EXPLORATION SPATIALE - LE BLOG DE PIERRE BRISSON

Description of a possible Space rotative station at L1 of the Earth Moon system

Last week, I told you that a space station located at the Earth-Moon Lagrange point L1 could be very useful for our future exploration of Space. Today, I’ll describe how I see this station: its structure, and the relationship between the torus and the central axis (radial tubes and the junction between the moving and fixed parts).

Station Structure:

The Torus:

It is rotating and held by four spokes (tubes) radiating from the still axis at the center of gravity of the station.

To achieve a gravity of 0.5g within the torus with a rotation speed of 2 rounds per minute (rpm), the distance from the torus to the center must be 112 meters. Why 0.5g and not more? Because this gravity allows humans and their robots to behave normally (as on Earth), enables relatively normal fluid mechanics, and is not too far from Martian or lunar gravity. Why 2 rpm and no more? Because we therefore maintain within reasonable limits the difficulty of the relationship between the rotating torus and the still axis, and the effect of the Coriolis force (which induces a loss of verticality). The result of such distance is that the gravity gradient between head and feet for a 180 cm tall person is reduced to less than 2% (exactly 1.6%) which is quite bearable. The only problem is the length of the connecting axes and of the torus. A radius of 112m implies a circumference of 703m. It takes time to walk around it and the corresponding mass is important. This is certainly a maximum, but it’s necessary to avoid a higher number of revolutions per minute (rpm), a higher head-to-toe gradient, and lower gravity within the torus. Furthermore, 0.5g instead of 1g reduces the negative consequences of impacts from falls (of objects or people). Rotation can be achieved using four small propulsion motors (electrical power and xenon ejections), attached to the outside of the torus, each at the height of a connecting tube (for maximum safety). Their direction can be reversed if braking is required.

Inside, the atmospheric pressure will be 0.5 bar to limit the pressure difference between inside and outside. Therefore, the oxygen level will be increased to 42% to maintain the 21% concentration prevailing in a ‘normal’ Earth atmosphere (at 1 bar).

The torus is a series of welded tubes, each 4 meters in diameter (the ISS is 3.5m to 4m) and of a length of 10 meters. It has a floor and a ceiling. The electrical wiring and communication fibers run through the ceilings, while the plumbing system, carrying fluids including heat transfer fluids, runs through the floor (through a pumping system). The 4-meter diameter is necessary for a real comfort; passengers will need it so far from Earth. It is also needed to take into account the ‘water wall’ (20 cm thick) needed to limit radiation (I’ll talk about it later). Spherical cupolas (6 meters) will be inserted every 40 meters to reduce the feeling of confinement, create a welcoming space, and allow for visual monitoring of the center. Double fire-resistant and depressurization-protective doors are positioned (open) at the level of each connecting tube. They close instantly in the event of an air leak or an abnormal temperature rise (of course, there will be fire extinguishers ‘everywhere’).

The torus is primarily a corridor. It will serve Bigelow-type modules that will alternate between private living spaces (with bathrooms) and functional areas requiring gravity (water purifying, oxygen production through spirulina culture, organic waste recycling, food production, etc.). One Bigelow module (4m x 8m x 4m) can be planned for each 10-meter tube segment, with a double access door in the corridor and the module. The private and functional modules attached to the torus must be located not in the plane of the torus but below it. Indeed, given the rotation, lateral access from the corridor will be through the side, not the outer bottom of the torus. It will be better to attach the private and functional modules to the side opposite the Sun (see ‘orientation’ next week). A Bigelow ‘sanitary’ module with two toilets (men’s and women’s) will be placed next to each cupola module. Next to each of the four ‘anchor’ modules (holding together the tube and the torus), there will be, in lieu of the Bigelow module, a small emergency vehicle (with a propellant stock), to be used to reach the moon or wait for rescue in the event of a general catastrophe affecting the station. This vehicle can also serve as an airlock (for depressurization and opening). These facilities are necessary on account of the size of the station (the main airlock, located at the end of the central axis, is too far away, and there cannot be only one). There will also be a storage/loading/workshop area for several humanoid robots near each anchor-module (the main storage area will be on the axis). The water reserves (20 to 30 cm thick) will surround the torus. In addition to the normal needs for any human group (3 to 5 tons per person), it will also serve as a radiation shielding. It will be recycled in several Bigelow modules of the torus and also refilled from time to time (to replace ejected black water).

The central axis:

The total length of the station’s axis will be 88 meters. Its modules will stretch above and below the plane defined by the torus. These modules will be either cylindrical or spherical, depending on their function. At the junction of the tubes and the axis, there will be a 6 meter diameter central-sphere.

