Efficiently using transfer windows

[fireblade274]

Alright, so I have about 2k hours of KSP under my belt, but most of that time (when going interplanetary) was using very low TWR and large atomic craft, and therefor did not make use of transfer windows. I'd escape Kerbins SOI and then get an encounter.

Now, i"m starting to utilize the windows more, which Kerbel Alarm Clock has been helping out with greatly.

However, I'm still finding it hard to get a direct path to my target planet(s); I'm fine making a second maneuver node at at my ascending/descending node to get my degrees of separation as close to 0.0 as i can, but even then there is usually still considerable distance between my craft and targets position, and (i'm not quite sure how to explain this) the encounter is not one that leave me with the least amount of Dv relative to the target to burn off upon entering SOI. The intersection points are not bright red, but purple or an off orange. The encounter is not smooth, i'm intersecting it at an angle, and not reaching it when i'm at my perapsis/apoapsis. 

How can I most efficiently use transfer windows? I know when starting your burn on either side (day/night) of Kerbin will either ascend you in solar orbit or descend you, and I know why, but I see these people on YouTube that just get an encounter with a planet without using any maneuver nodes, and I wonder how they do it. Are they waiting till the exact moment of perfect transfer and then burning while pointed at the target until they have an encounter? I don't care so much about doing this without nodes, but I have yet to learn the most efficient process of using transfer windows

If anyone can help id much appreciate it!

thank you

[Streetwind]

1 hour ago, fireblade274 said:

...the encounter is not one that leave me with the least amount of Dv relative to the target to burn off upon entering SOI. The intersection points are not bright red, but purple or an off orange. The encounter is not smooth, i'm intersecting it at an angle, and not reaching it when i'm at my perapsis/apoapsis.

Yeah, umm. I'm not exactly sure what you mean with the color of the "intersection points". The only thing I can think of that appears in interplanetary transfers and comes in those three colors are the conic patch sections of your trajectory. And the only reason they have different colors is so you can tell them apart more easily. Which color the final section has is not dependant on the quality of your transfer, but rather simply the number of SoI changes along the way. If you are used to escaping Kerbin's SoI first, and are now trying to fly a direct transfer from low Kerbin orbit, there will be one extra SoI transition along the way, and that changes the color of your trajectory.

Intersecting the target SoI at a weird angle often happens simply due to using ballistic trajectories - a single, direct transfer burn usually performed nowhere near the ascending and descending nodes, because the alignment of planets very rarely ever does you the favor of coinciding with the ascending/descending nodes. This means you automatically come at the SoI from out of plane. But that weird angle also completely irrelevant. Even with a direct ballistic trajectory, you first plan a node that gets an encounter, then you perform the burn, and then you discover in more than 50% of the cases that your burn was not precise enough and your encounter now looks completely different anyway. Additionally, correcting the location and altitude of your periapsis can be done with a 1-2 m/s course correction somewhere along the way - close enough to give you precision, far away enough to still be dirt cheap.

As for the very first part, that's also worded really strangely, but I'll try an educated guess here. Ultimately, the amount of dV you need to expend inside the target SoI is directly dependant on how similar your orbit is to the target. If you are coming in from a very similar orbit - like, if you first took the effort of leaving Kerbin's SoI, matching planes at AN/DN and positioning your apoapsis/periapsis very near the target orbit, like you would when performing a rendezvous in low Kerbin orbit, then it is indeed possible to slide into the target SoI with just a handful of m/s required to capture. But just because the capture burn costs almost nothing doesn't mean that the transfer was the most efficient. In fact, the method I've just described is among the most inefficient of all interplanetary transfer variants. The majority of your dV expenditure will be performed in deep space, far away from all gravity wells, where all your burns will cost far more fuel (see: Oberth Effect). Additionally, it takes absolutely forever until you arrive at the target. Meanwhile, if you are flying a direct, ballistic Hohmann transfer (like you would from Kerbin to the Mun), both your departure burn and your capture burn are executed deep inside gravity wells, where they are the cheapest. The capture burn is much more expensive, because the transfer orbit is not as similar as the target orbit, but the Oberth Effect helps keep the fuel cost low - and additionally you spend much less in other burns, because those other burns don't even exist in this transfer type.

