Flight Question Slingshot calculator?

[laukejas]

Hi all,

I'm over my head again. I want to plan some slingshots and perform them in Orbiter, but apart from using already known launch trajectories (those that NASA performed), I can't wrap my mind around the method to find possible routes. I just watched BBC documentary on Voyager trips, and it said that in 70-ies a guy named Gary Flandro, using best-at-the-time IBM computer, produced thousands of slingshot possibilities, out of which several were chosen for Voyager 1 and 2 flights.

So, more than 40 years have passed since then, and I still can't find any kind of calculator, any planner software to find such routes. For example, I have an idea in Orbiter to make a fly-by of Sedna with unmanned probe, followed by manned trip some centuries later, using conventional, existing technology. I think that Jupiter-Saturn-Uranus(?) slingshot would work, but I can't work out the dates and trajectories. I'm using Celestia to eyeball the possible windows, and then TransX to find if it's possible. Been doing this for several days now, and that is very, very inefficient. I don't have a problem with fine-tunning slingshot plan with TransX, I do it pretty well, but what about finding the initial windows? It would take a lot of time to find launch windows with TransX that may occur one in 200 years or so (like Voyager window). And eye-balling just doesn't quite cut it. It's very easy to miss a very good launch window.

Is there any software that would allow some rough estimates on what slingshots are possible? You know, just basic calculation on what slingshot can be done with initial burn of chosen dV, at what dates. Then I could plan it with TransX.

Please help me out here. There must be something. I don't think guys at NASA eyeball solar system, like "all planets look on the same side that year, maybe we should launch something?".

 

[SolarLiner]

Trajectory Optimisation Tool

 

[laukejas]

Trajectory Optimisation Tool

I have this one - how do you use it for slingshots?

 

[boogabooga]

Enter multiple waypoints.

 

[laukejas]

Sorry, but could you be a little more helpful? I know how to do that - but this tool can't even find the Grand Tour route of Voyagers. Also, it doesn't have a lot of planets, like Sedna (and they aren't available for download in links provided by help reference)

 

[boogabooga]

O.K. You just need to read the manual. Adding new bodies is covered. IIRC, you have to download spice files.

And the tool uses genetic algorithms. This uses a random initial seed. You won't get the EXACT same answer every time. Sometimes, you will get a "local minimum" instead of the global minimum. The trick is to run several times, until a "good" solution is approximately repeated a few times. There is a good chance that that this is the global min.

I have had great success with this tool.

 

[Arrowstar]

Thanks, boogabooga! It was a pleasure to write and I'm glad people enjoy it.

 

[laukejas]

Arrowstar, you wrote this program? Then maybe you can help me out, please? First of all, I can't find Sedna spice files anywhere on NASA ftp. Where are they?

 

[boogabooga]

I'm looking at that now. Apparently, you can use the Telnet HORIZONS to generate spk.

 

[Arrowstar]

Arrowstar, you wrote this program? Then maybe you can help me out, please? First of all, I can't find Sedna spice files anywhere on NASA ftp. Where are they?

Try JPL's NAIF: http://naif.jpl.nasa.gov/naif/data.html

 

[boogabooga]

Sedna is not included as a ready-made spk on naif.

Last night I learned how to telnet into the jpl HORIZONS system and make my own SPKs. It's easy. I made one for Sedna (aka 2090377). I recommend that you learn how to do it. Go to the jpl website and search for HORIZONS.

But, if you P.M. me your e-mail, I will send it to you.

I went ahead and optimized an Earth-Jupiter-Sedna mission three times. (If you just want to get to Sedna, a Jupiter pass alone is probably all that you need.)

This is what I got (full report attached):

