is it possible to put a ship stationary right at mun-kerbin barycenter

[lammatt]

if i gravity hack and put a ship right at mun-kerbin barycenter, with zero relative speed to kerbin and switch off the gravity hack, will i be able to stay still there?

[Maddmatts]

There is no barycenter for the same reason there are no Lagrange points. KSP's handling of planetary orbits and gravity doesn't allow for it.

[Spanier]

Even in real world this would be impossible, as the barycenter lies within the earth

[Pulstar]

That and the barycenter would be located under Kerbin's surface anyway IIRC.

EDIT: ninja'd

[Crush]

There is no barycenter for the same reason there are no Lagrange points. KSP's handling of planetary orbits and gravity doesn't allow for it.

To be more specific: KSP only simulates the gravity of one celestial body at the time. So any physical effect which is caused by interactions between the gravity fields of more than one body (barycenters, lagrange points, horseshoe orbits, tides...) aren't modeled by KSP.

Why?

Because simulating multiple sources of gravity would make precalculation of the trajectories in real-time too complex to handle for an average computer.

[bsalis]

Even in real world this would be impossible, as the barycenter lies within the earth

Well technically you could. It just would not be a space ship.

Just some other kind of ship made of unobtanium as seen in many terrible movies.

[zarakon]

Because simulating multiple sources of gravity would make precalculation of the trajectories in real-time too complex to handle for an average computer.

And also too unstable. Since you can't program automatic stationkeeping, you would lose a lot of orbiting craft any time you time-warped for a year to go to another planet

[rosenkranz]

Even in real world this would be impossible, as the barycenter lies within the earth

Really? I know someone did the math for Kerbin-Mun and the barycenter would be within Kerbin but I thought the barycenter for Earth-Moon was farther out.

[Synapse]

As discussed in another thread I think you can come close to Kerbin whilst in the influence of Kerbol, so you can effectively hover near the planet ala barycenter.

What would be the purpose of sending a ship underground to the barycenter anyway?

[maltesh]

As discussed in another thread I think you can come close to Kerbin whilst in the influence of Kerbol, so you can effectively hover near the planet ala barycenter.

What would be the purpose of sending a ship underground to the barycenter anyway?

If the simulation is operating as intended, from solar orbit, you cannot get any closer to Kerbin than about 84,000 km without entering the sphere of influence of Kerbin.

[innovine]

Because simulating multiple sources of gravity would make precalculation of the trajectories in real-time too complex to handle for an average computer.

Doesn't Orbiter do this?

[jaredkzr]

Doesn't Orbiter do this?

Yeah it definitely does. The engines running each game are completely different but your average computer can do the necessary calculations.

Edited August 2, 2013 by jaredkzr

[lazarus1024]

Really? I know someone did the math for Kerbin-Mun and the barycenter would be within Kerbin but I thought the barycenter for Earth-Moon was farther out.

No. Earth-Moon Barycenter lies at .721 radii from the Earth's center, IE below the surface.

The only two bodies (of at least Dwarf planet size or bigger) that I am aware of that have a Barycenter above the surface of the "parent" body are the Sun-Jupiter Barycenter and Pluto-Charon. Sun-Jupiter is 1.07 Radii and Pluto-Charon is 1.83 Radii. So Jupiter is actually massive enough to tug the Sun around like that I think is hugely impressive.

Also Pluto-Charon was considered a double planet for a little while because of its large Barycenter. As a comparison Charon lies 19,800km from Pluto with a radius something over 1,000km. Puto has a radius a little over 2,000km, the Barycenter lies at close to 4,000km from the center of Pluto, so the Barycenter is roughly 20% of the distance of the orbit itself!

Edited August 2, 2013 by lazarus1024

[chaos_forge]

Another thing to note is that even if the Earth-Moon barycenter was outside the Earth, it would still be impossible to remain stationary at that point. The barycenter is the system's center of mass, but not the point where the gravitational pull from both bodies is the same. That point is actually pretty close to L1. If you stopped all relative motion at the Earth-Moon barycenter, you would simply fall back towards Earth.

[lazarus1024]

Very true. However, a system with equal mass planets rotating a common Barycenter (instead of an eccentric eliptical orbit, which is what is common with bianary star systems) you COULD park right at the Barycenter and you would stay put. Not sure if it would cause your ship to be pulled in rotation or not, I'd think it likely would force your ship to spin at a rate equal to the orbital period of the bodies. This is the only instance when one of the Lagrange points for a two body system is coincident with the Barycenter of the system

[Hello moto]

With the sun being jerked about by jupiter, that's gotta make you think about how that could affect seasons and temperature, (if measurable)

[tntristan12]

Doesn't Orbiter do this?

Orbiter has some stability issues. If only I got paid every time I had to restart because I had killrot activated during warp and sent it into an uncontrollable spin at about 9001 RPM. Furthermore, Orbiter doesn't have to also worry about simulating the stresses between multiple parts.

