Astronomy Portal to the Heavens, Deep Sky and Universe

OrbiterSim | FAQ |Acronyms | Add-ons | Screen Shots | Orbiter Tutorials

Orbiter Instrument Training

Tutorial 7 - Rotate orbital planes (Align)

In principal:

In order to intercept another orbiting space craft you must first position your ship in the same orbital plane as the target.  Once positioned on the same plane as the target you can then intercept or "sync up" to that target by changing the shape of the orbit. The principal is that a vehicle in a circular orbit will make a complete pass around the globe before one in a larger elliptical orbit. This allows one vehicle to catch up to the other. 

Think of two ships in the same circular orbit. They will both be traveling at the same velocity and one would never catch the other. To change the time it takes to complete an orbit you can simple push apoapsis out a little with a small prograde burn at periapsis. It would then take your ship longer to complete an orbit then it does for the target station. In this case you are letting the target station catch up to you eventually. If you are behind station you would simple do the opposite to decrease the time it takes to complete an orbit.

It normally takes several of these eliptical orbits to come within range of station. When one catches the other it then becomes necessary to circularize your orbit again.  This means making some adjustment burns to match the ships orbit with that of station. Then you can close the gap with small thrust and prepare to dock.

The steps to intercept any station are as follows:

• Get to the same orbital altitude, Orbit MFD
• Align orbital planes, Align MFD
• Sync 'catch' up to target, Sync MFD
• Dock with target, Docking MFD

During launch you have the opportunity to place your ship at the proper altitude and inclination ( orbital alignment ).  Of course you want to end up somewhere near the stations position as well.  Therefore the first three bullets are being addressed during launch all at the same time. Once in orbit you can fine tune each of them one at a time.

In practice:

Launch

Bring up the Map MFD and select an orbiting station as your target. Increase time acceleration to 100 or 1000x until the target orbit intersects the launch site. Then wait until the station moves in position not far behind the launch site. This will provide time to launch our vehicle into orbit somewhere close to station making it easier to sync later. Return to normal time and launch into a heading that will bring you into the same alignment as station. At this point bring up the Align MFD and watch the relative inclination ( Rinc). Hopefully you will get within a few degrees relative to target, otherwise you will waste too much fuel adjusting while in orbit. Use the skills you learned in launch into stable orbit tutorial to reach desired altitude.

To match orbit altitude with target altitude press [Shift][T] in the Orbit MFD.  Select target and change your orbit using above technique. You can match numbers or just do a crude adjustment until the two orbits overlap in the graphic display.

Align Orbital planes

Now even if you did a good job during launch you will still need to make some adjustments, here how. Let's look at aligning the two orbits first.  It helps to think of an orbit as a disc, much like a computer CD, rather than a circle. This is referred to as the orbital plane. The ships orbital  plane will be at some angle to the targets  orbital plane.  The angle between the two planes is measured in degrees and noted in the Align MFD as Rinc. So bring up the Align MFD and target the station. Align MFD, [Shift][A] , and set your target, [shift][T].

The Align MFD is very simple to use, it will tell you when and where to thrust. Just do as it says and watch your Rinc decrease to zero. For example, the MFD will read KILL THRUST until the ship reaches best position. Once in position, the MFD will read Thrust NORMAL(+) or (-).  Simply use the autopilot to orient the ship, press [:] for NORMAL and ["] for ANTINORMAL.  If the relative inclination begins to decrease, you know that you did it correctly. If it increases, stop burn, orient your ship in the other direction and then burn.

You should end up with a relative inclination of < 1 degree. You may now synchronise with the target.

 

 Launch into stable orbit | Instrument page

OrbiterSim | FAQ |Acronyms | Add-ons | Screen Shots | Orbiter Tutorials