General Discussion > New Physics for Space Technology
Pushing against the universe - implications for propellantless propulsion
Jim Davis:
Back in August Gary Hudson was a guest on the Space Show podcast discussing the recent NAIC grant the Space Studies Institute received involving SSI's Mach effect thruster propelled Proxima B probe. I asked whether Mach effect thrusters violated any conservation laws. He replied that although it might seem that way if one only looked at the thruster and probe by themselves, one has to take into account the energy and momentum of the entire universe. This is my first crack at that.
Suppose we have a coordinate system fixed to a Mach effect thruster. The thruster developes thrust by pushing against the universe so the thrust can be calculated (in Newtonian terms for simplicity, the result is identical in relativistic terms) as the time rate of change of the momentum of the universe:
F = d/dt(mu)
where
F - Mach effect thrust
m - mass of universe
u - velocity of universe
Since m is constant we have:
F = m du/dt (equation 1)
Mach effect power is the time rate of change of the kinetic energy of the universe:
P = d/dt( m u^2 / 2)
where
P - Mach effect power
Again, m is constant so this becomes:
P = m u du/dt (equation 2)
Substituting equation 1 into equation 2 gives:
P = F u (equation 3)
Equation 3 implies that Mach effect thruster performance is heavily dependent on the velocity of the universe relative to the Mach effect thruster. In the SAIC proposal above 5 N/kWe was mooted. This implies a universal velocity of 200 m/s.
Some other implications:
1. The mach effect thruster would be an energy source if the thrust vector is aligned counter to the universal velocity but an energy sink if aligned with it. Have there been any propellant propulsion tests that claim to substantiate this?
2. Mach effect thruster performance would very wildly depending on the time of day or the time of year as the earth's rotates and revolves. Has any propellant propulsion tests noticed this effect?
I will confess up front that this is not a field I follow with any vigor; NASA Spaceflight is about my only source for news in this field. That said, my impression is that the universe is invoked more to evade discussion of conservation laws rather than to explain how they apply. Mach effect propelled ships in particular are analogized often to sailing ships that take momentum and energy from the wind. If there is any thing to the Mach effect the analogy is a good one. I just see little evidence that Mach effect proponents have taken that analogy nearly far enough.
meberbs:
--- Quote from: Jim Davis on 10/03/2017 11:45 pm ---Equation 3 implies that Mach effect thruster performance is heavily dependent on the velocity of the universe relative to the Mach effect thruster. In the SAIC proposal above 5 N/kWe was mooted. This implies a universal velocity of 200 m/s.
--- End quote ---
Some numbers you should be aware of when trying to figure out the relevant velocities:
Speed due to Earth rotation at Equator: 640 m/s
Earth's speed around the sun: 30 km/s (30000 m/s)
Speed of sun around center of galaxy: about 200 km/s (200000 m/s)
Earth's speed relative to the CMB: about 370 km/s (370000 m/s)
I am not a particular proponent of the Mach effect due to questions related to instantaneous interactions and relativity as well as whether a "velocity of the universe relative to you" can even be defined.
ThinkerX:
--- Quote from: meberbs on 10/04/2017 12:19 am ---
--- Quote from: Jim Davis on 10/03/2017 11:45 pm ---Equation 3 implies that Mach effect thruster performance is heavily dependent on the velocity of the universe relative to the Mach effect thruster. In the SAIC proposal above 5 N/kWe was mooted. This implies a universal velocity of 200 m/s.
--- End quote ---
Some numbers you should be aware of when trying to figure out the relevant velocities:
Speed due to Earth rotation at Equator: 640 m/s
Earth's speed around the sun: 30 km/s (30000 m/s)
Speed of sun around center of galaxy: about 200 km/s (200000 m/s)
Earth's speed relative to the CMB: about 370 km/s (370000 m/s)
I am not a particular proponent of the Mach effect due to questions related to instantaneous interactions and relativity as well as whether a "velocity of the universe relative to you" can even be defined.
--- End quote ---
I too, have severe doubts about the instantaneous interactions for Woodward/Mach.
However, I do note that even without the 'instantaneous effect,' gravity is binding over literally interstellar distances - aka stars in the Milky Way are constrained to follow galactic orbits. Given that kind of gravitational strength, it *might* be possible to tap into gravity as a viable source of interstellar travel, maybe even to the point of relativistic velocities.
aceshigh:
here the link to the specific Space Show program
http://thespaceshow.com/show/15-aug-2017/broadcast-2966-gary-hudson
there is a description of the questions and arguments by Jim Davies, in the 4th paragraph.
SteveD:
If the universe gives you a little energy for a MEGA drive, eventually you could get up enough energy to pop a planet or star. We probably do not live in a universe where such self accelerating objects exist.
If the Universe can give you a little energy why can't it give you a lot to warp spacetime? If the device only has KE= energy in but is gaining additional velocity by an effect that cannot be harvested to slam into a stellar object at reletavistic speeds, then once again we do not live in a universe where you can pop planets.
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