Flight Question Flight planning

[laukejas]

Hello all,

I've decided taking Orbiter to a next step. Rather than taking a futuristic ship with plenty of dV and looking where I could go when I'm already in orbit with tools such as TransX or IMFD, I decided to take a different approach: plan all the journey in advance, prepare a flight plan, and then execute it. Kind of like NASA does it.

So I'll take a medium-difficulty type of journey as an example.

Idea goes like this: launch from Earth, gravity-assisted slingshot past Jupiter, arrival at Titan, Saturn's moon, aerobrake using Titan's atmosphere for Saturn orbit capture, perform inclination change burn to align with Mimas, intercept Mimas with additional burn, and last, circularize orbit above Mimas.

First of all, I think I think I need to establish launch date. It has to have both Jupiter and Saturn in correct position. What kind of tool would you use for such thing? I could use Celestia and eyeball it, but it's not very fool-proof. I could choose wrong date, and only when planning the burn with TransX or IMFD I will see that, for example, slingshot has too low in Jupiter's atmosphere, therefore, not possible.

Assuming I have my dates, I need to find out how much delta V will be needed. I can use some utilities like Trajectory Planner (available on Orbiter Hangar) to find out how much delta V will be needed for trans-Jupiter ejection from Earth. But from that on, I have no idea. When I arrive at Jupiter, how much velocity will I gain? At what velocity I will arrive at Titan? How do I know what kind of heatshield will be required to realistically perform aerocapture? After capture, in what kind of orbit around Saturn will I end up?
Assuming I reached Saturn's orbit, how much delta V will be required for inclination change, Mimas intercept burn, and lastly, orbit circularization?

Right now, that seems awful complex to me. Of course, there is always the "easy way" - fire up Delta Glider, perform whole trip, and in the end, see how much delta V I have spent. But that takes a lot off the immersion - the really "true" way would be to plan everything in advance, leaving but a little of delta V for planning inaccuracies/middle course corrections.

When I have total delta V, I would need to decide what kind of vessel would I need for this trip. Right now, I'm thinking about making a stack of stages that have capacity for that kind of delta V starting from Earth orbit, and then just choose the launcher rocket that is capable of bringing that stack to the orbit.
Then again, I would need to distribute each stage deltaV so that it is consistent with each major burn (so that I don't have to jettison stage in middle of a burn). And choose a heating shield that is appropriate for the deceleration I'll have to make in Titan's atmosphere...

So, can somebody please put me on the right track? How should I find so many variables in advance, before starting the actual flight in Orbiter?

 

[Quick_Nick]

These charts and [ame=http://www.orbithangar.com/searchid.php?ID=4439]porkchop plots[/ame] are a good start.

 

[BruceJohnJennerLawso]

Hello all,

I've decided taking Orbiter to a next step. Rather than taking a futuristic ship with plenty of dV and looking where I could go when I'm already in orbit with tools such as TransX or IMFD, I decided to take a different approach: plan all the journey in advance, prepare a flight plan, and then execute it. Kind of like NASA does it.

So I'll take a medium-difficulty type of journey as an example.

Idea goes like this: launch from Earth, gravity-assisted slingshot past Jupiter, arrival at Titan, Saturn's moon, aerobrake using Titan's atmosphere for Saturn orbit capture, perform inclination change burn to align with Mimas, intercept Mimas with additional burn, and last, circularize orbit above Mimas.

First of all, I think I think I need to establish launch date. It has to have both Jupiter and Saturn in correct position. What kind of tool would you use for such thing? I could use Celestia and eyeball it, but it's not very fool-proof. I could choose wrong date, and only when planning the burn with TransX or IMFD I will see that, for example, slingshot has too low in Jupiter's atmosphere, therefore, not possible.

Assuming I have my dates, I need to find out how much delta V will be needed. I can use some utilities like Trajectory Planner (available on Orbiter Hangar) to find out how much delta V will be needed for trans-Jupiter ejection from Earth. But from that on, I have no idea. When I arrive at Jupiter, how much velocity will I gain? At what velocity I will arrive at Titan? How do I know what kind of heatshield will be required to realistically perform aerocapture? After capture, in what kind of orbit around Saturn will I end up?
Assuming I reached Saturn's orbit, how much delta V will be required for inclination change, Mimas intercept burn, and lastly, orbit circularization?

Right now, that seems awful complex to me. Of course, there is always the "easy way" - fire up Delta Glider, perform whole trip, and in the end, see how much delta V I have spent. But that takes a lot off the immersion - the really "true" way would be to plan everything in advance, leaving but a little of delta V for planning inaccuracies/middle course corrections.

