Scenario BrianJ and his Solar Probe Plus Mission

RAF Blackace

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I Love BrianJ's missions. I wait eagerly for every one and spend hours working out how to do each one. Up to now I have successfully accomplished every one.

But not this one.

I did the Jupiter slingshot one just fine, that was easy. But the Solar probe plus with seven slingshots past Venus has me stumped.

I usually use most of the fuel getting past the first slingshot using TransX.

BrianJ usually includes some hints in the read me document, but this mission has hints for the solar probe past Jupiter which in all honesty is easy anyway, but no real hints for the solar probe plus mission.

BrianJ. Can I have some hints please?

BTW, Thanks for all the great missions. You really have no idea how much time I have devoted (wasted according to my wife) to completing your missions.

More please.
 

BruceJohnJennerLawso

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Have you tried doing short burns at closest approach for each slingshot? I think that might help a little bit
 

RAF Blackace

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Well I can complete the Voyager 2 missions with 80% fuel remaining so I'm no novice to slingshots. Also BrianJ's missions are always tight on fuel, and that realism is what I like about them.

I always fly at maximum hard settings to try to get the most realism out of any mission I do.

But the first outward bound leg from the Earth to Venus uses most of the fuel for the initial Earth to Venus departure and subsequent course corrections to get the first flyby done. I usually give up after that.

I must be missing something. I am hoping BrianJ can give me some hints.

For his Vesta mission for example, he recommended passing over the pole of Mars and gave the angle and distance for the flyby as an example. That worked for me, otherwise I would have had no clue how to do that pass, because TransX gave me a completely different trajectory that would have used all the fuel.

Hoping here for a reply from the Man himself :)
 

boogabooga

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With realistic Delta-V budgets, IMFD is your friend.

You can learn to use the powerful map tool to cut delta-V requirements from MCCs. t will tell you more where you are headed, rather than where you should be headed as TransX does.
 

BrianJ

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Hi RAF Blackace,
glad you enjoy the add-ons! Nice to know I'm not the only one who spends far too much time on solving these "trajectory puzzles" (and for me, answering my own question of "Just how do they do that?")

SolarProbePlus is not an easy one - the spacecraft has a tight dV budget, and also you have to optimise the Trans Venus Injection(TVI) burn or you won't have enough dV in the Centaur/Star48. And also you have 7 Venus Gravity Assists(VGA) to execute.

A general hint is to minimise your Mid Course Corrections dV by adjusting the next flyby time. I made a note of the VGA dates in the SolarProbeReadme.pdf, but these are only approximate.

I tend to use IMFD5.5 for pretty much everything apart from planning slingshots(and a few other contingencies like launching from Earth to Earth flyby)and concur with boogabooga that IMFD "Map" is the most accurate tool to see what your flyby will look like some time in advance. So it's a combination of IMFD and TransX for me.

Sounds like you might not be getting an accurate/optimal TVI burn, so here's a couple of hints:
1. The burn is about 750s long. My usual rule-of-thumb is to start the burn 2/3 total time before the nominal start time on IMFD"Course/Orbit Eject" (same on TransX? don't know). So that's IMFD burn start time -500s. I just burn prograde until nominal start time, then switch to IMFD AutoBurn.

2. The dV of the Star48 is fixed at 3668m/s so cut short the Centaur burn with that in mind.

3. I over-burn the Centaur by maybe 50m/s to give myself time to jettison the Star48 and set up it's MFDs and prepare for the burn. During this time, the TVI dV-required will be increasing as you move away from Perigee.
So, I cut the Centaur when TVI dV-required is 3668-50 = 3618m/s, then jettison Star48+SolarProbe asap.

4. Set up your MFDs and orient the Star48 asap.
Remember, TVI dV-required will be increasing as the Star48 burn progresses, so I allow an extra 10m/s for this(just a guess), so I start the Star48 burn when the TVI dV-required is 3668-10 = 3658m/s.

I just gave the launch scenario a try(nice to take the AtlasV up again), and only had a post-Star48 burn error of 17m/s - and checking on IMFD Map I see that the Venus intercept alt. is about 1000km, about 2hrs early, so I'd just go with that and not bother making any corrections with SolarProbe until the 1/4 orbit mark.