 

So, it's possible that I've completely misunderstood anything you said, and not actually answered any of your questions. But in case I did, let me sum up:

- The color of your trajectory's conic patches is completely irrelevant
- Ballistic transfers almost always come in from out of plane; that is how they work. Finetune the location of your periapsis along the way, if you must. You can always get a perfect polar orbit, no matter your approach vector, but you may not be able to get a perfect equatorial orbit. If you need one, you'll have to work for it during your capture with some orbital mechanics tricks.
- Don't fall into the trap of trying to save a few dozen m/s at the capture burn by expending several hundred m/s more on a slow, inefficient transfer. The direct, ballistic Hohmann transfer orbit is the cheapest possible solution in all practical* cases.

If I did not succeed to answer your questions, maybe try providing an actual example of what you're trying to do?

 

 

* Bi-elliptic transfer orbits are slightly cheaper in some edge cases, but they take hundred times the travel time or more and are harder to plan. Don't bother.

[Chaos_Klaus]

Basically, you just want to do a basic hohmann transfer from one altitude to another. The only difference is that there is a planetary body at both your starting point and destination. These bodies mess up your trajectory.

You still want to do a hohmann transfer and that means you want your resulting interplanetary orbit to be tangent to Kerbin's orbit. So you want to leave Kerbin's SoI in parallel to Kerbin's orbit ... along Kerbin's prograde.

To do that, you need to do the ejection burn at the correct ejection angle. It's not sufficient to just burn on the day or night side (depending on your destination). You need to burn earlier. You can see this in an infographic here:

http://ksp.olex.biz

The transfer window just tells you when the planets are aligned so that you will get an encounter this way.

Edited February 14, 2016 by Chaos_Klaus

[fireblade274]

I'm familiar with the concept of burning at your highest/lowest point to get the most efficient burn, and I understand the different colored orbital trajectories, showing your path before and after your encounter with a SOI. The purple and orange icons that i'm referring to are the "target at intersect 1" and "target and intersect 2", one is orange and the other is purple. When there is only one intersect, the color of it is a bright red, and it usually indicates its a good encounter with your target; your velocity relative to the target will be much more encountering it at a 90 degree angle then if you slowly come up behind it. How do I get this with a planet when coming from LKO?

Example: lets say i'm trying to get from LKO to Moho. I wait till my transfer window, and then I must place a node somewhere on the side of Kerbin facing Kerbol and go prograde, so once I leave Kerbin, I will be decreasing my orbital altitude above Sol to get an encounter with Moho. I understand I will have to make a course correction to match planes with Moho. My questions are: where should the first node be optimally placed, and how do people get to their target (say moho) by simply burning towards the "target" icon on the NavBall?

My last trip to Moho started at LKO and the small craft had 2.1k Dv for its first stage with a TWR of over 2; I nailed the first node and the second one, and even though I got an encounter with Moho, I still encountered it from the side and did not come up right behind it. Take a look at this crude Paint sketch I made, when I got in this example is on the right, and what I wanted is on the left. (Obviously the planets wont be in the positions I drew but you get the point):

https://www.dropbox.com/s/3s1vn1b40no85bv/bad%20orbital%20drawing.png?dl=0

[fireblade274]

15 minutes ago, Chaos_Klaus said:

Basically, you just want to do a basic hohmann transfer from one altitude to another. The only difference is that there is a planetary body at both your starting point and destination. These bodies mess up your trajectory.

You still want to do a hohmann transfer and that means you want your resulting interplanetary orbit to be tangent to Kerbin's orbit. So you want to leave Kerbin's SoI in parallel to Kerbin's orbit ... along Kerbin's prograde.

To do that, you need to do the ejection burn at the correct ejection angle. It's not sufficient to just burn on the day or night side (depending on your destination). You need to burn earlier. You can see this in an infographic here:

http://ksp.olex.biz

The transfer window just tells you when the planets are aligned so that you will get an encounter this way.

Thank you for that link, it has the information i need, but its easier said then done and the info is still confusing. Ill have to read it alot and try and find a video tutorial on that exact subject. Thank you both for the information provided

[Geschosskopf]

3 hours ago, fireblade274 said:

How can I most efficiently use transfer windows? I know when starting your burn on either side (day/night) of Kerbin will either ascend you in solar orbit or descend you, and I know why, but I see these people on YouTube that just get an encounter with a planet without using any maneuver nodes, and I wonder how they do it. Are they waiting till the exact moment of perfect transfer and then burning while pointed at the target until they have an encounter? I don't care so much about doing this without nodes, but I have yet to learn the most efficient process of using transfer windows

Well, first off, the folks who don't use nodes usually just burn at the target marker in the navball and then watch the map view until an encounter happens.  This is not caring about efficiency because they're usually not leaving on a good window, and it could well be they have infinite fuel set anyway  So I wouldn't worry about such things.

