Two of four reaction wheels seized up, critical for precise photometry
Excerpt from the Kepler Mission Manager Update. (h/t to Dr. Leif Svalgaard)
At our semi-weekly contact on Tuesday, May 14, 2013, we found the Kepler spacecraft once again in safe mode. As was the case earlier this month, this was a Thruster-Controlled Safe Mode. The root cause is not yet known, however the proximate cause appears to be an attitude error….
…We attempted to return to reaction wheel control as the spacecraft rotated into communication…but reaction wheel 4 remained at full torque while the spin rate dropped to zero. This is a clear indication that there has been an internal failure within the reaction wheel, likely a structural failure of the wheel bearing. The spacecraft was then transitioned back to Thruster-Controlled Safe Mode.
An Anomaly Review Board concurred that the data appear to unambiguously indicate a wheel 4 failure, and that the team’s priority is to complete preparations to enter Point Rest State. Point Rest State is a loosely-pointed, thruster-controlled state that minimizes fuels usage while providing a continuous X-band communication downlink. The software to execute that state was loaded to the spacecraft last week, and last night the team completed the upload of the parameters the software will use.
The spacecraft is stable and safe, if still burning fuel…In its current mode, our fuel will last for several months. Point Rest State would extend that period to years.
…We will take the next several days and weeks to assess our options and develop new command products. These options are likely to include steps to attempt to recover wheel functionality and to investigate the utility of a hybrid mode, using both wheels and thrusters.
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.
Kepler had successfully completed its primary three-and-a-half year mission and entered an extended mission phase in November 2012.
Even if data collection were to end, the mission has substantial quantities of data on the ground yet to be fully analyzed, and the string of scientific discoveries is expected to continue for years to come….
Read the full Mission Manager Update.
In a New York Times article, astronaut John Grunsfeld, now in charge of NASA Science Mission Directorate under which Kepler operates, is quoted: “For Mr. Grunsfeld, who played mechanic to the Hubble telescope during several lengthy spacewalks, the Kepler malfunction looked particularly frustrating. ‘Unfortunately, it’s not in a place where I can go and fix it,’ he said.”
What does reaction wheel 4 look like?
(see photo at right)
Where are the reaction wheels on the spacecraft?
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too hilarious not to get into the WUWT comments ASAP, even if it’s O/T:
18 May: Sydney Morning Herald: Peter Hannam: Obama gives Aussie researcher 31,541,507 reasons to celebrate
It’s the social media equivalent of hitting the jackpot: having your study tweeted by US President Barack Obama.
Australian researcher John Cook, an expert in climate change communication, was inundated with requests for interviews by US media outlets after Obama took to Twitter to endorse his project’s final report…
Bullying
While most of the interest has been positive, Mr Cook expects some negative attention from those who reject the scientific consensus – something that some academics have found to their dismay.
“Generally the level of hate you get is in proportion to the impact you have,” he said.
“There’s an increase in academic bullying where climate deniers are sending complaints to journals or the university … and this actually works.
“I’ve have anecdotal examples of academics who are scared of that kind of reaction and who are playing things close to their chest – which is a real shame,” he said.
http://www.smh.com.au/environment/climate-change/obama-gives-aussie-researcher-31541507-reasons-to-celebrate-20130517-2jqrh.html
One is reminded of that old saying (I think originally by Robert Heinlein): “Nothing that contains moving parts is ever satisfactory from an engineering viewpoint”
date for Sydney Morning Herald tweet article should be 17 May.
can’t resist adding this:
24 Aug 2012: USA Today: David Jackson: Obama has millions of fake Twitter followers
President Obama’s Twitter account has 18.8 million followers — but more than half of them really don’t exist, according to reports.
A new Web tool has determined that 70% of Obama’s crowd includes “fake followers,” The New York Times reports in a story about how Twitter followers can be purchased.
“The practice has become so widespread that StatusPeople, a social media management company in London, released a Web tool last month called the Fake Follower Check that it says can ascertain how many fake followers you and your friends have,” the Times reports…
http://content.usatoday.com/communities/theoval/post/2012/08/obama-has-millions-of-fake-twitter-followers/1
Nothing lasts forever, at least, not at current levels of technology… and some things have never worked anywhere near as well in space, as they do in a gravity well.
