how does the Hubble tracks when it is moving so fast

[neelam]

hi guys i was wondering how does hubble tracks when it is moving so fast.isnt a long exposure required in space?

[narrowbandpaul]

guide stars..... a fair few are required

[skye at night]

It doesn't have to track the way we do as it is in space and does not have to deal with Earths movement...

it does however orbit so has to use gyroscopes to point where determined...

These are some of the bits that have failed in the past and required shuttle missions to service and replace...

Exposure works just the same as here,

the Ultra Deep images were gained from single LONG exposures.

I think James WEBB will be stationary, so will just be a case of pointing and remaining there for exposures..

Steve

[barkis]

The Hubble has something called Fixed Head Star Trackers (FHST), Small Wide field telescopes,and these are tied into the telescopes guidance control.

It also has a catalogue of field stars, which are used to lock on to, when imaging a particular object. They thought of everything when the built this wonder.

Ron.

[Merlin66]

The ultimate off axis guider! Never let it be said they don't work!!!

( Actually there wasn't room to mount the ED80 piggyback!!)

[brianb]

the Ultra Deep images were gained from single LONG exposures.

IIRC they were "track & stack" multiple exposures of the type we're all familiar with. Ultra long exposures would require ultra long dark frames for calibration, that would be a huge waste of telescope time.

I think James WEBB will be stationary, so will just be a case of pointing and remaining there for exposures..

Everything is stationary with respect to itself....

[skye at night]

Yes stacked.. but each one was over 20 minutes....

i think limited by the orbit of the HST...

Something like 8 or 900 images to produce the longest total exposures of a million seconds or 11 days...

Steve

[acey]

They thought of everything when the built this wonder.

Everything except spherical aberration of the primary mirror...

[661-pete]

I think James WEBB will be stationary, so will just be a case of pointing and remaining there for exposures..

I'm not sure if that's true: the JWST will be orbiting the Sun just like the Earth does, and it will presumably also need guide stars and tracking gyros. But it will be a lot further away from the Earth, and being at at a Lagrange point, it will not be subject to the same tidal forces that the HST experiences.

In theory, it ought to be possible to completely stop the HST's sidereal rotation, point it at a target, and expect it to stay there forever. But this would only work if the HST were a perfect sphere and hence not subject to rotational perturbation by the tide.

[brianb]

Everything except spherical aberration of the primary mirror...

But they did think of that .... some idiot built the test equipment to the wrong specification!

[acey]

What happened was that a tiny fleck of pain came off the null corrector, and nobody thought to check the accuracy of the null corrector, so they ended up with a flawed mirror.

They thought of everything except human fallibility.

[661-pete]

What happened was that a tiny fleck of pain came off the null corrector.

Superb typo! :D But nothing compared to the pain which the NASA guys felt when the mistake was discovered!

[NickH]

all $450,000,000 worth of it

Never trust a test engineer... :-)

[acey]

Or a typist!