Anyway, a transfer window is a point in time when planets are are so aligned that it takes the least amount of dV to get from one to the other.  Of course, there is some disagreement on when this happens.  Kerbal Alarm Clock has several different ways of calculating when this is.  One of those agrees with the famous website and also MJ's "Advanced Transfer to Another Planet", the others don't, but only by a few weeks.  Still, there's not much difference between the various solutions.

Then, within the window (however you determine when that is), you still have to execute the burn correctly.  This means placing the node at the correct ejection angle around your current orbit (which is considerably more picky than just being on the light or dark, side).  Use the wrong ejection angle and you need significantly more dV than the theoretical minimum for that window.

You also have the option of either doing a "ballistic" transfer with some plane change built into your transfer burn so you hit the target direct from your origin, or doing the classic Hohmann transfer where you burn out flat and then usually must do an inclination change at the AN/DN of your orbit en route to the target.  In general, it's a bit cheaper to go balllistic but not all that much.  But if you really want an exactly equatorial orbit at the target planet once you get there, then if you need a plane change en route, you'll need to change back on arrival.

Anyway, if you leave in a certified wndow, you'll be on the low end of the dV required for the trip.  If you place the node at the correct ejection angle, you'll be able to reap the benefit of the window.  But expect to spend a bit more due to the required plane changes.

[fireblade274]

Thank you Geschosskopf, you explained everything very well for me. Now I see the difference between the Hohmann transfer and ballistic transfer.

45 minutes ago, Geschosskopf said:

...execute the burn correctly.  This means placing the node at the correct ejection angle around your current orbit (which is considerably more picky than just being on the light or dark, side).  Use the wrong ejection angle and you need significantly more dV than the theoretical minimum for that window.

Using the link provided by Chaos, http://ksp.olex.biz/, it tells me for a 300km parked orbit to Moho the ejection angle is 114.75. It also tells me the the planetary phase angle is -251.79, but since Ill be using KAC's transition window alarm I dont have to worry about the latter, correct? I can look at the diagram and roughly place the node for the correct ejection angle I guess but it wouldn't be the most precise. Is there a way to see the exact phase angle value it is at the position where your trying to place a node? I want to say KerbalEngineer has a display for it but I also want to say its only relative to your crafts current position...

Is there an easy way to exactly place your maneuver node at your specific ejection angle?

[Snark]

Using a planner like http://ksp.olex.biz is a good idea.

Here's another thing you can do, if you're not in so much of a hurry:

• Do the necessary burn in LKO that brings your Pe down to the point where it just "kisses" Moho's orbit.  Don't worry if it's not on Moho itself.
• When you're there at Pe right at the distance of Moho's orbit. do a retrograde burn to lower your Ap somewhat, in order that you'll get an encounter with Moho within a few orbits.  The longer you're willing to wait, the smaller a burn you can get away with.

The advantage of that approach is that you can kill two birds with one stone.  Moho has quite an orbital inclination relative to Kerbin.  If you try to launch at the next "ideal" window, it's likely going to be when you're not at the AN/DN, so that means you'll need a pretty big, expensive plane-correction burn en route.  On the other hand, if you don't bother waiting for the window, and you do your launch right when Kerbin is at the AN/DN with Moho, then that will put your Pe right on top of the opposite node.  That means you can get a Moho encounter without having to do a plane correction at all, which is a big savings.

Admittedly, it means you won't be in an equatorial orbit when you get to Moho... but Moho is the one place where being in equatorial orbit doesn't matter much.  There are no moons to worry about, and the planet rotates so slowly it might as well be sitting still.

One thing to bear in  mind, if you use this technique:  the less dV you can spend on that Ap-lowering burn, the better, since you're doing that without any benefit of Oberth effect.  The ideal case is where you do not much of a burn there, and get your Moho encounter, and then can do your retro-burn at low Moho altitude so as to gain Oberth benefit.

