Here's a chart showing the elevation of the sun at noon and midnight at the Phoenix lander site for the next year or so:



During one of the press conferences it was mentioned that later this year the situation goes "energy negative" and it's lights out for the lander. What are the odds it could wake up next year when the sun returns? Also, when the sun is only up for a small portion of the day, is it possible to put the lander to sleep and just wake it up for brief periods to use whatever battery power it can get?

I'd say the odds are pretty remote...not to say null. Yes there is a mode on Phoenix which attempts to revive phoenix once it has enough energy hitting it's solar panels and it should also be possible to turn off much of the hardware to conserve power. The MERs however are in a much more benign environment than Phoenix is. Already temperatures never top -30C and get as low as -80C therefore phoenixs electronics shall need almost constant heating. Temperatures will only worsen after the primary mission. So we than get lower temperatures (=higher power requirement to survive) and less power input and both effects are a lot worse for MPX than the MERs.

Furthermore the MERs have small radioisotope heaters which Phoenix has not (??)

If the temperatures go really cold during that negative power phase ice could start to build up and wreak havoc with all sorts of things on Phoenix.

Not much hope I have in getting her to wake up.

I think of this survival as like the NEAR survival parked on Eros. They shut it down a few days after landing, then 22 months later, tried again to see if it was still alive after long periods of total darkness and cold soak. It's just not a survivable thing for complex electronics etc to handle. Phoenix will only have 3 months of TOTAL darkness, then about 6 months of partial sunlight before returning to an environmental situation like is has today. The solar arrays might have snapped off, the joints and soldering failed etc etc. If it DOES survive - it would be astonishing. And it is worth checking, just in case.

Doug

Nice chart Joe.

The solar panels have approximately 4.2m^2 of collecting surface (as far as I can tell but I have no reliable source for that) and assuming that they were built using Triple Junction PV tech that predates the MER's they should be approximately 20% efficient. Taking a rough ballpark of the solar constant @ mars being 600watt/m^2, assuming Tau ~0.5, say the efficiency of the overall power system between the panels and the batteries is ~80% then right now Phoenix should be good for around 2kW hours of power per Sol if the back of my envelope is working.

I must fix my solar power calculator and pump in the Phoenix numbers to see what the power extinction rate is actually going to be but if my memory serves me correctly things should be AOK through the 90 Sols and probably pretty good for a further 90 to 100 but at that stage the power will have started plumetting very rapidly.

I believe that the on board batteries are 25Amp\720Watt hour units.

I don't believe that the lander will be able to survive the winter but I really hope it can survive long enough to get images of the CO2 frost accumulating around it.

Good envelope work! I guess from what you say it's kind of an exponentially worsening situation, with higher power demands and failing sunlight. I wonder what the office pools at JPL might have the under/over lights-out date at--Christmas?



An English/philosophy-major friend says "it would be neat if it wakes up next year, free from the fetters of its masters."

I would imagine that the frozen CO2 ice will either crush it, or, when solid, rip it apart, or boiling off, blow it apart. The fact that the landler’s solar arrays were designed for an equatorial mission doesn't help. I suppose they could have gone further over budget by having panels that could track the sun, but most of the science will be accomplished during the first 90 days.





An interesting future mission with RTGs would be to have a survivable spacecraft designed to watch the full seasons and have the ability to crawl over the frozen ice and protect itself from explosive sublimination.



Superb chart. Thanks so much

Phoenix Solar Power.

They are lots of assumptions in this but hopefully it captures the general trend reasonably well.
Solar Cells - 20% conversion efficiency.
Effective Cell Area - 4.2m^2.
Array Tilt - 0.5deg [ facing due south ]
Power loss rate due to dust deposition - 0.2%/Sol.
Local surface albedo 0.23
Atmospheric losses - Tau constant at 0.5
Power Management system efficiency 80%.

Y-axis is kWhr per Sol, X-axis is the Phoenix mission Sol #.

