James Benford

Microwave beam-driven sail flight experiments

We have observed flight of ultralight sails of Carbon-Carbon microtruss material at several gees acceleration. To propel the material we sent a 10 kW, 7 GHz beam into a 10−6 Torr vacuum chamber and onto sails of mass density 5–10 g/m2. At microwave power densities of ∼kW/cm2 we saw upward accelerations of several gees and flights of up to 60 cm. Sails so accelerated reached >2000 K from microwave absorption, a capability of carbon which rules out most materials for high acceleration missions. Diagnostics were optical and IR video photography, reflected microwave power and residual gas analysis. Data analysis and comparison with candidate acceleration mechanisms shows that photonic pressure can account for 3 to 30% of the observed acceleration, so another cause must be present. Future research will measure the thrust precisely using a pendulum to try to identify the acceleration mechanism. In the future, microwave-driven acceleration might be used to propel probes to very high speeds for science missions t...

Flight of Microwave‐Driven Sails: Experiments and Applications

We have observed flight of ultralight sails of carbon‐carbon microtruss material at several gees acceleration. To propel the material, we sent a 10 kW, 7 GHz beam into a 10−6 Torr vacuum chamber and onto sails of mass density 5–10 g/m2. At microwave power densities of ∼kW/cm2 we saw upward accelerations of several gees: sails so accelerated reached >2000 K from microwave absorption. Data analysis and comparison with candidate acceleration mechanisms shows that photonic pressure can account for 3 to 30% of the observed acceleration and that the remainder comes from desorption of embedded molecules. This is a useful propulsion mechanism: A microwave beam source in orbit could illuminate a sail, provoking desorption and enhancing thrust by many orders of magnitude over solar sails, shortening the escape time to weeks (compared with years for solar sails).

Desorption-assisted sun diver missions

Solar-driven sails which can also accelerate by “boil off” of coated materials offer new high-velocity missions. These can take advantage of high temperature characteristics of the sail by using the large solar flux at perihelion. For the near term use of beamed power, beam illumination at ∼kW/cm2 in LEO can simulate conditions any solar grazer mission will experience to within 0.01 A.U. Sublimation (or desorption) thrust from LEO into interplanetary orbit can omit the several-year orbits conventional solar sails need to reach ∼0.1 AU. A second “burn” at perihelion, the highest available orbital velocity in the inner solar system, and thus optimum point for a delta-V, then yields high velocities of ∼50 km/s for >40 A.U. missions. The mission begins with deployment in Low Earth Orbit by conventional rocket. Then the launch begins, driven by a microwave beam (and much smaller solar photon thrust) from nearby in orbit. Beam heating makes a “paint” (polymer layer #1) desorp from the sail. Under this enhanced ...

POWER BEAMING LEAKAGE RADIATION AS A SETI OBSERVABLE

The most observable leakage radiation from an advanced civilization may well be from the use of power beaming to transfer energy and accelerate spacecraft. Applications suggested for power beaming involve launching spacecraft to orbit, raising satellites to a higher orbit, and interplanetary concepts involving space-to-space transfers of cargo or passengers. We also quantify beam-driven launch to the outer solar system, interstellar precursors and ultimately starships. We estimate the principal observable parameters of power beaming leakage. Extraterrestrial civilizations would know their power beams could be observed, and so could put a message on the power beam and broadcast it for our receipt at little additional energy or cost. By observing leakage from power beams we may find a message embedded on the beam. Recent observations of the anomalous star KIC8462852 by the Allen Telescope Array set some limits on extraterrestrial power beaming in that system. We show that most power beaming applications commensurate with those suggested for our solar system would be detectable if using the frequency range monitored by the ATA, and so the lack of detection is a meaningful, if modest, constraint on extraterrestrial power beaming in that system. Until more extensive observations are made, the limited observation time and frequency coverage are not sufficiently broad in frequency and duration to produce firm conclusions. Such beams would be visible over large interstellar distances. This implies a new approach to the SETI search: Instead of focusing on narrowband beacon transmissions generated by another civilization, look for more powerful beams with much wider bandwidth. This requires a new approach for their discovery by telescopes on Earth. Further studies of power beaming applications should be done, which could broaden the parameter space of observable features we have discussed here.

