David Burns' Helical Engine Won't Work

There was a little bit of a kerfuffle a week or so ago about an engineer from NASA (David Burns, reportedly the Manager of the Science and Technology Office of the Marshall Space Flight Center but I’ve not been able to independently verify that).  He put up a document on a NASA page talking about an engine that could reach large fractions of the speed of light (more than 90%) with pretty much no fuel.  That document has since been removed but it can still be viewed at the Wayback Machine.

I’m astounded that it got put up at NASA in the first place.  It simply won’t work, he’s got the physics wrong.  Looking at the “Thought Experiment” which has a weight on a spring in a box, one can see that the fundamental principle is incorrect.  Within the frame of the box (or the spaceship, or whatever), the mass inside would be slightly heavier at both ends of the cycle, within the frame of the container, so there won’t be an overall forward propulsion imparted to the container.  The best you could hope for is that the container (box, spaceship, whatever) would quiver (and even then that would contribute to the mass inside losing momentum).

It all comes down to the total energy.  I’m going to explain in terms that I introduced at On Time.

A spaceship with (stationary) mass M_o, when it's stationary, has energy M_oc² – we can think of this as the rest mass times it’s “speed through time”, or v_T = c.  When at a velocity through space, v_S, spaceship has energy M(v_T² + v_S²) where, v_T ≠ c but instead (due to time dilation) v_T = c.√(1 - v_S²/c²) = √( c² - v_S²), so energy is E(v_T)=Mc².

But M ≠ M_o, instead M = M_o/√(1 - v_S²/c²), which when you work it all through, observing that 1/√(1 - v_S²/c²) ≈  1 + v_S²/c² (accurate to within 10% to about 0.68c and within 2% to about 0.47c), gives you E(v_T)=M_oc² + ½M_ov_T ² (see On Time).

This means that you need to pump ½M_ov_T² into the system – which is the extra mass he’s talking about – or you aren’t going anywhere.

To get to from zero to 297 million metres per second (0.99c, one of the numbers being bounced around), assuming no losses, that’s 88 petajoules per kilo or 88000 million megajoules and noting that liquid hydrogen has an energy density of about 120 MJ/kg (according to a guy at Stanford) you are going to need a lot of fuel to get your spaceship up to that speed, even if you ignore the fuel burden and losses and assume some magical method by which the energy in liquid hydrogen is converted directly into kinetic energy.

To be fair to David Burns, his “paper” (it’s not a paper, it’s a few PowerPoint slides!) ends with these words:

• Basic concept is unproven
• Has not been reviewed by subject matter experts
• Maths errors may exist!

It's entirely possible that the document ended up where it was by mistake (as it clearly wasn't ready for publishing to the world).  The fact that so many organisations ran with this, so uncritically, as if it were something real is simply very sad.