When I have total delta V, I would need to decide what kind of vessel would I need for this trip. Right now, I'm thinking about making a stack of stages that have capacity for that kind of delta V starting from Earth orbit, and then just choose the launcher rocket that is capable of bringing that stack to the orbit.
Then again, I would need to distribute each stage deltaV so that it is consistent with each major burn (so that I don't have to jettison stage in middle of a burn). And choose a heating shield that is appropriate for the deceleration I'll have to make in Titan's atmosphere...

So, can somebody please put me on the right track? How should I find so many variables in advance, before starting the actual flight in Orbiter?

Good on you for going real in Orbiter! :thumbup: I think for any kind of trip like this, IMS is going to be necessary, but other things could work as well, just not as smoothly. Im unaware of when you could try that slingshot to Saturn, and I dont know where we could find the information. The grand tour of slingshots that the voyagers took only comes every 250 years or so, but that requires multiple planetary alignments, not just 2. Can anyone else check this for me?

---------- Post added at 10:53 PM ---------- Previous post was at 10:49 PM ----------

These charts and porkchop plots are a good start.

Never could properly set up that trajectory planner, everytime I tried to install my computer had the equivalent of a seizure.

Perhaps it might also be worth considering a vessel propelled by an ion engine? That would sound a bit more plausible for a mission to one of the gas giants than chemical. Nuclear could work well too.

 

[laukejas]

I know these charts and I use that plotter, but they deal with Hohman transfers, not slingshots, inclination change burns, aerocaptures, and so on...

 

[BruceJohnJennerLawso]

I know these charts and I use that plotter, but they deal with Hohman transfers, not slingshots, inclination change burns, aerocaptures, and so on...

Orbiter Navigator might help you with that.

Unfortunately, the silly thing about all of this is that the only way to properly plan your Orbiter mission down to perfection is to fly it in Orbiter :shrug:

I like creating a really basic setup with as little eyecandy possible just for doing that myself.

 

[laukejas]

Can't get that Orbiter Navigator to work.

Well, folks at NASA somehow calculate everything in advance, so there's got to be some kind of math here. I doubt they run their flights in Orbiter to find out delta V

 

[dgatsoulis]

So, can somebody please put me on the right track? How should I find so many variables in advance, before starting the actual flight in Orbiter?

Why not do it with a TransX plan? You set it up while you are still on the ground, no need to fly "blind". You will get a pretty good estimate on the ΔV and the dates.

 

[laukejas]

Like... How? I can click around with slingshot, although that will take a lot of time. I can get to as far as Jupiter-Saturn slingshot. I'll have no idea what my velocity will be like when I aerobrake at Titan, how much delta V will inclination change burn need, and so other things I wrote in original post...
Maybe I'm not that advanced with TransX, but I really don't know.

 

[dgatsoulis]

The encounter view of TransX will tell you exactly what your speed will be when you arrive at Titan and setting up maneuvers will tell you exactly how much ΔV you will need for the rest.

If you don't know how to set it up then you need to practise more with TransX. I believe you already know about flytandem's page with various TransX scenarios. Study those to see how he does it and you can also find good examples of similar flights on the Tutorials and Challenges section here.

The plan should be:

Stage1: Maj body: Earth→Escape
Stage2: Maj body: Sun, Target→Jupiter
Stage3: Maj body: Jupiter→Escape
Stage4: Maj body: Sun, Target→Saturn
Stage5: Maj body: Saturn, Target→Titan
Stage6: Maj body: Titan→Escape
Stage7: Maj body: Saturn, Target→Mimas
Stage8: Maj body: Mimas→Encounter

Keep in mind that this is a complicated journey that requires a good working knowledge of TransX. If you are not at that level yet, it would be best to start with simpler journeys, or even better, brake the plan above into "steps" and practise each step separately. You don't have to practise the exact same plan, but (for example) since you want to do an aerosling, you can set up one and try and practise just that.

One way to find the Jupiter-Saturn window this:
First setup all the stages. Go to stage4 turn the autoplan off and set advanced on. Select Plan type: Cruise plan, Plan:Eject. Now look for a Jupiter→Saturn window. Once you have that, write down the date, set the Plan back to Sling Direct and go to stage2, to find a date to eject Earth and arrive at Jupiter close to the date you wrote down.

 

[laukejas]

So you're saying that all this flight can be planned using only TransX? Even aerobrake? I remember going through all flytandem's tutorials, but that was a while ago.

I think I understand what you're saying.

But as I'm checking out TransX now, I can't seem to find any delta V data in planning stages. Only setting up maneuver tells me that info. And what about Mimas capture burn? Did you leave it out on purpose?