Sail deployment by microwave beam—experiments and simulations

Unfurling and deployment of large-area, membrane structures in space is essential for many NASA purposes, such as large ultralight antennas and mirrors, occulters, collectors for SPS, and sailcraft for deep space exploration. Deployment is a complicated electromechanical problem, exacerbated by the difficulty and expense of realistic lab or space experiments. The requirement is to open and control very light but very large structures with a minimum of mechanical contact (“hands-off”), deployed from a minimum stowed volume (maximum packing fraction), while providing for control after deployment. We report here on a project that addresses deployment of carbon and other light materials by use of spin, charge and elastic forces. Last year we demonstrated microwave-driven spin of several types of sail by using polarized microwaves at JPL. In the first phase, we conducted experiments to study microwave beam-driven spin deployment, simulating this deployment and its extension to large structures in space. We wil...

Spin of Microwave Propelled Sails

It is not widely recognized that a circularly polarized electromagnetic wave impinging upon a sail from below can spin as well as propel. Our experiments show the effect is efficient and occurs at practical microwave powers. The wave angular momentum acts to produce a torque through an effective moment arm of a wavelength, so longer wavelengths are more efficient in producing spin, which rules out lasers. A variety of conducting sail shapes can be spun if they are not figures of revolution. Spin can stabilize the sail against the drift and yaw, which can cause loss of beam‐riding. So, if the sail gets off‐center of the beam, it can be stabilized against lateral movement by a concave shape on the beam side. This effect can be used to stabilize sails in flight and to unfurl such sails in space.

Stability and control of microwave-propelled sails in 1-D

This paper is concerned with the stability of carbon fiber sail structures that are being studied in a series of experiments at the Jet Propulsion Laboratory (JPL) by a team led by Microwave Sciences, Inc. The passive dynamic stability in the one-dimensional (1-D) case is most easily understood in terms of the fixed points of the trajectories for the governing equations of motion. The simple 1-D model introduces the possibility of controlling a microwave-propelled sail using various nonlinear control strategies. This work will be extended in the future to control the full 3-D case. We present results of studies from the 1-D analysis. In addition to providing guidance to ongoing and near term proof-of-principle experiments, this work will lead to novel strategies for enabling a feedback power controller to maintain a sail fixed at a predetermined height.

Applications of high-power microwaves

We address a number of applications for HPM technology. There is a strong symbiotic relationship between a developing technology and its emerging applications. New technologies can generate new applications. Conversely, applications can demand development of new technological capability. High-power microwave generating systems come with size and weight penalties and problems associated with the x-radiation and collection of the electron beam. Acceptance of these difficulties requires the identification of a set of applications for which high-power operation is either demanded or results in significant improvements in performance. We identify the following applications, and discuss their requirements and operational issues: (1) High-energy RF acceleration; (2) Atmospheric modification (both to produce artificial ionospheric mirrors for radio waves and to save the ozone layer); (3) Radar; (4) Electronic warfare; and (5) Laser pumping. In addition, we discuss several applications requiring high average power that border on HPM, power beaming and plasma heating.

Near‐Term Beamed Sail Propulsion Missions: Cosmos‐1 and Sun‐Diver

Next year the Planetary Society plans to launch Cosmos‐1, the first solar sail. We are planning an experiment to irradiate the sail with the Deep Space Network beam from Goldstone. This can demonstrate, for the first time, beamed propulsion of a sail in space. The 450 kW microwave beam from the large 70‐m dish can show direct microwave beam acceleration of the sail by photon pressure, and we can measure that acceleration by on‐board accelerometer telemetry. In addition, we describe a mission scenario called ‘Sun‐Diver’ using a powerful microwave beam on a solar‐driven sail, to both heat and push the sail, accelerating by “boil‐off” of coated materials. Sublimation and desorption work well with the new carbon sail materials which can take very high temperatures (>2000 K), can use promising new materials for mass loss, and promise new classes of missions. These missions make a close pass near the Sun, hence the name, to take advantage of high temperature characteristics of the sail by using the large solar ...

Control of microwave-propelled sails using delayed measurements

Abstract This paper is concerned with the control of carbon fiber sail structures that are being studied in a series of experiments at the Jet Propulsion Laboratory (JPL). The passive dynamic stability in the one-dimensional (I-D) case is studied in terms of the fixed points of the trajectories for the governing equations of motion. The simple I-D model introduces the possibility of controlling a microwavepropelled sail using various nonlinear control strategies. In the case where the velocity is not available, we use a novel feedback that employs delays of the position measurements to stabilize the sail about an equilibrium position.