Advanced Gemini-Agena Rendezvous procedure

Advanced Rendezvous procedure for Simplified Docking Unchecked settings.

Advanced Rendezvous procedure

This short guide will help you performing the Rendezvous procedure while piloting the Gemini
spacecraft. Then, you will be ready to catch up the Agena or another Gemini spacecraft by using this advanced rendezvous method. Warning: (This is Exclusive only for die-hard space exploration fans, any one else may suffer a lot of frustration).

If you are having trouble performing this maneuver and also have encountered frustration, this is your guide. Performing a real missions in a realistic way is something with not comparison, but first Let's get back to school for a while, so we begin with some basic concepts as follow.

Kepler's laws of planetary motion Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun, here are his three laws:

a. The orbit of a planet is an ellipse with the Sun at one of the two foci.

b. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

c. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit.

According to Kepler's laws, If the target vehicle is ahead in the orbit and the tracking vehicle increases speed, its altitude also increases, actually moving it away from the target. The higher altitude then increases orbital period due to Kepler's third law, putting the tracker not only above, but also behind the target. The proper technique requires changing the tracking vehicle's orbit to allow the rendezvous target to either catch up or be caught up with, and then at the correct moment changing to the same orbit as the target with no relative motion between the vehicles (for example, putting the tracker into a lower orbit, which has a shorter orbital period allowing it to catch up, then executing a Hohmann transfer back to the original orbital height, please see pic bellow).


Hohmann transfer orbit, labeled 2, from an orbit (1) to a higher orbit (3). In orbital mechanics, the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different radii in the same plane. In general a Hohmann transfer orbit uses the lowest possible amount of energy in traveling between two objects orbiting at these radii, and so is used to send the maximum amount of mission payload with the fixed amount of energy that can be imparted by a particular rocket. Non-Hohmann transfer paths may have other advantages for a particular mission such as shorter transfer times, but will necessarily require a reduction in payload mass and/or use of a more powerful rocket.


Advanced Rendezvous Procedure:

If the Target Spacecraft is ahead of our tracking Spacecraft in the orbit (far from us) and our tracking Spacecraft increases speed, its altitude will also increase and will move our tracking Spacecraft away from the target Spacecraft, since our tracking Spacecraft will orbit slower than before, since our orbit period becomes larger due to Kepler's third law.

If the Target Spacecraft is behind our tracking Spacecraft in the orbit (far from us) and our tracking
Spacecraft decreases speed, its altitude also decreases and will move our tracking Spacecraft faster getting it far from the target Spacecraft too, our tracking Spacecraft will orbit faster than before, since our orbit period will be shorter due to Kepler's third law.

So, after the final rendezvous burn, If you encounter the following scenarios, do as requested:

Case One: If the Agena is Forward ahead far from our Gemini Spacecraft:

1. Translate those OAMS thrust Backwards carefully, pay close attention to the telemetry, check
the Map to see the Speeds, velocities, Altitude etc. it is important to notice that our orbit
altitude decreases making our Gemini spacecraft to go faster and catch the Agena.

2. Our Gemini spacecraft will orbit faster, pay attention at the Agena because we will get closer
to it, translate forward if necessary to adjust speed as desired, the main task is to be as closer to
the Agena as possible.

3. If everything went fine, transfer back to your former orbit by using Hohmann transfer, do this
by simple requesting a new target burn.

Case Two: If the Agena is far behind from our Gemini Spacecraft:

1. Translate those OAMS thrust Forwards carefully, pay close attention to the telemetry, check the
Map to see the Speeds, velocities, Altitude etc. it is important to notice that our orbit altitude increases making our Gemini spacecraft to go slower and allowing the Agena to catch us up.
2. Our Gemini spacecraft will orbit slower, pay attention at the Agena because we will get closer to it, translate backward if necessary to adjust speed as desired, the main task is to be as closer to the Agena as possible.

3. If everything went fine, transfer back to your former orbit by using Hohmann transfer, do this by
simple requesting a new target burn.

Bibliography and some links:
https://en.wikipedia.org/wiki/Space_rendezvous
https://en.wikipedia.org/wiki/Kepler's_laws_of_planetary_motion#Third_law
https://en.wikipedia.org/wiki/Hohmann_transfer_orbit

Credits:
Manual Author: Hector Melo aka: "Puma"
Reentry - An Orbital Simulator

For more info please visit:
https://store.steampowered.com/app/882140/Reentry__An_Orbital_Simulator/

[CapitanEvil]

Thanks that give me a good understanding of what happend and what to do