[fireblade274]

12 minutes ago, Snark said:

 

• Do the necessary burn in LKO that brings your Pe down to the point where it just "kisses" Moho's orbit.  Don't worry if it's not on Moho itself.
• When you're there at Pe right at the distance of Moho's orbit. do a retrograde burn to lower your Ap somewhat, in order that you'll get an encounter with Moho within a few orbits.  The longer you're willing to wait, the smaller a burn you can get away with.

Thank you Snark, ill have to try that sometime, I did not think of this

[Snark]

Just now, fireblade274 said:

Thank you Snark, ill have to try that sometime, I did not think of this

Main thing is to be sure you know the maneuver node trick to let you plan encounters multiple orbits ahead of time.  Will let you get a Moho encounter fairly efficiently and accurately with minimal dV expenditure, as long as you're willing to wait a few orbits.

(i.e. "I'll do this small burn now, so that I get a Moho encounter four orbits from now" ... the more orbits into the future you're willing to wait, the smaller the adjustment you need to make)

[Superfluous J]

Snark's way works great for all of the small, airless, moonless worlds. Moho, Dres, and Eeloo are all eccentric, tilted, and annoying to get to.

Of course, with Dres and (even moreso) Eeloo, taking that full Sun orbit until your encounter can be a bear.

[Temstar]

For Moho take the calculator result with a big grain of salt. There are three things going against you when going to Moho:

1. Moho is on a rather elliptical orbit for a planet, transfer calculators generally assuming a circular orbit which fits well for most planets in the Kerbol system but not Moho, Eeloo or Dres
2. Moho is on an inclined orbit, transfer calculators generally assume target planet is orbiting on the ecliptical plane, which fits well for most planets but not Moho, Eeloo or Dres
3. Moho is deep within the gravity well of Kerbol, which makes reaching it very expensive in terms of delta-V to start with and makes orbital maneuvers like inclination change or changing orbital phase very expensive, making Moho a much harder target than Eeloo or Dres.

Because of the above 3 reasons, a trip to Moho need a huge amount of delta-V, which generally mean your craft will have a very low TWR to squeeze as much delta-V out of a craft as possible. Since an ejection burn to Moho is on the order of 2000m/s it will take many minutes for a low TWR craft to complete the burn. Therefore it's not possible to both place and perform the ejection burn and hit the correct ejection angle with high accuracy from first principle. You will have to use quick load to recursively work out how long you need to start the burn early to hit the correct ejection angle by the end of the burn. As for the node, you will have to manually adjust to compensate for point 1 and 2 above, so don't worry about placing the node with 2 decimal places of accuracy - just eye ball it is good enough.

 

[Geschosskopf]

1 hour ago, fireblade274 said:

Thank you Geschosskopf, you explained everything very well for me. Now I see the difference between the Hohmann transfer and ballistic transfer.

Using the link provided by Chaos, http://ksp.olex.biz/, it tells me for a 300km parked orbit to Moho the ejection angle is 114.75. It also tells me the the planetary phase angle is -251.79, but since Ill be using KAC's transition window alarm I dont have to worry about the latter, correct? I can look at the diagram and roughly place the node for the correct ejection angle I guess but it wouldn't be the most precise. Is there a way to see the exact phase angle value it is at the position where your trying to place a node? I want to say KerbalEngineer has a display for it but I also want to say its only relative to your crafts current position...

Is there an easy way to exactly place your maneuver node at your specific ejection angle?

Well, first off, NEVER NEVER NEVER use a window to Moho.  There are 2 approved methods of getting to Moho, both of which completely disregard any and all transfer windows calculated by whatever navigational aid you use.  The 1st method is a bi-elliptic transfer leaving Kerbin when it's in line with the AN or DN of Moho's orbit relative to Kerbin's orbit.  The 2nd method is to leave Kerbin at an Eve transfer window and do a retrograde flyby of Eve manipulated to drop you into approximately Moho's orbit.  Depending on planetary alignments, one might cost less dV than the other, but never will the difference be significant.  And ONLY by using one of these methods will the dV to reach Moho orbit be anything resembling what's shown on the dV map.  If you treat Moho as any other planet and do a normal Hohmann or even ballistic trajectory, the dV cost will be WAY WAY more, especially on the capture burn.

