ESA has a nice post, walking through the challenges in trying to get data back from Philae.
After the uncontrolled landing on 67P/CG last fall, the Philae lander ended up in a shady spot and had to shutdown for lack of power. As the comet has closed on the Sun, Philae now has recharged the batteries and contacted the Rosetta orbiter—but only for brief periods.
Responding to this, the Rosetta team has decided to sacrifice some activities to maneuver the orbiter to try to get a good signal from Philae. To date, this is a gamble that has not paid off, since not much has been received from Philae.
In any project like this, the mission is working with extremely tight budgets of energy, bandwidth, and memory; not to mention orbital physics and severe time limits. Furthermore, we have limited information about what is going on, especially if we can’t get data via radio. Getting a link is the basic first step, which is why these problems are so frustrating and tense.
All that said, ESA’s post “Rosetta and Philae: Searching for a good signal” was very helpful. They lay out the basic problems, hypotheses about what may be going on, and what actions are possible. This helps us all understand what they are trying to do and why it is difficult. It also helps us understand the risks and tradeoffs.
It is very nice to get this sort of grown up information from ESA, without the shallow Hollywood stuff that some think the public wants. (I’m talking to you, NASA PR flacks.)