NIAC Phase I Award: Breakthrough Propulsion for Interstellar Precursor Missions

Breakthrough Propulsion Architecture for Interstellar Precursor Missions (Credit: John Brophy)

A Breakthrough Propulsion Architecture for Interstellar Precursor Missions

John Brophy
NASA Jet Propulsion Laboratory
Pasadena, Calif.

Value: Approximately $125,000
Length of Study: 9 months

Description

We propose a new power/propulsion architecture to enable missions such as a 12-yr flight time to 500 AU—the distance at which solar gravity lensing can be used to image exoplanets—with a conventional (i.e., New Horizons sized) spacecraft.

This architecture would also enable orbiter missions to Pluto with the same sized spacecraft in just 3.6 years. Significantly, this same architecture could deliver an 80-metric-ton payload to Jupiter orbit in one year, opening the possibility of human missions to Jupiter.

These are just a few examples of high-impact missions that simply cannot be performed today due to limitations in current technology. Our architecture accomplishes this by combining the following three innovations:

  1. A 10-km diameter, 100-MW laser array that beams power across the solar system.
  2. A 70% efficient photovoltaic array tuned to the laser frequency producing power at 12 kV.
  3. A 70-MW direct-drive, lithium (not xenon)-based ion propulsion system with a specific impulse of 58,000 s.

The key to the development of any system for rapid space transportation is the ability to process a lot of power level with little dry mass, combined with the ability to provide a very high total spacecraft velocity change (delta-V) without a lot of propellant. These two requirements translate into the need for a very low specific mass (kg/kW) and a very high specific impulse.

A specific mass of 0.25 kg/kW is enabled in our architecture by removing the power source and most of the power conversion hardware from the spacecraft and replacing them with a lightweight, photovoltaic array that outputs electric power at the voltage needed to drive a lithium-fueled, gridded ion thruster system at a specific impulse of 58,000 s. For comparison, the state-of-the-art for specific mass and specific impulse, as represented by the Dawn spacecraft, are 300 kg/kW and 3,000 s, respectively.

This architecture provides a breakthrough way to take advantage of very high-power lasers, of the type described by Lubin, to provide fast transportation though out the solar system and beyond for conventionally-sized spacecraft.

We take as a given the existence the “Orbital filled 10-km array” from, and assume that its output power has been derated by a factor of a thousand from 100 GW down to 100 MW. Our innovation is the recognition that such an array increases the power density of photons available to a spacecraft illuminated by the laser beam by two orders of magnitude relative to solar insolation at all the solar system distances beyond 5 AU, and that this enormous power can then be used to great effect by driving a highly-advanced ion propulsion system.

A high-voltage photovoltaic array tuned to the laser frequency converts the laser power to electric power at an efficiency of 70% and produces an output voltage of 12 kV.

The 12-kV output voltage is used directly to provide the net accelerating voltage for the lithium fueled, gridded ion propulsion system eliminating the heavy, inefficient, power processing hardware, and the associated thermal radiators, typically needed to drive ion propulsion systems.

The lithium-fueled, gridded ion propulsion system provides a specific impulse of 58,000 s, roughly 20 times the current state of the art. Lithium stores as a solid, is easily ionized, and very difficult to doubly ionize. This allows the thruster to be operated with nearly 100% ionization of the propellant which effectively eliminates neutral gas leakage from the thruster and the production of charge-exchange ions that are responsible for thruster erosion and current collection on the photovoltaic arrays. This key benefit enables very long thruster life and facilitates the development of the 12-kV photovoltaic array.

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  • Brainbit

    The picture matches this project, not like Breakthrough Asteroid Survey Telescope. which is actually based on 3 laser scanning theodolites.
    How safe lithium is depends on if you bought a Samsung Note 7 Tablet last year.
    There is also a problem with an orbital laser as it will not be able to point its laser at a craft continuously as it is going around its orbit even if that orbit is a Lagrange point. I suggested an idea to NASA about using the ISS to base a laser run from the solar arrays on the ISS to higher or lower the orbit of a space tug using a Stirling engine to generate power for a SEP from the laser. The obvious problem is it could only work if in the same orbit as the ISS just higher or lower.

  • Jacob Samorodin

    Put this in perspective. Pioneer 10, silent though it is now, has cruised through space for 45 years. In 45 years this deep-space craft (if it ever gets built) if it is launched before 2030, will reach 1000 AU before 2062.

  • I’m curious as to what he will propose that can use PV visible laser light.

    You need a high energy UV or in reality an X-Ray laser to properly bean the energy over such distances without too much beam spread (https://en.wikipedia.org/wiki/Beam_divergence). At Jupiter there would a lot of spread in the visible light spectrum to get more than a fraction of a fraction of a percent to the target. You’d need a GW scale visible light laser to even think of getting MW scale power near Jupiter let alone at the 550 AU of the Sun’s gravitational optical focal point.

  • Andrew_M_Swallow

    There will be other spacestations in other orbits. Also single purpose power satellites can be made.