Even so, you still need an efficient VGA-setup technique to make it through all 7! Without going into a whole IMFD/TransX tutorial, I'd say my usual method is to "Plan it with TransX - execute it using IMFD". And tweak the intercept dates if it saves you significant dV.

Hope this makes some kind of sense and is of some help.

BTW - more "Fun with Ion Engines" ready soon ;-)

Cheers,
Brian
 
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RAF Blackace

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Thanks.

Some good tips there. I already use both TransX and IMFD map function. Your suggestion for optimising the TVI burn I had already worked out. After a few ejection burns when getting no where near the trajectory I was starting the burn 350 seconds before IMFD TIG.

Just one other question, do you pass Venus behind or in front of it on the first flyby? Same question for the other flybys. I'm asking because I'm simply not sure.

Oh god, not another Ion engine mission, you have no idea how long it took me to work out the Dawn mission.

Looking forward to it. And yes, I really enjoy the trajectory missions. They take a lot more planning and thought and really pleasing once you get it right ...eventually.

Thanks for the hints.
 

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At the opposite side of the coin from these multi-sling missions is my 100 day Transit from 100km Lunar Orbit to 100 km Pluto Orbit via an initial sling by the Earth. The SSTV-01 vehicle I've designed using IMS has about 20 Mm/s of delta V, but it takes it quite a while to burn it all. First pass at the mission involved a 2 minute burn to get out of Lunar Orbit into a elliptical orbit around the Earth, then a 350km/s delta V burn at closest approach to the Earth with a direct accent to Pluto (no slings). There are 2 big problems. Getting a 350km/s delta V at Earth takes about a 45 minute burn. The 2nd big problem is slowing down once you get to Pluto. My first pass I ended up trying a 2 hour burn at Pluto and flew right past it still in a hyperbolic orbit out of the solar system....

Dantassii
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rseferino

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I'll have to learn more about iMFD, because I've also been trying to do this mission with TransX, but using the Falcon Heavy, although I have not seen the difference with the Delta IV. I recently did Eris Explorer and Deep Impact, and the first mission with slingshots I did was manned Venus flyby using a Saturn V. Although multi-sling missions with a single planet (eg Messenger or solar probe) is difficult in TransX
 

BrianJ

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Getting a 350km/s delta V at Earth takes about a 45 minute burn. The 2nd big problem is slowing down once you get to Pluto. My first pass I ended up trying a 2 hour burn at Pluto and flew right past it still in a hyperbolic orbit out of the solar system.....
0.001C - that's quite quick! But as you rightly say, slowing down can be a problem. I'd try IMFD "Delta Velocity" for the deceleration burn, I reckon.

I'll have to learn more about iMFD, because I've also been trying to do this mission with TransX, but using the Falcon Heavy, although I have not seen the difference with the Delta IV. I recently did Eris Explorer and Deep Impact, and the first mission with slingshots I did was manned Venus flyby using a Saturn V. Although multi-sling missions with a single planet (eg Messenger or solar probe) is difficult in TransX
Cool. I haven't tried SolarProbePlus full mission using the FalconHeavy to launch, just up to the TVI burn. Worth getting to grips with IMFD, in my view - the accuracy of the "Map" view can save you a few m/s dV over TransX in certain situations. But for slingshots and multiple-orbit intercepts you need TransX.

Just one other question, do you pass Venus behind or in front of it on the first flyby? Same question for the other flybys. I'm asking because I'm simply not sure.
TBH I can't remember how all the VGAs go! It's been 9 months since I did this one.
So I continued my SolarProbePlus mission from where I left it, just after TVI with an error of ~17m/s........

1st MCC was at Launch+3days, 5m/s dV using IMFD Target Intercept(with Offset enabled) and IMFD Map/PlanView, simply targeting centre of planet.
After the burn IMFD Map shows intercept alt. -2044km (see first image sp1.gif below).

2nd MCC was at VGA1-20days, 3.6m/s dV to set up the flyby using TransX Manouevre (see sp2.gif)

3rd MCC was at VGA1-10days, 9.7m/s dV final correction for flyby using TransX Manouevre (see sp3.gif)

During VGA1, you approach from Venus nightside as Venus catches you up and overtakes. You cross Venus' orbit just ahead of the planet and periapsis is just past the day/night terminator, on the day side at about "9am local time"on the surface(if you were on Earth) (see sp4.gif)

After VGA1, I was just setting up IMFD for a Target Intercept burn in about 1.5 orbits time (looks like it will be about 15m/s) to target VGA2. However, I forgot that SolarProbePlus is temperature sensitive - didn't place it in proper attitude during first Solar periapsis - BOOM! :facepalm:

I think this may be as far as I get at the moment - hope this helps get you through the VGA1 anyway. I do seem to remember that the VGAs don't always happen at the same intersection node of the spacecraft trajectory and Venus orbit(it might switch from the "inbound" node to the "outbound" node) - should be obvious from the dates though.

