In an important step toward developing better propulsion for space travel NASA announced on April 19th that Aerojet Rocketdyne, Inc. has been selected to “design and develop” an advanced electric propulsion system to be used on its Asteroid Redirect Mission and the manned mission to Mars. The system would also be made available for commercial use.
The phrase “design and develop” does not mean that Aerojet is starting at the theoretical level. Rather Aerojet will be working with theory and technology which has been evolving since the 1950’s
“Aerojet Rocketdyne will oversee the development and delivery of an integrated electric propulsion system consisting of a thruster, power processing unit (PPU), low-pressure xenon flow controller, and electrical harness. NASA has developed and tested a prototype thruster and PPU that the company can use as a reference design.”
Aerojet’s contract is for thirty-six months with an estimated value of $67 million.
In terms of what NASA wants at the end of the years . . .
“The company will construct, test and deliver an engineering development unit for testing and evaluation in preparation for producing the follow-on flight units.”
Electric propulsion creates thrust by introducing a gas into an electric field, creating a positively charged ion and then accelerating that ion out of a nozzle creating thrust. Electric propulsion engines deliver the same amount of power while using only 10% of the fuel a chemical powered rocket would.
There are two types of electric propulsion engines or ion thrusters. The first uses a drop in the voltage between an anode and a cathode to induce a positively charged ion to move through a chamber and out a nozzle creating thrust.
Hall thrusters overcome this problem by introducing electrons into a radial magnetic field which neutralizes the positive charge build up in technology which began to evolve in the early 1960’s. Until the mid-1990’s Russia did the most work on developing Hall thrusters when NASA showed increased interest.
The piece that Aerojet is working on could be described as “what you do once you have electrical power.” NASA has also been developing the piece that generates the electrical power, the solar arrays. Testing for the new solar arrays will begin soon at NASA’s Plum Brook Station near Sandusky Ohio.
The new arrays come in two forms. The first is one which deploys in a fan shape as shown in the picture at the top. The second rolls out like a window shade.
However deployed the new arrays generate approximately 20 KW of power from 100 square meters of array. Contrast that with a solar panel on the ISS which generates 30 KW of power from 300 square meters of surface.
Two key requirements for the new arrays are that they deploy autonomously and be lightweight enough to be included in the rocket carrying the mission into space. The solar arrays on the ISS took ten shuttle launches to lift and required assembly in space by astronauts.
The new arrays are also scalable, providing up to the 800 KW estimated to be needed for a manned mission to Mars.
While NASA did not treat its announcement of Aerojet’s contract as a major announcement, as a “here’s the next step on the journey to Mars”, it could be construed as that.