Forgive me, I'm traveling and can't always check the website. Wanted a reply up so I can get email notifications of new posts.

It's about 11:30 LST at Opportunity as I post this, and I see that DSN Now says they are uplinking to MER1 from Canberra. I wonder what they're trying to do? I thought they were in listen-only mode.
Click to view attachment

I believe they are trying to solicit a beep.

Paolo

The fault modes open a comm window - you have to Uplink to get a response as Paolo said

As a heads up to people watching DSN Now - you may, quite often, see what appears to be MER 1 transmitting to the ground for a few seconds, maybe half a minute. That’s not Opportunity. That’s the DSN getting a false lock on noise from MRO.

Were we to get a response from Oportunity - it would more than likely be a complete 5 minute beep.

Really? There's never any attempt to send anything on the X-band LGA autonomously? The fault protection paper implies that there is:



I read that as meaning that it's in receive mode as long as it's powered up and that it tries to send at 11 LST even if it hasn't heard anything. But I may be misinterpreting what "schedules a communication window" means.

In my experience it would be unusual to never transmit autonomously, since that would mean that if there was a receiver failure, you'd never hear anything even if the transmitter was healthy.

https://forum.nasaspaceflight.com/index.php...9668#msg1559668

Being designated as the uplink in an MSPA can be an artifact of the way the MSPA is set up. Uplink means that it gets the only two-way channel in the MSPA group. AFAIK, this doesn't preclude doing only downlink.

You'll have to explain what you meant by this. I don't know exactly how DSN Now works as far as MSPA is concerned. When DSN is looking for a signal from a drifting frequency reference (which may be the case here), I think they often record in wideband and don't even try to lock up in real time, and I suspect this doesn't show up on DSN Now as a downlink (Doug would know for sure.)

However, if DSN Now says the uplink is to a specific spacecraft, I'm pretty sure it really is to that spacecraft.

Hopeful tweet from yesterday

https://twitter.com/AnthonyJCook2/status/1009920728546754561

Really. To be specific, we are commanding 5 minute beeps when we believe every fault window opens.....the expected behavior is thus just 5 minute beeps to preclude a lengthy power hungry DTE.

Interesting paper. I coded up the equations and tested it to reproduce tables 2 and 3, so now I can plug in additional values. A tau of 10.8 still seems to be a few percent for green light depending on solar elevation angle. For practical powering up purposes it is rather dark, though quite a brighter than the full moon. With tau=15 I get between 0.4% and 1.2%.

https://mars.nasa.gov/mer/mission/status.html#opportunity

You are right, I thought that day/moonlight difference was corresponding to a Tau of 14 or thereabouts but it was the closest thing I could find. I would not be surprised if Oppy experienced a Tau at that level anyway.

Paolo

As a bit of nuance, a Tau of 14 sounds about right to make the direct solar illumination match the full moon, so one could look for an (Earth) moonlike orb to be somewhat visible through the dust. Otherwise there is brighter overall illumination from diffuse scattered light. How about a full Phobos ?

The faint sun appearance shows up in a sky that is not quite black on the right panel of the second picture shown in this link posted earlier. Turning up the monitor brightness helps to see this. This is a useful example for expanding the envelope with my sky simulation software.

As further nuance, exp(-tau) is only appropriate when the Sun is straight up. Later in the mid-afternoon, a (normal) tau of 10.8 might have an effective extinction of, say, exp(-14.5). That would seem very similar to the right-most frame in the panel from that link--if you look very closely, the Sun is still visible as a faint, bluish disk.

Remember that the panel view in the link is a simulation. The other point is that the brightness of the sun in any "real" image will be a function of the exposure time.

Comparing simulations, mine so far is rather simplified given the high Tau values, though I'm getting a notably redder sky color than the one posted by the team. I'm pretty much developing a sky hue from color ratios derived using the paper discussed in post #110. This is reminiscient of the YouTube video posted earlier from a dust storm on Earth, and consistent if we extrapolate some of the redder colors in Curiosity images to higher Tau.

you have to remember that the values quoted in that paper, at least the one relevant for the visible, is actually only appropriate for red, and for diffuse dust. you need to adjust the single scattering albedo for blue and green (and particle size, though not a huge change here). The single scattering albedo values for 400 nm, 500 nm, 600nm, and 700nm assuming the average (cross section-weighted mean) particle size is 2.0 micron

0.716001 0.816507 0.938796 0.968714

respectively.

