10
$\begingroup$

If a satellite is to be inserted into a retrograde orbit (opposite to Earth rotation direction) is it accelerated straight in the desired "westwards" direction until (after overcoming Earth rotation speed) orbital speed is attained, or is it first inserted into a prograde orbit and then some engines of lower thrust but better specific impulse are used to gradually turn its orbit, through polar, into retrograde - or maybe is some other trick used?

$\endgroup$
  • $\begingroup$ I can delete this answer if you feel it's not helpful. If you mean to restrict to Earth orbit, it might be good to change the title to "...retrograde geocentric/Earth orbits..." or something similar. The bump in activity will give you a few points as well ;-) $\endgroup$ – uhoh Apr 16 '19 at 7:59
  • $\begingroup$ I think we had a discussion somewhere about how to turn a prograde into a retrograde orbit. One solution was to accelerate to almost escape velocity and then "fall back" to earth and the other solution was to use the moon. I think while both are possible they are not very useful except maybe if you fly as secondary payload and got a lot of time. Maybe someone can find it. $\endgroup$ – Christoph Apr 16 '19 at 9:20
  • $\begingroup$ update: I will delete it, now that it was pointed out I was completely wrong! $\endgroup$ – uhoh Apr 16 '19 at 10:05
  • 1
    $\begingroup$ @uhoh: Ah, and there I was thinking how a maneuver that would be good 60km/s "the straightforward way" was optimized to get completed... $\endgroup$ – SF. Apr 16 '19 at 10:15
  • 1
    $\begingroup$ @Christoph That first approach is called a bi-elliptic transfer (en.wikipedia.org/wiki/Bi-elliptic_transfer). In the case of an object like the sun, reversing your orbit can take a little more delta-V than twice that of the solar excape velocity (~32 km/s) if you don't mind sending it out to beyond pluto and waiting a couple of hundred years. Otherwise, you gotta stump up the budget for 60 km/s. $\endgroup$ – Ingolifs Apr 16 '19 at 22:53
11
$\begingroup$

For retrograde launches, the launch azimuth is westwards from the beginning. It would not be viable to first go into prograde orbit and then change the inclination into retrograde trajectory. Such huge inclination change would require an awful amount of fuel, because effectively it would be like killing the speed in the prograde direction (over 7 km/s) and gaining the same speed in the opposite direction.

Scienceworld

$\endgroup$
3
$\begingroup$

A common example of a launcher that always launches retrograde, is Israel's Shavit booster. Due to the nature of its neighbours to the east, and the fact most space launches closely resemble ICBM style launches (which might cause some concern on launch) and no where safe to drop empty stages, they launch west over the Mediterranean Sea.

For more on that see answer(s) to The strange orbit of Ofeq 11 - how does it (actually) do this?

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.