Background information describing Hubble's Pointing Control System.
 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:
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 will to do science originates in the urge to explore. Whether we're spending the money to send people or robots, it's not a rational pursuit. We explore because we want to. Why do we want to? No one knows for sure.
Human spaceflight is valuable because things are emotionally different when a human is doing them. That's why spaceflight is so much more expensive when humans are aboard: because we have higher standards for humans, despite the obvious evidence that human life is abundant and cheap. The value of a human to another human is primarily an emotional calculation, not economic.
Even when the mission remote asset is a robot, we focus on the human element. Coverage of robot missions always includes a lot of people cheering at the launch, reactions in the control room, interviews with project leads, etc.
So, I would not be so quick to dismiss human spaceflight based on metrics of efficiency. The whole thing of exploring space is inefficient, and serves no practical purpose. Spaceflight runs on inspiration, and that's something we haven't figured out how to automate (and IMO never will).
> [Peter Flannigan, Nixon's assistant] also had become attuned to the reality that there was limited public support for ambitious post-Apollo space activities. On December 6, he sent a memorandum to the president reporting that “the October 6 issue of Newsweek took a poll of 1,321 Americans with household incomes ranging from $5,000 to $15,000 a year. This represents 61% of the white population of the United States and is obviously the heart of your constituency.” Of this group, Flanigan reported, “56% think the government should be spending less money on space exploration, and only 10% think the government should be spending more money” (Logsdon, 92).
Which is ridiculous, and grossly ignores the economic impacts of NASA's efforts (whether manned or unmanned). But no politicians have ever really bothered to make those arguments. During the FY1971 budget process, a robotic grand tour of the solar system (Jupiter, Saturn, Uranus, Neptune, possibly Pluto due to the alignment of the outer planets) was quasi-considered and rejected due to cost. The Voyager program came out of that debate, at least. But FY1971 was a nasty year for budgeting, and NASA's budgeting in particular:
> NASA had been caught up in a chaotic confrontation between budget choices and broader fiscal considerations, reinforced by a breakdown in the White House policy-making process. That chaos obscured a stark reality—that through its decisions on the FY1971 NASA budget, the Nixon White House and ultimately the president himself had significantly reduced the priority of the space program among the whole range of government activities. In the form of modest funds for continued study of the space station and space shuttle, NASA’s hopes for the future were still alive, but just barely (99).
That's from John Logsdon's After Apollo? Richard Nixon and the American Space Program, which is a fascinating glimpse into some of the challenges NASA faced.
You're right that, had we aggressively pursued--and funded--unmanned space flight, we likely could have done more science. But realistically, that was never on the cards. The problem with counterfactual scenarios is that we're often comparing them to an idealized scenario that relies on hindsight bias. In 1971, nobody at NASA genuinely thought we'd be limited to LEO for decades afterwards. Likewise, it's easy to look at STS and how it shaped manned spaceflight, and then come up with a list of better policy alternatives that could have been pursued with the same money.
That ignores how the program's original approval was tied to specifics of the Space Shuttle. The program's approval was, in large part, due to NASA's acceptance of major engineering changes to gain support from the military and intelligence community though most of the capability they demanded was never actually used. Likewise, the expected cost savings of a reusable space plane were fundamental to its approval. Those cost savings never materialized, and in fact things went the opposite direction. We know that today, and there were clues even enough early on. But while there were probably better manned spaceflight options, STS--flaws and all--was able to build a wide enough base of political and institutional support to get approval. Other post-Apollo options didn't and couldn't.
But the biggest factor, I think, is that manned spaceflight has cultural meaning. Politicians might eye NASA's small fraction of the federal budget covetously as something they could probably get away with raiding, but to date no one has had the guts to kill our manned spaceflight program outright. Probably because nobody wants to play the bastard who tells kids "sorry, astronauts aren't an option now" or destroy those childhood dreams adult voters remember fondly. Even if those adults now think money could be better spend "here at home" (as if we're spending it "out there" at a Space-Walmart or something...sigh). Instead of crowding out unmanned opportunities, manned spaceflight served as a sort of umbrella to give them just enough political protection to make it.
Absent those perceptions, I think there's a damned good chance that the alternative to manned spaceflight wouldn't have been unmanned spaceflight. It'd have been no spaceflight. Maybe not right away, but eventually. Perhaps that could have changed had there been a president along the way willing to genuinely fight for NASA and was willing to spend the political capital needed to persuade enough voters to recognize the economic and scientific benefits offered. Unfortunately, the electorate was never interested in it enough and politicians never saw fit to try and change that. Particularly because the political benefits of successful space missions generally accrue years after the politicians who initially funded the program are out of office. Compared to that, a bridge with their name on it is practically an immediate win.
