Asteroid Intercept Fuel?

[Stickyhammy]

Having just returned from Eeloo I have found an asteroid that is going to fly by Kerbin at about 5 million meters. I would like to capture it and bring it into a circular Kerbin orbit but I don't want to not have enough fuel to move it. Does anyone have a chart with estimated delta V values needed to slow down different asteroid classes? Here is the asteroid in question.

Edited June 13, 2014 by Stickyhammy

[Black_Tomcat]

The delta-V needed only depends on the trajectory, not on the size of the asteroid. However, the asteroid will decrease your ships dV when you grab it, and if you don't want to send a probe first to weigh the asteroid you'd have to guesstimate the fuel needed. By catching it early and aerobraking you might be able to cut it down by quite a bit.

[cantab]

An E class, that's going to be tough. They weigh in at up to 3000 tons, with rare outliers even heavier.

The most fuel efficient approach will be to encounter it while it's in solar orbit. It may take more delta-V to make the intercept, but that's delta-V expended without the asteroid attached. You then only need a small correction, delta-V-wise, to bring periapsis to 50 km or so for aerocapture. Even if you don't want to risk an aerocapture, getting your incoming trajectory close to equatorial and into a low periapsis will give you an economical capture burn.

The "trick" to making a solar orbit interception is to leave Kerbin's SOI in the same direction the asteroid is predicted to arrive. I'm not sure why, but that seems to make things work out nicely.

If you're aerocapturing, I suggest rating your ship for 250 m/s when pushing 3000 tons, and then 1500 m/s for getting to the asteroid from LKO.

Also, don't overlook the challenges of turning such a large asteroid and keeping it on course. My approach has been to use little control sections that can be clawed on dotted around the asteroid to help turn it. That's handled a 500 ton D class fine, but even I don't know how it would deal with a 3000 ton E. An alternative is to actually unclaw the tug and reclaw it facing the way you need for a burn.

[LethalDose]

In my career mode game, I've captured 3 asteroids (an A, B, and D). What I've generally done is built my asteroid capture probes to be sufficient to just capture the asteroid and have a docking port. After the asteroid has been captured (usually in a big, ugly eccentric orbit), I can refuel the capture probes in situ to clean up the orbit and bring it into LKO. In my game, I'm trying to be sure that everything that goes up does so under a fairing if it's not nice and cleanly aerodynamic. I could probably be more agressive in my approaches if relaxed that restriction.

With the big asteroids, the D's & E's, I agree with cantab: Don't even try to change the beast's orientation to thrust in different directions, just detach and re-attach.

[Claw]

Here is a tutorial I built that will get you out to that asteroid in roughly 30-40 days for an initial look (or first attempt mission). That gets you to it around 90 days before it gets to Kerbin. You can then claw on and either get an idea for how much that thing weighs (for further designs) or send a ship to move it around.

http://forum.kerbalspaceprogram.com/threads/75759-Asteroid-Rendezvous-Outside-of-Kerbin%E2%80%99s-SOI

[Skorpychan]

Aerocapture of an asteroid. I weep for Kerbin's biosphere.

[KerbMav]

Aerocapture of an asteroid. I weep for Kerbin's biosphere.

What do you expect to happen?

[running]

I've captured an E type and landed it on the science station at KSC.

Attach rocket with lots of SAS. When fuel is spend, ditch the tank and engine but keep the SAS part attached.

Repeat as often as needed. For extra power also use RCS.

First prio should be to get it into orbit.

Then you can start working on decreasing the orbit and adjusting the inclination.

If you want to land it.... attach small modules that are basically just a bunch of parachutes.

You can bring up a lot of these modeles on one ship that then launches them one by one at the astroid.

(use the small seperation rockets. reduce the fuel load and output, so it's like a homing missile that you can shoot at the astroid. Or make small ships.)

Then try to deorbit and open the parachutes at the right time.

