Helene is a small, prograde moon of Saturn. It is a Trojan of the moon Dione. From all the moons of Saturn, Helene is the best candidate for an orbital station, designed to handle the passenger and cargo traffic inside Saturnian System and towards other destinations in the Solar System.
Physical Characteristics[]
Helene is a small moon, about 40 km in diameter. It is made probably mainly of water ice. Nothing is known of its interior. What we do know is that its surface is covered with dust. This dust originates from the E ring, which is maintained from water plumes ejected by the active moon Enceladus. The dust is in fact ice, made of tiny particles, too small to cause damage to a spacecraft.
Helene has craters, which suggests that the moon is solid and not a pile of dust. So, it will not break apart.
Orbital Characteristics[]
Helene has the same orbital period with the larger moon Dione (it is a Trojan), orbiting in the leading Lagrangean point L4. From its relation with Dione, Helene benefits of a safe orbit. Perturbations from other moons will not pull it out of orbit. Also, Dione clears the path of meteors and debris. Still, particles that move relatively slow compared to the moon, are able to remain in orbit around Saturn in the same place with Helene. However, moon's tiny gravity cleans its nearby space.
As Helene shares the same orbit with Dione, it is close to all the other large Saturnian moons. Spaceships can reach Helene very fast.
Why Helene?[]
A space station can be free-floating in the space or can use the advantage of an existing small moon. A moon can host buildings beneath its surface, protecting cargo and passengers from impacts and radiation. Also, a moon has some gravity, preventing objects (like a not well anchored container) to escape into space. With small gravity, it is more easy for a large spaceship to dock on a small moon then on a planet or a large moon. Also, it is more feasible to send a single large cargo ship from Earth to Saturn then to send 10 smaller ships, one towards each moon. A space station is needed to sort containers and to facilitate transport between moons and with the other planets.
Saturn has many small moons, but the vast majority are not suitable for a space station. The inner moons, like Pan, Daphnis, Pandora, Janus or Aegaeon, orbit within the rings. There is a high risk of collision, especially for large interplanetary ships. The outer moons are too far away from the planet and many of them are retrograde. Luckily, Saturn has a few small moons between the large satellites, that are close enough and are on safe orbits. There are four Trojan moons: Telesto, Calypso, Helene and Polydeuces, with Helene being the largest of all. The other 3 moons are also suitable for a space station. Another moon, Hyperion, could be used for a base, but its much stronger gravity might be a problem.
The Base[]
We know nothing about Helene's interior. Given its small size and the large craters, we might say that it is not differentiated. The main component must be ice. The dust layer covering the moon is made if very small particles of ice, originated from the plumes of the moon Enceladus. Given the size of the particles, this dust must be extremely smooth. It will offer thermal insulation from the -150 to -200 degrees Celsius outside. Many buildings can simply be covered with this ice dust.
Transport Schedule[]
Flight windows often occur between the inner planets and Saturn:
To Mercury - every 89 Earth days To Venus - every 230 Earth days To Earth - every 377 Earth days To Mars - every 733 Earth days.
However, every 59 Earth years, Jupiter and Saturn are perfectly aligned, to offer the best gravity slingshot, for the cheapest transport route.
Perfect flight windows between Saturn and the other gas giants occur at 20 to 62 Earth years:
Ceres - Saturn: 5.42 Earth years Jupiter - Saturn: 19.9 Earth years Saturn - Uranus: 61.8 Earth years Saturn - Neptune: 35.7 Earth years.
If a ship lands at every flight window or at least every 1000 days, we will have 9 landings every Earth year or a landing every 41 Earth days. If we also consider departures, there will be an interplanetary flight event every 20 Earth days.
However, maneuvering a spaceship far away from the Sun requires less energy to change course. Probably, ships to Jupiter, Uranus and Neptune will be launched at every 1000 Earth days.
Around Saturn, best launch windows occur much often, because the moons orbit much faster:
Mimas - Helene: 1.5 Earth days Enceladus - Helene: around 2 Earth days Tethys - Helene: 3 Earth days Helene - Dione: anytime Helene - Rhea: 3.5 Earth days Helene - Titan: 3 Earth days Helene - Hyperion: nearly 3 Earth days Helene - Iapetus: nearly 3 Earth days Helene - Phoebe: over 2.5 Earth days
Now, if we consider departures to Dione to occur daily and launches to other moons each time we have a flight window, we have 1529 departures every Earth year or 4 departures every Earth day. Overall, this implies 8 local flight events daily.
As one can see, cargo and passengers will not have to wait more then 3 days on Helene, suppose there is a scheduled traffic that uses each launch window.
Delta-v[]
The Delta-v shows the amount of energy required to travel from a place to another. For Helene space station, the values are as follows:
Mercury Space Station – Saturn Helene 30.457 Venus Space Station – Saturn Helene 24.872 Earth Space Station – Saturn Helene 22.447 Mars Phobos – Saturn Helene 17.914 Ceres Space Station – Saturn Helene 12.613 Jupiter Himalia – Saturn Helene 9.876 Saturn Helene – Uranus Perdita 11.335 Saturn Helene – Neptune Halimede 9.978 Saturn Helene – Pluto Styx 9.154 Saturn Helene – Eris low orbit 10.029 Saturn Helene – Sedna low orbit 10.010
Saturn orbit (1000 km) – Saturn clouds 25.707 Saturn orbit – Helene 12.772 Pan – Helene 6.415 Mimas – Helene 3.995 Enceladus – Helene 2.837 Tethys – Helene 1.750 Helene – Dione 0.441 Helene – Rhea 2.232 Helene – Titan 7.089 Helene – Hyperion 4.498 Helene – Iapetus 5.939 Helene – Phoebe 5.644
For comparison, an Earth surface - Moon surface flight will require a delta-v of 14.466.
