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Kullat Nunu
2013-May-15, 07:51 PM
Equipment Failure May Cut Kepler Mission Short (http://www.nytimes.com/2013/05/16/science/space/equipment-failure-may-cut-kepler-mission-short.html?_r=1&)


Kepler was launched with four reaction wheels, but one failed last year after showing signs of erratic friction. Three wheels are required to keep Kepler properly and precisely aimed. Loss of the wheel has robbed it of the ability to detect Earth-size planets, although project managers hope to remedy the situation. The odds, astronomers said, are less than 50-50.

Nasa teleconference starting in a moment (http://www.nasa.gov/home/hqnews/2013/may/HQ_M13-078_Kepler_Status.html).

Kullat Nunu
2013-May-15, 07:55 PM
Kepler has already passed its primary mission time, but larger instrument noise + more noisy stars mean that the original observation time is not enough to find true Earth analogs.

So unfortunately it seems that Kepler cannot tell us how many Earth twins there are...

However, what it has already told us is that compact systems composed of terrestrials are the most typical type of planetary systems in the universe. Given the fact that most stars are red dwarfs, terrestrials in habitable zones are very common! Just different from what was excepted, and their real suitability for life is a big unknown.

Kullat Nunu
2013-May-15, 08:27 PM
Yup. (http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130515.html)


With the failure of a second reaction wheel, it's unlikely that the spacecraft will be able to return to the high pointing accuracy that enables its high-precision photometry. However, no decision has been made to end data collection.

With the earlier death of COROT mission, we have now a total of 0 active space-borne extrasolar planet hunting missions. :(

Romanus
2013-May-16, 05:16 AM
This is profoundly depressing news, though I'll admit that my fixation on exoplanet research (even at the cost of our Solar System) is a bias of mine. That Kepler exceeded its primary mission is a major plus, but that's kind of offset by the noisier-than-expected data which would've made a longer mission at full capacity much preferred.

In any event, hats-off to the Kepler team; I hope they can salvage something wonderful for us, something I've come to expect from the space engineer crowd (and have not yet been disappointed by).

BetaDust
2013-May-16, 09:15 AM
Planet-Hunting Kepler Spacecraft Suffers Major Failure, NASA Says

From Space.com (http://www.space.com/21167-alien-planets-kepler-spacecraft-crippled.html)


The planet-hunting days of NASA's prolific Kepler space telescope, which has discovered more than 2,700 potential alien worlds to date, may be over. More... (http://www.space.com/21167-alien-planets-kepler-spacecraft-crippled.html)


The second of Kepler's four reaction wheels devices that allow the observatory to maintain its position in space has failed, NASA officials announced Wednesday (May 15). More... (http://www.space.com/21167-alien-planets-kepler-spacecraft-crippled.html)

Wikipedia: Kepler Space Observatory (http://en.wikipedia.org/wiki/Kepler_(spacecraft))
NASA website: Kepler Mission (http://www.nasa.gov/mission_pages/kepler/main/index.html)

-- Dennis

Swift
2013-May-16, 12:46 PM
And this from Science News (http://www.sciencenews.org/view/generic/id/350445/description/Kepler_mission_may_be_over)

The telescope that has discovered thousands of exotic, quirky worlds — and a few tantalizingly Earthlike ones — orbiting distant stars is no longer capable of finding planets, at least temporarily and probably for good. Officials with NASA’s $600 million Kepler space telescope announced May 15 that an essential piece of hardware on the spacecraft has failed.

Since May 2009, Kepler has been staring at 170,000 stars and looking for tiny shadows cast by planets crossing in front of them. To enable Kepler to make such precise measurements, engineers installed four pointing devices, called reaction wheels, that turn the telescope and keep it dialed in on its stellar targets. One of the wheels stopped working last July, but the telescope requires only three.

On May 14 Kepler scientists learned that the spacecraft had entered safe mode, which occurs when something is awry. When they tried to restore the telescope to normal operations, another reaction wheel failed to activate. That wheel had been behaving erratically for months, so its failure was not a total surprise. “This is something we’ve been anticipating for a while,” said John Grunsfeld, NASA’s associate administrator of the science mission directorate.

...

While the telescope’s search for planets is over, researchers’ analysis of the data it collected is not. Kepler data has yielded more than 2,700 likely planets and 132 confirmed ones, with more yet to come. In all, Kepler collected almost exactly four years’ worth of data, and the last year or so of that has barely been analyzed.

...

Still, Kepler’s original mission was scheduled for four years, and that’s exactly how long it did its job. Early last year, when Kepler was still at full health, Borucki commented on the importance of the mission: “There is no mission that’s comparable,” he said. “Kepler is the greatest mission NASA has ever flown.”

Even if they cannot get it operational again, and even if there are no further discoveries in the remaining data, it does have to stand as one of NASA's greatest missions.

iquestor
2013-May-16, 01:08 PM
Oh My. :( This is horrible! I know there is a year of data unprocessed, but I am just at a loss for words. :(

weatherc
2013-May-16, 01:10 PM
And this from Science News (http://www.sciencenews.org/view/generic/id/350445/description/Kepler_mission_may_be_over)

Even if they cannot get it operational again, and even if there are no further discoveries in the remaining data, it does have to stand as one of NASA's greatest missions.