Above the central-sphere will be aligned: a 4-meter by 8-meter cylinder « storm shelter, » to withstand solar storms radiation, with internal surrounding protection of 50 to 100 cm (polyethylene layer and water wall); a 4-meter diameter by 2.5-meter-long cylinder for restrooms (men’s and women’s); a 6-meter spherical « cupola » module with side windows (for viewing and monitoring; a cylinder 4m in diameter and 6m long for experiments or work in zero gravity; a cylinder 4m in diameter and 6m long for computing/data center; a cylinder 4m and 6m long for telecommunications, with peripheral antennas (see below). The top of this last cylinder will be fitted with a thermal protection cap (see next week).

Under the central sphere there will be: a cylinder 4m by 6m long, main « home » (with storage, workshop, electrical outlets) of the station’s 20 Optimus humanoids; a propulsion sphere, 6m in diameter with, in the lower hemisphere, 3 retractable engines tilted at 45° (with equal thrust); this sphere will be closable at the top and bottom with isolation airlocks; a cylinder 4m in diameter and 6m long for the xenon (propellant) tanks; Two 4m x 6m cylinders for storage (freight, supplies); an 8-10m sphere for docking, with three ports, one of which will be for a permanent rescue vehicle; a 4m diameter x 2.5m long cylinder restrooms (men’s and women’s); at the end of the axis, a 4m diameter x 6m long cylinder with an airlock for EVAs, including spacesuits, MMUs (Manned Maneuvering Units), and tools.

Outside, the airlock will provide immediate access to continuous safety rails running from module to module throughout the station. All modules on this axis will be stationary (i.e., they will not rotate like the rest of the station). This is essential for communication antennas, docking, and EVAs.

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Relationship between the torus and the central axis:

Conflicting requirements (rotation of the torus and stability of the axis) induce the need for a delicate connection between the two horizontal and vertical elements. The solution is to have a fixed, vertical service tube, 1.5m in diameter, passing through the central sphere, connecting the two fixed parts of the axis. The central sphere itself will rotate on bearings around this axis. The four tubes of the torus will connect to this sphere (it will rotate with them). Fluids/electricity will pass through slip rings at the axis/sphere junction. At this junction it will therefore be necessary to have (1) large ball bearings (already proven space technology); (2) slip rings for electricity and data; (3) rotating seals for fluids (water, ventilation air). (4) Rotating doors for personnel access (one of the reasons for not exceeding 2 rpm). All of this implies lubrication and monitoring of seal wear (as it is in the ISS).

The connecting tubes, like the torus, have a 4 meters diameter. They should be viewed as wells rather than corridors, because the greater gravity within the torus will cause any mass coming from the center to accelerate downwards (this is also why it is best to limit gravity at the bottom of the wells to 0.5g). They will benefit from the same thermal and radiation protection as the torus. This protection (without solar panels, as there are enough above the torus) will be located outside the tubes. Inside, and extending the full height of the wells, the circumference will be occupied by a 20 cm wide ring-shaped compartment containing the water wall and a 30 cm deep ring-shaped volume housing all the fluid tubes and fibers carrying electricity and data. This will also contain the pumps allowing the fluids to move up and down the torus, as well as the elevator machinery. In the remaining space (slightly less than 3 meters in diameter), three out of the four tubes will house an elevator platform. This elevator will travel from the floor of the torus to a distance of 5 meters from the intersection sphere. As the gravity of the moon (0.16g) will only be reached 35 meters from the center (at 2rpm), gravity at the bottom of 5 meters compartment, will be very ‘light’ (0.04g). This will not hinder access to the sphere upon exiting the elevator but will prevent congestion in the sphere (a net can be set to prevent falls when the elevator platform is not available). The fourth tube will be equipped with a spiral staircase (emergency exit). This could be supplemented by a platform the width of the steps, moving perpendicularly to the tube walls.

Since the torus is massive and connecting tubes long, and since there will be trajectory adjustments, it is safer to reinforce the torus’s stability. Unfortunately, it is not possible to create more radial connecting tubes (mass of the tubes, diameter of the central sphere). A solution is proposed by the physicist Emmanuel de Survire in his book, ‘Ni Monde ni Etoiles’: guy wires connecting the modules to each other and to the central axis.

Next week, I will present the station’s orientation, its radiative environment, and the resulting implications regarding energy harvesting and protection against heat and radiation.

title illustration: scheme drawn with claude.ai

Copyright Pierre Brisson