3 ms·

"And what is the major power draw that leads to such a short battery life? The heater to keep the electronics warm?" Yes, it's in the other post: "It is v

"And what is the major power draw that leads to such a short battery life? The heater to keep the electronics warm?" Yes, it's in the other post: "It is very unlikely right now. We have 1.5 hours [of sunlight] at less than 1 watt, and 20 minutes of 3 or 4 watts. The lander needs 5 watts to boot….In order to charge the secondary battery, we have to heat it to 0 degrees Celsius. We need about 50-60 watt-hours a day in order to reach 0 degrees and still have daylight left to charge the battery." http://elakdawalla.tumblr.com/post/102615327170/philae-update-my-last-day-in-darmstadt-possibly http://elakdawalla.tumblr.com/post/102615327170/philae-updat...

jessriedel 12y ago
I knew they are partially shaded, but are they literally only getting ~2% of the power they expected? Is this just a thin sunbeam or something?
- throwaway_yy2Di 12y ago
  I guess so. The rated power [0] is 32 watts at 3 AU (current distance from sun), and it's getting 10% of that, for 20 minutes a day. (I'm not sure what a "day" is; maybe it's the comet's rotational day, which is 12.4 hours). [0] [PDF file] http://www.dlr.de/dlr/Portaldata/1/Resources/documents/Philae_Lander_FactSheets.pdf http://www.dlr.de/dlr/Portaldata/1/Resources/documents/Phila... 20 minutes per rotational period, does sound like a very narrow sunbeam!
- acqq 12y ago
  "Asteroids and comets rotate, but not exactly like the Earth. Because Earth is a sphere, its mass is distributed relatively evenly, so it rotates smoothly. Asteroids and comets aren’t uniformly shaped, so their rotation can be more of a tumble. NASA equates their rotation to the spin you see on a badly thrown football." (1) Now imagine that you target landing close to the wobbling equator but eventually end somewhere closer to the wobbling south pole, and maybe even in the shadow of something bigger (that helped you stay on the comet). Less sunshine and freezing gets much more certain. 67P/Churyumov–Gerasimenko has the rotation period of cca 12 hr. (2) 1) http://science.opposingviews.com/asteroids-comets-rotate-20105.html http://science.opposingviews.com/asteroids-comets-rotate-201... 2) http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimen...

jessriedel 12y ago

I knew they are partially shaded, but are they literally only getting ~2% of the power they expected? Is this just a thin sunbeam or something?

throwaway_yy2Di 12y ago
I guess so. The rated power [0] is 32 watts at 3 AU (current distance from sun), and it's getting 10% of that, for 20 minutes a day. (I'm not sure what a "day" is; maybe it's the comet's rotational day, which is 12.4 hours). [0] [PDF file] http://www.dlr.de/dlr/Portaldata/1/Resources/documents/Philae_Lander_FactSheets.pdf http://www.dlr.de/dlr/Portaldata/1/Resources/documents/Phila... 20 minutes per rotational period, does sound like a very narrow sunbeam!
acqq 12y ago
"Asteroids and comets rotate, but not exactly like the Earth. Because Earth is a sphere, its mass is distributed relatively evenly, so it rotates smoothly. Asteroids and comets aren’t uniformly shaped, so their rotation can be more of a tumble. NASA equates their rotation to the spin you see on a badly thrown football." (1) Now imagine that you target landing close to the wobbling equator but eventually end somewhere closer to the wobbling south pole, and maybe even in the shadow of something bigger (that helped you stay on the comet). Less sunshine and freezing gets much more certain. 67P/Churyumov–Gerasimenko has the rotation period of cca 12 hr. (2) 1) http://science.opposingviews.com/asteroids-comets-rotate-20105.html http://science.opposingviews.com/asteroids-comets-rotate-201... 2) http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimenko http://en.wikipedia.org/wiki/67P/Churyumov%E2%80%93Gerasimen...