Good luck! :cheers:

1st MCC(sp1.gif) http://postimg.org/image/zdfk597d9/
2nd MCC(sp2.gif) http://postimg.org/image/dp3kzhfrv/
3rd MCC(sp3.gif) http://postimg.org/image/hnfpjpnnl/
VGA1 just after periapsis (sp4.gif) http://postimg.org/image/raj7tfgn5/

P.S. Apologies in advance for inflicting more Ion Engine madness :lol:
 

RAF Blackace

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On Course

Thanks BrianJ

Thanks to your advice I am now on course for Venus and all set up for the first flyby as you can see from the image.

:thumbup:
 

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RAF Blackace

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Unexpected Flyby

BrianJ

Oops. Just to let you know how I'm getting on and to ask if you knew of, or if you came across, this small problem.

I have completed flypast 5 with enough fuel remaining for the rest of the trip. Took me a while as it is not so straight forward, but I'm happy I'm on course.

I had the last two flybys plotted in TransX and the dates of these flybys agree well enough (I think) with the dates you have in the read me.

Your flyby dates were..

6 = 60171
7 = 60614

Mine are currently..

6 = 60158
7 = 60607

Whilst flying the 5 orbit leg between flybys 5 and 6. I came across an unexpected encounter with Venus again on 59708. This completely throws the trajectory off course for the last two flybys. (see image).

What would you recommend I have to do?

1. Add this encounter to the flight plan and try to create the same for 6 and 7 around the same dates.

2. Completely rewrite the flight plan from this unexpected encounter.

Did you come across this encounter? or.. in your flight was you clear enough of it for it not to affect you?

Amazed to see I came across Venus again even though the encounter was not planned. What are the chances of that?

I'm certainly buying a lottery ticket this week.
 

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RAF Blackace

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Hmm. I thought I had this cracked but I don't. It seems that one of the flybys was over a pole and that produced no deflection at all creating this unexpected flyby. Now it is locked into the same orbit doing a flyby of Venus every two orbits. I need to go back and try to redo the flyby that created the situation.

Still, I'm learning a lot about multi-sling missions :)
 

BrianJ

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Hi,
nope, don't remember any unexpected flybys when I tried this one out! Can you post a scenario?
 

RAF Blackace

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I can do better than that, I always keep a record of the flights, just in case something goes wrong and I need to go back or review where I went wrong.

I have zipped up the saved missions from this entire flight, the one of particular interest is the one named "018-On Course for 6 and 7 Course Trimmed.scn"

This was saved after flyby 5 and when I was on the 5 orbit leg between flybys 5 and 6. Flybys 6 and 7 are planned in TransX

I use TransX-2, the one with the auto-min function.
[ame="http://www.orbithangar.com/searchid.php?ID=6393"]TransX 2014.04.26 ModuleMessaging[/ame]

If you continue this scenario, you come across the first unexpected encounter on 59708, and then a subsequent encounter every second orbit. The orbit is now locked into this and it encounters Venus every second orbit without getting any closer to the Sun.

I think I understand what is going on. TransX plans a course based on where you tell it you want to go, it has no idea that you are trying to lower the perehelion of your orbit. So it simply creates a flight plan to suit.

If your orbit hits a harmonic of Venuses orbit (you do 2 orbits for every 1 orbit of Venus), it simply sends you on the same flight path ad infinitum.

Obviously this gives you no deflection so you get no closer to the sun.

It seems I need to almost totally ignore the transX flight plan for flyby 5 and fly blind, but then it would be almost impossible to get a rendesvous for flyby 6 which is 5 orbits later using IMFD alone.

Interesting situation, might not be right, but it is very interesting.
 

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BrianJ

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Excellent! Got the .zip - I'll take a look.
 

