Asteroid Capture Difficulty vs. Your Expectations

[TheBadAstronomer]

To be honest, I thought it was much easier than expected. My C class asteroid was nearly in orbit once it entered Kerbin's SOI, so I only needed a 20 m/s burn to capture it. Because I had tons of delta v left, I decided to land it. Next time I'll try my hand at an E class asteroid!

[elxverde]

Way easier than what I expected. I admit my first capture (100000kg C class) required more than one ship, but it included an orbit reversal (from 180º to 0º inclination) which was possible only thanks to the Mun. With the second asteroid (30000kg B class)I pulled a NASA and even used SLS replicas to do it, easy as all hell.

First asteroid is on a synchronous orbit:

http://i.imgur.com/GOG2YCH.gif

Second one is on a retrograde 100x100km mun orbit.

I think the harder part for most people is the initial rendezvous with something so close to Kerbin but so far at the same time (inclination/radial wise), once you overcome that, it's a cakewalk.

That's a great gif.

I like that the results are pretty even right now. I'm planning to build a protective Dyson shield with asteroids. It'll make for an interesting game of pinball when one gets hit.

[bsalis]

I would say rendezvous was easier than expected. Mainly because I was expecting the Roids in highly elliptical solar orbits.

Have captured a Class-A into Kerbin orbit. That was easy. Number two is a class E.... well... that's a different story that is still being played out.

[Voculus]

The one and only asteroid I've "mated" with was a class E. Kerbal Engineer reported over 5000 delta V prior to latching on, which then droped to 19 with the additional mass! Holy buckets! Not sure how I'm going to wrangle one of those monsters, unless I find one in a more favorable orbit.

[Sean Mirrsen]

Way easier than expected for me. The new rocket parts make lifting an intercept vehicle out of the atmosphere a breeze. Even if I weren't using the small VASIMR from Near Future Propulsion as my transfer engine, the catch-up-and attach maneuver, even though it required split-hour timing on the orbit (did a bi-elliptic transfer with orbit reversal at high apoapsis to align course... asteroid's time to flyby periapsis - 11 days; my time to high apoapsis - 5 and a half days), took barely any effort at all, and even after pushing the asteroid into a stable orbit around Kerbin, my craft returned with way more than half its fuel (Argon) tanks full. If I did it stock, I would have been cutting it far closer, but the maneuvers themselves were trivial, especially with how much lift capacity you get out of very simple rockets.

It would probably be very different in career, with research and costs factored in, but the principle of the thing was not very difficult at all.

[Mr. Speed]

I thought it would be a bit harder, but I haven't yet captured an E class asteroid. I decided I would do it without nuclear engines and that is perfectly doable. The first asteroid I captured was about 40 tonnes and I grabbed it before it entered kerbins SOI. as luck would have it my tug was perfect for an object this size. Initially it would have a very high periapsis just barely entering kerbin SOI but because of the early capture I could get it in a 300 by 400km equatorial orbit without a refuelling mission. the second asteroid I captured was way heavier and I grabbed it only one hour before periapsis. It was in a about 200 tonnes and I had to refuel it two times before I got it from its retro obit to a prograde orbit of 200 by 600. A final mission with an updated tug with 4 little RCS reaction wheel probes to grab the asteroid from the sides gave much better control, and I now have the two asteroids docked together in a circular 200km orbit. Station building can now begin!

[WhiteWeasel]

For those wondering how big a class E is:

[BrianMcNett]

Orbital mechanics... Understanding the math makes missions easier.

Okay... Working on some orbital mechanics. Trying to capture a class-B asteroid.

Asteroid PJF-369 has a current velocity of 9512 m/s, and is at an altitude of 13,567,000km. It will intersect the orbit of the planet Kerbin in 66 days, 2 hours, 23 minutes, reaching perike (Kerbin periapsis) of 234.34km in 72 days 5 hours 13 minutes.

How fast will it be going at periapsis, and how much delta-v will be required to circularize its orbit around the planet Kerbin?

Bonus question: After orbit circularization, how much additional delta-v will be required to a) reduce orbital inclination from 12.5 degrees to 0 degrees, and reduce orbital altitude by 34.34km?

It is not necessary to answer these questions. This is the math problem I've handed myself. Because I am cruel and inflict harm on myself.

BTW, captured my very first asteroid (a class-A) in just one attempt. Then had to rescue the crew because I didn't have enough fuel to perform an inclination change from 75 degrees. Decided to automate future captures. Jeb can plant flags on them when they're in Kerbin orbit.

