"Mike Dworetsky" wrote in
:

Yousuf Khan wrote:
On 18/07/2011 11:39 PM, eric gisse wrote:
Yousuf wrote in
I'm not even sure why they are doing such an elliptical orbit like
that? Any advantages for viewing angles or stuff like that?

Yousuf Khan


No ****ing idea.

The distance isn't enough to alter the view seen, but it _might_ be
enough to play VLBI games but I don't believe the orbital
information and transmission setup is precise enough to preserve
phase/timing information down to the nanosecond.

I was thinking maybe the orbit would allow it to avoid the day side
of the planet and avoid being blocked by the planet as it looks at
distant stars. Also avoid it'll the radio noise of the planet. Earth
is supposedly much brighter than the Sun when it comes to radio.

Orbits are not accidental so either they wanted it to be there, or a
higher purpose was served that has putting it there as a byproduct.
I just can't figure it out.

Maybe they don't have a strong enough booster to put it in a circular
orbit that far up? That's almost as far as the Moon.

Yousuf Khan

It always helps to read the articles about which you post links. It
is stated that the orbit is designed to allow the telescope to work
with the interferometric network of radio telescopes on Earth to
provided higher resolution than can be obttained from the ground.
From this I assume that the ground stations can track the position of
the telescope accurately enough to permit good interferometry to be
done.

http://space.skyrocket.de/doc_sdat/spektr-r.htm

I only noticed the VLBI link _after_ I read this, and revisited the
original link. Somehow it escaped notice on the first read.

I'm truly impressed that they can do space-ground interferometry with a
radio telescope. This will be very valuable.


A high-eccentricity orbit costs less than a low-eccentricity distant
orbit in terms of thrust required, yet it allows the radio telescope
to be at a large distance from Earth about 80-90% of the time (near
apogee) in accord with Kepler's 2nd law of planetary motion.


A subtlety that doesn't appear until you think about it.