The Naked Scientists

The Naked Scientists Forum

Author Topic: Why can't Philae be recharged?  (Read 2099 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
Why can't Philae be recharged?
« on: 13/01/2015 16:30:01 »
Chris Martin asked the Naked Scientists:
   
If I charge my mobile phone for half an hour each day for a week (with it switched off), it will be fully charged by the end of the week. Why doesn't Philae work in the same way and start working again?
What do you think?
« Last Edit: 13/01/2015 16:30:01 by _system »


 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2760
  • Thanked: 38 times
    • View Profile
Re: Why can't Philae be recharged?
« Reply #1 on: 14/01/2015 01:38:22 »
Quote from: thedoc
Why doesn't Philae work in the same way and start working again?
What's "Philae"? Is it the spacecraft that has too little power to operate now because its too far from the sun?
http://en.wikipedia.org/wiki/Philae_(spacecraft)

I would assume that its because when you charge your cell phone its being charge with a fully powered charging system whereas Philae has a solar cell charging system which when far from the sun produces very little electrical energy. I don't know how solar cells work so I can't tell you anymore but I'm sure that you need to learn about solar cells before you get an answer to your question.
« Last Edit: 14/01/2015 01:49:46 by PmbPhy »
 

Offline JohnDuffield

  • Sr. Member
  • ****
  • Posts: 488
  • Thanked: 1 times
    • View Profile
Re: Why can't Philae be recharged?
« Reply #2 on: 14/01/2015 10:01:52 »
I saw something on TV where somebody said they were hoping to recharge Philae when the comet got closer to the sun. Pete: Rosetta is the spacecraft, Philae is the lander, see wiki.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4107
  • Thanked: 245 times
    • View Profile
Re: Why can't Philae be recharged?
« Reply #3 on: 16/01/2015 11:12:17 »
The power budget for Philae was pretty tight. They were aiming to land on a wide, flat space that would be exposed to sunlight almost half of the time. That would provide enough power to keep its instruments operating continually.

However, as it happened, the anchoring harpoons failed to deploy, and it bounced a couple of times, eventually coming to rest at an awkward angle, wedged against a large mass of ice or rock that allows only 90 minutes of sunlight per 12 hour rotation of the comet. With so little solar power, the non-rechargeable battery went flat after 60 hours, and Philae went into hibernation.

I imagine that if they had designed it with a low-power charging system, they could have slowly recharged the battery for 5 days, then reawakened Philae for a few hours, then go into hibernation. They would also need a rapid reboot - if it spent a few hours restarting the computers, checking the equipment and reestablishing communications, they wouldn't get much science done! Most rechargeable battery technologies don't work very well when the temperature is well below zero, and the intermittent charging might not allow the battery to keep warm enough to retain a charge. However, the goal was to land in an open site with solar heating, so intermittent charging wasn't a design goal.

The comet is spinning like a gyroscope, so it points in the same direction (relative to the stars) as it goes around the Sun. This allows for the possibility that although Philae is badly shaded now, in another 6 months the angle of the Sun will be different, and they may get more sunlight. As the comet moves closer to the Sun, the sunlight gets much stronger (due to the inverse square law), so they can charge the battery more effectively. So maybe they could get some longer-term observations later in 2015...
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 11987
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Why can't Philae be recharged?
« Reply #4 on: 23/01/2015 21:38:28 »
The glass half full there?
 

The Naked Scientists Forum

Re: Why can't Philae be recharged?
« Reply #4 on: 23/01/2015 21:38:28 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums