not above the WFC2 (Score:5, Informative)

on Monday May 18, 2009 @11:41AM (#27997599)
It's actually Wide Field Camera 3 now. It has been exchanged in the first spacewalk.
• #### First tweets from space (Score:5, Informative)

on Monday May 18, 2009 @11:54AM (#27997903)

one of the astronauts is live blogging on twitter from the shuttle

• #### Re:The batteries weigh what? (Score:5, Informative)

on Monday May 18, 2009 @11:55AM (#27997919)
According to my back-of-an-envelope calculations, I get their true weight to be 1729N.

F=GMmr^-2
=G * Mass of earth * mass of box * (Earth's radius + Hubble orbit height)^-2
=(6.67x10^-11 * 5.9742x10^24 * 208.7) * ((6378 + 559)x10^3)^-2
=1729.20 N
• #### Re:The batteries weigh what? (Score:3, Informative)

<hutnick@gmail.com> on Monday May 18, 2009 @12:02PM (#27998063) Homepage Journal

Um, it's the pound [wikipedia.org]. Doesn't everyone know that? 2.2 lbs to the kilo.

While weight certainly means the force created between two masses due to gravity, it is almost always used interchangeably with mass in practice.

-Peter

• #### Re:Can't wait for the Duracell commercial... (Score:3, Informative)

on Monday May 18, 2009 @12:03PM (#27998081)

Sorry to reply to my own post but... I just realized that Duracell already did a space commercial [youtube.com] about an IMAX camera being used in space.

• #### Re:The batteries weigh what? (Score:5, Informative)

on Monday May 18, 2009 @12:06PM (#27998141)

• #### Re:The batteries weigh what? (Score:5, Informative)

on Monday May 18, 2009 @12:07PM (#27998167)

Um, it's the pound. Doesn't everyone know that? 2.2 lbs to the kilo.

While weight certainly means the force created between two masses due to gravity, it is almost always used interchangeably with mass in practice.

Still messed up. Trying to compare a metric unit of mass to a imperial unit of weight using a conversion factor that only works at roughly sea level on earth.

Metric unit of weight - Newton N
Metric unit of mass - Gram g

Imperial unit of weight - Pound lb (you know, like Pound Sterling being a pound of silver?)
Imperial unit of mass - Slugs

• #### Re:The batteries weigh what? (Score:2, Informative)

<hutnick@gmail.com> on Monday May 18, 2009 @12:16PM (#27998333) Homepage Journal

Did you click the link? No one uses slugs. Pounds are commonly used to express mass as well as force (weight).

Since there is a mass version of the pound, and it is defined in terms of kilos the conversions actually work perfectly in any (or no) gravitational field. (Though the conversion factor is exactly 2.20462262, not 2.2.)

Don't get me wrong in all of this. I advocate the metric system. But I don't understand the seemingly willful misunderstanding of the modern imperial system.

-Peter

• #### Re:Proof... (Score:5, Informative)

on Monday May 18, 2009 @12:22PM (#27998451) Homepage

Technically the batteries have the same mass while on Earth as they do while orbiting it. The weight in orbit is zero. (which is the point the above are making)

See here: http://en.wikipedia.org/wiki/Mass_versus_weight [wikipedia.org]

• #### Re:Proof... (Score:1, Informative)

by Anonymous Coward on Monday May 18, 2009 @12:36PM (#27998701)

Are you "weightless" while skydiving?

Only briefly. Once you hit terminal velocity, there is no longer any sensation of falling (no acceleration). For the vast majority of your dive, you "weigh" the same as you do on the ground. Instead of being held up by the floor or a piece of furniture, you are held up by a (relative to you) fast-moving updraft.

• #### Re:Proof... (Score:3, Informative)

on Monday May 18, 2009 @12:57PM (#27999045) Journal

Technically the batteries have the same mass while on Earth as they do while orbiting it. The weight in orbit is zero.

Okay, but you're talking about the lack of the sensation of weight [wikipedia.org].

If there is no contact with any surface to provide such an opposing force then there is no sensation of weight (no apparent weight). This happens in free-fall, as experienced by sky-divers (until they approach terminal velocity) and astronauts in orbit, who feel "weightlessness" even though their bodies are still subject to the force of gravity: they're just no longer resisting it. The experience of having no apparent weight is also known as microgravity.

I wasn't confusing mass with weight, but you still need to exert force to support an object in a gravitational field, and the measure of that force is its weight. The fact that we're in free fall and the object is weightless relative to us doesn't change that.

(IANAAP, so correct me if I'm wrong).

• #### Re:I love NASA TV (Score:4, Informative)

on Monday May 18, 2009 @01:00PM (#27999095) Homepage Journal

mms://209.73.189.79/bcpenc252181?StreamID=81684353&pl_auth=56e0ca2df8a3b81fa447c77c49dbf0f1&ht=120&pl_b=00CEBE2C2D18A488577820B4444A1179CB&CG_ID=1369080&Segment=149773

• #### Re:The batteries weigh what? (Score:2, Informative)

<hutnick@gmail.com> on Monday May 18, 2009 @01:20PM (#27999455) Homepage Journal

There's no question that it's a kludge.

The "mass pound" and "weight pound" may be equal at sea level in a certain location or whatever, but probably not equal at any other gravitational potential

There's no "may" about it. For the Math to work they can only be equal at exactly 1G. The thing is, we never really use the "weight pound" in practice. I mean, if someone asks you what you weigh do you ask for a reference altitude (or gravitational force)? Absurd.

Put it this weigh (yuk-yuk), if you want to buy a pound of bananas, are you looking for half a kilo of bananas? Or four and a half newtons of bananas?

Always glad to rise above the hoi polloi ;-)

-Peter

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