Orbiter-Forum  

Go Back   Orbiter-Forum > Orbiter Space Flight Simulator > MFD Questions & Help
Register Blogs Orbinauts List Social Groups FAQ Projects Mark Forums Read

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

Reply
 
Thread Tools
Old 02-19-2013, 10:56 PM   #16
Screamer7
Orbinaut
 
Screamer7's Avatar
Default

Why do you not try IMFD?
You do not have to worry about launch windows, although it can cost you a lot of fuel.
Screamer7 is offline   Reply With Quote
Old 02-19-2013, 11:20 PM   #17
blixel
Donator
 
blixel's Avatar
Default

Quote:
Originally Posted by DutchPlayer View Post
 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.









blixel is offline   Reply With Quote
Old 02-19-2013, 11:33 PM   #18
TMac3000
Evil Republican
 
TMac3000's Avatar
Default

Quote:
Originally Posted by DutchPlayer View Post
 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
TMac3000 is offline   Reply With Quote
Old 02-20-2013, 04:08 AM   #19
sorindafabico
Orbinaut
 
sorindafabico's Avatar
Default

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.
sorindafabico is offline   Reply With Quote
Old 02-20-2013, 08:44 AM   #20
DutchPlayer
Orbinaut
 
DutchPlayer's Avatar
Default

Quote:
Originally Posted by blixel View Post
 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.
DutchPlayer is offline   Reply With Quote
Old 02-20-2013, 11:24 AM   #21
blixel
Donator
 
blixel's Avatar
Default

Quote:
Originally Posted by DutchPlayer View Post
 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.
blixel is offline   Reply With Quote
Old 02-20-2013, 05:43 PM   #22
Mister Mxyzptlk
Orbinaut
 
Mister Mxyzptlk's Avatar
Default 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.
Mister Mxyzptlk is offline   Reply With Quote
Thanked by:
Old 02-20-2013, 06:22 PM   #23
AlfalfaQc
Future Rocket Engineer
 
AlfalfaQc's Avatar
Default

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.
AlfalfaQc is offline   Reply With Quote
Old 02-20-2013, 06:49 PM   #24
blixel
Donator
 
blixel's Avatar
Default

Quote:
Originally Posted by AlfalfaQc View Post
 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
blixel is offline   Reply With Quote
Old 02-20-2013, 07:14 PM   #25
Ripley
Tutorial translator
 
Ripley's Avatar
Default

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:


Last edited by Ripley; 02-28-2014 at 10:58 PM.
Ripley is offline   Reply With Quote
Thanked by:
Old 02-20-2013, 07:15 PM   #26
C3PO
Donator
 
C3PO's Avatar

Default



And learning IMFD just to avoid understanding launch windows is a bad move IMHO.
C3PO is offline   Reply With Quote
Thanked by:
Old 02-21-2013, 03:04 AM   #27
AlfalfaQc
Future Rocket Engineer
 
AlfalfaQc's Avatar
Default

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)?
AlfalfaQc is offline   Reply With Quote
Old 02-21-2013, 03:35 AM   #28
sorindafabico
Orbinaut
 
sorindafabico's Avatar
Default

Quote:
Originally Posted by AlfalfaQc View Post
 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)?
IMFD Full Manual/Playbacks


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.
sorindafabico is offline   Reply With Quote
Reply

  Orbiter-Forum > Orbiter Space Flight Simulator > MFD Questions & Help


Thread Tools

Posting Rules
BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
Forum Jump


All times are GMT. The time now is 11:05 AM.

Quick Links Need Help?


About Us | Rules & Guidelines | TOS Policy | Privacy Policy

Orbiter-Forum is hosted at Orbithangar.com
Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2007 - 2017, Orbiter-Forum.com. All rights reserved.