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

[Vultur]

How big would Siding Spring appear in the Martian sky near closest approach? I would think it would be bigger than the camera FOV...

[mcaplinger]

I haven't seen chemcam's optical speed anywhere...

Sorting through various references (the Chemcam fact sheet and some LPSC abstracts), the IFOV is 80 microrads and the pixel pitch is 14 microns, so the focal length is 175mm. The aperture is 100mm, so the f/number is f/1.75. The beamsplitter passes between 8% and 18% of the incoming light depending on wavelength.

[Hmm, on review the fact sheet says the "spatial resolution" is 80 urad, but that may be 2x what I would call the IFOV, in which case the focal length and f/number double.]

[Deimos]

Siding Spring's coma would be much bigger then RMi or MCAM FOVs. The light would be so spread out as to likely be invisible. Inner coma jets and the nucleus could be visible. The nucleus will pass 7+-1 Deimos_distances away from the surface, but be moving several times Phobos' angular speed. But, closest approach is between dawn at Meridiani and dusk at Gale. MSL likely has the best view, but at at least twice the closest approach distance.

[Greenish]

Hesitant to correct the optics expert, but I'm pretty sure based on multiple references (incl. Maurice et al) the RMI IFOV is 20 mrad/1024 px. That gives a focal length of 717 mm and primary diameter is 110 mm from that same reference, so it's f/6.5.

[mcaplinger]

...I'm pretty sure based on multiple references (incl. Maurice et al) the RMI IFOV is 20 mrad/1024 px.

Could be. I don't have a copy of Maurice et al and this is far from clearly stated (IMHO) in all the published stuff I could find.

[fredk]

I did the calculation and agree with Greenish's value of f/6.5 (that assumes IFOV along the side, rather than diagonal). Maurice etal do say 20 mrad for FOV, and also 80 microrad for resolution (at 0.2 contrast, but there is astigmatism). (This means chemcam is a bit better in resolution than M100). 20 mrad is a bit over a degree, which sounds about right compared to MC100.

Anyway, beamsplitter loss of ~87% means a few stops slower speed than f/6.5. So my guess is MC100 (f/10) or MC30 (f/8) will top it for diffuse sources (although chemcam should be better for point sources). But there's still the question of bandpass to complicate things...

[fredk]

Here are a couple of the sol 397 nighttime chemcam shots. Both are differences of what appear to be identical exposure frames, to cut the noise. This one shows what could be a star trail near centre (Sirius??). It doesn't really look like a cosmic ray hit, but I suppose still might be:

This one shows a pair of streaks that don't look at all like cosmic rays:

[jmknapp]

The pointing information is available now--looks like as expected they were pointing CHEMCAM more or less at Andromeda.

E.g.,

2013 SEP 18 08:41:17 UTC
bearing 359.32° (N), elevation 32.45
http://mars.jpl.nasa.gov/msl-raw-images/pr...CCAM04397M_.JPG

According to Stellarium at that time, Andromeda was at 5.8° (N), elevation 32.05°.

Then they pointed at something a bit higher--NGC595?

[fredk]

bearing 359.32° (N), elevation 32.45
http://mars.jpl.nasa.gov/msl-raw-images/pr...CCAM04397M_.JPG

According to Stellarium at that time, Andromeda was at 5.8° (N), elevation 32.05°.

Then they pointed at something a bit higher--NGC595?

The second of the two differenced images I posted above (with the two long, faint trails) corresponds to that direction (Andromeda). The first image I posted (with one bright trail) corresponds to bearing 152.28 (SSE), elevation 45.02, which is on the other side of the sky. The plan was to image Sirius - maybe that's it?

[jmknapp]

Ah, you're right, I missed the azimuth change--around Sirius, it is, for those shots.

[vikingmars]

Here are a couple of the sol 397 nighttime chemcam shots.

Thanks a lot Fredk : very interesting indeed !
==> Yes ChemCam could be also seen as a small telescope being fitted on Curiosity.
It could be great to have ChemCam pointing also at PHOBOS and DEIMOS and see from Mars much more details there ! And not forgetting the EARTH of course : maybe we could even discern the MOON too !
What is ChemCam CCD sensitivity, by the way ? And is it enough sensitive to have nighttime short exposures (to avoid seeing the targets blurred) ?

[fredk]

What is ChemCam CCD sensitivity, by the way ?

Chemcam CCD QE is roughly 10% from Maurice etal, compared with around 40% for MH/MC. So combined with the beamsplitter losses it's a fairly slow optical system.

But for bright sources - planets and moons - I'd love to see what Chemcam can do...

[vikingmars]

But for bright sources - planets and moons - I'd love to see what Chemcam can do...

Thanks a lot Fredk : me too ! Maybe even JUPITER could be imaged then with its four Galilean satellites...

[Deimos]

Many people would love such images. But RMI cannot image everything Mastcam can image. As Emily indicated in a blog post some time back, planners have to consider the implications of certain failure modes. You'd hate to have a minor problem overnight result in Chemcam's optics or detector being damaged by the Sun the next day, before the situation could be resolved from Earth. So if something is in a part of the sky near where the Sun will soon be, more caution may be warranted.

[fredk]

Region of Andromeda as seen by Mastcam30 on sol 397. Difference of two frames, stretched. The arrowed stars should be familiar to anyone who follows them to find the Andromeda galaxy, M31. I've circled the location of M31 - no sign of it yet: