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Mukita12

How to Flyby Multiple Planet

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so i'm going to do a Probe mission to Eeloo but since im using earth timing on setting It might take a couple year so How do i Flyby multiple planet like cassini pls help i want to do my mission next week

 

 

PS.Sorry for bad grammar

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6 hours ago, Mukita12 said:

so i'm going to do a Probe mission to Eeloo but since im using earth timing on setting It might take a couple year so How do i Flyby multiple planet like cassini pls help i want to do my mission next week

Fly by multiple planets are rarely done because the opportunity present itself, that requires a fortuitous alignment that don't happens that often.

Spoiler

voy_traj.jpg

Voyage Program took advantage of an alignment that happens once in every 175 year.

Most of the multiple flyby mission are done to take advantage of the gravity assists to save fuel. Those are not free of charge since every detour made from a direct trajectory takes it toll on mission time.

Spoiler

 

1280px-Cassini_Interplanet_traject_DE.svimage004.jpg

Rosetta_trajectory_English.jpeg

 

I suggest you to just get the mod Kerbal Alarm Clock, set an alarm for your arrival at Eeloo and do something else in the meantime

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First of all, you must know how to gravity assist using celestial body to boost your DeltaV. This maneuver saves fuel compared to burn directly to target when being done correctly. The way to flyby multiple planets on long journey is mostly using your probe to get a stable orbit on a celestial body, then doing prograde burn at periapsis of the celestial body while at the same time predicting the transfer window of nearby celestial body that you will use next for gravity assist. The higher the gravity of a celestial body, the better the gravity assist that can be performed. If you are able to predict next transfer window, then it should be easy to do multiple flyby. For me, I'm usually just hopping from one celestial body to another (stable orbit >wait transfer window for next target > burn to target > make stable orbit > repeat)

Hope it helps :)

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There is a simple answer to any KSP question, especially those regarding complicated missions.
P L A N   A H E A D

Look at the planets, figure out where they will be at your optimal launch time, and figure out exactly when to launch, where to go up, and where/when to maneuver node out of orbit.

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11 hours ago, Spricigo said:

 

Fly by multiple planets are rarely done because the opportunity present itself, that requires a fortuitous alignment that don't happens that often.

  Hide contents

voy_traj.jpg

Voyage Program took advantage of an alignment that happens once in every 175 year.

Most of the multiple flyby mission are done to take advantage of the gravity assists to save fuel. Those are not free of charge since every detour made from a direct trajectory takes it toll on mission time.

  Hide contents

 

1280px-Cassini_Interplanet_traject_DE.svimage004.jpg

Rosetta_trajectory_English.jpeg

 

I suggest you to just get the mod Kerbal Alarm Clock, set an alarm for your arrival at Eeloo and do something else in the meantime

OK

16 hours ago, ARS said:

First of all, you must know how to gravity assist using celestial body to boost your DeltaV. This maneuver saves fuel compared to burn directly to target when being done correctly. The way to flyby multiple planets on long journey is mostly using your probe to get a stable orbit on a celestial body, then doing prograde burn at periapsis of the celestial body while at the same time predicting the transfer window of nearby celestial body that you will use next for gravity assist. The higher the gravity of a celestial body, the better the gravity assist that can be performed. If you are able to predict next transfer window, then it should be easy to do multiple flyby. For me, I'm usually just hopping from one celestial body to another (stable orbit >wait transfer window for next target > burn to target > make stable orbit > repeat)

Hope it helps :)

Well that's help A lot because i'm still noob :) thank you for helping

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On 06/08/2017 at 3:39 PM, ARS said:

First of all, you must know how to gravity assist using celestial body to boost your DeltaV. This maneuver saves fuel compared to burn directly to target when being done correctly. The way to flyby multiple planets on long journey is mostly using your probe to get a stable orbit on a celestial body, then doing prograde burn at periapsis of the celestial body while at the same time predicting the transfer window of nearby celestial body that you will use next for gravity assist. The higher the gravity of a celestial body, the better the gravity assist that can be performed. If you are able to predict next transfer window, then it should be easy to do multiple flyby. For me, I'm usually just hopping from one celestial body to another (stable orbit >wait transfer window for next target > burn to target > make stable orbit > repeat)

Hope it helps :)

No, sorry but making orbit negates the benefits of gravity assists,  you need to go zooming past these bodies in a situation where they speed you up, not slow you down.

I see where you're coming from with the oberth though. 

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On 8/6/2017 at 7:46 AM, Mukita12 said:

so i'm going to do a Probe mission to Eeloo but since im using earth timing on setting It might take a couple year so How do i Flyby multiple planet like cassini pls help i want to do my mission next week

Well, in the stock KSP system, going to Eeloo isn't all that much further than going to Jool (Eeloo is actually closer than Jool sometimes).  And Jool is the only thing between Kerbin and Eeloo (when Eeloo is beyond Jool) that can give you a worthwhile gravity assist anyway.  So it's really not worth bothering with gravity assists when going to Eeloo.

I have only found gravity assists to be useful in 3 situations in the stock solar system:

  1. Gravity braking off Eve to save on getting to Moho.  However, this is NOT the best way to get to Moho---the cheapest way doesn't involve a gravity assist, just perfect timing of when you leave Kerbin.  HOWEVER, those departure days only come twice a year.  If you can't wait for the next one (say your stranded crew on Moho is running out of food), Eve provides an acceptable alternative to the sheer brute force of a direct (but fast) shot from Kerbin.
  2. Doing flybys of all of Jool's moons without using a huge amount of fuel.  These moons are so close together, and most of them are massive enough, that opportunities are always arising and they give you good boosts (or brakes as desired) within the system.
  3. Doing some absurd challenge like going some huge distance on only 1 fuel tank, where that's the ONLY reason for this particular save and elapsed gametime is of no concern at all.

Now, if you play with the Outer Planets Mod, so the solar system is set up essentially just like our own, the gravity assists like we use in real life become viable options.  Now you've got analogs of Saturn, Uranus, and Neptune between Jool and the analog of Pluto, so can actually re-do Voyager and other such missions.  However, as already mentioned by others, such missions require rare alignments of the planets, which only happen decades or centuries apart.  Otherwise, you'll spend decades or centuries just hanging out in space between planets waiting for the next encounter.  So if you want to get somewhere at any time you want, regardless of planetary alignments, it's best to just go direct.

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8 hours ago, Geschosskopf said:

Well, in the stock KSP system, going to Eeloo isn't all that much further than going to Jool (Eeloo is actually closer than Jool sometimes).  And Jool is the only thing between Kerbin and Eeloo (when Eeloo is beyond Jool) that can give you a worthwhile gravity assist anyway.  So it's really not worth bothering with gravity assists when going to Eeloo.

Well, there's always the option to get gravity assistance from Eve and Kerbin. Eve is not in between but is easy to get a strong enough boost to justify the detour. 

In any case there Is the question of complexity and time. Going directly to the target is faster and simple.

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11 hours ago, Geschosskopf said:

Gravity braking off Eve to save on getting to Moho.  However, this is NOT the best way to get to Moho---the cheapest way doesn't involve a gravity assist, just perfect timing of when you leave Kerbin.  HOWEVER, those departure days only come twice a year.  If you can't wait for the next one (say your stranded crew on Moho is running out of food), Eve provides an acceptable alternative to the sheer brute force of a direct (but fast) shot from Kerbin.

Actually, the cheapest transfer only comes up ONCE per year, when the transfer gets you to both node and periapsis.  Burning for apoapsis is cheaper on the Kerbin end, but you pay a LOT more to capture...

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52 minutes ago, Kryxal said:

Actually, the cheapest transfer only comes up ONCE per year, when the transfer gets you to both node and periapsis.  Burning for apoapsis is cheaper on the Kerbin end, but you pay a LOT more to capture...

Are you talking about going direct to Moho from Kerbin or doing the bi-elliptic 2-step?  I never go direct, always a 2-step, usually bi-elliptic but occasionally using Eve.

For the bi-elliptic, it doesn't really matter whether you plan to meet Moho at its AN or DN because it all evens out when doing the 2 steps of the transfer burn.  You either burn more leaving Kerbin or more for the 2nd step, but they add up to essentially the same thing.  Either way, you don't have to include (much) inclination change in the transfer so you've minimized the total transfer cost, plus you've minimized the capture burn by minimizing your relative velocity compared to Moho, which is the whole point of doing this.