BrianJ

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OK, I think I see what's going on.
In your scenario no.11 (about 5 days before VGA4) you're targeting VGA5 on the "outbound" node at MJD 59484(see below).
rafba_vga4.jpg

But should be targeting the "inbound" node at MJD 59496.6(see below).
bj_vga4.jpg

So, yup, you get locked into a resonant orbit with Venus - which is quite interesting!

I've attached a .zip with a scenario based on your scenario no.11 but with a different TransX2 plan(as shown above).

Unless you want to make a ~28m/s dV manouvre from scenario 11, you may need to go back to scenario 10 or earlier.

Thanks for reminding me about TransX2 - it's rather good :)

Good luck with it and have a good Christmas:cheers:

BrianJ
 

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RAF Blackace

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Looks like the problem was with flyby 5, the set up for that flyby is wrong.

After flyby 4 the solar perihelion was 13.8Gm. Flyby 5 causes it to go up, not down thus causing the locked orbit and unexpected encounters.

I have tried going back but I cant seem to get a good set up for flyby 5.

I have gone back to the scenario - "013-Course Planned for 5 and 6.scn" which you have and am trying to get an alternate flight plan to work.

You will see the mistake as soon as you look at the TransX flight plan in this scenario.

Sheesh this is a hard mission :)


Ahh. I see you posted the above as I was posting. Thanks for the help, and have a good Christmas yourself. Wont bother you again. I'll nail it or I'll die trying LOL.
 
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RAF Blackace

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Completed.

That was fun in an odd kind of way.

Went back to scenario 10 and created a new plan for fly by 4 to 5.

Completed the rest of the mission. Final perihelion altitude was 5.6Gm at 6.36 degrees inclination (Ecliptic).

As you can see from the screen shots taken at closest approach, I did rather use most of the available fuel. Kinda running on fumes she was.

Thanks for the great mission BrianJ, and the help of course. Hopefully I have now learnt all I need to know about multi-sling missions.

Looking forward with dread to your impending new ion mission.

:hailprobe:

I have included the full set of scenarios for my mission, not a perfect set, but hopefully a great help to anyone struggling like I was.
 

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RAF Blackace

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Seeing as I found that a bit hard, simply because of my mistakes. I decided to do the whole mission again in one single sitting.

If anyone is struggling with this mission like I was. Here is the zip file of the mission with the TransX-2 course planned well before launch. Every course correction (22 in total) and flyby is saved in a scenario file.

Final Mission Perihelion is 5.82Gm at Inclination 3.12 Degrees (Ecliptic).

Launch is at 13:21:30 (Not 13:31:30 which the scenario text says) which gives alignment with the TransX-2 plan. Because the auto pilot tries to send you off on the original azimuth you need some manual intervention to adjust the course during launch to get you onto the new TransX-2 azimuth. I used the LaunchMFD which is required for the launch scenarios.

After launch the TransX plan can be inherited from the booster using the TransX inherit plan function.

Some of the flybys are a little close which makes it more interesting, but there is nothing that should give you any major worries. Flyby 6 TranX stage plan was adjusted a tad before flyby as it had dropped during the trip making it burn up in the atmosphere, but that was no real issue and the adjustment was only small to get it back on course. Unfortunately the subsequent course correction required around 30dV to correct. But there is plenty of fuel and the mission was completed with 61dV still in the tank.

TransX has a nasty habit of forgetting orbit increments, so if it does that I have listed the number of orbits for each flyby below so you can set the stage back to what it should be.

Flyby 1 = Approx MJD58388
Flyby 2 = Approx MJD58838 after 3 Orbits
Flyby 3 = Approx MJD59035 after 1 Orbit
Flyby 4 = Approx MJD59260 after 2 Orbits
Flyby 5 = Approx MJD59497 after 2 Orbits
Flyby 6 = Approx MJD60171 after 7 Orbits
Flyby 7 = Approx MJD60614 after 4 Orbits

Once again, thanks to BrianJ for his superb work. I know as a developer for other things, it is always nice to know that your work is appreciated by others.
 

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BrianJ

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Hi,
nicely done!:thumbup:
I reckon 61m/s dV still remaining is pretty impressive.
Some excellent points and info in your post, above.
If you need to change the launch azimuth, you can always change the "Roll" parameter in Config/Vessels/SolarProbe/av100_guidance.txt. Just change the "94" to your required azimuth.
 
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