[Stickyhammy]

So here is my asteroid grabber. Standard claw, 12 massive fuel tanks, 6 massive engines, and a nuke engine in the center because whats asteroid catching without nukes? Do you think it will have enough power to slow down the E class asteroid into Kerbin orbit? Obviously the delta v isnt as high as it will be as the cans are not full yet.

Edited June 12, 2014 by Stickyhammy

[Skorpychan]

What do you expect to happen?

Heat dumping, air displacement, tidal effects, and dust deposits from the rock itself.

[Black_Tomcat]

So here is my asteroid grabber. Standard claw, 12 massive fuel tanks, 6 massive engines, and a nuke engine in the center because whats asteroid catching without nukes? Do you think it will have enough power to slow down the E class asteroid into Kerbin orbit? Obviously the delta v isnt as high as it will be as the cans are not full yet.

[pic]

Those big engines must seriously hurt your delta V. Using one of these would increase it already by reducing your mass, and relying solely on nukes would make it skyrocket. Obviously using nukes only would make burn times incredibly long, but using just one big engine would still be an improvement without making it obscenely low thrust.

[Claw]

Heat dumping, air displacement, tidal effects, and dust deposits from the rock itself.

I'm sure someone will point out that these things don't happen in KSP. However (off topic) these things wouldn't be that bad.

Heat - the Sun dumps way more heat on the planet than a passing asteroid ever could.

Air - It doesn't have enoughvolume to displace a significant amount of air. It might drag some of it out of the atmosphere, but it wouldn't be much.

Tide - It's nowhere near large enough to cause changes to the tides. It's not even big enough to have gravity to keep a kerbal on it.

Dust - is constantly raining down already. It just doesn't make the fiery entrance of a meteor.

----

Stickhammy,

You can guesstimate what the dV of that ship will be using the dV equation. That ship looks massive enough that you might have over 1k dV with a 'roid attached.

As for all those big engines, you might actually need them. As it stands, MJ estimates over 17 minutes to use all that dV. I'm sure it's a bit out of whack with that nuke, but if the burn takes too long the asteroid may be on it's way, or at the very least, make you use all your dV to keep it on track.

Edit: I did some estimates based on pure guesswork. I estimated your ship to be about 1200t wet with 1000t of fuel.

With a 2000t asteroid you have around 1300 dV, and a 3000t asteroid will have around 900-1000dV. I don't recall how much you need from an approach such as what you have, but I have a gut feeling that 1300 dV is enough. I would say definitely enough if you are also going to aerobrake.

Oh yes, and pushing an asteroid that big can be pretty difficult. They tend to get wobbly and it's hard to line up the CoM.

Edited June 12, 2014 by Claw

[Stickyhammy]

I have a new design for an interceptor. Only one main engine. Approx 6800 deltav without refueling in a 100000 km orbit. Unfortunatly I must be asteroid mission stupid because I tried to follow the linked tutorial from page one and I just cant get it to work. I think the first step says to make the AN of the asteroid as target read 180, but I cant seem to get a launch that lines me up at 180. Trying to burn to 180 AN takes a lot of fuel. I will just have to keep trying I guess.

Here is the new rocket design on the launchpad.

[LethalDose]

I have a new design for an interceptor. Only one main engine. Approx 6800 deltav without refueling in a 100000 km orbit. Unfortunatly I must be asteroid mission stupid because I tried to follow the linked tutorial from page one and I just cant get it to work. I think the first step says to make the AN of the asteroid as target read 180, but I cant seem to get a launch that lines me up at 180. Trying to burn to 180 AN takes a lot of fuel. I will just have to keep trying I guess.

Here is the new rocket design on the launchpad.

I don't know if "making the target asteroid AN read 180" is very good advice... Unless I'm misunderstanding something That would mean your orbiting in the opposite direction of the asteroid, which means you have to dump ~ 2x your velocity in dV to match the asteroids orbit at that AN. E.g. if you're travelling at 500 m/s, you have to burn 1000 m/s

It's usually most efficient to match the asteroid's inclination and direction straight off the launchpad. You won't go into an equitorial orbit, but that's okay.

