Orbiter-Forum  

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

Tutorials & Challenges Feel free to publish your tutorials, challenges, & flight scenarios in this forum.

Reply
 
Thread Tools
  #1  
Old
MontBlanc2012 MontBlanc2012 is offline
Orbinaut
Default Low energy Moon-Earth transfer
by MontBlanc2012 11-13-2017, 06:57 AM

Here (below) is a simple challenge designed to test your thinking about ways of making transfers from low lunar orbit to the Earth.

The scenario set out in the attached .scn file is as follows: A Delta Glider starts in a 20 x 20 km lunar orbit with a total 700 m/s of main fuel and 10 m/s of RCS. The challenge is to land anywhere on Earth. For the purpose of this exercise, achieving an Earth approach orbit with an Earth-centric periapsis < 70 km altitude constitutes a 'landing'.

Now, at first blush, this sounds simple enough - after all, it is one of the first 'missions' that budding Orbinauts will set themselves. However, Apollo-style Moon-Earth transfers typically require around 1,000 m/s of fuel. But in this challenge, the DeltaGlider starts with just over two-thirds that amount. In fact, the fuel needed to lunar escape from a 20 km parking orbit is 692 m/s - so, you have barely enough fuel to 'escape' from the Moon let alone set up a low perigee encounter.

Finding a Moon-Earth transfer solution that meets the rather restricted fuel constraints of this scenarion requires a little 'out of the box' thinking. As will all problems of this kind, the solution is quite simple once you frame the problem in the rightway; and devilishly hard if you don't. But once you know what you are doing, it's quite easy to set up in Orbiter using standard tools.

As a hint, you may find that TransX is not of much use in finding a solution.

For those that easily manage to find the solution, well done! - and you may wish to pay appropriate hommage to Messrs. Lagrange and Belbruno.

I'm happy to provide a solution upon request.

As for the challenge scenario itself, here it is:


Code:
BEGIN_DESC
Delta Glider in a 20 x 20 km lunar orbit with a total 700 m/s of main fuel and RCS.  The goal is to land anywhere on Earth.  For the purpose of this exercise, achieving an Earth approach orbit with an Earth-centric periapsis < 70 km altitude constitutes a 'landing'.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 52006.7542552436
  Help CurrentState_img
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-NT
END_FOCUS

BEGIN_CAMERA
  TARGET GL-NT
  MODE Cockpit
  FOV 40.00
END_CAMERA

BEGIN_SHIPS
GL-NT:DeltaGlider
  STATUS Orbiting Moon
  RPOS 1677740.022 -137005.718 -506935.076
  RVEL 477.7254 -65.8104 1598.8449
  AROT 15.788 -10.126 42.772
  AFCMODE 7
  PRPLEVEL 0:0.015058 1:0.004584
  NAVFREQ 0 0 0 0
  XPDR 0
  HOVERHOLD 0 1 0.0000e+000 0.0000e+000
  AAP 0:0 0:0 0:0
END
END_SHIPS
And for those requiring a .scn file, see the attached .zip file.
Attached Files
File Type: zip Moon Earth transfer.scn.zip (1.2 KB, 0 views)
Reply With Quote
Views 181 Comments 2
Total Comments 2

Comments

Old 11-14-2017, 01:27 PM   #2
MontBlanc2012
Orbinaut
Default

And just as a demonstration, here is a link to a YouTube video demonstrating the basic scheme (contains spoilers!):

https://www.youtube.com/watch?v=m4FD...ature=youtu.be

Sadly, I fluffed the step back to real time upon Earth approach and ended up scooting by Earth with a ~ 70 km encounter. But, meh!, not a big deal.

Last edited by MontBlanc2012; 11-14-2017 at 02:28 PM.
MontBlanc2012 is offline   Reply With Quote
Old 11-17-2017, 05:30 PM   #3
BrianJ
thing
Default

Hi,
I couldn't resist this one :-)
I managed to land close to Overberg base in SA after a fairly rough reentry (8g at one point) with 220g fuel remaining in RCS.

I used the IMFD "Delta Velocity" + IMFD "Map - Plan View" to plan the escape burn. Set up a Prograde burn of 670m/s and tweak the burn time until you get reasonable solution, then tweak the dV.
Here's my escape burn solution:
Click image for larger version

Name:	challenge1.jpg
Views:	8
Size:	367.6 KB
ID:	15476

Coming up on Moon-flyby:
Click image for larger version

Name:	challenge2.jpg
Views:	6
Size:	334.5 KB
ID:	15477

MCC at first Apogee:
Click image for larger version

Name:	challenge3.jpg
Views:	6
Size:	369.3 KB
ID:	15478

Scraping the tanks for a last Perigee adjust burn before reentry:
Click image for larger version

Name:	challenge4.jpg
Views:	5
Size:	398.4 KB
ID:	15479

On the ground:
Click image for larger version

Name:	challenge5.jpg
Views:	5
Size:	393.2 KB
ID:	15480

Thanks for the challenge, I enjoyed it
Tip o' the hat to Mssrs.Lagrange and Belbruno!
Cheers,
Brian
BrianJ is offline   Reply With Quote
Thanked by:
Reply

  Orbiter-Forum > Orbiter Space Flight Simulator > Tutorials & Challenges


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 02:54 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 - 2017, Jelsoft Enterprises Ltd.
Copyright 2007 - 2017, Orbiter-Forum.com. All rights reserved.