 Trajectory Optimization Tool v2
                                            Written by Adam Harden ("Arrowstar"), (C) 2011
#####################################################################                     
Starting optimization...                                                                  
Optimization finished in 91.8012 seconds with message: Average change in trajectory       
fitness function less than tolerance.                                                     
Results of the analysis are as follows:                                                   
The optimal departure from EARTH occurs at 4/1/2022 14:58:58 (C3=651.8353 km^2/s^2)       
The optimal flyby of JUPITER BARYCENTER occurs at 3/17/2023 1:12:0 (deltaV=2.499e-008     
km/s, pass radius=526491.0451 km)                                                         
The optimal arrival at 2090377 occurs at 3/2/2038 13:27:51 (arrival velocity=24.7088      
km/s)                                                                                     
The optimal trip duration is 5813.9367 days.                                              
Generating report file...Done!                                                            
#####################################################################                     
Starting optimization...                                                                  
Optimization finished in 90.8685 seconds with message: Average change in trajectory       
fitness function less than tolerance.                                                     
Results of the analysis are as follows:                                                   
The optimal departure from EARTH occurs at 5/3/2021 4:45:55 (C3=132.7347 km^2/s^2)        
The optimal flyby of JUPITER BARYCENTER occurs at 6/26/2022 12:6:41 (deltaV=0.00016747    
km/s, pass radius=426707.4558 km)                                                         
The optimal arrival at 2090377 occurs at 8/12/2040 17:58:23 (arrival velocity=20.5543     
km/s)                                                                                     
The optimal trip duration is 7041.5503 days.                                              
Generating report file...Done!                                                            
#####################################################################                     
Starting optimization...                                                                  
Optimization finished in 88.8564 seconds with message: Average change in trajectory       
fitness function less than tolerance.                                                     
Results of the analysis are as follows:                                                   
The optimal departure from EARTH occurs at 5/6/2021 10:5:58 (C3=147.6025 km^2/s^2)        
The optimal flyby of JUPITER BARYCENTER occurs at 6/1/2022 6:1:3 (deltaV=1.511e-008       
km/s, pass radius=313239.6723 km)                                                         
The optimal arrival at 2090377 occurs at 7/30/2038 3:46:55 (arrival velocity=23.2995      
km/s)                                                                                     
The optimal trip duration is 6293.7368 days.                                              
Generating report file...Done!                                                            
#####################################################################

Translation:

First of all, Sedna is nearly a stationary target. I suspect that every 20 years or so, Earth and Jupiter will be in alignment to reach Sedna. (Synodic period). I searched for something departing in the 2020s and arriving in the 2040s, but I didn't add any further constraints. I used a population of 100, crossoverheuristic and selectionstochunif. I use a loose tolerance of 1e-4, since there is a limit as to how precisely you can fly the trajectory in Orbiter anyway. My cost function weights in order are 2, 5, and 3. I have found that this gives a "balanced" solution.

So, the first solution seems to be a dud. It happens. The second two, are very similar to each other, so I suspect that they represent at least a "very good" solution in the time frame. It looks like you will want to leave in early May of 2021 and arrive at Jupiter sometime in June, 2022. Depending on the specifics, you will then have a 15-20 year cruise to Sedna. It looks like you can trade some energy to shave a few years off of this coast, if you wish.

Here is what it looks like:





If you wanted to be thorough, you could constrain your earth departure and Jupiter arrival to May 2021 and June 2022, respectively, then use a large population with tight tolerance to get the very best solution possible. I suspect that you can just do that in TransX, and could never fly that accurately in Orbiter anyway.

Hope this helps.

 

[laukejas]

Thank you. Sorry for late reply, I was away from internet connection for a while, couldn't write back sooner. Thank you for extensive information. I'll try my luck in jpl website, but please send that spk, just in case.

 

[downloaderfan]

Alright, I know this is a really, really, really old post & the op must have moved on & become a millionaire by now but this post propelled me to plan yet another fuel efficient slingshot scenario, this time with my main target being sedna.

Boogabooga has already posted some high dv solutions to sedna, so I thought I should find a low dv solution to sedna using multiple inner planet slings.

I already have planned a EVVEJU Sedna slingshot scenario here which takes me to sedna in 31 years, but while planning that scenario, sedna was not my primary target, uranus was, sedna just happened to be available at the right place & at the right time for me to be able to sling to after uranus.

So with my fuel limit being the fuel required only to get to venus, I began planning a trip to sedna, while trying to minimize the time of flight as much as I could. And yes, I did find a solution, starting from Sep 2015, with a pretty reasonable TOF.

The sling sequence is Earth - Venus - Earth - Earth - Jupiter - Uranus - Sedna. Almost similar to the above sling scenario, but has 2 earth passes instead of 2 venus passes to get a larger boost in velocity so as to increase the encounter velocity at jupiter, which decreases my TOF to sedna.

Has a fuel requirement of 4.2k dv from a 300x300 km earth orbit, somewhat higher than my usual transfers to venus which take around 4k, but is significantly lower compared to a hohmann's transfer to jupiter, which requires about 6.2k or boogabooga's lowest dv solution, which requires 8.1k.

Has a total TOF of 22.7 years, which is 8.3 years lower than my previous scenario, but higher than boogabooga's solutions due to inner planet slings.

Scenario attached below. Sedna addon I'm using - [ame="http://orbithangar.com/searchid.php?ID=610"]Sedna v2.0[/ame]