Flight Question Mars orbit to Moon orbit with IMFD?

[Spacethingy]

Evenin' everyone, the title says it all - how would I go straight from Mars to the Moon, using IMFD? (Or from any planet to a moon of another planet?)

I'm fine going to and from Earth/Mars and Earth/Moon with IMFD, I'm just not sure what procedure I'd do for Mars-Moon.

:tiphat:

 

[jedidia]

Do everything pretty much as you would when planning a trip for earth.

Just that when you get close, you use the moon as a target of the planet approach program. I think that should work.

 

[Tommy]

You start out just like Mars-Earth, but it changes after you leave Mars' SOI.

Keep in mind that timing the arrival correctly can save almost 2000 m/s on the lunar insertion burn. You want to intercept the Moon's orbital path on the tangent - so pay attention to the Moon will be at TIn. For this flight, you want the Moon to be on the opposite side (of Earth) from the Sun, maybe leading slightly.

Once you leave Mars' SOI, you will need to adjust your course using Target Offsetting or by using Delta V program. Both would be used with IMFD's map set to TGT "Moon", CNT "p-moon", with Int and Plan enabled.

Either method is a bit to complicated for a forum post to cover, but I find Delta-V is easier for me. You need to watch three things - intercept the Moon's orbit at an "edge", time it so the Moon is there when you get there, and ensure the intercept is at a node.

Adjusting any one velocity vector will change all three targets, so there is a lot of back and forth adjusting. Early corrections should be made with mostly dVf to adjust the arrival time, and dVp to adjust the node, then dVi to correct the course to hit the Moon's orbit. Just get in the ballpark at first - and narrow it down during the later corrections. Done properly, Planet Approach won't be needed, Delta-V and Map can put you into the correct insertion orbit for your target base.

Simply using Planet Approach set to Moon instead of Earth MAY work sometimes (but will likely be inefficient), other times it won't work - and sometimes it will take you directly into the Earth! Remember - Planet Approach doesn't consider the gravity or even existence of any bodies other than vessel and target.

 

[dgatsoulis]

Tommy is describing the single burn method, which has an upside and a downside.
The upside is the simplicity (you arrange your arrival at the Moon as Tommy described and you need only a single burn -the LOI- to get into orbit around the Moon).
The downside is Delta-V usage, which is typically upwards of 500 m/s relative to other ways to perform this flight.

A better method as far as Delta-V usage goes, is to arrive at low Earth periapsis as much in plane with the Moon as possible, and perform a braking burn to get captured and get the apoapsis out to the Moon's orbit.

With careful timing (the Moon should be ~65° away from the apoapsis when you perform the braking burn) you will arrive at the Moon with a low encounter velocity. Typical savings are at the ~500 m/s region and they go up with the higher encounter velocity.

Pros:
-Delta-V savings upwards of 0.5 km/s
Cons:
-Careful timing of the arrival at Earth Periapsis. The Moon needs to be ~65° away from the apoapsis of the trajectory after the first burn.
-Additional flight time ~5 days.

For example, let's compare two different encounters with Earth using both methods. The first one is a "slow" encounter at 3.5 km/s and the second one is faster at 5.5 km/s (That's the iV in IMFD's Course program).

Single burn solution:
Encounter Vel with Earth 3.5 km/s → Burn to Enter LLO* directly 1.97 km/s
Encounter Vel with Earth 5.5 km/s → Burn to Enter LLO directly 3.56 km/s

*The LLO is calculated at the 20km altitude around the Moon.

