UFO -3: Ultra High-Speeds are Impossible (Part 3 of 8)
The Thrust SSC racing for the land speed record
In the previous chapter I said that it would take us 8,200 years to reach the nearest star if our spaceship was traveling 340,000 mph (which is 10 times faster than our fastest spaceship). Although I used this number as an illustration, we don’t even know if this speed is possible. Currently, technology needed for this type of speed doesn’t even exist on our planet. This, of course, doesn’t mean it isn’t possible; it just means we currently can’t obtain these speeds.
While I believe we can go much faster than our current speeds, it’s important to understand that there are upper limits to spaceship speeds. There are certain inescapable laws of physics that limit the speed of every type of vehicle. Cars, boats, and aircrafts are good examples of this. When these vehicles were in their infancy, they were slow and clumsy. As they were made more efficient, their speeds increased greatly. However, after a period of time, the increases in speed became smaller and less frequent. Although future refinements will probably squeeze out a few more mph here and there, there will no longer be frequent and substantial increases in speed. These vehicles have already come close to their upper limits.
What is the maximum speed for a spaceship? At this point, no one really knows. My guess is the limit will probably be less than 1 million mph (which is a great jump from our current speed of 34 thousand mph). Of course, I could be wrong. The limit could be as high as 2 million mph (555 miles per second). Even with this speed, it would still take 1,200 years to reach our closest star.
As we saw in the previous chapter, it would take thousands of years to fly to our closest star. The only way we can bridge this incredible gap is if we could fly near to the speed of light. Even flying at half the speed of light would still take 8.4 years to reach our nearest star. While this is still a long time, it can at least be done within a person’s lifetime.
Although I believe there are structural limitations that will keep spaceships from flying this fast, there is another limitation. There is no power source great enough to propel a spaceship to these speeds. As we will see shortly, even propelling a small object to these speeds would require an impossible amount of energy.
Many people assume that when something becomes "weightless" in space, it can be easily moved. This is not the case; the object still has the same mass in space as it does on earth. The more mass an object has, the more energy is needed to move it.
To illustrate, let’s say that an astronaut is on a space walk and is going to throw two objects. The first object is a "one-pound" ball and the second object is a "30,000-pound" ball. Neither ball "weighs" anything because there is virtually no gravity up there.3.1 If the astronaut has a good baseball arm, he would be able to throw the small ball very fast. However, he would barely budge the large ball. It would feel like he was pushing against a wall. The only movement taking place (apart from a slight movement of the big ball), would be the astronaut moving backwards.
How much energy will it take to propel a spaceship to ultra high-speeds? To keep things easy to visualize, we are going to calculate the energy needed to propel a one-pound object to 50% of the speed of light. The formula to determine this is:
Kinetic Energy = (1/2) (mass) (velocity) (velocity)
See footnote 3.2 for more information. To propel an object that weighs one pound to a speed 50% of the speed of light would require an energy source equal to the energy of 98 atomic bombs. That’s a tremendous amount of energy. Think about the size of an engine and the fuel that would be needed to supply that much energy. Remember, this is the energy needed to propel just a single pound. How much energy do you think would be needed to propel a whole spaceship?
Since most people can visualize NASA’s space shuttle, I will use its weight for our calculations. Although this obviously would be way too small for a trip of this duration and distance, it does provide us something tangible in which to base our calculations. For the sake of simplicity, we will not include the weight of the extra supplies needed for a trip of this length. (Note: These calculations will not include the tremendous energy needed to push the spaceship out of earth’s gravitational pull. Instead, my calculations are based on the spaceship already being outside of our solar system.)
Using the above formula, we see that it would take energy equal to the energy of 23 million atomic bombs to propel the space shuttle to 50% of the speed of light. I have another way of looking at it. Visualize all the energy (from utility companies) consumed in the U.S. in a whole year. Multiply that number by 108 and that is amount of energy needed to propel the spaceship to 50% of the speed of light. To propel the spaceship to 90% of the speed of light would equal the energy of 73 million atomic bombs or 351 years of U.S. energy.3.3
Of course, once the spaceship reaches its desired destination, it will need to slow down. To stop the spaceship would require the same amount of energy as it took to get it moving. Of course, if the spaceship plans on returning back to earth, it will need energy to speed up and slow down one more time. This means we need four times the energy listed above. One trip over and back will consume more energy than what the entire United States does in 432 years (or 1,406 years flying at 90% of the speed of light).
