BOX 4.1
Interstellar Observatory

Mission Type: NEP-class


  • Explore the nature of the interstellar medium and its implications for the origin and evolution of matter in our galaxy and universe;

  • Explore the outer solar system in search of clues to its origin and to the nature of other planetary systems;

  • Explore the influence of the interstellar medium on the solar system, including its dynamics and evolution; and

  • Explore the interaction between the interstellar medium and the solar system as an example of how a star interacts with its local galactic environment.


  • Two RPS-powered subsatellites carrying identical payloads are released from an NEP-class ferry. Each has a science payload of 100 kg, a power requirement of 100 W, and a bit rate (direct to Earth) of 1,000 bps.

  • The ferry may carry instruments that are insensitive to the reactor’s radiation and particulate contamination and that can make use of a much higher data rate using the power from the reactor.

  • Travel time to 150 AU (toward the nose of the heliosphere and into interstellar flow) is 15 years.

  • The first subsatellite is released when the ferry has reached between 80 and 90 percent of its terminal velocity. The ferry then performs a small trajectory-deflection maneuver, continues to accelerate until its propellant is depleted, and then releases the second subsatellite. The diverging trajectories of the two subsatellites allow them to sample separate regions of the boundaries of the heliosphere and interstellar medium.

various options. The preliminary nature of the cost estimates for an interstellar probe, the ill-defined nature and capabilities of the different nuclear and non-nuclear implementations of this mission, and the fact that both nuclear-electric propulsion and solar sails have yet to be demonstrated in space strongly suggest that nuclear as well as non-nuclear mission concepts should be held as options in detailed trade-off studies.

Decadal Survey Missions Enhanced or Enabled by RPS

The missions selected in the SSP decadal survey that might be enhanced or enabled by RPS technologies are as follows:

  • Solar Probe. A Science and Technology Definition Team established in 2003 is working to finalize the scientific objectives, spacecraft design, payload complement, and mission profile for the Solar Probe. The baseline launch date is October 2014.16 An assumption of the ongoing studies is that the Solar Probe will make use of three of the multi-mission radioisotope thermoelectric generators (MMRTGs) that are being designed for use on the

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