

The NASA Innovative Advanced Concepts (NIAC) program recently awarded 25 grants for the development of visionary new technologies. Here we’re going to take a closer look at the following three Phase II awards focused on advanced propulsion.

Mach Effect for In Space Propulsion: Interstellar Mission

James Woodward

Space Studies Institute, Inc. A Breakthrough Propulsion Architecture for Interstellar Precursor Missions

John Brophy

NASA Jet Propulsion Laboratory Pulsed Fission-Fusion (PuFF) Propulsion Concept

Robert Adams

NASA Marshall Space Flight Center

Each award is worth up to $500,000 for a two-year study. Descriptions of the awards are below.



Mach Effect for In Space Propulsion: Interstellar Mission

James Woodward

Space Studies Institute, Inc.

We propose to study the implementation of an innovative thrust producing technology for use in NASA missions involving in space main propulsion. Mach Effect Gravity Assist (MEGA) drive propulsion is based on peer-reviewed, technically credible physics. Mach effects are transient variations in the rest masses of objects that simultaneously experience accelerations and internal energy changes. They are predicted by standard physics where Mach’s principle applies as discussed in peer- reviewed papers spanning 20 years and a recent book, Making Starships and Stargates: the Science of Interstellar Transport and Absurdly Benign Wormholes published in 2013 by Springer-Verlag.

In Phase I we achieved the following:

Implemented chirped pulses to reduce heating and provide a longer duration thrust capability.

Designed and developed circuits to allow for 1f and 2f frequency impedance matched AC input to the device, to improve efficiency of the MEGA drive.

Developed a better theoretical model for the device and conceptualized a probe for an interstellar mission to Proxima b. In Phase II, the next critical step in the development of these thrusters is to test new designs with higher frequency to increase the output thrust.

We have been using Steiner Martin’s SM-111 PZT for our devices. We also expect to test new materials, for example APC-840 PZT, and PIN-PMN-PT, which we have procured but not had the opportunity to yet evaluate. It would also be advantageous to operate multiple devices to determine the thrust scales in arrays of 2 or more devices.

We view the independent verification of the MEGA Drive effects by experts in the vacuum testing of micropropulsion as a crucial step in Phase II. We envision a collaboration with several entities (from academia and industry) to enable the testing of new devices.

Mach effects have the revolutionary capability to produce thrust without the ejection of propellant, eliminating the need to carry propellant as required with most other propulsion systems. Ultimately, once proven in flight, these thrusters could be used for primary mission propulsion, opening up the solar system and making interstellar missions a reality.

This aerospace concept is an exciting TRL 1 technology, ready to take the next step to providing propellantless propulsion, first in incremental NASA smallsat missions, but later enabling revolutionary new deep space exploratory capabilities beyond anything achievable by conventional chemical, nuclear or electric propulsion systems.

A Breakthrough Propulsion Architecture for Interstellar Precursor Missions

John Brophy

NASA Jet Propulsion Laboratory

Our breakthrough architecture uses a kilometer-scale, multi-hundred-megawatt phased-array laser to beam power to a vehicle that converts it to electrical power for a multi-megawatt electric propulsion system that produces a specific impulse of 58,000 s. Such a system would enable missions with characteristic velocities of 100 to 200 km/s, and would enable a mission to the solar gravity lens location of 550 AU in less than 15 years.

Our Phase I study investigated all of the key assumption made in the original proposal including: the feasibility of developing photovoltaic arrays with an areal density of 200 g/m^2; the feasibility of developing a highpower electric propulsion system with a specific power of less than 0.3 kg/kW; the feasibility of developing photovoltaic cells tuned to the frequency of the laser with efficiencies of greater than 50%; and the feasibility of being able to point the laser array with the required accuracy and stability necessary to perform the reference mission to the solar gravity lens location.

The Phase I work identified plausible approaches for achieving each of these technology goals. In addition, the Phase I work looked at the system engineering of the entire propulsion system architecture with the objective of minimizing the laser aperture size. The original proposal postulated the existence of a phased-array laser with a 10-km diameter aperture, a 100-MW output power at a laser frequency of 1064 nm. This laser was assumed to power a 70-MW electric propulsion vehicle with a 175-m diameter photovoltaic array directly coupled to lithium-fueled ion thrusters operating at a specific impulse of 58,000 s.

The Phase I scaling work indicated that a better approach would be a laser with a 2-km diameter aperture with an output power of 400 MW at a laser frequency of 300 nm driving a vehicle with a 110-m diameter photovoltaic array powering a 10 MW electric propulsion system at a specific impulse of 40,000 s.

In Phase II we propose to continue to develop the Phase I concept in the context of the solar gravity lens mission. We will address the still outstanding technical feasibility issues including:

(1) Demonstrating that photovoltaic (PV) coupons can be operated at more than 6 kV in the plasma environment created by the lithium-ion propulsion system. (2) Demonstrating PV cell efficiency of 50% or greater for monochromatic inputs. (3) Modeling the characteristic of the lithium plasma plume created by the ion propulsion system. (4) Demonstrating operation of a small aperture (0.3 m to 1 m dia.), low power (a few hundred watts) phased array with long a coherence length and beacon feedback that is scalable to large apertures. (5) Investigation of beacon phase locking for long round-trip light time delays. (6) Investigating laser location impacts on cross-track thrust.

Finally, the proposed Phase II work will develop a technology roadmap including technology demonstration missions recommended as stepping stones to get to the final system architecture.

Pulsed Fission-Fusion (PuFF) Propulsion Concept

Robert Adams

NASA Marshall Space Flight Center

The pulsed fission fusion propulsion (PuFF) system envisions using a pulsed z-pinch to compress a fission-fusion target. The resulting deflagration expands against a magnetic nozzle to produce thrust and generate recharge energy for the next pulse. A z-Pinch is a device that is commonly used to compress laboratory plasmas to high pressures (~1 Mbar) for very short timescales (~100 ns).

An electrical discharge produces a high axial current along the outer surface of a column of plasma; this current in turn generates a very strong toroidal magnetic field. This self-generated magnetic field interacts with the axial current via the Lorentz force and radially compresses the plasma column, bringing it to very high densities and temperatures.

This team is exploring a modified Z-pinch geometry as a propulsion system by encasing the fission- fusion target in a sheath of liquid lithium, providing a current return path. Numerical esults have been promising, the level of compression is sufficient to reach fission criticality. The fission energy boosts the fusion reaction rate, generating more neutrons which boost the fission process. This concept will potentially reach specific impulses of 30,000 sec with thrust levels sufficient to travel to Mars in a month and to interstellar space in a few decades.