General Question A few general questions about Orbiter/Interplanetary Travel?

[jmr1068204]

I have been using Orbiter on and off for probably 2-3 years now. I have basically taught myself how to get to a stable orbit using the standard space shuttle included with Orbiter (before any Add-Ons are added) and basically any rocket. I don't understand the technical terms/words and procedures for what I am actually doing, however, I understand enough about the vertical acceleration, speed required to get to orbit, etc. to obtain an orbit around earth.

I would like to work on actually learning what all of these things mean that I see in the two panels brought up by the "Power" buttons on either side. Is there any simple tutorial that will tell me the true terms of what each of these shortened words means and how to use them? I am referring to the stuff like SMa, SMi, PeR, ApR, Rad, Ecc, T, Pet, etc., as well as the buttons on the side...Ref, AR, TGT (which I presume to mean Target), NT, Mod, FRM, etc.

I want to start learning how to do transfers out of earth orbit and to the moon, learn how to slingshot around earth, the moon and other planets to reach planets further out and things like that. I'm sure everyone has had these general questions, however. I'm also trying to figure out the complicated diagrams in TransX, and the MFD procedures of trying to program the targets to the moon or other planets back to back so that it is basically in the flight computer.

Another thing is...I see a lot of issues with Add-Ons. I use the newest version of Orbiter (100830), I make sure that when searching for Add-Ons that I find one compatible with the exact version of Orbiter that I have. I read the comments to look for any issues before installing and yet...it seems that half (or more) of the Add-On rockets, ships, etc. that I install give a random and generic error in Orbiter with no explanation as to what caused it. Is this pretty common with other people, too? When I download an Add-On, I make sure to download and install all of the extra things listed as a requirement to make it work. Yet most of them still do not work. I have done other things such as install C++ from Microsoft, because that seems to be a requirement for most of the Add-Ons to run. Yet they still throw errors in Orbiter.

 

[garyw]

I am referring to the stuff like SMa, SMi, PeR, ApR, Rad, Ecc, T, Pet, etc., as well as the buttons on the side...Ref, AR, TGT (which I presume to mean Target), NT, Mod, FRM,

Off the top of my head:

SMa = Semi-Major Axis
PeR = Periapsis (time to)
ApR = Apopsis (time to)
FRM = Frame of reference
PeT = Time to Periapsis
T = Time of orbit (i.e. how long an orbit takes to complete)
Mod = Modify (as in the change the view)

I'd have to look the others up, most are there to describe the orbit you are in.

 

[BruceJohnJennerLawso]

Off the top of my head:

SMa = Semi-Major Axis
PeR = Periapsis (time to)
ApR = Apopsis (time to)
FRM = Frame of reference
PeT = Time to Periapsis
T = Time of orbit (i.e. how long an orbit takes to complete)
Mod = Modify (as in the change the view)

I'd have to look the others up, most are there to describe the orbit you are in.

Periapsis is the low point of your orbit, in kilometers from the planets center when PeR is set, and from the surface of that planet when PeA is set (click dst in the Orbit MFD)

Apoapsis is the high point of your orbit, described identically to above (thankyou for the correction risingfury)

Frame of reference is whether the MFD is telling you data relative to the solar systems ecliptic or Earths equator

Anything else? :tiphat:

Oh, yeah If you want to learn various transfers, I highly reccomend doing a lunar flight first. TransX and interplanetary flights are usually a great deal of frustration to learn at first :lol:

 

[CrimsonDoc]

Is there any simple tutorial that will tell me the true terms of what each of these shortened words means and how to use them? I am referring to the stuff like SMa, SMi, PeR, ApR, Rad, Ecc, T, Pet, etc., as well as the buttons on the side...Ref, AR, TGT (which I presume to mean Target), NT, Mod, FRM, etc.

Tex has produced a really good video tutorial on the subject of orbital elements here: http://www.orbiter-forum.com/showthread.php?p=365515&postcount=22

As far as the buttons go, Tex covers the ones for the Orbit MFD. The Orbiter manual covers stock MFDs supplied with Orbiter and those manuals provided with the downloaded MFD add ons should tell you what those buttons do in more detail.

Hope these answers help.

 

[jmr1068204]

Okay, so other things that I'm still confused about are:

Once in a stable orbit doing say...8,000m/s @ 200+KM altitude, if I wanted to basically "slingshot" off from Earth and gain more speed to get to the moon or another planet more quickly...do I perform a burn as I'm leaving Periapsis and all the way until right before Apoapsis to gain more speed? Or is it the other way around? Can this burn and cutoff be done multiple times as long as I do not burn myself on a trajectory out of the earth's atmosphere? Or is it just a one-time deal and the next time around will basically boot me out of the amosphere or cause an increasingly larger orbit until I am ejected from the atmosphere?

