Question Proper Planet Approach

[XonE32]

Hi all,

I've used IMFD for years now and don't have any real problems with it , but I'm curious to know if I can use it more efficiently.

Example situation: A simple flight from moon to earth in say an Aries II from WO2001, but I wish to do my orbit insert around the Earth so it matches the same plane as an orbiting station (e.g. Station V).

I know when going from the moon to earth I use the "Planet Approach" option and you can set your orbit insert altitude and inclination. Setting the same alt as the station is no prob, but I always find that I'm "guestimating" when it comes to setting the proper inclination so that after my orbit insertion the planes between the Aries and the Station are aligned.

Can IMFD do this ( I assume it can if you put in the correct inclination data), but whenever I try it is always off. I assume I'm missing or misreading data from somewhere and so I'm not inputting the correct inclination value?

Ps: I believe the inclination data for "Planet Approach" in IMFD is Ecliptic and so I DO use the Ecliptic inclination data for the Station on the Orbit screen. But I still find that I'm make too many "eyeball" based burns though.

Any thoughts/links to help me be more fuel efficient would be greatly appreciated.

Cheers,

XonE32

 

[markl316]

Try using planet approach (if you can) in equatorial mode, and use the space station's equatorial inclination. Also, your inclination can match, but your longitude of ascending node can be completely different and that would not be good. And above all, always, always use the map program of IMFD as a cross-reference. It is way more accurate than the planet approach or any other program.

 

[XonE32]

Try using planet approach (if you can) in equatorial mode, and use the space station's equatorial inclination. Also, your inclination can match, but your longitude of ascending node can be completely different and that would not be good. And above all, always, always use the map program of IMFD as a cross-reference. It is way more accurate than the planet approach or any other program.

Thanks Mark,

I think it is the LAN (which I need to read up on more) that's probably the issue. I should've also mentioned that these trips are taken on the fly as it were (ie I'm not waiting for the right launch window) although I don't think that's as important when going from the moon>earth.

I managed to tinker around with it last night and got into my earth insertion burn with only 1.14 deg differential in the planes between my ship and the station.

I'm not sure what's more irritating; not being able to do it or being able to do it and not know what I did right:blink:

It's the initial burn (Inc setting) from the moon that's the question. Just using the station's Inc is not going to work if the trip is not aligned by launch window.. i think. So I'm assuming on these trips there's some simple math I'm missing with regard to the relationship with the LAN and Inclinations.

Using the map window and it's "find" option works well and also setting the target (once your out of the moon's SOI) to the station by typing it in helped a bit as well.

Cheers.

 

[jarmonik]

Correct LAN is vital if you want to intercept a space station from the Moon. And that means waiting a proper launch window. I can outline the method for that.

1. Open Planet Approach.
2. Ref=Earth, Src=Moon, Tgt=Station
3. Set PeA = 150k
4. Increase TEj until the green dashed line is aligned with the blue line. EIn should read 0.0 or atleast to be close to it. (This will point the launch window)
5. Increase EqI so that RIn reads about 0.0 (This will match the inclination with the station)
6. Then wait until you are closer to the launch window and repeat steps 4. and 5. if needed. (The values will drift a little while waiting).

It's probably a good idea to liftoff from the Mood when the time to launch window is about 5 hours. This shouldn't be a critical matter.

 

[XonE32]

Correct LAN is vital if you want to intercept a space station from the Moon. And that means waiting a proper launch window. I can outline the method for that.

1. Open Planet Approach.
2. Ref=Earth, Src=Moon, Tgt=Station
3. Set PeA = 150k
4. Increase TEj until the green dashed line is aligned with the blue line. EIn should read 0.0 or atleast to be close to it. (This will point the launch window)
5. Increase EqI so that RIn reads about 0.0 (This will match the inclination with the station)
6. Then wait until you are closer to the launch window and repeat steps 4. and 5. if needed. (The values will drift a little while waiting).

It's probably a good idea to liftoff from the Mood when the time to launch window is about 5 hours. This shouldn't be a critical matter.

Ah the master speaks. Love IMFD Jar. And agreed for the most fuel efficient flight to an earth orbiting station waiting for the right launch window is critical although not so much if yer just going to the earth.. I think.