Now, as to the easy way to place the maneuver node at the proper ejection angle, use MechJeb.  Select your target planet (unless it's Moho, in which case go via Eve or bi-elliptic)., bring up "Advanced Transfer to Another Planet" in MJ, tell it you want a porkchop plot, and pick your spot on it.  The porkchop is the same as the Olex website.  Zoom in and out with the mouse wheel looking for the darkest blue areas.  Left-click in one of them and then hit the "Create Node" button.  MJ will then create a node for that burn at the proper ejection angle at the proper time.  Use KAC to create an alarm 5-10 minutes prior to then, warp to it, and do the burn,

 

Edited February 15, 2016 by Geschosskopf

[fireblade274]

59 minutes ago, Geschosskopf said:

Now, as to the easy way to place the maneuver node at the proper ejection angle, use MechJeb.  Select your target planet (unless it's Moho, in which case go via Eve or bi-elliptic)., bring up "Advanced Transfer to Another Planet" in MJ, tell it you want a porkchop plot, and pick your spot on it.  The porkchop is the same as the Olex website.  Zoom in and out with the mouse wheel looking for the darkest blue areas.  Left-click in one of them and then hit the "Create Node" button.  MJ will then create a node for that burn at the proper ejection angle at the proper time.  Use KAC to create an alarm 5-10 minutes prior to then, warp to it, and do the burn,

 

This. is going. to be fantastic.

[Streetwind]

8 hours ago, Geschosskopf said:

If you treat Moho as any other planet and do a normal Hohmann or even ballistic trajectory, the dV cost will be WAY WAY more, especially on the capture burn.

That is so not true...

Moho doesn't possess any mystical property that suddenly makes a normal ballistic Hohmann transfer magically stop working. What Moho has is an incredibly short year length - it is screaming around the sun in a tight, fast circle. As a result of this, Moho is simply incredibly sensitive to your departure burn. @fireblade274 literally could not have picked a more difficult destination if he tried to, because none exists in stock KSP.

However, "difficult" doesn't mean "impossible". With a target like Eeloo, your transfer window is as fuzzy as a kitten; you can miss your node by a week and still not pay a noticably higher dV cost. Moho, on the other hand, absolutely demands that you nail it on time. Even the slightest deviation ramps up the cost; being off by one hour can be considered as having missed the window. Without mods, this is really hard to pull off, but it can be done.

If you perform your ejection with the required precision, the ballistic Hohmann transfer to Moho works exactly as advertised by transfer planners. You don't pay anything extra, and you get there orders of magnitude faster than when using a bi-elliptic transfer. You don't need to wait for a three-planet alignment either, and the window repeats every 30-40 days. (That's not to say that bi-elliptic or Eve assist trajectories aren't valid choices as well - just that "Hohmann doesn't work" is flat-out wrong.)

 

As for the whole ejection angle thing: That's something that I've always found incredibly irksome about transfer window calculating tools or websites. "Here's your angle relative to prograde down to the decimal digit, now all you need to do is burn there!" That's about as helpful as saying "Here's a maximum security safe with one million dollars inside it, now all you need to do is open it!". This immediately conjures the question: "And how praytell would I possibly do such a thing? I have no tools!" Basically, most transfer calculators are borderline unusable for a pure stock game. They all want you to have access to a tool that lets you measure angles ingame. All, except one: https://alexmoon.github.io/ksp/

What this planner does different is, it has a little expanded info button next to your ejection dV, which tells you the split into prograde and normal dV values. And with that, you can get by without tools, because this info lets you treat the ejection angle as a variable you don't need to know to create the maneuver node. All you need to do is set up the node anywhere in your orbit, and first add exactly the amount of normal dV required, then add prograde dV until the total node cost is equal to the total ejection dV. Then, now that the dV is already set, you click and drag the node around until you get an encounter. The position at which the node happens to be when you get this encounter is automatically at the correct ejection angle (because you won't get an encounter with the pre-set dV anywhere else). Voila, you just plotted a precise ejection vector in stock KSP with no additional tools required.

 

[Chaos_Klaus]

KAC gives you an alarm when the phase angle is correct. You are correct. No need to worry about that.

There is a way to get the ejection angle right without holding a protractor onto your screen.

Place the maneuver roughly where you think it should be. Day or night side ... that's about as precise as you have to be. 

Next, add the amount of delta v (prograde) to the node that you estimated by looking at a delta v map or using the transfer planner. Doesn't have to be precise either.

