Problem Slingshot will not compute.

[RAF Blackace]

Hi.

I am flying Brianj's Excellent Vega missions. I am on course and four days away from a Venus encounter on MJD46226.645. From here I need to slingshot to Comet 1p_Halley for an encounter on MJD46495.

I normally use IMFD, but it does not do slingshots very well. I am no friend of TransX but I do know (roughly) how to use it.

Looking at the current orbit and required orbit in IMFD, it should be a straightforward slingshot. But whatever I do in TransX I cant get it to either agree or even get close to computing this slingshot trajectory.

Is there any other way of computing a slingshot trajectory without using TransX? I must say I am so frustrated with TransX I detest even looking at it right now now.

I've attached am image of the current state and the scenario file if you want to try yourself.

The scenario file requires Brianjs Vega missions...

[ame="http://www.orbithangar.com/searchid.php?ID=4733"]Vega1 & Vega2[/ame]

 

[garyw]

Any chance of larger screenshots. Trying to look at the MFD's screens in that JPG is very hard.

 

[RAF Blackace]

It was the site that compresses it not me.

Here is a better image.

 

[dgatsoulis]

Hi.

I am flying Brianj's Excellent Vega missions. I am on course and four days away from a Venus encounter on MJD46226.645. From here I need to slingshot to Comet 1p_Halley for an encounter on MJD46495.

What exactly are you trying to do?

If by "encounter" you mean a high speed impact (at ~80 km/s !!!) then there is a slight chance that you might be able to do it.
It's going to be pretty tough, because right now you are headed straight for the center of Venus (PeA = -5.7 M) and you have only 190 m/s of ΔV. It's going to take ~ 60 m/s just to keep from hitting the cloudtops, let alone proceed to get in the path of Halley to "get hit".

So, please confirm if a high velocity impact is the goal and I'll look for a solution. (If one exists).

If you are planning to rendezvous with Halley, forget it. You don't have anywhere near the Venus encounter velocity needed to make it.
If that was your goal, then there is something really wrong with the plan from the start.

For a landing on Halley you'll need to setup a very different plan. A simple "Hohmann-type" transfer from Earth to Venus will not help you, because you will need to have a much higher velocity. If you could provide the goal of the mission and the start date and ΔV budget, we could look for a landing solution.

 

[RAF Blackace]

What exactly are you trying to do?

I suggest you read up on the actual historic mission. There is no question that a solution is available because it has been done for real.

The mission is intended to have a high speed encounter (flypast) with 1P_Halley after releasing a lander capsule (which has no thrusters of its own) on a course to enter the Venusian atmosphere at a 20 degree re-entry angle 3 days away from Venus encounter.

I have not released the lander yet, Hence the reason I am heading straight for Venus.

Maybe I could have saved 50 dV by setting up this approach much further out. But that is not the point. I have more than enough fuel to release the lander in a days time and orient the ship for a slingshot to 1P_Halley for an encounter on MjD 46495.

If I knew what that slingshot angle was of course, which TransX cannot seem to answer.

 

[dgatsoulis]

So, please confirm if a high velocity impact is the goal and I'll look for a solution. (If one exists).

I suggest you read up on the actual historic mission.

Seriously? Don't you think that since you are the one that is asking for help, you should also be the one that provides the necessary information?
Do you think that people that are offering to help, should be expected to download 3-4 different addons and do research on a mission that interests you?

Perhaps it was a poor choice of words, or I -not being a native English speaker- perceived it the wrong way, but to me that sounded very rude.

Anyway... here is the IMFD solution from the scenario you provided.

1.Open IMFD on both sides
2.Right MFD: Course→Target Intercept→Reference Sun, Source Venus, Target 1P_Halley
3.Left MFD: OpMode: 1 (Share from right MFD), Slingshot ("course" should be auto-selected)→Reference: Venus
4.Adjust the date to intercept (MJD first and then Tin) on the right MFD untill you get a minimum "Enroute: dV" on the left side. You probably will not see anything on the left MFD until you get close to the correct date on the right MFD.
Minimum "Enroute: dV" should happen at MJD 46494.88 with the dV at 322.4 m/s.
You may want to use the Z+ and Z- buttons to get a better view on both sides.

There is no question that a solution is available because it has been done for real.

The problem is that even if you jettison the lander immediatelly, you still come up short on ΔV (you'll have 288.97 m/s and you will need corrections), so I think it would be better to pickup the mission from an earlier save, if you have one.

I could look for a solution with TransX but it will take a lot more of my time since it requires changing more parameters. If you want to try it yourself here is what to do:

TransX on both sides:

LeftMFD:
Stage1→Maj Body: Sun, Target Venus→FWD
Stage2→Maj Body: Venus, Escape→FWD
Stage3→Maj Body: Sun, Target 1P_Halley→FWD
Stage4→VW (Encounter)

Go to stage 3, get a better view (Scale to view: Craft)
Select inherit velocity: No and start changing all 3 parameters, starting with velocity.

RightMFD:
Go to stage2. You already have an idea of what the trajectory should look like from the IMFD pic above.

Another way to do it, is to see the burn in IMFD and copy it as a maneuver in TransX. (dVf, dVp, dVi → Prograde, Ch.plane, Outward)
Same plan as above, you will need stage1 (maneuver) on one side and "Plan: None" (through "advanced: on, autoplan: off") on stage3 on the other side. Look for minimum Cl.Approach on that stage.
Remember that Ch.plane and Outward are reversed in IMFD. (if the value is positive in IMFD you will need negative in TransX)

 

[RAF Blackace]

Thank you for your reply.

Your solution is not correct (run it and you will see), but I have since worked it out for myself from some of the information you have provided.

I thank you for your help.

 

[jean pierre]

Hi Raf Blackace

Making an encounter with a comet is difficult because they travel much faster than your ship... I would suggest to study a little bit about the Roseta mission : it was launched in in march 2004 in Kourou and is expected to meet 67P/Churyumov-Gerasimenko next year ( ie 2014 ) after 10 years of travelling with multiple gravity assist sling shots and near encounters of big asteroîds in the asteroîd belt.
Hope this can help you !