Let's plan the Asteroid Redirect Mission!

[Wayfare]

Right, let's get our thinking caps on and figure out the best way to do this I've come up with a number of considerations and basic mission profiles. They are yours to think about, shoot full of holes, modify and/or add to as you see fit. What we're looking for is the most efficient way to get the job done in terms of delta-v - that cold equation which ultimately governs all of our endeavors in spaaaaaaace...

Assumptions:

- All asteroid trajectories are close to Kerbin's solar orbit and will cross Kerbin's SOI Soon. This is based on the videos I've seen so far.

- We want to capture an asteroid into an orbit around the Mun. It could be Minmus or Kerbin itself, but let's go for the Mun as a baseline.

- SLS parts and stronger joints allow us to put a lot of payload into space reliably. Still, let's leave the absurdly big stuff to the expert (yes, expert, singular - I'm looking at you Whackjob).

Profiles:

- Heliocentric Orbit Rendezvous (HOR). Launch a spacecraft as soon as possible and rendezvous with the target before it reaches Kerbin's SOI. This gives the lowest relative velocity at rendezvous and allows you to tune the target's Kerbin encounter at minimal delta-v expense. It does mean you need to push your craft beyond Kerbin escape velocity to get an intercept, greatly increasing the initial delta-v investment.

- High Kerbin Orbit Rendezvous (HKOR). Launch a spacecraft to intercept the target as soon as possible after it enters Kerbin's SOI. The spacecraft will not need to be accelerated up to escape velocity and the relative velocity to the target will be fairly low still. It does make it more expensive to adjust the target's trajectory because you'll be deeper inside Kerbin's gravity well.

- Low Kerbin Orbit Rendezvous (LKOR). Launch a spacecraft to intercept the target as close to its Kerbin periapsis as possible. This requires the least amount of intercept delta-v, but rendezvous and orbital adjustments will be much more expensive due to the high relative velocity and being so deep inside the gravity well.

- Munar Orbit Rendezvous (MOR). Launch a spacecraft to intercept the target inside the Mun's SOI. This requires a target that is going to encounter the Mun naturally and you need to push your spacecraft out to there first. On the other hand, it is potentially the least complicated mission, requiring only one burn after rendezvous to complete. Delta-v cost of capture is lower that H/LKOR profiles as the target will not be as deep inside Kerbin's gravity well, and with any luck you can use the Mun's gravity well to help out.

Other Considerations:

- Number of spacecraft. It seems sensible to have two separate spacecraft: one dedicated probe to capture the target, and one crewed follow-up spacecraft to meet the captured target and perform SCIENCE! This way the capture craft won't need to haul around scientific equipment and crew, saving dry mass on the most delta-v intensive part of the mission. On the other hand, the additional cost/hassle of a second launch may not outweigh the savings made on a lighter capture craft. This becomes more pronounced the heavier the target is. On a particularly challenging rock, you could consider using even more craft: one for the initial capture into Kerbin orbit, another for adjusting the target's orbit to a Munar encounter, etc.

- Target trajectory. Your mission profile may be dictated to some degree by the trajectory of the target. A target which will naturally encounter the Mun will lend itself to an MOR profile. A target on a highly inclined Kerbin encounter might be best captured with the HOR profile. A target coming in at a gentle inclination might best be captured using H/LOR, depending on its Kerbin periapsis. The target trajectory may in turn inform the choice of number of spacecraft.

- Kerbin aerobraking. This would totally get you fired at NASA. It would also be totally awesome. Kerbin has that stinking atmosphere doing nothing but making our launches more expensive - why not put it to use? A Kerbin aerobrake/-capture could shave a lot off your delta-v budget.

So ladies and gentlemen... How do you think we should capture a spacerock?

[SirusKing]

LOTS OF FUEL AND NEWCLEARAIR ENGINES!!!1

My plan is to send a reasonable size ship with fairly efficient engines into LKO, Dock some more fuel tanks onto it, then send it off to grab a Class D Asteroid.

Bring the Asteroid into LKO Again, then let it go and refuel the asteroid collector.

Send it off again, bring another Class D Asteroid into LKO, within a few hundred meters of the previous asteroid.

Repeat 3 more times.

Send up a large fuel tank with two grabbing claws on it, grab the first asteroid and rendezvous with another.

