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Basic Hubble Space Telescope Q&A
by
I14R10
on 28 May, 2009 15:17
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I see that there is no Hubble Q and A thread (there's a Q&A with a HST manager on L2), so I would like to start one.
How does Hubble change magnification?
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#1
by
cozmicray
on 28 May, 2009 17:02
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Really different magnification for the different instruments
The focal plane is split up into sections that each of the instruments
and the fine guidance sensors utilize. Each uses relay lenses and mirrors
to direct the light gathered by the main mirror to the sensors. The scope is pointed so the image desired falls on the appropriate area of the
focal plane and directed to instrument sensors.
The telescope is an f/24 Ritchey-Chretien Cassegrainian system with a 2.4 m diameter primary mirror and a 0.3 m Zerodur secondary. The effective focal length is 57.6m.
the Ritchey-Chretien main optics design shown at
http://hubble.nasa.gov/technology/optics.phpUsing the old standard Magnification = 2 x aperature in mm
about 4800x but is limited by diffraction limits.
Light gathering power without atmospheric disturbance is
it's real forte.
http://hubble.nasa.gov/technology/instruments.phpshows the current focal plane arrangement.
Most of the magnification and magic done with computers
manipulating the raw image
I see that there is no Hubble Q and A thread, so I would like to start it
How does Hubble change magnification?
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#2
by
kevin-rf
on 28 May, 2009 18:43
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Using the old standard Magnification = 2 x aperature in mm
about 4800x but is limited by diffraction limits.
Light gathering power without atmospheric disturbance is
it's real forte.
Huh
In a simple visual optical system it focal length of objective divided by the eyepiece focal length.
It gets a bit more complicated when you have a sensor, you need to take into account the size of the pixels.
So to answer you question, you change it by changing the focusing lense on the sensor.
Magnification goes hand in hand with how much of the sky can you see in a single image and in what detail.
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#3
by
mdo
on 30 May, 2009 00:20
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How does Hubble change magnification?
It doesn't.
The magnification is fixed mostly by detector pixel size.
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#4
by
glen4cindy
on 23 Jun, 2009 05:50
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During the first servicing mission, astronauts installed COSTAR to correct the optics problem caused by the improper grinding of the mirror.
I've read that all the the future generations of imaging devices on Hubble were built to correct the error without the use of the COSTAR unit that was removed on STS-125.
This seems to me that it would be like wearing glasses in front of contact lenses. If the COSTAR unit corrected the optics, and future instruments were built with provisions for correcting the optics without COSTAR, then why didn't COSTAR interfere with the optics of the remaining instruments?
Are there multiple image paths within the telescope so that the same "beam" of whatever is being observed is split to various parts of the telescope?
I just cannot understand how COSTAR could be removed without affecting whatever was "looking" at the observations thru the COSTAR unit.
A 2nd observation. It seems really strange that the main computer of the HST is a computer that uses a 486 processor. I guess it's possible that many of the systems on the shuttle are also based on older computer hardware due to them being designed in the late '70's, but, it does not seem possible that a 486 based computer would be capable of operating something as advanced as Hubble. I'm assuming that Hubble is fairly advanced and that aiming and attitude control is somewhat advanced, although there were alot of really complicated things that were accomplished in the Mercury, Gemini and Apollo programs, and ALL of those, of course, came before the 486 processor.
Would I also be correct to assume that NASA was able to accomplish more from the 486 processor than a home or business user would have expected from the processer when it was the one being most used in the PC's of the day?
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#5
by
Comga
on 23 Jun, 2009 06:21
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I don't have time to embed
images , but COSTAR consists of deployable arms, each holding a pair of mirrors. Once faces forward towards the telescope's secondary mirror and the other faces backwards towards the instrument. This second one blocked the light that was headed for the instrument and relayed the light from the first mirror. The image is left in the same focus position, but with the spherical aberration of the precisely but incorrectly shaped primary mirror cancelled by the two mirrors.
Here is to the memory of Dr. Murk Boettema, who derived that fantastic concept.
When an instrument is replaced, and the new one does not require that particular COSTAR relay, that specific arm is retracted. (The fewer reflections the better.) Once they were all retracted, the unit could be and was removed.
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#6
by
tva
on 23 Jun, 2009 07:23
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How long the "exposure time" for a typical "picture" ?
How is the process effected by the fact that the Earth is blocking the line of sight more then half of the time ?
How far is the closest object ever depicted ?
How close can it be ?
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#7
by
Jim
on 23 Jun, 2009 09:42
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1. How long the "exposure time" for a typical "picture" ?
2. How is the process effected by the fact that the Earth is blocking the line of sight more then half of the time ?
3. How far is the closest object ever depicted ?
How close can it be ?
