Getting into Orbit (for both Atmospheric bodies and none atmospheric bodies).

[BenG]

I've not used Orbiter since 2006 but recently I've been watching my DVDs of "From the Earth to the Moon", and fancied re-loading orbiter on my new PC and giving it a whirl.
I know the DG IV and the Apollo space-craft have an auto-pilots capable of achieving orbit from both Atmospheric bodies and none atmospheric bodies.
But other spacecraft don't (e.g. the Earth to the Moon in 24hrs addon). When I manual put a space craft into orbit If I try to complete the orbit in one burn I usually end up with a highly eccentric orbit. I usually need two burns, one to achieve a suitable apoapsis and then a second pro-grade burn at apoapsis to raise the periapsis. I suspect this probably isn't too fuel efficient. It's gets even harder when I'm using a spacecraft with hoover thrust only, and I have to change all the axis by 90°.
Is there anything that can help me with this? (e.g./i.e. a suitable MFD)???

 

[PeterRoss]

You want to perish all the fun...

 

[Kaito]

The two-burn process is pretty normal. The way to achieve orbit in a single burn is to as you normally would, and once you're above the atmosphere (200km), burn to keep your VV (velocity Vector, the little ball in surface HUD) about on the 0 mark. In other words, keep your Vertical Speed ABOUT zero (if not zero, at least going up slightly, like +20). Use orbit MFD to know when you're actually in orbit

 

[Lucy]

IMFD does have a set of orbital operation autopilots which can circularise your orbit from your current position in it. Like Kaito said, the two-burn method is a pretty standard way of getting into a circular parking orbit, and I haven't personally noticed any real economical difference between that way and the single-burn way.

 

[Ark]

The non-autopilot method I use for getting into orbit with one burn is to climb at about 60 or 70 degrees until your ApA reaches the desired orbit altitude, then pitch down until you find the point that your ApA stays relatively unchanged. Usually this is ten or so degrees below the artificial horizon. From there, just adjust your pitch as needed to keep the ApA as close to your target altitude as possible. Eventually you reach a roughly circular orbit, suitable for an eject or sync operation.

 

[BenG]

Thanks for the advice.

 

[Tommy]

The "single burn to orbit" method is rarely the most efficient for any vessel. It has been used IRL for two primary reasons. One is safety, you aren't counting on being able to re-start an engine during flight. The other is that many vessels, especially realistic ones, have a very limited number of re-starts - if they have any at all. For instance, on the Saturn V, only the last stage could be re-started, and that only five times if memory serves.

Check this thread for a discussion of ascent profiles for winged craft such as the DG or XR series:

http://www.orbiter-forum.com/showthread.php?t=9587&highlight=ascent

For a non-winged craft (the Shuttle falls into this category since the wings don't provide nearly enough lift to be useful during ascent) the profile will be higher, of course. Since you don't need lift you want to reduce drag more. However, it still pays to gain tangential (horizontal) velocity as soon as possible. Remember, the faster you are going the more centrifugal force is available to counter gravity. I typically pitch over to about 70 degrees as soon as I'm on heading, and reduce that slowly as I climb. I tend to be at about 35 degrees or less by 40 k alt. MECO usually occurs at about 120k alt, with an ApA of 210k about one sixth of an orbit after MECO.