Two burn solution: (one burn at 120 km above Earth and the second to enter lunar orbit)

Enc.Vel 3.5 km/s → Burn at periapsis 0.63 km/s → Burn to Enter LLO 0.85 km/s Total 1.48 km/s
Enc.Vel 5.5 km/s → Burn at periapsis 1.38 km/s → Burn to Enter LLO 0.85 km/s Total 2.23 km/s

As you can see the savings go up with the encounter velocity. In the first example you save ~0.49 km/s and on the second ~1.33 km/s

If your spacecraft allows for it, you can have maximum savings (and a much more fun and challenging flight) by letting Earth's atmosphere "perform the first burn" for you.
With a carefully executed aerocapture, you can arrange it so you exit the atmosphere when your apoapsis is at the Moon's orbit and you will only need one burn to enter LLO. This one is harder because you also need to take into consideration the angular distance you will cover inside Earth's atmosphere during the aerocapture and take it into account in the timing with the arrival at the apoapsis.

Pros:
-Maximum deltaV savings. If executed correctly you need only ~0.85 km/s to enter LLO.
-You can take care of any plane change needed to arrive in plane with the Moon by using the atmosphere.
Cons:
-Same as the previous method, plus the calculation of the angular distance inside Earth's atmosphere plus the execution of the aerocapture.

 

[MaddogK]

Am curious as I've been trying to setup a similar trip (MIR - Mars) with IMFD, what Dv budget would I expect to have with a DG-IV with mk IV engines and stock fuel load configuration ? I'm concerned that with my (est) 90 day travel window I'll use up all my fuel trying to get there before I run out of O2. In the launch window I'm looking at (3/11/16) I might can make it in 92 days provided I have a 21K budget but I have no idea what the DG-IV fuel burn envelope looks like, and I don't want to run the sim in 'cheat' mode.

http://clowder.net/hop/railroad/EMa.htm

 

[dgatsoulis]

[ame="http://orbithangar.com/searchid.php?ID=6413"]BurnTimeCalcMFD (BTC) 2.7[/ame] or you can calculate it yourself with the [ame="http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation"]rocket equation[/ame]

 

[MaddogK]

Umm..ok, I was hoping I wouldn't have to work for it.
:shifty:

 

[dgatsoulis]

If you don't want to "work" for it, use the first link. (unless you consider installing an addon "work").

If you want to learn how you can calculate it for yourself, use the second link.

 

[MaddogK]

If you don't want to "work" for it, use the first link. (unless you consider installing an addon "work").

If you want to learn how you can calculate it for yourself, use the second link.

Now now, I was only joking.
:tiphat:
Besides, I think I've forgotten more trig than I actually learned. Anyway, having incredible luck with my 'best guesses' lately I decided to try it by my gut feeling and tho I made it within my O2 supply window I somehow got myself into a sync orbit around the sun a mere 24K from mars on the ecliptic and never got orbital capture before running out of fuel. I cheated and refuelled and was in the process of setting up for orbital insert when the sim locked up so I killed the process and restarted. Apparently the last state scn file is corrupt as well as all my enroute quicksaves so I have to wipe everything and start over.
:facepalm:

Least I know the route is good even tho my fuel calcs still need tweeking. Anyway, sorry for the thread hijack.

 

[sorindafabico]

Both would be used with IMFD's map set to TGT "Moon", CNT "p-moon", with Int and Plan enabled.

I have a problem here. I can't set CNT to "p-Moon". I'm afraid it's because the Moon is "outside" Earth's SOI in Map.

 

[dgatsoulis]

The problem is that I see in the pic, is that map's trajectory prediction doesn't extend as far as your intersection with the Moon.

Hit MOD until you are in the Map's configuration page and change "Hyper. Limit" from "Yes" to "No".

 

[sorindafabico]

The problem is that I see in the pic, is that map's trajectory prediction doesn't extend as far as your intersection with the Moon.

Hit MOD until you are in the Map's configuration page and change "Hyper. Limit" from "Yes" to "No".

This makes things easy. Thanks!

By the way, where an explanation can be found for these Map options? I don't remember if I saw them in the IMFD manual.

 

[dgatsoulis]

[ame="http://orbithangar.com/searchid.php?ID=4142"]IMFD full Manual [/ame]pages 14-22. You will find details for the main configuration page and the map configuration.