[cantab]

Claw gave the dV estimates for your first ship. For your second one, I make it ~870 tons wet and 110 dry. Pushing a 3000 ton asteroid, you'll have ~800 m/s of delta-V. Of course once you're there you won't have so much fuel left. Plenty enough for an aerocapture, but not enough for a purely powered one.

As for matching inclination with the asteroid's predicted path, well the best thing to do is:

Sit the rocket on the pad.

In map mode, target the asteroid.

Wait until KSC is under the asteroid's predicted path.

Launch, and make your pitchover in roughly the right direction.

In map mode, try and keep your trajectory in line with the asteroid's path.

But if you've already launched into an orbit with the inclination way off, your next best option is:

Burn at or opposite the ascending/descending node to raise your apoapsis nice and high, but be mindful of how long your orbit will take. And you want your apoapsis towards the "open" side of the asteroid's path.

Burn to match inclinations at apoapsis, this will take much less delta-V than doing it in a low orbit.

Burn for ejection near periapsis.

I don't know if "making the target asteroid AN read 180" is very good advice... Unless I'm misunderstanding something That would mean your orbiting in the opposite direction of the asteroid, which means you have to dump ~ 2x your velocity in dV to match the asteroids orbit at that AN. E.g. if you're travelling at 500 m/s, you have to burn 1000 m/s

It applies for when you're going to intercept the asteroid in solar orbit. You leave along the path it's predicted to arrive, which means that when you're still in Kerbin's SOI you want an inclination 180 degrees from the asteroid's predicted path. Edited June 12, 2014 by cantab

[problemecium]

Did- did I just read someone say Es can run over 3 THOSAND tons?

Can somebody verify that, i.e. point me to some kind of reference for size classes vs. mass? I thought I remembered from one of the streams back around the update that Es run up to about 30 tons. That I can handle. 3000 is another matter.

[cantab]

E class asteroids certainly do run up to three thousand tons, with rumours of even heavier ones. Here's the one I encountered:

Big E Class by cantab314, on Flickr

The only thing clawed is the little "lander" you can see, so almost all the mass given is that of the asteroid. I didn't even try to move it, the mission was a simple visit.

[Claw]

If you are using my tutorial, it is meant for you to launch along the inbound leg of the asteroid. The inbound leg does not have the circle on it (the circle shows Kerbin escape). If you follow the pictures and description, it shows that you need to warp time until the launch pad is under the asteroid's path. Then launch toward the inbound leg. You must also target the asteroid in order to get all the info to show up. If you do all that correctly, you AN will end up as 180 (or close to it).

If you have already launched the other way or your orbit isn't aligned, then it's too late to follow the first several steps of my tutorial. If you try to reverse your orbit, it will cost a lot of dV (unless you do some other tricks).

Also realize that you need to plan a dV budget for getting there. So far all we have been discussing is dV to move the asteroid.

[Stickyhammy]

Yes I tried to follow that tutorial. But the problem is "launch towards the inbound leg" I know what the inbound leg is but my problem is launching along the right inclination. The new launch rocket thankfully doesn't rotate so I can put myself into any orbit, even polar, with no problem. I just don't seem to be very good at lining up the leg or something. Maybe if I do it enough times I will do it right and I will understand. It only takes me one success before I can do it over and over forever.

I can keep retrying because when it doesn't work I just reset to launch and try again. I only have 130 days left to do it right. Cant be late.

Edit: I am going to try again launching along the brown line.

Edit: That got my to 135.8 AN Logic suggests I need 40 more degrees so I will launch along the 45 line next.

Edit: Launching along the 45 line put me 42 degrees AN from my other ship I left in orbit. But 134.2 to the asteroid. This leads me to believe I can launch normal at 90% for best fuel and its in fact the pink marker that needs to be sitting on a different line. This is why I am confused as the tutorial to me suggests I launch along different lines.