Now the important part: By clicking and draging the center white circle of the node, you can drag it around along your current orbit. Be careful not co click any of the other symbols on the node by accident.  Zoom out a little until Kerbin's orbit line just appears. You should now see Kerbin's orbit and your escape trajectory. Just drag the node around so that you exit Kerbin's SoI parallel to Kerbin's orbit. 

You automatically get the ejection angle right this way. Getting this kind of parallel (or tangent) ejection, is what the ejection angle is all about. So rather then getting the ejection angle right by eye, it's easier to align the actual SoI exit vector.

Ahh. This probably reads more complicated then it is.

Edited February 15, 2016 by Chaos_Klaus

[Warzouz]

11 hours ago, fireblade274 said:

...

Is there an easy way to exactly place your maneuver node at your specific ejection angle?

 

Yes, I don't SET the ejection angle, I get the most efficient burn (which is implicitly the correct ejection angle). Some explanations :

Knowing your correct ejection angle is 115,7° doesn't help you because you don't have any other tool than your basic eyeballing / guestimate...

• First, I always use some kind of "Precise Node" mod feature (also included in MechJeb). I mostly dislike the stock "Node". It's very unfriendly for interplanetary tweaking.
• I set a node nearly anywhere at LKO, I set some prograde burn to escape velocity, so I get a ellipse into Kerbol SOI (anywhere, it doesn't matter).
• Then I delay the burn location so the ellipse will have the highest eccentricity (inward or outward depending on where you want to go).
• When I get this maximum, I'm around the bes ejection angle I can get even without knowing it.
• Then I just have to extend the burn a bit more to touch the target planetary orbit.
• If the tool I use has the feature, I add full orbits until I get an encounter on the other side of the sun.
• If there is inclination, I add a secondary node at AN/DN before burning the first one and try to get the encounter by tweaking the 2 nodes.

This can be combined for more ballistic, but I must say I don't care too much about efficiency. If my ship arrive there, it's a success.

I reliably go to Moho with that method, only knowing a approximative transfer window.

[Geschosskopf]

2 hours ago, Streetwind said:

Moho doesn't possess any mystical property that suddenly makes a normal ballistic Hohmann transfer magically stop working. What Moho has is an incredibly short year length - it is screaming around the sun in a tight, fast circle. As a result of this, Moho is simply incredibly sensitive to your departure burn. @fireblade274 literally could not have picked a more difficult destination if he tried to, because none exists in stock KSP.

However, "difficult" doesn't mean "impossible". With a target like Eeloo, your transfer window is as fuzzy as a kitten; you can miss your node by a week and still not pay a noticably higher dV cost. Moho, on the other hand, absolutely demands that you nail it on time. Even the slightest deviation ramps up the cost; being off by one hour can be considered as having missed the window. Without mods, this is really hard to pull off, but it can be done.

This is, actually, why I said not to use traditional transfer windows to Moho.  The degree of precision required to set-up and execute a Hohmann transfer to Moho, which includes launching at exactly the right time so you're in the correct orbital position (given that an orbit takes about 25 minutes) is much greater than the amount of precision allowed by the stock game interface,  Thus, doing this is as close to being physically impossible as can be and still have the slightest chance of actually working.  For all practical purposes, it's impossible.

OTOH, doing bi-elliptic transfers or braking off Eve are well within the capabilities of the stock interface and produce roughly similar results in terms of dV needed compared to an impossibly perfect Hohmann.  The drawback to these methods, however, is that they impose a longer and generally unknown travel time because you usually end up having to make 1 to several solar orbits at some point to sync up with Moho, whereas the Hohmann will get you to Moho on a date certain.  But this only matters if you use life support, and it's not all THAT long a trip anyway.

2 hours ago, Streetwind said:

As for the whole ejection angle thing: That's something that I've always found incredibly irksome about transfer window calculating tools or websites. "Here's your angle relative to prograde down to the decimal digit, now all you need to do is burn there!" That's about as helpful as saying "Here's a maximum security safe with one million dollars inside it, now all you need to do is open it!". This immediately conjures the question: "And how praytell would I possibly do such a thing? I have no tools!" Basically, most transfer calculators are borderline unusable for a pure stock game. They all want you to have access to a tool that lets you measure angles ingame. All, except one: https://alexmoon.github.io/ksp/

What this planner does different is, it has a little expanded info button next to your ejection dV, which tells you the split into prograde and normal dV values. And with that, you can get by without tools, because this info lets you treat the ejection angle as a variable you don't need to know to create the maneuver node. All you need to do is set up the node anywhere in your orbit, and first add exactly the amount of normal dV required, then add prograde dV until the total node cost is equal to the total ejection dV. Then, now that the dV is already set, you click and drag the node around until you get an encounter. The position at which the node happens to be when you get this encounter is automatically at the correct ejection angle (because you won't get an encounter with the pre-set dV anywhere else). Voila, you just plotted a precise ejection vector in stock KSP with no additional tools required.

