Author Topic: NASA - Kepler updates  (Read 162029 times)

Offline Jim

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Re: NASA - Kepler updates
« Reply #240 on: 05/15/2013 10:32 PM »
So what kind of redundancy does Kepler have for its reaction wheel system?

Is there a potential case for adding more redundancy for this in future similar spacecraft?

It has redundancy.  It already surpassed its design life.

Offline AnalogMan

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Re: NASA - Kepler updates
« Reply #241 on: 05/15/2013 10:45 PM »
Kepler Mission Manager Update
May 15, 2013
 
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. The spacecraft was oriented with the solar panels facing the sun, slowly spinning about the sun-line. The communication link comes and goes as the spacecraft spins.

We attempted to return to reaction wheel control as the spacecraft rotated into communication, and commanded a stop rotation. Initially, it appeared that all three wheels responded and that rotation had been successfully stopped, 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 teamís 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. Our fuel budget is sufficient that we can take due caution while we finish our planning. In its current mode, our fuel will last for several months. Point Rest State would extend that period to years.

We have requested and received additional NASA Deep Space Network communication coverage, and this morning the Anomaly Review Board approved the transition to Point Rest State later today. Because this is a new operating mode of the spacecraft, the team will closely monitor the spacecraft, but no other immediate actions are planned. 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.

Updates will be provided as information is available.

Regards,
The Kepler Team

http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130515.html

Offline Lee Jay

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Re: NASA - Kepler updates
« Reply #242 on: 05/15/2013 10:52 PM »
So what kind of redundancy does Kepler have for its reaction wheel system?

Is there a potential case for adding more redundancy for this in future similar spacecraft?

It has redundancy.  It already surpassed its design life.

I think Opportunity's design-life exceedance ratio has us spoiled!

Offline jimvela

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Re: NASA - Kepler updates
« Reply #243 on: 05/15/2013 10:56 PM »
AFAIK, these reaction wheels are pretty bulky, so as far as redundancy goes they put in just one spare, which in this case bought them a year of extra time.

Kepler flew with tungsten ballast, cost was the concern not mass.

Quote
You can always make the case for more wheels/more redundancy but in the end there's a number of constraints. Cost, schedule, weight, complexity, reliability.

Armchair pundits always assume that this wasn't done- but it absolutely was.  As one of my colleagues points out, one can buy $10^5 reaction wheels, or one can buy $10^6 reaction wheels.

Kepler at one point was in budget trouble, and program leadership made the bold decisions necessary to get the system on orbit and returning science.  The alternative was cancellation and no science return at all.  Guess which class of wheels the program could afford? 


Quote
A better approach for future spacecraft would probably be to learn what happened to these reaction wheels and make future ones more reliable.

A better approach would be to continue to fund development of new technologies to the point where they could be used on exploration or science missions.  For example, there was discussion about some kind of deployable sail or device to balance solar torques- but no such devices are available and mature enough to risk a great observatory on.

Offline Jim

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Re: NASA - Kepler updates
« Reply #244 on: 05/15/2013 11:04 PM »


AFAIK, these reaction wheels are pretty bulky, so as far as redundancy goes they put in just one spare, which in this case bought them a year of extra time.

You can always make the case for more wheels/more redundancy but in the end there's a number of constraints. Cost, schedule, weight, complexity, reliability. A better approach for future spacecraft would probably be to learn what happened to these reaction wheels and make future ones more reliable.


These were reliable enough.  It exceeded the design life.  There ones with longer design lives, just more expensive.

Offline iamlucky13

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Re: NASA - Kepler updates
« Reply #245 on: 05/15/2013 11:13 PM »
So what kind of redundancy does Kepler have for its reaction wheel system?

Is there a potential case for adding more redundancy for this in future similar spacecraft?

It has redundancy.  It already surpassed its design life.

I think Opportunity's design-life exceedance ratio has us spoiled!

Quite a few different spacecraft have spoiled us. SOHO is a better mission to compare against, since it also depends on reaction wheels. It had a 2 year primary mission, and a pre-planned 4 year extension. It is currently 17 years in and still going.

Of course, as jimvela points out, Kepler had a more restricted budget than SOHO, and it still managed to meet its design life, and more importantly, meet one of its primary goals of setting a lower bound on the estimated numbers of detectable exoplanets. There's a lot of new exoplanet targets to choose from now for study by higher resolution observatories, with 132 confirmed discoveries so far, 2740 candidates, and a decent stack of data still to sift through.

