Interplanetary Asteroid Rendezvous

[The-MathMog]

Hey guys, so I am looking for some tips on how to efficiently rendezvous with asteroids in interplanetary space, as I've heard that it would be more fuel efficient in the end, when dealing with bigger asteroids (starting of with C-Class and then going bigger). I want it to be fuel efficient too, as I am planning on mining them in my career mode.
Rendezvous with them, when they are in Kerbin's sphere of influence, I've got pretty much nailed down, as all that need is some "basic" rendezvous.

I did do a few quick searches, but they didn't help me out much, so sorry if there if there is a topic with it (link then maybe?)
All tips help, as it is always good to refresh some old knowledge too (been playing it for almost 4 years I think)

[eddiew]

The classic thread: 

 

[The-MathMog]

2 hours ago, eddiew said:

The classic thread: 

 

Thanks, that's what I was looking for!

[Xyphos]

I've experimented A LOT with Ast. HSJ-227 which is a Class E asteroid and the very first one to spawn (within 10s) of a new game, capturing it outside of Kerbin's SOI is definitely more fuel efficient. I suggest you experiment a lot too, as I learned a great deal from them. and even if you mess up, just start a new sandbox and try again.

the test vessel was using a single Rhino engine attached to three full-sized Kerbodyne tanks (and a couple of twin-boar boosters to get it into orbit)

I was able to (using mechjeb node planner) eject from Kerbin's SOI in the opposing direction of the asteroid, fine-tune closest approach, match velocities at closest approach, capture and then proceed to redirect for an aerobrakeing using a PE of 42Km  (any lower and it'll burn on re-entry, any higher and it wont capture at all)

each test had a different delta-V for redirect, as I captured it at different times, but none of which was more than 150 m/s, and for a Rhino engine, that's pretty easy to do. it seems the sooner you capture the asteroid, the less delta-V is required for redirection, but also required more delta-V for ejection and matching velocities, you might need Big Mac's Fancy Mathematics to find the optimal time for capture to reduce overall delta-V used during the life of the mission.

after these tests, I've experimented even further using different vessel builds, including LV-N and ION engines;

LV-N was great for ejection, rondevous, and matching velocities allowing me to do all aforementioned things A LOT sooner than normal, which saved redirection delta-V, but I actually lost A LOT of overall delta-V after capturing, due to the overall mass of the asteroid and vessel.

in fact I ended up using more LF than the previous LF+OX build of the Rhino engine, and now that I think back, I probably should have tested a hybrid of LV-N and Rhino for the heavy stuff

the ION engine test was very, very interesting, I was able to eject, rondevous and match velocities MUCH sooner than LV-N but the burn times were awful. when I captured the asteroid, it was a full 52 days ahead of SOI entry and about 32 m/s for redirection, but again, it lost overall delta-V due to the mass of the Asteroid and ran out of XenonGas after spending 2 hours burning only 5 m/s of the 32 m/s required, definitely not a good choice for heavy-hauling, and a hybrid probably would have been better suited.

I also found out that if you plan on turning the asteroid into a refueling station, it is NOT a good idea to bring mining equipment with you and refuel mid-flight as you'll be dragging dead-weight with you and losing delta-V for majority of the mission and using more ore during the redirect than what would be profitable, just launch a big rocket with enough fuel to do everything in one go, launch a mining rig once it's in orbit and re-use the rocket(s) as aux tanks for storing fuel, just be sure to bring all 3 docking ports on the mining rig so you can dock different vessels to it.

I hope this helps, and I wish you best of luck and many happy landings.

Edited November 6, 2016 by Xyphos

[Tyko]

I spent the whole weekend (literally ) experimenting with asteroids. Good news is that I have a design that can capture and redirect up to Class E. Bad news is that my longest burn time was 37 minutes. The Tug uses an LV-N plus one and a half Kerbodyne orange tanks. It develops 12700m/s DV on its own.

When I docked with a 1700 metric ton Class E the Tug (minus fuel spent on rendezvous) had 170m/s DV to move the rock around. This was enough to divert it into a stable highly eccentric orbit. I'll revisit that asteroid when I have higher tech. The Tug with a Class C had over 1700m/s DV to work with and was easily capable of parking the asteroid in a stable LKO.

The biggest issue was rotating the craft to execute burns. With two 1.25m Reaction Wheels plus RCS I was able to turn the Class E, but it was really slow

[The-MathMog]

Thanks for the astounding amounts of info guys! I will test out a lot of it myself, and try to get a better grasp at what it exactly takes.

So far after the initial post, I've managed to put a C-Class asteroid into orbit around Kerbin, using a vessel with around 10.000 delta-v, in the form of 2 Nuclear engines. I did forget about using the atmosphere as aerobreaking, and I've not put it in a highly inclined (polar) orbit, and I need to bring it down into an equatorial orbit, which will take a few more missions (my current spacecraft can put 500+ delta-v into the 130+ ton heavy rock). I am using stage-recovery mod too, so the missions are not thaaat expensive in the end, but I probably still loose a bit more cash than what I'll actually gain from it. Oh well, I am paid with a learning experience. Launching one bigger mission is probably a better way, than having to launch 4 medium sized ones. (Even had to do a salvage mission, to add parachutes to the first mission, and de-orbit it, to gain the value back of the nuclear engines.

Ion engines is probably not something I'm gonna play around with, as my patience isn't thaaat big. Nuclear only just makes the cut

[Tyko]

4 hours ago, The-MathMog said:

Ion engines is probably not something I'm gonna play around with, as my patience isn't thaaat big. Nuclear only just makes the cut

the thing that saved my sanity for the 30+ minute burns is using alt-period to force a time acceleration while engines are running. It maxes out at 4X acceleration, but that still cuts the burn time to 25%.

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions. 

[Xyphos]

21 hours ago, The-MathMog said:

I've not put it in a highly inclined (polar) orbit, and I need to bring it down into an equatorial orbit

in your game settings, if you set your conic patch mode to 0 (far left button until it stops), and the number of patches to 6, which is strongly recommended for gravity assisted maneuvers, you can actually aim the asteroid during the redirect on a fly-by past Kerbin to alter it's inclination on it's first pass by without capturing it, then later setup another Kerbin rondevous for an equatorial aerobrake and capture, it takes more time, but uses much less delta-V than altering the inclination after capturing, and you can do it all in a single mission.

that's the beauty of orbital mechanics, what goes around, comes around, not everything has to happen all at once, for time is just an illusion,

I think the hardest part of this game is learning patience, but learning to use gravity-assisted maneuvers can save you TONS of delta-V.
in fact, gravity assisting makes it possible for an SSTO spaceplane to reach Laythe and back without refueling mid-flight, but we'll cover that lesson some other day.

and before I forget, to setup the second rondevous, burn radial in/out at the solar AP but make sure the PE crosses into Kerbin's orbit, you should be able to see the node flags line up. try to get them as close as possible and fine-tune the trajectory later on when you're less than half-way there.

Edited November 8, 2016 by Xyphos