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| This idea is good compared to some on this list... |
As a race, humanity has used brilliant and unconventional ideas to take our spacecraft to the Moon, Mars, and most recently Pluto. Since the 1920's, scientists and aerospace engineers have been designing and tweaking rocket propulsion to more efficiently reach for our nearest celestial neighbors.
So far, we haven’t done a bad job, conjuring a wide range of propulsion methods varying from conventional chemical rockets, to electrical and nuclear rockets of the near future.
However, the pressure induced upon the space travel industry during the Cold War lead to a lot of improbable, impractical, and downright awful ideas for propelling payloads into orbit and beyond that make Han Solo’s ‘bucket of bolts’ look like a space travel masterpiece (no disrespect to Star Wars or the Millennium Falcon). So with no further ado, I give you the top 5 worst ideas for space propulsion!
5) The Space Tether
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| Space tether (cord shortened for detailed craft) |
Take a small spacecraft in orbit. Now take a 4 kilometer long rope and tie it to another spacecraft. Now have them both fire up their engines and whip around each other like a ladder ball, until the centrifugal force on both objects is barely enough for the rope to withstand. Finally, cut the cord. This is the space tether.
In theory, the idea of a space tether is sound. If you have the two crafts attached to each other in orbit, then they are both already traveling at orbital velocity. If you get them both to swing around each other at significant speeds, then you could send one of the crafts whizzing into space at pretty astonishing speeds.
But what about the other craft? Well, the added velocity to the first craft is identical to the subtracted velocity of the second craft (if they are the same mass). Either we use more fuel to speed the second craft back into orbit, or we just let it fall back down to Earth. So even though the first spacecraft gets off using very little fuel, the second will end up using all of the necessary fuel that the first craft didn’t use just to return to its initial orbit. Either that, or fall back to Earth, and with NASA charging $10,000 to put up a pound of material in space, I don’t think anyone would want to launch up another space tether to try this experiment again.
All things aside, the space tether would actually work, which is more than some of the other items on this list will be able to prove.
4) Star Tram Magnetic Launch System
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| Star Tram proposed magnetic launch system |
This whole idea was a disaster waiting to be constructed and then happen. Fortunately, it never got to phase 1.
The Star Tram launch system was proposed as a way to completely eliminate the use of rocket fuel at all. It was to be a 5 kilometer long magnetic track propped up against a mountain to force a payload to astonishing velocities in order to blast them into orbit. If you have ever taken a physics introductory course, you can already see every problem with this idea.
First of all, the amount of power necessary to launch even a small payload to high enough velocities to blow through the atmosphere and into orbit is unbelievable; upwards of 3000 Gigajoules. That’s enough energy to power 100 households for a year.
Secondly, the shear material and construction prowess required to build such a track is immense. And to build it up against a mountain no less.
Another major issue with such a launch mechanism is the acceleration undergone for the payload. Astronauts reach low Earth orbit in about 8 minutes, accelerating the entire way up into space. The Star Tram system intends to launch the payload to orbital velocity in 30 seconds within a few kilometers of the ground where it still has the entire atmosphere to traverse. Atmospheric conditions are chaotic, and often difficult to predict.
Finally, the payload would still need some form of propulsion on board to guide it into a stable orbit, at which point a scientist on Earth should probably ask himself if it was worth the $40 billion to build what is essentially a giant space gun.
3) Project Orion
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| Artist's rendition of Project Orion |
It takes a lot of expelled scientific knowledge and prowess to remember that at one point, Project Orion was a real idea. In fact, the idea was so prominent that in the early 1960's, the math for such a craft had already been worked out and was actually small scale tested! Project Orion was proposed as a means for interplanetary travel in the near future.
Devised by Ted Taylor in 1958, Project Orion was the study of using nuclear bombs to propel a spacecraft at extreme velocities (upwards of 3% the speed of light) so it could cover large distances relatively quickly. Yup. This was a thing.
The craft was to be designed as such: The payload (or crew) would be positioned at the front of the craft. Stowed away just below them would be hundreds upon hundreds of nuclear warheads. During flight, the craft was to launch a nuke out the back of the craft, and detonate shortly after exit. The resulting explosion would push on a shock absorber and consequently force the craft forward. What could possibly go wrong?
Temperatures within a nuclear explosion exceed 67,000 K. Even if you could find a material that remains solid in such heat, repeated subjection to a nuclear blast isn’t ideal for structural integrity. This temperature would also correspond to a ton of high energy radiation, dousing any crew or equipment in a deadly shower ultraviolet photons.
