Before going to Mars, however we have to consider the actual propulsion techniques available to humans for travel. Certain types of propulsion are more readily available while others are far off. Each of these has benefits but we will have to be careful in choosing the one that will get us the over 78 million kilometers to Mars (1).
(The old space shuttle) (2)
The Old Stand-by
There is of course the existing material that we have: chemical propulsion. Under this method the reaction between hydrogen and oxygen creates heat which then pushes gas out the rocket nozzle otherwise known as thrust (3) Chemical rocket engines are readily available meaning if we wanted to leave now, we use them. The only problem with this method of propulsion is its speed and weight. There are simply too many limitations which we have discovered with chemical engines (although for many of these other technologies, we don’t as yet know their limitations). In the chemical-rocket situation it’s a simple question of specific impulse (Isp), weight, and thrust to weight ratio(4). Isp is a ratio between thrust and the weight consumption rate of propellant which boils down to how long the engine will provide force to gain a certain momentum (5). In chemical rockets this is unfortunately short lasting perhaps 500s. Thankfully, the thrust to weight ratio is high at 50-75 so we got around the short Isp by using stages and jettisoning the useless empty stages (6). That may seem like a lot of technical-language but it simply means that chemical rockets need a lot of fuel to change momentum at all. This seems slightly unfeasible however, for a long trip in which you would still rely on these short burn, heavy, and jettisoning rockets. The prediction is that under this system it would take six months to reach Mars and it would have to wait 18 months until the return six months journey could be made. That would be a 2.5 year round trip (7).
(8)
Nuclear Propulsion
Research into this technology was first pioneered during the Cold War by both the U.S.A. and the Soviet Union (9). The first way a nuclear propulsion engine would work is to have a reactor with a solid core generating heat. This heat is then radiated to a separate gas propellant which when heated ionizes. When this ionized gas is pushed out of a magnetic nozzle, we achieve forward thrust (10). The other method uses a gas core which is radiated through a tube to heat the gas surrounding it to an even higher temperature (11). The Isp on a solid core Nuclear propulsion system is 1000s (12). The thrust to weight ratio is also 1-20 meaning we can go farther, faster, with much less fuel (13). In comparison to chemical rockets they take a lot less fuel to change the momentum and thus it is a more efficient way to travel. The nuclear propulsion does have one major setback: launching a nuclear rocket in earth orbit is probably not the best thing for the people down below (14).
(solar sail concept) (15)
Forget the Engines: Solar Sails
Of course, if conventional and pseudo-conventional (nuclear power) rockets are too tough why not just get rid of them altogether? Solar sails attempt to do that. The concept is actually much older then many would believe. During his observations of a comet, Johannes Kepler believed that what was moving the comet was actually solar winds and hypothesized that the best way for humans to move through space would be to do likewise (16). Kepler had the wrong source but the right idea and today there have been several developments in solar sails which are powered by light itself (17). Modern solar sails use a very thing sheet of aluminum reinforced Mylar to reflect photons as they hit the sail (18). The photons released by the sun push the sail forward as they strike it and reflect back (19). The solar sail powered ship would eventually reach 56 mi/sec (200,000 mph) or 10 times faster then the Space Shuttle’s orbital velocity (20). The only problems with solar sails are that you have to use conventional rockets to get them into space and that little word: eventually. Acceleration at the beginning of the trip is very slow so it might not be best for a mission to Mars (21). Regardless, the technology is already being used for deep-space missions, by Japan as of 2004, and by NASA with its nano-sail as of last summer which eventually failed but still proved the concept (22).
(concept of mag-beam propulsion)(23)
The Round Trip in 90 days on plasma
The Magnetized-beam plasma propulsion system is a new idea from the University of Washington’s professor Robert Winglee (24). Basically it places a space station above earth which generates plasma, magnetizes it, and then has it interact with a ship with magnetized sails pushing it forward(25). The larger the nozzle for the ions the greater the thrust and Winglee believes one 32 meters wide could propel a craft at 11.7 km/s (26,000 mph) (26). This is slower then the top speed of the solar sail but then again it will go at this speed throughout most of the journey. Under this speed it would take 76 days to get to Mars but they believe by increasing the stream of plasma they can bring that down to a 90 day round trip (27). The problem is this is still very experimental and the ship itself wouldn’t carry much in the way of propulsion itself so it would need another such station around Mars to slow it down and pinpoint accuracy to put it inline with that station (28).
(concept of anti-matter to matter collision propelled spaceship) (29)
Enterprise, do you read me?
Yes, there is always the sci-fi favorite anti-matter. Anti-matter is what it says it is, the opposite of matter. When the two are forced together, they annihilate each other and create a massive amount of energy (30). Such spaceships using an idea similar to that of Nuclear propulsion, according to a Penn State research team, would have an Isp of 100,000-1,000,000 seconds (31). Anti-matter would be an incredibly efficient way to explore space except for one glaring problem: anti-matter. It seems we just don’t have enough and it is really expensive at 62.5 trillion dollars a gram (32).