Absolutely. Kepler has changed how we view the universe, perhaps as much as Hubble has. I hope we have something like it sent out to replace it sooner than later.

iquestor
2013-May-16, 01:17 PM
Absolutely. Kepler has changed how we view the universe, perhaps as much as Hubble has. I hope we have something like it sent out to replace it sooner than later.

As far as I know, the JWT is still on track for 2018 . Not sure about TPF though. Im just stunned at this news. I knew there was a problem with one of Kepler's reaction wheels but I didnt know its loss would be a deal breaker.

Buttercup
2013-May-16, 01:50 PM
:(

Terrible.

But I guess we can be grateful all other missions and/or instruments "out there" are okay and doing very well (MESSENGER, Cassini, New Horizons, Hubble)...etc.

Nick Theodorakis
2013-May-16, 02:23 PM
It's funny how we got so used missions that have gone way beyond their designed specifications that we are now disappointed when a mission only lasts as long as it was supposed to.

Nick

Swift
2013-May-16, 02:45 PM
I've merged the simlar threads from Astronomy and Space Exploration into a single thread. I've put it in Space Exploration, as it seems to be more on the "mechanics" of the mission, rather than the findings of the mission.

ToSeek
2013-May-16, 02:46 PM
As far as I know, the JWT is still on track for 2018 . Not sure about TPF though. Im just stunned at this news. I knew there was a problem with one of Kepler's reaction wheels but I didnt know its loss would be a deal breaker.

The problem is that one of the reaction wheels had failed already. With this second one (presumably) failing, they're down to two, and there's no way to do three-axis stabilization with only two reaction wheels.

iquestor
2013-May-16, 03:06 PM
The problem is that one of the reaction wheels had failed already. With this second one (presumably) failing, they're down to two, and there's no way to do three-axis stabilization with only two reaction wheels.

Yeah, I forgot that the first one died months ago; saw repoorts of the 4th failure and thought they were discussing the first one.

iquestor
2013-May-16, 03:19 PM
The problem is that one of the reaction wheels had failed already. With this second one (presumably) failing, they're down to two, and there's no way to do three-axis stabilization with only two reaction wheels.

Yeah, I forgot that the first one died months ago; saw repoorts of the 4th failure and thought they were discussing the first one.

Amber Robot
2013-May-16, 08:24 PM
As far as I know, the JWT is still on track for 2018 . Not sure about TPF though.

I thought TPF was canceled.

Romanus
2013-May-17, 04:35 AM
TPF is cancelled, along with SIM (which I was really pulling for at the time). Aside from TESS, there are no other dedicated planet-finding missions on NASA's to-do list. I think JWST will be more useful for characterizing a few planets we already know than helping us find new ones.

Warren Platts
2013-May-17, 08:52 AM
No doubt it's the result of an alien conspiracy. Kepler was on the verge of discovering where they live....

KozmoDean7
2013-May-17, 12:13 PM
We sent a manned mission to fix hubble, would fixing kepler be out of the question?

Swift
2013-May-17, 12:52 PM
We sent a manned mission to fix hubble, would fixing kepler be out of the question?
As best as I understand it, it is out of the question. We currently don't have a vehicle that can reach Kepler (it is not in Near Earth Orbit) and secure it so that repairs could be made (and there is no such vehicle even on the drawing board). And the Hubble was designed for in-orbit repairs, Kepler was not.

iquestor
2013-May-17, 12:58 PM
Kepler is at L1, right?

KozmoDean7
2013-May-17, 02:54 PM
As best as I understand it, it is out of the question. We currently don't have a vehicle that can reach Kepler (it is not in Near Earth Orbit) and secure it so that repairs could be made (and there is no such vehicle even on the drawing board). And the Hubble was designed for in-orbit repairs, Kepler was not.

Could we some how navigate Kepler back to NEO? Fix it then send it back out? It just really sucks we could be losing Kepler, James Webb scope isnt projected till 2018. Thats a lot of waiting haha, Ill get anxious!

Swift
2013-May-17, 03:15 PM
Could we some how navigate Kepler back to NEO? Fix it then send it back out?
Again, I don't have the numbers in front of me, but I really doubt it. I don't think it was designed for such an orbital change once it was "on location". But even if you could, that's only part of the problem. Neither the currently flight ready vehicle for getting humans to orbit (Soyuz), nor the next likely one (Dragon from SpaceX) are designed for such a mission. One of the nice things about the Shuttle was that it was both a means to get humans to orbit, and a platform for working on the satellite. For the Hubble repair missions the Shuttle could use its arm to capture the Hubble and secure it in the cargo bay. None of the vehicles currently in operation or in planning can do anything like that.

