Saturday, 15 June 2013

Solar Power Satellite VI

Percobaan yang dikenal dengan nama Suaineadh (yang artinya ‘memutar’ dalam bahasa Gaelic skotlandia) merupakan langkah maju yang penting dalam desain konstruksi luar angkasa dan menunjukkan bahwa struktur yang lebih besar dapat dibangun di atas sebuah jaring ringan yang berputar.

Hal tersebut akan membuka jalan untuk tahap berikutnya dalam proyek tenaga surya luar angkasa.
Dr. Vasile menambahkan:
“Keberhasilan Suaineadh memungkinkan proyek kami  bergerak maju pada tahap berikutnya, dimana akan melibatkan reflektor yang diperlukan untuk mengumpulkan tenaga surya."

“Proyek yang diberi nama SAM (Self-inflating Adaptable Membrane) ini akan menguji peluncuran struktur selular sangat ringan yang dapat berubah bentuk pada saat diluncurkan."
Struktur terbuat dari sel-sel yang dapat menggembungkan diri dalam ruang hampa udara dan dapat mengubah volumenya sendiri melalui nanopumps (pompa nano).
“Struktur tersebut meniru struktur selular alami yang ada pada semua makhluk hidup. Kontrol independen dari sel akan memungkinkan kita untuk merubah struktur menjadi konsentrator surya yang akan mengumpulkan sinar matahari dan memproyeksikannya pada rangkaian sel surya surya. Struktur yang sama dapat digunakan untuk membangun sistem ruang angkasa yang besar dengan merakit ribuan unit individu kecil.”

Lofstrom launch loop

Lofstrom loop could conceivably provide the launch capacity needed to make a solar power satellite practical. This is a high capacity launch system capable of reaching a geosynchronous transfer orbit at low cost (Lofstrom estimates a large system could go as low as $3/kg to LEO for example). The Lofstrom loop is expected to cost less than a conventional space elevator to develop and construct, and to provide lower launch costs. Unlike the conventional space elevator, it is believed that a launch loop could be built with today’s materials.

Space elevators

More recently the SPS concept has been suggested as a use for a space elevator. The elevator would make construction of an SPS considerably less expensive, possibly making them competitive with conventional sources.

However it appears unlikely that even recent advances in materials science, namely carbon nanotubes, can make possible such an elevator, nor to reduce the short term cost of construction of the elevator enough, if an Earth-GSO space elevator is ever practical. A variant to the Earth-GSO elevator concept is the Lunar space elevator, first described by Jerome Pearson in 1979.

Because of the ~20 times shallower (than Earth's) gravitational well for the lunar elevator, this concept would not rely on materials technology beyond the current state of the art, but it would require establishing silicon mining and solar cell manufacturing facilities on the Moon, similar to O'Neill's lunar material proposal, discussed above.


The use of microwave transmission of power has been the most controversial issue in considering any SPS design, but any thought that anything which strays into the beam's path will be incinerated is an extreme misconception. Consider that quite similar microwave relay beams have long been in use by telecommunications companies world wide without such problems.

At the earth's surface, a suggested microwave beam would have a maximum intensity, at its center, of 23 mW/cm2 (less than 1/4 the solar irradiation constant), and an intensity of less than 1 mW/cm2 outside of the rectenna fenceline (10 mW/cm2 is the current United States maximum microwave exposure standard).

In the United States, the workplace exposure limit (10 mW/cm2) is at present, per the Occupational Safety and Health Act (OSHA), expressed in voluntary language and has been ruled unenforceable for Federal OSHA enforcement.

The beam's most intense section (more or less, at its center) is far below dangerous levels even for an exposure which is prolonged indefinitely. Furthermore, exposure to the center of the beam can easily be controlled on the ground (eg, via fencing), and typical aircraft flying through the beam provide passengers with a protective shell metal (ie, a Faraday Cage), which will intercept the microwaves.

Other aircraft (balloonsultra-light, etc) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace. Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world.

The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe death ray levels, even in principle.

In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.

Some have suggested locating rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.

Phased array transmission was originally developed in 1905 by Nobel Physics Laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal.

This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.

It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities would rapidly decrease, so nearby towns or other human activity should be completely unaffected.

The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.

Kunjungi Juga:

Semoga Bermanfaat.

To Be Continued 

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