NASASpaceFlight.com Forum
General Discussion => Q&A Section => Topic started by: I14R10 on 05/28/2009 03:17 pm
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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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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.php
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.
http://hubble.nasa.gov/technology/instruments.php
shows 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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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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How does Hubble change magnification?
It doesn't.
The magnification is fixed mostly by detector pixel size.
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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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I don't have time to embed images (http://www.spaceaholic.com/us_artifacts.htm/) , 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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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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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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3. Mars
Moon.
Analyst
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3. Mars
Moon.
http://photojournal.jpl.nasa.gov/catalog/PIA01541
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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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Moon.
Analyst
It must have been quite challenging for the giros to maintain resolution while aiming at the Moon.
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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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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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Who was the lead manager in charge of preparing the last Hubble servicing mission?
Ross.
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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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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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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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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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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?
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Since it was being discussed off topic in another thread I thought I would ask this in the Hubble thread.
I have never under stood how (and why) Hubble's CMG's (Gyro's) wore out and broke. Anyone have any insight and a reasonable layman's explanation for it?
Is it bearings, is it rotors or stators fowling up.
I just don't understand, I would have thought in Zero G you can use a magnetic bearing that keeps the shaft centered, or an air bearing, and a brushless motor. I'm just a little curious what the issue was.
I look at all the spin stabilized GEO birds over the decades and how the motor's despun the antenna's. They seemed to last the life of the satellite.
Though, wasn't it the gyro's that did in the International Ultraviolet Explorer.
Just looking for a layman's explanation.
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http://asd.gsfc.nasa.gov/archive/hubble/a_pdf/news/facts/FS12.pdf
I don't know if this was ever confirmed by a postmortem. It would be interesting to find that out.
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So the working theory is corrosion of wires. So a material choice issue. I was not expecting that answer.
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So the working theory is corrosion of wires. So a material choice issue. I was not expecting that answer.
Better read it more carefully. It wasn't the wires or the fluid, it was the way the fluid was injected.
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Yes, oxidation of the wires by the fluid reacting with O2 in the pressurized air. In my book that is a materials compatibility issue.
If the working fluid can break down and create corrosive residue when exposed to O2, then either a different fluid should be used (which is most likely not realistic) or an O2 (or corrosive residue) scavenger should be inserted. Either as an additive or built into the chamber. Switching to an N2 pressurization removes the bulk of the O2 contamination, but is it 100% removed?
Maybe just a rant,
I was really expecting some sort of strange physical wear down effect that limited the life of a component or two.
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It's quite simple to purchase extremely pure N2.
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The last service mission of Hubble was fantastic to watch.
My question would be about the storage of video of that mission.
Does NASA keep all the hours of video of that mission?
If So, how would I request a DVD's of it?
What would be the proper process?
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The last service mission of Hubble was fantastic to watch.
My question would be about the storage of video of that mission.
Does NASA keep all the hours of video of that mission?
If So, how would I request a DVD's of it?
What would be the proper process?
Start Here:
http://archive.org/search.php?query=STS-125%20AND%20mediatype%3Amovies
Specifically Hubble: http://archive.org/details/GMM-10346
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
It has torque bars that react against the earth's magnetosphere for desaturation.
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Another question about the gyros: how come they don't get saturated like the ISS gyros? Hubble doesn't have any thrusters to desaturated them with right?
As Jim said, magnetic torquers - there is a little more info in this old thread:
http://forum.nasaspaceflight.com/index.php?topic=17121.0
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
1) Probably gyroscopes and some method of propulsive deorbit.
2) No. It doesn't make sense to give up orbital altitude for orbital inclination. What in deep space do you want to photograph that can't be photographed from 28.5 deg?
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HST service Mission #4, was executed in 2009.
1) If STS was to be retired in 2016 and a final Servicing Mission #5 was planned for 2015, what modifications would be a priority for this hypothetical HST Service Mission?
b)Guesses on how much Service Mission #5 would extend HST's service life?
2) If ISS was on orbit at it's current inclination of 51.6° and HST was to be launched afterwards. Would planners have launched HST on a different orbit other than 28.5°
1) Probably gyroscopes and some method of propulsive deorbit.
2) No. It doesn't make sense to give up orbital altitude for orbital inclination. What in deep space do you want to photograph that can't be photographed from 28.5 deg?
Thanks
2) I wasnt thinking of imaging capability, I was thinking more in terms of the HST servicing missions having the posibility of using the ISS as a safe haven.
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Although Hubble's 11-tonne mass doesn't sound like a lot compared to the 20+ tonnes that the Shuttle could haul to LEO, I'll bet the Shuttle would have really struggled to lift Hubble to 600 or so kilometers at 51.6°.
The payload capability of a typical expendable launch vehicle would decrease by -- making a WAG here -- 10-ish percent as the altitude is raised from LEO to 600 km and the inclination is increased by 20-30 degrees. The same would be true for the Shuttle, but with the Shuttle plus payload weighing, what, 100 t, the decrease in payload capability would be (0.1-ish)(100 t) = 10 t. Take a due-East LEO capability of 20-some tonnes, reduce it by 10 t or so, and it's not obvious that the Shuttle could lift Hubble to its operational orbit if the inclination were raised to 51.6°.
