Inclination (Dres mission)

[Solarapple]

I am currently awaiting a Dres mission for the first time (after my successful Duna and Ike missions, and failed return from Gilly mission, I have landed on the bodies listed within these parentheses and the Mun and Minmus) and I am a bit worried about how to approach it. Should I change my inclination while in Kerbin orbit, or during my Hyperbolic trajectory to Dres? What are the Delta V differences? Please respond soon.

[Kelderek]

The cheapest is to burn close to the AN or DN when doing an inclination change. If Kerbin is not near one of those nodes at the time of your transfer window (which is based more on phase angles), then you would need to do a course correction en route when you get close to the AN or DN.

[MartGonzo]

The cheapest is to burn close to the AN or DN when doing an inclination change. If Kerbin is not near one of those nodes at the time of your transfer window (which is based more on phase angles), then you would need to do a course correction en route when you get close to the AN or DN.

I don't think that's necessarily true, in my experience it's more expensive in Dv to burn when going fast so if the AN and DN are perpendicular to where the initial burn was and fairly close to Kerbin it's much cheaper to wait until you're a long way out, maybe 3/4 of the way to apoapsis when you're traveling much slower.

The slower you're going the less Dv it takes to change direction but it can be harder to plan for an intercept that way, so it's best to use multiple maneuver nodes to plan both burns in advance.

[Solarapple]

Thanks!

[Jaeleth]

Try to align as best you can while on kerbin's low orbit, correct, if necessary, enroute.

[Hannu]

You can make a transfer to Dres with two reasonable ways. One is ballistic transfer which is one elliptical trajectory which starts from Kerbin and ends to Dres. Other is three burn transfer. You boost the ship first to elliptic orbit in Kerbin's orbital plane. When you arrive to node line you make inclination correction burn to Dres's orbital plane. At arrival you make a normal braking burn. It depends of launch window which method needs less dv between Kerbin and Dres. However, the ballistic transfer is much more easy to do with KSP's defective trajectory planning tools and I recommend that for beginners.

You need proper tools to calculate orbits and burns. Alexmoon's launch window planner is a good one. It takes inclinations and eccentricities into account and it can calculate ballistic and three burn trajectories. I hope you find out that it is fun to plan difficult trajectories to inclined targets.

[Warzouz]

If you change you inclination to match Dres' one in Kerbin SOI, you will not get the same inclination in Kerbol SOI, because you speed is not the same.

Test : get to a polar orbit around Kerbin, then exit Kerbin SOI. You won't end in polar orbit around Kerbol, only a slighly inclined orbit around it.

You can even do better :

- When you have your window and ejection angle mosly calculated, take off when the launchpad is opposit side to the ejection point.

- Go to an opposite inclination angle but larger than you target one. If Dres has +10° inclination, target -20, -30° or even -40° (you'll have to try)

- Set you parking orbit where you want.

- Quickly set a manoever node on you ejection point. You should do less than half an orbit. Only go prograde

- Warp to SOI exit, then check you inclination. It should be mostly wright. If no, start over and tweak you take-off inclination

- In any case, you'll have some mid-course correction.

I used that for my Eeloo trip, it took me 6 tries to get it right.

But it's much easier to stack an additional fuel tank and change plane at DN or AN.

[MarvinKitFox]

You have already been to Duna.

Going to Dres is exactly the same, but about 10% more needed.

The distance, and inclination, are more than for Duna but the difference is only a slight one of size, not type.

(you may want a handful more solar panels, as sunlight gets a bit feeble that far out.)

[Hannu]

If you change you inclination to match Dres' one in Kerbin SOI, you will not get the same inclination in Kerbol SOI, because you speed is not the same.

Test : get to a polar orbit around Kerbin, then exit Kerbin SOI. You won't end in polar orbit around Kerbol, only a slighly inclined orbit around it.

You can even do better :

- When you have your window and ejection angle mosly calculated, take off when the launchpad is opposit side to the ejection point.

- Go to an opposite inclination angle but larger than you target one. If Dres has +10° inclination, target -20, -30° or even -40° (you'll have to try)

- Set you parking orbit where you want.

If you do not want to trial and error fancy tricks you get correct orbital parameters from Alexmoon's calculator and use suitable mod (I use MechJeb2) to achieve correct Kerbin parking orbit. You can use angle to prograde to get correct longitude of ascending node.

- Warp to SOI exit, then check you inclination. It should be mostly wright. If no, start over and tweak you take-off inclination

- In any case, you'll have some mid-course correction.

But in optimal case it is less than 10 m/s.

But it's much easier to stack an additional fuel tank and change plane at DN or AN.

Of course that is other way of easy thinking. If you do it right it is also optimal way in many Dres launch windows but as I said it is practically quite difficult to do more optimal than ballistic transfer because every burn effects to each others and errors will accumulate.

[maltesh]

The Second Hohmann Transfer Window to Dres after a New Game (Using Kerbal Alarm Clock's Model option, or Alexmoon's Calculator) is almost too perfect to miss. Dres is passing through the plane of Kerbin's orbit on your arrival, so mid-course corrections can be quite minimal. The last time I threw a fleet to Dres during that window, the largest mid-course correction any of the spacecraft needed to make was about 30 m/s.

And the return window was about 10 days after arrival.

The window occurs about 244 Earth Days after the beginning of a new game.

[Hannu]

You have already been to Duna.

Going to Dres is exactly the same, but about 10% more needed.

Can you show how you do that. First Duna window needs 981 m/s for ejection from 200 km equatorial orbit and 642 m/s for insertion to 100 km orbit around Duna. Three burn transfer is optimal in first Dres window. It needs 1411 m/s for ejection, 524 m/s for plane change and 1560 m/s to insertion. Totals are 1623 m/s and 3495 m/s. Dres takes more than double.

Dv needed to Dres varies much between Windows. I examined 15 years. Lowest dv is at year 5 day 291 3009 m/s.

The distance, and inclination, are more than for Duna but the difference is only a slight one of size, not type.

(you may want a handful more solar panels, as sunlight gets a bit feeble that far out.)

This is good advice if somebody wants to practice rescue operations in Dres.

[Warzouz]

Optimizing dV for Duna is not too hard : it has the same inclination as Kerbin and circular (IIRC), you can cross the orbit nearly anywhere, the dV only depends on the phase angle.

For Dres, you have the phase angle, but you must also consider WHERE you cross Dress orbit. the best target spot on AN or DN, becaus you'll get the most shallow angle there. Dress, Moho and Eeloo are more difficult for that matter.

In beta 0.9, I did a Triple mission to Moho, using different technics. All missions were launched at the same time and ships where stricly identical. I got very differents results in travel time and dV.