But... it’s a telescope. Couldn’t it determine direction from images received from a spotting or wide angle lens? Does it not have one?
Each of the Hubble's gyroscopes only measures rotation around a single axis.
> But... it’s a telescope. Couldn’t it determine direction from images received from a spotting or wide angle lens? Does it not have one?
Hubble does have imaging sensors to allow it to track the stars and orient itself. But the orientation needs to be not only measured very accurately (to within a few millionths of a degree), but also kept stable over long periods of time, in order to avoid motion blur. So the attitude control system needs to have low latency.
In principle it would probably be possible to do this using only image sensors, but it would have been very challenging when that Hubble was designed in the 1980s. It has a number of CPUs, the fastest of which is an 80486 running at 25 MHz.
The fact that we can even achieve this level of precision from a piece of hardware blows my mind.
Not unexpected but reading that now... Absolutely remarkable.
Hmm, I think the second time the gyros needed replacing, and the gyros were the limiting factor on the telescope's lifetime, I'd have installed a redundant set.
There is the star tracker camera (widefield, fast), and the imaging camera (narrowfield, slow).
Star trackers use a fast widefield camera because it's easy to get a good signal:noise ratio (there is a lot of contrast between the stars and the background).
The imaging camera, on the other hand, generally takes much longer exposures (HST subjects are generally very dim, relative to stars). All those beautiful, nebulous HST photographs you see? Those have exposure times on the order of hours or days. In practice, being off by a pixel momentarily is not a big concern -- the amount of "bad" photons you collect during that time is very small.
The gyros are only used for coarse pointing, guide stars are used for much more accurate and precise position sensing during exposures (which is why they are called Fine Guidance Sensors).
So whether it's via robot or human spacewalk (though a manned operation is even more expensive obviously) the issue is the prohibitive expense of getting to the Hubble to fix it.
So 'getting to the Hubble' is pretty low in price, all things considered. Now the hard part: building something that can fix the Hubble. Humans would be good at making repairs, but the SpaceX Dragon capsule doesn't have an airlock, so that won't work easily. Repairs might be doable by a robot, but I suspect the easier option would be to simply attach new parts to it to perform the broken functionality.
If you can build the new piece for $40m, that's $100m to add another 20+ years to the lifespan of this incredible piece of equipment. Heck, sounds like something Bezos might do just for fun and as a test for his New Glenn rockets.
Remote repair using a robot is a whole other issue, and I don't think we have the tech developed to do this reliably any time soon.
I think you'd basically have to engineer something from scratch, which is a big ask. It would be really interesting though! Imagine if you just left the robot up there, plugged in and on standby- ready to activate and do some repairs as needed. We should have one on every major satellite. Give him a box of spares, plug the remote into a 12 year old hopped up on adderall, mute the mic and watch it go.
However, figuring out budget (X-37B is a USAF asset, not a NASA vehicle), designing & constructing a robotic repair system that fits in the cargo bay, etc. would be nontrivial both in terms of price/ROI and the hopefully impending debut of the Webb telescope.
but, please, change my mind and fix it! =)
However, there is a HUGE amount of data still to collect from space-based telescopes. Even a crippled HST is a desperately wanted resource. It benefits us to have as many space telescopes as we can right now.
(NASA estimated the marginal cost of launching a shuttle to be $450 million, which is going to be most of the cost of assembling a big telescope. Note that I said "assembling" and not "developing".)
As soon as this happens, most astronomers will jump ship anyway
Hubble was as successful and long-living as it was because of several manned maintenance, upgrade and repair missions mentioned by others already - but Hubble is in a LEO, only a few 100km from Earth. The JWST? 1.5 million km. So missions like these aren't going to happen, this has to work on the first try.
https://www.youtube.com/watch?v=dlJtO7EbK-U
This video makes me far more nervous than "7 Minutes of Terror", depicting Curiosity's entry/descent/landing sequence. Far more things have to go right in order for JWST to become operational.
I guess the increased complexity will increase the risk of failure.
The final mission, STS-125/SM4 (servicing mission 4), was done to prolong the life of the telescope. During the 12-day mission, they installed two (2) new instruments and performed two (2) repairs of failed equipment, and six new batteries in addition to replacing gyroscopes. This expected to extend Hubble’s lifespan by five (5) years from 2009.[2] So we were looking at an expected 2014 EOL date.
The 2009 mission was an interesting event in itself with Hubble’s durability aside. During a talk from Dr. Andrew Fuestel, he mentioned how NASA developed specialized tools for him to repair Hubble mid-orbit—which he said were the scariest times of his life—during his three (3) spacewalks.
[1] https://asd.gsfc.nasa.gov/archive/hubble/missions/sm4.html
[2]http://www.cbsnews.com/network/news/space/home/spacenews/fil...
I mean, obviously going on a spacewalk must be pretty intense. But is there a particular difference in doing it to the Hubble?
Or was it scary because he was repairing a very expensive piece of equipment?
[1] https://www.newscientist.com/article/dn7051-gyro-sacrifice-m...
Background information describing Hubble's Pointing Control System.
https://www.spacetelescope.org/about/general/gyroscopes/
[1] 2005 article: https://www.newscientist.com/article/dn7051-gyro-sacrifice-m...
To bad the replacement James Webb Space Telescope is not scheduled till March 20, 2021, 14 years past it's initial launch date of 2007.
It's initial budget was 1.6 billion and it will hit over 9.5 billion when it launches, if it launches. In 2011 Congress moved to cancel the whole thing. If the cost estimate exceeds the $8 billion cap Congress put in place in 2011, as is unavoidable, NASA will have to have the mission re-authorized by the legislature.
Fingers Crossed (My Nasa Photo of the Day Wall Paper isn't going to be so great for the next 3 years I am afraid)
We’ve had this discussion several times:
https://news.ycombinator.com/item?id=4315339
We can iterate faster, making less costly mistakes, and blanket the solar system with robots.
It took about a decade for humans to get to the moon once America entered the space race. Everything is taking several times longer now.
The deputy mission head seems to disagree with you