The delta-v requirement for reaching inner planets is huge. Ships can take advantages of a Jupiter flyby (which occurs every 59 Earth years) and of Earth and Venus flybys. For missions to other gas giants, to the Asteroid Belt and the Kuiper Belt, the delta-v is small, but the flight route will take too much time. Also, correct alignments are rare. Ships will prefer to go on more expensive routes to save time.
Because Helene is close to other moons of Saturn, delta-v requirements are not high. Many corporations will prefer to send their goods to Helene, then sell them at an auction, to be shipped to other moons. It is also possible that people will prefer to take a flight with a stop at Helene. For example, a flight on the route Enceladus - Titan will not require much more delta-v then a flight on route Enceladus - Helene - Titan.
From the inner, touristic moons, like Pan and Daphnis, to the larger moons suitable for terraforming like Titan, Iapetus and Rhea and from the mysterious Enceladus that has conditions in its subsurface ocean for microorganisms to the distant Phoebe that might host tholins and other useful minerals, Helene will play an important role in commerce, because of its position.
Cargo Facilities[]
The base must be able to handle the entire cargo traffic between Saturn and other planets, as well as traffic between Saturn's moons. The base must have enough space for storage. Many goods will be shipped with containers, like today on Earth. Opened containers are out of question, since in space they will lose all their goods. A wide range of containers can be stored on the ground or in special storage buildings, but some of them need to have their goods protected from the extreme cold. They should be stored in underground chambers, well insulated and heated. Transporting frozen products will be very easy.
In addition, the base will also offer facilities for transporting fluids. Many liquids and gasses are frozen on the surface of Helene. they can be stored frozen, but heated to be liquefied and transferred from or to spaceships. Still, some substances, like hydrogen, are gasses at -150 C.
Gravity on the surface of Helene is very small. A man that on Earth weights 80 kg, on Helene might weight 400 g. This means that, if you jump with all your force, you might end-up as a satellite. Low gravity means a very low gravitational inertia. Once an object is moving up, you will have to wait even hours for it to stop its movement. On Earth, cargo containers are moved with a crane, by anchoring wires and chains on top of them. On Helene, that will not be an option. Instead of a crane with ropes and a hook, we should consider a device with a moving, telescopic arm. A container will weight as much as an adult human, but we cannot let inertia take it to nobody knows where.
The dock cannot use ground vehicles (cars or trains). The low gravity means that there will be little to no friction between the vehicle and the ground, making acceleration using the brakes impossible. Instead, vehicles can be fixed to rails or to suspended wires. There can also be used small vehicles with chemical engines, able to fly through the dock and move objects that are running away.
Passenger Facilities[]
From Helene, launch windows to the other Saturnian moons are frequent and flight time is not too long. However, launch windows towards other planets are not so often. The base will probably work as an inter-moon base too. People would prefer to move from Titan to Enceladus via Helene if connections are often. So, we expect there will be limited passenger traffic all the time.
The number of passengers will dramatically increase close to flight windows towards other planets, mainly Earth. Settlers coming from Earth, after a long journey, will have from a few hours to up to 3 days before going to Titan and other moons. This is not a lengthy period and the base can used stored food, air and water for peak periods. People can wait 3 days.
Passenger ships will attach to insulated and heated underground tunnels that will allow people to reach the base. There, they will enter a large room or dome. The base must have enough beds for all passengers. People will need places to eat and hangout. Also, baths are required. The best way to take a bath in low gravity is to enter your body except for the head inside a tube, where you will be washed with jets of water. A small clinic is also required. Since Helene is a Trojan of Dione, ships can depart and arrive from Dione at anytime. This means that there will not be needed a hospital on Helene. If anything bad happens, people can be moved to Dione at every moment, in only two days.
The base must have a sustainable ecosystem, to provide people with food, water and air. However, for peak periods, all those can be stored. Given the average low temperatures, all the goods can be kept frozen for many years, even centuries.
Construction[]
Helene base will consist of 3 parts: cargo facilities, passenger facilities and maintenance. The maintenance part will consist of many parts. A nuclear generator is vital to provide the base with energy and heat. It is good if the generator has two units or if there is also a backup generator. Without energy, everything will freeze to death. The base also must have stored fuel of all kinds for spaceships: hydrogen, oxygen, hydrazine, xenon or nitrogen for ion engines and other types, required for future ships. A spaceship repairing facility would be needed too.
Using solar power might not be an option. Helene is covered with ice dust that slowly accumulated from the plumes of Enceladus. This dust will affect solar panels, which, given the low solar output at Saturn's orbit, will need to be very large, probably covering over half of the moon's surface.
For any bad scenario, it is good to have on Helene one ship prepared to move to Dione.
Because Helene is close to the other Saturnian moons, trading corporations would like to build their private docks on the moon and keep their fleets there. This will make Helene an important trade center.
The Future[]
As colonies will develop around Saturn, Helene will remain an important point for all Trade Routes. When Saturn will become an independent state or federation, Helene will be its gateway to the Universe. And unlike Jupiter's outer Himalia base, Helene will play an important role for internal traffic.