Final Project

Alicia T.

Legislator:  Rodney Ellis, Senator

What a Ride!

Tired of spending years on your way to Mars using ships that require you to be in perfect physical condition?  Well now you can have your cheesecake and eat it too!  Be sure that you are strapped in tightly!  A space elevator has just been built for faster, cheaper service from Earth to orbit, and YOU are one of the lucky astronauts chosen to ride it into microgravity.  The ride on the space elevator begins somewhere near the Earth’s equator to the space station at 35,786 kilometers up.  Do not close your eyes on the way because if you look out the window in as little as 10 minutes, you will see the outline of the blue Earth turning below you. 

The space elevator is a 47,000-kilometer long tether reaching from the equator past the space station and further into space.  The space station is located at exactly 35,786 kilometers because that is the height of a geosynchronous orbit around the Earth.  By placing an object on the tether in a geosynchronous orbit, it creates a center of gravity for the tether.  This center of gravity allows the elevator to stay in one position above the Earth or a geostationary orbit.  The elevator would not give way to gravity because of the tension created by the differing altitudes.  Below the space station the tether would be moving more slowly than necessary to maintain a stable orbit, therefore would start to feel the gravitational pull.  Above the space station the tether would be moving faster than needed to hold a stable orbit, which would try to move the tether further afield.  These forces would equal each other and cause tension in the tether.  The tension created would cause the cable to remain taut in orbit. 

The tension would be the greatest at 35,786 kilometers, so the tether would have to be the thickest at that point and narrowest at the extremities.  A steel cable only 1 millimeter wide at an extremity would have to be 40 billion kilometers wide at geostationary orbit.  Even Kevlar, would need to widen to 16 meters requiring 2 gigatonnes of it.  The problem is that the minimum diameter needed would be closer to 10 centimeters instead of 1 millimeter.  NASA requires a material with the tensile strength of about 62.5 gigapascals, which is 30 times stronger than steel and 17 times stronger than Kevlar.  A new material has been developed: carbon nanotubes, having a tensile strength of about 130 gigapascals.  Due to the fact that any combination of materials such as fiberglass to bind the nanotubes together would dilute the strength, one continuous cable must be made for the entire length of the elevator. 

When the cable is in place an almost frictionless track can be created by using opposing magnets.  An electromagnetic car could then reach speeds of thousands of kilometers per hour.  By developing a track that uses opposing magnetic fields, the malfunctions and wear of wheeled mechanisms could be avoided.        

Using this method of placing payloads in space, the costs would plummet to as low as $1.48 per kilogram as opposed to $22,000 per kilogram using a rocket. 

But that’s only part of the ride!  You (the lucky astronaut) are about to experience the Mars-Earth Rapid Interplanetary Tether Transport or MERITT system.  The space elevator has brought you to the exact place where your ship will now attach to the Earth whip.  The Earth whip is a tether that completes a highly elliptical orbit around the Earth.  It will pick up the ship just before perigee and tosses it half a rotation later, just after perigee.  You are now being flung into space towards Mars at such high speeds that it is possible to make it to Mars in as little as 90 days.  Your ship has no propulsion except for midcourse guidance.  Once you reach Mars, the Mars whip will catch the ship in the vicinity of periapsis and release it later at a velocity and altitude that will allow you to enter the Martian atmosphere.  The system works both ways and is completely reusable. 

The only requirements are that the tether system is as little as 15 times the mass of the payload, and that there is some method of getting the payload out of the planetary atmosphere.  One problem is solved by the weight of the tether’s material and the space elevator solves the other.

How do you feel?  You made it to Mars, completed your assignment, and are back home in less than a year! 

What a ride!

Sources:

http://www.tethers.com/MARITT.html

http://www.tethers.com/main/html

http://www.tethers.com/LEO-Lunar.html

http://www.spacescience.com/headlines/y2000/ast07sep_1.htm?list

http://flightprojects.msfc.nasa.gov/fd02_elev.html

http://spacedaily.com/news/future-01f.html

Last Updated:  09/10/01