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Author Topic: Okay I need some SERIOUS help!!!  (Read 3203 times)

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Offline unknown.exe

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04 April 2008, 01:04:16
I have tried over and over and over to do the KSC - Moon transfer. I am talking like 20-some attempts! I can't get it!
The closest I have come is I've gotten up to bringing my PeA down to ~186. After that it all goes downhill. Now I can't
even get THAT far!!! I aling my orbital plane w/ Brighton Base... but now my PeA is negative! Sometimes during transit
the Transfer MFD suddenly displays 'No Intersect', then the whole mission is a bust! After getting orbit around Earth, I
have my Rinc down to 0.9 (very good, better than the tutorial), and on the Transfer MFD, DTe = ~3.100, Dv = 3.184,
and the solid gray and yellow dotted lines are overlapping. I go prograde at DTe = 60, I kill rot. at DTe = 0, I begin
slowing down at Dv = 600, and I shut down engines completely at Dv = 0.6.
I go 100x warp until 40,000Km Alt, then I go 1000x until the moons gravitational pull = .50. I wait until .64, then I got
Orbit(+) and line up my flight path with Brighton Base... that's when it all goes to ****.
Someone plesse give me some step-by-step thing here! I am ready to just kamakaze the Moon!
PS: I am never able to get a good initial orbit around the Earth after take-off. It looks like a Ven diagram with a VERY
large middle. Is this an issue?


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Offline unknown.exe

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Reply #1 - 04 April 2008, 04:04:29
Plrs sum helps yallz :bug:


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Offline GXE3

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Reply #2 - 04 April 2008, 04:33:41
You need to download the "Go Play in Space" ebook.

Google "Orbiter Go Play in Space"
or go to "orbiter.migman.com"


-GXE3
A 15 year old.
Long Live Java


Offline markl316

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Reply #3 - 04 April 2008, 05:51:06
First just take a deep breath.  We're here to help you, and you will get it.
Your initial earth orbit is a good place to start.  You don't need to have a perfect 300x300 orbit right at MECO.  It's
actually more fuel efficient to do a gradual climb and cut off the main engines (MECO) at around 110 km.  I usually
burn until my ApA is 310 km (just a little higher to be safe).  At apoapsis, just burn prograde at about ApT = 5
seconds for the delta glider.  And like I said earlier, try to have a MECO vertical speed of about 120 km, and MECO at
ApA = 310 km.

Next -- your plane alignment.  If you meant 0.09 degrees (you said 0.9) then you are fine.  But 0.9 degrees is a bit
stretching the limit.  Remember, use translational thrusters and be methodical.  It will pay off.

Your transfer burn.  You said you began bringing the throttles back at dv = 600.  I'm not sure if this makes much of a
difference, but try to bring them back much later in the burn (dv = 70)

I think your biggest problem is your lack of mid course correction.  There is an extremely slim chance that your initial
burn from low earth orbit will put you on the trajectory you want.  Here are the steps for a correction burn:
1.  Open an orbit MFD and set the reference to moon. (REF button, arrow keys, blah blah blah)
2.  When the G factor at the bottom says about 0.20, burn retrograde until PeA = 1000 km.  You want to make it high
because the orbit MFD does not take into effect the distortion that the moon's gravity will have on your orbit.  As you get closer, your PeA will go down in value.  And, sometimes, prograde and retrograde are reversed in trans-lunar space.  If prograde decreases your PeA, just turn retrograde and burn, and it will also have the opposite affect.

Repeat at G = 0.50.  You now want a PeA of 300 km.
Remember, your distance is inversely proportional to how much fuel needed to make a correction (big distance =
small amount of fuel and vice versa).  It's better to do things early.

Also at G = 0.50, align your orbit with the base.  It will use about 1/20 of the amount of fuel it would take to do the
same manuver from low lunar orbit (due to the less speed).  To answer your question above, you are correct, unless you burn orbit normal (+) or (-) at the exact node, your ApA or PeA will be affected.  This is why you should start in a 300x300 orbit and align yourself, then bring your orbit down to a 40x40 or so.  This allows room for PeA or ApA shift without crashing.

