[Magdalen] Philae has landed!

[Roger Stokes]

On 12/11/2014 20:34, Grace Cangialosi wrote:
> This is totally beyond my comprehension! I think of comets literally streaking across the sky...how would you know where it was going to be when you tried to land?!

In principle it's very easy as it has a regular orbit (6.45 years long) 
around the Sun.  This means you can predict where it will be at any 
particular time from the observations that have been made of it. That is 
when it starts getting calculated as powerful computers work out how you 
can get a spacecraft travelling at about the same speed (currently just 
over 41,000 mph) which is significantly higher than the velocity needed 
to escape Earth's gravity, and when a spacecraft does escape Earth's 
gravitational pull that pull will have reduced its speed considerably so 
it needs to increase its speed very significantly.

That is why the gravity of other planets is used in a slingshot effect 
to accelerate it. This is what makes the calculations complex as you 
need to calculate how best to utilise those other planets to achieve the 
desired effect.  Once you have made the requisite calculations you then 
need shedloads of money to bring your plan to fruition.  Fortunately 
Rosetta started its journey before the great economic downturn.  Whether 
you would have got the necessary funds together now is problematic.

Roger