So about that transfer angle calculation...

[Wobbly Av8r]

Long story short: I picked up a "Go get a comet sample" contract and found it was not the animal I thought it was. I was hoping to get it done in the usual "asteroidal" time frame of ~100 days or so but it's beginning to look like a minimum 5 year venture, which is, well, more realistic but a pain to have that open contract for such a long time (BTW, Thank you Kerbal Alarm Clock!).

So the scenario is depicted below with some of the orbital info listed. If I'm missing something about what I *think* is the best way to do this, please share your knowledge with me!

My take on the matter is that, due to the comet's 7 degree relative inclination, I will have to intercept either the comet (best) near the Kerbin orbit DN, or the join the comet's orbit inclination at the DN (which basically coincides with the comet's Kerbol Pe and is 92 days out) and chase it, i.e. wait for it to come around again. Unfortunately Kerbin is 208 days away from that DN so to meet the comet near DN on THIS orbit would require some creative retro-Kerbin burn that lets me "cut the corner" but would of course require a mid-course correction at some point to rejoin on the other side. Any way I've calculated this, we're talking 5000+ dV requirement not to mention my relative velocity at approach would be around 1500 m/s, which is no bueno.

While trying to figure this one out, I'm seeing that Kerbal Engineer Redux, with the comet as the target, claims I have a "Time to Transfer" in 28 days (as well as a transfer angle of ~77 degrees...) and seeing as how I can't even figure out how to catch up to this comet NOW, I'm not sure what this calculation means, if anything, especially because my target is in a non-circular and crossing orbit. I can't figure out an efficient way to catch this comet (total of <5000 dV? Or am I smokin' crack?) without waiting the 208 days to leave Kerbin and enter into the identically inclined comet's orbit followed by a small adjustment burn to time the meeting when the comet comes by again in 5+ years.

Is this typical? Did I miss something here? If KER says I have a transfer window in 28 days, what is this based on? What kind of a burn would I be looking at in 28 days that would improve my ability to "transfer" to this comet before my Kerbals retire?

And finally, any suggestions for chasing comets (other than I shoulda' looked at the contract a little more carefully) would be appreciated!

[bewing]

Generally, you will always get the best dV result by catching the comet very near its Ap, especially if it has a node near the Ap (if so, aim for the node!). Then do a full intercept at that point. Then you have to get back to Kerbin, using any technique you like. Yes, this method takes one large orbit, which can take a decade.

There's no way you can catch this comet at the upcoming Pe without burning 10km/s of dV, so don't even bother looking at any Pe intercepts. If you happen to get a lucky Kerbin close approach at the Pe (which you didn't) then you can do an intercept there quickly and cheaply.

[Fierce Wolf]

Are gravity assists with Jool or Eve possible?

[Wobbly Av8r]

1 hour ago, Fierce Wolf said:

Are gravity assists with Jool or Eve possible?

Well, I was gonna say straight out no, but reconsidering that Eve's year is ~262 days, maybe? I don't think it would help me catch it in the optimal location (making the assumption that the optimal is when it is closest to Kerbin's orbital plane) but it could sling shot me to help catch it...

I'm pretty sure Jool is a no from what I can see.

[Spricigo]

21 hours ago, Wobbly Av8r said:

Long story short: I picked up a "Go get a comet sample" contract and found it was not the animal I thought it was. I was hoping to get it done in the usual "asteroidal" time frame of ~100 days or so but it's beginning to look like a minimum 5 year venture, which is, well, more realistic but a pain to have that open contract for such a long time (BTW, Thank you Kerbal Alarm Clock!).

After reading this, I don't know if i should feel better or worse for taking a very similar contract knowing the mission will take years.

Anyways, my plan to Rendezvous With Hama Natarlof

1. Depart from Kerbin when passing by comet's periapsis (which in my case coincides with AN) aiming from a high elliptical orbit just inside Natalorf's Orbit
2. Match inclination at Apoapis(/DN )and setup the approach to happen near periapsis
3. Refine the encounter along the way. Meet Natarlof, take samples, transmit one
4. Find the most convenient way back..or not. (very likely I send the kerbals to a colony and the extra samples to a lab)

My 'calculation' with the help of Astrogator, are 2km/s departure from kerbin 0.5km/s inclination change and 0,5km/s for matching orbit and position. more the return, more extra fuel required in the actual mission and 5km/s don't seem atypical. 

 

 

 

[Wobbly Av8r]

6 hours ago, Spricigo said:

Anyways, my plan to Rendezvous With Hama Natarlof...

That all reflects my experience and what I've settled on - it is good to know that others are looking at the same type of thing and coming up with with similar solutions. (We may not be right, but we are in agreement!)

Still, any idea where/what the "transfer" information means as regurgitated by KER relative to such an orbit? In my example, which after a lot of contemplation of efficiency requires the same approach you took, what event would occur in 28 days that is meaningful in a "transfer" sense? Again, any ideas are welcome!

[Fierce Wolf]

8 hours ago, Spricigo said:

Anyways, my plan to Rendezvous With Hama Natarlof

 

 

Isn't it Rendezvous with Rama?

[Spricigo]

On 10/14/2020 at 2:00 PM, Fierce Wolf said:

Isn't it Rendezvous with Rama?

No, it's Natarlof.