Hello everyone!
I first wanted to make a scenario re-creating the Hiten mission - then I decided to keep it simple and make a new mission instead, based on what Belbruno described in his paper
http://www.astrogatorsguild.com/wp-content/papers/0800_wsb.pdf
(paper describes the procedure of sending a spacecraft in low Moon orbit from the low Earth orbit using weak stability boundary, WSB)
I tried to use the paper as a cookbook and just follow the instructions. Here's how it went:
1. I picked a spaceraft- for simplicity, let's keep it round, small and classic - Luna 2.
2. The Sun-Earth-Moon angle has to be about 130° as in case of Belbruno's example - on Apr 27 2007 at 21:52. OK, using NAIF SPICE (SIMPLE, to be more precise) I got a date and time with almost identical angle - Dec 23 2012, at 21:32.
3. Spacecraft-Earth-Sun angle as the transfer from LEO starts has to be between 20 and 40 degrees - my solution uses simple trig since Dec 23 is close to winter solstice, so I find the RPOS coordinates as (r+H)cos(alpha), zero and (r+H)sin(alpha), respectively. RVEL is the tangent to the orbit in that point, hence scalar product is zero, i.e. x*vx=-z*vz (y=0, vy=0 - keeping all in the ecliptic plane). Since I know that the final velocity for the transfer is (from the vis viva equation) 10.907 I obtain the velocity components, put the negative signs so it physically matches the situation - and I'm off.
Unfortunately, this doesn't work. Belbruno states that the craft reaches the apoapsis of approx. 1.5 million km after 45 days - I usually get 1.6 or more. Then it should reduce as the craft returns, but no such thing occurs in my case.
Scenario code is below (using R7 pack).
I first wanted to make a scenario re-creating the Hiten mission - then I decided to keep it simple and make a new mission instead, based on what Belbruno described in his paper
http://www.astrogatorsguild.com/wp-content/papers/0800_wsb.pdf
(paper describes the procedure of sending a spacecraft in low Moon orbit from the low Earth orbit using weak stability boundary, WSB)
I tried to use the paper as a cookbook and just follow the instructions. Here's how it went:
1. I picked a spaceraft- for simplicity, let's keep it round, small and classic - Luna 2.
2. The Sun-Earth-Moon angle has to be about 130° as in case of Belbruno's example - on Apr 27 2007 at 21:52. OK, using NAIF SPICE (SIMPLE, to be more precise) I got a date and time with almost identical angle - Dec 23 2012, at 21:32.
3. Spacecraft-Earth-Sun angle as the transfer from LEO starts has to be between 20 and 40 degrees - my solution uses simple trig since Dec 23 is close to winter solstice, so I find the RPOS coordinates as (r+H)cos(alpha), zero and (r+H)sin(alpha), respectively. RVEL is the tangent to the orbit in that point, hence scalar product is zero, i.e. x*vx=-z*vz (y=0, vy=0 - keeping all in the ecliptic plane). Since I know that the final velocity for the transfer is (from the vis viva equation) 10.907 I obtain the velocity components, put the negative signs so it physically matches the situation - and I'm off.
Unfortunately, this doesn't work. Belbruno states that the craft reaches the apoapsis of approx. 1.5 million km after 45 days - I usually get 1.6 or more. Then it should reduce as the craft returns, but no such thing occurs in my case.
Scenario code is below (using R7 pack).
Code:
BEGIN_DESC
For alpha=30 degrees.
END_DESC
BEGIN_ENVIRONMENT
System Sol
Date MJD 56284.897220000000
END_ENVIRONMENT
BEGIN_FOCUS
Luna
END_FOCUS
BEGIN_CAMERA
TAGET Luna
MODE Cockpit
FOV 50
END_CAMERA
BEGIN_HUD
TYPE Surface
END_HUD
BEGIN_SHIPS
Luna:r7_VL\Luna2
STATUS Orbiting Earth
RPOS -5777264.12 0.00 3335505.00
RVEL -5453.741 0.000 -9446.157
AROT 0.00 0.00 0.00
AFCMODE 7
PRPLEVEL 0:1.000000
NAVFREQ 94 481
=========== LUNA vars
END
END_SHIPS
