Wednesday, March 13, 2013

A Trip Into Space - Low Earth Orbit Space Station

I am taking this week to talk about space development – looking at where research time and money ought to be going with the idea of developing a space-faring community.

I am doing this by taking you on an imaginary trip into space to live – to start a new job and become a member of a community in space.

You have left Earth and are now in low-earth orbit over the equator. As you drift to the orbiting space station, the captain has just turned on the seatbelt sign, directing passengers to strap themselves in for docking.

Outside your window, you can see the space station. But this is not your new home. This is just a stop along the way.

To understand what you see, here are some relevant facts about objects orbiting the earth.

Assume that you are standing in an object in low earth orbit over the equator, facing east (the direction of travel), with the earth below your feet.

There is another object orbiting 1 kilometer to your right.

Forty-five minutes from now, that object will be 1 kilometer to your left. Forty-five minutes after that, it will back to your right again. Thirty-two times per day, it will cross your path. If you are in its way (if it is not at the same time a little ahead of you or a little behind you, then there will be a collision.

If there is an object orbiting 1 kilometer above you then, slowly, it will drift further and further back. Objects in a higher orbit travel more slowly. An object 1 kilometer below you will drift further ahead – the way the inner planets in the solar system speed ahead of the outer planets.

Consequently, you should not expect to see a group of disconnected objects in space orbiting in formation over an extended period of time. When you look out your window, you will see a space station – a single object, perhaps with one or two space ships hovering nearby waiting to dock.

Another relevant fact is that long-term weightlessness is known to cause serious health problems. However, this long-term problem has a solution - a rotating community that simulates gravity through "centrifugal force". The simple fact is that until we have rotating space communities, people will not be living in space. At best, they will visit during short-term work assignments.

One of the reasons for this series (other than the fact that the subject interests me and I enjoy writing about it for its own sake) is to look at what is needed for space settlement. Where should we be investing our time and money?

From the first post - we should be developing a space station in a low equatorial orbit and the least expensive way to get there.

From the second post - we need to find answers to the problem of space sickness for a community whose members will transition from weight to weightlessness on a regular basis.

And we should be working on creating rotating habitats.

The simplest, least expensive form of rotating space station will take two habitats, connect them – perhaps even with something as simple as a set of cables around a central hub, and set it spinning. The resulting station would have a "dumbbell" shape - a sphere or set of disks at each end of a long bar - spinning in space like a baton.

A reasonable distance from the center hub to the outer habitat for the best effect will be about one kilometer. With a rotation of 270 degrees (three quarters of a spin) per minute, this habitat will simulate 0.6 G - which will balance the interest in preventing the harmful effects of weightlessness with the engineering reasons to keep the “weight” of the module, its contents, and the connecting material low.

The space station can be made modular, so that it can grow. A second dumbbell can be built and attached to the first to provide additional living and working space. These modules would be added in pairs of equal mass, perhaps connecting to the first in such a way that, eventually, the dumbbell space station becomes a wheel with spokes.

You will not be fastening one outside module directly to another. The outer module is actually travelling at a rate of more than 275 kilometers per hour in an arc around the central hub. Instead, one would need to set the two new modules spinning at the same rate as the station and then fasten them. Perhaps they will be set spinning on a short cable. Then, when attached, the connecting material will be lengthened as the new habitats move further and further away from the station.

This is going to be a serious engineering challenge – and something that we have many and strong reasons to investigate today.

While there is an interest in spinning the places where people live and work, there are reasons not to spin a lot of the mass that the station would find useful. The solar power arrays that feed the station, for example, would best be attached to the non-spinning hub so that the structure experiences less stress.

The best place for your rocket to dock with the orbiting station will be at this non-spinning hub attached to the center of the station.

After leaving the rocket, you will find your way to an elevator shaft, that will take you 1 kilometer “down” to the habitats. As the elevator descends, you will feel 60 percent of your weight return. Of course, it is not the case that all habitats must be the same distance from the center. Some can be built at 0.25 G, and perhaps others far enough out to simulate 1 G or more. What matters is keeping the wheel balanced.

To do that, there is a weight in the central hub that is shifted around to balance the movements of people and objects though the station. This is the same technology currently used to dampen the effects of swaying in tall buildings.

You have now finished the first leg of your journey. You are in a small room. After settling in to a small room, you have wandered into an observation station. From where you stand, the wheel of the space station – 2 kilometers in diameter – stays motionless “above” you. Meanwhile, the stars and the earth spin at a rate of 1 turn every 80 seconds – like the second hand on a slow clock. You can enjoy something to drink. You can use the bathroom. You can watch rocket ships as they dock and leave. As you do, you can recognize a difference between the long cylinders that travel to and from the Earth, and the stubby non-aerodynamic spheres that travel from station to station in space.

Enjoy your stay. We will be moving along shortly.


Tor Hershman said...

What makes you think you're "Leaving" let alone "Better"?

Jim Baerg said...

Re: the level of 'artificial gravity' in rotating space stations.

By what is probably an odd coincidence the surface gravities of solar system bodies cluster about values that differ by a ratio of about 2.5 or 0.4. Jupiter is 25 m/s^2, Venus Earth Saturn Uranus & Neptune are all not far from 10 m/s^2, Mercury & Mars are both just under 4, & our moon & the larger satellites of the outer planets are close to 1.6 m/s^2. (This oddity was 1st pointed out by Gerald D. Nordley)

We want to know the health effects of gravity levels between 10 m/s^2 & 0, but 2 values 4 m/s^2 & 1.6 m/s^2 would cover the major bodies we could land on. So I think an early rotating space station should have 4 m/s^2 'gravity' and maybe 1.6 as well, but a moon base would give us that information.