The EM Drive: Exploring the Possibilities of Laser Propulsion

In summary, the conversation discusses the concept of using 2 lasers and prisms to create thrust and propel a craft through space. However, it is determined that this method is not practical due to the vast amount of power required and the fact that the additional "bounces" of the lasers cancel each other out. The idea of using CO2 as a propellant is also suggested but it is pointed out that the astronauts already use CO2 scrubbers to recycle the air. In the end, it is concluded that there are more efficient methods of propulsion available.
  • #1
Misha2010
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I just had this thought while watching a video about the EM drive...basically using 2 lasers to bounce them off prisms inside an object to push the craft through space at a small but constant acceleration...could someone explain why this would not work?...please see attached image :)

Laser_Thruster_zpss2yotioh.jpg
 
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  • #2
Hi and welcome to PF
Using a beam of EM waves is a possibility for obtaining thrust but it requires a vast amount of power. An on board laser isn't good value as you don't need such a well collimated beam and you can get more power out of other sources.
PS you may as well fire the lasers straight out of the back. It would achieve the same amount of momentum transfer (Newton's Third Law and reaction) and wouldn't involve heating up the prism reflectors.
 
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  • #3
sophiecentaur said:
Hi and welcome to PF
Using a beam of EM waves is a possibility for obtaining thrust but it requires a vast amount of power. An on board laser isn't good value as you don't need such a well collimated beam and you can get more power out of other sources.
PS you may as well fire the lasers straight out of the back. It would achieve the same amount of momentum transfer (Newton's Third Law and reaction) and wouldn't involve heating up the prism reflectors.

yea I realize you wouldn't get much thrust, but these kind of devices never would, like a solar sail...plus the idea for using prisms would be to get a double bounce effect...but you would probably have to angle the second prisms, so you get more fwd push than sideways push...but anyway...i'm an animator, i just wanted to understand why this wouldn't work! :)
 
  • #4
Misha2010 said:
to get a double bounce effect.
The drive can only deliver the same amount of momentum change as the momentum in the beam that's leaving out of the back. All the other 'bounces' cancel each other out. Shame but that's Newton for you.
There are a lot of discussions about this topic on PF and elsewhere and sometimes the Physics isn't always well understood. But, as you are hardly likely to be investing all your money in such a system, it's not that desperate.
Cheers
 
  • #5
Misha2010 said:
I just had this thought while watching a video about the EM drive...basically using 2 lasers to bounce them off prisms inside an object to push the craft through space at a small but constant acceleration...could someone explain why this would not work?...please see attached image :)

View attachment 203483
Hi,
I also just had a thought!
What happens to the CO2 that the astronauts breath out? If this was collected, then perhaps it could be used to propel the craft?
[I did say I had a thought, but not that I had thought it through:) ]
Camerart.
 
  • #6
camerart said:
What happens to the CO2 that the astronauts breath out?

you should read up on space flight :wink:

you would have found they use CO2 scrubbers to get back breathable oxygen/air
 
  • #7
Hi S,
I did say I hadn't thought it through :smile:
Thinking back, I used to service oxygen producing machines, which included CO2 scrubbers.
I'm sure they recycle almost everything.
C.
 
  • #8
camerart said:
If this was collected, then perhaps it could be used to propel the craft?
davenn said:
you would have found they use CO2 scrubbers to get back breathable oxygen/air

But there's a more fundamental problem. How does collecting CO2 propel the craft? Do the astronauts blow it out the back? (Make a wish everyone!) You need to impart momentum somehow.
 
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  • #9
Hi,
Yes, anything blown or thrown "out the back", will push the craft forward, CO2, Computers etc.
(So far I don't think wishing helps)
C.
 
  • #10
Misha2010 said:
...plus the idea for using prisms would be to get a double bounce effect...
One of the bounces is canceled by the recoil of the laser. With ideal refection it would be the same as simply pointing the laser back. But in reality it's worse, due to partial absorption at the reflector.
 
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FAQ: The EM Drive: Exploring the Possibilities of Laser Propulsion

What is the EM Drive?

The EM Drive, or electromagnetic drive, is a proposed form of propulsion that uses microwaves to generate thrust without the need for traditional propellant. It has gained attention for its potential to revolutionize space travel.

How does the EM Drive work?

The EM Drive works by bouncing microwaves back and forth within a closed, cone-shaped chamber. This creates a difference in radiation pressure, which results in a net thrust in one direction. The exact mechanism behind this thrust is still being studied and debated by scientists.

What are the potential applications of the EM Drive?

The EM Drive has the potential to greatly reduce the cost and time of space travel, as it eliminates the need for heavy and expensive propellant. It could also be used for long-duration space missions, such as to Mars, as it does not rely on external fuel sources.

What are the challenges and limitations of the EM Drive?

One major challenge of the EM Drive is that it goes against the laws of classical physics, specifically Newton's third law of motion. This has led to skepticism and criticism from the scientific community. Additionally, the thrust generated by the EM Drive is currently very small and may not be enough for practical use.

What is the current status of research on the EM Drive?

Research on the EM Drive is ongoing, with various studies and experiments being conducted to further understand its potential and limitations. While some studies have reported positive results, others have not been able to replicate these findings. Further research and testing are needed to fully explore the possibilities of laser propulsion and the EM Drive.

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