Still as they say, there are years of analysis yet to be done on what Kepler has picked up. Looking forward to seeing it!
Ironic that probably one of the oldest toys known to man, the spinning top, should be the cause of a failure in one of the most sophisticated instruments built by mankind.
“the proximate cause appears to be an attitude error….”
It’s bound to have an attitude problem, it’s a youngster!
Well, I never! Watched a program on BBC TV Channel 5 last titled “Aliens: Are we Alone?”. It was about the Kepler spacecraft and all the planets it had discovered. Impressive science. Photo-shopped aliens we rather junior grade. Sad it’s bust.
Perhaps in the years it can stay in safe mode, a civilian ‘space shuttle’ can go and repair it. It would be cheaper than building yet another orbiting telescope.
This one, again, seems like a misallocation of public funds. Other than the gee-whiz announcements wouldn’t public funds be better spent on things like the Sun, the Moon and all those rocks and comets zooming around a bit closer to home?
I’m all for gathering knowledge just for the sake of knowing but shouldn’t private donations fund projects like these?
I used to build little mechanical devices that had to operate in UHV (ultra high vacuum) as part of my graduate research. You immediately appreciate how engineering becomes a lot more complicated once you have no air. Lubricants vaporize, temperature control is tough; you lose convective and most of conductive heat transfer, and metal likes to “gall” especially stainless steel. I’m amazed the vast amount of stuff sent into space that works as well and as long as it does. From my experience I don’t think ” why did this fail” but “why did it ever work”?
@Ian, nope. It’s orbiting the sun in a slightly longer period orbit than the earth and is already something like half an AU behind us. By the time we have the technology to travel out, repair it and return it’ll probably be on the far side of the sun and cooked like a rotisserie chicken.
David L says “Lubricants vaporize”. But of course that is what they do in a vacuum – and that is why you should not use a lubricant. There are such things as magnets. Where you have an important control function that depends on movement, such as these reaction wheels, you use magnetic bearings. Magnetize the axle, N pole at one end and S pole the other. Then put three small magnets around the N pole end, 120 degrees apart, with their N end to the axle and one more longitudinally with the axle, similar at the S end. Then all magnets repel the axle and since the wheel is not affected by gravity the axle and the wheel “float” in space unaffected by friction. I say “Not affected by gravity” on the grounds that the force of gravity on it is exactly balanced by the outward acceleration due to the orbit.
@Dudley Horscroft on May 17, 2013 at 2:43 am
Very true. My point is one needs complicated engineering solutions to rather simple operations here on the surface such as you described to get around the inability to use simple ball bearings and lubricants. Which, by the way, we used pure Molybdenum Disulphide (the active imgredient in Never-Seez) as a dry lubricant for a lot of applications.
“…the mission has substantial quantities of data on the ground yet to be fully analyzed, and the string of scientific discoveries is expected to continue for years to come….”
…which should be released in full instead of greedily hoarded. FOIA, anyone? 😉
…We attempted to return to reaction wheel control as the spacecraft rotated into communication…but reaction wheel 4 remained at full torque while the spin rate dropped to zero….
I’ve got a bike in my garage like that…..
Off topic:
Are we having a sea ice minimum poll this year?
Would be nice to beat the “experts” over at Neven’s.
And humorous comments aside, this is sad. Of all the ways to fail… sigh.
On the other hand, it did accomplish its primary mission.
Erik Anderson says:
May 17, 2013 at 3:10 am
“…the mission has substantial quantities of data on the ground yet to be fully analyzed, and the string of scientific discoveries is expected to continue for years to come….”
…which should be released in full instead of greedily hoarded. FOIA, anyone? 😉
=================================
Why don’t you ask them for a copy the data? I suspect, don’t know for sure, that it won’t take you long to discover that the problem isn’t that you can’t have the data, but that you won’t be able to make much sense out of it without many years of work and R&D on your part?
But first check http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml and see what is already available to the public
….”the mission has substantial quantities of data on the ground yet to be analyzed”….
Translation: NASA has some ‘data adjustment’ and photo-shopping yet to do….
can’t have the raw space alien flyby photos on the super market tabloid covers….
with those silly “Take Us to Your Leader” bumper stickers showing….
because….obviously….we are now leaderless….what, me worry ?