Link with the next asteroid. Repeat this for the other 3 asteroid, until you have an asteroid pentagon ring thing.

Dock a bunch of random science, habitat and life support stuff to it.

Boom, Asteroid Space Station.

Edited March 24, 2014 by SirusKing

[Wayfare]

I like the way you think. I was thinking of chaining a bunch of asteroids behind each other and cruise them around the solar system shouting "Choo-choo!" at every encounter

[Kasuha]

Heliocentric orbit rendezvous, definitely. Followed by nudging the asteroid to get gravity slingshot off Mun to park in Kerbin orbit. Then eventually another ship can be sent to push the asteroid further and park it in Mun orbit eventually or do whatever needs to be done with it.

[cantab]

The earlier you can get to it, the better. So I expect the best strategy will be HOR, getting the earliest reasonable intercept possible. By "reasonable" I mean not needing a silly amount of dV to match speeds.

As for absurd profiles, how about lithocapture? Rendezvous with the asteroid and connect a big block of girders or whatever to it. Then make a course correction such that the block of girders just clips a peak on an airless body. The asteroid itself needs to miss, but be decelerated by the impact forces. Hopefully this works in the physics engine. Do it right and the asteroid will be captured, only needing a small burn to raise periapsis.

[samiamthelaw]

LOTS OF FUEL AND NEWCLEARAIR ENGINES!!!1

My plan is to send a reasonable size ship with fairly efficient engines into LKO, Dock some more fuel tanks onto it, then send it off to grab a Class D Asteroid.

Bring the Asteroid into LKO Again, then let it go and refuel the asteroid collector.

Send it off again, bring another Class D Asteroid into LKO, within a few hundred meters of the previous asteroid.

Repeat 3 more times.

Send up a large fuel tank with two grabbing claws on it, grab the first asteroid and rendezvous with another.

Link with the next asteroid. Repeat this for the other 3 asteroid, until you have an asteroid pentagon ring thing.

Dock a bunch of random science, habitat and life support stuff to it.

Boom, Asteroid Space Station.

I'd like to land a bunch of them near KSC and build a cairn the size of the VAB.

Though I'd also like to use a few of them for bowling down rocket-pins on the runway.

[UmbralRaptor]

I'm leaning towards a heliocentric rendezvous. The combination of an orange tank and an LV-N will give you at least a few hundred m/s even for a 1000 tonne asteroid. The craft as a whole need not be more than 80-90 tonnes (launchable by 6 asparagus'd mainsails) From what I saw, the masses run from a few thousand to under ten tonnes, so an adequately large craft won't be a problem. Pushing away one that is going to hit Kerbin is easy enough. So is pushing a class A (or maybe into whatever orbit I want. Larger ones will require aerobraking and/or a Munar flyby, which should prove... interesting...

edit: note that a capture orbit has minimum ÃŽâ€Ã¯Â¼Â¶ cost when as eccentric as possible (so, ~70 x 80,000 km for Kerbin)

[Wayfare]

As for absurd profiles, how about lithocapture? Rendezvous with the asteroid and connect a big block of girders or whatever to it. Then make a course correction such that the block of girders just clips a peak on an airless body. The asteroid itself needs to miss, but be decelerated by the impact forces. Hopefully this works in the physics engine. Do it right and the asteroid will be captured, only needing a small burn to raise periapsis.

Hmm. I wonder what the impact tolerance of an asteroid is. A sufficiently massive and/or fast impactor probe might just knock one into Kerbin orbit if you hit it at the right time without vaporizing it.

[Sandworm]

Is an intercept in the sun's SOI really the most efficient? Yes, 10m/s of push far away is better than 10m/s close to Kerbin, but you still have to get the tug craft/fuel out there and back to Kerbin. Rather than push the craft out there, stay close to home and use the fuel in Kerbin's SOI to actually push the rock.

I guess it would depend on the relative masses of the tug and asteroid. For smaller asteroids it may be better to wait for them to approach.

[vger]

I want to give Kerbin a third moon.

[Rakaydos]

Have the capture craft waiting in minmus orbt. When an asteroid enters Kerbin SoI, the capture craft catches up to it, docks, and tweaks the asteroid's slingshot around kerbin so that it will get another encounter in about a year or two. Tune this orbit to slingshot Mun for a capture orbit.