The deputy mission head seems to disagree with you
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.
This instrument can resolve an angle change of < 0.3 millionths of a degree in one second.
Disclaimer -- am an author.
Edit: and this instrument, using the autocollimator above, can do the same thing for inertial sensing. Same disclaimer applies. https://aip.scitation.org/doi/10.1063/1.4862816
Not unexpected but reading that now... Absolutely remarkable.
Was it installed as a later update? The PowerPC G3 was released in Apple computers in 1997, just a few years later.
It was roughly 45 centimeters (1.48 ft) by 45 centimeters (1.48 ft) by 30 centimeters (0.98 ft), weighed 50 kilograms (110 lb)
It had about 96KB of usable plated-wire memory (32K 24-bit words).
That seems like a lot of weight. I wonder how much was radiation shielding?
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.
But as other mentioned, they had redundant set of gyros...
This is a common fallacy in computer vision. Often people get to a within a pixel and stop because they assume they can't get better. Most times you can get substantially better. I worked on a qr-code like system where the scanner could reconstruct the code from an image with (slightly) less pixels than 'pixels' in the code.
Not obvious a priori, but makes sense.
The light is blurred, with a fairly predictable pattern, so if you fit a function to the shape, you can find the peak of the function and that is the most likely center position for the point source.
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).
“For example, if the Hubble, or its replacement, needs to be fixed, we should have an unmanned answer, for instance”
(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".)
(See "Can we rebuild Saturn V in 2018") https://www.youtube.com/watch?v=mhIfeS3OumY
As soon as this happens, most astronomers will jump ship anyway
Like saying "it just needs to work until Longhorn ships" ;)
In any case, JWST doesn't have UV capability, so it is not a straightforward replacement of what Hubble does. It just able to look at more distant objects because they've all been red shifted into the IR.
Basically it will be launched in March 2021, if at all.
By the way, every-time the launch year approaches they delay it by a good 2 - 3 years, and this has been the case almost forever.
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.
Neither did the Apollo moon landers, or the Gemini missions where NASA first tested spacewalks. Instead they just depressurized the whole cabin, making it into one big airlock. Presumably this would work for the Dragon as well.
Can Dragon 2 do what most capsules do and just cycle the capsule interior into vacuum then open the door? (With everyone in suits first, obviously).
At that point you’d just launch a new one. Earth’s gravity well assesses a steep tax.
The key thing to remember when it comes to space is energy/momentum. Right now, the Hubble Space Telescope is 24,000 lb of mass moving at 4.7 miles per second. To get it back down to earth, you need to somehow slow it down. First, slow it down enough to reach the atmosphere and then protect it as the atmo drag slowed it the rest of the way. I don't even think the Space Shuttle, were it still around, would be capable of doing that.
I think it's instructive that they never tried that with any of the earlier Hubble repair missions.
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.
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. 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.
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?
One of the first was this mission was the last one, it was a difficult repair—SC4 did the first in-orbit repair—to do at the time, especially outside of the telescope. Because when you leave the safety of the shuttle, you’re traveling at a rate of ~17,000MPH and where the hubble orbits, there is a much higher chance of debris floating around than as if they were lower in the atmosphere. So in laymen terms, you’re attached to a cord that is supplying you with O2 and spinning at 17,000 MPH while trying to avoid rocks and other dangerous floating objects.
One other danger was the O2 levels. He said the suits are heavy, all of your tools are attached to you via cords and you have limited time to be outside. If something where to happen in this situation, not only would you become unconscious within seconds from the lack of O2, you’d pretty much be a forever piece of debris floating around the galaxies as your body will never decompose or fall from orbit.
The latter part was one of his biggest worries. He knew that he’s on limited time, he also had to renter the shuttle slow because it’s similar to divers and decompression. If for some reason he went too fast or there was a leak somewhere, his suit would have instantly filled up and the pressure would have blew him apart inside the suit.
Definitely not a walk in the proverbial park.
Thanks for the details!
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.
In the mid-1990s, after Hubble had its optics corrected, researchers were already planning its successor. The catch phrase in NASA at the time was “faster, better, cheaper.” JWT was announced in 1996 to a standing ovation, yet it's current planned launch is due 25 years after that announcement. (note that it's infrared, not optical)
It's pretty easy. Did those missions cost more or less than making a copy of Hubble and launching it?
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.