The three wavelengths I've been using for calculations are 615nm, 551nm, and 450nm with corresponding single scattering albedo (SSA) values of .958, .904, and .800. This can be checked with the values you're mentioning and the figure I referenced in post #92. There is some subsequent interpolation that is done when estimating a full spectrum to convolve with the CIE color matching functions. Angstrom exponent is assumed to be -0.05. Would you happen to have SSA values for the three wavelengths I'm using?

Here's my animation of thickening dust with Tau ranging from 0.5 to 10.0. The sun is 45 degrees up.

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As a more general comment I wonder if there are single scattering phase functions vs wavelength published anywhere? This could help me get the chromaticity better when using the quoted SSA values. For some reason I can tend to show a grayer sky.

I'm wondering about the effect of the dust storm on the atmospheric pressure at the surface of Mars. Given that the force exerted by the atmosphere on a square meter of surface depends on the weight of the atmospheric column over that surface, does it follow that the added weight due to suspended dust will increase that pressure?

Would such an increase be sufficient to extend significantly the range of temperatures at which ephemeral liquid water (just after dawn) could exist? The newly added dust on rocks might provide a convenient probe for testing this hypothesis; presumably a brief wetting would affect the texture of the dust deposits in a way that might be observable.

The additional weight of the dust is certainly less than 1/1000 of the weight of the atmosphere. But it might drive a greenhouse effect or increase albedo in the polar regions, and result in additional sublimation of CO2 or water near the poles.
MSL REMS should be able to test this hypothesis.

The effect of dust storms is to loft water vapor into the middle atmosphere, with a significant decrease in absolute humidity near the ground. This reduction in the amount of water vapor means that the formation of films or brines is even less likely during a dust storm despite higher minimum temperature or minor variations in atmospheric pressure.

I am more interested in the aftermath of the dust storm, when (hopefully) Opportunity will be able to observe changes in the resultant dust deposits. Is the above hypothesis still applicable at that point?

I don't think there's really an appreciable pressure signature from dust storms, but this has been measured. Note that some of the graphs below are more about diurnal variation in pressure and less about absolute pressure.

https://www-k12.atmos.washington.edu/k12/re...ion/overlay.gif

https://mars.nasa.gov/resources/4902/atmosp...ing-dust-storm/

https://mars.nasa.gov/msl/mission/instrumen...onsensors/rems/

Dates (2018) Mean Pressure (Pascals)

June 05--June 10
758 756 758 762 764 765
June 11--June 16
766 767 768 770 768 769
June 17--June 21
771 772 776 780 778

Looks quite suggestive. Of course it might be just the normal seasonal signal.

And the maximum temperatures are also decreased, dramatically, during the storm. Rendering windows when such events might occur astonishingly small, if they existed at all.

The second linked graph measures atmospheric pressure hundreds of miles from a dust storm and compares pressure changes above the daily minimum. Given the general atmospheric heating and the localised heating referred to wouldn't the minimum absolute pressure be different for each of the graphs, possibly implying that the absolute maximum temperatures would tend to align?

Of course. Without finding the raw data I can only show what the team chose to plot. My only point in posting this was to indicate that the pressure was being measured and eventually we would be able to see those measurements (see http://pds-atmospheres.nmsu.edu/data_and_s.../Mars/Mars.html although if this page is right the REMS team is way behind on releasing data.)

Going back to the Viking 1 data would be the best way to look at the pressure through a dust storm as of today, probably.

This simulated version shows the blue scattering surrounding the sun a bit better. Tau ranges from 0.5 to 10. I'll try to make a plot of the phase functions being used for this.

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Pressure is of course modified by the storm--but there is no measurable enhancement from the dust loading, the original question (I think). The modification is not as simple as a perturbation to the existing profile (e.g., shifting the absolute minimum pressure up or down or compressing/expanding the range of variation).