If I were you, however, I would not be concerned at all right now with alligning yourself with the base.  Once you get
four or five successful transfers in, then you can concentrate on aligning yourself with the base.  Baby steps, my
friend.

Also, if the transfer MFD says No Intersect, disregard it.  At that point the moon's gravity has taken over and it is time to use an orbit MFD with Reference (REF) set to moon for your navigation tool.  All of this is assuming it says no intersect AFTER you have left earth.  To avoid it, I make my dotted HTO orbit extend a small amount beyond the moon's orbit.

Good luck!  And certainly post here if you have any more trouble!
:)



Post Edited ( 04-04-08 05:57 )

MarkL

Offline Dig Gil

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Reply #4 - 04 April 2008, 10:59:56
Sometimes using 1000X Time Compression messes everything.:bug:


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Offline ar81

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Reply #5 - 04 April 2008, 15:19:15
I prefer to use Interplanetary MFD v4.2 for planetary transfers.


Offline Urwumpe

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Reply #6 - 04 April 2008, 15:57:54
I recommend using IMFD5.1g, the new upgrade fixes many problems and the 5.x series of IMFD is much more accurate as the 4.2
version.


Offline unknown.exe

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Reply #7 - 04 April 2008, 21:03:16
KK thanks guys... BTW: I already did the "GoPlayInSpace manual " and that is how I knew how to do it in the first
place :stupid:


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Offline unknown.exe

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Reply #8 - 04 April 2008, 21:06:46
Thanks a lot MarkL, I'll try all of that. But your instructions are a LOT different then the manuals...


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Offline markl316

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Reply #9 - 04 April 2008, 22:19:54
Thanks for listening, unknown.exe.  Lots of the stuff I told you about is not in the manuals, I just have figured it out
over the 4 years of me being an orbinaut.


MarkL

Offline unknown.exe

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Reply #10 - 05 April 2008, 03:58:37
What do you mean by 300 x 300 orbit? Are you referring to an ApA and PeA of 300? IF you are then please tell me I was
actually right (my guesses have sucked so far during my orbiter education)


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Offline unknown.exe

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Reply #11 - 05 April 2008, 06:41:49
Okay I'm ready to just screw it... After I align with the base, I have to burn retrograde to get my PeA down to ~ 200,
thus causing a very eliptcal yet closed orbit around the moon... yet after following all of your instructions, I still have
to go into the negative PeA to get a closed orbit. Which screws everything up! Help me please!


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Offline Urwumpe

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Reply #12 - 05 April 2008, 12:29:25
First: What is a closed Orbit for you? Use eccentricity to tell the right terms: Circular, elliptic, parabolic, hyperbolic.

Try the following sequence: (You need Map MFD and Orbit MFD for that)

After you established a nearly circular orbit (perfection is not needed, just a very low Ecc is enough for accuracy later),
you burn retrograde on the opposite side of the planet (use Map MFD to be sure) to lower the periapsis down to 14 km.
(If you started in 300 x 300 km, you should now be in 14 x 300 km).

Now, you can either try landing directly on the moon that way, or make a pass over the base in low altitude to check if you
are making a good approach. The moon rotates so slow, you can do that well.

When to start the braking burn depends on many factors, especially the spacecraft you use. Use Surface MFD in GS mode and
VTOL MFD.

When you are in 4 km altitude, you should be less than 130 m/s fast, with vertical speed being about -60 m/s (distance to the
pad is about 16 km). This limit means you can quickly stop vertical motion with most spacecraft and hover in about 1 km
altitude above the base, when you are too far away from the landing pad. Enable level horizon autopilot mode, if you did not
do it yet.

Slow down to less than 25 m/s GS and 10 m/s vertical speed. Rotate nose forward, if you did not do it yet (Distance about 600
m to the pad, altitude about 100m). For the final approach, just modulate hover thrust to drop towards the distant corner of
the landing pad (velocity marker is kept on the edge). At the same time lower velocity. Aim for coming to a stop in 30m
altitude above the pad. Now just drop slowly and use linear RCS for staying over the pad.