So is this assumption (hate assumptions) correct?

If I leave the moon on an unaligned or (improper launch window). And set everything as I wish in order to hopefully intercept the station at a minimal Rin (ie planes aligned); my initial burn from the moon is just as inefficient as if i had just launched toward the earth and then had to do a plane change burn later in the flight?

In other words, I assume I'm using an inefficient amount of fuel whether I get the initial burn direction correct and don't have to do a plane change or whether I do a regular burn and then have to do a plane change all because I'm trying to intercept a station and NOT waiting for the correct launch window?

LOL, i think that's what you said in one sentence which took me 2 paragraphs.

Cheers and thanks

PS I hate waiting for launch windows, but will give yer method a go and see the dv differential.

---------- Post added at 07:55 PM ---------- Previous post was at 04:29 PM ----------

Niiiice job Jarmo.

Fisrt time=FAIL. heh, not sure what I did wrong, but despite your clear instructions my orbit eject burn directed me into the surface of the moon.

2nd attempt using the same vehicle & .scn was complete success. Hopefully you can see the pic below, but if not the bottom line is that earth-insert completed with 0.01 deg in plane alignment between myself and StationV.

I did use quite a lot of dv. In addition to solving the alignment issue i needed to make the transit in 23h.

Thanks again. (Will test without waiting for launch window as I'd like to see the diff in fuel consumption)

 

[jarmonik]

And agreed for the most fuel efficient flight to an earth orbiting station waiting for the right launch window is critical although not so much if yer just going to the earth.. I think. So is this assumption (hate assumptions) correct?

Yes, pretty much. If you wan't to land on a specific location on the Earth there is a launch window once in a day and you can also effect in landing location by changing time of flight and inclination. So the launch window isn't as critical.

If I leave the moon on an unaligned or (improper launch window). And set everything as I wish in order to hopefully intercept the station at a minimal Rin (ie planes aligned); my initial burn from the moon is just as inefficient as if i had just launched toward the earth and then had to do a plane change burn later in the flight?

No, you can't get into the orbital plane of the station with a single burn. Later plane change is needed. Inefficient (High dV) orbit eject burn won't change that.
The idea in a launch window is that you eject from the Moon when the Moon is already in the orbital plane of the station, so, no plane change is needed. In that case an efficient burn is all that is needed.

 

[XonE32]

Great tips Jarmonik, I've been using IMFD since I started with orbiter I think.. long time ago. But I get the sense I've only used it inefficiently. I would imagine a simple challenge of using a vehicle with severe fuel restrictions would probably get me lost in space as it were. Most, if not all the vehicles I use are near-future/plausible and they're pretty forgiving when it comes to fuel use.

I would like to learn more TransX, but haven't had the time to figure it out.

I'm gonna have to do some reading up on determining launch windows for various occasions. The info is hard to find or at least I haven't found a good source yet.

If I wanted to reverse the trip and go from say stationV to a specific base on the moon or moon-orbiting station AND i was able to determine a proper launch window do I still have to use the "Target Intercept" method due to the fact I have to eject from earth orbit (ie I can't use planet approach?) is that correct?

Thanks J; and if anyone has info re determining proper launch windows it would be greatly appreciated.

Thanks in advance

Cheers

XonE 32

 

[Tommy]

Part of the update for IMFD Full manual than Mark and I are working on will be a trip from the ISS to Brighton Beach. While I'm doing it with Delta Velocity, there are some tips for "aiming" at a ground base. Targeting a station is a bit more difficult, but the offsetting tricks shown in the Advanced Concepts tutorial may help some with that using Target Intercept.

 

[XonE32]

Part of the update for IMFD Full manual than Mark and I are working on will be a trip from the ISS to Brighton Beach. While I'm doing it with Delta Velocity, there are some tips for "aiming" at a ground base. Targeting a station is a bit more difficult, but the offsetting tricks shown in the Advanced Concepts tutorial may help some with that using Target Intercept.

Good stuff Tommy, look forward to it.

I have read the manual, but it was a loong time ago, but it was good to reread a bit of it a cpl nights ago. You guys are doing a great job with it so far.

Cheers