[Brotoro]

I've had several of my rockets apparently attempt to reach the Kerbin-Mün barycenter... Especially if Jeb is driving.

[TouhouTorpedo]

Because simulating multiple sources of gravity would make precalculation of the trajectories in real-time too complex to handle for an average computer.

KSP already simulates the trajectory from the gravity influence directly when in off-rails mode, hence it is possible to affect trajectory just by turning your craft under reaction wheels, as its a little too sensetive. Adding in another gravity source would be no less taxing than adding one extra engine on a rocket, at least while off-rails. (<5x timewarp)

[Enigma179]

KSP already simulates the trajectory from the gravity influence directly when in off-rails mode, hence it is possible to affect trajectory just by turning your craft under reaction wheels, as its a little too sensetive. Adding in another gravity source would be no less taxing than adding one extra engine on a rocket, at least while off-rails. (<5x timewarp)

Yeah, as stated in a different thread, the issue isn't computer load. Your computer could handle it just fine. The issue is that if it weren't on rails, gameplay would be significantly less fun; if you sent a probe out to Jool, you'd have to timewarp a year forward, only to find that over the thousand or so orbits that occurred with your LKO station in orbit, the Mun and Minmus managed to jerk it quite a ways around, possibly even de-orbiting it. This means you'd have to constantly be stationkeeping, instead of just hitting time warp and getting a coffee.

[lammatt]

Another thing to note is that even if the Earth-Moon barycenter was outside the Earth, it would still be impossible to remain stationary at that point. The barycenter is the system's center of mass, but not the point where the gravitational pull from both bodies is the same. That point is actually pretty close to L1. If you stopped all relative motion at the Earth-Moon barycenter, you would simply fall back towards Earth.

o ya...

i think i had some misconception when i asked the question... and after reading a bit...

my question was indeed...

is it possible to put a ship at the barycenter with a motion such that it stays right at the barycenter's locus?

(it seems to me the loci of them are conic sections w.r.t either one of the two planets anyways (judging from the pics on wiki...))

---i aint physics/ math major.... those equations are almost Martians to me who happens to be a chemistry major graduate a few years ago and forgot most of my math training already

Edited August 2, 2013 by lammatt

[lazarus1024]

I don't believe you could.

[lazarus1024]

With the sun being jerked about by jupiter, that's gotta make you think about how that could affect seasons and temperature, (if measurable)

Probably pretty minor. The Barycenter of the sun with respect to all of the planets is of course maxed out when all of the planets are in alignment on the same side of the sun (this pulls it the furthest from the Barycenter). Jupiter has the biggest impact by far due to its mass (which is greater than all of the other planets put together). The further an object orbits and the greater its mass, the more it pulls the more massive object from the Barycenter. Saturn and the outer planets do not orbit far enough, nor have enough mass to influence the Barycenter of the Sun more than Jupiter does.

Overall influence I believe is roughly 1.8 Solar radii or something there abouts for the Barycenter. Of course this Barycenter wanders all the heck over the place as the planets move around in their orbits and tug differently. Its how we are able to detect planets around other Stars is by detecting the frequency shift in their light due to their planet(s) tugging their star around as they orbit (also by planetary occulation if/when a planet passes in front of its star with respect to the Earth).

Oh, uh, back to influence. Earth's orbit is at around 180 million km (rounded) and the Barycenter of the sun is only around 50,000km, so the Barycenter influence is less than 1%, which is a much smaller pertrubation than the eliptical orbit of the Earth around the Sun (which is, what? About 2-3%?)

[DMagic]

Probably pretty minor. The Barycenter of the sun with respect to all of the planets is of course maxed out when all of the planets are in alignment on the same side of the sun (this pulls it the furthest from the Barycenter).

And just as important to note, while Jupiter may pull the Sun around, it's pulling the Earth around at the same time. So if Jupiter is on the opposite side of the Sun, it's pulling the Sun away from the Earth's orbit, but it also pulls the Earth towards Jupiter, and therefore, towards the Sun.

My guess is that, over the 10 year orbit of Jupiter, there is only a negligible total impact on the distance of the Earth from the Sun. And, as you mention the other planets are scattered all around, pulling the Sun and the Earth this way and that way, making it all the more unlikely that this causes any real, short-term effects on the Earth's climate.

[lazarus1024]

And just as important to note, while Jupiter may pull the Sun around, it's pulling the Earth around at the same time. So if Jupiter is on the opposite side of the Sun, it's pulling the Sun away from the Earth's orbit, but it also pulls the Earth towards Jupiter, and therefore, towards the Sun.

My guess is that, over the 10 year orbit of Jupiter, there is only a negligible total impact on the distance of the Earth from the Sun. And, as you mention the other planets are scattered all around, pulling the Sun and the Earth this way and that way, making it all the more unlikely that this causes any real, short-term effects on the Earth's climate.

Mmm, good point.