Sliding into 'Home Plate North', Heading for Spirit's 2008 Winter Retreat Options

[djellison]

Someone could figure out the solar elevation at X O'clock, at the time of a sundial image, and establish rover tilt through that. Otherwise, the only other tilt measurement is from the database which Mike pulls out for MMB.

Doug

[alan]

Could we get a reasonable estimate from the angle of the horizon next time they do a 360 Navcam panorama?

Some news from JPL's latest update:

To make the most of waning sunlight during the approach of Martian winter, Spirit's handlers have returned to "Mars time." This means their working hours coincide with the Martian day, as they did for the first three months after the rover landed on the red planet.

That explains how they've managed so many drives days recently.

Spirit's solar power levels continue to drop, with solar array energies recently ranging from 293 watt-hours to 254 watt-hours, depending on the vehicle's orientation relative to the Sun.

No time to waste, good thing they found a nice spot.

[ngunn]

Otherwise, the only other tilt measurement is from the database which Mike pulls out for MMB.

The degree markings on AndyG's endless pan could be used to find the elevation angle of horizon features. We haven't travelled too far from that spot. I'm linking to his whole post here for those who may have missed our obscure little endless panoramas thread. Please try out the panorama!

http://www.unmannedspaceflight.com/index.p...st&p=103348

Edit - Oops that's linked the whole thread. We want the panorama from post 11:
http://personal.strath.ac.uk/andrew.goddard/pan.html

[fredk]

Current relative tilt is about 15º, comparing to the attitude on sol 1404 (120 pix. difference, measured from the rover's deck to Haskin Ridge).
I'm still wondering / asking how to determine the absolute tilt. Ideas are welcome.

I get about 9 degrees of absolute tilt using the sol 1406 forward hazcam image. What I did was to look at several of the very early forward hazcams from near the lander, and assumed that the average visible horizon in those images was the true horizon. Then I counted pixels from that horizon position to my estimate of horizon in the 1406 forward hazcam (easier than the rear hazcam), and divided by 2.1 mrad/pixel.

I could easily be out by a few degrees if the plain near the lander was sloped by a few degrees. In fact, the front hazcams are supposed to be tilted 45 degrees downwards. Using that to fix the horizon, my measurement of 9 degrees becomes 12 degrees or so.

These numbers are probably consistent with yours, Tesheiner, since the top of HP is tilted southwards near the edge.

[mhoward]

My measurement makes it about 15.3 degrees absolute tilt on Sol 1406. That's based on measuring from a visual rendering in MMB based on the tracking data. I could probably work out how to get the real number from the tracking data, but I'm worried that even the basic math to derive the angle from the rover orientation quaternion would probably make my head explode.

[Astro0]

WH3 Plunge.

Enjoy
Astro0

[BrianL]

So, is that it? Have they reached all the tilt they are going to get at this location, or will further driving down the slope improve that?

Brian

[mhoward]

I don't think that's it. The front and possibly even the mid wheels aren't over the edge yet, and according to Steve Squyres via the planetary.org rover update they're hoping for more like 25 degrees.

[Astro0]

I think that they'll try for another move forward (downslope) of about two or three more wheel diameters - somewhere near the red line. The forward wheels are just about over the edge of HP, certainly no more than a wheel diameter or two. Any more than that and they are on sandy ground and the tilt will surely decrease.
I hope that this gives them the 25 degrees (or near enough) that they are looking for.


Astro0

[Tesheiner]

Well, yestersol (1407) was planned for driving and included a "post-drive" 360º navcam mosaic.
Images are down as usual, and I can see that a new "site" (AX00) was also declared.
I've checked the planned activities for sol 1408 too and no driving is expected to take place.

IMO, all this data are telling us that this will be Spirit's winter haven.
I'm a bit concerned about the tilt. This navcam image is pointing at -90º (due west) --i.e. it's almost orthogonal to the rover's front-rear axis-- so it can give us the absolute tilt we were looking for.
And it's ... 13.7 degrees.

I'm looking forward the next status report.

[djellison]

Well - there is more to come from driving a little further I would have thought - they're not 'over' the edge yet, nor are the front wheels near the bottom.

It may be that they're simply declaring a new site to pause for a sol or two, survey, and plan the next drive. 13.7 degrees will be a big help for now - it'll pop us back away from the <240 zone for a few sols.

I was trying to think of interesting names. Pardo Ridge is a feature on Elephant Island, where the bulk of Shackleton's Endurance expedition had to hold out while Shackleton and a few others sailed for South Georgia in the James Caird to seek rescue.

Captin Louis Pardo was the captain of the Yelcho - the vessel Shackleton used in his fourth attempt to get back to Elephant Island.

Yeah - I've been reading Worsley's diary again. WH3 isn't really a ridge, but Pardo Pan has a ring about it!

Doug

[alan]

Mars equinox was on Dec 10 (its going to be a long winter) so the current ideal tilt is roughly equal to Spirit's latitude: 14.8 degrees. It would make sense to stay here for now and move farther down the slope, assuming that will increase the tilt, as the seasons progress.

[djellison]

its going to be a long winter

As I see it - it'll be a nice 'pause' till Phoenix has fninshed it's Primary mission

Doug

[Tesheiner]

Ok. So here's an exercise/attempt to calculate the maximum tilt Spirit could get on this slope.
[attachment=12921:Slope.jpg]
Assuming:
1) the front wheels are not at the edge yet, at a distance D (a good assumption),
2) the downslope is more or less constant (not so good assumption but let's take that),
3) I did my math correctly (don't put your money on that)
4) Me or somebody else is able to find the distance from the front to the rear wheels (L) and to estimate the distance D to the edge (put 2c on that, no more)

I'll come later with some data...

[djellison]

The distances involved between wheels are detailed here - http://hobbiton.thisside.net/rovermanual/

Doug