Orbital Rendezvous Techniques

[levans]

I've read the "Go Play in Space" section on ISS rendezvous, and elsewhere I have read about "phasing" (only the term, not an exact definition).
The GPiS tutorial suggests making your orbit more eccentric (or I suppose just larger in general, with larger orbital period) so as to allow a trailing target to catch up. I'm wondering if this is what is meant by "phasing" (as I can imagine how this would exactly look like 'phasing' over multiple orbits, particularly with two circular orbits of different orbital periods having exactly the same shape of ground track).

Nevertheless, the tutorial says that the eccentricity technique is only a "basic method". This being the case, what other approaches might be used?

As I'm playing around with Orbiter, it strikes me that there are probably a lot more 'non-simple' maneuvers that are possible (combining several 'primitive' orbital maneuvers into more complex vector changes). Presumably these require much more tools support than Orbiter currently possesses (and accurate burns)... or maybe I just haven't found all the cool stuff yet

 

[Urwumpe]

Phasing means, that you move around Earth in a orbit, which has a different orbit period as your target. This will make you change your position on Earth relative to the target.

Orbit period depends only on Sma (semi-major axis), all other parameters have no effect. You can have a lower circular orbit, or the same apogee and a lower perigee - the result is the same as long as both orbits have the same Sma.

 

[YL3GDY]

As I'm playing around with Orbiter, it strikes me that there are probably a lot more 'non-simple' maneuvers that are possible (combining several 'primitive' orbital maneuvers into more complex vector changes).

It depends on your fuel reserves. Basically, Hohmann (or semi-elliptical) transfer is mostly used in real space missions, because of minimum fuel required for it. Any other method can be brought to combination of Hohmann-like transfers. To make your life more difficult, you can try using TransX MFD in maneuvre mode. It's developed for interplanetar trips, but can be used in some extravagant purposes.

 

[V8Li]

As I'm playing around with Orbiter, it strikes me that there are probably a lot more 'non-simple' maneuvers that are possible (combining several 'primitive' orbital maneuvers into more complex vector changes). Presumably these require much more tools support than Orbiter currently possesses (and accurate burns)... or maybe I just haven't found all the cool stuff yet

You could be at periapsis wanting to higher your apoapsis to set a rendezvous. At the same time you could be closer to a plane chage node so you have to first burn prograde and then change to a anti-normal (for example) direction to align with the target. You could simply turn prograde and yaw 45 deg to the right and when you do the burn you're gonna change both the Ap and RInc values.

Also maybe you have noticed that when you burn at PeT 100 (prograde to higher Ap) you will alter the Pe value slightly too. So you could pitch more or less to keep the Pe value uncahnged. The prograde example is not the best, but imagine returning from the Moon and burning retrograde to set a circular orbit around the Earth. Since you have some extra energy to bleed you have to start at a high PeT to give you enough time. This will alter your Pe too.

Overall it is best to burn in fixed directions for the most efficient results. You should use combinations of directions only for interplanetary travels. For example I've once got to the Moon, and when I was in it's SOI the Pe was so low that my prograde was pointing to the center of the Moon (I was gonna crush big time). It was a trip in which I used only the OrbitMFD so I had no precise tool to use, like the TransX. In theory I should have burned prograde or retrograde to modify my Pe value, right? But I would have used too much fuel. So I burnded half way there, not prograde nor retrograde. And with very little fuel I got my ship in front of the Moon (I was doing a "free return") and saved myself. You're gonna use tools like the TransX and IMFD for that and they will calculate exactly the direction to burn in a more efficient way. My burn was basically a prograde burn in Eart's orbit but you might not know that when you're in the Moon's SOI.

 

[Giezer1984]

STS guidance MFD

For realistic rendevous i like to use the "STS guidance MFD" (you can use it on Deltaglider i think). This MFD creates a real life rendevous trajectory which is very safe. It is safe because when for example you engine's would lose all power, you would never hit the target.

When you try it you get the idea. By staying under you're target you will always be going slower then you target.

 

[Urwumpe]

When you try it you get the idea. By staying under you're target you will always be going slower then you target.

You get an F in orbital mechanics.

Also, STS Guidance MFD recreates the Soyuz rendezvous system, not the Shuttle Relative Navigation Guidance. But that is a minor flaw.

 

[Belisarius]

It can work in almost any craft, but it has an annoying bug... If you change from cockpit to external view (or even to another panel like in the DGIV) while the rendezvous programme is running, it stops. Then you're in mid-maneuver with no clear indication of where you're going.

More robust is the RendezvousMFD, this gives you a graphical display of the rendezvous trajectory and allows to you see your deviation from the nominal path.

 

[clive bradbury]

When I first started in orbiter I found rv very difficult, and used every mfd I could lay my hands on. With practice, however, rv with orbit, synch, and attitude mfds is dead simple. Take a look at my 'soyuz to iss' tutorial on OH and try it yourself.

 

[Giezer1984]

Orbital mechanics

You get an F in orbital mechanics.

Also, STS Guidance MFD recreates the Soyuz rendezvous system, not the Shuttle Relative Navigation Guidance. But that is a minor flaw.

Ah *piep* I mean you go faster when your'e under the target, Ich bin ein dumkopf, but I wonder, when is the spanish inquisition coming? no kidding, I wonder which add-ons are yours? You seem to know a lot on the forum.

btw I found a nice link for interested guys on real orbital mechanics (not that I know it all, anyway)
http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm

 

[Whatu]

btw I found a nice link for interested guys on real orbital mechanics (not that I know it all, anyway)
http://ocw.mit.edu/OcwWeb/Physics/8-01Physics-IFall1999/VideoLectures/index.htm

Hey thats a nice link Giezer!

Im gonna spend a couple of hours watching those videos...