Flight Question Constant shifting ApA - PeA

[coffeene]

I had to abandon my mission to mars that I was going to try a few days ago. Transx is not working properly, at least... something isnt working properly.

Currently I am practicing manual docking so I launched a DeltaGlider4 in orbit at ~230 as the AP launches it. Then launch a Ravenstar to meetup with it to get practice docking at different alt's. Problem I'm having is the orbit of both ships constantly shifts from between 50-120KM, sometimes more, in distance from its ApA and from its PeA. When I get a meetup point, say 350km PeA and 500ApA by the time I reaqch my PeA it has shifted to either a higher alt or a lower alt, usually over 50k and this is on the first orbit. The ecc of the target ship is 0.0005 but has shifted to 0.0012 or more and is no longer going to be able to meetup. I did a fresh install thinking that was the problem as I had a problem a while ago and it fixed it. This time it didn't

after fresh install I added sound 3.5, Deltaglider4, Ummu, UCGO, Ravenstar, and Vanguard. Same problem.

if this is normal, is there something I'm not doing right?

I've looked at the manual and the abreviations are not mentioned what they mean so hopefully that might help a bit. I'll put them all down even though I know what a few mean, just incase I'm wrong.

Sma
SMi
PeA
ApA
Alt
Ecc
T
Pet
ApT
Vel
Inc
LAN
LPe
AgP
TrA
TrL
MnA
MnL

Unless I was looking in the wrong place (Go play in space pdf) a lot of them were not listed.

 

[PeterRoss]

Shifting of PeA/ApA is an absolutely normal situation caused by nonspherical form of gravity field. You can uncheck 'nonsperical gravity sources' box in the Launchpad and it will be much easier for you to fly by the price of some realism lost.

Or you could learn to fly as is. For starters, try more circular orbits with less difference between PeA and ApA, let's say 350 km for both numbers.


Speaking about abreviations you should check manual Doc\Orbiter.pdf, I believe it have all explanations you want.

 

[agentgonzo]

Speaking about abreviations you should check manual Doc\Orbiter.pdf, I believe it have all explanations you want.

I believe there is also a page on these forums that lists a lot of common acronyms? Or am I thinking about NSF?

NSF has a handy additional bit of code where it detects common acronyms (from a user-configured database) and uses the HTML abbr tags to add a mouse-over text explaining what they are. I mentioned it to tex and wrote a proof-of-concept code but it was adding too much overhead to the server. I was thinking of writing a firefox plugin to do the same thing but never had the time.

 

[PeterRoss]

NSF has a handy additional bit of code where it detects common acronyms (from a user-configured database) and uses the HTML abbr tags to add a mouse-over text explaining what they are. I mentioned it to tex and wrote a proof-of-concept code but it was adding too much overhead to the server. I was thinking of writing a firefox plugin to do the same thing but never had the time.

It would have been a great plugin. Maybe even able to tell me what the NSF acronym means :lol:

 

[agentgonzo]

Maybe even able to tell me what the NSF acronym means :lol:

Sorry... after a while you'll get used to it. NSF

 

[N_Molson]

Also, the Moon tidal effects have an influence on your orbit.

When using TransX, the key is to use "update orbit" on a regular fashion and adjust the settings.

 

[Izack]

Knowing the meaning of the abbreviations won't help you. If you knew the meanings well, the abbreviations would make themselves apparent.

 

[Tommy]

As others have pointed out, the shifting Ap and Pe are caused by "Non-Spherical Gravity Sources". Many people like to disable this in the launchpad while they are first learning - it will make it easier for you to grasp the basics first, then learn to adjust for the shifting. Syncing orbits in particular, is much more confusing with Non-Shperical Gravity Sources enabled.

If/when you decide to have NSG, the trick is to know that the effects sort of cancel out over the course of an orbit. Your periapsis may wander during the orbit - but every time you reach your periapsis it will be in the same point of your orbit as it was last time.

The shifting becomes MORE pronounced in a more circular orbit.

As for the terms, you should find a listing of them in the Orbiter.pdf, check the section on OrbitMFD. I'll give you the most important ones now as well.

First, I'll note that OrbitMFD displays Altitude, Apoapsis (High point of orbit) and Periapsis (Low point of orbit) in two ways. It can display Radius (distance from the center of the planet) or Altitude (Distance above the Surface (think in terms of "Sea Level)). You can switch between the two using the [DIST] button. You can tell which is being displayed by looking at the third element on OrbitMFD, it will either be ApR or ApA.

Also, OrbitMFD can use different reference frames. You can use the [FRM] button to switch between (solar) ecleptic frame (ECL), or (local) equatorial (EQU). I suggest using Equitorial frame unless you will be traveling to another planet. Inc and LAN are affected by the frame.

PeR - Periapsis Radius - the distance of the periapsis from the center of the planet.
PeA - Periapsis Altitude - The distance from the periapsis to the planet surface.
ApR - Apoapsis Radius
ApA - Apoapsis Distance
Alt - Your current Altitude. This is affected by the [DIST] setting
Ecc - Eccentricity. An Ecc = 0 is perfectly circular orbit, Ecc >= 1 is escape trajectory.
T - Time, your orbital period. How long, in seconds, it takes to complete one full orbit.
Pet - Periapsis Time. Time (in seconds) until next periapsis.
ApT - Apoapsis Time. Time (in seconds) until next Apoapsis.
Vel - Velocity. Your current orbital velocity.
Inc - Inclination. In degrees, how far above and below the reference frame your orbit goes.
LAN - Longitude of Ascending Node. Where your orbit crosses the reference frame to the "North"

The other terms can be useful in certain circumstances - mostly for planning complex flights - but can be ignored while learning the basics. You can perform most missions without needing these other numbers.