Using Venus in the Parker Solar Probe mission

[sophiecentaur]

The Parker Solar Probe mission will be launched soon and I was reading that it will use gravity assist from Venus to bring its orbit closer and closer to the Sun over about seven years.
The diagram in this link shows the plan for seven flyby's of Venus to lower the orbit. Now, to get down close to the Sun, the probe needs to lose potential energy so , unlike with space shots that take probes to outer planets, where the probes acquire Kinetic Energy on their flyby's, the probe's orbital energy needs to be reduced. So it looks like the probe needs to pass Venus 'on the other side' so that it accelerates Venus and slows down the probe, just as if it were using retro rockets.
Can someone confirm this or put me right on the details, please?

 

[sophiecentaur]

I'm bumping this because it strikes me as a topic worth discussing - when you read so many comments about getting out of the Solar system using the same method.
I'm wondering about posting a similar question in General Physics.

 

[JMz]

The Parker Solar Probe mission will be launched soon and I was reading that it will use gravity assist from Venus to bring its orbit closer and closer to the Sun over about seven years.
The diagram in this link shows the plan for seven flyby's of Venus to lower the orbit. Now, to get down close to the Sun, the probe needs to lose potential energy so , unlike with space shots that take probes to outer planets, where the probes acquire Kinetic Energy on their flyby's, the probe's orbital energy needs to be reduced. So it looks like the probe needs to pass Venus 'on the other side' so that it accelerates Venus and slows down the probe, just as if it were using retro rockets.
Can someone confirm this or put me right on the details, please?

The figure is not helpful for your questions, but you are correct. In Venus's frame, the probe accelerates it slightly by passing "in front" of Venus on the probe's path to the inner Solar System and pulls it to a higher orbit. "In front" here means, in the direction of Venus's instantaneous orbital velocity -- let's say, for concreteness, that means between Venus and Antares at that moment.

Conversely, in the probe's frame, by passing between Venus and Antares (they agree on the geometry when expressed this way!), the probe experiences an acceleration that sends it more directly toward the Sun. Even though its asymptotic speed [that is, pre & post-encounter] relative to Venus does not change, it has given Venus some of its orbital energy and "falls" into a smaller orbit about the Sun.

 

[sophiecentaur]

it has given Venus some of its orbital energy and "falls" into a smaller orbit

I guess that's oneway of describing what goes on. But, if there is just a change of direction, with no loss of speed (KE), then where is the equivalent action of a retro rocket which is the more common way of dropping down an orbit?
The retro rocket method involves a (-KE) burst whilst at apogee to reduce orbital energy. Your interpretation implies a change in position, after passing by Venus. That's hard to visualise but I could be convinced, I suppose.
PS I take your point about the usefulness of the diagram but it's all I could get hold of.

 

[sophiecentaur]

@JMz I just re read your post and I had missed out the Frame of Venus bit. Its KE is not changed in that frame but are we not concerned by the KE change in the Sun's Frame?
I don't think this needs to be pursued much further as I am getting the idea now.
Cheers.

 

[JMz]

Sounds good. You might see some more useful material on this at https://en.wikipedia.org/wiki/Gravity_assist