The blue line is the net power available per sol, it is the total of the cyan (diffuse) and yellow (direct beam) values.

I've no idea how much power Phoenix actually needs to operate but unless she is very unlucky and has a huge degradation in atmospheric quality or has a bunch of dust land on the arrays she should be still be generating ~80% of her initial power levels at the end of the primary mission.

Click to view attachment

Does anyone know at what temperature C02 will start freezing at the Phoenix site?

-125 C I believe.

The web page with the sundial disappeared, anyone know what happened ?

I found a press release from ATK, the manufacturers of the solar arrays, that says that each of the two panels will [initially] generate "770 Watts" and are 1.2 meters in diameter. 1.2m in diameter makes for a total surface area of 6.93m^2 so the stated solar panel area of 4.2m^2 seems about right if it refers to the actual collection area of the cells themselves. The 770 Watt number is odd though. If the units are incorrect and they are actually meant to say was 770 Watt Hours then the cells themselves must be only about 13% efficient. If they genuinely do mean Watts then assuming that the panels actually do generate 770 Watts at some stage then the efficiency of the cells would need to be about 85% efficient, which is certainly not correct.

The 770 Watt Hour assumption seems most likely to me so I've amended my power chart to reflect that. Without any info on what sort of power levels Phoenix needs to survive at each stage of the mission the numbers still don't really tell us much.

As a quick indication of the accelerating rate at which power will drop off:

Click to view attachment

...impressive work, Helvick, as always!

That 13% efficiency figure is certainly odd, though. Are they trying to say that the cells would optimally function at 85% on Earth, but the solar flux on Mars is (IIRC) around 45% on average with respect to Earth due to distance & atmospheric dust? Might be some sort of conversion loss in the power distribution system as well.

the %'ge is the %'ge of electricity produced as a function of the total radiation in watts / sq metre from the sun at that location

Doug

The 770 Watt Hour number as a per Sol amount of power is the only one that really makes much sense.

If they really meant that the panels could generate 770 Watts then they would each generate at least 5 kiloWatt Hours per sol, which just seems way too much to me, after all MSL is only going to need around 2.5 from its RTG.

On top of that the value is not actually possible as far as I can tell. The solar constant at Mars (the amount of solar energy per M^2 at Mars' current distance from the Sun) is about 490 Watts / M^2. If you ignore all potential losses in the chain such a panel would need to be built of cells that had a 75% conversion efficiency rate. Once you add in atmospheric losses and the power distribution system losses then you'd actually need magical cells that were >100% efficient.

My calculations tell me that the 770 Watt Hour value means that the cells must be around 13% efficient but my calculations could be wrong. The model that I use for diffuse insolation gets less reliable when the sun angle is very low and it's possible that I'm substantially overestimating the amount of diffuse power available, if I were to discount diffuse insolation then that number would be around 20-25% which brings it into line with the MER solar cells.

http://atk.mediaroom.com/index.php?s=press...es&item=821

"Each Ultraflex array unfolded like an oriental fan into a circular shape 2.1 meters in diameter and will generate 770 watts of power from sunlight at the distance Earth is from the sun. Since Mars is approximately 1.5 times farther from the sun, the solar arrays will produce less than half the power possible on Earth."

My guess is that they meant both panels together (6.92 m2) generate a peak of 770 watts at 1 AU without atmospheric losses, which would put the efficiency at around 23%, which seems believable.

It would help if I actually read my own link properly.

Thanks Mike, that's exactly correct.

I love graphs like this. Though I thought this thread might be about the basketball team, from the name.

