David Burns, Manager, Science and Technology Office
Marshall Space Flight Center, NASA has proposed a Helical Engine. It is a propellantless engine design similar to the Mach Effect propulsion system by Woodward.
Burns goal is to use proven physics and technology
• Focus on extreme duration
• Current state-of-the-art is not sufficient, but has potential to scale
Megawatts of power + space-rated synchrotron = 1 N of thrust
• Not a compelling reason to build this engine
• Equivalent Specific Impulse over 10^17
• “Net” power less than 10 watts
• Options for increasing thrust and efficiency
• Technology is extension of space flown hardware
• Many technical challenges ahead
• Basic concept is unproven
• Has not been reviewed by subject matter experts
• Math errors may exist!
A new concept for in-space propulsion is proposed in which propellant is not ejected from the engine, but instead is captured to create a nearly infinite specific impulse. The engine accelerates ions confined in a loop to moderate relativistic speeds, and then varies their velocity to make slight changes to their mass. The engine then moves ions back and forth along the direction of travel to produce thrust. This in-space engine could be used for long-term satellite station-keeping without refueling. It could also propel spacecraft across interstellar distances, reaching close to the speed of light. The engine has no moving parts other than ions traveling in a vacuum line, trapped inside electric and magnetic fields.
The existing technology would be to try to make a mobile version of the large hadron collider. It would be 200 meters long and 12 meters in diameter – and powerful, requiring 165 megawatts of power to generate just 1 newton of thrust, which is about the same force you use to type on a keyboard. For that reason, the engine would only be able to reach meaningful speeds in the frictionless environment of space.
Below is the large hadron collider.
Nextbigfuture Reader Goatguy Provides Analysis
The ‘nut that isn’t being cracked’ is that it takes 165,000,000 Watts of power to generate 1 Newton of force.
If I shoot a LASER beam of power P out the back of an orbiter, I’ll get a force (from good ol’ Physics)
F = P / c
F = 165,000,000 W ÷ 299,792,458 m/s
F = 0.55 N
Likewise, if we reflect a laser beam with a ‘perfect reflector’ (having 100% reflectivity, no absorption) then
F = 2P / c
F = 2 * 165,000,000 ÷ 299,792,458
F = 1.10 N
Which is almost exactly what the article’s authors cite.
What would make this invention ‘special’ (if it works, of course) is that the 2P/c thrust seems possible without needing anything at all to leave the spacecraft. On the other hand, it requires the humungous power supply to be onboard, which of course carries its own mass … for the fuel, for the machinery turning fuel into power, and for getting rid of the heat and byproducts because it wouldn’t be 100% efficient. Maybe fuel-to-electricity conversions of only 20%. 80% waste heat. More likely only 10%
A real world space-ship, trying to attain relativistic velocities would definitely need WAY more power than 165 MW. Question is … how much? Unfortunately, no matter how much science fiction wishfulness I employ to find a solution, I find it really hard to envision a fusion energy system having a specific energy over 20 kW/kg. Much of that would go into heat-sinking. Unfortunately, it also defines the specific acceleration, absolute.
20 kW × 2 ÷ 299,792,458 m/s = 133 µN/kg.
F = ma, a = F/m … = 0.000133 ÷ 1.0
a = 0.000133 m/s² per kilogram.
Putting that into a PER-DAY perspective
ΔV/day = a × 24 × 60 × 60 = 11.53 m/s per day or 996,000 m/day² … perhaps it would be better expressed in years?
a = 132.7 billion m per year² … and with normalizing that to AU
a = 0.888 AU/y²
Not all that impressive. But let’s use it.
Since the distance to Alpha Centauri is 4.1 LY × 60 × 60 × 24 × 365.25 × 299,792,458 m/s = 3.88×10¹⁶ m … ÷ 149.5×10⁹ m/AU = 259,000 AU
d = ½at²
d = ½ 0.888 AU/y² t²
t = √( 2 × 259,000 ÷ 0.888 )
t = 764 years.
And that’s for a flyby without slowing down to take a look-see.
And assuming nearly-infinite fuel energy density. And very low overhead for the vehicle’s infrastructure mass.
And all that.
The time to get there and slow down would be
t = 2 √( (2 × ½) D ÷ 0.888 )
t = 2 √( 259,000 ÷ 0.888 )
t = 1,081 years.
Now, I don’t know about your thinking dear reader, but this doesn’t sound promising.
The only way it could work would be to beam hundreds of gigawatts of power from Earth or the Solar System in generation to the craft, where the power would be picked up efficiently out to, oh, maybe 20 AU? or so. You’d get the P/c acceleration for free, just receiving the power. Then the power could go at nearly 80% efficiency to electricity, which then converts to about 1.8 P/c extra thrust. Moreover, the mass of the ship is markedly reduced. Maybe by 1000 times! (Talk about ‘wishful thinking! ‘)
a = 0.133 m/s² (with some conversion yields…)
a = 0.014 LY/y²
t = 2 √( d / a )
t = 2 √( 4.1 ÷ 0.014 )
t = 34 years.
Unfortunately that is also bogus, because there’s no power source at the far end to beam power to decelerate the craft to local vectoring ambient conditions. And, if the power is only reasonably beam-able out to 20 AU, …
a = 0.014 LY/y² (with more conversion calculations)
a = 886 AU/y²
d = ½ at²
t = √( 2 d / a )
t = √( 2 × 20 ÷ 886 )
t = 0.212 year and
v = at
v = 886 AU/y² × 0.212 y
v = 188 AU/y …
Which turns the 259,000 AU Earth-to-Alpha-Cen distance into a 1,375 year adventure.
Which is NO WIN, obviously. The only real win is when Earth power can be received at high fidelity over a 5,000 AU or greater distance. And good luck to that.
d = ½ at²
t = √( 2 d / a )
t = √( 2 × 5000 AU ÷ 886 )
t = 3.36 year and
v = at
v = 886 AU/y² × 3.36 y
v = 2977 AU/y about 4.7% of c!
t = 259,000 / 2,977 AU/y
t = 87 years plus 3.3y
t = 90 years or so.
This is much MUCH better. Hibernation, metabolic slow-down, advance biomechanics and drugs to allow for a nominal 250 year lifetime (even if not hibernating), radiation repair, collision avoidance, all the InterStellar movie stuff.
Still … 5,000 AU beaming power?
We can’t even image the surface of Pluto at 40 AU worth a blip, with our largest Earth based telescopes.
Imagine trying to focus on a rapidly fleeing spacecraft far, far, far tinier than Pluto, at 100x its distance!
So we’re back in the ‘’OK, NASA fly-boys, the theory is great, and how again are we getting to Alpha Centauri?’’ questioning.
Because that’s the question needing answering.
Not the magic tech.