And even if you solved all that, the Hubble was designed for in-space repairs, with doors that allowed access, and components that were designed for removal. And even with that designed in, the repair missions were very complex, needed a lot of planning and preparation, and still had a fair amount of "ad-hoc" to them. I doubt Kepler is designed for that sort of repair.

ToSeek
2013-May-17, 03:15 PM
Kepler is at L1, right?

No, it's in an Earth-trailing orbit, gradually receding from us because the period is 372.5 days instead of 365.25 - http://www.nasa.gov/centers/ames/research/2007/kepler-story.html

ToSeek
2013-May-17, 03:17 PM
And even if you solved all that, the Hubble was designed for in-space repairs, with doors that allowed access, and components that were designed for removal. And even with that designed in, the repair missions were very complex, needed a lot of planning and preparation, and still had a fair amount of "ad-hoc" to them. I doubt Kepler is designed for that sort of repair.

Still, there were repairs made to Hubble that were never planned to be made. (Those were the ones that really needed a lot of preparation.) But, still, it would be cheaper and easier to build and launch a new Kepler than to repair the old one.

KozmoDean7
2013-May-17, 04:34 PM
Still, there were repairs made to Hubble that were never planned to be made. (Those were the ones that really needed a lot of preparation.) But, still, it would be cheaper and easier to build and launch a new Kepler than to repair the old one.

Really? Cheaper to build one than repair it, thats crazy. You would think we would design things today, with out current state of technology, to be repairable so we wouldnt have to waste a whole telescope over a part failing.

Swift
2013-May-17, 04:47 PM
Really? Cheaper to build one than repair it, thats crazy. You would think we would design things today, with out current state of technology, to be repairable so we wouldnt have to waste a whole telescope over a part failing.
Making the telescope repairable, and making the parts for the repair are the least expensive part. But there is no vehicle/platform to make sure repairs. It is almost certainly cheaper (relatively) to build a new Kepler, versus reinventing the Space Shuttle.

Solfe
2013-May-17, 05:08 PM
Could Kepler be re-purposed, to look for or image trans-Uranus objects by taking lots of short duration images and stacking them via computers*?

*Edit - or by crowdsourcing... Yes, Cosmoquest, go buy us a space telescope! :)

NEOWatcher
2013-May-17, 05:15 PM
Really? Cheaper to build one than repair it, thats crazy. You would think we would design things today, with out current state of technology, to be repairable so we wouldnt have to waste a whole telescope over a part failing.
Would you pay to have a technician to fly across the country to fix your TV?

KozmoDean7
2013-May-17, 05:27 PM
Would you pay to have a technician to fly across the country to fix your TV?

Completely different, but thanks for trying to be sarcastic, you almost made it.

Amber Robot
2013-May-17, 05:35 PM
Making the telescope repairable, and making the parts for the repair are the least expensive part. But there is no vehicle/platform to make sure repairs. It is almost certainly cheaper (relatively) to build a new Kepler, versus reinventing the Space Shuttle.

Even in the era of the Space Shuttle, it would probably be cheaper to build a new Kepler.

NEOWatcher
2013-May-17, 05:50 PM
Just to keep it in perspective (numbers found mostly on wiki, so I'm not sure of the inclusions or accuracy)

Cost of the scope (and mission?)
Spitzer $800M
Kepler $600M
Hubble $2500M

Plus, I found a reference that the 2008 servicing mission was $900M (more expensive than Spitzer or Kepler)

cjameshuff
2013-May-18, 12:08 AM
Also note that much of the telescope costs are development and design, not just hardware. A replacement telescope wouldn't cost the same as the first one. Even if the Shuttle could reach it, we could probably launch a small constellation of Kepler clones for the cost of one Shuttle launch.

Also, every kilogram of propellant costs thousands of dollars to lift into orbit and takes up mass that could be devoted to redundant or more robust or more capable components. Servicing makes limited sense while we're stuck with using propellant launched from Earth. It takes more work to design things to be serviced in orbit, in some cases it may impair function or reliability, and there's always a chance of something going wrong that can't be repaired. And what you're repairing inevitably falls further and further behind the state of the art, while replacements can be updated as components become obsolete.

Kepler is now years-old hardware in an inaccessible location. It's done its job, proven the approach and given us the observations it was launched to get. We should repeat the success and extend the capabilities in followup missions, not get hung up on keeping the first example of its kind running.

MaDeR
2013-May-18, 11:26 AM
Really? Cheaper to build one than repair it, thats crazy.
Welcome to current state of space technology. Get used to it, it will not change any time soon.

molesworth
2013-May-18, 01:58 PM
TPF is cancelled, along with SIM (which I was really pulling for at the time). Aside from TESS, there are no other dedicated planet-finding missions on NASA's to-do list. I think JWST will be more useful for characterizing a few planets we already know than helping us find new ones.

Don't forget us folks over the pond here. Gaia (http://sci.esa.int/science-e/www/area/index.cfm?fareaid=26) will be launching later this year. It probably won't be detecting smaller, earth-sized planets, but it should find every jupiter-ish-containing planetary system out to about 150 light years, which will be useful in estimating the frequency of earth-like planets.