The spirit of the MERs is still with us. We want to see more of this scenery, the changing seasons, and have it go on and on. But this site was chosen as a place which is almost dimensionless in time and space. That's a sea of ice underfoot and aside from the polygons and some pebbles, this area is isotropic all the way to the horizon. Phoenix's whole mission will essentially be one long weatherless day with nothing happening to its right, its left, its front or its back. The story is in the nuclei of the atoms underfoot. How long has the ice on the surface of the sub-dust layer been there -- since the last change of seasons, the last change in obliquity, or since the planet was put together from its building blocks? We're sitting on a crime scene with no body, no weapon... just lots of fingerprints. For me, the mission hasn't started until TEGA and MECA have their measurements and then it will essentially be done.

If the D:H of the ice is sufficiently different than that of the atmosphere, we'll basically have a synopsis of the last billion as well as the next billion years of this site, which would be: No change. Nothing new for the cameras to reveal if it woke up the next spring or 5000 springs from now.

If the D:H matches the atmosphere, then we can wonder what we'd be missing if we dug trenches at odd intervals throughout the seasons.

Beyond that, we have lots of MOC imagery of these latitudes from the winter. If you want to see what's coming:

http://www.msss.com/moc_gallery/r16_r21/fu...17/R1702309.jpg

You mean the Mars Science Lab rover?

I found this http://www.fabtech.org/content/view/6540/ which says the panel efficiency is 28.3%.

How thick does the ice get? I was wondering if maybe the layer of dust on top of the "Snow Queen" material (assuming it's ice) comes from melting of dirty ice above. I.e., the way glaciers dump till when they melt.

Another attempt at estimating the power generated by the solar panels. Mike's links clarified the cell efficiency and confirmed that the panel area is 4.2M^2 so it now appears that Phoenix started off generating almost 3.5 kWatt Hours per Sol. The only major variable I'm not accounting for is the conversion efficiency of the power management system which I'm assuming is 80% but that is just a guess.

I dropped in a variant of jmknapps solar elevation chart in aswell - I thought it was a nice way to see the link between the sun's change in elevation and the drop off in power.

Temperature would be a neat component to add now - anyone know of an easy way to approximate\estimate the change in surface temperature given that I have the overall rate of change in insolation? I'm having some trouble getting my head around thermal inertia so any pointers would be welcome.

Click to view attachment

TES provided some "ground truthing" as did the Vikings and Pathfinder. Roughly speaking, you can assume a phase shift between insolation and temperature, and from Pathfinder, it looks like it's about 3 hours during daylight and 10 hours during the night.

A key factor is: Which temperature do we care about? Pathfinder showed a difference based upon very slight difference in altitude. We probably don't care if the footpads are at absolute zero but rather about the instrument deck, and with Pathfinder, the difference was small at night but about 6C in the afternoon. The actual instruments may experience a nanoclimate based upon the reflectance of the craft (as opposed to the Pathfinder sensors).

Basically, I think TES will hand you the answers. It was scanning a full line of longitude every day. This data ought to already be on the books. Pathfinder can let you map surface temperatures onto "1 meter" temperatures.

(A Newbie's first post.. yay)

I'm doing a painting of Phoenix on the surface at midnight - the view will be from the Northwest looking Southeast, so a good bit of it will be looking nearly down-sun.

I was really hoping that we would have gotten the midnight "Holy Cow!" shot by now so there would be something to get a sense of what low sun, down-sun looks like on Mars. I have trolled the MER pancam shots but haven't found anything relevant yet, nor have I found that one picture I've seen (probably from a Haz Cam?) with the shadow of the rover extending far out in front. Is there a group that is interested in the low-sun/sunrise look of the surface? I have seen some cool stuff of what the sun looks like rising (from Viking as well as MER) but nothing looking the other way.

The sun elevation graph here is really helpful, which is why I'm posting to this thread. (This whole enterprise (UMSF) is incredibly useful and interesting!). I'll post a pic of my work when it is done if that's appropriate.

Thanks!

Paul

I'd like to see a simulated view of a Martian analemma. It's an ellipse (or teardrop) on MPL/Spirit/Oppy site, but what about the Phoenix site?

