[DrCaleb]

BartSimpson BartSimpson:

DrCaleb DrCaleb:

Plus, the gyros cannot perform beyond their capabilities. It simply can't rotate Hubble fast enough to track an object on Earth.

The whole device doesn't rotate to track anything. You know this so what are you playing at?

Yes, Hubble, in it's entirety, rotates along 3 axis stablized by gyros. Otherwise it would not be able to view the entire sky.




http://hubblesite.org/the_telescope/nut ... nting2.php


Seriously man, I'm getting worried about you.

[DrCaleb]

Lemmy Lemmy:

When I was in highschool, my physics class built a telescope (8" reflector). The mirror grinding process was interesting. We'd open a bag of soluble grit and take turns massaging it into the glass. Then it got sent away, measured and returned with a different bag of grit and markings on the glass where to rub it. The whole process took months. So when we're talking Hubble, that's a piece of glass more than 100 times larger than that 8" mirror. Even when it's being shaped mechanically, using a computer, it's not hard to understand how easily a small error can occur, affecting its performance.

I read an article about the newest telescope being built, and when the glass is poured it takes several months to cool or something!

The first to come into operation will have seven of these mirrors:



http://arstechnica.com/science/2015/11/ ... -universe/

[Winnipegger]

BartSimpson BartSimpson:

Hubble is a spy satellite. Don't think it hasn't been turned around from time to time to take a look at the earth. All those refueling missions it's needed over the years speak to the numerous times it's been retasked.

BartSimpson BartSimpson:

They're the same mirrors.

I've heard a lot of conspiracies, but this one is wrong. Yes, the military will use anything they can. And there is military heritage. When Richard Nixon was elected, he told the military and NASA they can't have separate launch systems, either combine their funding or neither get anything. NASA was planning a Shuttle to carry astronauts and supplies to an international space station, the design process began in 1968. But it wasn't supposed to construct the space station; they would use Saturn 1B or its successor for that. The military had their own launch vehicles: Atlas and Delta. But they had to combine. Shuttle was originally designed to carry 7 astronauts and 11 metric tonnes of cargo to a station in the same orbit that ISS is now, and the orbiter would be a lifting body to reduce weight. They expanded to lift 27.85 tonnes to Low Earth Orbit. It was later modified to lift 28.8 tonnes, but that was it's initial capacity. It was also changed from a lifting body to delta wing and fuselage to increase it's glide range, to safely re-enter the atmosphere from a polar orbit. Ironically, it never flew a polar orbit. A delta wing and fuselage is heavier than a lifting body. And Shuttle originally was to have a piloted fly-back booster, but Nixon cut their budget so they couldn't afford that. The fly-back booster was replaced by solid rocket boosters, and what the air force calls a drop tank. NASA called that the external tank.

The cargo bay was expanded to accommodate the spy satellite of the time. It was designed for the KH-9 Hexagon, and KH-11 Kennan. This made the cargo hold 15 feet diameter and 60 feet long. Ironically, neither spy satellite were carried by Shuttle. Hubble was designed to fit in the Shuttle's cargo hold, since the cargo hold was designed for military spy satellites, it shouldn't come as a surprise that Hubble ended up looking like a spy satellite.

There was one spy satellite (KH-12?) that used a primary mirror that was flexible, able to compensate for fluctuation in Earth's atmosphere. Hubble has a rigid primary mirror, made of glass, it can't do that. Furthermore, Hubble instruments have a very long focal length. The planetary instruments can focus on planets in our solar system, but can't focus on anything closer than the Moon. Galactic instruments can't focus on anything within our galaxy, much less a planetary object. They certainly can't focus on the Earth.

So, no, Hubble can't be used for Earth observations. It can't be used as a spy satellite. It isn't built for it. But there are spy satellites that look very similar to Hubble.

[BartSimpson]

Not too many years ago NASA received a gift of two surplus spy satellites to be used as space telescopes.

http://www.space.com/16000-spy-satellit ... -nasa.html

Now of what use would these satellites be to NASA if they can't look into outer space?

[DrCaleb]

BartSimpson BartSimpson:

Not too many years ago NASA received a gift of two surplus spy satellites to be used as space telescopes.

http://www.space.com/16000-spy-satellit ... -nasa.html

Now of what use would these satellites be to NASA if they can't look into outer space?

They also don't have instruments useful for space exploration, like are fitted on Hubble or the James Webb Telescope. But, they can, with a refit. And it's cheaper and faster than building new telescopes.

But there is no budget for it.

[BartSimpson]

Winnipegger Winnipegger:

Ironically, it (space shuttle) never flew a polar orbit.

Almost. Had it not been for the Challenger disaster I believe it was Discovery that was being prepped to launch from Vandenberg AFB.

When Challenger blew up Vandenberg was cancelled as a launch site due to scheduling concerns.

[BartSimpson]

DrCaleb DrCaleb:

BartSimpson BartSimpson:

Not too many years ago NASA received a gift of two surplus spy satellites to be used as space telescopes.

http://www.space.com/16000-spy-satellit ... -nasa.html

Now of what use would these satellites be to NASA if they can't look into outer space?

They also don't have instruments useful for space exploration, like are fitted on Hubble or the James Webb Telescope. But, they can, with a refit. And it's cheaper and faster than building new telescopes.

But there is no budget for it.

My point is that while they need to be refitted due to classified equipment being removed the mirrors remain and there are no references whatsoever about replacing them.

[Winnipegger]

Hubble images of Pluto.

[BartSimpson]

DrCaleb DrCaleb:

Yes, Hubble, in it's entirety, rotates along 3 axis stablized by gyros. Otherwise it would not be able to view the entire sky.

You're quite right. I thought they were using the KH-11 model where the gyros and thrusters are used for large movements but a different system is used for smaller movements like tracking ground based targets.

[BartSimpson]

Winnipegger Winnipegger:

Hubble images of Pluto.

The guy who calibrated the telescope probably thought this was pretty decent, too.

[Jabberwalker]

Why would NASA want to see Mickey Mouse's dog?

[Winnipegger]

Actually, that image is very good considering it's from a telescope how far away? It's aphelion (farthest distance from the Sun) is 7,311,000,000 km. It's perihelion (closest to the Sun) is 4,437,000,000 km; last time was September 5, 1989. Here is an image from 4 August 2011, taken by the Keck observatory on a mountain in Hawaii. If you look closely, you can see the moon Charon, above and to the left:


And here is a comparison. An image taken in 1994, and one taken this year by New Horizons:

[DanSC]

Winnipegger Winnipegger:

And here is a comparison. An image taken in 1994, and one taken this year by New Horizons:

Nah, that's just the improvement of graphics once they moved the Hubble from console to PC.

[DrCaleb]

BartSimpson BartSimpson:

DrCaleb DrCaleb:

BartSimpson BartSimpson:

Not too many years ago NASA received a gift of two surplus spy satellites to be used as space telescopes.

http://www.space.com/16000-spy-satellit ... -nasa.html

Now of what use would these satellites be to NASA if they can't look into outer space?

They also don't have instruments useful for space exploration, like are fitted on Hubble or the James Webb Telescope. But, they can, with a refit. And it's cheaper and faster than building new telescopes.

But there is no budget for it.

My point is that while they need to be refitted due to classified equipment being removed the mirrors remain and there are no references whatsoever about replacing them.

Because the mirrors can be adjusted to purpose before launch, just like Hubble was. Once in orbit, you can't change the focal length of the telescope. That's why they had to send a shuttle mission to fix Hubble when the mirror defect was discovered.