University of Sydney doctoral candidate in Physics, Paddy Neumann, has developed a new kind of ion space drive that has 153% more fuel efficiency than the previous record ion drive built by NASA.
The current record, held by NASA’s HiPEP system, allows 9600 (+/- 200) seconds of specific impulse. However, results recorded by the Neumann Drive have been as high as 14,690 (+/- 2000), with even conservative results performing well above NASA’s best. That suggests the drive is using fuel far more efficiently, allowing for it to operate for longer. Furthermore NASA’s HiPEP runs on Xenon gas, while the Neumann Drive can be powered on a number of different metals, the most efficient tested so far being magnesium.
The drive works through a reaction between electricity and metal, where electric arcs strike the chosen fuel (in this case, magnesium) and cause ions to spray, which are then focused by a magnetic nozzle to produce thrust. Unlike current industry standard chemical propulsion devices, which operate through short, high-powered bursts of thrust and then coasting, Neumann’s drive runs on a continuous rhythm of short and light bursts, preserving the fuel source but requiring long-term missions.
The drive—which allegedly outperforms NASA’s HiPEP in fuel efficiency, but not acceleration—could potentially function as the packhorse of space travel, allowing for the transportation of cargo over long distances. Most interestingly, as it runs on metals commonly found in space junk, it could potentially be fuelled by recycling exhausted satellites, repurposing them into fresh fuel.
Hall thrusters produced 30 to 40 µN/W of thrust, the Neumann drive managed only in the 20s micronewtons per watt.
The Neumann Drive uses solid fuel and electricity to produce thrust. It is a “wire-triggered pulsed cathodic arc system” and works kind of like an arc welder.
Arc welders have a cathode (the welding rod, charged negative) and an anode (the work piece, which has the anode-lead clamped to it). When the tip of the welding rod gets close enough to the work piece, an arc of electricity sparks between them. This happens because the electric field between the cathode and anode is strong enough to rip electrons off the air molecules between them and causes a giant “spark” to jump. The arc allows electrical current to flow through the cathode, which heats the material on the tip of the welding rod.
As the electrons jump off the end of the rod and enter the arc, they carry along with them some atoms from the rod in the form of plasma. In an Arc Welder, these iron and carbon atoms then get deposited on the work piece at high energy, creating a small melt pool and the desired weld. In the Neumann Drive, these atoms will be hurled off into space, producing thrust in the drive itself.
In our system the cathode is a cylindrical rod of conducting material that we choose to use as fuel (eg magnesium, vanadium etc). The cathode is charged negative with respect to the anode, and a charging voltage of between 80 and 250V is typically used. The anode is a hollow cylinder that is aligned coaxially with the cathode, but offset slightly forwards.
The cathode rod has a hole bored down the centre of it, which holds the insulated trigger pin. It needs to be insulated so that the arc can be triggered only at the right time. Our system uses an electrical flashover system to trigger the arc, which means that we pulse a high voltage signal from the trigger pin to the cathode, creating the conditions necessary for plasma formation to occur. There are other methods for triggering an arc (including lasers), but they are not as robust as this.
Once the arc has been triggered, plasma will be created in very small and very bright spots located on the cathode surface close to the trigger location; these plasma generation sites are called “cathode spots” for obvious reasons. The cathode spots erode material from the cathode, ionising and accelerating it into the vacuum chamber so that the plasma moves downstream at high velocity through the anode mouth.
This so-called “drifting plasma” is the exhaust of our rocket, and pushes the rest of the system forwards as it hurtles away. Higher exhaust velocities mean more efficient fuel use which is measured in specific impulse, often called “bounce per ounce.”
Some of the fuels that work with the system are
SOURCES – Neumann Space, honisoit, University of Sydney