(I'm watching with interest as my company has some involvement in Gaia (and in JWST too :) )).

Romanus
2013-May-18, 03:11 PM
^
A little perspective is always welcome; I've also been waiting for GAIA with baited breath. :)

ToSeek
2013-May-20, 03:36 PM
Really? Cheaper to build one than repair it, thats crazy. You would think we would design things today, with out current state of technology, to be repairable so we wouldnt have to waste a whole telescope over a part failing.

Well, as noted before, two parts - Kepler was launched with four reaction wheels but only needed three. Unfortunately, this particular brand of reaction wheels was found not to be the most reliable a bit too late to change them out. (The Fermi mission I worked on for a while uses the same ones, and they're holding their breath right now.)

And, as others have pointed out, the issue is not the repairability but the difficulty of getting the repairman there.

Swift
2013-May-23, 03:18 PM
The latest from NASA (http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130521.html)


Following the apparent failure of reaction wheel 4 on May 11, 2013, engineers were successful at transitioning the spacecraft from a Thruster-Controlled Safe Mode to Point Rest State at approximately 3:30 p.m. PDT on Wednesday, May 15, 2013. The spacecraft has remained safe and stable in this attitude and is no longer considered to be in a critical situation.

As part of a normal spacecraft response to a pointing error, redundant electronics were automatically powered off to isolate them as a possible cause. However, once the team recovered the spacecraft to Point Rest State (PRS) and exonerated those systems, they were turned back on, providing full redundancy to the spacecraft. The reaction wheels remain offline. The photometer, which was turned off to reduce the power load, will be turned back on in the near future to keep thermal conditions of the spacecraft within nominal operating parameters. Kepler is not in science data collection.

PRS was developed in order to preserve fuel for an eventual recovery effort once a second wheel failed. This state uses thrusters to control the pointing of the spacecraft, tipping it towards the sun and letting the solar pressure tip it back away, resembling the motion of a pendulum. This is a very fuel-efficient mode, and it also provides an on-demand telemetry link to allow engineers to monitor and command the spacecraft. With nearly a week of PRS operations, the fuel usage appears to be on the low end of our estimates, allowing time for recovery planning.

The operations staff at Ball Aerospace did a wonderful job at developing and implementing PRS. As a result, the spacecraft is not in an emergency condition, and work can be conducted at a more deliberate pace. For the next week or so, we will contact the spacecraft on a daily basis to ensure PRS continues to operate as expected.

Over the coming weeks, an anomaly response team (ART) will evaluate wheel recovery options. The ART includes members from NASA Ames, Ball Aerospace, the Jet Propulsion Laboratory and UTC, the wheel manufacturer. This team has access to a broader reach of experts throughout NASA and industry, and will manage the wheel recovery efforts.

The team will continue to analyze recent telemetry received from the spacecraft. This analysis, and any planned recovery actions, will take time, and will likely be on the order of weeks, possibly months. Any planned commanding will first be vetted on the spacecraft test bed to validate command operability.

Swift
2013-Jun-18, 08:11 PM
From Space.com (http://www.space.com/21570-nasa-kepler-alien-planet-candidates.html)

NASA's Kepler spacecraft has spotted 503 new potential alien worlds, some of which may be capable of supporting life as we know it.

"Some of these new planet candidates are small and some reside in the habitable zone of their stars, but much work remains to be done to verify these results," Kepler mission manager Roger Hunter, of NASA's Ames Research Center in Moffett Field, Calif., wrote in an update last Friday (June 7).

The latest haul brings Kepler's tally of exoplanet candidates to 3,216. Just 132 of them have been confirmed by follow-up observations to date, but mission scientists expect at least 90 percent will end up being the real deal.

And as far as the telescope itself:

Engineers have identified a number of tests that could help gauge the likelihood of bringing back the balky wheels, Hunter said. They're currently developing these commands on the Kepler testbed at Ball Aerospace in Boulder, Colo., where the spacecraft was built.

"It will likely be several weeks before they are ready to implement the commands on the reaction wheels aboard the spacecraft," Hunter wrote in the June 7 update. "We will continue to provide updates on significant changes as these plans develop and mature."

Kullat Nunu
2013-Jun-25, 09:24 PM
Related news -- COROT mission is now officially kaput (http://www.skyandtelescope.com/news/COROT-Mission-Ends-212973011.html) after the engineers fail to revive it.

Swift
2013-Jul-01, 01:09 PM
From Newscientist.com (http://www.newscientist.com/article/dn23715-new-lease-of-life-for-hobbled-planethunter-kepler.html)

Shaky eyesight doesn't have to mean curtains for Kepler, says Keith Horne of the University of St Andrews, UK. He and Andrew Gould at Ohio State University in Columbus suggest that the hobbled telescope can use its gear to take up microlensing, an alternative way to spot planets.

When two stars align in our line of sight, the gravitational pull of the closer star bends and magnifies the light of the further star. If the nearer star has orbiting planets, their gravity provides added magnification.

