Starwisp is a hypothetical unmanned

interstellar probe An interstellar probe is a space probe that has left—or is expected to leave—the Solar System and enter interstellar medium, interstellar space, which is typically defined as the region beyond the Heliopause (astronomy), heliopause. It also r ...

design proposed by the late Robert L. Forward. It is propelled by a

microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

sail, similar to a

solar sail Solar sails (also known as lightsails, light sails, and photon sails) are a method of spacecraft propulsion using radiation pressure exerted by sunlight on large surfaces. A number of spaceflight missions to test solar propulsion and navigati ...

in concept, but powered by microwaves from a human-made source. It would fly through the target system without slowing down.

Description

"Starwisp" is a concept for an ultra-low-mass interstellar probe pushed by a microwave beam. It was proposed by scientist and author Robert L. Forward in 1985, and further work was published by

Geoffrey A. Landis Geoffrey Alan Landis (; born May 28, 1955) is an American aerospace engineer and author, working for the National Aeronautics and Space Administration (NASA) on planetary exploration, interstellar propulsion, solar power and photovoltaics. He h ...

in 2000.Landis, Geoffrey A. "Microwave Pushed Interstellar Sail: Starwisp Revisited" (paper AIAA-2000-3337, presented at the

AIAA The American Institute of Aeronautics and Astronautics (AIAA) is a professional society for the field of aerospace engineering. The AIAA is the U.S. representative on the International Astronautical Federation and the International Council of ...

36th Joint Propulsion Conference and Exhibit, Huntsville AL, July 17–19, 2000). The proposed device uses

beam-powered propulsion Beam-powered propulsion, also known as directed energy propulsion, is a class of aircraft or spacecraft propulsion that uses energy beamed to the spacecraft from a remote power plant to provide energy. The beam is typically either a microwave or a ...

in the form of a high-power microwave antenna pushing a sail. The probe itself would consist of a mesh of extremely fine carbon wires about 100 m across, with the wires spaced the same distance apart as the 3 mm

wavelength In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...

of the microwaves that will be used to push it. Forward proposed that the wires would incorporate

nanoscale Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...

computer circuitry, sensors, microwave power collection systems and microwave

radio transmitters In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna with the purpose of signal transmission ...

fabricated on the wire surfaces, giving the probe data collection and transmission capability. Being distributed across the entire sail, no "rigging" is needed, as would be the case if the mission electronics were placed in a separate probe that was pulled by the sail. The original Starwisp concept assumed that the microwaves would be efficiently reflected, with the wire mesh surface acting as a superconductor and nearly perfectly efficient mirror. This assumption is not valid. Landis showed that a grid will absorb a significant fraction of the power incident on it, and therefore cannot stay cool enough to be

superconducting Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases g ...

. The design is thermally limited, hence the use of carbon as the material in Landis's concept. Low mass was the key feature of the Starwisp probe. In Landis's calculations, the mesh has a density of only 100 kg/km², for a total mass of 1 kg, plus a payload of 80 grams. Although the

diffraction limit In optics, any optical instrument or systema microscope, telescope, or camerahas a principal limit to its resolution due to the physics of diffraction. An optical instrument is said to be diffraction-limited if it has reached this limit of res ...

severely constrains the range of the transmitting antenna, the probe is designed to have an acceleration of 24 m/s², so that it can reach a significant fraction of the speed of light within a very short distance, before passing out of range. The antenna uses a microwave lens 560 km in diameter, would transmit 56 GW of power, and would accelerate the probe to 10% of the speed of light. The probe would cruise without power for decades until it finally approached the target

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

, at which point the antenna which launched it would again target its beam on Starwisp. This would be done when the Starwisp was about 80% of the way to its destination, so that the beam and Starwisp would arrive there at the same time. At such extreme long range the antenna would be unable to provide any propulsion, but Starwisp would be able to use its wire sail to collect and convert some of the microwave energy into electricity to operate its sensors and transmit the data it collects back home. Starwisp would not slow down at the target star, performing a high-speed flyby mission instead. Since the antenna is only required for a few days at Starwisp's launch and again for another few days several decades later to power it while it passes its target, Starwisp probes might be mass-produced and launched by the maser every few days. In this manner, a continuous stream of data could be collected about distant solar systems even though any given Starwisp probe only spends a few days travelling through it. Alternatively, the launching transmitter could be used in the interim to transmit power to Earth for commercial use, as with a

solar power satellite Space-based solar power (SBSP or SSP) is the concept of collecting solar power in outer space with solar power satellites (SPS) and distributing it to Earth. Its advantages include a higher collection of energy due to the lack of reflection ...

Possible methods of fabrication

Constructing such a delicate probe would be a significant challenge. One proposed method would be to "paint" the probe and its circuitry onto an enormous sheet of plastic which degrades when exposed to

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

light, and then wait for the sheet to evaporate away under the assault of solar UV after it has been deployed in space. Another proposed method noted that the Starwisp probe wires were of the same physical scale as wires and circuit elements on modern computer microchips and could be produced by the same photolithographic fabrication technologies as those of computer chips. The probe would have to be built in sections the size of current chip fabrication silicon wafers and then connected together.

Technical problems

A major problem this design would face would be the radiation encountered en route. Travelling at 20% of

light speed The speed of light in vacuum, commonly denoted , is a universal physical constant exactly equal to ). It is exact because, by international agreement, a metre is defined as the length of the path travelled by light in vacuum during a time i ...

, ordinary interstellar hydrogen would become a significant radiation hazard, and the Starwisp would be without shielding and likely without active self-repair capability. Another problem would be keeping the acceleration of the Starwisp uniform enough across its sail area so that its delicate wires would not tear or be twisted out of shape. Distorting the shape of the Starwisp even slightly could result in a runaway catastrophe, since one portion of the Starwisp would be reflecting microwaves in a different direction than the other portion and be thrust even farther out of shape. Such delicate and finely-balanced control may prove impossible to realize. The possibility of using a

dusty plasma A dusty plasma is a Plasma (physics), plasma containing micrometer (10−6) to nanometer (10−9) sized particles suspended in it. Dust particles are charged and the plasma and particles behave as a plasma. Dust particles may form larger particles ...

sail in which a dusty substance that is maintained as a plasma within space is responsible for the reflection of electromagnetic radiation could circumvent problems associated with radiation damage to the medium responsible for the transfer of

radiation pressure Radiation pressure (also known as light pressure) is mechanical pressure exerted upon a surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of ...

(the dusty plasma sail might not be as easy to damage as a thin film or the like). Dusty plasma sails can also adapt their three-dimensional structure in real time to ensure reflection perpendicular to any incident light/microwave beam.

In fiction

*In a

science fiction Science fiction (often shortened to sci-fi or abbreviated SF) is a genre of speculative fiction that deals with imaginative and futuristic concepts. These concepts may include information technology and robotics, biological manipulations, space ...

story Forward suggested that the beam from a solar power satellite could be used to push a Starwisp probe while the solar power satellite was being tested after construction.

References

External links