There are many modes, and they interfere. There's a diurnal tide--the surface gets warmer and heats the air, warm air rises, circulation happens--that can be diminished by the the diminished temperature cycle, but also by more complex interactions (VL1 diurnal tide went away, http://science.sciencemag.org/content/213/4506/437--at least the abstract can be seen). There's a semi-diurnal tide from heating by dust in the air and can be seen from orbit and the ground (http://www.planetary.org/blogs/guest-blogs/2013/mysterious-tides-martian-atmosphere.html). It increases in amplitude significantly when there is a lot of dust in the hemisphere or globe (Fig. 2 in https://journals.ametsoc.org/doi/full/10.1175/JAS3718.1)

The tides are enhanced in Gale as opposed to Meridiani; they correlate with dust as seen by Curiosity--two pay-walled papers discuss this: https://www.sciencedirect.com/science/artic...0531?via%3Dihub and https://www.sciencedirect.com/science/artic...5850?via%3Dihub. It might be cool if Scott (or Scot) would do a blog post at Planetary Society.

To visualize the modes, see Figs. 3, 9, 10 in http://sirius.bu.edu/withers/pppp/pdf/with...014atmo_v02.pdf.

So, there is no particular effect from the dust mass; but there will be a substantial impact from the dust heating and cooling effects, and those would be expected to significantly alter the shape of the pressure wave, based on how much the first two modes would be expected to change with tau>5 over possibly large regions.

https://mars.nasa.gov/mer/home/


http://www.planetary.org/multimedia/space-...lakdawalla.html
This doesn't seem right---Opportunity is at the opposite side of the planet from Spirit, so the LST times should be around 12 hours apart. Having the correct local time for Oppy is useful for checking the DSN Now comm schedule.

According to this article
http://curious.astro.cornell.edu/physics/6...re-intermediate
the atmospheric dust in a Martian dust storm would correspond to a layer about 3mm thick if deposited on the surface.

Assuming the dust has a density of about 1.5 gm/cc, a 3mm layer over 1 cc of surface would weigh about 1.5 x 1/3 x 3 x 1/10 = 0.15 gm on Mars. Thus, all else being equal, the pressure due to dust loading should be about 0.15 gm per sq. cm, which is equal to about 0.15 x 98 = 14.7 pascals. That is small but it should be measurable by the REMS instrument.
[EDIT: Perhaps the article linked above is confusing mm with microns (mu-m). Indeed a layer only 3 microns thick would not contribute significant loading.]
[EDIT: As a clarification, the "1/3" factor in the formula "1.5 x 1/3 x 3 x 1/10" is the correction for Mars gravity (with a slight abuse of units).]

On Mars, 0.15*38 = 5.7 pascals, I believe, unless you tried to compensate for this in your gram number (improperly, since a gram is a unit of mass, not weight.)

The article you linked cites https://www.sciencedirect.com/science/artic...2855?via%3Dihub which is behind a paywall, although I guess I could walk upstairs and get a copy from the author I think unit confusion is likely.

For amateur observations and updates on Mars during the dust storm, keep an eye on these sites:

https://britastro.org/node/10908
http://alpo-j.asahikawa-med.ac.jp/indexE.htm

Note that the Cornell link got to the estimate of a few mm thick using dust diameter of 3 mm. Using a more traditional 3 microns, you can take the result down 3 orders of magnitude. I get close to 1 mPa per unit optical depth (order of magnitude), which ends up in the same ballpark.

Even at a few Pa, I'd be skeptical--certainly REMS could measure a few Pa, but I'm not sure it could measure a few Pa of dust. There are many thermal perturbations. There are tidal perturbations, changing stationary and traveling waves. The polar cap sublimation rate and mass transport rate in the atmosphere may be affected.

[For tau=1, there is 0.5 m^2 per m^2 of dust (dust area fraction) given a likely extinction efficiency of ~2. Volume is roughly cross-sectional area times 4/3 R. So, tau=1 implies 1 micron thickness for dust that is uniformly 3 microns in diameter. Being generous, since we're talking cohesive dust particles, not the actual thickness a powdery pile would have, 3000 kg/m^3 implies 0.003 kg/m^2, or 0.001 Pa in Mars gravity.]

This site http://www.dmuller.net/spaceflight/realtim...amp;mode=planet lists the current time as Sol 5127, 23:32. The MER site has Sol 5128, 22:51

It's all good, until you look at more than one clock. The tau site has a reasonably accurate clock, just checked against NAIF. If you change '-b' to '-a' or '-c' in the URL, the clocks are off by several seconds due to lack of leap second correction, and maybe due to precision issues for Spirit. The Opportunity version seems to agree with the dmuller.net link to <10 sec, too.

Maybe overkill, but I use https://www.giss.nasa.gov/tools/mars24/ -- right now it says it's 11:24 at Meridiani and 01:14 at Gale, which sounds about right.

