[Magdalen] Philae has landed!

[Jon Egger]

Since I asked that question, I found out on reddit that the "lag" from
comet to Earth is ~27 minutes, which to me is simply amazing!

+++
Grace & peace,
jon


On Thu, Nov 13, 2014 at 3:48 AM, Roger Stokes <roger.stokes65 at btinternet.com
> wrote:

> On 13/11/2014 03:02, Jon Egger wrote:
>
>> What I'm wondering is the time issues involved.  Surely the landing isn't
>> "live" as in happening right now, given the distance the signals must
>> travel to Earth to receive them.  Yes, the probe landed there, but how
>> long
>> ago given the time constraints.
>>
>> Does that make any sense?
>>
>
> It makes perfect sense.  Currently a radio signal to or from the
> spacecraft will take about 30 minutes for the one way trip. That means that
> if data is sent from Rosetta (the orbiting craft) to Earth, processed here
> and then a command sent back it takes an hour for the command to get to the
> spacecraft.  There needs to be a degree of "artificial intelligence" on the
> two craft so they can respond to data in real time.
>
> All the scientists on earth can do is anticipate what is going to happen
> if there is no interbention, calculate what adjustment is needed and then
> send a command allowing enough time for it to be implemented at the right
> instant.  The manouevering has to be incredibly precise given the small
> size of the comet.  The gravity is so weak that the escape velocity, the
> speed needed to escape its gravitational pull, is estimated at 3 ft/sec.
> That is less thanthe speed we need to achieve to jump a couple of inches
> into the air. Getting Rosetta in orbit around the comet was another complex
> piece of fine adjustment of the craft's paramaters, not helped by the fact
> that the comet is not a regular shape.
>
> Roger
>