P.S. One more thing about aerobraking - how do I determine what kind of heat will I encounter, what altitude I need to aim for, what kind of heatshield to take? Aerobrake MFD predictions doesn't work well when you're not in the atmosphere - and when you're in the atmosphere, it's usually too late to make PEA correction.

 

[dgatsoulis]

So you're saying that all this flight can be planned using only TransX? Even aerobrake?

Yes.

But as I'm checking out TransX now, I can't seem to find any delta V data in planning stages. Only setting up maneuver tells me that info.

Check again. Once you have an Eject plan in Stage2 you have an Escape plan in Stage1 that shows you the ΔV (lower left). For Earth you need to add ~2km/s to that because of the gravity losses till you reach orbit, but that depends your ship.

And what about Mimas capture burn? Did you leave it out on purpose?

I didn't leave anything out, I have already mentioned in the previous post that you setup maneuvers. But I am starting to get the feeling that I am doing your "homework" for you.

Anyway, once you have a working plan that has you arriving at Mimas, you setup a maneuver at periapsis (with negative prograde) to see how much ΔV you need to get captured.

P.S. One more thing about aerobraking - how do I determine what kind of heat will I encounter, what altitude I need to aim for, what kind of heatshield to take? Aerobrake MFD predictions doesn't work well when you're not in the atmosphere - and when you're in the atmosphere, it's usually too late to make PEA correction.

That's a tough one. Look up the Orbiter docs to see how you can find atmospheric pressure at any altitude (OrbiterSDK\API_Guide.pdf page 40)
and then you can calculate what the dynamic pressure will be (since you will already know the periapsis altitude and velocity from TransX). Then you can multiply that with the velocity to get the heatflux in w/m^2

To convert that into degrees for a particular ship, you'll need to ask the developer of that ship. Make a search for heatflux and you will find a thread by Marcogavazzeni with more info on that.

 

[laukejas]

Okay, thanks. Sorry, I didn't mean to transfer my homework to anybody, so I did some actual planning with what you said.

I'm making this mission in 1996. Not the best date in means of fuel use, but it's close enough.

I tried setting up stage 4 as you said, but when I tried to arrive to Jupiter at that date, it's too late for good slingshot, requiring to go beneath Jupiter surface. And earlier launch doesn't work because of Earth position.
Anyways, I added prograde velocity and initial ejection, so now slingshot past Jupiter has Pe/pl ratio of 1.132, which should be clear from atmosphere.

Was a bit of a headache, but I managed to set up slingshot and fine tune initial ejection so that my arrival vector at Titan is (almost) tangent to Titan's orbit (I guess that makes lowest encounter speed) (this is visible in stage 5)

So I got as far as stage 6. I'm now reading about heat flux, but in the meantime, I hope I wouldn't be too impertinent if I asked how would I set up that aerobrake in TransX? I can't seem to find any info on that right now.

I'm attaching my scenario file with TransX plan (don't mind 1st stage, I didn't tweak it yet, since it doesn't affect anything)

 

[BruceJohnJennerLawso]

Okay, thanks. Sorry, I didn't mean to transfer my homework to anybody, so I did some actual planning with what you said.

I'm making this mission in 1996. Not the best date in means of fuel use, but it's close enough.

I tried setting up stage 4 as you said, but when I tried to arrive to Jupiter at that date, it's too late for good slingshot, requiring to go beneath Jupiter surface. And earlier launch doesn't work because of Earth position.
Anyways, I added prograde velocity and initial ejection, so now slingshot past Jupiter has Pe/pl ratio of 1.132, which should be clear from atmosphere.

Was a bit of a headache, but I managed to set up slingshot and fine tune initial ejection so that my arrival vector at Titan is (almost) tangent to Titan's orbit (I guess that makes lowest encounter speed) (this is visible in stage 5)

So I got as far as stage 6. I'm now reading about heat flux, but in the meantime, I hope I wouldn't be too impertinent if I asked how would I set up that aerobrake in TransX? I can't seem to find any info on that right now.

I'm attaching my scenario file with TransX plan (don't mind 1st stage, I didn't tweak it yet, since it doesn't affect anything)

If you're planning an aerobrake, you'll probably want to use this.

[ame="http://www.orbithangar.com/searchid.php?ID=5702"]http://www.orbithangar.com/searchid.php?ID=5702[/ame]

Has multiple sizes for different ships. IMS could go haywire during an aerobrake though.

