[X] My Assistant

[djellison]

Expect a quiet few sols - http://www.lpl.arizona.edu/~lemmon/mars-tau-b.html
SOL TAU
5097 0.65
5098 0.64
5099 0.67
5100 0.64
5101 0.60
5102 0.60
5103 0.61
5104 1.55
5105 ****
5106 2.12

[hendric]

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

From the paper - "The Mission Clock in the MER rovers uses a custom hybrid crystal oscillator from Q-Tech Corporation. " which however is proprietary, at least at the time the paper was published. The skew of +-10s over 10 sols with temperature is pretty reasonable for a typical +-50 ppm crystal oscillator. (~900,000s for 10 sols, so about +- 10ppm with 10s drift). To get better PPMs clocks in your phones use temperature compensation, ie they adjust the voltage based on temp, with <2 ppm or less commercially available. Of course, that costs power too (~mA), and isn't space rated. A COTS RTC (real-time clock, think wrist-watch in a tiny package) without temperature compensation can be < 1uA though, again not space rated.

[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).

[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.