[SkyRender]

I want to give Kerbin a third moon.

Nowhere near ambitious enough, if you ask me. Kerbin deserves as many moons as it can get. I'm thinking at least a few dozen. Enough to make Jool jealous, if nothing else.

[Sylith]

Hmmm, why not creating a ring of asteroids around Kerbin *laughs maniacal*

[Javster]

If one (read: me) were to make a few new Muns for Kerbin, one (read: also me) would try to clump a bunch of asteroids together (maybe using KAS)

[Wayfare]

Have the capture craft waiting in minmus orbt. When an asteroid enters Kerbin SoI, the capture craft catches up to it, docks, and tweaks the asteroid's slingshot around kerbin so that it will get another encounter in about a year or two. Tune this orbit to slingshot Mun for a capture orbit.

That may very well be the most efficient way to do it. It's basically the method of incremental gravity assists that folks have been using to send probes towards far-off destinations for a long time. Sure it takes patience, but it gets a lot done on a relatively small budget. Good thinking!

I'm still not sold on what the most efficient rendezvous profile would be. Catching up in high-Kerbin orbit is definitely a good option, as it reduces the initial transfer delta-v for only a small loss in relative velocity at rendezvous. But you'll be pushing your craft out a long way in its heaviest, fully-fueled condition. Ideally you'd want to catch up to the asteroid just as it enters Kerbin's SOI, thereby minimizing the amount of extra velocity it picks up due to Kerbin's gravity (gotta love two-body physics). This seems to be the best of two worlds (HOR and HKOR).

On a practical note, I don't know if the "closest approach" display will work if the bodies are in different spheres of influence. So if the asteroid is still orbiting the sun, but has a patched conics trajectory in Kerbin's SOI, could I get a closest approach indicator on a maneuver node trajectory while I'm orbiting Kerbin? Or, to make it even more complicated, while I'm orbiting Minmus and plotting a maneuver out of Minmus' SOI? There's a lot of SOIs to keep track of there and I don't know if KSP can handle all of that.

Finally I don't think Minmus would make a very good waiting station. The odds of an asteroid encountering Kerbin while Minmus is in a good intercept position are pretty low, even less than the MOR profile which is also a long shot. Given that you'll have to burn out there anyway, you might as well park in low Kerbin orbit and take it from there.

So yeah, I really like the idea of catching up with an asteroid and using a string of incremental gravity assists to achieve capture, but I don't think Minmus is the best place to hang out and wait for it.

Edited March 24, 2014 by Wayfare

[Francesco]

Anyone knows what an asteroid's speed relative to Kerbin would be?

[vger]

If one (read: me) were to make a few new Muns for Kerbin, one (read: also me) would try to clump a bunch of asteroids together (maybe using KAS)

Oh gosh, how about... a space station for docking asteroids...

[Lohan2008]

Didn't someone make an earlier comment on another thread about landing an asteroid ? How much fuel will I need after aero-braking ?

[Wayfare]

Didn't someone make an earlier comment on another thread about landing an asteroid ? How much fuel will I need after aero-braking ?

That depends on the size of the asteroid and the number of parachute probes you're willing to clamp on to it before it hits atmo...

[magnemoe]

I'm leaning towards a heliocentric rendezvous. The combination of an orange tank and an LV-N will give you at least a few hundred m/s even for a 1000 tonne asteroid. The craft as a whole need not be more than 80-90 tonnes (launchable by 6 asparagus'd mainsails) From what I saw, the masses run from a few thousand to under ten tonnes, so an adequately large craft won't be a problem. Pushing away one that is going to hit Kerbin is easy enough. So is pushing a class A (or maybe into whatever orbit I want. Larger ones will require aerobraking and/or a Munar flyby, which should prove... interesting...

edit: note that a capture orbit has minimum ÃŽâ€Ã¯Â¼Â¶ cost when as eccentric as possible (so, ~70 x 80,000 km for Kerbin)

My plan too, note that we can mount 8 LV-N around one of the new 3.75 meter tanks, now put another 3.75 meter drop tank below it, drop tank is primarily to intercept and match orbit with asteroid.

