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2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

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7166811 No.7166811 [Reply] [Original]

The Dawn Blog has published a new update. There's a lot of fluff text in it, but there's also some important information for people who will inevitably wonder where the new pictures of the bright spots are.

http://dawnblog.jpl.nasa.gov/2015/03/31/dawn-journal-march-31-2/

As seen in the attached image, Rotation Characterization 3 will take several weeks, and will involve the capture of ~2,500 images.

Due to remaining uncertainty in the rotation period of Ceres and the amount of time since OpNav5, OpNav6 and OpNav7 might not see the bright spots. If worst comes to worst, we'll have pictures of the bright spots in May.

>> No.7166843

Thx OP.

>> No.7167758

>It's been reported that thermal measurements of the bright spots reveal that they have the same temperature as their surroundings. This was considered surprising since light-colored areas should reflect more light, and, so, remain cooler than dark ones.

The mystery continues.

>> No.7167788

>>7166811
ayy lamo

>> No.7169367
File: 304 KB, 1600x1200, WhereDawnIsNow.png [View same] [iqdb] [saucenao] [google]
7169367

Just a few more days...

>> No.7169953

>>7169367
Wow. Thats a complicated path.

>> No.7170093

>>7169953
Yup. It's an unfortunate consequence of the loss of two of Dawn's reaction wheels, forcing it to use hydrazine for spacecraft orientation. Since their fuel budget is low, they needed to optimize their fuel use to complete their science objectives. The consequence of this decision is the complex flight path and increased time to orbit.

>> No.7170120

>>7170093
I hope that wont impact the mission in the long term.

>> No.7170130
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7170130

>>7170120
Low Ceres orbit is the end-game. Dawn has sufficient fuel reserves to complete all of its science objectives and then some. All in all, the ship's in good shape.

>> No.7170161

>>7170093
>the loss of two of Dawn's reaction wheels
I read that was due to bearing failures, but with no further detail. Why did they fail?

>> No.7170165

>>7170161
I honestly don't know, and I'm not sure the NASA guys do either. They shut themselves down after the flight computers detected excessive friction, which would, presumably, leave them ineffective for controlling spacecraft orientation.

>> No.7170169

>>7170165
My brother, a Mechanical Engineer, said they failed because of "Lowest-Bidder Syndrome", is that just cynicism, or is he right?

>> No.7170175

>>7170169
Dawn, like Kepler, used mechanical bearings rather than magnetic bearings in their reaction wheels to save money. The wheels would not have failed if they hadn't been cheap, so I'd say he's spot on.

>> No.7170194

>>7170175
Thanx, I'm gonna e-mail him about this, he's always happy to be right about things.

>> No.7170198

>>7170175
Ok, I am going to bite... I am mech eng.
Bearings, are like, the oldest mechanical device ever, older than the wheel (logs under monolithic blocks). In a spacecraft they (should) have been tested for years to eliminate failure.

Is there a property of zero gravity that effects the workings of bearings (roller, ball, needle i assume)?

>> No.7170204

>>7170198
Lubrication is a tremendous challenge without gravity; oil does weird things in space. In addition, if the temperatures get too low, metal components can cold-weld themselves together.

>> No.7170217

>>7170198
This page from the European Space Agency might be of interest:
http://www.esa.int/Our_Activities/Space_Engineering_Technology/Mechanisms/Tribology

>> No.7170891

>>7170217
Thank you. Fascinating. Needless to say a little knowledge just feeds in to a whole chamber of ignorance, I have more questions now !!

>> No.7170970

>>7170204
>>7170217
1st time you will see an Eng. get into the detail. I found this, most interesting (to me anyway).

http://cdn.intechopen.com/pdfs/13470/InTech-Lubrication_of_attitude_control_systems.pdf

>> No.7171056

>>7170194
He e-mailed me back, confessing to once "saving" money on cheap imported bearings for a large stationary engine (maybe a water pump?) that failed after four weeks.

>> No.7171086
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7171086

Back then they used VHS recorder bearings made in Japan even for mil spec gyros.

>> No.7171103

>>7170198

My guess is that there was some brinneling occuring which is basically an indention in the bearing caused by vibration occuring in the same spot over a period of time. One thing that is done to stop this is to rotate the bearings periodically so it isn't in the same spot.