US Air Force Targets Energy Technology Advances

A recent report released by the USAF, Energy Horizons: United States Air Force Energy S&T Vision 2011-2026 PDF, looks at a number of new energy technologies which might advance the USAF's mission in space -- including small modular reactors for space-based systems.

In terms of nuclear power in space, several satellite systems have been energized by Radioisotope Thermoelectric Generators (RTG). This source provides consistent power, and at a much higher energy and power density than current technologies.

Work on small modular nuclear reactors on Earth is highlighted in the Air Force report: "While the implementation of such a technology should be weighed heavily against potential catastrophic outcomes, many investments into small modular reactors can be leveraged for space-based systems. As these nuclear power plants decrease in size, their utility on board space-based assets increases."

The report explains that the Air Force space systems portfolio should consider piloting small modular nuclear systems, a view previously recommended by the Air Force Scientific Advisory Board. _Space

Space.com Orbital Concentrator Solar Array

In the sweeping report a number of desirable high-tech advances are mentioned.

For example, the Air Force is currently limited to 27 kilowatt (kW) arrays for satellite power. But more power is required for some future space missions, the report states, such as flights currently being eyed by the Air Force, national security organizations and NASA. "Employing larger and more efficient arrays will enable missions that require very high power, such as space-based radar or space-based laser missions," the report states.

In the long term, the report says, increased solar cell efficiencies and revolutionary materials foreshadow the potential of 500 kW on-orbit power generation technologies, "which would be transformational for performing missions from space-based systems."

Furthermore, there are other breakthrough space energy technologies that have the potential of achieving up to 70 percent efficiency, the report adds. Examples include quantum dots and dilute nitrides in solar cells. But there are also totally new technologies such as space tethers that could harvest energy from the Earth's geomagnetic field.

...The Air Force report also delves into the wireless transfer of power, a technology that continues to offer big promises despite the daunting challenges involved in making it a reality.

While there are many challenges in "space-to-earth" power beaming, "space-to-space power beaming" could be transformational, the report stresses.

An energy-beaming benefit for the military is powering sets of fractionated, distributed satellite systems, the report explains. Doing so would enable spacecraft to be smaller, more survivable, and more capable than current systems.

A power paradigm change

In orbit, many spacecraft systems — sensors, communications equipment and on-board processing — can require intense amounts of power.

Like all computing architectures, these systems are currently composed exclusively of silicon- based technology. However, decades of work has begun to change this paradigm, the report points out. Newer systems require less energy and offer a reduced thermal load in comparison to their silicon counterparts, the report adds.

Advances in satellite propulsion are also spotlighted in the newly issued report. Today, the ability of space-based systems to alter their orbits is based on blasts of on-board fuel. The possibility of on-orbit refueling for these systems is now being studied.

In the mid- and far-term, the report suggests, other propulsion technologies will provide exceptionally efficient propulsion. That will allow the fuel onboard orbiting systems to be utilized for longer periods of time. Hall and electric thrusters, for instance, promise extended utility of limited onboard propellants.

Whatever the technology, new methods of generating power in space hold great promise for the Air Force's plans for new satellites and other space missions. _Space.com

Combining Nuclear Fission and MagnetoHydroDynamics for Space Propulsion

via NBF
In two recent blog postings, both here, and here, cutting edge science and technology blogger Brian Wang takes a look at nuclear / magnetohydrodynamic (MHD) approaches to space propulsion and electrical power generation in space.

MHD involves the acceleration of ionised plasma through a strong magnetic field to generate electric power. Such a system could provide electric power and space-based propulsion as long as plentiful fuel mass is available.

This NextBigFuture article also discusses ground based MHD systems as a clean and economic alternative for burning coal.

An interesting combination of "ground-based" and "space-based" MHD propulsion would involve the gradual ongoing hollowing out of a small asteroid, using the mining tailings as propellant fuel, and the asteroid itself as a spacecraft. Such a system could be used for either a long-range outbound space mission, or for an outer-system to and from inner-system, shuttle.

Fusion Propulsion, FRC Fusion, Fusion:MSR Fission Co-location

Brian Wang presents a trio of fusion-related articles recently:

Pulsed Field-Reversed Configuration Thrusters

Fusion Plasmoid Space Propulsion

Quasi-Steady Fusion Reactor Based on the Pulsed High Density FRC

From the last link above:

By co-locating a molten salt reactor with FRC QSFRs, a waste mitigating closed nuclear cycle is achieved that is highly proliferation resistant. Only non-fissile material enters the plant in the form of thorium. All fuel for the reactor is produced on-site by the FRC QSFR. Only a relatively small fusion power source is required (~ 7% of the fission reactor output) as it is leveraged by the much larger energy yield from the fissile fuel enriched thorium reactor. The fissile fuel doubling time can be as short as 5 years, and essentially all the thorium can be consumed in fission reactions, thus extending the energy reserves from thorium to several thousand years, limited only by the lithium reserves required for DT fusion. Waste from the thorium cycle is orders of magnitude smaller than that of a current PWR, and decays to background levels in less than 500 years – only slightly longer than that from fusion neutron activation. By using the FRC QSFR to enable a thorium based energy cycle, nuclear power can finally deliver what the current uranium based fission can not: abundant, safe, and clean energy. Most importantly, it can be done in a timeframe to allow fusion to play a role in the effort to move from a carbon based energy economy. _NBF

Brian also points to the Advanced Space Propulsion Workshop by Centauri Dreams, which covered the topics above and more. It would be great if the workshop made videos available of the talks.