I wonder if the team can potentially calibrate multiple pixels around each target star to give them close to the same photometric accuracy while relying on less accurate pointing, albeit with more data processing being necessary. If I understand right, the processing to do this would have to take place aboard Kepler, due to bandwidth constraints.

Offline Bubbinski

Re: NASA - Kepler updates
« Reply #246 on: 05/16/2013 01:58 AM »
If this is the end of the road for Kepler's planet hunting mission, at least the craft discovered Kepler 62e and 62f before the gyro gave out.  Kepler did a great job, opened a new frontier of exploration.  Hoping TESS and other missions can discover a true earth analog soon!
I'll even excitedly look forward to "flags and footprints" and suborbital missions. Just fly...somewhere.

Offline jimvela

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Re: NASA - Kepler updates
« Reply #247 on: 05/16/2013 05:09 AM »
If this is the end of the road for Kepler's planet hunting mission, at least the craft discovered Kepler 62e and 62f before the gyro gave out.  Kepler did a great job, opened a new frontier of exploration.  Hoping TESS and other missions can discover a true earth analog soon!

There is still Kepler data in the science pipeline! 

Kepler isn't done giving us discoveries, it will be many years of discoveries from the data set that it has returned.

Online jebbo

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Re: NASA - Kepler updates
« Reply #248 on: 05/16/2013 07:55 AM »
I wonder if the team can potentially calibrate multiple pixels around each target star to give them close to the same photometric accuracy while relying on less accurate pointing, albeit with more data processing being necessary. If I understand right, the processing to do this would have to take place aboard Kepler, due to bandwidth constraints.

Generally the aperture for each target is already multiple pixels and the processing is done on the ground.  To do what you're suggesting would make the optimal aperture for each target significantly larger.  This means light from other stars would be included.

The Kepler data is already limited by dilution from nearby stars and, in particular, eclipsing binaries.  So I don't think trying to collect data from the current target list works.

I've heard speculation about use for finding NEOs which might be possible using two wheels + thrusters.  And it might just be possible to look for transits around bright stars while doing this, but this has problems (e.g. charge-bleed).

Online jebbo

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Re: NASA - Kepler updates
« Reply #249 on: 05/16/2013 08:00 AM »
There is still Kepler data in the science pipeline! 

Indeed there is!  Lots of it . . . there were some 18,000 "threshold crossing events" still to examine in the Q1-Q13 data and data from Q14, Q15 and a partial Q16 will increase that.

Many of these will be false-positives but there are many real candidates in there as well, and I'd be astonished is some didn't have a better ESI than Kepler 62e/f.
 
Quote
Kepler isn't done giving us discoveries, it will be many years of discoveries from the data set that it has returned.

I think Boruki said on the conference call last night that there is at least two years of just data analysis and about a decade of work in total . . .
« Last Edit: 05/16/2013 08:01 AM by jebbo »

Offline Chris Bergin

Re: NASA - Kepler updates
« Reply #250 on: 05/16/2013 07:30 PM »
If you're in the UK, there's a pretty decent show on Channel 5 about Kepler's findings and what potential aliens would look like if they were on those planets.

Not as silly as it sounds. Got some decent scientists on.


Offline gospacex

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Re: NASA - Kepler updates
« Reply #251 on: 05/16/2013 07:34 PM »
AFAIK, these reaction wheels are pretty bulky, so as far as redundancy goes they put in just one spare, which in this case bought them a year of extra time.

You can always make the case for more wheels/more redundancy but in the end there's a number of constraints. Cost, schedule, weight, complexity, reliability. A better approach for future spacecraft would probably be to learn what happened to these reaction wheels and make future ones more reliable.

These were reliable enough.  It exceeded the design life.  There ones with longer design lives, just more expensive.

Jim, what sums we are talking about here?

Online jebbo

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Re: NASA - Kepler updates
« Reply #252 on: 05/16/2013 08:45 PM »
Not as silly as it sounds. Got some decent scientists on.

Watching it on 5+1. It's got all the usual suspects: Marcy gets on all these things:-). But more unusually folks like Charbonneau who's done a bunch of work on M dwarfs. Made in 2012, I think based on numbers of candidates.

Offline jimvela

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Re: NASA - Kepler updates
« Reply #253 on: 05/16/2013 10:28 PM »
AFAIK, these reaction wheels are pretty bulky, so as far as redundancy goes they put in just one spare, which in this case bought them a year of extra time.