"The signals from planets are quite large in this case, sometimes even a 100 per cent change of brightness of the star, so it's relatively easy to see these things," says Horne.

The pair estimates that Kepler could find a few dozen exoplanets a year with microlensing. These would be very different from its previous quarry. With transits, it is easier to spot planets that orbit close to their stars crucial for finding worlds warm enough to host liquid water, and maybe life.

Microlensing is better for finding planets further from their stars past a region dubbed the snow line where it would be too cold for liquid water. Studying both extremes would help us understand the borders of the habitable "Goldilocks" zone in between, says Horne.

...

Kepler was not designed for microlensing though, so it might be more cost-effective to use funds for a dedicated mission, says Geoff Marcy of the University of California, Berkeley. NASA is considering one such proposal called the Wide Field Infrared Survey Telescope (WFIRST), which may be built from one of the two spy telescopes the agency received from the US Department of Defence last year.

WFIRST isn't due to launch for at least a decade, though, says Horne. "We think it is better to do microlensing with Kepler now," he says. "You could learn so much that you might change the design of the future mission."

Swift
2013-Jul-08, 03:43 PM
From NASA.gov, a July 3 update (http://www.nasa.gov/content/kepler-mission-manager-update-preparing-for-recovery/)


Operations in Point Rest State (PRS) have continued for the spacecraft. The spacecraft was placed in PRS on May 15, 2013, after the failure of reaction wheel 4. It has been 53 days since the spacecraft collected new science data.

As noted in the last update, the team has made adjustments to onboard fault parameters for the star trackers to lessen the possibility of entry into safe mode. We have also made additional adjustments to the Thruster-Control Safe Mode to improve its fuel efficiency. This provides yet more protection for spacecraft fuel reserves while the team continues to work on reaction wheel performance assessment and recovery plans.

The engineering team has devised initial tests for the recovery attempt and is checking them on the spacecraft test bed at the Ball Aerospace facility in Boulder, Colo. The team anticipates that exploratory commanding of Kepler’s reaction wheels will commence mid-to-late July. The Kepler spacecraft will remain in PRS until and during the tests.

Later this month, an update to the data processing pipeline software will be deployed. Called SOC 9.1, this enhancement has been underway for several months and is in the final stages of verification and validation. This software release provides additional refinements to better tease out small planet signatures from the four years of Kepler data. It will also decrease the frequency of false positives.

The team continues to disposition Kepler Objects of Interest (KOIs) found by searching the observational data from Quarters 1 to Quarter 12. With 63 more planet candidates added since the last report, the count now stands at 3,277.

Swift
2013-Jul-19, 12:19 PM
Testing 1, 2, 3.... test... test...

From CNN.com (http://edition.cnn.com/2013/07/18/us/nasa-kepler/index.html?hpt=hp_mid)

Kepler has been sidelined since mid-May, when a reaction wheel that helps aim the spacecraft's telescope failed. Controllers launched a series of tests that will determine whether that device can be restarted, or whether another reaction wheel that quit in July 2012 can be reactivated.

Controllers have remained in communication with the craft, which is about 45 million miles from Earth. It takes about four minutes for a radio signal to traverse that gap.

In the first round of tests, telemetry from the craft indicated the wheel that shut down in May spun counterclockwise, but didn't respond to commands to turn clockwise, NASA reported. Controllers will go ahead with tests scheduled for next week on the other wheel while they study the results of Thursday's effort.

Kepler project manager Roger Hunter called Thursday's findings "an interesting development."

"While this is a positive start, it is very early in the multi-stepped process to characterize the performance of the reaction wheels and to determine if one could return to operation," Hunter said in a written statement. "The team will remain focused on the upcoming tests and report the cumulative test results at the end of the month."

Grant Hatch
2013-Jul-21, 06:57 AM
Unbelievable! I just read an article about the reaction wheels. The motors in them use BALL BEARINGS which are suspected of causing the failure! Hasn't anyone ever heard of MAGNETIC BEARINGS!!! Sheesh....


http://www.skf.com/group/products/magnetic-systems/technology-key-benefits/active-magnetic-bearings/index.html


http://www.skf.com/group/products/magnetic-systems/magnetic-systems-applications/semiconductor-vacuum-equipments/index.html

profloater
2013-Jul-21, 11:21 AM
Unbelievable! I just read an article about the reaction wheels. The motors in them use BALL BEARINGS which are suspected of causing the failure! Hasn't anyone ever heard of MAGNETIC BEARINGS!!! Sheesh....


http://www.skf.com/group/products/magnetic-systems/technology-key-benefits/active-magnetic-bearings/index.html


http://www.skf.com/group/products/magnetic-systems/magnetic-systems-applications/semiconductor-vacuum-equipments/index.htmlAha you see the limits of mechanical engineering even in space where vacuum and temperature fluctuations abound. Ball bearings seem a good choice to me, magnetic bearings are not stable you need a reference thrust bearing at least, and they are not anything like as stiff as a ball bearing. you want a passive (no energy use) bearing and in high performance systems like this you will find angular contact ball bearings with preload offer the highest stiffness, lowest friction longest life and the quality of precision in these is at the limits of what is theoretically achievable. There will be dust issues, or in other words sealing issues, plus weird stuff like static discharge pitting the balls. even maybe heat transfer issues.