 

[laukejas]

Thanks, I know these shields, they are kinda large though... But I haven't seen any other, so thanks again

dgatsoulis, I found out that "Capture delta" at Titan will be around 10.69km/s. So I guess that's the encounter velocity, right? By the way, I can't find out how to set up maneuver at Titan (if I wanted to circularize orbit there instead of Mimas). Nothing in Setup or Encounter view. Sorry for stupid question, but what am I missing? I know that I will be able to set up maneuver when I actually fly to it, but how do I set it up in TransX plan while still on Earth so that I know how much dV it'll require?

P.S. Never mind, I found out that turning Advanced on, Plan - None and Plan Type - Through point and Intercept with - maneuver allows me to set up maneuver. I guess that's what you meant.

 

[laukejas]

I experimented some more, and I think I found something: I set up Titan - Mimas slingshot, turned off "Inherit velocity", and set it up manually, and added velocity until projected course intercepts Mimas orbit. Am I doing this right?

Attaching another scenario file.

 

[dgatsoulis]

P.S. Never mind, I found out that turning Advanced on, Plan - None and Plan Type - Through point and Intercept with - maneuver allows me to set up maneuver. I guess that's what you meant.

That's right. Once you select Plan:None the Plan Type doesn't matter. When you want to do advanced level planning in TransX, you have to set the plan yourself and not let TransX deside for you (through the "autoplanff" and "advancedn").

I experimented some more, and I think I found something: I set up Titan - Mimas slingshot, turned off "Inherit velocity", and set it up manually, and added velocity until projected course intercepts Mimas orbit. Am I doing this right?

Yes, for aeroslings it is better to select "Inherit velocity: No" and set them up manually. This way you will know how much velocity you need to lose inside the atmosphere. It can also be done with "Inherit velocity: Yes" and aim for a Pe/Pl ratio that's less than 1.0 but the first way removes some of the guess work.

Keep in mind that an aerosling one of the most difficult maneuvers to perform. You can find an example at the playbacks section of flytandem's site.

In my opinion you have "too much on your plate" with procedures that you are not yet experienced how to perform. The flight-plan you have chosen is pretty difficult to plan and execute even for expert TransX users.
And that's without the added difficulty of predicting the temperatures the ship will encounter during the aerosling.

But I applaude the "diving in the deep" method you have chosen. Just don't get discouraged if things don't work out at first (they almost never do) and have the persistence to try it again if you fail.

 

[laukejas]

Well, I have performed similar flights (except for aerosling), it's just that I have never planned them like this, all in advance. I usually planned things "on the fly", since there was a lot of dV to spare.

I think I'll finish setting up all this plan, and then try to execute with Delta Glider for starters (just to see if it works).

I remember from experience that TransX predictions, especially with long journeys, are often very inaccurate in terms of date. And in this type of plan, date is crucial. If I don't arrive at Jupiter at the exact date, I might not be able to perform sling anymore, or my arrival trajectory won't be in tangent with Titan's orbit. So I guess I should write down all the dates, and then execute burns with IMFD or something, right? (a lot of folks suggest this kind of plan execution if one aims for accuracy)

I have a few questions. First, in Encounter view at Titan, "Capture Delta" was 10.7km/s, but with setting up custom velocity for aerosling, it was 12km/s (or more, I don't remember right now the exact number). How come second number is larger than the first one? And what exactly is "Capture Delta" then? Velocity I need to lose to bring down orbit around Titan eccentricity to exactly 1, that is, just barely be captured? If so, how do I find out the actual fly-by (aerosling) velocity at Titan PEA?

And next, since I can only aerosling at Titan to bring down my orbit around Saturn PEA to match Mimas orbit, I can't really intercept Mimas right after aerosling on Titan: Mimas is too far away, and if I arrive at different date, Titan won't be in perfect position for aerosling, which, I guess, is a priority.

So, from the latest scenario I posted, how do I set up further plan to intercept Mimas? I guess after aerosling on Titan, I'll need to arrive at PEA of my Saturn orbit, and make apoapsis adjustment to intercept Mimas after some orbits. Could you please help me out a bit here?

 

[dgatsoulis]

So I guess I should write down all the dates, and then execute burns with IMFD or something, right? (a lot of folks suggest this kind of plan execution if one aims for accuracy)

So do I. Using TransX with IMFD will give you the best results. The most useful feature in this case will be the Map program. For a journey this long, you'll need to use the config pf the map program, in order to be able to extend the trajectory prediction. Write down the dates and also the inclinations and PeD from TransX. (The most important one is the Jupiter sling).

