When Should I Launch?

[Zosma Procyon]

I am planning a launch mission to plant a small, well not really small, space station on a D-Class asteroid with a LONG period, because I can. The crew will four 5-Star veterans. The trick is I am not sure when I should launch. My space station launch vehicle has 13,447 m/s of delta-V to work with. I know I should aim for a rendezvous a or shortly after the asteroid reaches its periapsis, but I'm not sure of the best way to do that. On the picture below I have marked the current location of the asteroid (red star), and the four options I can think of. As it says on the picture, the asteroid will reach periapsis in just over 1 Kerbin year. I would like opinions on which option I should use. Please note the asteroid's orbit is moderately inclined to Kerbin's, and descends below the ecliptic just before periapsis.

The first option is marked by the green triangle, and that is the current location of Kerbin. The idea of launch now is to put the space station into an elliptical orbit out beyond Duna, and have the space station arrive at or near the asteroid's periapsis at about the same time as the asteroid and importantly on about the same plane, so I have to do is burn like hell to match velocity. An earlier launch attempt that I aborted because I only had one Kerbal aboard showed the delta-v required to match velocity would be about 6000 m/s. Perfectly doable with this vehicle. The the other options would involve direct flights, and not launching for at least a Kerbin year.

The next option is to launch when the asteroid is at its periapsis, and I have marked the approximate location Kerbin will be in with the yellow pentagon. An advantage of this is that I won't need to muck around with timing arrival at the periapsis. I will also be catching up to the asteroid while it is decelerating, which might save some delta-v. The disadvantages are that I have to wait (I hate to wait), and rendezvous will probably not happen until the asteroid is out past Jool (meaning more waiting).

The third option marked by the blue rhombus is to wait a few weeks after periapsis, and catch up to the asteroid as it decelerates out. In retrospect I think launch there is about the worst option.

The forth option marked by the pink square is to launch when I can get the maximum boost from kerbin, in about 1.5 years. The burn to catch up the asteroid will be enormous, and as will the burn to match velocities.

So which one would you choose.

Below is a picture of the asteroid's orbit. I'm sending my Kerbals on a very long away mission. And I'm not sure I will ever try to get them back.

Edited November 23, 2017 by Zosma Procyon

[Zeiss Ikon]

I'm not an expert on this kind of rendezvous, but I think the earliest launch option is the best choice.  You'll be making a classic orbital rendezvous, with planes already matched and an orbital intercept established, so all you have to do is kill your relative velocity to match with the asteroid.  Once you've done 95% of that, you'll gain time (because you'll stay near the target for a longer period) in which to finish matching and actually grapple into place.

For a mission like this, a written checklist is a strong recommendation -- forget a critical piece of equipment, like a science instrument or (assuming you use KIS/KAS) a spare part, and you'll have a much, much harder job to send it along from Kerbin after the fact.

[xkerbal]

Mod list pls

 

[Corona688]

I agree, launch ASAP.  The closer it gets, the more delta-V it takes to match it (lots of energy is wasted leaping sideways).

Don't go outside Duna, though.  Right location, wrong speed, wrong time.  The asteroid will be zooming far past its periapsis before you get close.  The asteroid will be going like a bat out of hell by the time it hits the inner system, you see.  To catch up, you need to go even faster.

Instead of heading out for duna, fall towards the sun.

Your own periapsis around the sun will be the best time to effect changes on your course.

Disclaimer:  That was just mocked up in a paint program, not a real course, just my vivid imagination of how it would go.

Edited November 23, 2017 by Corona688

[Zosma Procyon]

7 hours ago, Corona688 said:

I agree, launch ASAP.  The closer it gets, the more delta-V it takes to match it (lots of energy is wasted leaping sideways).

Don't go outside Duna, though.  Right location, wrong speed, wrong time.  The asteroid will be zooming far past its periapsis before you get close.  The asteroid will be going like a bat out of hell by the time it hits the inner system, you see.  To catch up, you need to go even faster.

Instead of heading out for duna, fall towards the sun.

Your own periapsis around the sun will be the best time to effect changes on your course.

Disclaimer:  That was just mocked up in a paint program, not a real course, just my vivid imagination of how it would go.

I'm going with you're idea. Gives me time for a few orbits and a chance to refuel the station. The station will be cuttings closer to the sun than I've ever sent a manned rocket.

[Corona688]

Sound interesting, I hope for pictures!