Grant Hatch
2013-Jul-21, 04:10 PM
Aha you see the limits of mechanical engineering even in space where vacuum and temperature fluctuations abound. Ball bearings seem a good choice to me, magnetic bearings are not stable you need a reference thrust bearing at least, and they are not anything like as stiff as a ball bearing. you want a passive (no energy use) bearing and in high performance systems like this you will find angular contact ball bearings with preload offer the highest stiffness, lowest friction longest life and the quality of precision in these is at the limits of what is theoretically achievable. There will be dust issues, or in other words sealing issues, plus weird stuff like static discharge pitting the balls. even maybe heat transfer issues.

Given the problems that plague the contact bearings.....dust, sealing, static discharge pitting, FAILURE..... I think I'd be looking at solving the stability problems of magnetic bearings! Perhaps a series of "reference" thrust bearings which could be brought online one after the other as they inevitably fail could be used to stabilize. The magnetic main bearings should last much longer.

profloater
2013-Jul-21, 04:30 PM
Given the problems that plague the contact bearings.....dust, sealing, static discharge pitting, FAILURE..... I think I'd be looking at solving the stability problems of magnetic bearings! Perhaps a series of "reference" thrust bearings which could be brought online one after the other as they inevitably fail. The magnetic main bearings should last much longer.

The magnet bearings you referenced are active, not passive active magnets can be stable when the control circuit is faster than the perturbation. However these reaction wheels have to survive launch accelerations and then work with minimal friction and quite large gyro forces. In a watch you might use a needle in a diamond socket, diamond gets rid of heat well but clearly the needle strength is a limit. However a plain bearing using a diamond ring might be interesting. Indeed plain bearings can do quite well but there is always some friction. If you had energy to spare, hydrostatic bearings would be even better with hydrodynamic taking over when the wheel is spinning. The bearing would be off if the wheel is locked, fired up before and during acceleration then off again above a certain speed. The fluid would be like diff pump oil, very low vapour pressure and hopefully sealed into the system. Or you might use a gas such as nitrogen. If one wheel is spinning you might even harvest the pressure to help the other wheels. This might outlast a ball bearing but the balls win on simplicity. I would hope the wheels could be directly driven as rotors avoiding separate motors and seals.

Grant Hatch
2013-Jul-21, 05:04 PM
Aha, interesting about the active mag bearing control circuit. I wonder how much cost and weight a magnetic bearing system would have added to Kepler?

profloater
2013-Jul-21, 05:17 PM
Aha, interesting about the active mag bearing control circuit. I wonder how much cost and weight a magnetic bearing system would have added to Kepler?

do you happen to know the mass and second moment of inertia of the reaction wheels used on Kepler, afraid I don't ?

Grant Hatch
2013-Jul-22, 05:21 PM
No I don't.

ToSeek
2013-Jul-22, 05:28 PM
do you happen to know the mass and second moment of inertia of the reaction wheels used on Kepler, afraid I don't ?

They're apparently the same models as described in this paper: www.spiedl.org/data/Conferences/SPIEP/28116/589904_1.pdf

profloater
2013-Jul-22, 05:33 PM
well the whole thing is about one ton and looking at a diagram the wheels are maybe 10 kg or so, they spin all the time. Has done four years like that. Hard dust is bad news for angular contact ball bearings, even small dust, but I would expect something like ferrofluid (magnetic) seals to eliminate dust ingress.

Swift
2013-Sep-03, 08:49 PM
There is an interesting piece on UT about a new mission proposal for Kepler, looking for exoplanets around white dwarfs, for which two reaction wheels would be sufficient.

LINK (http://www.universetoday.com/104484/kepler-can-still-hunt-for-earth-sized-exoplanets-researchers-suggest/)

antoniseb
2013-Sep-03, 09:08 PM
There is an interesting piece on UT about a new mission proposal for Kepler, looking for exoplanets around white dwarfs, for which two reaction wheels would be sufficient.
...
Which was also noted in this morning's Fun Papers entry in the Astronomy section.

Swift
2014-Dec-22, 12:03 AM
I thought there might be another, more appropriate thread... but this will do (I'm open to other suggestions).

From Science News (https://www.sciencenews.org/article/revived-kepler-telescope-finds-first-exoplanet?tgt=nr)

The Kepler space telescope has bagged its first confirmed planet since being benched in the summer of 2013 by a broken part used to steady the spacecraft (SN: 9/21/13, p. 18).

The planet, named HIP 116454b, sits 180 light-years away in the constellation Pisces. Kepler detected the planet, which is about 2.5 times as wide as Earth, as a brief dip in starlight as HIP 116454b passed between its sun and the telescope. Follow-up observations at the Telescopio Nazionale Galileo, an Italian telescope on the Canary Islands, provided the planet’s mass: roughly 12 times that of Earth. HIP 116454b is probably either a water world or a mini-Neptune, astronomers report in a paper posted online December 18 and accepted to the Astrophysical Journal.