Important rule: Speed limits are best calculated as square root of the distance or altitude. 10 km distance on the ground ~
100 m/s horizontal speed.


Offline unknown.exe

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Reply #13 - 05 April 2008, 20:22:28
Erm when I have a 300 ApA x 300 PeA, I re-enter the Earth's atmosphere eventually. Why do you guys keep sayng to get 300 x 300?


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Offline Urwumpe

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Reply #14 - 05 April 2008, 20:37:37
MAAAAN! :worry:

PeA and ApA. Is it sooo hard to read the correct values based on the labels in OrbitMFD?

300 km (300 kilometer or 300.0k)  periapsis altitude are 300 km above the ground. The atmosphere ends in Orbiter in 150km.
you can't reenter if you have 300 km periapsis altitude.

But if you have 300 km PeR or Periapsis Radius, which is suspect by what you complain about, you have 300 km distance from
the center of earth. Unless you have a good drill you can't reach a 300 x 300 km orbit based on Radius.

You have to switch the OrbitMFD to the surface relative distance mode (DST) to display PeA and ApA. By default, it displays
radius.


Offline unknown.exe

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Reply #15 - 06 April 2008, 05:06:08
AHA! Thanks urwumpe... now I know what DST does :stupid:...
But right now I am in a closed, circular orbit around the moon, PeA = 1.092, ApA = 1.095... I am now lined up w/
Brighton Beach also... But I have followed the manuals instructions and there still seems to be issue. The biggest one
is when I burn prograde 300 Km from base in order to bring GS down to 130, I am able to but it keeps going up 1 per
second. Thim makes life pretty difficult... any one got sum help how to land at brighton beach with my current
situation?


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Offline Urwumpe

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Reply #16 - 06 April 2008, 12:57:59
1000 km is too high. Burning prograde 300km from the base is pretty stupid. You want to slow down, not gain speed.

Orienting prograde and using retro-thrusters works - that is again a retrograde burn (acceleration is in the opposite
direction of current velocity vector)


Offline unknown.exe

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Reply #17 - 06 April 2008, 22:43:41
Yeah sorry I meant retro-grade... I zlways mix the two up cuz they sound similar. What should my PeA and ApA be
before I try to land?


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Offline Urwumpe

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Reply #18 - 06 April 2008, 23:11:53
Depends. Lets say you start in a lunar 250 x 250 km orbit.

When you fly above the base, lower perilune to 100x250 km.
At the opposite side, lower to 14 x 100 km.
When approaching the base again, do the following at 700 km distance: Autopilot level horizon (L). Yaw until you are pointing
retrograde (use orbit HUD to be correct).

At about 350 km, start main engines. Keep an eye on surface MFD. Use hover engines for keeping descent rate under control -
not too slow (too slow = you need more fuel), not too fast (too fast = you will land very hard).


Offline unknown.exe

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Reply #19 - 07 April 2008, 23:27:52
Ok this is probably a stupid Q... but what do you mean by "250 x 250", lowering the perilune to "100 x 250"?


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Offline markl316

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Reply #20 - 08 April 2008, 06:24:10
That means that you start out with ApA = 250 and PeA = 250.  You lower your PeA to 100, so now:
ApA = 250 and PeA = 100
Which is 250x100


MarkL

Offline unknown.exe

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Reply #21 - 08 April 2008, 23:42:39
Ok thanks! I'm still trying to friggin land but if i suceed I will tell y'all...


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Offline unknown.exe

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Reply #22 - 09 April 2008, 00:00:01
ARGH!!! Another issue... when I am performing the slow down for landing, after I get down to 1130 m/s GS, My yellow
and green arrows in the VOL/VORTAL MFD are not lined up... How do I get them to line up so I am heading for the
base?


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Offline Dig Gil

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Reply #23 - 14 April 2008, 18:22:57
Linear RCS Thrusters, or Rotational RCS Thrusters to align the wheels with the ground.


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Offline Pirx

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Reply #24 - 15 April 2008, 05:20:29
Correct the alignment of the velocity vector with the direction towards the base like that

« Last Edit: 15 April 2008, 05:20:29 by Pirx »