Mercury~Venus~Venus~Venus~Mars



OVERVIEW:
Start from sitting on the surface of Mercury. Set up a flight plan that comprises of an Eject to Venus with free coasting slings to Venus again, then Venus a third time then Mars. There is nothing especially opportunistic about this flight. The starting time is random and the choices are also random. After you get the feel for planning the slings you may choose to try it again but with different target planets or starting planets or eject dates. Remember in general, the inner planets will often need to coast complete orbits or more between slings and give only slight boosts in energy while the outer planets are able to boost massively so going sling to sling within a fraction of an orbit is typical.

Run Orbiter in a Window with scenario "Venus triple sling" found in the Flytandem Tutorials subfolder. To get this scenario click here. (extract into your Orbiter directory).


EJECT TO VENUS:

Transx in both MFD's. click "VW" for "Setup"
click "++" for "Escape"
click "FWD" for "Stage 2:2"
click "VW" for "Select Target"
click "++" for "Venus"
click "VW" for "Eject Plan" For an exercise in setting up the eject variables you can do this on your own but in order that we have the same starting trajectory to plan the free coasting slings go ahead and set the variables to the following...
Prograde vel.=7.182k
Eject date = 53805.3231
Outward vel.= 0
Ch. plane vel.= -3.867k

Click "FWD" to stage 3:3
click "VW" for "Encounter". You should have something like the following. Adjust the variables in stage 2 slightly on "Ultra" to get a close pass with a close but comfortable miss of the planet and an inclination of a low number not a high number like 170 or 180. The concept is that we know we will want to gain extra energy and since we are climbing up to the orbit of Venus we pass behind it with respect to the direction it's in orbit around the sun.
GENERAL SLING ALGORITHM:
After you get through this exercise you will notice that the basic sling setup starting with an Encounter is...
1. Encounter
2. Escape
3. Forward
4. Sling Direct
5. ChooseTarget
6. Adjust Deflection Variables including future orbit numbers to get a finely tuned next encounter.
return to step 2 above and repeat

DETAILS
1st Sling: Target Venus:
In stage 3...
click "VW" for "Setup"
click "++" for "Escape"
click "FWD" for "Stage 4:4"
click "++" for "Venus"
click "VW" for "Sling Direct"
Find a better graphic...
click "VW" for "Setup"
click "VAR" for "Scale to view"
click "++" for "Craft" or "Target" (your preference)
ADJUST the SLING
click "VW" for "Sling Direct" again
click "VAR" for variables "Outward angle" Adjust using "++" and "--" initial set "Coarse"
Make the dashed yellow ellipse about the same as the green orbit. We know we are passing Venus on a fairly close sling so this is a ballpark first sling. You probably have a close encounter about like the following.
The two yellow dashed radius lines are the locations at the closest approach. You will want to adjust the sling deflection angles to bring these two lines together. Start by adjusting the "Outward angle".
Note: You won't need to adjust the "Inc. angle" on this or the next sling since the default value is zero which is what you want in order to sling back to the same planet. But the 3rd time at Venus you'll sling to Mars which will require both "Outward angle" and "Inc. angle" adjustments.
With the outward angle at about 100 degrees, you probably can get something like the following...
Now check that the required 1st sling isn't making you pass below the surface of Venus by looking at the image above and the ratio of "Pe/Pl" (Pe to planet radius). That value needs to be greater than 1 to miss the surface and perhaps greater than 1.07 to miss the atmosphere too.

The dashed yellow line in the image below is pointing at your closest pass position (Pe) at Venus. (allow for the thick atmosphere)
click "BCK" to "Stage 3"
click "VW" for "Slingshot"
I have the following, your mileage may differ.

Make the 2nd Sling: Target: Venus (again)
click "FWD" to "Stage 5:5"
click "VW" for "Encounter"
click "++" for "Escape"
click "FWD" for "Stage 6:6"
click "++" for "Venus"
click "VW" for "Sling Direct"

Find a better graphic...
click "VW" for "Setup"
click "VAR" for "Scale to view"
click "++" for "Craft" or "Target"

ADJUST the SLING
click "VW" for "Sling Direct" again
click "VAR" for variables "Outward angle" Adjust using "++" and "--" initial set "Coarse"
Make the dashed yellow ellipse about the same as the green orbit. You probably have the Outward angle set to about 105 degrees. Now start expanding the dashed yellow orbit by changing the Outward angle (reducing it) . Keep expanding perhaps with increment to Medium or smaller. You might find a close pass when the Outward angle is about 63 degrees. But checking stage 5 we see the dashed yellow line is inside the surface of Venus. Let's try a milder sling that goes around more orbits allowing more time to let Venus gain a lap on us.
In Stage 6:6...
click "VW" for "Setup"
click "VAR" for "Orbits to Icept"
click "++" to scroll up through higher orbit numbers.
I like to have one MFD adjusting the orbit numbers choices and the other in the same stage but adjusting the sling angle variables (in this case "Outward angle"). You might find when the "Orbits to Icept" value is 2.0 and the "Outward angle" is about 83 degrees, that a potential encounter is something like the following...

Fine Tune the Deflection Angle
click "VW" for "Sling Direct"
click "VAR" for "Outward angle"
click "++" or "--" to adjust with small increments to bring the "Cl. App." to a minimum.
Since we are dropping down onto Venus from a high orbit the sling that gives extra energy is to pass behind the planet so bring up Stage 7 ("Encounter" view) with one MFD while adjusting Stage 6 with the other to make the pass jusa missing the planet with a~180 inclination like the following.
CHECK the Sling Pe Distance
click "BCK" to "Stage 5"
click "VW" for "Sling Direct"
to check the yellow dashed line is still outside the edge of Venus atmosphere like in the following image. (Ignore the position of the green line as there will be plenty of time during the actual flight to get on course.)


Make the 3rd Sling: Target: Mars

REPEAT the process of making the last sling this time choosing the target as Mars; ie, Escape, FWD, Setup, Mars, Sling Direct, Better Graphic view, choose future slings.

One difference now is that we are not slinging back to the same planet so adjusting "Inc. angle" is now going to be necessary.
I found that with "Orbits to Icept" set to 2.5 or 3.0 that a future sling came up with Mars in the following image of Stage 8.
And checking back to Stage 7 the sling necessary was barely outside of the planet but it should work.
FINAL STAGE: From Stage 8 (2 images above) we see that the closest approach to Mars is about 1.6 G. It's also several orbits in the future with the time between the 3rd pass at Venus and arrival to Mars a bit less than 5 Earth years. There should be plenty of time to make a small correction burn as needed to arrive on target.

ANOTHER OPTION (my preferred)... is to set the "Orbits to Icept" = 4 which allows a more comfortable pass at Venus with more of the sling going to handle the plane inclination and less the outward and a final Encounter is coming back on the inward leg of the orbit with ability to adjust the the encounter approach very close in the following image. See if you can find that option.
...or maybe try the Earth instead of Mars. Or Venus again for 4 slings. Or maybe only 2 times at Venus then Earth. Or 1 time Venus then Earth, or maybe....