When trying to maintain an orbit and/or orbit and burn to gain more speed at the same time, is it okay to keep the Horz LVL switch on or should it always be slightly above the flat 90 degree AOA degree at all times? The reason why I'm asking is...it seems that varying the AOA while in orbit and yet not even burning thrusters...alters the course of the craft for some reason. Or is that just the way it appears?

Finally...upon reaching a closer orbit to say...the moon. How would one figure out how high or low they can orbit safely? It puzzles me how even NASA figured out the same distance before they orbited the moon. Obviously, the characteristics and gravity are different from that of earth. Would TransX give me the inclination to come in at in order to reach orbit and not slam into the moon directly?

Thanks everyone for helping a newbie!

 

[Quick_Nick]

Experiment! Orbiter is very forgiving.
You cannot burn without modifying your orbit. Velocity doesn't have the meaning you might expect. For example, if you burn forward, you go up. When you go up, you slow down.
Open up OrbitMFD and watch what happens when you burn prograde or retrograde at different points in your orbit. And eventually try normal and antinormal. Have fun!

For a more guided approach: http://www.amcsorley.dsl.pipex.com/play_in_space.htm

 

[Keatah]

Don't try to learn too much all at one time. Orbiter is possibly the most complex PC "game" ever made. And it has one of the steepest learning curves. Take one thing at a time. Read the tutorials. Ask specific and clear questions right here. And soon enough, if you're any good at this, you'll get summa'doze ah-hah! moments.

http://smithplanet.com/stuff/orbiter/orbitaloperations.htm
http://gworbitersite.webs.com/apps/links/
[ame="http://en.wikipedia.org/wiki/Orbital_elements"]Orbital elements - Wikipedia, the free encyclopedia[/ame]

I've been flying ships in orbiter since 2000, and I still learn something new from time to time!

 

[RisingFury]

Periapsis is the high point of your orbit,...

Apoapsis is the low point of your orbit,...

Periapsis is the lowest point of the orbit and apoapsis is the highest point.

 

[orbekler]

Also this could be useful:
http://www.youtube.com/watch?feature=player_embedded&v=Am7EwmxBAW8

 

[Tommy]

This forum has a tutorials section, why not use it? The first tutorial mentioned is "Go Play In Space", and that is the best starting point - period. It will answer all the questions you have asked here - and a ton that you didn't even know to ask yet!

 

[statickid]

i agree with everyone else here. you can fly intuitively (such as how you have been doing it) but that will only get you so far (LEO, more or less) so if you read more about orbital mechanics, and learn the terminology, you will start to WANT the numbers on the side of the orbit HUD. Until you find yourself WISHING you knew how many seconds it will take you to get to your periapsis, and how many meters it is, those numbers probably won't do you any good. There is a huge amount of information on the orbit HUD. a beginner is probably ok knowing only a few of those numbers, but as your mission complexity and understanding grows, you will want to learn what more of them mean. Unless you just get good at using the other MFDs, in which case you can start using THEM intuitively, without knowing any of the math behind it, in which case, you still probably don't need to know all the information on the orbit HUD. I use the numbers on the orbit HUD in conjunction with programs I wrote for my Ti-92 for navigating, but until I could do that or was interested in that, i didn't care about any of them except for Pe, Ap, Pet, and Apt

 

[TMac3000]

Not intending to hijack, but although I know all the really important numbers and what they mean (I can get into orbit, and do interplantary shots), there are still a few I am confused about. Specifically:
I know what semi-major axis is, but what is it used for? Isn't it basically the same as ApR?
What exactly are argument of periapsis, true anomaly, and mean anomaly, and what can I do with these numbers? I usually ignore them...longitude of periapsis sounds pretty self-explanatory, but what is that used for?

 

[asbjos]

Not intending to hijack, but although I know all the really important numbers and what they mean (I can get into orbit, and do interplantary shots), there are still a few I am confused about. Specifically:
I know what semi-major axis is, but what is it used for? Isn't it basically the same as ApR?
What exactly are argument of periapsis, true anomaly, and mean anomaly, and what can I do with these numbers? I usually ignore them...longitude of periapsis sounds pretty self-explanatory, but what is that used for?

Orbiter defines a two-dimensional orbit with Semi-major axis and eccentricity. It could also use perigee radius/distance and apogee radius/distance, but it doesn't work for hyperbolic trajectories, because then the apogee is infinitely high.

For the other parameters, they help to define an orbit around a planet in three dimensions.

 

[Rtyh-12]

I know what semi-major axis is, but what is it used for? Isn't it basically the same as ApR?

No, it's the average of PeR and ApR (technically, it's the half of the major axis, which runs from periapsis to apoapsis, but that's just another way of saying the same thing).