Glom
2014-Dec-22, 10:51 AM
I'm amazed that they can use solar wind to stabilise the spacecraft. I would have thought the aspect would need to be huge to allow such a small force to have an effect

Launch window
2014-Dec-24, 01:59 PM
Interesting planet either way so its going to be a watery world or a a gaseous atmosphere like a mini-Neptune. Love seeing the artists speculative illustrations of these worlds.

selvaarchi
2016-Mar-21, 10:41 PM
Almost 3 years ago this thread was started with a sad note Kepler mission may end soon. And now it is still doing great science :D :clap:

http://news.xinhuanet.com/english/2016-03/22/c_135210231.htm


Scientists using the U.S. Kepler space telescope said Monday they have captured for the first time the brilliant flash of an exploding star's shockwave, called a "shock breakout," in the visible light range.

The researchers, led by Peter Garnavich, an astrophysics professor at the University of Notre Dame, Indiana, analyzed light captured by Kepler every 30 minutes over a three-year period from some 50 trillion stars.

They were hunting for signs of massive stellar death explosions known as supernovae, which begin when the internal furnace of a star runs out of nuclear fuel causing its core to collapse as gravity takes over.

During an supernovae, a supersonic shockwave is sent out from the star's core, which will then cause a bright flash of light, called a "shock breakout," when it reaches the surface of the star.

"The flash from a breakout should last about an hour, so you have to be very lucky or continuously stare at millions of stars just to catch one flash," said Garnavich.

selvaarchi
2016-Apr-09, 10:25 AM
RED ALERT Kepler spacecraft in emergency mode

http://www.nasa.gov/feature/mission-manager-update-kepler-spacecraft-in-emergency-mode


During a scheduled contact on Thursday, April 7, mission operations engineers discovered that the Kepler spacecraft was in Emergency Mode (EM). EM is the lowest operational mode and is fuel intensive. Recovering from EM is the team's priority at this time.

The mission has declared a spacecraft emergency, which provides priority access to ground-based communications at the agency's Deep Space Network.

Initial indications are that Kepler entered EM approximately 36 hours ago, before mission operations began the maneuver to orient the spacecraft to point toward the center of the Milky Way for the K2 mission's microlensing observing campaign.

The spacecraft is nearly 75 million miles from Earth, making the communication slow. Even at the speed of light, it takes 13 minutes for a signal to travel to the spacecraft and back.

The last regular contact with the spacecraft was on April. 4. The spacecraft was in good health and operating as expected.

selvaarchi
2016-Apr-11, 04:33 PM
Good news - Mission operations engineers have successfully recovered the Kepler spacecraft from Emergency Mode (EM).

http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-from-emergency-and-stable


On Sunday morning, the spacecraft reached a stable state with the communication antenna pointed toward Earth, enabling telemetry and historical event data to be downloaded to the ground. The spacecraft is operating in its lowest fuel-burn mode.

The mission has http://deepspace.jpl.nasa.gov/cancelled the spacecraft emergency, returning the Deep Space Network ground communications to normal scheduling.

Once data is on the ground, the team will thoroughly assess all on board systems to ensure the spacecraft is healthy enough to return to science mode and begin the K2 mission's microlensing observing campaign, called Campaign 9. This checkout is anticipated to continue through the week.

bknight
2016-Apr-11, 05:48 PM
I couldn't open you link:
http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-from-emergency-and-stable

I meant this link:
http://deepspace.jpl.nasa.gov/cancelled

selvaarchi
2016-Apr-11, 08:54 PM
I couldn't open you link:
http://www.nasa.gov/feature/mission-manager-update-kepler-recovered-from-emergency-and-stable

I meant this link:
http://deepspace.jpl.nasa.gov/cancelled ;

The link is within the NASA article and I cannot open it either :(

01101001
2016-Apr-11, 09:52 PM
If you go to the first-cited page, the NASA article, you'll see the offered snippet is a misquote, and the "cancelled" link is bogus -- and should have been a link to Deep Space Network home page.

selvaarchi
2016-Apr-11, 11:47 PM
If you go to the first-cited page, the NASA article, you'll see the offered snippet is a misquote, and the "cancelled" link is bogus -- and should have been a link to Deep Space Network home page.

Thanks 01101001

selvaarchi
2016-Apr-23, 01:24 PM
To the Kepler team - congratulations :clap: They have put it back on the job as the K2 mission searching for exoplanets—planets beyond our solar system.:D

http://www.nasa.gov/feature/ames/kepler/mission-manager-update-kepler-recovered-and-returned-to-the-k2-mission


The team began the process of returning the spacecraft to science late on Tuesday. The process involved a succession of steps over the course of the next two days. The pointing tables and science targets—instructions that tell the spacecraft where to look and at what—were reloaded and confirmed, onboard logs and counters were reset and a new command sequence was created, tested and uploaded to account for the late start of the campaign. The spacecraft is now ready for science operations, officially starting K2's new gravitational microlensing campaign, known as Campaign 9 or C9.

