The terraforming of Mercury is a complex process that will require huge quantities of materials and many cargo ships filled with equipment. Then, when the planet will be terraformed, an orbital station will be needed for both passenger and cargo ships.
Interplanetary transport is cheaper with larger ships, that will be probably over 2 km long. It is difficult for such large ships to land. This is why Space Stations are needed in orbit around each planet. from there, people and goods will be transported to the surface with smaller landing ships. In addition, Trade Routes between planets are based on flight windows, which, in case of Mercury, occur at roughly 100 Earth days. Since flight windows are rare, it makes more sense to use large interplanetary ships.
The Base[]
Mercury does not host any natural satellite. Because it is close to the Sun, solar gravity is strong and Mercury's Hill sphere is very small. Also, since the planet has an elliptical orbit, gravity of the Sun increases and decreases, affecting the orbits of any satellites. On a long time scale, an orbital station will be ejected into a heliocentric orbit or will collide with Mercury. NASA's probe Messenger maintained orbit for a limited time using propellant, then impacted the planet.
At Mercury's orbit, there are a few hazards. First of all, the Solar Constant has a high value, meaning that it is very hot, with average temperature reaching 400 C. It is an environment with high luminosity. Secondly, solar flares have a strong effect on any spacecraft and on any electronic device. Mercury has its own magnetic field, but it is too weak to completely protect an orbital station. A third hazard comes from a higher risk of meteorite impact. Being closer to the Sun, meteorites fly with much higher speeds, as Mercury itself orbits the Sun much faster then any other planets.
The base has a big advantage, that there is plenty of light. Solar panels can provide enough energy.
NASA's Messenger probe had a large shield, always oriented towards the Sun, that protected it against solar radiation. In addition, the shield reflects light, keeping all instruments at a lower temperature. An orbital station must do the same, it must have a large shield, always pointing towards the Sun. Solar panels can be mounted on the shield or sideways.
The chosen orbit must be the most safe possible, to avoid using too much fuel. Around Earth, the orbital station can be placed on lower altitude, where it is protected by Earth's magnetosphere. In case of Mercury, there is little protection in outer space. A nearly safe orbit will be at 2000 km above surface. However, the station must have its own engines and stored propellant, to adjust orbit changes.
We can create artificial gravity by making the station to spin. However, this will make docking more difficult and will affect cargo transport. It should be better to only make some parts of the station rotate, allowing some gravity exist only for the area inhabited by people. For that reason, we can design a small part of the base to be wheel-shaped and to rotate slowly. However, it must be protected by the solar shield, or people will be fried by the extreme heat.
The base can support its own biosphere, it can produce food and oxygen by growing plants inside. However, given the proximity of Mercury and the fact that the base will be crowded only close to flight windows, there will not be a significant need of food, water and oxygen for lengthy periods of time. In these conditions, it could be better to ferry all goods from the planet.
Spaceport[]
Being close to the planet, a landing ship can reach the base at every Earth day. Passengers will not have to wait too much here. Still, they will need a to wait for a few hours. During this period, they will need to eat, drink water, breath and go to a toilette. A shopping center, a central dome, a coffee-bar and a few other facilities will be needed, maybe even a hotel. Also, the base will need enough electricity for periods of time with many visitors.
For cargo, things are a bit more complicated. Without gravity, ships will need to dock slowly. The base will have robotic arms that will help ships to dock. Then, other robotic arms will manipulate all cargo.
It makes highly plausible the use of containers, just like we see today on Earth. Most containers are of a certain type and can be easily maneuvered with the right equipment. Some containers, carrying frozen stuff, will need to be moved to certain areas, with access to electricity. However, even at the orbit of Mercury, it is easy to get low temperatures. A shield with very good thermal insulation will block all light from the Sun and will create temperatures below -100 C.
Fluids can be uploaded or downloaded using pipes and into large tanks. Everything that is liquid or gaseous on Earth, can be shipped as a liquid here.
Unlike the stations serving the giant planets (Himalia for Jupiter, Helene for Saturn, Perdita for Uranus or Halimede for Neptune), where passengers and cargo will have to wait for flight windows to reach the moons, for Mercury everything can be shipped from and to the planet fast.
Flight Windows[]
For Mercury, flight windows are more often then for other planets:
Mercury - Venus: 143 Earth days Mercury - Earth: 115 Earth days Mercury - Mars: 101 Earth days Mercury - Ceres: 93 Earth days Mercury - Jupiter: 90 Earth days Mercury - Saturn: 89 Earth days Mercury - Uranus: 88 Earth days Mercury - Neptune: 88 Earth days.
These flight windows take into consideration only alignments of the two planets and don't account for additional gravity assists or deep space maneuvers. For passenger ships, direct flights will be more convenient, while for cargo, the chosen routes can take into account additional flybys of Venus or Earth.
Suppose that a ship will be launched each time a flight window occurs, we will have a total of 29.71 launches per Earth year or a launch at every 12 Earth days. If we consider both launches and landings, we will have one flight event every 6 Earth days. Compared to any other space station in the Solar System, Mercury station has the highest number of flight windows.
Because of this, sometimes Mercury will be used as a bypass destination. For example flight windows between Mars and Jupiter occur at every 816 Earth days, but traveling through Mercury, you might find a connection more often. Because of this, some people will prefer to make a stop of up to 50 Earth days on Mercury and visit the planet.
Delta-v[]
The Delta-v shows the energy needed to send a ship towards other planets. For Mercury, the delta-v chart is as follows:
Mercury station – Venus Space Station 13.987 Mercury station – Earth Space Station 19.309 Mercury station – Mars Phobos 22.566 Mercury station – Ceres Space Station 24.871 Mercury station – Jupiter Himalia 27.677 Mercury station – Saturn Helene 30.457 Mercury station – Uranus Perdita 28.699 Mercury station – Neptune Halimede 24.564 Mercury station – Pluto Styx 23.921 Mercury station – Eris low orbit 23.472 Mercury station – Sedna low orbit 21.676
Mercury station – Mercury orbit (100 km) 0.851 Mercury station – Mercury surface 3.095
For comparison, an Earth surface - Moon surface flight will require a delta-v of 14.466.
One can see that flying between Mercury station and any other station in the Solar System will require a lot of energy. However, because Mercury is close to the Sun, ships can take advantage of a space sail. Economic engines like the ion engine can be used with great results.
Traveling between various orbits around Mercury is not expensive. Once Mercury will be terraformed, landing will be more easy with the use of a parachute. Sending a payload from Mercury surface to the station requires a delta-v half that of Earth.
Special Ships[]
Flying to or from Mercury is difficult. First of all, ships must have shields against solar radiation and heat. Not every spaceship is prepared for this. And secondly, because Mercury is so close to the Sun and it has a high orbiting speed, sending a ship from Earth to Mercury requires the same amount of energy like sending a ship from Earth to Pluto.
On the other hand, because Mercury is close to the Sun, the use of solar-powered ion engines and of solar sails is feasible. Ships can travel much cheaper using these technologies.
Mercury is a good destination for mining, since it has huge deposits of metals. Refined ores can be transported to the space station, then shipped to other destinations using large solar sails.
The Mercury station will be of crucial importance for terraforming and later for colonizing the planet. Settlers will use the station as their gateway to Mercury. Also, the station will be of high importance for the economy. Freight can be sent from the planet, from many surface bases, towards the space station, where large interplanetary ships will transport all the goods to each destination of the Solar System.