Deboning the porkchop plot

[HopDavid]

For Hohmann transfers to an inclined orbit, Lambert iterations tend to give polar transfer orbits! This results in huge plane change expense at both ends, destroying the Hohmann transfer's advantage.

A midcourse plane change can take much of the ridge out of the porkchop plot. But what is the best "broken plane" transfer orbit? For me this remains an open question, but I've been thinking about it. My notes so far:

http://hopsblog-hop.blogspot.com/2013/01/deboning-porkchop-plot.html

I am hoping this page will be a work in progress. Suggestions, observations, corrections are most welcome.

 

[BruceJohnJennerLawso]

For Hohmann transfers to an inclined orbit, Lambert iterations tend to give polar transfer orbits! This results in huge plane change expense at both ends, destroying the Hohmann transfer's advantage.

A midcourse plane change can take much of the ridge out of the porkchop plot. But what is the best "broken plane" transfer orbit? For me this remains an open question, but I've been thinking about it. My notes so far:

http://hopsblog-hop.blogspot.com/2013/01/deboning-porkchop-plot.html

I am hoping this page will be a work in progress. Suggestions, observations, corrections are most welcome.

Hi :hello:, are you the genius behind the cosmic train schedules site?

 

[HopDavid]

Hi :hello:, are you the genius behind the cosmic train schedules site?

That's me, thanks!

The Cosmic Train Schedule is based on circular, coplanar orbits. Since orbits are actually elliptical and inclined, that model can give poor approximations at times.

If you browse through some of the stuff at that page, you'll see I'm trying to come up with ways to deal with inclined and elliptical orbits.

 

[BruceJohnJennerLawso]

That's me, thanks!

The Cosmic Train Schedule is based on circular, coplanar orbits. Since orbits are actually elliptical and inclined, that model can give poor approximations at times.

If you browse through some of the stuff at that page, you'll see I'm trying to come up with ways to deal with inclined and elliptical orbits.

Pleasure to meet you, an excellent site for sure :thumbup:. On the topic of what you asked, is it a question of when is it optimal to do the plane change for an off-plane transfer? From what Ive heard the rule of thumb is usually a half as to do it at the lowest velocity, and to do so when not positionally too far out of plane, but its only an approximation. Ill take a look & see at what youve got :tiphat:.

 

[HopDavid]

Pleasure to meet you, an excellent site for sure :thumbup:. On the topic of what you asked, is it a question of when is it optimal to do the plane change for an off-plane transfer? From what Ive heard the rule of thumb is usually a half as to do it at the lowest velocity, and to do so when not positionally too far out of plane, but its only an approximation. Ill take a look & see at what youve got :tiphat:.

Yes, I think those are the major considerations. Make the plane change too far from launch and and the transfer plane can swing quite a ways from departure and destination planes. But plane change expense further out is lessened by slower velocities.

I'm pretty sure the plane change should be at least 90 degrees from launch. Been fooling around with different scenarios. I seem to get good results doing the plane change at r = a, which I'd describe as halfway. Your rule of thumb sounds like a good one.

Best case scenario is when transfer orbit's line of apsides coincides with an ascending or descending node. In such a happy event, no midcourse plane change is needed at all. Plane change expense can be minor even to destinations like Ceres.

Worst case seems to be when transfer orbit's line of apsides is 90 degrees from line of nodes. In this case it might be good to move time of launch to reduce plane change expense. Especially if the destination orbit has a healthy inclination like Ceres' 10.6 degrees.

Deviating from Hohmann launch window pushes arrival vector from local horizontal and thus makes direction change expense. But in some cases this might be a good trade if it can reduce plane change expense.