I have a few questions. First, in Encounter view at Titan, "Capture Delta" was 10.7km/s, but with setting up custom velocity for aerosling, it was 12km/s (or more, I don't remember right now the exact number). How come second number is larger than the first one? And what exactly is "Capture Delta" then? Velocity I need to lose to bring down orbit around Titan eccentricity to exactly 1, that is, just barely be captured? If so, how do I find out the actual fly-by (aerosling) velocity at Titan PEA?

Exactly. The Capture Delta is the ΔV to get captured by Titan and not the velocity at periapsis. That value is just above that (Pe velocity). You can switch between "Plan types" and "Plans" to get the value you need.

And next, since I can only aerosling at Titan to bring down my orbit around Saturn PEA to match Mimas orbit, I can't really intercept Mimas right after aerosling on Titan: Mimas is too far away, and if I arrive at different date, Titan won't be in perfect position for aerosling, which, I guess, is a priority.

So, from the latest scenario I posted, how do I set up further plan to intercept Mimas? I guess after aerosling on Titan, I'll need to arrive at PEA of my Saturn orbit, and make apoapsis adjustment to intercept Mimas after some orbits. Could you please help me out a bit here?

You got it right, if going directly from Titan to Mimas isn't an option, you'll need to increase the number of orbits around Saturn. (Orbits to Icept) Mimas is orbiting Saturn pretty close, it shouldn't take long to find something that works. But do try to make it directly and only increase the number of orbits if that is impossible.

I haven't seen any of your scenarios yet, I'll be able to do so tomorrow. In the mean time keep trying to see if you can find something better. Here are some other dates I found (if you don't want to make the flight in the "past").

Earth Departure ~58140 → arrival at Jupiter 59095 → arrival at Saturn 62825. (It takes a while to reach Saturn, but you have a nice low encounter velocity). Keep note that my dates are not more "correct" than whatever you may have chosen. A faster Jupiter→Saturn transit time can also be useful, since you'll have Titan's atmosphere to stop you.

 

[laukejas]

Okay, I'll try to set it up with the dates you provided.

Anyways, is there some faster way to check slingshot dates (when it is possible, check if Pe/pl ratio doesn't drop beneath 1.1)? Because with TransX, it's a lot of clicking and fine tunning, very time consuming, and not very intuitive (for example, simply advancing arrival date requires to restart all the fine-tunning). TransX, as I see it, is very good at planning everything in detail, but isn't very inuitive at finding slingshot dates. I guess if I would need to find out Voyager type of journey window (without knowing it), it would take forever with TransX. So, is there any faster way for initial sketch-planning?

And one more question, apart from heat flux you wrote about earlier, is there some good way to calculate what altitude at Titan do I need to aim for to lose these exact 12km/s? (apart from Aerobrake MFD, which, as I said, does calculations too late)

 

[dgatsoulis]

Okay, I'll try to set it up with the dates you provided.

Anyways, is there some faster way to check slingshot dates (when it is possible, check if Pe/pl ratio doesn't drop beneath 1.1)? Because with TransX, it's a lot of clicking and fine tunning, very time consuming, and not very intuitive (for example, simply advancing arrival date requires to restart all the fine-tunning). TransX, as I see it, is very good at planning everything in detail, but isn't very inuitive at finding slingshot dates. I guess if I would need to find out Voyager type of journey window (without knowing it), it would take forever with TransX.

Speed and intuition will come with practise.

So, is there any faster way for initial sketch-planning?

In the initial setup of multi-slings I use a combination of TransX and IMFD with surrogate ships. I do that just to find the eject date and arrivals and then I run the scenario with just my ship and fine tune the plan in TransX. Fine tuning before you have dates that work for what you intend to do is useless, since it will most likely need to be changed.

For example in this plan you can place a ship in Jupiter orbit and use the Target Intercept program of IMFD to find a Jupiter→Saturn transfer. Then do the same to find an Earth→Jupiter transfer that has the arrival at Jupiter on the date you had for the Jupiter→Saturn sling. It's a bit faster than doing it just with TransX.

And one more question, apart from heat flux you wrote about earlier, is there some good way to calculate what altitude at Titan do I need to aim for to lose these exact 12km/s? (apart from Aerobrake MFD, which, as I said, does calculations too late)

There isn't an "exact" altitude. You can choose to go "deep" and stay there for a small amount of time or go "shallow" and stay there longer. (That's for winged vessels that can perform inverted aeroslings, such as the DG) Calculating the dynamic pressure (and the heatflux) at the altitude you choose, will only help you predict the temperature, not the time you need to stay in the atmosphere.

I repeat, try flytandem's aerosling playback in the link I posted before and also try to setup and fly one yourself, before incorporating it in a complicated flight.