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Author Topic: The eagle has landed  (Read 1929 times)
Odyssey
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« on: March 24, 2007, 06:53:29 PM »

Well, I fiannly made it to the moon  Excited!

I started right from lift off and did the whole mission my self with out the help of the scenarios. I'd like to thank everyone who offered their advice and guidance along the way to get me there.

Now I'm there obviously I'd like to go home. I was never successful at docking with ISS in the Delta Glider so is there any really simple and explanetary methods/guidlines to help me with rendezvous and docking?

Thanks
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Tschachim
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« Reply #1 on: April 02, 2007, 04:41:30 AM »

Well, I fiannly made it to the moon  Excited!

Congratulations!  Happy

I was never successful at docking with ISS in the Delta Glider so is there any really simple and explanetary methods/guidlines to help me with rendezvous and docking?

As far as I know no, but practicing with the Delta Glider is a good idea...  Wink

Cheers
Tschachim
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aftercolumbia
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« Reply #2 on: April 23, 2007, 08:24:45 PM »

One problem is that you have to do the stuff in the right order.  In reality, they combine all these maneuvers, however in Orbiter, there is no practical way to do that (except possibly using IMFD and targeting your command module like a planet, but I haven't tried that.)

1. Ascent:  Do your best to launch into the plane of the command module's orbit.  This is probably not possible if you've been sitting on the moon for a couple of days, but you should still be able to get fairly close by launching into a direction parallel and in the same heading to the command module's trace (which should still be pretty close to your landing site.)  Ascend into an orbit no more than 100km circular, you need to preserve your propellant.

2. Align planes (Shift-A): This instrument shows the relative inclination and the crossing nodes.  It is best to have it alongside your OrbitMFD (Shift-O) during maneuvers.  The new Orbit HUD works really nicely at finding your normal+ and normal- points (usually called "normal" and "anti-normal")  If you aim ahead "heads up and wings level" into the direction of flight, normal+ will be on your left, and normal- will be on your right.  To help visualize which way you need to turn, use the Map MFD (Shift-M).  Plane change maneuvers are only practical shortly before you reach a crossing node.  I learned very much the hard way that you _must_MUST_ start the maneuver before you reach the node.  Once past the node you are moving away from the target plane, which makes it very hard to "turn into" it, which is what this maneuver is supposed to do.

For Apollo, I recommend doing it with the Command Module.  I haven't actually flown NASSP, but from reading the history books, I know that the Command Module did these maneuvers.  What I wouldn't recommend for your first attempt is doing the plane alignment maneuver before lifting off in the LM...which is what they did historically.  The first three landing missions didn't need to do this...the third one especially, 'cus it didn't actually land.

3. Phasing, known in Orbiter as Synchronize, (Shift-Y): This is often where I get screwed, especially if I have non-spherical gravity turned on.  If ascent and plane alignment went well, you'll probably have a situation where your LM orbit is well below the CM and you have "No intersect" on the Synch MFD.  Gently raise the LM's orbit until the Synch MFD lights up.  At this point you should have a rendezvous longitude (a dotted line sticking out from the center of the Moon in the MFD, you should always have the two solid lines tracking the craft.)  Finally, you should have two columns of numbers.  One's something like "Sh-ToR" and the other is something like "Tg-ToR".  The first is the craft you're in (the LM), the second is the rendezvous target (the CM).  What you want to do is get one pair of these numbers within one second of each other (the MFD will highlight the closest pair; if it is the bottom pair, accellerate time and wait for it to move up to being the second last pair.  When it's at the bottom, it means your rendezvous opportunity a long way away.)  If Sh is getting to a spot a few seconds early, raise the orbit to slow it down.  If Sh is getting there late, lower the orbit to speed it up.  Make sure you are doing these raise/lower maneuvers carefully aligned to prograde or retrograde so you don't screw up your orbital planes (established in Step 2).  If you are lowering your orbit and going to "no intercept", raise it again, even though you're getting there early, and then wait for the apoapsis to try again.  This should keep the intersect.  Also be aware that the intercept moves when you maneuver.  Watch for this as sometimes it produces really counterintuitive behaviour.  I got pretty confused on my first couple tries.

4. Wait for the Synch intercept.  You should be very close to the CM when the time arrives.  The maneuver to match speeds with the CM is called Terminal Intercept (at least in modern parlance.)  You should be within 2000m.  Use the Dock HUD, set up your comm channels, and the Dock HUD will put up a pip for you to aim at.  Simply aim at the pip, thrust until it reaches less than 1m/s and there you have it.

If you are too far away for a docking approach or visual contact, the first thing you need to do is make sure you aren't going to crash.  Once I did such a maneuver while 20km from the ISS (suicidally distant) and accidentally deorbited myself.  If this sort of thing happens, you have to go back to step 2, probably wasting a huge amount of fuel and time.

5. Thrust towards the target, close at about 10m/s.  Your "reverse" pip should be on the target.  If it is sliding off the target and it is hard to keep it on target using infrequent pulses of your RCS, or the velocity value is changing too quickly, then you are too far away.  Once you arrive within about 100m, switch to the Orbit HUD, and then circle the around the CM laterally (i.e. relative to the surface of the Moon) until the CM is directly prograde or retrograde to your orbit.  Make sure to halt your lateral motion.  This keeps you from entering a scissor-like, really, really annoying orbital oscillation called a "wifferdill" (by the Gemini crew who first experienced it.)  The wifferdill is caused by being close to, but slightly out of plane with you're rendezvous target.  The Alignment MFD (Shift-A) can help make sure you're not in one.  Once in place, switch back to the Dock HUD and cancel out any relative velocity.

6. You are now stationkeeping.  Dock at your liesure in much the same way as the initial approach in Step 5.  The Dock MFD instrument (Shift-D) is really good at keeping your ports aligned, once you've figured out how to use it (instructions are in the Orbiter Manual, but you really haven't done it until you've done it.)

NASSP might have some more specifics.
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Odyssey
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« Reply #3 on: April 25, 2007, 07:13:15 AM »

Wow!!! Thanks very much. I will follow these steps and see if it helps.

Thanks again.
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Odyssey Wink
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