Mars 24 will do that for you.

Doug

Great, thank you Doug, I found that option!

It should be exactly the same shape as viewed from anywhere on Mars, just lower or higher in the sky (and inverted as viewed from the southern hemisphere relative to the northern view).

my confusion was because the sun never sets during the summer and it's complete darkness during the winter. We expect to see a partial ellipse.

You may be thinking of this famous shot at Endurance:
http://marsrovers.jpl.nasa.gov/gallery/all...52P1214L0M1.JPG
There was also a similar shot from just inside Vicoria:
http://marsrovers.jpl.nasa.gov/gallery/all...00P1156L0M1.JPG
I can't think of any more looking-away-from-the-low-sun shots at the moment...

I'd love to see your result when it's done...

The analemma drops lower as you move north (but keeps its shape). Once you cross the arctic circle, the bottom of the analemma dips below the horizon. By the time you get to the north pole, you can see only the upper half of the analemma. All of this is observing at local noon. At other times of day you'd see even less of the analemma.

Gee, with all the clear skies on Mars, it would be quite easy to do one of those one-photograph-a-week analemma shots...

That's it! Thanks!

I also went here:
http://mars.jpl.nasa.gov/MPF/science/clouds.html
... Mark Lemmon's(!) page from Pathfinder, which maybe gives me some hints about the atmospherics - although the best descriptions are of the area around the sun. Maybe I can put some bluish, light clouds off in the distance. Got to be clouds right? Got to have other colors besides browny,pinky,orangy??... (oh yah, I'm on Mars.)

I'll put the final image up on a private/UMSF page when it's done and released. Another week if I'm lucky.

Paul

Phoenix has plans for night imaging. Most of it supports atmospheric science, but some will include a photometric campaign (anit-Sun imaging is key), and I'd hope for a few midnight Sun shots. The "night-time" ("daytime" being the lander work-day) science is delayed, since the systems engineering crowd is fully occupied with the core activities involved in sample acquisition and transfer. Things like a camera pre-heat test are needed before going ahead with "first-time activities". It sounds conservative, but I certainly won't forget that attempting a wake-up for night-time MET and imaging is the last set of commands Pathfinder attempted to obey.

Thanks Deimos - it sure sounds like you know what you are talking about!!

My deep hope was that the interest in finding out more about "Holy(#$%@^!!)Cow" and thus an early midnight shot looking down-sun with the arm shadow through that feature, would trump engineering concerns. You have made starkly clear a professional tilt for caution! So I'll have to wait or guess what the scene will look like at midnight. Since I service the media, I'll have to guess! ('Why wait when you can speculate' is, I think, the motto...)

Thanks to the LPL PAO, I have the overnight arm position for SOL 12 so that is the view that I'm doing. It was parked over near the +Y (east) Solar Array, out of the way of the work area for photo coverage. I'm now looking more SSW through the lander from the Northeastern edge of that workspace, about a foot and a half off the surface. That great shot fredk pointed me to - MER downsun - looks to have a sun elevation of about 10 degrees (based on where the MER deck shadow cuts the Hi-gain antenna shadow) which is somewhat higher than the nearly 4 degrees at Phoenix midnight (jmknapp's thread-start post here).

Some of the effects that I would expect on the surface seem apparent in that MER hazcam pic, such as the surface brightening as you approach directly downsun (the camera shadow). But the effect of the sky to go "darker" as you move from the horizon then up is something that I want to nail down a bit. Is that an artifact of the camera and extreme fish-eye lens? I've noticed that B/W pics have a lot more interesting contrast than their color versions; Mars seems to want to blandify everything in a haze of pinkish/orangy-brown!

And then, could there have been any clouds on SOL 12 at midnight? One of the benefits of art is that I can use something akin to artist's licence here (but not a 007 licence) - that is, I need to be plausible. Of course, any painting of some clouds would have to be a lie in the specific case, but perhaps acceptable as an illustration of fact: there are clouds at the Phoenix site - this is what they could look like.

