delta V needed for a retrograde orbit

[Starchaser]

I am having to launch my first retrograde satellite orbit, and I couldn't find the delta-v required for it. I can't imagine it's the same as a regular orbit.

Edited March 28, 2015 by Starchaser

[Deutherius]

Your imagination is correct - it costs more dV to launch into retrograde orbit. By how much I'm not entirely sure, but I would confidently say it's not going to cost more than 400 m/s dV extra to the normal 4500 m/s (probably even less, but better safe than suborbital)

EDIT: Oh yeah, and the reason it costs more is because you have to counter the velocity the planet's rotation is giving you. That velocity is about 200 m/s prograde if my memory is correct.

Edited March 28, 2015 by Deutherius

[AlexinTokyo]

It's roughly the same.

Kerbin's spin gives you about 174 m/s 'free' ÃŽâ€v when you launch east. If you need to launch west, you'll need twice that (once to cancel it out and once to add it back in the opposite direction).

So if your regular launch is 4,500 m/s, you'll need (about) 4,850 m/s. If you're anything like me, that's probably inside your safety/LV recovery margin.

Edited March 29, 2015 by AlexinTokyo
GRAMMAR!

[Kerbart]

With a diameter of 1,200 km, the circumference of Kerbin is 3,781 km and the rotation period is 6hr. That means the surface velocity at the equator (which is pretty much where KSC is at) is around 175 m/s. Normally you get that for free, but now you have to overcome that instead; so I'd say the penalty is 350 m/s.

[Starchaser]

It's not west I have to launch. Somewhere between WNW and NW I think. (236°) I'll get a better idea when I line up the orbit. Yeah, my standard satellite launch can handle that. Thanks for the assistance.

BTW, an unrelated question, but I've seen a few people with those ribbon awards in their sig. Where are they from?

[Deutherius]

BTW, an unrelated question, but I've seen a few people with those ribbon awards in their sig. Where are they from?

You can create your own here.

[Starchaser]

Mission Accomplished.

[Starhawk]

Interestingly, if you take a spaceplane in stock and fly due west to orbit, it changes everything.

That 350 m/s make all the difference if you use a highly efficient spaceplane ascent which relies on turbojets to maintain some thrust all the way up through the thin atmo at orbital speeds and rockets only for a tiny circularization burn at apo. You can't make those speeds inside the atmo going west, because the turbojets max out their airspeed way before you can get your orbital-relative velocity that high.

As a result, I was only able to make orbit going west by using a very different profile. I just tried to get up to max speed for the turbos about 35 km up and then kicked on the rockets and pitched up. Massively less efficient, but I managed to make orbit after several tries using different ascent profiles. Didn't have enough fuel to deorbit on target and landed far from KSC.

All this will change come 1.0, but for now, in stock, you can get a spaceplane to orbit way more efficiently going East than West. All thanks to the magical stock turbojet.

Happy landings!

[Deutherius]

Interestingly, if you take a spaceplane in stock and fly due west to orbit, it changes everything.

That 350 m/s make all the difference if you use a highly efficient spaceplane ascent which relies on turbojets to maintain some thrust all the way up through the thin atmo at orbital speeds and rockets only for a tiny circularization burn at apo. You can't make those speeds inside the atmo going west, because the turbojets max out their airspeed way before you can get your orbital-relative velocity that high.

As a result, I was only able to make orbit going west by using a very different profile. I just tried to get up to max speed for the turbos about 35 km up and then kicked on the rockets and pitched up. Massively less efficient, but I managed to make orbit after several tries using different ascent profiles. Didn't have enough fuel to deorbit on target and landed far from KSC.

All this will change come 1.0, but for now, in stock, you can get a spaceplane to orbit way more efficiently going East than West. All thanks to the magical stock turbojet.

Happy landings!

Very true. If anyone is unsure, the theoretical top speed of the turbojet is 2400 m/s (surface velocity - after that it entirely stops producing thrust), realistically you'll get acceptable performance up to 2250 m/s (read: "produces about 1 kN of thrust and doesn't flameout if you alternate tapping shift and X") - if you're going east, that's 2430 m/s orbital velocity (you should only need about 30 m/s vacuum dV for circularisation). Going west, however, this will only net you ~2080 m/s orbital velocity, which means you'll have to supply about 300 - 400 m/s vacuum dV to reach orbit.

I don't think this is going to change in 1.0 - getting into a retrograde orbit will always be more costly, regardless of the engine type used.

[Starhawk]

I don't think this is going to change in 1.0 - getting into a retrograde orbit will always be more costly, regardless of the engine type used.

I agree that getting into a retrograde orbit will always be more costly. It has to be, says physics.

If the turbojet weren't so overpowered, it wouldn't be possible to make orbit using only 30 m/s from rocket power. I anticipate that with a complete rebalancing and new aerodynamics that are coming in 1.0, we may well see a much less powerful engine. Of course, I could be wrong.

Happy landings!