EDIT: "it's" -> "its" in final sentence
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Around 650lbs of capability for every degree of inclination and 100 lb per nautical mile of altitude
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2) I wasnt thinking of imaging capability, I was thinking more in terms of the HST servicing missions having the posibility of using the ISS as a safe haven.
HST is a big satellite with no thrusters for station keeping. I don't think you'd want it in exactly ISS's inclination.
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Another point is because of the South Atlantic Anomaly (Van Allen dips down over the South Atlantic) you want to be in as low an inclination as possible. The radiation speckles the CCD's.
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Another point is because of the South Atlantic Anomaly (Van Allen dips down over the South Atlantic) you want to be in as low an inclination as possible. The radiation speckles the CCD's.
Good point. Here's another - beta angle. Thermals are worse at higher inclinations.
More I think about it, you really want a telescope as close to equatorial as you can get. Looking out into space, go 0 deg. Looking back at Earth (clouds and bad guys), go polar. :)
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Yet another point--the low-inclination orbit made the original Hubble Deep Field possible, as the telescope cound stare at a single place in space near the north celestial pole for days straight without worry of occultation by the Earth during an orbit. I'm almost certain that the Deep Fields, among HST's greatest achievements, would have been impossible from a high-inclination orbit.
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Yet another point--the low-inclination orbit made the original Hubble Deep Field possible, as the telescope cound stare at a single place in space near the north celestial pole for days straight without worry of occultation by the Earth during an orbit. I'm almost certain that the Deep Fields, among HST's greatest achievements, would have been impossible from a high-inclination orbit.
I think that at least some of the newer Deep Fields are not in the Continuous Viewing Zone.
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Yet another point--the low-inclination orbit made the original Hubble Deep Field possible, as the telescope cound stare at a single place in space near the north celestial pole for days straight without worry of occultation by the Earth during an orbit. I'm almost certain that the Deep Fields, among HST's greatest achievements, would have been impossible from a high-inclination orbit.
Actually, L2 would have been the proper orbit and not LEO
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Yet another point--the low-inclination orbit made the original Hubble Deep Field possible, as the telescope cound stare at a single place in space near the north celestial pole for days straight without worry of occultation by the Earth during an orbit. I'm almost certain that the Deep Fields, among HST's greatest achievements, would have been impossible from a high-inclination orbit.
Actually, L2 would have been the proper orbit and not LEO
Then it would have been impossible for a shuttle to reach Hubble for repairs. Since the primary mirror was figured incorrectly, Hubble would have been a useless piece of junk. The only fix would have been a replacement space telescope.
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Thank you all.
Appears to be no advantage of ISS and HST sharing inclinations.
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Then it would have been impossible for a shuttle to reach Hubble for repairs. Since the primary mirror was figured incorrectly, Hubble would have been a useless piece of junk. The only fix would have been a replacement space telescope.
Which would be cheaper in the first place since it wouldn't have to be manrated or EVA and can be launched by a less expensive launch vehicle.
Four new equivalent ELV launched HST would be cheaper than 4 repair missions.
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Then it would have been impossible for a shuttle to reach Hubble for repairs. Since the primary mirror was figured incorrectly, Hubble would have been a useless piece of junk. The only fix would have been a replacement space telescope.
Which would be cheaper in the first place since it wouldn't have to be manrated or EVA and can be launched by a less expensive launch vehicle.
Four new equivalent ELV launched HST would be cheaper than 4 repair missions.
In hindsight, yes. But would Congress have funded replacements, especially since the first one would have been a failure?
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In hindsight, yes. But would Congress have funded replacements, especially since the first one would have been a failure?
It wouldn't have been as expensive. And, multiple spacecraft is not out of the question.
HST had many compromises due to LEO and Shuttle serviceability.
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Any idea if there is a black astronomy budget?
What value is physics/astronomy research to the military/intelligence sector?
[I'm wondering what 15years of research with a 3-4m hubble could have already revealed]
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Any idea if there is a black astronomy budget?
What value is physics/astronomy research to the military/intelligence sector?
There isn't one
Near zero, and nothing that would have be done covertly.
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New discoveries and science have come out of black programs.
1. Gamma Ray Bursts (GRB's) where first detected by the Vela program (designed to look for evidence of nuclear explosions).
2. The early warning satellite systems (DSP, SBIRS) have and continue to observe and record large meteors/small asteroids that explode in the upper atmosphere. Turning the data over to scientists have not been a smooth process over the years.
3. Some of the KH-9 color film data was used for counting whales.
4. Part of the reason (during the Clinton Admin) for declassifying the KH-1/2/3/4/4a/4b/5/6 data sets was to help researchers better understand climate change.
They are not the primary data from the missions, but it is secondary data that is obtained as a byproduct.