You can always make the case for more wheels/more redundancy but in the end there's a number of constraints. Cost, schedule, weight, complexity, reliability. A better approach for future spacecraft would probably be to learn what happened to these reaction wheels and make future ones more reliable.

These were reliable enough.  It exceeded the design life.  There ones with longer design lives, just more expensive.

Jim, what sums we are talking about here?

[different jim  :) ]

It's in the ballpark of $X*10^5 vs Y*10^6  (*4 for the spacecraft).

It isn't the only design trade or programmatic cost / benefit decision that impacted mission life (e.g. the gimbal for the HGA was deleted).

The manufacturer of the Kepler wheels is widely known.

"If we could only spend a few more millions" stopped being an option during the Kepler program, so very difficult and disciplined decisions were made.  It worked.  We got Kepler launched and it eventually went into extended mission.

Offline baldusi

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Re: NASA - Kepler updates
« Reply #254 on: 05/16/2013 11:32 PM »
I wonder if Kepler could be used to look into Alpha Centauri, for example. That's three starts with at least one candidate. Of course they are so close that simple land based telescopes should be enough. But maybe some other targets in the 100ly range.

Offline Star One

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Re: NASA - Kepler updates
« Reply #255 on: 05/17/2013 07:20 PM »
If you're in the UK, there's a pretty decent show on Channel 5 about Kepler's findings and what potential aliens would look like if they were on those planets.

Not as silly as it sounds. Got some decent scientists on.



Saw that, rather unfortunate timing though considering.


Offline LouScheffer

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Re: NASA - Kepler updates
« Reply #256 on: 05/24/2013 02:26 AM »
I was trying to figure the odds of Kepler recovery.  To complete the extended mission, they need to (a) restart at least one wheel, and (b) have this wheel, and the other 2, last 8 years total.  So I looked at the other missions that used these wheels:

FUSE was launched June 1999 on a three year mission.  All four wheels failed (2.4 years, 2.5 years, 5.5 years, 8.1 years).  Since they had 2-axis control with magnetic torquers, they could work around all but the last failure. They tried to restart all 4; none succeeded.

HAYABUSA was launched May 2003 on a 4 year intended mission.  2 of 3 wheels failed, at 2.2 years and 2.5 years.  Last one worked until re-entry (7 years).  Failures were worked around since imaging was complete and thrusters could be used after that.

DAWN was launched Sept 2007, on an 8 year mission.  2 of 4 wheels have failed so far; 2.75 years, and 4.9 years.  Currently using thrusters + wheels.

So it does not look good for Kepler.  No dead wheel has ever been restarted that I could find.  Even if it does restart, of the 11 wheels on other missions, at most 4 will make it to eight years, assuming the last Hayabusa wheel would have made it, and the two remaining Dawn wheels keep working.
« Last Edit: 05/24/2013 03:08 AM by LouScheffer »

Offline jimvela

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Re: NASA - Kepler updates
« Reply #257 on: 05/24/2013 02:58 AM »
I was trying to figure the odds of Kepler recovery. 

So it does not look good for Kepler. 

I'm highly constrained with respect to what I can say (vs. what I'd really like to say about those wheels)...

Read this:
http://www.nature.com/news/the-wheels-come-off-kepler-1.13032
« Last Edit: 05/24/2013 02:58 AM by jimvela »

Offline Lar

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Re: NASA - Kepler updates
« Reply #258 on: 05/24/2013 03:15 AM »
I was trying to figure the odds of Kepler recovery. 

So it does not look good for Kepler. 

I'm highly constrained with respect to what I can say (vs. what I'd really like to say about those wheels)...

Read this:
http://www.nature.com/news/the-wheels-come-off-kepler-1.13032

Thanks. That puts a new spin[1] on a lot of things...

1 - ya, I went there. Gotta go.
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Online catdlr

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Re: NASA - Kepler updates
« Reply #259 on: 06/06/2013 06:18 PM »
News release: 2013-190                                                                    Jun. 6, 2013

Stars Don't Obliterate Their Planets (Very Often)



The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2013-190&cid=release_2013-190

Stars have an alluring pull on planets, especially those in a class called hot Jupiters, which are gas giants that form farther from their stars before migrating inward and heating up.