For using Eve, you're leaving Kerbin on a window for Eve, regardless of where this is compared to Moho's AN/DN line.  By setting up your Eve fly-by on the sunny side, you can drop your Pe down to Moho while also dropping your Ap down to Eve, thus accomplishing both steps of the bi-elliptic transfer in 1 go for the very low price of going to Eve (cheapest transfer burn in the game).  HOWEVER, your inclination is very unlikely to be anything at all like Moho's because you weren't caring about that when you went to Eve.  Thus, after passing Eve, you'll have to make a fairly large inclination change to get a Moho encounter.  This plus the Eve transfer burn will almost always add up to about 1000m/s more than the 2 steps of the bi-elliptic transfer, but the capture burn will be the same because you've still pretty much matched velocities with Moho before you get there.

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3 hours ago, Geschosskopf said:

For using Eve, you're leaving Kerbin on a window for Eve, regardless of where this is compared to Moho's AN/DN line.

Where Kerbin is conpated to Moho AN/DN is irrelevant. Make the gravity assist when Eve is at AN/DN and  enjoy a free inclination change.

The arguments that takes time and is more difficult to plan remain. But there is no question a well planed and well executed slingshot is the cheaper option.

 

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20 minutes ago, Spricigo said:

Where Kerbin is conpated to Moho AN/DN is irrelevant. Make the gravity assist when Eve is at AN/DN and  enjoy a free inclination change.

If you'd bothered to actually read what I said, you'd have noticed that the ONLY reason EVER to use Eve to get to Moho is when you need to get to Moho quickly and an Eve window comes along before Kerbin reaches Moho's node line.  IOW, you're willing to spend more dV in the interests of speed.  This means the cost of the inclination change is luck of the draw and is usually significant. If you're not pressed for time, then wait for Kerbin to be on the node line and do it right with a bi-elliptic.  Eve is far less efficient.

Besides, the solution you propose almost never happens,   It requires a 3-way alignment, with Eve in the right place relative to Moho's node line at the same time Kerbin's got a window to Eve.  On top of that, Eve simply isn't big enough to give you the full inclination relative to the sun change to match Moho anyway, even if you do happen to get there when it's on Moho's node line.  If you go to Eve, you'll always have to do an inclination burn after leaving it.

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6 hours ago, Geschosskopf said:

If you'd bothered to actually read what I said, you'd have noticed that the ONLY reason EVER to use Eve to get to Moho is when you need to get to Moho quickly and an Eve window comes along before Kerbin reaches Moho's node line

I read your post and noticed that is the only reason the player @Geschosskopf would consider.

No withstand your preferences,  other options exist. You conclusion that a direct transfer is cheaper comes from you ignoring those options and thus is incorrect.

6 hours ago, Geschosskopf said:

On top of that, Eve simply isn't big enough to give you the full inclination

[snip] you ... think the 2nd heavier celestial body will not be able to provide a meager extra 7 degree  of deviation. 

Edited by Vanamonde

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I have to intervene here

Thanks to mentioned earlier KSP-TOT, I managed to set up a plan: Kerbin > Eve > Moho.

Then, according to latest Delta-v chart, average need for direct transfer to Moho (and capture) from LKO is far over 4km/s. And it takes approximately 135 days.

From what I can see in my mission plan, it is going to take 296 days which is twice as long, BUT: initial burn from Kerbin is ~1400m/s, then I have to make minor maneuver at Eve, which is 200m/s, and that should make an encounter with Moho. Capture burn is still quite long, little less than 2km/s, but overall my mission is going to need about 3600m/s, from orbit to orbit. Is it worth it? I personally think yes.

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7 hours ago, Geschosskopf said:

Are you talking about going direct to Moho from Kerbin or doing the bi-elliptic 2-step?  I never go direct, always a 2-step, usually bi-elliptic but occasionally using Eve.

For the bi-elliptic, it doesn't really matter whether you plan to meet Moho at its AN or DN because it all evens out when doing the 2 steps of the transfer burn.  You either burn more leaving Kerbin or more for the 2nd step, but they add up to essentially the same thing.  Either way, you don't have to include (much) inclination change in the transfer so you've minimized the total transfer cost, plus you've minimized the capture burn by minimizing your relative velocity compared to Moho, which is the whole point of doing this.

I was talking about going direct to Moho's orbit, though not to Moho itself (probably).  You'll need more delta-v to reach the node at Moho's PE, but your capture burn is considerably less so you come out ahead.  Also, you combine the plane-change with your ejection maneuver, when the Oberth effect is helping you and when plane changes are cheaper.

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5 hours ago, Spricigo said:

I read your post and noticed that is the only reason the player @Geschosskopf would consider.

No withstand your preferences,  other options exist. You conclusion that a direct transfer is cheaper comes from you ignoring those options and thus is incorrect.