Might be smart to have something like an mainsail or an ring of T-30 to do the push, Myself is a bit exited to aerobrake the asteroid into LKO, hopefully mods get updated so they contains kethane and ore so I don't have to go all the way to Minmus to mine.

For an Mun orbit I would probably try to get it into an orbit between Mun and Minmus first and then plan an Mun intercept. this also give the option to refuel the pusher, and yes the pusher can be reused.

Hmm. I wonder what the impact tolerance of an asteroid is. A sufficiently massive and/or fast impactor probe might just knock one into Kerbin orbit if you hit it at the right time without vaporizing it.

I think people will rush to find out this.

[Rakaydos]

Didn't someone make an earlier comment on another thread about landing an asteroid ? How much fuel will I need after aero-braking ?

Terminal velocity at ASL is 100-120 ms.

If you can get the asteroid to have a TWR of at least 2:1, you should be able to manage a 15 second suicide burn for a powered landing.

[JedTech]

Here's what I'm thinking for performing a Powered Landing of a Class E Asteroid:

1. Dock/Claw a few dozen booster ships with really big engines directly to the asteroid (all in the same hemisphere).

2. Attach all ships together via KAS attachments

3. Aim for land that is near sea level, and wait to do a 15-20 second suicide burn.

4. Use Throttle Control Avionics to even out the thrusting and come in nice and controlled.

Edited March 24, 2014 by JedTech
adding awesome graphic

[cantab]

Is an intercept in the sun's SOI really the most efficient? Yes, 10m/s of push far away is better than 10m/s close to Kerbin, but you still have to get the tug craft/fuel out there and back to Kerbin. Rather than push the craft out there, stay close to home and use the fuel in Kerbin's SOI to actually push the rock.

I guess it would depend on the relative masses of the tug and asteroid. For smaller asteroids it may be better to wait for them to approach.

I've not proven it, but my feeling is it's probably better to intercept early. After all, it takes 4500 m/s of delta-V just to get to low Kerbin orbit. You'll only need another thousand or so to get out of Kerbin's SOI and to the asteroid encounter.

[Gravitas Shortfall]

Is an intercept in the sun's SOI really the most efficient? Yes, 10m/s of push far away is better than 10m/s close to Kerbin, but you still have to get the tug craft/fuel out there and back to Kerbin. Rather than push the craft out there, stay close to home and use the fuel in Kerbin's SOI to actually push the rock.

I guess it would depend on the relative masses of the tug and asteroid. For smaller asteroids it may be better to wait for them to approach.

We'll have to match speed with the asteroid regardless, so whether you intercept in Kerbin's SOI or the sun's, you'll be spending the dV to reach interplanetary velocities, so where would you actually save by doing the intercept around Kerbin?

[Horn Brain]

You will not save any dV by rendezvousing in Kerbin's SoI, or any SoI other than the Sun's.

The asteroid is going to be on a hyperbolic flyby trajectory when it enters Kerbin's SoI, probably with a very high periapsis. That means that to rendezvous with it you'll have to do a big burn to get your apoapsis out near the asteroid's path, then accelerate from basically a dead stop at the top of your highly-elliptic orbit all the way up to the speed of the asteroid, which will be some fraction of Kerbin's orbital velocity around the Sun, so we're looking at around 1 or 2 km/s, maybe more if the asteroid has a very different orbit from Kerbin's. THEN you have to dock and slow the rock down to below escape velocity, which at the high periapsis you'll be at will be almost the entire velocity of the asteroid, so double whatever that big burn you just did to rendezvous, but this time you're hauling hundreds of tons of space rock.

Best case with this strategy: About 2 km/s without the asteroid, and about 1 km/s with the asteroid.

Muuuuuuch more efficient is (surprise!) the NASA strategy: Do the escape burn at a convenient time to get yourself a cheap rendezvous with the asteroid several Kerbin years in advance of the close encounter, perform a small dV adjustment to cause the asteroid to fly by Kerbin with as low a periapsis as you can get, then either use a burn at periapsis, a munar flyby, or a combination of the two to bleed off the extra speed and capture the asteroid. Once it's caught, then it becomes relatively straightforward to send fuel up to the rock if you now need to make a big correction of its orbit.

Best case with this strategy: about 1 to 1.5 km/s without the asteroid, a few hundred m/s or less with the asteroid.