It's worth pointing out that they still have terabytes of data on the ground that hasn't been sifted through, so even if the spacecraft's mission isn't resurrected, we can still expect to hear about new Kepler discoveries over the next year or two.
From the article, this is the second reaction wheel to fail in 8 months. They had redundancy, but I wonder what the cost/benefit would have been to have more backup wheels.
Obviously, I'm an armchair/hindsight 20/20 observer here. I have no clue whether it would have been an been an infeasible engineering feat to have more than 4 wheels. Also, I don't really have a clue what a reaction wheel is.
In your hindsight bit, don't forget to look at not just wheels but every other piece of equipment on the spacecraft. Otherwise, you're just playing a game of whack-a-mole. Add more reaction wheels, then the coolant system fails. Add redundancies there, then the computer fails. Sure, you can include twice as much of everything, but then you end up with something that's vastly more expensive.
Reaction wheel bearings are notorious for failing, having killed numerous science spacecraft. I remain amazed that they have not standardized on magnetic bearings.
It's possible that there's some engineering reason why they haven't. From a quick search and skimming a couple of research papers, it looks like magnetic bearings are used on smaller craft, but it sounds like they're still being actively developed for larger craft.
I guess the tech might not have been available for use on Kepler when they were designing it (they seem to have started design work in the late '90s sometime), or it had some kind of limitation or drawback that they couldn't accept.
Reaction.Wheels.are vert heavy, adding too much redundancy of then make they all more prone to failure, add to rocket fuel costs, and also increase the needed fuel on the ship thrusters and battery size, thus making everything even more heavy.
In short, add more reaction wheels and end with a much more heavy machine, more complex, expensive, and more expensive to launch.
I had a hunch that was the case, but this quote from Wikipedia suggests otherwise
> Since the reaction wheel is a small fraction of the spacecraft's total mass...
The gist from the Wikipedia article suggests momentum wheels (used in Hubble) are very heavy, but reaction wheels, not so much, due to their use for precision movement.
Obviously I defer to someone that has more than a cursory Wikipedia articles breadth of knowledge on the subject.
Am I misinterpreting Wikipedia, or are the reaction wheels on Keppler more than a "small fraction of the mass"?
Momentum wheels are reaction wheels. I'm not sure why the wikipedia article on them thinks differently-- Hubble wasn't gyrostablized at all, it's a telescope, it can't be allowed to spin.
Hubble also masses eleven times that of Kepler. (11,000kg vs 1,000kg) I don't know the actual numbers, but attitude control systems possibly take up a larger percentage of spacecraft mass on Kepler than it does on Hubble.
Given that the kepler telescope exceeds its original mission lifespan by 4 years, it's safe to say that the kepler mission is not really "cut short", more like "cannot keep going".
Kepler was launched 4 years ago, so I think your first sentence is misworded. Its original 3.5-year mission was pushed out 3 years due to issues with noisy data, so it hasn't really completed its original mission yet.
(Not that it hasn't done a great deal of excellent work already, but much more is/was still to come.)
An obvious question that wasn't addressed in the article - could they manually fix it? I don't think most people remember what a punchline Hubble was immediately after its launch, until the rescue mission turned things around.
Obviously, our access to space is much more limited currently, but it seems like finding a way to make it happen via the Russians or even SpaceX (depending on how quickly they can get to manned launch capability) would make a lot of sense.
The saddest news I've read today. However there's still hope that they might resurrect one of the 2 reaction wheels that are currently down so maybe they'll be able to figure that out (in the article they mention that they'll even try that with the first reaction wheel that was shut down a year ago).
Yeah, the killer is the lead times, if it were decided right now to build a replacement it would be a long time before any results would be seen. Too bad the program wasn't devised it terms of building more than one from the start.