[snip] I in fact said that the direct transfer is the least desirable method.  [snip]

 

Quote

... you ... think the 2nd heavier celestial body will not be able to provide a meager extra 7 degree  of deviation. 

[snip] While it might look like you're getting a huge inclination change while you're in Eve's SOI, when you pass it and get back in the sun's SOI. you'll have way less than you thought.  Moving relative to Eve is nothing compared to moving relative to the sun.

 

3 hours ago, Kryxal said:

I was talking about going direct to Moho's orbit, though not to Moho itself (probably).  You'll need more delta-v to reach the node at Moho's PE, but your capture burn is considerably less so you come out ahead.  Also, you combine the plane-change with your ejection maneuver, when the Oberth effect is helping you and when plane changes are cheaper.

There are 2 things that reduce the capture burn at Moho (or, conversely, increase it if you don't do these things).  The 1st is meeting Moho at your OWN Pe (instead of somewhere else along your orbit), which minimizes the capture burn for whatever transfer orbit you're in.  But not all transfer orbits are created equal.  The less difference there is between your current Ap and your Pe at Moho, the smaller the capture burn, and vice versa.

When you go direct from Kerbin to Moho, your Ap and Pe are as far apart as they can get, so your capture burn will still be larger than if you lowered your Ap before the encounter, as with a bi-elliptic transfer.  So the question is, do you save enough on the transfer burn vs. the bi-elliptic to hit on the AN/DN line to make up for that?  In my experience, you do not, if for no other reason than the need to include a large inclination component in the direct burn, which you completely avoid with the bi-elliptic.  Changing inclination relative to the sun, while within the inner solar system, is very expensive.

Edited by Vanamonde

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Some personal remarks have been removed from posts in this thread. We can disagree about spaceflight methods without resorting to scornful terms and attitudes. 

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3 hours ago, Geschosskopf said:

I in fact said that the direct transfer is the least desirable method

You should notice in my post 'direct' only means 'no gravity assist'. Because the only point I referred is the use or not of gravity assist.

Your idea don't prevent a previous gravity assist and as result diminishes the effect of a gravity assist. 

 

Anyway,  the thread have enough info for someone just considering gravity assists.  Time to talk about something else.

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If I recall correctly, Kerbal Flyby Finder and similar programs let you specify a reasonable amount of planets to be flied by. 2-3 should be okay for plotting a course, but a flyby-only grand tour would be extremely hard.

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On 10/14/2017 at 8:42 PM, Geschosskopf said:

There are 2 things that reduce the capture burn at Moho (or, conversely, increase it if you don't do these things).  The 1st is meeting Moho at your OWN Pe (instead of somewhere else along your orbit), which minimizes the capture burn for whatever transfer orbit you're in.  But not all transfer orbits are created equal.  The less difference there is between your current Ap and your Pe at Moho, the smaller the capture burn, and vice versa.

When you go direct from Kerbin to Moho, your Ap and Pe are as far apart as they can get, so your capture burn will still be larger than if you lowered your Ap before the encounter, as with a bi-elliptic transfer.  So the question is, do you save enough on the transfer burn vs. the bi-elliptic to hit on the AN/DN line to make up for that?  In my experience, you do not, if for no other reason than the need to include a large inclination component in the direct burn, which you completely avoid with the bi-elliptic.  Changing inclination relative to the sun, while within the inner solar system, is very expensive.

Being at your own PE is a good idea, for two reasons: for Moho you'll meet the AP or PE of Moho and so are going in the same direction, and you're moving your fastest relative to Kerbol so using delta-v reduces energy by a greater amount.  However, I don't agree with the bit about the difference between your current AP and PE at Moho.  To capture to Moho is roughly matching orbits, give or take a bit.  It's VERY like a bielliptic transfer.  You can either drop your PE to match Moho's AP, then drop your AP to match Moho's PE (and in the process switch AP and PE) or drop PE to match Moho, then drop AP to match Moho's AP.  Will you accept that going to Moho's PE is cheaper, or do I have to prove it?

Also, I explicitly said the plane change was part of the ejection burn, so what's this about changing inclination while in the inner system?  This is the ejection burn FROM KERBIN, by the way.

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11 hours ago, Kryxal said:

Will you accept that going to Moho's PE is cheaper, or do I have to prove it?

Also, I explicitly said the plane change was part of the ejection burn, so what's this about changing inclination while in the inner system?  This is the ejection burn FROM KERBIN, by the way.