- - - Updated - - -

And if they gave me "word problems" like this in school I'd have done them with glee.

[SkyRender]

Orbital mechanics... Understanding the math makes missions easier.

Okay... Working on some orbital mechanics. Trying to capture a class-B asteroid.

Asteroid PJF-369 has a current velocity of 9512 m/s, and is at an altitude of 13,567,000km. It will intersect the orbit of the planet Kerbin in 66 days, 2 hours, 23 minutes, reaching perike (Kerbin periapsis) of 234.34km in 72 days 5 hours 13 minutes.

How fast will it be going at periapsis, and how much delta-v will be required to circularize its orbit around the planet Kerbin?

Bonus question: After orbit circularization, how much additional delta-v will be required to a) reduce orbital inclination from 12.5 degrees to 0 degrees, and reduce orbital altitude by 34.34km?

It is not necessary to answer these questions. This is the math problem I've handed myself. Because I am cruel and inflict harm on myself.

BTW, captured my very first asteroid (a class-A) in just one attempt. Then had to rescue the crew because I didn't have enough fuel to perform an inclination change from 75 degrees. Decided to automate future captures. Jeb can plant flags on them when they're in Kerbin orbit.

- - - Updated - - -

And if they gave me "word problems" like this in school I'd have done them with glee.

I can help you work out that information, but if you can give me the mass tonnage for the asteroid as well, I can also tell you what kind of dV you can expect from whatever ship you send up once it has its payload grappled. Because as ever, the more mass you're trying to move, the lower your dV budget gets no matter what you're pushing it with.

[BrianMcNett]

Class-E is big. I'm working my way up to it. Eventually, class-E will be the only asteroids I'm interested in, but for now, I'm working on class-B asteroids.

[SkyRender]

Class-E is big. I'm working my way up to it. Eventually, class-E will be the only asteroids I'm interested in, but for now, I'm working on class-B asteroids.

Fair enough. That said, even Class-B asteroids will lower your ship's dV, potentially by quite a lot if you're using engines with an already poor ISP.

I can tell you right away, incidentally, that the capture dV necessary for that asteroid will be fairly small (probably less than 100m/s, without actually running any calculations on it), but the circularization burn will be far larger due to how low the orbit is. Expect to need at least 2000m/s dV, and that's post-attachment dV I might add. As for adjusting inclination, as long as you do your maneuvers at or near the slowest point in the orbit (ie. just barely capture the rock and rotate it on its axis at apoapsis), you'll barely need any dV to do so. In my experience, 50m/s is overkill for an inclination change of 45 degrees when out that far, just to give you some idea of how easy that part will be. So if you want to be safe, send up a ship that will have about 2500dV once it's intercepted and attached, accounting for the added weight of several tonnes of dead weight. If you want more exact numbers, we'll have to get into some rather annoying calculations to get the inverse of the semi-major axis to calculate the velocity of the hyperbolic trajectory at periapsis. That's the most valuable piece of information at this point, since our primary unit of change is m/s.

[BrianMcNett]

I can help you work out that information, but if you can give me the mass tonnage for the asteroid as well, I can also tell you what kind of dV you can expect from whatever ship you send up once it has its payload grappled. Because as ever, the more mass you're trying to move, the lower your dV budget gets no matter what you're pushing it with.

Is there a way to derive that information? I know that it's a class-B, which is between 4m and 7m in diameter. It's not possible to obtain the mass of the object directly that I can see. Am I missing something?

[SkyRender]

Is there a way to derive that information? I know that it's a class-B, which is between 4m and 7m in diameter. It's not possible to obtain the mass of the object directly that I can see. Am I missing something?

If you view it on the map screen from any vessel you've already launched, you can get its orbital parameters (including its mass). If I remember right, Class-B asteroids tend to be real lightweights, maybe 20 tonnes at most. Basically they're pretty close to the mass of an orange fuel tank; not certain since I've never bothered with anything quite that small.

[BrianMcNett]

The good news is that I have just around 10,000m/s delta-v, NTRs are the way to go, so iSP is around 800s, TWR for this 0.54 (poor, but usable). It may be overkill, fuel is a Jumbo-64 and an X200-16. I'm not entirely stock, the engine is from a mod, but its stats are balanced.

I may have enough info here to derive the semi-major axis of the encounter parabola. Knowing that, and Kerbin's mass, Kepler's Third Law would give the mass of the asteroid, but until I do that, I'm going to use your figures as a ballpark.

