Description: Iodine is highly attractive as an alternate electric propulsion propellant to xenon. It is easily stored in a compact volume on a spacecraft as a solid (greater than twice the storage density than pressurized xenon), which negates the need for a large pressurized tank. This, combined with its low cost and lower ionization energy, makes iodine an ideal propellant for a smallsat Hall thruster system. Currently, the heaterless C12A7 electride hollow cathode is the only low power electron source available to operate with an iodine electric propulsion thruster. C12A7 electride is a conductive ceramic with a measured work function of 0.76 eV. Busek proposes to mature the heaterless C12A7 electride hollow cathode technology to be conducive to low power applications and compatible with an iodine propellant. The proposed Phase I effort will focus on the design and fabrication of a durable C12A7 electride insert that will be compatible with future efforts to produce a qualification model cathode. Potential insert designs will be evaluated based on their operation within a laboratory model cathode body. The designed insert will be incorporated into an iodine-resistant cathode barrel and keeper and the full cathode will be characterized and delivered to NASA.

Benefits: The major aerospace market for hollow cathodes is as the electron source for Hall Effect thruster (HET) propulsion systems. NASA has numerous plans for upcoming Mars, NEO sample and return missions in this decade that utilize electric propulsion. Recently NASA issued six contracts to study high power HET demonstration missions with plans extensibility for to 300kW systems. Most recently NASA/GRC and Busek collaborated on a proposal for a low power iodine demonstration submitted to NASA's Edison Small Satellite Broad Area Announcement.

In 2010, the Department of Defense launched the first AEHF satellite using HET propulsion with plans to launch five additional satellites in the next six years. Each satellite carries a sting of four HET thruster systems based on Busek technology. In March 2012 Boeing Co. announced plans for building four electric propulsion commercial ComSats. Space Systems/Loral has five electric propulsion satellites on orbit with plans to launch six more by 2015. SES, the world's second largest satellite operator, has announced plans to request bids for electric propulsion GEO ComSat. We estimate the potential HET propulsion system value of these aggregate markets at $20-60M annually: cathodes for those thrusters would account for $3-6M. Busek intends to focus exclusively on the space-based market. Should a terrestrial market become available for a C12A7 electride cathode, Busek would most likely license the technology to a commercial entity that has more experience in the field.