So how are we getting there?
What is the best way to Mars, and the corollary, what is the fastest and most efficient? In this writer’s opinion, chemical propulsion is too ineffective for long range transportation. It is still perhaps the best way to get into orbit (not due to effectiveness but more so due to the lack of extremely volatile or radioactive byproducts), but not to get to Mars. Solar sails are perhaps the most efficient but they take too long to reach their max speed. The technologies which seem most viable at this point are further developments in nuclear propulsion and magnetized-beam plasma propulsion.
Endnotes
(1) J. Bennett, M. Donahue, N. Schneider, and Mark Voit, The Solar System, (San Fransisco: Pearson Education), A-15.
(2) “Space Shuttle: Image Gallery,” NASA, http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts125/multimedia/gallery/gallery-index.html, 04/07/2009.
(3) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(4) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(5) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(6) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(7) Behar, Michael, “5 ways to get to Mars” Wired: Issue 12.12, December 2004, http://www.wired.com/wired/archive/12.12/mars.html, 04/07/2009.
(8) Babula, Maria, “Nuclear Thermal Rocket Propulsion,” Space Propulsion and Mission Analysis Office, NASA, http://trajectory.grc.nasa.gov/projects/ntp/, 04/07/2009.
(9) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(10) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(11) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(12) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(13) Bromley, Blair P., “Nuclear Propulsion: Getting More Miles per Gallon,” Space Exploration, Astrodigital, 2001, http://www.astrodigital.org/space/nuclear.html, 04/07/2009.
(14) Behar, Michael, “5 ways to get to Mars” Wired: Issue 12.12, December 2004, http://www.wired.com/wired/archive/12.12/mars.html, 04/07/2009.
(15) Coulter, Dauna, “A Brief History of Solar Sails” Science@NASA, NASA, 07/31/2008, http://science.nasa.gov/headlines/y2008/31jul_solarsails.htm, 04/07/2009.
(16) Bonsor, Kevin, “How Solar Sails Work,” How Stuff Works, Discovery Company, http://science.howstuffworks.com/solar-sail4.htm, 04/07/2009, pg. 2.
(17) Bonsor, Kevin, “How Solar Sails Work,” How Stuff Works, Discovery Company, http://science.howstuffworks.com/solar-sail4.htm, 04/07/2009, pg. 2.
(18) Bonsor, Kevin, “How Solar Sails Work,” How Stuff Works, Discovery Company, http://science.howstuffworks.com/solar-sail4.htm, 04/07/2009, pg. 3.
(19) Bonsor, Kevin, “How Solar Sails Work,” How Stuff Works, Discovery Company, http://science.howstuffworks.com/solar-sail4.htm, 04/07/2009, pg. 3.
(20) Bonsor, Kevin, “How Solar Sails Work,” How Stuff Works, Discovery Company, http://science.howstuffworks.com/solar-sail4.htm, 04/07/2009, pg. 5.
(21) “Solar Sails,” BBC Science and Nature: Space, http://www.bbc.co.uk/science/space/exploration/futurespaceflight/solarsails.shtml, 04/07/2009.
(22) Coulter, Dauna, “A Brief History of Solar Sails” Science@NASA, NASA, 07/31/2008, http://science.nasa.gov/headlines/y2008/31jul_solarsails.htm, 04/07/2009.
(23) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(24) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(25) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(26) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(27) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(28) Stricherz, Vince, “New propulsion concept could make possible 90-day round trip to the red planet” University of Washington News, University of Washington, 10/14/2004, http://www.uwnews.org/article.asp?articleID=5817, 04/07/2009.
(29) Dooling, Dave, “Reaching for the stars: Scientists examine using antimatter and fusion to propel future spacecraft,” Science@NASA, NASA, 04/12/1999, http://science.nasa.gov/newhome/headlines/prop12apr99_1.htm, 04/07/2009.
(30) Dooling, Dave, “When Isaac met Albert,” NASA: Marshall Space Flight Center, http://science.nasa.gov/newhome/headlines/msad12nov97_1.htm, 04/07/2009.
(31) Dooling, Dave, “Reaching for the stars: Scientists examine using antimatter and fusion to propel future spacecraft,” Science@NASA, NASA, 04/12/1999, http://science.nasa.gov/newhome/headlines/prop12apr99_1.htm, 04/07/2009.
(32) Dooling, Dave, “Reaching for the stars: Scientists examine using antimatter and fusion to propel future spacecraft,” Science@NASA, NASA, 04/12/1999, http://science.nasa.gov/newhome/headlines/prop12apr99_1.htm, 04/07/2009.
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