AMSO AMSO: CM Fuel Conservation

[Slaintemaith]

Hello all,

I've been playing with AMSO again lately. I'm LOVING Jarmo's Lunar Transfer MFD as well as the latest version of AMSO.

My issue has been: somewhere along the way, I've forgotten how to save fuel in the CM; the autopilots seem to think I have tons of fuel to waste aligning with bases and getting into parking orbits with 0.00 eccentricity.

And so I'm able to get men on the moon just fine. I just wind up 5-60 seconds short of fuel for the Trans Earth Injection.

...this is bad.

Anyone have any fuel-conserving procedures that'll get my people home with fuel to spare?

Thanks in advance,
Slaintemaith

 

[Grover]

yes, just remmber the general rules of fuel conservation/orbital mechanics:

do it higher, and save on fuel

instead of doing your base alignment AFTER reaching orbit, try doing it manually using the mapMFD and orbit HUD

this way, you change plane when it costs next to nothing
heres how to do it:

as soon as the moons gravitational influenve becomes 0.6 or greater (as shown on the bottom of the orbitMFD), orient normal+ or normal- (ensure that the orbit hud says MOON and not SUN)

make a small burn with RCS fine either forwards or backwards to check which way you need to burn (your aim is to get your orbital line on the MapMFD over your target). then open the taps on the RCS engines, burning in lin mode nice and slowly to avoid adding any velocity into the mix other than planar (if you burned the mains and did it in a fraction of a second, the plane would turn faster then the craft, and you'd end up burning away from the moon (with reference to your orbital plane)

now that youre on the right plane, reset your guidance MFD so that it loads your current inclination (or edit the target orbit properties yourself) and ensure that your new perapis altitude is positive (mine usually goes negative after my planar burn) and run an automatic MCC

now, because youve dont it nice and high, you probably only used a few kgs of fuel on plane alignment


that should give you the few seconds you need for TEI

good luck!

 

[Mantis]

The Lunar Transfer MFD will align you automatically with the correct base. When you setup your TLI burn, set Mode to Surface and set Target to your desired base. LTMFD will then use the TLI burn to place you on the correct inclination for your desired base. You might need a small correction once you are there but nothing dramatic. I just tried it out with Apollo 17 which was the one furthest off plane and it got me within 0.36 km of perfect alignment upon LOI.

 

[Slaintemaith]

I've done what Mantis has said--set Lunar Transfer MFD to get me over my selected base. In fact, I'll use the same program during mid-course to nudge me , then use the same program again to nudge me again once inside the moon's gravitational influence. These tend to be one second or even less than a second burns.

...this isn't the issue. When I do my LOI, I'm perfectly lined up with my base.

Here's where everything falls down...

Lunar Transfer MFD, by default, wants to put you in a nice, tight, 0-eccentricity orbit. I'm not sure that this is the most fuel efficient. I've done it this way, plus entered in my own apoapsis/periapsis using the "Apollo by the numbers" documents that are available, then circularize later. If I'm going 'by the numbers,' I have quite a few orbits before I have to worry about preparing the LEM and getting into a orbit conducive for the LEM to do a DOI.

...which is the other problem. Once those orbits have happened, I'm no longer passing over my target base. That pesky moon has rotated slightly enough that I have to do a plane-change burn to re-align. This is probably where all my gas is going, since this can go in excess of a minute--at least if I use the AMSO CM Autopilot that aligns me with the mission's planned base.

Of course, once on the moon, there's stuff to be done. This takes enough time to force -yet another- plane change maneuver to get in position to meet up with the LEM.

And these kill me, because in the mission I'm doing (Apollo 12) in the -real- mission there's only one 18 second plane change while the crew is on the moon.

...so I think I'm missing something.

 

[Cras]

I use the advanced LOI feature and get the lunar orbit to be as close as I can get it to the real one. Saves on fuel having a higher apoapsis than what the "Simple" LOI will aim for.

 

[Slaintemaith]

I've done that as well, and had the most success with it--managing to get a valid TEI with about three seconds left of fuel to spare. I don't expect to have much fuel after TEI, but I shouldn't be on fumes.

So I'm burning it up on plane changes. I have noticed the "by the numbers" orbits are nowhere close to 0.000 eccentricity.

 

[Cras]

I have noticed the "by the numbers" orbits are nowhere close to 0.000 eccentricity.

Indeed. Even when LTMFD isn't able to come up with a solution for the exact orbit, I am usually able to come up with something close. I think a perfect 0 eccentricity orbit is nice and all, but I figure there was a reason Apollo didn't use them.

 

[Slaintemaith]

Looks like the "separation maneuver" they refer to might be what I need here. CM can stay in it's orbit until it's time for the LM to leave the surface of the moon. Looks like the plane change to realign with the base before landing will have to be done manually, and with the LM.

---------- Post added at 10:57 PM ---------- Previous post was at 08:39 PM ----------

Yah. Still not having the fuel I need. Off by 12-16 seconds on the TLI. The plane change for matching the LM is killing me fuel-wise.

---------- Post added at 11:10 PM ---------- Previous post was at 10:57 PM ----------

Is 42.4% of CM fuel good for post LOI arrival at the moon?

 

[Mantis]

Is 42.4% of CM fuel good for post LOI arrival at the moon?

That's usually about what I've got when I get there.

 

[cymrych]

I'd set your inital LOI burn so that your orbit is in sync over the base when it's time for the LM to begin its ascent. This way, you'll do no plane change burns with the CM at all. The only plane change needed can be performed by the LM after seperation. Should save you some juice for TEI.

As for circular 0.00 ecc orbits, I wouldn't worry at all about it. A11, for instance, had something like a 121 x 105km orbit for most of its lunar time, if I recall correctly. You could even set the pe a little lower so that the LM's descent autopilot can engage right from the gate (following the plane change burn, of course.)

 

[Slaintemaith]

I'd set your inital LOI burn so that your orbit is in sync over the base when it's time for the LM to begin its ascent.

...of course I'm going to ask, "How?"
Will I need some other MFDs or will Lunar Transfer MFD work?

It looks like I'm setting LOI for closest approach, and not base sync.

Nevermind. So -that's- what TOA is. How useful!

---------- Post added at 03:45 PM ---------- Previous post was at 01:48 AM ----------

...and that got it. I had about 3% of fuel left in the LEM (probably because I forgot my whole normal/antinormal thrust directions on the LEM. (with its axis change)

...but I got it. Still had to nudge the CM's plane, but for less than a second.

Looks like I might make it home!