On top of this (or on the bottom of this), the shock absorber would be a feat to engineer. Subjected to such rapid fluctuations in heat and pressure, the absorber would most definitely be the first piece of equipment to fail on the ship.
Even if you could design a safe absorber and crew compartment to shield from radiation, this craft would be dangerous to launch on, or anywhere relatively near to Earth. Even in space, radioactive particles could still get caught in Earth’s magnetosphere and directed back to the Earth’s surface.
And even if one could engineer a safe, practical, and reasonable design for a Project Orion spacecraft, it would still be illegal due to the nuclear testing ban treaty of 1963! That’s right, this idea was so bad, they banned it. Under world law.
2) A Space Cannon
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| A 1940's space cannon proposition |
The other ideas on this countdown wouldn’t be half bad if they could overcome a few key issues. This idea for spacecraft propulsion, however, is the issue.
The theory is as simple as it sounds; to use an extreme explosion to thrust a projectile into space. As one can already predict, this one is going to have a pile of problems.
Like the Star Tram, we face the issues traveling through the atmosphere for the majority of the trip and the fact that we would need some form of propulsion to guide the craft into a stable, circular orbit once at altitude. The cannon, however, has even larger issues.
To launch a projectile from the base of a cannon to orbital speeds (about 7 kilometers per second) would require an impossibly immense explosion. So much so, that you probably wouldn’t have a cannon anymore after launch. But now that you’ve got your payload up to speed, it’s all smooth sailing, right? Nah.
Unlike Star Tram, where you have at least cleared the bulk of the atmosphere by launching from a mountain, a cannon would face the difficulty of actually burning up its projectile within a couple kilometers of the ground. Meteorites, which are composed of mainly iron, burn up in just a few kilometers traveling just 5 or so kilometers per second. Name a material that can sustain that heat for 60 kilometers of atmosphere traveling 40% faster and you’ve got a lot in the aerospace industry!
What could be worse that a space cannon?
1) Current Conventional Rockets
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| The Saturn V, a conventional rocket |
Shots fired? Maybe, but let’s take a step back and analyse our current methods of spacecraft propulsion.
Since the dawn of the space age, we have utilized the same basic formula for rocket propulsion:
Liquid hydrogen (LH)+ liquid oxygen (LOX) + fire = thrust.
Granted, the reaction between LH and LOX has the highest specific impulse of any potential chemical rocket (with some minor exceptions, but these are mostly dangerous and volatile reactions). Hydrogen and oxygen are also two of the most abundant elements in the universe, making them cheap and ease to get a hold of. Both gasses are easy to store and transport as well, and not difficult to synthesize into their liquid counterparts.
Okay, here comes the kicker. We have been using this method for 60 years. If we were still using the same computers from 60 years ago, we would all be using Touring Machines. Most of our parents don't even know what those are!
You may say to yourself, “so what? why fix something that isn’t broken?” Well brace yourself. Here comes more.
Conventional rockets are extremely dangerous. When you launch a LOX-LH rocket into space, you are basically putting a pile of astronauts on the top of a massive chemical bomb. About 500 people have been to space. 18 have died, 14 of whom were killed in fuel related explosions. This equates to roughly 3%, which is a huge fatality fraction. If NFL football had this magnitude of fatality ratings, 300 players would have been killed on the field since the dawn of the sport, compared to the actual value of 1.
Chemical rockets are also insanely inefficient. The space shuttle has a mass of 75,000 kg. The culmination of LOX and LH fuel weighes in at 754,000 kg, meaning that only 10% of the space shuttle’s mass at launch is the mass of the shuttle itself.
Traditional propulsion is also highly expensive. As I have already discussed, it costs $10,000 to send every extra pound of material into space due to the shear cost of fuel for a space flight.
Finally, though exhaust velocities for conventional rockets are suitable for orbital flight, they are incredibly slow for reaching out to farther destinations. Using our best chemical engines today, it takes days to reach the moon, years to reach Mars, and hundreds of millennia to get close to any neighboring stars. If we ever want to leave our doorstep, we are going to need more powerful propulsion systems.
Conclusion
Are chemical rockets really a worse method than a cannon for achieving space travel? No, obviously not. But we have been squeezing every last ounce of efficiency out of these engines since the 1960's, and it’s about time that someone made a change. Whether it be some form of fusion powered rockets, or a higher impulse ion drive, we need to replace traditional propulsion in the near future if we ever expect to get off the ground and begin to study and colonize other planets and star systems. Earth is a great place, but there is so much more offered out there than we can ever achieve by staying here.
The universe is a big place. And some forms of propulsion just won’t cut it.