But even with this tool, you still need to put the node at the correct ejection angle.  The prograde and normal dV components are just to do a ballistic transfer without the mid-course plane change of the traditional Hohmann.  But even if you use some mod tool like MJ or PreciseNode to enter these dV values into the node, if you don't have the node in exactly the right place you won't hit the target.  To get the angle right, you need Protractor.  Or just have MJ create the node for  you, which includes it being created at the correct angle.

[Streetwind]

27 minutes ago, Geschosskopf said:

Thus, doing this is as close to being physically impossible as can be and still have the slightest chance of actually working.  For all practical purposes, it's impossible.

Well, suit yourself. I'll continue flying finetuned direct transfers, as I have for my past three playthroughs...   It's an underappreciated challenge, IMHO.

 

9 minutes ago, Geschosskopf said:

But even with this tool, you still need to put the node at the correct ejection angle.  The prograde and normal dV components are just to do a ballistic transfer without the mid-course plane change of the traditional Hohmann.  But even if you use some mod tool like MJ or PreciseNode to enter these dV values into the node, if you don't have the node in exactly the right place you won't hit the target.  To get the angle right, you need Protractor.  Or just have MJ create the node for  you, which includes it being created at the correct angle.

Hmmm?

The whole point of the exercise is that "putting the node at the correct ejection angle" is a problem that automatically solves itself. You drag and move the node around until you do hit the target. Therefore, you don't need a protractor, or MechJeb, or any other tool - you just need to drag and drop with the mouse. Since your amount of dV is pre-set, there is only one position at which you will be able to get an encounter. That position automatically is the correct ejection angle. You do not measure it, you simply drop the node wherever it happens to give you an encounter.

As for ballistic vs. mid-course correction, you can select which one you want on the transfer planner website. For mid-course correction, you will receive an ejection dV that's 100% prograde, as well as the exact timestamp of, and normal dV required for, the mid-course correction itself. That too is enough information to forgo measuring angles (although it is significantly more involved). First, plot the ejection node with the specified prograde dV. Second, on your predicted trajectory, plot a second node with the specified normal dV. Third, calculate the time difference between the given dates for departure and plane change. Fourth, move the second node to be exactly that amount of time after the first. Fifth and finally, now you can again drag the first node around until you find an encounter. No angle measurements required.

Still, unless you absolutely needed a perfectly equatorial orbit at the target, I would fly ballistic. It's just so much less effort.

Or you could install one of the many available addons that aid this process, of course   I was just talking about how to do things on a completely stock installation, without those ingame tools available.

[Warzouz]

 

46 minutes ago, Geschosskopf said:

But even with this tool, you still need to put the node at the correct ejection angle.  The prograde and normal dV components are just to do a ballistic transfer without the mid-course plane change of the traditional Hohmann.  But even if you use some mod tool like MJ or PreciseNode to enter these dV values into the node, if you don't have the node in exactly the right place you won't hit the target.  To get the angle right, you need Protractor.  Or just have MJ create the node for  you, which includes it being created at the correct angle.

Well, I don't do that. As I explained before, I set a node anywhere at LKO and move it (not with the stock node feature, it's too clumsy) with a "Precise Node"-mod like tool, 10s or 100s at a time. When the ellipse is maxed out, I've the correct ejection angle, I just have to increase prograde until it touches the target orbit at the other side of the sun. Then I delay the node orbits by orbits until the target body shows-up. A secondary node at AN/DN is needed for plane change.

I usually launch 2 weeks before the transfert window and prep my node immediatly, then I do other stuff while waiting for the correct time. That's why KAC is useful.

 

[Geschosskopf]

45 minutes ago, Streetwind said:

The whole point of the exercise is that "putting the node at the correct ejection angle" is a problem that automatically solves itself. You drag and move the node around until you do hit the target.