Unfortunate — Kepler was making a huge number of discoveries. Seems like reaction wheels/gyroscopes are a weak-link for many satellites.
Here’s more on some possible actions:
http://www.universetoday.com/102188/more-insight-on-how-nasa-might-revive-the-kepler-space-telescope/
Re Neil’s comment “David L. masterfully handled Dudley Horscroft’s attempted affront. Even the heights of scientific snobbery are no match for true humility. Well done David.” I’ve carefully checked my comments and David’s and see no ‘affront’ to anyone. I have no problem with David L’s response, either. If anyone was affronted, then I apologize!
Bigger problem is dwisehart’s comment: “@Dudley Horscroft the problem is that these are reaction wheels, which means you want to develop a torque through the bearings–magnetic or otherwise–that will right the spacecraft. So magnetic bearings will work only if they develop a fair bit of torque between the spinning wheel and its mount. That would make any magnetic system large and heavy, two bad qualities for spacecraft.”
Perhaps the problem is my understanding of a “reaction wheel”. If you have a spinning wheel, as per gyroscope, to keep a body correctly aligned in space, if there is friction at the axle bearings the body will start rotating and gradually accelerate as the wheel slows till they are both rotating at the same rate. So you must have no friction at the bearings. What you must be able to do is put a force on the wheel to turn it one way, and the reaction (Newton!) will turn the body the amount you want in the other way. When correctly aligned, remove force. So the force should be applied to the circumference of the wheel – standard three phase AC stuff where rotor and stator are not in contact and hence no friction.
Rob L comments:”Magnetic bearings are not a particularly great solution – they require active electromagnetic control systems to maintain stable operation if operating through zero speed (checkout Earnshaw’s theorum for explanation), or superconducting elements that are just not feasible on a spacecraft. They also need mechanical bearing backups for when/if power or control fails.” The whole point is that a magnetic bearing as I described needs no control system whatsoever. The axle is held away from all contact with other materials by magnetic repulsion. The inverse Square law means that the axle cannot contact the bearings. As it is not spinning except when actually being used to rotate the craft, there are no gyroscopic forces which may overcome the repulsion of the magnets. No back up bearings are needed as there is no power or control system to fail. The only conceivable failure mode is for a permanent magnet to become demagnetized. Far more unlikely than a lubricant failure. See for example one of those toys, where a magnetic ring hovers above a base staying permanently at the same height and the same distance from the rod through the ring. No power employed, no control system. Thinks: you could probably use two of them, glue bits of copper wire between them, and use a few hidden coils around the room to start and stop the rings rotating “as if by magic”! Introduction to elementary electricity and magnetism for High School students.
Attitude error huh? Just like my teenager….
Just about every satellite I have seen fail either lost its gyroscopes or ran out of fuel. Without attitude control, they are just so much space junk. At least this one won’t be a hazard to navigation, and it did give us a bonus year beyond design specs.
Its kind of quaint that some folk here seem to think We’ll ever have another space shuttle or such technology as to be able to repair something in a solar orbit.
@ur momisugly tty
Your quote reminds me strongly of lines to similar effect in Arthur C. Clarke’s novel ‘The City and the Stars’.
Even if that’s not the source that you’re looking for, the book is worth reading for its own sake.
It’s a shame that Cook didn’t think to give a citation to his ‘bullying’ claims. If he had, we could then deplore it, the way we deplore the attempts to bankrupt Anthony’s business, or to ‘re-examine’ a Doctorate award, or to ‘redefine what peer reviewed literature is’, or to call for death camps for climate sceptics. All those bullying instances cited in WUWT. But without such a citation, it’s perfectly reasonable to conclude that just like the ‘death threats that weren’t’, this is a case of DARVO- Denial, Anger, and Reversing Victim and Offender.
@Dudley Horscroft the problem is that these are reaction wheels, which means you want to develop a torque through the bearings–magnetic or otherwise–that will right the spacecraft. So magnetic bearings will work only if they develop a fair bit of torque between the spinning wheel and its mount. That would make any magnetic system large and heavy, two bad qualities for spacecraft.