I will have a chance to correct any massive errors after the painting's first release. But before that, any speculation is welcome!

Paul

In that Oppy shot looking into Endurance I'd guess the sun is somewhat higher than 10 degrees - local time was only around 4:30pm (the rover may be on a significant slope itself). I'd guess 20 to 25 degrees for the solar elevation.

The sky gradient is a combination of lens vignetting and a real gradient. To see the true sky gradient, look at the MRD image on this page:
http://an.rsl.wustl.edu/mer/merbrowser/pro...FF3352P1214L0M1
This image has been corrected (flat-fielded) for lens vignetting etc. You can see that the opposition surge and sky gradient are reduced, but are still visible.

The direct link to the corrected image is:
http://an.rsl.wustl.edu/mer/merbrowser/pro...RD3352P1214L0M1

Thanks!

I wonder how much that vignetting would be apparent in color and, more importantly, to the eye. I'm sorry that the MER shot has such a high solar elevation after all. I'd like to guess that the gradient effect is even more pronounced at low sun, but I've never seen any pic from Mars with that, other than the hazcam shot.

Paul

Using midnight mars browser with Dan Crottys calibrated Pancam imagery, you can often see quite extensive sky surveys showing what you're after, I think.

Doug

The vignetting part of the gradient is purely a camera effect - you wouldn't see it by eye. The corrected image I linked to should be close to what the eye would see in terms of sky gradient.

Okay, great. I'll do the >gradient< close to that.

Doug: thanks for the Midnight Mars Browser suggestion (man, I really am a newbie...). It is very cool. I need a couple of days to troll through these many years(!) of roving, but it is amazing. So is Emily's library of Phoenix raw images with the LST,Az/El and Camera ID. Sad she's on vacation...

Paul

BTW, Deimos is the author of the Pathfinder clouds, sunrises, and sunsets page you referenced earlier.

I had an inkling... this is a great site!

Saw the atmospheric shots taken from the Phoenix SOL 14/15 downlink to coincide with one of the orbiters' data takes. It looks like you can see stars in a few of the shots! I will find out what the starfield should have been at the time and see if anything fits. In daylight, I didn't think you could see stars on Mars.

Paul

Before you go through the trouble of fitting stars, could you point to a particular image? They took a bunch of solar filter images to characterize the noise, which might be what you're seeing. The Martian daytime sky is really quite bright...

Agreed, it's exceedingly unlikely those pixels are stars. Rather, they're hot pixels in the CCD. When doing long exposures, differences in sensitivity (dark current actually) of each pixel becomes quite noticeable.

Okay, that saves me some trouble. I could swear I recognized a constellation!

Paul

I was struck by this image from Sol16.
Click to view attachment

I'm wondering if, when everything else is done, that near the end of the mission they could try for something like this.
Click to view attachment

Just a thought.
Astro0

Cool! I've often wished that some of the operations "budget" could be used for dramatic shots like this or, at least, pictures when the sun is low. I think it would make for some very neat images that might wind up iconic.

Paul

I'm not really sure where to put this little nugget of information but I found this paper detailing the power requirements for arm heating and operations on the NASA Technical Report Server that gives some idea of the power requirements for digging operations.
Heating from a ~-90C overnight temperature of the arm components to the levels that are required for early morning operations requires a total of about 50 Watt Hours of power over a three hour heating schedule. During operations the four arm actuators are limited to drawing between 3.6 and 5.3 Watts of power each so as to limit heating the actuators over 85 deg C during 3.5 hours of use. At most the arm could use 55 Watt Hours of power during a 3.5 hour session and in practice would probably use less than 25% of that. The heaters remain active during operations so the total power budget for a single trench digging session per sol during the primary mission is somewhere between 120 and 165Watt Hours.

Some related information from JPL's website:



Including this deployment video