MSL - Astronomical Observations, Phobos/Deimos, planetary/celestial observations and more Options

[fredk]

MER never imaged the ground while imaging a transit.

Thanks for the info, Deimos. I see now that what I was thinking of was that we fantasized about this years ago with MER - see Doug's post and my reply. We talked about how cool it would've been to do this from the top of Husband Hill. Maybe we'll get another chance from Oppy or MSL showing the shadow racing across the landscape from a high vantage point...

[vikingmars]

Yeah, this image was simultaneous with the RLB sequence. Very cool indeed! Was this never done with MER?

No with MER, but yes with Viking Lander 1.
Here is the image taken ("rescan" mode) on its mission Sol 423 : the darkening of the Phobos shadow flying above its Chryse Planitia site can be seen easily also. Cheers !

[Gerald]

In the meanwhile, six of the Sol 363 MR eclipse images are there. Here a 10x time-lapsed gif:

(based on NASA/JPL-Caltech/MSSS)

Well, the Sol 368 eclipse will be much cooler, as Emily pointed out.

[fredk]

Well, the Sol 368 eclipse will be much cooler

The sol 369 transit looks not bad too - in fact, it looks very close to central:
http://mars.jpl.nasa.gov/msl-raw-images/ms...0784Q1_DXXX.jpg

[Gerald]

Bullseye!

[fredk]

Here's what I dreamed of doing 7 years ago - I've subtracted the average of the 8 post-transit RLB hazcam frames from each transit frame, then added 128 and did a small symmetrical stretch. So neutral grey means the same as after the transit, dark grey means darker, and light grey lighter than after transit:

As the transit ends, everything goes to neutral grey, with the last bit of shadow fading off into the east. The sky looks brighter during the transit (first two frames) than after, which can't be true of course. So what's probably happening is that different exposures, or more likely just different auto-stretching, are being applied. We'll have to wait for PDS (or a press release) to see how much the sky darkened during the transit...

[mcaplinger]

Bullseye!

All we had to do was get the sun in the field of view at the right time, Phobos did the rest.

[elakdawalla]

Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused in the middle of DRIVING ACROSS ANOTHER FREAKING PLANET??? Pshaw, that's nothing

[PaulH51]

Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused in the middle of DRIVING ACROSS ANOTHER FREAKING PLANET??? Pshaw, that's nothing

Hats off to the team

[DeanM]

Quoting Emily: "Point a camera with a 5-degree FOV at a moving speck crossing a moving spot from a rover that was only briefly paused.."

This can have been no easy feat!

Indeed, how is such precise 'pointing' achieved: gravity provides one vector but Mars (now) has no magnetic field to provide a second.

Dean

[Gerald]

A gyro could do the job.

[Deimos]

Indeed, how is such precise 'pointing' achieved: gravity provides one vector but Mars (now) has no magnetic field to provide a second.

Sun images show the Sun's position and (optionally) direction of motion in the rover's frame. These allow a full attitude solution or a yaw-only solution. Initial measurement units (gyro-based) update attitude between sun images. MER used a subset of Pancam Sun images. MSL uses Navcam Sun+sky images. The IMU propagates attitude forward, but error builds with drive-time. So the attitude, especially for Sun aims, is precise after a Sun update and before the next drive, and degrades until the next Sun update. The midnight planets page for sol C/369 shows such an update after the drive (and mid-drive imaging). Sol B/3387 shows an update for Opportunity. (In both cases, look for the Sun image/images after "driving...".)

[fredk]

MSL uses Navcam Sun+sky images.

I didn't realize that - I had assumed MSL used mastcam. Why navcam? Surely it's harder to pinpoint the sun's position in a navcam frame, or in other words the uncertainty on the sun's position would be much larger in a navcam frame than a mastcam frame. That's both because of the lower resolution of navcam, but also because of the overexposure due to lack of solar filter. (I guess you could pinpoint the position from navcam pretty well in one direction, due to the CCD bleeding.)

FredK: "Subtracted the average..." Brilliant idea... just freaking brilliant.

Thanks a lot Ed, but I have to say I was inspired by what we did several years ago with Spirit's dust devil images. I have no idea who started differencing the images to show DD's more easily.

[john_s]

Why navcam? Surely it's harder to pinpoint the sun's position in a navcam frame, or in other words the uncertainty on the sun's position would be much larger in a navcam frame than a mastcam frame.

I presume it's simply that Navcam has a much wider field of view, so you can find the sun even if the accumulated error in the rover's orientation is quite large.

John

[mcaplinger]

I presume it's simply that Navcam has a much wider field of view...

On MER they do sun-finding with Pancam, which has the same FOV as the 34mm Mastcam.

It was more a political/requirements-driven issue related to Mastcam being a non-JPL instrument. Mastcam could be used if needed but Navcam is completely sufficient.