1. Varies immensely
2. It is a factor, but objects can be above or below the ecliptic
3. Mars
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#8
by
Analyst
on 23 Jun, 2009 09:52
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#9
by
ugordan
on 23 Jun, 2009 09:56
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#10
by
mdo
on 23 Jun, 2009 10:10
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1. How long the "exposure time" for a typical "picture" ?
2. How is the process effected by the fact that the Earth is blocking the line of sight more then half of the time ?
3. How far is the closest object ever depicted ?
4. How close can it be ?
1. 10-20 min. is
typical.
Obviously it varies a lot.
2. Celestial targets close to the orbital poles, that is normal to the orbital plane, are in a continuous viewing zone. For other targets the scheduling process places the exposure periods inbetween the occultations. Several exposures of a single target are routinely combined electronically on the ground.
In general the following viewing constraints apply:
- 50 degree solar avoidance angle
- 20 degree from illuminated Earth
- 6 degree from dark Earth limb
3. Galaxy A1689-zD1 at a distance of 13 billion light years, i.e. redshift 7+, is a candidate in the distance category. To be fair though and as so often it was found in collaboration with other observatories, in this case in tandem with Spitzer.
4. Short calibration exposures (flatfielding) of the Earth's atmosphere were taken with WFPC1. The Earth avoidance constraint was apparently waived for that one which otherwise is there to safeguard the sensitive detectors which could be grilled by the intense albedo.
Edit: point 4
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#11
by
tva
on 23 Jun, 2009 10:14
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Moon.
Analyst
It must have been quite challenging for the giros to maintain resolution while aiming at the Moon.
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#12
by
mdo
on 23 Jun, 2009 10:34
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3. Mars
Moon.
Analyst
Earth.
Admittedly, just WFPC1 looking at the dark atmosphere for external flatfield calibration. But it appears the question was more about the theoretical limit anyway.
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#13
by
Jim
on 23 Jun, 2009 11:31
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3. Mars
Moon.
Analyst
Earth.
Admittedly, just WFPC1 looking at the dark atmosphere for external flatfield calibration. But it appears the question was more about the theoretical limit anyway.
Yes, since it can't rotate fast enough to stay pointed at an object on earth.
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#14
by
kraisee
on 13 May, 2010 20:43
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Who was the lead manager in charge of preparing the last Hubble servicing mission?
Ross.
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#15
by
ugordan
on 13 May, 2010 20:48
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It must have been quite challenging for the giros to maintain resolution while aiming at the Moon.
It couldn't track the moon, couldn't keep up with its apparent angular rate in the sky. They just pointed it that way and let the moon slide across the FOV.
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#16
by
Archibald
on 23 Feb, 2011 11:48
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Thread necromancy
Why is Hubble in a 28.5° inclined orbit ? Why not, say, 51.6° (like the ISS) ?
Thermal problems ? or perhaps observing the sky ?
Where different orbits considered at one point in history ?
Thank to the experts...
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#17
by
Jim
on 23 Feb, 2011 12:56
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Thread necromancy
Why is Hubble in a 28.5° inclined orbit ? Why not, say, 51.6° (like the ISS) ?
Thermal problems ? or perhaps observing the sky ?
Where different orbits considered at one point in history ?
Thank to the experts...
There was no 51.6° ISS when HST was developed and launched. SSF was going to 28.5.
28.5 get more performance for the higher orbit (HST is in the highest flown STS orbit)
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#18
by
JayP
on 23 Feb, 2011 17:59
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Thread necromancy
Why is Hubble in a 28.5° inclined orbit ? Why not, say, 51.6° (like the ISS) ?
Thermal problems ? or perhaps observing the sky ?
Where different orbits considered at one point in history ?
Thank to the experts...
Just for clarification, Launch site orbital mechanics 101.
The best performance you are going to get from llifting off from any point on the eart is by launching due east. That is because you get the most advantage from the earth's spin. Standing on the equator, you would allready be travelling eastward at over 1100 MPH. That is 1100 out of the 17,500 MPH needed to get into orbit that you don't have to use your rocket for. Any other direction reduces the amount of velocity your rocket is adding to your eastward velocity.
When you launch due east from a specfic site on the earth, you will end up in an orbit that is inclined to the same degree as was the value of the latitude of your launch site. (unless you make a plane change, but that involves fuel wich ultimately robs you of performance) Since KSC is just about 28.5 deg N. lattitude, max performance launches from their end up in a 28.5 deg orbit.
It's not really this simple, but that is the basics of it.
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#19
by
vsrinivas
on 15 Mar, 2012 23:49
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Thread necromancy act II.
When HST lost the Faint Object Camera to ACS (in '02), it traded resolving power for field-of-view (to ACS/HRC); why was that a tradeoff worth making, given HST already had a wide-field-of-view camera (WFPC/2)?
And with the loss of ACS/HRC, was there enough time/any discussion towards a new high-resolution camera for SM4 (either as part of WFC3 or in place of COS or somesuch?).
Who/how were the instruments for SM4 decided by/on anyway?
Huh