# Entering the Sphere of Influence

1. May 30, 2004

### Venus50

In an article by Larry Bogan " The Orbit of a Space Probe from Earth to Jupiter",it mentioned about a slingshot or gravity assist by the planet-Jupiter and this could change the orbit and velocity of the space probe that leaving the Sphere of Influence[SOI].In entering the SOI of the planet[by the already calculated Transfer Orbit of the space probe] the space probe would intersect with the planet's orbital path at an angle and a velocity. This means that the space probe would exactly hit the planet if no any trajectory correction is made during entering the SOI.The trajectory correction of the space probe should be made by controller on Earth,right?,to avoid collision with the planet.What I wonder and would like to ask is ,[1] at which point the trajectory correction of the space probe should be made?At the point of entry to SOI or it could be at any point closer to the planet,of course,before collision occurs.[2]The velocity of the space probe at the point of entry to SOI would not be the same as that at the interception point[the point of Rendezvous],right?. So,actually,the calculations of the space probe velocity relative to the planet by different values[point of entry vs interception point]should give different space probe relative velocity to the planet and hence the direction of the vector. This would affect the "Angle of Trajectory Correction". Is that right? Thank you so much.

2. May 31, 2004

### remcook

Really? Why is that?

3. May 31, 2004

### Janus

Staff Emeritus
No. The probe is given a trajectory upon launch that would cause it to miss the Planet by some distance (called the Impact parameter). By picking the right trajectory at launch, you get just the right exit angle and velocity you want upon exiting the SOI. The only reason the probe would be on an course to hit the planet would be if that was the purpose of the mission.