During NASA's Deep Space Network (DSN) contact with the spacecraft yesterday, flight operations engineers at Ball Aerospace and the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado, both located in Boulder, turned the spacecraft to point the telescope towards the center of the Milky Way galaxy to start collecting data for C9.

The K2 microlensing team and the ground-based observatories collaborating on C9's global experiment in exoplanet observation are searching through the collected data from the ground telescopes for possible events suitable for observations on larger telescopes, such as the 10-meter telescopes at the W. M. Keck Observatory atop Mauna Kea in Hawaii. During the three-day campaign break, beginning on May 24, data accumulated to that point will be downlinked from the spacecraft to Earth. Shortly thereafter, the scientists will have their first chance to see K2’s view of the same events seen on the ground.

01101001
2016-May-10, 11:19 PM
Takes a lickin'. Keeps on tickin'.

space.com: NASA Finds 1,284 Alien Planets, Biggest Haul Yet, with Kepler Space Telescope (http://www.space.com/32850-nasa-kepler-telescope-finds-1284-alien-planets.html)


The number of known alien planets has just gone up by more than 60 percent.

Swift
2016-May-11, 01:07 AM
Takes a lickin'. Keeps on tickin'.

space.com: NASA Finds 1,284 Alien Planets, Biggest Haul Yet, with Kepler Space Telescope (http://www.space.com/32850-nasa-kepler-telescope-finds-1284-alien-planets.html)
Wow. :clap:

The size distribution graph at that link is very interesting.

CJSF
2016-May-11, 12:57 PM
That graph is interesting, but I think the large number of detections in the super-Earth to sub-Neptune range is due to the instrument and detection method making those planets easier to detect. Otherwise it would seem the Solar System is quite unusual.

CJSF

Grey
2016-May-11, 01:33 PM
That graph is interesting, but I think the large number of detections in the super-Earth to sub-Neptune range is due to the instrument and detection method making those planets easier to detect.I was thinking something similar. I'd love to see someone take those raw numbers, and make an estimate of how frequent planets of various sizes are after accounting for the bias introduced by some being easier to detect than others.

Swift
2016-May-11, 03:29 PM
That graph is interesting, but I think the large number of detections in the super-Earth to sub-Neptune range is due to the instrument and detection method making those planets easier to detect. Otherwise it would seem the Solar System is quite unusual.

CJSF
Absolutely, though I still think it interesting. IIRC, several years ago, a similar graph would have had the peak around Jupiter-sized or larger, and I suspect the shift to super-Earth/sub-Neptune is largely from improved detection.

bknight
2016-May-11, 06:25 PM
Absolutely, though I still think it interesting. IIRC, several years ago, a similar graph would have had the peak around Jupiter-sized or larger, and I suspect the shift to super-Earth/sub-Neptune is largely from improved detection.
I believe your memory is correct as I remember the same distribution, prior to further studies using Kepler.

CJSF
2016-May-12, 03:47 AM
The one fly in the ointment of this assessment is that if it were a case of better detections, there should have been a bigger jump in more large (Saturn-Jupiter) sized planets. Also bear in mind that this graph is across all stellar types. What would a graph look like with just "Sun-like" stars?

CJSF

Superluminal
2016-May-12, 07:28 AM
The one fly in the ointment of this assessment is that if it were a case of better detections, there should have been a bigger jump in more large (Saturn-Jupiter) sized planets. Also bear in mind that this graph is across all stellar types. What would a graph look like with just "Sun-like" stars?

CJSF
Here you are. Section 8.3 on page 8, summarizes G type stars. Estimate is 5.02 planets per G star. Fig. 6 on page 9 has the graph you're asking about.

http://arxiv.org/pdf/1605.02255v1.pdf

CJSF
2016-May-12, 08:24 AM
Thanks!

Sent from my LGL22C using Tapatalk

ToSeek
2016-May-18, 06:18 PM
I was thinking that the "real" distribution would be quasi-asymptotic toward the smaller sizes, but according to this (http://exoplanetsdigest.com/2014/07/25/exoplanet-statistics-and-demographics-update/), there are actually two peaks, one around Jupiter size and one around Neptune size. "The origin of this distribution is not understood and it cannot be due to observational biases alone."

selvaarchi
2016-May-18, 08:43 PM
I was thinking that the "real" distribution would be quasi-asymptotic toward the smaller sizes, but according to this (http://exoplanetsdigest.com/2014/07/25/exoplanet-statistics-and-demographics-update/), there are actually two peaks, one around Jupiter size and one around Neptune size. "The origin of this distribution is not understood and it cannot be due to observational biases alone."

Could that be because we are better at detecting the bigger planets?

ToSeek
2016-May-26, 08:52 PM
Could that be because we are better at detecting the bigger planets?

I believe that would be covered under "observational biases". If it were just observability vs. size distribution, I'd expect a curve that peaks (as planets become of a size to be detected) and then falls (as planets of larger and larger size become less common), not one with two peaks.