[X] My Assistant

[jmknapp]

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?

[helvick]

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.

[JRehling]

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.

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.

[Paul Fjeld]

(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

[Deimos]

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.

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.

[Paul Fjeld]

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