# Calculating Robert Zubrin's Dipole Drive Mass Flow

• I
• Sebastiaan
In Summary, Robert Zubrin presented a new concept for space propulsion called the Dipole Drive. He explained that a Coulomb of protons has a mass of 0.011 milligrams, and if the jet power is 400 W and the potential difference is 64 V, so the proton current will be 6.25 A and have a mass flow of 0.0652 mg/s.

#### Sebastiaan

I'm trying to understand calculation made Robert Zubrin in his presentation on Dipole Drive

source:

In here he made the following statement

"A Coulomb of protons has a mass of 0.011 milligrams. If the jet power is 400 W, and the potential difference is 64 V, so the proton current will be 6.25 A, and have a mass flow of 0.0652 mg/s"

My question is, how did he derive to "a mass flow of 0.0652 mg/s"?

Sebastiaan said:
My question is, how did he derive to "a mass flow of 0.0652 mg/s"?
I haven't checked to see if the calculation is right, but the idea is pretty simple. We're given the power and the voltage, so can calculate the current, and hence the amount of charge per second.

Be aware that getting this calculation right doesn't necessarily validate the rest of the video.

Nugatory said:
I haven't checked to see if the calculation is right, but the idea is pretty simple. We're given the power and the voltage, so can calculate the current, and hence the amount of charge per second.
If the obvious computation is used then the maths, at least as reproduced by Sebastiaan, is wrong. A current of 6.25A is 6.25C/s. The given mass of a Coulomb of protons is 0.011mg, which means 6.25×0.011 mg/s, which I make 0.06875 mg/s.

Either there's a typo or there's something more sophisticated going on that I can't think of right now (I can't watch the video at the moment).

• Sebastiaan
The 11µg are probably the result of poor rounding, the actual value is 10.4 µg and multiplied by 6.25 we get 65.25 µg.

Edit: Oops, µg.

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• Sebastiaan and Ibix
That's 10.4 µg.

Ibix said:
If the obvious computation is used then the maths, at least as reproduced by Sebastiaan, is wrong. A current of 6.25A is 6.25C/s. The given mass of a Coulomb of protons is 0.011mg, which means 6.25×0.011 mg/s, which I make 0.06875 mg/s.
That exactly what I though. So I though I was missing something

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mfb said:
The 11µg are probably the result of poor rounding, the actual value is 10.4 µg and multiplied by 6.25 we get 65.25 µg.
Edit: Oops, µg.
I guess you mean 0.0104396 mg * 6.25 A = 0.06524803 mg/s. Thanks, now it makes sense

Still the question why did he round 0.0104396 down to 0.011 ? Seems to me this is a mistake which will result in confusion

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## 1. How does the Dipole Drive work?

The Dipole Drive is a theoretical propulsion system proposed by Robert Zubrin that uses magnetic fields to accelerate and decelerate a spacecraft. The spacecraft would have two large electromagnetic coils, or dipoles, that would create a magnetic field. By switching the polarity of the dipoles, the spacecraft can accelerate or decelerate by interacting with the magnetic field of a nearby planet or moon.

## 2. What is the mass flow rate of the Dipole Drive?

The mass flow rate of the Dipole Drive is calculated by taking the ratio of the force exerted on the spacecraft by the magnetic field to the acceleration of the spacecraft. This value is then multiplied by the velocity of the spacecraft to determine the mass flow rate.

## 3. How does the mass flow rate of the Dipole Drive compare to other propulsion systems?

The mass flow rate of the Dipole Drive is significantly lower than traditional chemical rockets, but higher than ion thrusters. However, the Dipole Drive has the potential for much higher specific impulse, making it a more efficient and effective propulsion system for long-distance space travel.

## 4. What factors affect the mass flow rate of the Dipole Drive?

The mass flow rate of the Dipole Drive is affected by several factors, including the strength of the magnetic field, the size and orientation of the dipoles, and the distance between the spacecraft and the planet or moon. Additionally, the mass of the spacecraft and its velocity can also impact the mass flow rate.

## 5. Is the Dipole Drive feasible for use in real spacecraft?

Currently, the Dipole Drive is still a theoretical concept and has not been tested in space. However, with advancements in technology and further research, it is possible that the Dipole Drive could be used in future spacecraft. Its potential for high specific impulse and low mass flow rate make it a promising option for long-distance space travel.