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For example in case of failure next gyroscope can we send small / cheap satellite with gyroscopes and attach itself to Hubble via Soft Capture Mechanism (SCM) ?
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It would cost less in the long run, compete & launch James Web Telescope, WFIRST, & true successor to Hubble. 8 meter optical telescope Super Hubble.
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For example in case of failure next gyroscope can we send small / cheap satellite with gyroscopes and attach itself to Hubble via Soft Capture Mechanism (SCM) ?
there was a study circa 2004-2005, when the Shuttle was grounded post STS-107, and STS-125 (May 2009) was threatened.
The National Academies made a detailed report about robotically servicing Hubble - no Shuttle, no humans.
https://www.nap.edu/read/11169/chapter/7
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It would cost less in the long run, compete & launch James Web Telescope, WFIRST, & true successor to Hubble. 8 meter optical telescope Super Hubble.
But always better have two operational telescopes in space :)
Cheap satellite from off the shelf parts launched as secondary payload on Falcon 9 or heavy will cost fraction of Hubble ;)
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For example in case of failure next gyroscope can we send small / cheap satellite with gyroscopes and attach itself to Hubble via Soft Capture Mechanism (SCM) ?
there was a study circa 2004-2005, when the Shuttle was grounded post STS-107, and STS-125 (May 2009) was threatened.
The National Academies made a detailed report about robotically servicing Hubble - no Shuttle, no humans.
https://www.nap.edu/read/11169/chapter/7
I not mention servicing simply attach cheap Satellite to humble to serve ass gyros do not require this level of complexity.
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Cheap satellite from off the shelf parts launched as secondary payload on Falcon 9 or heavy will cost fraction of Hubble ;)
There are no off-the-shelf telescope systems anywhere near as good as Hubble, so you'd end up with a far less capable system.
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Cheap satellite from off the shelf parts launched as secondary payload on Falcon 9 or heavy will cost fraction of Hubble ;)
There are no off-the-shelf telescope systems anywhere near as good as Hubble, so you'd end up with a far less capable system.
To prolong Hubble life not to send new one.
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Cheap satellite from off the shelf parts launched as secondary payload on Falcon 9 or heavy will cost fraction of Hubble ;)
Why does the type of launch vehicle have to enter the picture. There are many ways to get a satellite into orbit and SpaceX is not the first choice.
Also, cheap satellite and off the shelf parts is not going to work for HST pointing requirements.
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Since it just needs new gyros why not send up one of the commercial crew vehicles with a Strela crane to perform the servicing?
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For example in case of failure next gyroscope can we send small / cheap satellite with gyroscopes and attach itself to Hubble via Soft Capture Mechanism (SCM) ?
Soft capture mechanism may not be strong/rigid enough to translate the precision of movement Hubble needs for pointing.
Since it just needs new gyros why not send up one of the commercial crew vehicles with a Strela crane to perform the servicing?
Many of those options really start to get into the realm of economics. No commercial crew option has the standalone capacity for crew plus parts plus robotics. So it would be a minimum of two launches just to extend certain mechanical parts. With further launches if there's a desire to get the electronics and instruments back to peak condition. Then something has to boost its orbit.
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How about a Spacex Starship recover and return hubble for upgrades?
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For example in case of failure next gyroscope can we send small / cheap satellite with gyroscopes and attach itself to Hubble via Soft Capture Mechanism (SCM) ?
Soft capture mechanism may not be strong/rigid enough to translate the precision of movement Hubble needs for pointing.
Since it just needs new gyros why not send up one of the commercial crew vehicles with a Strela crane to perform the servicing?
Many of those options really start to get into the realm of economics. No commercial crew option has the standalone capacity for crew plus parts plus robotics. So it would be a minimum of two launches just to extend certain mechanical parts. With further launches if there's a desire to get the electronics and instruments back to peak condition. Then something has to boost its orbit.
If they do make Orion launch on a commercial LV it might be an option for servicing Hubble since it can support spacewalks though without an airlock module similar to Pris brought along it would be like the Apollo Skylab repair missions.
I wonder if the airlock module could be left attached to the docking ring?
Orion plus the parts should fit on a single Delta IV Heavy or Falcon heavy the capsule should be refurbishable after an LEO flight as EFT-1 is being reused.
Remove some of the propellants tanks to make room for storage like on the Skylab Apollo missions since even half the delta V would be overkill might even be able to omit the OME for the mission.
If launched on FH only an ESM and FH upper stage along with several smaller parts would be expended which should be fairly low cost mission probably less than a what typical shuttle servicing mission costs.
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How about a Spacex Starship recover and return hubble for upgrades?
just stop
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Not now.
Recover and deorbit and reorbit by Starship has many problems, not many of which scream cheap to solve.
If, and only if Starship actually works well, and is crew-rated, and suitable suits are available at the time it fails (or a mission is decide) might it approach 'cheap'. (lots cheaper than the last servicing mission anyway)
That is - NASA bears no cost whatsoever for their development, just a crewed flight.
Hubble may last this long.
(If you think this means three or twelve years.)