Dust Storm- Opportunity EOM, the end of the beginning of a new era in robotic spaceflight |
Dust Storm- Opportunity EOM, the end of the beginning of a new era in robotic spaceflight |
Jun 5 2018, 03:05 PM
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#1
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Founder Group: Chairman Posts: 14434 Joined: 8-February 04 Member No.: 1 |
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 |
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Jun 15 2018, 07:19 PM
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#2
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Director of Galilean Photography Group: Members Posts: 896 Joined: 15-July 04 From: Austin, TX Member No.: 93 |
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. -------------------- Space Enthusiast Richard Hendricks
-- "The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C Clarke Mother Nature is the final inspector of all quality. |
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Jun 16 2018, 02:58 AM
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#3
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Member Group: Members Posts: 507 Joined: 10-September 08 Member No.: 4338 |
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: 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). |
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