General Question Earth's SOI in Orbiter

[Peter3210]

What is the Earth's sphere of influence in Orbiter? I couldn't find that information in the manual. I'm trying to do a retrograde burn inside the Earth's SOI to trim the ship's radial and tangential velocities to zero relative to Earth. I may be mistaken but it appears that one must be inside Earth's SOI to do that.

Thanks,
Peter

 

[kuddel]

I don't think Orbiter "uses" or "implements" any specific SOI. This "boundary" just happens to be at the logical right 'place' in Orbiter.
See http://en.wikipedia.org/wiki/Sphere_of_influence_(astrodynamics)
for actual values if you need 'em.

/Kuddel

 

[Ripley]

I'm not sure to understand your question 100%, but fire up IMFD and it will show you the SOI for each planet.

 

[Urwumpe]

Sphere of influence only means, being in a place, where Orbit MFD shows a green "gravity quality" indicator at the bottom and thus, in a place where maneuvers based on the theory of Kepler orbits are possible (All other gravity sources can be ignored safely).

 

[Screamer7]

The Sun and every planet have a SOI.
The Sun SOI is by far the greatest, followed by Jupiter etc.
You can imagine the SOI as a gravity well.
The closer you are to a planet, the greater the SOI.
In Orbiter the SOI is represented in the ORBIT MFD.
I see it like this:
An SOI of 1 is 100 %. This is normally a LEO Orbit.
An SOI of 0.50 is 50 % and a SOI of 0.10 is 10 %.
That means that the Earth attract you with 10 % of it's gravity and the Sun with 90 % with it's gravity field.
Maybe you are close to the Moon and that means the Earth gravity field attract you with 10 % and the Moon with 90 %.
Just switch the Orbit MFD reference to the closet body will reflect that.

 

[Peter3210]

Thanks everyone. Just to clarify the reason I asked about Earth's SOI, here's the problem I encountered: I was in Low Earth Orbit and engaged the main thrusters to take the XR5 Ravenstar out to an altitude of 700,000 km (outside of Earth's SOI); I then did a retrograde burn and engaged the thrusters until the ship's radial velocity with respect to Earth was zero. Then I used Attitude MFD to point the ship's longitudinal axis toward to center of Earth. I then engaged the main thrusters and accelerated to 2 km/sec in an attempt to impact the Earth but instead I headed away from Earth rather than toward it. When I did the same thing from an altitude of 70,000 km (inside Earth's SOI) I did indeed impact the Earth. I was wondering what accounted for the difference. Why did the ship move away from the Earth when I started from outside Earth's SOI?

I believe that Urwumpe answered the question when he said that "Sphere of influence only means, being in a place, where Orbit MFD shows a green "gravity quality" indicator at the bottom and thus, in a place where maneuvers based on the theory of Kepler orbits are possible". When I was 70,000 km from Earth the Orbit MFD showed 0.82G in green characters at the bottom of the display however when I was 700,000 km from Earth Orbit MFD showed 0.05G in red characters. If I understand Urwumpe correctly that would mean that even though the gravitational field was 5% of Earth gravity at 700,000 km I was outside the sphere where a Keplerian orbital maneuver with respect to Earth was possible.

Thanks again,
Peter

 

[Urwumpe]

Thanks everyone. Just to clarify the reason I asked about Earth's SOI, here's the problem I encountered: I was in Low Earth Orbit and engaged the main thrusters to take the XR5 Ravenstar out to an altitude of 700,000 km (outside of Earth's SOI); I then did a retrograde burn and engaged the thrusters until the ship's radial velocity with respect to Earth was zero. Then I used Attitude MFD to point the ship's longitudinal axis toward to center of Earth. I then engaged the main thrusters and accelerated to 2 km/sec in an attempt to impact the Earth but instead I headed away from Earth rather than toward it. When I did the same thing from an altitude of 70,000 km (inside Earth's SOI) I did indeed impact the Earth. I was wondering what accounted for the difference. Why did the ship move away from the Earth when I started from outside Earth's SOI?

I believe that Urwumpe answered the question when he said that "Sphere of influence only means, being in a place, where Orbit MFD shows a green "gravity quality" indicator at the bottom and thus, in a place where maneuvers based on the theory of Kepler orbits are possible". When I was 70,000 km from Earth the Orbit MFD showed a 0.82G in green characters however when I was 700,000 km from Earth Orbit MFD showed 0.05G in red characters. If I understand Urwumpe correctly that would mean that even though the gravitational field was 5% of Earth gravity at 700,000 km I was outside the sphere where a Keplerian orbital maneuver with respect to Earth was possible.

Yes.

If you are near Earth, stopping and accelerating towards Earth puts you into a highly eccentric orbit or even hyperbolic Orbit with very low perigee, usually below Earths surface.

if you are far away from earth, you are rather in an orbit around the sun. Just stopping relative to Earth and then accelerating towards Earth is now changing a solar orbit. depending on the direction in which you left Earth, it can have various effects, if you execute your maneuver, but it should not make you collide with Earth. Alone stopping your motion relative to Earth will often have the effect that you will after a few seconds start moving away from Earth, the direction depends on where you are relative to Earth and Sun.