Yeah, that's the theory.  I used to (try to) do things that way.  In practice, though, the stock interface, which was never designed for going further than Mun to begin with, makes it totally frustrating, very time-consuming, and at the bottom line, still rather inexact.

Duna or Eve are about the limit of the precision of this method, because they're close enough that you have a fair chance of being able to see both the node and the target at the same time while still having reasonably fine control over the node's position.  Also, you can tolerate a bit coarser control over the node.  But even with them, often your control of the node's position when you can also see the effect at the target isn't fine enough to even hit the target, let alone get the Pe there you want.

Certainly that's the case for going anywhere further afield.  The longer the trip, the more precision is required with the node's position, which means you have to zoom in very close to Kerbin to be able to move the node just a tiny bit.  Which means you can't see the effect at the far end at all.  So it's all a bunch of  zooming the view in and out, and moving it from one end to the other, with the node constantly collapsing and sometimes being deleted for no apparent reason,,forcing you to start all over again.

And even if you get your trajectory kinda where you want it, quite often you really need to put the node between 2 of the discrete positions it can occupy around the orbit, so you still have to tweak the burn amounts, sometimes significantly, from what you got from the website.  The fine-r control via the mousewheel that we now have over nodes helped a bit with this, but in general at this point you've got the map zoomed in on your target, the node is way back at Kerbin, and is usually at an angle that precludes tweaking the dV handle you want to manipulate anyway.  Or the node collapses and you can't reopen it without moving the view all the way back to Kerbin.

So is it possible?  Yes, vaguely, for relatively short trips.  Will you get exactly what the website says?  No.  Is it an attractive method when compared to various mod alternatives?  No.  Does doing it this way demonstrate a better understanding of orbital mechanics?  No, because the interface is so clunky that even if you have a PhD in it, you'll still get frustrated and have great difficulty getting close to what you want.  Is it worth doing anyway?  That's personal taste, but I worry a bit about those who find this an attractive option 

I think that anybody who doesn't understand orbital mechanics would benefit from reading one of the various excellent tutorials explaining how to do things this way.  But I don't recommend actually using this method, at least for any trip further  than Duna or Eve, because of the frustrations of the clunky interface.  Maybe do it once you've already become addicted to the game, but doing things this way from the get-go might turn off pre-addicted new players  .  I hope that 1.1 does something about the interface here.

[Warzouz]

I agree with @Geschosskopf, the map view is nice but very hard to manipulate. Either :

• you focus on you starting body and can't really view the target body orbit. You're never really sure that the overlap
• you focus on the target body and you can't see the node, move it or grab handles. I invariably end by messing it and have to restart.
• you focus on Kerbol and get neither of them, or a bit of both...

I don't remember who suggested to have a replicated node handle near the navball so you could always grab it whenever you are on the map.

[Geschosskopf]

4 minutes ago, Warzouz said:

I don't remember who suggested to have a replicated node handle near the navball so you could always grab it whenever you are on the map.

There have been many such suggestions.  Adding buttons to the navball, having a pop-up window like PreciseNode, or picture-in-picture of the actual node you could rotate and zoom independently of the main map view.  All would work and all would be infinitely better than what we have now.  I really, really hope Squad implements some such thing during the interface overhaul of 1.1, and will very disappointed if they don't.

[Warzouz]

6 minutes ago, Geschosskopf said:

There have been many such suggestions.  Adding buttons to the navball, having a pop-up window like PreciseNode, or picture-in-picture of the actual node you could rotate and zoom independently of the main map view.  All would work and all would be infinitely better than what we have now.  I really, really hope Squad implements some such thing during the interface overhaul of 1.1, and will very disappointed if they don't.

I wouldn't bet on it. It seems 1.1 focuses on the technical migration. There is no really new feature (maybe a better or alternative sorting for the tracking station). My hopes goes for 1.1.x (x>0)

[Snark]

9 minutes ago, Warzouz said:

I wouldn't bet on it. It seems 1.1 focuses on the technical migration. There is no really new feature (maybe a better or alternative sorting for the tracking station). My hopes goes for 1.1.x (x>0)

This.

If they were really implementing a new feature as nice as an improved maneuver node UI, you can bet they would have mentioned it.

And we're not even getting a new sorting option for the tracking station-- all we're getting is a time-until-node display for the existing buttons, in their current sort order.

So... no new features, just bug fixes and minor quality-of-life improvements in 1.1.  It's all about the Unity 5.