Propulsion

Spacecraft Systems

We will separate our discussion of the design of the propulsion subsystems operating onboard the spacecraft into four parts:

  • Choosing a reliable propulsion system and background of propulsion method
  • Mission requirements for exploration of Epsilon Eridani
  • Team Bound's specifications for ion thruster system to achieve mission
  • Contracting the design of the propulsion system for development by a third party specializing in electrodeless plasma ion thrusters

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    Research & Background

    Deep Space 1

    Team Bound chose Ion Propulsion for its interstellar mission because of its high efficiency, lack of reliance on external energy sources, and larger level of research and data available on the technology.

  • Chemical rockets produce significantly less impulse than ion propulsion1. Additionally, ion thrusters can fire for much longer than chemical rockets. Because of Team Bound's interstellar mission's long distance, chemical rockets will be far too inefficient and not reach nearly a high enough velocity to reach Epsilon Eridani in a reasonable amount of time.
  • Nuclear propulsion systems could potentially be very ideal for interstellar propulsion; however, NASA disbanded its Nuclear Fusion propulsion research after the Nuclear Test Ban Treaty, and the feasibility of nuclear propulsion is much further away than already tested ion thruster technology. Additionally, an interstellar system will require large amounts of fuel, and launching large amounts of radioactive material from Earth and over the Earth has many environmental and societal concerns and implications.
  • Solar sails were also discussed, however they are very slow, and their payload capabilities are very small. This makes the solar sail impractical for an interstellar craft.

    • Initial research for the propulsion system was based upon the Deep Space 1 probe launched on 24 October 1998. This probe used a 2.3 kW Xenon-fueled Ion Propulsion System, but was constrained to run below 2.1 kW due to power limitations2. The probe reached a maximum speed of approximately 53,100 km/hr using only 74 kg of Xenon propellant3. The total mass of the system was 486.3 kg including propellant. Picture courtesy of NASA and part of the public domain.


    Mission Information & Trajectory

    Epsilon Erandni

    Based on Team Bound's exoplanet mission information requiring the system to travel 10.5 light years and a desired travel time of 1000 years, the necessary top speed of the system can be calculated. Because Ion Propulsion systems are intended to thrust for a long period of time, the velocity of the system is assumed to be a linear ramp up to a maximum speed, followed by a linear ramp down to slow the vehicle down for its mission upon reaching Epsilon Erandni. Thus, the system will be speeding up for the first half of its travel, reach its maximum speed, and then begin slowing down for the second half of its trip.

    Based on these assumptions, the necessary top speed of Team Bound's system to travel 10.5 light years in 1000 years is 2.1% the speed of light or 6300 km/s. This equates to an average speed of 1.05% the speed of light or 3150 km/s for the entire duration.

    As for trajectory, methods such as a gravity slingshot around were analyzed6. However, they are marginally useful for our situation becased of the speeds we want to achieve and the relative mass of our vehicle. Thus, trajectory will be a straightforward path towards Epilson Eridani:




    Team Bound's Requirements

    10.5 Light Years

    Due to the duration of the mission and the excessive amount of vibration that will occur, minimizing the amount of electronics and junctions on-board is a high priority. Team Bound will be using electrodeless plasma ion thrusters to reduce points of failure in the thrusters over the voyage. Four ion thrusters will be used for redundancy, with 2 oriented for the first half of the trip, and 2 oriented to slow the system down on the second half of the trip.

    In order to make the 10.5 light year journey in one millienium, Team Bound's system will require a much larger ion thruster than in Deep Space 1. Team Bound plans to use a 250 kW ion thruster with 20% thrust improvement and 30% fuel efficiency improvement over Deep Space 1's ion propulsion system. With these improvements and the large power increase, Team Bound's interstellar system will achieve its mission with approximately 32,000 kg of Xenon propellant for a system of 100,000 kg mass (including the propellant)4. Team Bound's ion drives will also require longer lifetimes than are currently available in most ion drives. The electrodeless plasma thruster has significantly less erosion than gridded ion thrusters and thus allows for longer lifetimes5. A user-adjustable calculator for determining these mission specifications is available here.



    Design Contract

    The Elwing Company

    Based on the propulsion requirements of Team Bound's mission as well as research, patents, and work already completed by Elwing Corporation, Team Bound will be seeking a design contract with the Elwing Corporation to produce four 250 kW electrodeless plasma ion thrusters. The contract is expected to last 30-40 years and be valued at over $1 billion with materials. Elwing Corporation will be awarded $5 million for a 1 year feasibility study of the technology and will continue on an award-fee basis. More information can be found in the Budget Section.