Well, it's all in the total cost, transfer + capture.  There are various ways of distributing this cost.

If you match both of Moho's Ap and Pe, and also its inclination, then of course the capture burn will be as small as possible..  However, you pay for it in the transfer, which is spread over the 2-3 burns needed to match all these parameters.

Alternatively, you leave Kerbin when its on the line of Moho's AN/DN, and put your Pe at one of those points.  Then you bring your Ap down to somewhere between Eve and Moho, so you can sync up with Moho and hit it at your Pe, which is at Moho's AN or DN.  In this method, the transfer is considerably less expensive because 1) you're not doing any inclination change at all, and 2) you're not moving your Pe and Ap as close to the sun as when you're matching Moho's orbit totally.  The capture burn is, of course, more expensive with this method but generally never more than about 1000-1300m/s.

In my experience, if you separate out the inclination change and consider this all happening on the same plane, these 2 methods are nearly equal in terms of total cost.  You're changing your ship's orbital energy state by the essentially same amount.  Thus, because the 1st method includes the cost of matching Moho's inclination while the 2nd method does not, the 1st method is more expensive overall.  By about 500-1500m/s, depending on when you leave Kerbin in comparison to the line of Moho's AN/DN.  If you can prove otherwise, I'd love to see it so I can change my methods :wink:

As to inclination changes relative to the sun in the inner solar system, yes, they're always expensive.  It doesn't matter if you're doing it as you leave Kerbin, what you're doing is changing your inclination relative to the sun.  In fact, if you're leaving Kerbin so as to put your Pe at Moho's Pe, then Kerbin will be about lined up with Moho's Ap, and thus about as far off from Moho's AN/DN line as it's possible to get.  Thus, the cost of the inclination change is as big as it can be.  It would be cheaper to do the inclination change between Kerbin and your Pe, when your ship reaches Moho's AN/DN line, so you have the move "leverage".  But it's still way cheaper not to bother with an inclination change at all.

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OK, here are some numbers for a transfer from Kerbin to Moho, via the method I stated.

Burn#1: 2288 m/s; 1960 m/s prograde -1180 m/s normal

This burn is to escape LKO, and is probably somewhat unrealistic for being plotted too low, around the 200 km mark in a 40 minute orbit.

Burn #2: 23.4 m/s, -23.4 m/s prograde

This burn is at the periapsis of the solar orbit, and is to adjust for a closer intercept at Moho's PE

Burn #3, 75 m/s, -75 m/s normal

This burn is to fine-tune the orbit's plane not long before intercept, could be cheaper if done at the other node, probably more like 25 m/s

Burn #4, 1974 m/s, -1974 m/s prograde

This is the Moho capture orbit, into a 350 km orbit.  This all comes out to 4350 m/s to make this transfer, extra losses for non-instantaneous burns are a given but that would happen with ANY transfer.

How well would your proposed transfer do?

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Hey,

 

just for a tip: you can use the program Flyby Finder to find the most optimal flyby route. It calculates the deltaV and time required, and tells you where to put your manouevre nodes, and how big they should be. It's very helpful to get very precise flyby routes throughout the kerbol system!

Here is the KSP forum topic:

[WIN] Flyby Finder V0.86 [KSP1.3]

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On 15.10.2017 at 12:10 AM, The Aziz said:

I have to intervene here

Thanks to mentioned earlier KSP-TOT, I managed to set up a plan: Kerbin > Eve > Moho.

Then, according to latest Delta-v chart, average need for direct transfer to Moho (and capture) from LKO is far over 4km/s. And it takes approximately 135 days.

From what I can see in my mission plan, it is going to take 296 days which is twice as long, BUT: initial burn from Kerbin is ~1400m/s, then I have to make minor maneuver at Eve, which is 200m/s, and that should make an encounter with Moho. Capture burn is still quite long, little less than 2km/s, but overall my mission is going to need about 3600m/s, from orbit to orbit. Is it worth it? I personally think yes.

I'm quoting myself, but now I can confirm that the predictions were more or less correct. I think I will spend 100m/s more than planned overall, but on the other hand, I'll hit Moho few days sooner: https://imgur.com/a/WhZGK

On 17.10.2017 at 6:09 AM, Kryxal said:

OK, here are some numbers for a transfer from Kerbin to Moho, via the method I stated.
[...]
This is the Moho capture orbit, into a 350 km orbit.  This all comes out to 4350 m/s to make this transfer

Man, that's a lot.

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