I was looking at
http://cristianopi.altervista.org/as/ and selected the Juno probe.
One of the graphs shows Juno approaching Jupiter from the "Sun" side, then "backing" into the eventual orbit. I think I heard that some Mars probes have done that too, rather than approaching from the "outer" side and going head-first directly into the eventual orbit.
This is a fun detail to think about, and might fit into this Q&A thread:
Q1) What are the trade-offs in using either approach method? Direct orbit entry verses "backing" into the orbit.
Q2) Could an approaching probe/capsule/lander even optimize the backing" maneuver so as to meet the planet at almost no (or minimum) relative velocity, hence reducing the heat-shield requirement needed to enter the atmosphere?
Q3) The "backing" maneuver seems to be used when approaching an outer planet from an inner planet (eg: probe is going from Earth to Mars). What are the issues in a probe/capsule returning to an inner planet (eg: Mars to Earth)?
Image from the referenced site showing Juno approaching Jupiter is attached: "Sun"-side is to the right. You can see Juno (green color) approaches, slows, and "backs" into Jupiter to be captured.
Q1 - "Backing" in to the orbit is the more energy efficient one, since you are doing the opposite of a typical momentum transfer slingshot - but instead the planet helps you slow down. That will reduce the delta-v needed to capture into an orbit of the planet, BUT it will tend to leave you in a retro-grade orbit. (Bad if you plan on reaching the moons)
Q2 - No, there is no such trajectory. If there was, the opposite trajectory would also exist, where you could leave a planet with no or minimum relative velocity.
The best way to learn about this stuff is to play Kerbal Space Program.
There are also 'low power' aerocaptures.
Several Mars satellites have done this.
Start off in the lowest energy transfer orbit, and then do a ~800m/s burn to put you in a week period orbit or so with a minimum distance of just over what you think the worst case atmosphere is.
Gradually lower your orbit until you start touching the atmosphere - gently enough that you can use solar panels as drag surfaces, and then carefully continue slowly braking down each orbit for a few months till you're in low orbit.
This is a much kinder gentler approach than hitting the atmosphere at 10km/s and relying on your atmospheric model being Juuust right.
