EmDrive
The EmDrive is a controversial and highly debated concept for a spacecraft propulsion system. It was proposed by British aerospace engineer Roger Shawyer in the early 2000s.
The Claim:
The EmDrive supposedly generates thrust by bouncing microwaves inside a closed, cone-shaped container. It's claimed to produce thrust without the need for any propellant, which would be a revolutionary breakthrough in space travel.
Why it's Controversial:
The problem is that the EmDrive's claimed operation seems to violate the fundamental law of conservation of momentum. This law states that in a closed system, momentum cannot be created or destroyed. For a rocket to accelerate, it must expel mass (propellant) in the opposite direction. The EmDrive, however, supposedly produces thrust without expelling anything.
Experiments and Results:
Despite the controversy, several research groups, including some at NASA, have conducted experiments to test the EmDrive. Some of these experiments have reported small, anomalous thrust measurements. However, these results have been difficult to replicate consistently, and there are concerns about potential sources of error in the experiments.
Current Status:
As of now, the EmDrive remains highly speculative. There is no conclusive evidence that it actually works as claimed. The scientific community is largely skeptical, and most physicists believe that the reported thrust measurements are likely due to experimental errors or other unknown factors.
Potential Implications (If it Worked):
If the EmDrive were to work as claimed, it would have profound implications for space travel:
- Propellantless Propulsion: Spacecraft could travel vast distances without needing to carry large amounts of propellant, making deep space missions much more feasible.
- Faster Travel Times: Travel times to distant planets and even other star systems could be drastically reduced.
- Lower Costs: The cost of space missions could be significantly lowered, as propellant accounts for a large portion of the overall cost.
In Conclusion:
The EmDrive is a fascinating but highly controversial concept. While some experiments have reported positive results, there is no definitive proof that it works, and it appears to violate fundamental laws of physics. More research is needed to determine whether the EmDrive is a real breakthrough or simply a result of experimental errors.
Principle of Operation
At first sight the idea of propulsion without propellant seems impossible. However the technology is firmly anchored in the basic laws of physics and following an extensive review process, no transgressions of these laws have been identified.
The principle of operation is based on the well-known phenomenon of radiation pressure. This relies on Newton’s Second Law where force is defined as the rate of change of momentum. Thus an electromagnetic (EM) wave, travelling at the speed of light has a certain momentum which it will transfer to a reflector, resulting in a tiny force.
If the same EM wave is travelling at a fraction of the speed of light, the rate of change of momentum, and hence force, is reduced by that fraction. The propagation velocity of an EM wave, and the resulting force it exerts, can be varied depending on the geometry of a waveguide within which it travels. This was demonstrated by work carried out in the 1950’s. (CULLEN, A.L. ‘Absolute Power Measurements at Microwave Frequencies’ IEE Proceedings Vol 99 Part 1V 1952 P.100)
Thus if the EM wave travelling in a tapered waveguide is bounced between two reflectors, with a large velocity difference at the reflector surfaces, the force difference will give a resultant thrust to the waveguide linking the two reflectors. If the reflectors are separated by a multiple of half the effective wavelength of the EM wave, this thrust will be multiplied by the Q of the resulting resonant cavity, as illustrated in fig 1.
Fig 1. Diagram of an engine concept.
The inevitable objection raised, is that the apparently closed system produced by this arrangement cannot result in an output force, but will merely produce strain within the waveguide walls. However, this ignores Einstein’s Special Law of Relativity in which separate frames of reference have to be applied at velocities approaching the speed of light. Thus the system of EM wave and waveguide can be regarded as an open system, with the EM wave and the waveguide having separate frames of reference.
A similar approach is necessary to explain the principle of the laser gyroscope, where open system attitude information is obtained from an apparently closed system device.