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Posted by: karolp Sep 2 2006, 03:03 PM

I am currently digging in the Planetary Radio archives and heared Bill Nye saying that the Mars sundial sitting on the solar panels takes about 1 to 2 percent of power by covering them. The sundial itself is of course a great outreach idea and probably does not affect the mission as Bill said. BUT: what if the 2 percent were the LAST 2 percent left? What is the minimum power requirement for MERs? And namely a) for being able to rove for being able to use the RAT c) for being able to sit calmly and just send data to the orbiters. No intention to question the "Two Worlds One Sun" thing, I really love it. Just made me curious about the power as it might be relevant in speculations about their expected lifespan.

Posted by: tfisher Sep 2 2006, 03:29 PM

The "sundials" are the most photographed things on mars for a reason -- their major function is as the calibration targets for the pancam. So, yes, they take up space and weight and reduce the surface area available for solar energy generation. But they add a lot to the scientific value of all the images that are coming down. They allow scientists to translate the "pretty pictures" into actual spectrographically calibrated measurements. So this isn't just wasted space...

Posted by: dot.dk Sep 2 2006, 04:01 PM

And the HGA and the PMA takes up much more than 2 percent

Posted by: karolp Sep 3 2006, 04:31 PM

And I was not suggesting to toss'em as worthless but asking what the MERs could do with only 2% of power left Could they at least send some bits to the orbiters?

Posted by: climber Sep 3 2006, 04:46 PM

Do NOTHING and wait untill the batteries charge the next day
I talked will Bill Nye on the very day of Spirit landing and he was very proud of the sundial be in fact a by product of the calibration target.

Posted by: djellison Sep 3 2006, 04:47 PM

2% of 280 Whrs = 5.6 Whrs...

Via UHF - data costs about 0.8 Whr / Mbit - so you could get perhaps 7 Mbits of data home via UHF

But of course, with onlly 5.6 Whrs - you've not got enough to warm up some instruments to take data to fill that 7 Mbits

However - to put this into some sort of context..

Shadowing causes losses of up to around 20% per sol

Doug

Posted by: Jeff7 Sep 4 2006, 04:12 AM

But is the "mast" portion of the sundial truly necessary? Aren't the colored portions, mirrors, and B&W circles the truly important parts?


The real problem is that the http://imprint.uwaterloo.ca/legacy/story.php?f=2&t=8238&i=&v=f&story=8238&.

"Mars is very dusty; it was thought that dust coating the solar panels may kill the rovers by choking out the sunlight. Designers worried about it so much, the rovers actually have small fans designed to blow dust off the panels. But the fans have gotten a boost."

Posted by: bergadder Sep 4 2006, 05:00 AM

You do know that the last part about DD is going to drive our " Administrator" nuts...

Posted by: climber Sep 4 2006, 07:26 AM

That's old story now! DD stuffs are buried in concrete under a shed

Posted by: djellison Sep 4 2006, 07:29 AM

Yup - by casting a shadow onto the black/grey rings it allows one to calculate the direct illumination and indirect illumination properties

And the times when the gnomen ( to give it a technical name ) might cast shadows on the arrays are only very close to sunrise and sunset - a time when the angle if incidence between sun and array is such that you're barely going to drop any power at all.

Doug

Posted by: RNeuhaus Sep 4 2006, 02:37 PM

I learned it too late!!! I haven't tought that MER has a small fan pointing to sundial? I haven't see it on the picture?

I have enclosed the picture which shows sundial and their blowers at right and left sides. Correct me!



Rodolfo

Posted by: djellison Sep 4 2006, 03:20 PM

No no - there ARE no blowers on the rovers - that's the point

What you point out are the pyrotechnic bolts that held the solar arrays together before the thing deployed on Sol 1

Doug

Posted by: RNeuhaus Sep 4 2006, 04:40 PM

Good!

They were referring to the wind as the blower!

Rodolfo

Posted by: Jeff7 Sep 4 2006, 04:55 PM

That works for me then. The entire sundial stays.

Posted by: ljk4-1 Sep 5 2006, 12:51 PM

The sundial was the very first object image radioed to Earth by Spirit after it landed on Mars.

Not quite sure if they used the same target with Opportunity's first image.

Posted by: djellison Sep 5 2006, 02:08 PM

Top of the list in priority to be returned, but not the first image taken

Doug

Posted by: ElkGroveDan Sep 5 2006, 02:55 PM

I work with the media and the press as part of my job. I've seen them say and do some really dumb things over the years, but that example has got to be one of the best I've ever seen. I'm going to save that in my "stupid things reporters say" file.

Posted by: MaxSt Sep 6 2006, 03:20 PM

No way the sundial can shadow 5-10 cells from total 500 cells.

On the other hand, it takes some place, which could be used for cells.

Posted by: djellison Sep 6 2006, 03:27 PM

It takes approx 2% of the deck area physically - area that could be repalced by solar cells - I think that was the argument being made.

Doug