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Are All Rockets the Same?
Published in Travis S. Taylor, Introduction to Rocket Science and Engineering, 2017
Electrothermal engines use electric and magnetic fields in order to improve the performance of a propellant. This is done by increasing the thermal energy of the system by turning the propellant into a hot plasma by arcing an electric current flow through it, ionizing it with microwaves, or ionizing it with radio waves. The electrothermal engine might also make use of the electromagnetic fields to accelerate the ionized propellants. A typical example of an electrothermal engine is the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) concept invented by astronaut Franklin Chang-Diaz. Figure 5.22 is a photo of the VASIMR tested and a diagram of the concept. The engine consists of superconducting magnetic cells, a plasma source, a radio- frequency (RF) booster, and magnetic field lines shaped to act as a nozzle. A neutral gas is injected into an ionization chamber where the plasma energy is boosted by RF electromagnetic waves. The ionized plasma is accelerated by the magnetic nozzle to generate thrust. The VASIMR can generate specific impulses in a large range between 3,000 and 30,000 sec with thrust up to half of a newton.
Temperature and Power Specific Mass Scaling for Commercial Closed-Cycle Brayton Systems in Space Surface Power and Nuclear Electric Propulsion Applications
Published in Nuclear Technology, 2020
Table I delineates the effects of four fundamental variables for the and equations. The spacecraft-specific mass is the key variable that when decreased favorably affects both and . It was shown in a previous publication that nuclear electric propulsion becomes competitive with chemical propulsion and nuclear thermal propulsion with a specific mass of 15.6 and 12.8 kg/kW(electric), respectively, based on the mission analysis of a human mission to Mars.2 This specific mass comparison used the NASA Design Reference Architecture 5.0 (DRA5), which contains analyses on nuclear thermal and chemical payloads and time to Mars supporting human missions.3 An equivalent nuclear electric system (matching payload, transit time, and initial mass in low-earth orbit) utilizing the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) electric propulsion system’s performance was designed4 against the chemical and nuclear thermal DRA5 missions, enabling the specific mass of the power systems to be determined.