Edit: I give up. Launched at 90 with the picture below and ended up with 106 degrees. I don't know why. Looking for a solar intercept orbit tutorial for kerbals with stupidity at maximum level if anyone has one.

Edited June 13, 2014 by Stickyhammy

[Claw]

Inclination is not the same as cardinal direction. If you launch straight east, your Kerbin inclination is zero.

Let's look at the last picture. Hopefully that orbit line is in front of Kerbin (sometimes it disappears when you zoom in). Make sure it is in front, and not behind. Based on what you said, I think your inbound leg is down and to the left.

The reason why your inclination is 106 when you launched east is because the inbound leg is 106 degrees clockwise from straight east. So you really need to launch on an orbital heading of around 196. It actually looks slightly more than that to me, but it's a start. Also, you MUST make sure you time warp and launch when KSP is on the correct side (under the orbit). Don't be on the far side when you launch, or you'll be going the wrong way.

Perhaps it would make more sense to simply try a launch, and burn toward the heading you think. Watch the map. If your orbit line doesn't line up with the asteroid, try turning your ship more. Remember if you launch to the west, you need to give the orbit line time to switch direction.

[Stickyhammy]

I decided since I had 122 days and unlimited budget i would just take the hit and burn to 180 AN with the asteroid. I am now refueled and I think heading in the right direction. The next step should be to launch towards the asteroid. If everything is setup properly I should be able to reach it soon. Here is the setup in case I am missing something. Interesting note launching the fuel ship with a Kerbin inclination of 72.4 degrees got me right on track. My fuel ship had more fuel left then the ship i am using to grab the asteroid with. Oh well.

Looks like its working. Got the intercept down to 800ish. As Applejack would say, Here I go!

Edited June 13, 2014 by Stickyhammy

[Stickyhammy]

I made it to the asteroid. It weighs approx 3470 tons so its a small one. Very sad. I have 70 days before I enter Kerbins Soi, so plenty of time to figure out how I am going to bring it into an orbit with my paltry delta V. Suggestions are welcome. My current plan is to attach as close to the orbit retrograde marker as possible and burn for all I got and maybe she will enter a capture orbit.

[Kasuha]

I made it to the asteroid. It weighs approx 3470 tons so its a small one. Very sad. I have 70 days before I enter Kerbins Soi, so plenty of time to figure out how I am going to bring it into an orbit with my paltry delta V. Suggestions are welcome. My current plan is to attach as close to the orbit retrograde marker as possible and burn for all I got and maybe she will enter a capture orbit.

http://i59.tinypic.com/207apg6.jpg

Gravity slingshot off Mun can save you a hell lot of dv to get it into orbit in Kerbin SOI. And from this distance it may still only need a kick in single units of m/s.

[Stickyhammy]

It would seem I dont have the power to do anything but start the asteroid spinning. Even if center of mass as close as i can make it to the claw on point, lined up with the green retro orbit marker the speed never changes. Go low power or full blast it doesn't budge. Rocket may swing to the side then get pulled back when the asteroid starts spinning. Once that happens its all she wrote. Maybe I am doing it wrong or I might need bigger engines. Whatever the case it seems this time around the block I cant orbit the rock.

[Stickyhammy]

Never send a probe to do a Kerbals Job. I had 69 days so I sent a new ship piloted by Melvin. 6 engines, 13 advanced SAS, 8 nuclear reactors for power, and front mounted asteroid floodlights. May Melvin fair better than the probe.

Edit: Melvin should have stayed home. Somehow my arrival and clamping the asteroid has pushed it even farther from Kerbin. After less than a week of time acceleration i lose my Kerbin intercept. Melvin what have you done?!

Last Edit for post: My question was answered so I can let this post stop now. I have not yet finished my asteroid moving but I have high hopes. Reloaded to 70 days before I sent my mover ship to the asteroid. Also built an rcs prober ship. Has 6 small clawing RCS-Inlines that I can spike into the asteroid on different spots. That combined with the power of the ship pictured above should be enough. Thanks to all for your help.

Edited June 13, 2014 by Stickyhammy