Now, a new study using data from NASA's Kepler Space Telescope shows that hot Jupiters, despite their close-in orbits, are not regularly consumed by their stars. Instead, the planets remain in fairly stable orbits for billions of years, until the day comes when they may ultimately get eaten.

"Eventually, all hot Jupiters get closer and closer to their stars, but in this study we are showing that this process stops before the stars get too close," said Peter Plavchan of NASA's Exoplanet Science Institute at the California Institute of Technology, Pasadena, Calif. "The planets mostly stabilize once their orbits become circular, whipping around their stars every few days."

The study, published recently in the Astrophysical Journal, is the first to demonstrate how the hot Jupiter planets halt their inward march on stars. Gravitational, or tidal, forces of a star circularize and stabilize a planet's orbit; when its orbit finally become circular, the migration ceases.

"When only a few hot Jupiters were known, several models could explain the observations," said Jack Lissauer, a Kepler scientist at NASA's Ames Research Center, Moffet Field, Calif., not affiliated with the study. "But finding trends in populations of these planets shows that tides, in combination with gravitational forces by often unseen planetary and stellar companions, can bring these giant planets close to their host stars."

Hot Jupiters are giant balls of gas that resemble Jupiter in mass and composition. They don't begin life under the glare of a sun, but form in the chilly outer reaches, as Jupiter did in our solar system. Ultimately, the hot Jupiter planets head in toward their stars, a relatively rare process still poorly understood.

The new study answers questions about the end of the hot Jupiters' travels, revealing what put the brakes on their migration. Previously, there were a handful of theories explaining how this might occur. One theory proposed that the star's magnetic field prevented the planets from going any farther. When a star is young, a planet-forming disk of material surrounds it. The material falls into the star -- a process astronomers call accretion -- but when it hits the magnetic bubble around it, called the magnetosphere, the material travels up and around the bubble, landing on the star from the top and bottom. This bubble could be halting migrating planets, so the theory went.

Another theory held that the planets stopped marching forward when they hit the end of the dusty portion of the planet-forming disk.

"This theory basically said that the dust road a planet travels on ends before the planet falls all the way into the star," said co-author Chris Bilinski of the University of Arizona, Tucson. "A gap forms between the star and the inner edge of its dusty disk where the planets are thought to stop their migration."

And yet a third theory, the one the researchers found to be correct, proposed that a migrating planet stops once the star's tidal forces have completed their job of circularizing its orbit.

To test these and other scenarios, the scientists looked at 126 confirmed planets and more than 2,300 candidates. The majority of the candidates and some of the known planets were identified via NASA's Kepler mission. Kepler has found planets of all sizes and types, including rocky ones that orbit where temperatures are warm enough for liquid water.

The scientists looked at how the planets' distance from their stars varied depending on the mass of the star. It turns out that the various theories explaining what stops migrating planets differ in their predictions of how the mass of a star affects the orbit of the planet. The "tidal forces" theory predicted that the hot Jupiters of more massive stars would orbit farther out, on average.

The survey results matched the "tidal forces" theory and even showed more of a correlation between massive stars and farther-out orbits than predicted.

This may be the end of the road for the mystery of what halts migrating planets, but the journey itself still poses many questions. As gas giants voyage inward, it is thought that they sometimes kick smaller, rocky planets out of the way, and with them any chance of life evolving. Lucky for us, our Jupiter did not voyage toward the sun, and our Earth was left in peace. More studies like this one will help explain these and other secrets of planetary migration.

The technical paper is online at http://iopscience.iop.org/0004-637X/769/2/86/ .

NASA Ames manages Kepler's ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler mission development. Ball Aerospace & Technologies Corp. in Boulder, Colo., developed the Kepler flight system and supports mission operations with JPL at the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. The Space Telescope Science Institute in Baltimore archives, hosts and distributes the Kepler science data. Kepler is NASA's 10th Discovery Mission and is funded by NASA's Science Mission Directorate at the agency's headquarters in Washington.

NASA's Exoplanet Science Institute at Caltech manages time allocation on the Keck telescope for NASA. JPL manages NASA's Exoplanet Exploration program office. Caltech manages JPL for NASA.

More information about the Kepler mission is at http://www.nasa.gov/kepler .

More information about exoplanets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov .

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

Michele Johnson 650-604-4789
Ames Research Center, Moffett Field, Calif.
michele.johnson@nasa.gov

- end -
« Last Edit: 06/06/2013 06:18 PM by catdlr »
Tony De La Rosa

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