## Thursday, May 14, 2009

### Final Frontier 7: Space Flight

I am writing a series of posts on the virtue of moving into the final frontier. To call this a virtue, in desire utilitarian terms, means that people generally have many and strong reasons to promote a love of developing space. This, in turn, means that such a sentiment would tend to fulfill many and strong desires. A lot of those desires are built into the survival of humanity – the desire for the well-being of one’s descendents, a type of immorality by being a member of a community that lives on, etc.

I have also sought to describe this community. It is different from what we tend to see in science fiction. Teaching children to love the exploration an development of space should begin with a healthy respect for the facts regarding what that life would be back.

I got an imaginary character from the ground in Los Angeles to a space station in low earth orbit. However, our character has a job further up in space, managing a satellite repair business for satellites that are in geosynchronous orbit.

There is another economic reason why we build our “port station” on an equatorial orbit. All geosynchronous satellites are in equal orbits. A craft carrying people from the low earth orbit station to the satellite maintenance station will not have to spend fuel changing directions.

It takes a lot of energy to change directions in space. This is one of the odd things that people in space would have to get used to and which we never see depicted in movies and television.

You are travelling at 17,500 miles per hour in space. How much energy does it take to make a 90 degree turn?

Answer: It takes twice as much energy as it would have taken to go from a dead stop to 17,500 miles per hour – or approximately twice as much energy as it took to launch the object into orbit to start with.

Why?

Well, first, in order to turn 90 degrees to the right you have to stop going forward. Going from 17,500 miles per hour to a dead stop takes just as much energy as going from a dead stop to 17,500 miles per hour.

Now, to move at 17,500 to the right you have to go from a dead stop to 17,500 miles per hour.

Combined, these two maneuvers take twice as much energy as it took to get to 17,500 miles per hour to start with.

These movie and television scenes that you see of space ships fighting like atmospheric fighters – that will not happen in space. It takes way too much energy.

It works in the atmosphere because the air itself creates forces on the airplane other than the thrust of the engines. Air flowing over the wings creates lift – a force that is perpendicular to the direction of travel. The air itself provides friction – which provides drag. These two factors combined help to slow down a craft and to change the direction of travel. Space ships do not have lift or friction. They only have the thrust of their engines (and their maneuvering engines).

The most common mode of travel in space If you keep your foot on the accelerator, you will continue to accelerate. Once you reach the speed you like you must then take your foot off of the accelerator and coast. If you want to stop, taking your foot off of the accelerator is not good enough. You have to put as much energy into stopping as you put into going.

Space movies like to show a spaceship’s engines burning constantly in order to maintain velocity. This is what we are familiar with on earth where friction and drag work to constantly slow things unless energy is provided to overcome these forces. Space travel is different. In space, you fire the engines for a few minutes until you are heading in the right direction at the right speed. The rest of the time is spent simply coasting – until you need to slow down. Then the engines are fired in the opposite direction to slow down.

Another difference between space travel and earth travel is that earth travel is all done against the mass of the earth. When you jump into the air, you move away from the earth at a particular velocity and direction. Your action produces an equal and opposite reaction in the earth. However, given the differences in mass, there is no perceptible (or even measurable) change in the velocity of the earth.

In space, all of your actions are conducted against entities that have significantly less mess, and will have a measurable effect that must constantly be considered.

I have already mentioned how a space station’s orbit will decay and that it will need an occasional boost. We can also expect that, from time to time, ships will depart the station in order to return to Earth. It is possible to engineer a system that accomplishes both of these ends at the same time without expending any fuel (or mass) in the process.

You put the ship that will be returning to Earth on a long catapult – like the type that launches jets from an aircraft carrier only longer and less brutal. Then, you throw the earth return vehicle out of the back end of the space station. The effect will be to give the earth return vehicle a slower velocity (relative to the earth), causing it to fall to the earth and enter the atmosphere. At the same time, this will produce an equal and opposite reaction of pushing the station itself to a higher orbit.

This is a constructive use of these principles of physics. However, these points come with a word of warning as well. Every ship that docks or leaves, every movement of people and objects inside the station, has an effect on the whole station. It would be risky to forget this fact and to think that things will work in space as they worked on earth. People will need to change their expectations. In some cases, their very survival will depend on this.

#### 1 comment:

Baconsbud said...

Wow. I have read most of your post on this topic and there are a lot of things I have never thought about before. I always known space travel is very complicated but there are so many things that have to come together to make it possible. As I see it we are even further from it then I thought we were.