How does one fly around in space? When considering that space is essentially a low temperature vacuum, this question actually becomes quite challenging to address. Propulsion has been used- mechanical, chemical, ion, etc. The basic idea is that if one gives a slight ‘push’ in space, there are no resistive forces in the vacuum to resist motion. To change direction, simply sending power to a select combination of thrusters would guide the spacecraft in the desired direction. This is shown in the image below.
The problem with this method of thinking is that it’s very slow, as it’s difficult to accelerate in space. To really pick up speed, you’d either have to spend a lot of fuel in a short burst of time to increase your momentum. Then the question arises- how do you stop? Perhaps instead of thinking about space as a vacuum we need to navigate by pushing against, we need to think about space as a medium to transition through.
15 years ago, Roger Shawyer presented a radical idea that seemed to violate our conventional laws of physics: a concept called the EMDrive. It’s a propellant-less engine that operates by reverberating microwaves through the chamber of a truncated cone, shown below.
The crazy fact about this system is that it violates the conversation of momentum by creating a thrust towards the narrow end of the cone via the microwaves bouncing off the sides of the chamber. How is this possible? This question has left scientists baffled for the last ten years, and yet Shawyer’s initial experiment has been reproducible by everyone from NASA to amateurs.
We fast forward to earlier this month, where a highly anticipated paper from Michael McCulloch was published presenting a theory as to how the EMDrive could work. The core of this idea is based upon the Unruh effect, which states that accelerating objects in space experience blackbody radiation. To understand this, we need to visualize space in a different way: a vacuum isn’t particularly empty space as much as it the lowest energy state of a combination of quantized fields in space.
Without getting into too much more detail, we can see that the EMDrive has been reproducible on Earth. However, as it’s still a controversial topic, there have been back and forth discussion on the truth of the measurements. NASA defended its results in relation to account for certain characteristics of being on the planet Earth, and McCulloch incorporated that into his paper. Can’t wait to see test results in space!
So the EMDrive is one up and coming attractive option for space travel, but clearly it comes with its own disadvantages. For one, it still involves the idea of low-speed travel through space. Is there an alternative that allows one to travel faster, say at 30% the speed of light?
The answer, of course, is yes! Philip Lubin is a strong proponent of laser, or photonic, propulsion that uses electromagnetic acceleration in space. As space is essentially a low temperature vacuum as previously discussed, EM acceleration holds more promise than mechanical propulsion options may have (0.3c vs. 0.0006c). We can see this huge difference in the figure below, taken from his paper on the subject:
Is it possible? Could we in fact travel to Mars in 3 days? The short answer is a conditional yes. Lubin and his team have already shown the calculations and simulations for their technology to work, and the idea has been proven to work in smaller scales. The scaleup process has already been written in detail, so once again, we eagerly await the results from Lubin’s real life space investigation!
With both of these examples of alternative space propulsion systems, they showcase important characteristics of science: the beauty of visualizing a problem in a new light. Sometimes, as the picture below depicts, instead of thinking outside of the box, one should wonder why the box is there in the first place. Let’s hope for the best with the results of these experiments!