Actually, the required energy would be much greater. We’ve only calculated the amount of energy needed to move the actual spaceship. We didn’t calculate the amount of energy needed to move the massive engines and fuel. To illustrate this, let’s look at the launching of NASA’s space shuttle.
The first step is to calculate the amount of fuel needed to get the spaceship to the desired location. For example, if the space shuttle and its payload weighs 230,000 pounds, 210,000 pounds of fuel would be needed to get it into orbit. Unfortunately, adding this fuel also added more weight to the space shuttle. Therefore, we have to calculate the amount of fuel needed to get this new weight into orbit. This turns out to be 190,000 pounds of fuel. Again, another calculation is required. When it is all said and done, the 230,000-pound space shuttle now weighs 4.5 million pounds. As you can see, 94% of the weight is now fuel and massive engines. (There is, of course, a more complex formula that does all of these calculations at one time.)
In reality, only 6% of the fuel is used to get the shuttle into orbit. The other 94% of the fuel is needed to get itself off the ground. This is the reason it takes large rockets to put small satellites into orbit. I would like to point out that when I refer to the "weight of the fuel," I am actually talking about the weight of the fuel, its storage tanks, and the extra rocket engines. Therefore, from now on, I will use the term "rocket" to refer to all of these items.
Let’s look at a couple variations of the fuel calculations. Let’s says scientists have discovered a new fuel so powerful that a 100-pound rocket could push 230,000 pounds into orbit. After we recalculate the extra fuel needed to get the rocket itself into orbit, we see that we need a rocket that weighs less than 101 pounds.
Let’s go to the other extreme where the fuel is less powerful than our current fuel. In this situation, it would take a 250,000-pound rocket to put 230,000 pounds into orbit. This presents a serious problem. The rocket isn’t powerful enough to even get itself to the desired location, let alone the shuttle. The mass-to-thrust ratio is too great. Therefore, it doesn’t matter how many rockers are added to the shuttle, they won’t be able get the shuttle to the desired location.
When we calculated the energy needed to propel the spaceship to 50% of the speed of light, we did not include the extra weight for the rockets. How much would the rockets weigh? To answer this question, we will look at the one-pound object that we had been talking about earlier.
Our previous calculations showed us that we need the energy equal to 98 atomic bombs (5.1 x 1015 joules of energy) to get one pound to the desired speed. Therefore, we need a rocket that can provide this much energy and still weigh less than a pound. Since conventional rockets don’t even come close to this mass-to-thrust ratio, we need something more powerful. Nuclear power, of course, provides more energy per pound of fuel, than any other energy source. Therefore, we will see if it can provide the needed energy and still stay under a pound.
The atomic bomb dropped on Hiroshima produced 5.1 x 1013 joules of energy (which is about 1/98th of what we need). Although the bomb had 16 pounds of Uranium-238, it is estimated that only one pound reached critical mass and split. Therefore, as a rough estimate, we can say that it would take about 98 pounds of uranium-238 to produce the energy needed. This is obviously way above the one-pound limit. Keep in mind we still haven’t included the extra weight for the nuclear reactor itself.
I realize that the uranium-238 used in the Hiroshima bomb was not as refined and "enriched" as what is currently used in nuclear reactors today. Nevertheless, nuclear power still doesn’t come close to producing the amount of energy for the needed mass-to-thrust ratio.
Up until now, we have been assuming that our engines are 100% efficient. Nothing is 100% efficient, and most engines and power generators are very inefficient. Usually this "loss" occurs in the form of heat. For example, even if a car could efficiently burn 100% of its fuel, about 75% of the energy would still be lost in the form of heat. Utility companies are not much better (30 – 35% efficient). Therefore, when we calculate the necessary energy to propel a spaceship, the inefficiency factor must be taken into consideration.
Footnotes: The footnote section for the UFO chapters has 10 pages of calculations. I have, therefore, put all of the footnotes and calculations on another web page to keep these web pages cleaner looking. Click on the link below to go to the footnotes:
Other Chapters in this Section
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