Dust Storm- Opportunity EOM, the end of the beginning of a new era in robotic spaceflight Options

[serpens]

As siravan noted the spectrum at the surface would be skewed towards the red. The spectral response of Opportunities solar cells extends into the near infrared and it would not surprise if this is where the remnant charge is coming from. While comparing Earth to Mars is a bit chalk and cheese the attached link shows the effect on visible light of a dust storm in my old stamping ground. https://www.youtube.com/watch?v=BrlD22HwPvI

The descriptions of current (human) visibility on Mars as a cloudy day may be a trifle optimistic, even given the range of visibility of the human eye:

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[marsophile]

On the 22 WH just to keep the clock alive, maybe that number is accounting for the stuck IDD heater?

According to the paper cited here:

https://trs.jpl.nasa.gov/handle/2014/37750

the stuck on heater causes a drain of 0.5 amps, but it is actually really only on when the temperature drops sufficiently. The paper estimated a cost of 180 WH per day at the time the anomaly occurred.

Assuming 24 volt battery power, 1 watt corresponds to around 40 milliamps, which doesn't seem too unreasonable for the mission clock (plus alarm mechanism).

[Deimos]

The descriptions of current (human) visibility on Mars as a cloudy day may be a trifle optimistic

Not sure what is meant. The chart describes a factor of ~30 below full sun (ok, a factor of 60 below given Mars-Sun distance) as 'near windows'. Moreover, overcast days on Earth literally have optical depth >10 quite frequently (well, frequency is location dependent, but I grew up in Seattle).

If blue is the limiting factor for the triple junction cells (per siravan), the light providing array energy cannot be all IR; frankly, there should be more red light available than IR (per unit wavelength) given the Sun's spectrum and the albedo of dust in the red.

[mcaplinger]

Assuming 24 volt battery power, 1 watt corresponds to around 40 milliamps, which doesn't seem too unreasonable for the mission clock (plus alarm mechanism).

Normally you don't use linear regulation from battery voltage, because most of the power is used in the regulator. 40 mA at 5V is only 200 mW (which is still a lot for a simple clock -- for example, a Chronodot RTC http://docs.macetech.com/doku.php/chronodot_v2.0 -- admittedly not rad-hard -- uses 840 nanoamps in standby timekeeping!). But it's not impossible that in this case they did use linear regulation because it's simpler and losing all solar power wasn't really a credible fault for the short mission design life.

At any rate, if the clock is lost, we may see a lot of X-band "sweep & beep" commanding once there's any expectation that the rover is getting enough power during the day to communicate. On Spirit they started this about 4 months after the loss of comm. See https://mars.nasa.gov/mer/mission/status_spiritAll_2010.html for some descriptions of this.

[Don1]

I did try to estimate the illumination based on the solar panel output, and I was puzzled by why that was coming out so differently from the estimate based on tau. What bothers me about the 22 Watt-hr quoted for the solar panel production is that seems way too much to just run a clock. Are we certain that number is accurate?

Also, if there was a break in the storm the rover might have gotten half an hour of sun which would charge the battery a little. We don't know how much the panels were producing at the time the tau was measured.

On a different topic, the 8 RHUs are providing 192 Watt-hours of energy in the form of heat. If I remember correctly, sunny day production from the panels is about 600 Watt-hours of electricity. So a big chunk of the energy budget of this "solar" powered rover is actually from nuclear sources, even when it is sunny. That surprised me when I worked out the numbers.

[fredk]

If blue is the limiting factor for the triple junction cells (per siravan)

Another point is that if blue limits the power, and the sky is very red, then estimates of the overall brightness on the ground based on the 22/700 ratio will be underestimates, due to the extra red light not contributing to array power. Probably not a huge factor, though.

[mcaplinger]

What bothers me about the 22 Watt-hr quoted for the solar panel production is that seems way too much to just run a clock. Are we certain that number is accurate?

No, and it was a bit of an off-the-cuff answer, but barring some additional information from the project it's all we have to go on, and it's not implausible given what details of the design we do know. For example, some types of Q-Tech oscillators really do draw 40 mA just for the oscillator, and then for a complete clock there has to be a counter and maybe some other stuff -- the fault protection paper references a "mission clock FPGA".

I also don't fully understand how the scheduling of transmission and reception periods happens if the mission clock is lost. This seemed to introduce a lot of complexity into the attempted recovery process for Spirit. Presumably without the mission clock there's no way for the rover to figure when 11 LST is (in theory it could do with from solar power production but that would vary a lot based on tau, tilt, dust on the panels, etc.); AFAIK this scenario isn't described in the fault protection paper.

[MahFL]

No, and it was a bit of an off-the-cuff answer, but barring some additional information from the project it's all we have to go on, and it's not implausible given what details of the design we do know. For example, some types of Q-Tech oscillators really do draw 40 mA just for the oscillator, and then for a complete clock there has to be a counter and maybe some other stuff -- the fault protection paper references a "mission clock FPGA".

I also don't fully understand how the scheduling of transmission and reception periods happens if the mission clock is lost. This seemed to introduce a lot of complexity into the attempted recovery process for Spirit. Presumably without the mission clock there's no way for the rover to figure when 11 LST is (in theory it could do with from solar power production but that would vary a lot based on tau, tilt, dust on the panels, etc.); AFAIK this scenario isn't described in the fault protection paper.

The rover transmits roughly around midday on Mars, so the orbiters listen then. Once the signal is received they can send commands to the rover, which listens periodically, eventually getting back into sync with Earth.

[Don1]

I also don't fully understand how the scheduling of transmission and reception periods happens if the mission clock is lost.

The only thing I got from the press conference is that when the rover detects sunlight it sets a timer so that it can wake up periodically to attempt to phone home. I think it is a 4 hour interval, so presumably the DSN will listen for 4 hours during daylight to see if it hears from the rover.

[serpens]

While the GaInP top cell is the limiting (short circuit) control its spectral response extends out to 750nm with a high response out to 600nm. So low levels of solar power will continue to be generated when much of the visible spectrum is suppressed. This link provides some information on MER solar panel performance https://ntrs.nasa.gov/archive/nasa/casi.ntr...20070010752.pdf
Absorption due to dust is highest towards the blue, decreasing to level out around 650 nm. Scattering increases with wavelength. So with the optical depths over the course of the day with tau of 10.8 it is possible that the small charging occurred around midday and if the tau has increased, has terminated.

[mcaplinger]

The rover transmits roughly around midday on Mars...

As noted before, if it was that easy, then how do you explain the need for the "sweep&beep" campaign done for months with Spirit?

[hendric]

I don't see how, that heater is turned off when the battery controller is turned off, that being the whole point of deep sleep.

Yes, but when the rover wakes up to phone home/listen, the IDD current draw could be a factor then if the temp is low enough to turn it on uncommanded.

[fredk]

I guess the question is: how does the rover decide if it's midday? One idea would be exceeding some minimum power level. More elaborate would be to take several power level samples over at least a day and fit a sinusoid. If it's something like the former it may get stuck thinking it's not midday until tau drops sufficiently.

[mcaplinger]

when the rover wakes up to phone home/listen, the IDD current draw could be a factor...

I expressed the same concern back in post #51, yes.

[mcaplinger]

More elaborate would be to take several power level samples over at least a day and fit a sinusoid.

Perhaps, but this kind of elaborate solution that requires state to be recorded and used from sol to sol is usually not used in deep fault responses, because it's really hard to test all the possible permutations.