The integrated specific impulse, or ISP, for SOTV is roughly 750-850 seconds -- about double that of the highest efficiency chemical engines such as the Space Shuttle SSME which is about 452 seconds.
What makes SOTV truly different from chemical stages, however, is that once on orbit, the same system used for propulsion could provide tens of kilowatts of electrical power for the life of the satellite.
Boeing leads a nationwide team of companies in the development of the SOTV Space Experiment:
We believe the development of solar thermal propulsion technologies will significantly benefit future space missions," said Ed Cady, Phantom Works SOTV program manager.
The proposed solar orbit transfer vehicle design uses an advanced solar thermal propulsion engine to provide both propulsion and electric power for the SOTV space experiment.
The SOTV specific impulse of 800 seconds is roughly twice that of chemical propulsion.