What exactly are argument of periapsis, true anomaly, and mean anomaly, and what can I do with these numbers? I usually ignore them...longitude of periapsis sounds pretty self-explanatory, but what is that used for?

You need them to fully describe your orbit, they are part of the 6 orbital elements. LAN is used for plane alignments as well (next time when you do one, note how the MFD will not only lead you to the same Inc, but also LAN). [ame="http://en.wikipedia.org/wiki/Orbital_elements"]Orbital elements - Wikipedia, the free encyclopedia[/ame] has more information, or just refer to this image, taken from the same article:

Orbiter is possibly the most complex PC "game" ever made.

You're forgetting Dwarf Fortress Well, Orbiter is certainly one of the most complex, anyway.

Edit:

{...} but it doesn't work for hyperbolic trajectories, because then the apogee is infinitely high.

Technically, it's higher than infinite when Ecc>1... well, I suppose it doesn't really matter.

 

[Urwumpe]

Sma is essentially "(PeA + ApA)/2"

It is one half of the longest axis of the ellipse, and is also defined for other curves, like hyperbolic orbits (Then usually negative unless a different notation is used)

 

[TMac3000]

No, it's the average of PeR and ApR (technically, it's the half of the major axis, which runs from periapsis to apoapsis, but that's just another way of saying the same thing).



You need them to fully describe your orbit, they are part of the 6 orbital elements. LAN is used for plane alignments as well (next time when you do one, note how the MFD will not only lead you to the same Inc, but also LAN). Orbital elements - Wikipedia, the free encyclopedia has more information, or just refer to this image, taken from the same article:

You're forgetting Dwarf Fortress Well, Orbiter is certainly one of the most complex, anyway.

Edit:

Technically, it's higher than infinite when Ecc>1... well, I suppose it doesn't really matter.

Okay, I understand what LAN is, though I can't see needing to know it unless the Align Plane screen suddenly became unavailable...

Am I to understand then that a zero arugment of periapsis would would mean that my ascending/decending node and my semimajor axis lie along the same vertical "slice" of sky?

That, and one more question--then I'll hush and turn it back over to the OP. I take it that pilots don't need to "use" the more obscure numbers (to decide when/where to burn)? They are simply "there"--and I wouldn't need to pay attention to them unless I was trying to define an object's orbit?

 

[Capt_hensley]

Periapsis is the lowest point of the orbit and apoapsis is the highest point.

AFAIK IMO

Reference for the uninclined.
[ame]http://en.wikipedia.org/wiki/Apogee[/ame]

Apoapsis: Is the point furthest away(highest) from your point of origin. It is your "max altitude" in your current orbital path relative to your "present" position. Apogee can never be less than the higest altitude you have achieved from your launch site. Which is automaticaly sector 0,0,0 when your journey begins. Distance is always measured from your point of origin or launch site.

To be clear, launch can ocure from an established orbit around any body of mass, as well as a launch pad on a given body with sufficient mass to have gravity.

Periapsis: Is the point closest to you point of origin, in the "relatively" stable orbit around the body which harbors your point of origin. The lowest altitude you can safely orbit, without rapid decay or sudden impact.

A "Crash" is Periapsis gone very wrong. I use the "A" for away from launch point of origin,

and the P for "Point of impact" on any body that has sufficient mass to cause catostrophic failure of your vehicle.

everything in space in between(travel or station keeping)is called an orbit.

Of all the things I've learned, Rapid prograde followed by a sudden impact can ruin your orbiter day. But if you can walk away from it, then it was a good landing!:facepalm:

 

[dgatsoulis]

For the OP and anyone else interested: After reading Go Play In Space, this site is great in helping get a better understanding of orbital mechanics, interplanetary flights and more.

 

[sorindafabico]

Okay, I understand what LAN is, though I can't see needing to know it unless the Align Plane screen suddenly became unavailable...

Am I to understand then that a zero arugment of periapsis would would mean that my ascending/decending node and my semimajor axis lie along the same vertical "slice" of sky?

That, and one more question--then I'll hush and turn it back over to the OP. I take it that pilots don't need to "use" the more obscure numbers (to decide when/where to burn)? They are simply "there"--and I wouldn't need to pay attention to them unless I was trying to define an object's orbit?

When argument of periapsis = 0, periapsis = LAN.


The more obscure numbers (like true anomaly) define your position.

[ame="http://en.wikipedia.org/wiki/True_anomaly"]True anomaly - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/Mean_anomaly"]Mean anomaly - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/True_longitude"]True longitude - Wikipedia, the free encyclopedia[/ame]
[ame="http://en.wikipedia.org/wiki/Mean_longitude"]Mean longitude - Wikipedia, the free encyclopedia[/ame]