So, if we can just get Spirit to Gale everything will fit.

Phil

Pedantic much? They're at about the same longitude and who cares what time it is at Gusev? [Well, in fairness, they're not that close -- Mars24J says there's about 2 hours different between Gale and Gusev. If it's right.]
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I'm going to blame either Deimos or bad typesetting at Science for this -- in http://science.sciencemag.org/content/306/5702/1753 the abstract says "The dust's cross section weighted mean radius was 1.47 ± 0.21 micrometers (mm) at Gusev and 1.52 ± 0.18 mm at Meridiani." "mm" is, as far as I know, not a valid SI abbreviation for micrometer, which is mu-m. https://en.wikipedia.org/wiki/Micrometre

Pedantic, moi?

You're right of course, I was pedantic! It was a slow morning... but the discussion arose out of this recent post:

-------------------------------------------------------------
marsophile: (post 130 above)

https://mars.nasa.gov/mer/home/

QUOTE
Opportunity at Meridiani
Sol: 5127 Time: 12:51

Spirit at Gusev
Sol: 5148 Time: 14:18

This doesn't seem right---Opportunity is at the opposite side of the planet from Spirit, so the LST times should be around 12 hours apart. Having the correct local time for Oppy is useful for checking the DSN Now comm schedule.
--------------------------------------------------------------

So it really did concern Gusev, not Gale.

However, I will try not to give in to temptation in future, unless it's a really big juicy temptation.

Phil

MRO MARCI Weather report for the week of 18 June 2018 – 24 June 2018. Published June 28, 2018.

http://www.msss.com/msss_images/2018/06/27/

I was always taught that the symbol for a micron or micrometre is μm. In fact the link confirms this and the SI spelling convention, although I appreciate that this is one of the words where US spelling deviates. Personally I feel that errors in nomenclature or symbols should be considered more than just a passing annoyance given the fate of the Mars Climate Orbiter.

[ADMIN MODE]...and on that note we're done with the abbreviation debate, or 'abd'. Moving on...

https://mars.nasa.gov/mer/mission/status_spiritAll_2008.html
It could be said that the great dust storm of 2007 indirectly led to the loss of Spirit in 2010. As the sky cleared, dust falling on the solar panels forced Spirit to seek an extreme slope of 25 degrees at "Winter Haven 3" on the northern edge of Home Plate for the subsequent Martian winter. When spring came, Spirit was unable to climb back onto Home Plate, which caused it to take an alternative route below, which ultimately proved fatal.
To ensure a similar fate does not befall Opportunity. it may be worthwhile to seek immediate cleaning of the solar panels in the aftermath of the storm. Perhaps observing wind trails in the new dust deposits would provide information about the current wind regime at Perseverance so that Oppy could position itself where cleaning is most likely in the months before the coming of winter. It is true, though, that Opportunity is closer to the equator so maybe, hopefully, that will not be an issue.

Opportunity experienced a major cleaning event in Perseverance Valley at the end of 2017. The rover couldn't be in a better place to get cleaned than it is now.

http://www.spaceflightinsider.com/space-fl...ian-dust-storm/

July 1 update.

http://www.planetary.org/explore/space-top...dust-cloud.html
The monthly MER update.

This might be a good theme song for Oppy under current circumstances:
https://www.youtube.com/watch?v=gYkACVDFmeg
"I Will Survive"

Here is an updated simulation with Tau ranging from 0.5 to 11.0 in 0.5 steps. This shows the reversal to a darker horizon somewhat better. The software roughly estimates solar horizontal irradiance, ranging from 360 W/m^2 down to 13.5 W/m^2. The solar elevation angle is 45 degrees.

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I'll consider adding a strip of land at the bottom next. Below is a table of the estimated global horizontal irradiance.

Tau GHI (W/m^2)
--- -----------
0.5 360.4
1.0 311.3
2.0 230.6
3.0 169.7
4.0 124.4
5.0 90.9
6.0 66.2
7.0 48.2
8.0 35.1
9.0 25.5
10.0 18.5
11.0 13.5

I had some excellent terrestrial weather last night for observing the Opportunity site which still has terrible martian weather. Meridiani is near the left side of the disc here, and the state of the dust storm is evident in the wispiness of the dark areas, including Syrtis Major at right. However, it's not quite a blank disc, which is a hopeful sign.