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 MFD Questions & Help Post your questions here for help with the Multi-Function Displays.

 02-19-2013, 10:56 PM #16 Screamer7 Orbinaut Why do you not try IMFD? You do not have to worry about launch windows, although it can cost you a lot of fuel.
 02-19-2013, 11:20 PM #17 blixel Donator Quote: Originally Posted by DutchPlayer  What I'm asking is: how do I see (or know) when the launch window is open or not? When I brought up the scenario you sent me, I set up TransX and used the Eject date variable to find out when the two dashed yellow lines would line up. This is a basic outline of the steps that I used to find the right time to launch.
 02-19-2013, 11:33 PM #18 TMac3000 Evil Republican Quote: Originally Posted by DutchPlayer  What I'm asking is: how do I see (or know) when the launch window is open or not? I use a simple rule: draw a line between your starting planet and the Sun, then draw a line between your destination and the Sun. If the angle between the two lines is about 90 degrees, then you have a launch window. If it's less than about 60 degrees, or more than about 120, then you need to wait
 02-20-2013, 04:08 AM #19 sorindafabico Orbinaut For me, the rule of thumb have been intersecting orbital planes. The launch window occurs when plane change is minimal. And, of course, the position of planets allows the format of a Hohmann transfer (or almost). If you use IMFD target intercept transfer, try to keep the numbers from EjA, InA and EIn/RIn near zero. EjA is your ejection angle from Earth; InA your injection angle at Mars; and EIn/RIn is the relative inclination between EjA and InA points. You'll only get zero in both three if the orbits were circular and coplanar, probably, so don't worry if they are a little offset. If you use transx, you can guess like blixel did. The main advantages of IMFD are its autopilot and map program, but transx is more user-friendly for planning. You can save time using the already cited trajectory planning utilities and Cosmic Train Schedule website, they are great to find launch windows. I knew that of November 2011 (when MSL and Phobos-Grunt were launched), so I got the examples I'm posting here in a few minutes (just the time to fine-tune them). In transx, I found this using only 2996 m/s of prograde, no outward or plane change: But the IMFD example - got with Trajectory Optimization Tool - is, despite the longer trip, more fuel-wise if you are not intending to aerobrake. Last edited by sorindafabico; 02-20-2013 at 04:44 AM.
 02-20-2013, 08:44 AM #20 DutchPlayer Orbinaut Quote: Originally Posted by blixel  When I brought up the scenario you sent me, I set up TransX and used the Eject date variable to find out when the two dashed yellow lines would line up. This is a basic outline of the steps that I used to find the right time to launch. {image} {image} {image} {image} {image} Why do you reduce the eject date? I always advance the date (clicking +), is that wrong? BTW, I understand the steps but I don't understand why you reduce the eject date.
 02-20-2013, 11:24 AM #21 blixel Donator Quote: Originally Posted by DutchPlayer  Why do you reduce the eject date? I always advance the date (clicking +), is that wrong? BTW, I understand the steps but I don't understand why you reduce the eject date. Normally I would move the date forward, but in the scenario you sent me, the closest launch date was 2 1/2 months earlier, so I went with that. I simply picked it because it was closer. Since we were on the ground and hadn't gone anywhere yet, it was acceptable to go backwards in time. If, on the other hand, you are already in space and on the way to your destination, then you always have to plan your maneuver for some point in the future.
 02-20-2013, 05:43 PM #22 Mister Mxyzptlk Orbinaut synodic periods Dutch player, if you want to understand the launch window relationship a little better look up synodic period and understand that launch windows occur at regular fixed intervals for each pair of bodies in a hohmann transfer.
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 02-20-2013, 06:22 PM #23 AlfalfaQc Future Rocket Engineer I have a question here, it's not related to mars in particular but it's about interplanetary travel. I'm really used to TransX, but someone mentioned IMFD. My question is, is one better than the other? What can IMFD do that TransX cannot. I have good results with TransX but if IMFD is better, I might try to learn it.
 02-20-2013, 06:49 PM #24 blixel Donator Quote: Originally Posted by AlfalfaQc  I have a question here, it's not related to mars in particular but it's about interplanetary travel. I'm really used to TransX, but someone mentioned IMFD. My question is, is one better than the other? What can IMFD do that TransX cannot. I have good results with TransX but if IMFD is better, I might try to learn it. dgatsoulis knows both TransX and IMFD inside and out. The way he explains it is that you can combine the advanced planning capabilities of TransX with IMFD's superior n-body Map program in order to get the best results. In other words, it's not the case that one is "better" than the other. They each have their own strengths and work well together. They are not mutually exclusive. Bottom line - learn both. Last edited by blixel; 02-21-2013 at 09:14 AM. Reason: fixed typo
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 02-20-2013, 07:14 PM #25 Ripley Tutorial translator I wrote a Earth->Mars tutorial some time ago (unfortunately for most of you, it's in Italian). About launch windows, I came up with these: Image credit: SunAeon Image credit: EOTSS Last edited by Ripley; 02-28-2014 at 10:58 PM.
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 02-20-2013, 07:15 PM #26 C3PO Donator And learning IMFD just to avoid understanding launch windows is a bad move IMHO.
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 02-21-2013, 03:04 AM #27 AlfalfaQc Future Rocket Engineer Yeah, I've heard IMFD is better to target a base to do a direct reentry, I might want to use that in the future. Is there a good IMFD tutorial out there (maybe one by dgatsouli)?
 02-21-2013, 03:35 AM #28 sorindafabico Orbinaut Quote: Originally Posted by AlfalfaQc  Yeah, I've heard IMFD is better to target a base to do a direct reentry, I might want to use that in the future. Is there a good IMFD tutorial out there (maybe one by dgatsouli)? There are a donzen tutorials at O-H, but you'll learn A LOT reading the full manual. I know IMFD better than TransX, so I don't know the answer about direct reentries, but IMFD's Base Approach tool works fine.

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