Hubble Replacement?

Ground-based telescopes can match HST in some ways using adaptive optics,
but there are some things HST does (such as UV) that ground-based
telescopes will never be able to do.
Don't forget loooooooonnnng exposure times.

Nope. Nobody does single long exposures anyway - that happens later on in
the computer. And ground-based telescopes routinely do several-hour integrations.

Jan

On Thu, 21 Apr 2005 13:42:28 +0200, Jan Vorbrüggen wrote:

Ground-based telescopes can match HST in some ways using adaptive optics,
but there are some things HST does (such as UV) that ground-based
telescopes will never be able to do.
Don't forget loooooooonnnng exposure times.

Nope. Nobody does single long exposures anyway - that happens later on in
the computer. And ground-based telescopes routinely do several-hour integrations.

Is the raw data from "all" exposures routinely saved over the years? A
particular target that is observed this year, last year, 10 years ago?


--
Craig Fink
Courtesy E-Mail Welcome @

Is the raw data from "all" exposures routinely saved over the years? A
particular target that is observed this year, last year, 10 years ago?

In the case of the HST, I'm pretty sure you can get the raw data even
from the first images. At least semi-recent stuff is regularly re-processed
when, for instance, new algorithms for defect removal etc are implemented
or just the calibration constants improved. As computer storage is not a
big cost factor anymore, and the raw data is only a small fraction of all
the data in any case, I can't imagine anybody not archiving the raw data
"just in case".

Jan

On Thu, 21 Apr 2005 15:35:33 +0200, Jan Vorbrüggen wrote:

Is the raw data from "all" exposures routinely saved over the years? A
particular target that is observed this year, last year, 10 years ago?

In the case of the HST, I'm pretty sure you can get the raw data even
from the first images. At least semi-recent stuff is regularly
re-processed when, for instance, new algorithms for defect removal etc
are implemented or just the calibration constants improved. As computer
storage is not a big cost factor anymore, and the raw data is only a
small fraction of all the data in any case, I can't imagine anybody not
archiving the raw data "just in case".


I've heard that the limiting factors wrt Hubble's current life span are
the batteries or the gyros. The batteries being an obvious one, while the
gyros may not be. If they are just being used for attitude determination
during maneuvers, and not the actual maneuver, it should be possible to
extend it's life so that the batteries or orbital decay are the limiting
factors.

Using a wide field camera and decent star map, I would think it would be
possible to use a visual attitude determination algorithm for maneuvering
the Hubble between targets. As the Hubble rotates away from one target, it
could determine it's attitude and attitude rates, then make adjustments
along the way as other stars come into view, and get close enough to it's
new target to acquire it. Kind of like using an old fashioned approach to
finding it's way from one target to the next.


--
Craig Fink
Courtesy E-Mail Welcome @

On Thu, 21 Apr 2005 09:10:12 -0500, Craig Fink wrote
(in article ):

I've heard that the limiting factors wrt Hubble's current life span are
the batteries or the gyros. The batteries being an obvious one, while the
gyros may not be. If they are just being used for attitude determination
during maneuvers, and not the actual maneuver, it should be possible to
extend it's life so that the batteries or orbital decay are the limiting
factors.

HST doesn't "maneuver" at all. It used to rely on occasional visits
from servicing crews for periodic reboost.

--
Herb Schaltegger, GPG Key ID: BBF6FC1C
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." - Benjamin Franklin, 1759
http://www.individual-i.com/

I've heard that the limiting factors wrt Hubble's current life span are
the batteries or the gyros. The batteries being an obvious one, while the
gyros may not be. If they are just being used for attitude determination
during maneuvers, and not the actual maneuver, it should be possible to
extend it's life so that the batteries or orbital decay are the limiting
factors.
HST doesn't "maneuver" at all. It used to rely on occasional visits
from servicing crews for periodic reboost.

Tsk, tsk, Herb - "manoeuver" includes changing the pointing to look at
something interesting.

AIUI, the gyros were expected to last longer, but they have some sort
of design/manufacturing problem that makes them die much earlier than
expected. They are not only required as sensors for pointing - fine
guidance is done seperately by the fine guidance sensors - but to
stabilize the whole craft against torques. Not enough gyros, not enough
stability against random torques.

Jan

On Thu, 21 Apr 2005 10:40:23 -0500, Jan Vorbrüggen wrote
(in article ):

HST doesn't "maneuver" at all. It used to rely on occasional visits
from servicing crews for periodic reboost.

Tsk, tsk, Herb - "manoeuver" includes changing the pointing to look at
something interesting.

Just playing along with Craig's typically-sloppy language. He didn't
specify whether he meant "translation", "rotation" or both, either. :-p

--
Herb Schaltegger, GPG Key ID: BBF6FC1C
"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." - Benjamin Franklin, 1759
http://www.individual-i.com/

On Thu, 21 Apr 2005 17:40:23 +0200, Jan Vorbrüggen wrote:

I've heard that the limiting factors wrt Hubble's current life span are
the batteries or the gyros. The batteries being an obvious one, while
the gyros may not be. If they are just being used for attitude
determination during maneuvers, and not the actual maneuver, it should
be possible to extend it's life so that the batteries or orbital decay
are the limiting factors.
HST doesn't "maneuver" at all. It used to rely on occasional visits
from servicing crews for periodic reboost.

Tsk, tsk, Herb - "maneuver" includes changing the pointing to look at
something interesting.

AIUI, the gyros were expected to last longer, but they have some sort of
design/manufacturing problem that makes them die much earlier than
expected. They are not only required as sensors for pointing - fine
guidance is done separately by the fine guidance sensors - but to
stabilize the whole craft against torques. Not enough gyros, not enough
stability against random torques.




Ah, ok, thanks. So, they are used for attitude control in addition to the
magnetic torquers.

Do, i have this right?:

Course Attitude determination (navigation) - Gyros as sensor

Fine Attitude determination (navigation) - optical (fine guidance sensors)

Course Attitude control (maneuvering) - Magnetic torquers as effector

Fine Attitude control (maneuvering) - Gyros as effector

So, the minimum number of gyros should be one, to look at a star. One gyro
to control body pitch and yaw, allowing for sloppy roll control. Two gyros for
proper roll control. That is, if the gyro's rotational attitude can be
moved to the proper body attitude before the exposure, and the fine
guidance sensors can get the star in the center of the cross hairs.

--
Craig Fink
Courtesy E-Mail Welcome @

On 2005-04-21, Jan Vorbrüggen wrote:
Is the raw data from "all" exposures routinely saved over the years? A
particular target that is observed this year, last year, 10 years ago?

In the case of the HST, I'm pretty sure you can get the raw data even
from the first images. At least semi-recent stuff is regularly re-processed
when, for instance, new algorithms for defect removal etc are implemented
or just the calibration constants improved. As computer storage is not a
big cost factor anymore, and the raw data is only a small fraction of all
the data in any case, I can't imagine anybody not archiving the raw data
"just in case".

Storage is cheap - and all the data is certainly archived for almost all
major telescopes as a routine matter - but it's worth noting the sheer
amount of data involved... several GB per day. Not much now, but fifteen
years back it was certainly a nontrivial investment to handle.

--
-Andrew Gray