Just for the record, MechJeb2 isn't particularly useful for asteroid encounters just yet. I'm running a dev build, which is the only thing compatible with 0.23.5 yet. I expect that complaints about MechJeb and docking will soon be a thing of the past, after playing with this build, but for the moment it's not at all useful for catching asteroids. Kerbal Engineer also falls short (can't see asteroids), but at least I have statistics I can look at, which is helpful when doing calculations.

So... Here's my unmanned asteroid interceptor, all 57 tons of it. Should have shown off the launch vehicle. It was BIG.

[SkyRender]

That craft could capture and circularize a Class-B at your intended height, no problems whatsoever. Or even a class-C for that matter. Class-D would be a bit trickier to pull that off (but still doable), and Class-E would be a "no way in heck" scenario for anything save capture. (Class-E asteroids really are that huge!)

[RocketPilot573]

I chose an E for my first asteroid, it is harder than I predicted....

And it's even more difficult because my mission plan says that I need to soft land it at my Minmus Base.

[SpaceSphereOfDeath]

I've currently got 2 C types and a D type orbiting kerbin and a class B soon to be around the Mün.

So it's safe to say I found it easier then expected

[NeoMorph]

I made a BIG mistake with my first try (even though I got my 104T rock into Kerbin orbit)... I WAYYYYYY underestimated the amount of RCS fuel I would need due to the fishtailing.

[The Destroyer]

I landed an asteroid, class A, in Kexico. Now, the real challenge- bringing it to the KSC!

[BrianMcNett]

A useful bit of information about bodies in parabolic orbits:

"At any position the orbiting body has the escape velocity for that position." http://en.wikipedia.org/wiki/Parabolic_trajectory

This would have saved me a lot of trouble remembering that from the start. One need only know the escape velocity for Kerbin from the altitude of the periapsis to get a rough idea of how fast an object on a parabolic encounter at that altitude will be traveling. For a hyperbola, you have "excess orbital velocity," that is velocity in excess of that needed to escape the SoI. Not all encounters will be true parabolas, but close enough.

[Superfluous J]

I'm starting to wonder if I can attach wings and a probe core (and maybe landing gear. Who knows) to an asteroid and land it on the runway.

[DaPatman]

Given the following:

(a) I have never successfully docked two ships together

( The first asteroid I went for was an E class on a collision course with Kerbin

© The ship I sent to divert its course had no monopropellant

(d) Despite all this, I didn't just divert its course, but also put it in a ~10km x ~10,000km highly inclined retrograde orbit

I have to say actually capturing an asteroid is actually pretty easy, thoygh having said that, I imagine doing anything more complicated with an E-class' orbit is alot harder.

[Carter]

I'm not very good at KSP and I get hung up in the design phase for 90% of the hours I put in. The Career Mode Update helped with that a lot, and it forced me set up landing missions on Mun and Minmus that I never would have before, and just before my last hiatus I actually did a flyby of Duna because I was starving for science. I had never done interplanetary before that.

Now these asteroids are flying around and I've got new parts with which to go get them. After getting a little inspiration from the forums I slapped together a bunch of fuel, RCS, and four nukes on top of the launch engines and with just two or three trial-runs to work out kinks and deficiencies, I went chasing after a Class E coming in on a 285 degree trajectory. All I did was force it to get captured, by orienting my nose retrograde and then translating to get the COM under my claw, it was no fuss. I had to detach and reattach several times because I'd lose control while burning, but seeing that for every second I burned I added several hours to its escape time, it was stress free. My Kerbin system now has a fourth body named The White Whale.

http://imgur.com/a/SOvlk

[helaeon]

Both way easier and way harder.

Way harder in that I spent a lot of time contemplating what I needed my first ship to do what any kind of retro engines would need to be like to kill relative velocity, that kind of thing.

Way easier when I grabbed my first A class realized it was tiny so, re-directed it to land within 2 km of KSC because I had a lot of deltaV left in my ship once I grabbed it. I was expecting 100T for the little ones and something more like 100,000T for the E classes. Where getting them moved just enough to not hit anything (or the other way around) would be a challenge. Instead A class was more like 10 tons. My landers are heavier than that!

[ScottyDoesKnow]

Rendezvous was easier than I thought. It felt really strange working with both Kerbin and the sun's SoI but it all worked out. Pushing a class E was a bit harder than I'd imagined, and can be really painstaking with a TWR of 0.04.

PSA: remember to change inclination as far out as possible. Took me 3 hours of burning and 2 700t ships of fuel for a 2000 m/s inclination change.