How Do I Get Manoeuvre Nodes?

[The Flying Kerbal]

I'm in a bit of a hole regarding manoeuvre nodes.

I've upgraded both Mission Control and the Tracking Station to level three - I've read level two is sufficient - but still I can't lock my spacecraft onto the node.  When I place a node on the orbit to set up a manoeuvre, the blue marker appears on the navball, but the manoeuvre icon which I should click beside the stability control on the panel beside the navball never appears.

It isn't the end of the world when I'm scooting around Kerbin's system, but when I come to plan missions to the other planets, it would be nice to be able to lock onto the marker instead of having to try to do it all by hand.

So what do I have to do to have the ability to use this node?

[swjr-swis]

7 minutes ago, The Flying Kerbal said:

So what do I have to do to have the ability to use this node?

If you're using kerbals: a pilot with 3 stars (level 3). If you're using probe cores, the probe core needs to have 'Maneuver Hold' in its SAS capabilities... not all do; rightclick on them in the part list to see the details and scroll down.

Or, add a CH-J3 avionics hub somewhere on your craft to automatically add all SAS capabilities to your pilots or probe cores.

Edited April 23, 2017 by swjr-swis

[bewing]

Also, it's rare to actually need Maneuver Hold. Usually, prograde/retrograde/normal/antinormal are perfectly sufficient. There are times when you want to combine several axes into a single burn, but it's rare.

 

[The Flying Kerbal]

3 hours ago, swjr-swis said:

If you're using kerbals: a pilot with 3 stars (level 3). If you're using probe cores, the probe core needs to have 'Maneuver Hold' in its SAS capabilities...

Thanks very much for such a concise and informative answer.  I was aware of some probes not being able to hold a manoeuvre, but it's the first time I heard about pilots needing to be three stars.  So it looks like my planned landings on Mun and Minmus are going to have to be brought forward.

 

26 minutes ago, bewing said:

Also, it's rare to actually need Maneuver Hold.

 

 I was wondering about this.  I had come to the conclusion the Normal and Antinormal were sufficient to adjust the inclination without having to hold on the manoeuvre node, but I couldn't make up my mind about the prograde and retrograde.

I have a small - almost microscopic actually - lander waiting to shoot at Duna but was trying to hold out until the manoeuvre hold finally did become available.  So let me just get this right, if I set up the burn to take me to Duna and just lock on prograde, then all else being equal, that will work over such a long distance?

Two great answers guys and both are very much appreciated.

[FancyMouse]

5 minutes ago, The Flying Kerbal said:

I had come to the conclusion the Normal and Antinormal were sufficient to adjust the inclination without having to hold on the manoeuvre node

You'll be wasting fuel - intuitively, it's because you're changing your velocity vector along an arc instead of straight line.

I do maneuver not aligning to axes all the time. One example is rendezvous - my inclination burn is usually combined with other components so that my orbit is tangent to the target's, so the final burn is easy enough. Second example is mid-course correction burn - Not only I adjust inclination, but also prograde/retrograde to adjust entry time, and radial/antiradial for correct argument of periapsis (if I'm not targeting equatorial orbit). It's much better to plan ahead and burn exactly what's planned, than burn in 3 directions trying to figure out along the way.

It's all about efficiency - you could of course do them with 3 components decomposed and it is "sufficient" in terms of getting to a target velocity, but you could do better in terms of consuming less fuel by not burning in standard axis directions.

[bewing]

20 minutes ago, The Flying Kerbal said:

if I set up the burn to take me to Duna and just lock on prograde, then all else being equal, that will work over such a long distance?

It will definitely work, yes. Depending on the TWR of your microscopic probe, the burn may be fairly long -- for a long burn, a prograde lock may be somewhat less efficient than a maneuver lock. For a burn of less than maybe 3 minutes, a prograde lock can actually be more efficient than a maneuver lock. But the difference is only maybe 30 dV. But if you ignore the minor efficiency difference, then yes it always works.

And I disagree with the "wasting fuel" argument. A probecore capable of maneuver hold generally weighs more than one that can only do lesser modes. So what you gain on the maneuver node efficiency, you lose on dragging around extra mass.

 

Edited April 24, 2017 by bewing

[FancyMouse]

9 minutes ago, bewing said:

A probecore capable of maneuver hold generally weighs more than one that can only do lesser modes. So what you gain on the maneuver node efficiency, you lose on dragging around extra mass.

RC-001S is just 60kg heavier than OKTO2 that I would argue the extra mass is negligible comparing to the fuel saved, but this is not my point. I was merely saying burning maneuver hold has its advantages. I don't deny in some cases the extra mass will make a difference, but making the decision whether to use a probe core capable of doing maneuver hold (balancing mass etc.) comes after you know the pros and cons, not before. As a matter of fact, if you want a burn to change 45 degree inclination without other orbital parameter change, burning all the way normal/anti-normal is wasting about v*2% fuel (in terms of delta V, v is your current orbital velocity), comparing to plotting a maneuver node that points straight to the target velocity (which is not a pure normal/antinormal burn, btw). Let alone some other cases that could save even more.

[Ketatrypt]

1 hour ago, The Flying Kerbal said:

 I was wondering about this.  I had come to the conclusion the Normal and Antinormal were sufficient to adjust the inclination without having to hold on the manoeuvre node, but I couldn't make up my mind about the prograde and retrograde.

I have a small - almost microscopic actually - lander waiting to shoot at Duna but was trying to hold out until the manoeuvre hold finally did become available.  So let me just get this right, if I set up the burn to take me to Duna and just lock on prograde, then all else being equal, that will work over such a long distance?

Two great answers guys and both are very much appreciated.

 

Personally, for the most accurate trajectories (especially for longer burns) I like to keep the maneuver node on the prograde/retrograde marker. That way its easy to compensate for the local gravity fields, and all in all, seems to be the most reliable way to make accurate burns. This means at the start of the burn, I am generally start with my nose slightly below the manouver node, and even further below the horizon, and as the burn progresses, and I pass thru perapsis, this flips to being slightly nose high, while fighting gravity as I climb towards the moon or whatever.

Its definitely not as efficient as a pure prograde burn, but its much more accurate, and the 1-2% more dv it takes pays off by not having to do any sort of mid course corrections.

[Spricigo]

4 hours ago, bewing said:

There are times when you want to combine several axes into a single burn, but it's rare.

Quite the opposite in my personal experience.