2012年3月26日星期一

Now here's the tricky part. Getting the power back to the ground is non-trivial


We are accustomed to using copper wire for power transmission.The sexy lingerie shop will offer your lingerie that will be just what you need for celebrating your anniversary, for marking a special day or just for making every day special. There's a wide choice of the naughtiest Sexy Garter & Corset which will prove handy for a number of occasions. The offered erotic and exotic lingerie will greatly enrich your sexual life. For the space-Earth interconnect, we must resort to electromagnetic means. Most discussions of electromagnetic power transmission centers on lasers or microwaves. I'll immediately dismiss lasers as impractical for this purpose, because clouds block transmission, because converting the power into electricity is not as direct/efficient as it can be for microwaves, and because generation of laser power tends to be inefficient (my laser pointer is about 2%, for instance, though one can do far better).
So let's go microwave! For reasons that will become clear later, we want the highest frequency (shortest wavelength) we can get without losing too much in the atmosphere. Below is a plot generated from an interactive tool associated with the Caltech Submillimeter Observatory (where I had my first Mauna Kea observing experience). This plot corresponds to a dry sky with only 2.0 mm of precipitable water vapor.Online lingerie stores also offer extremely provocative and passionate collection of sexy lingerie. Month after month Sexy Long Gown& Sexy Sleepwear stores tend to renew their products in order to meet the needs and requirements of the most fervent women shoppers. Shopping in online lingerie stores you'll forget about flow of time and will be amazed with the fresh choice each time you enter the store. Even so, water takes its toll, absorbing/scattering the high-frequency radiation so that the fraction transmitted through the atmosphere is tiny. Only at frequencies of 100 GHz and below does the atmosphere become nearly transparent.
At 100 GHz, the wavelength is about λ ≈ 3 mm. In order to transmit a microwave beam to the ground, one must contend with the diffractive nature of electromagnetic radiation. If we formed a perfectly collimated (parallel) beam of microwave energy from a dish in space with diameter Ds—where the 's' subscript represents the space segment—we might naively anticipate the perfectly-formed beam to arrive at Earth still fitting in a tidy diameter Ds. But no. Diffraction imposes an angular spread of about λ/Ds radians, so that the beam spreads to a diameter at the ground, Dg ≈ rλ/Ds, where r is the distance between transmitter and receiver (about 36,000 km in our case). We can rearrange this to say that the product of the diameters of the transmitter and receiver dishes must approximately equal the product of the propagation distance and the wavelength: DsDg ≈ rλ
So? Well, let's first say that Ds and Dg are the same. In this case, we would require the diameter of each dish to be 330 m. These are gigantic, especially in space. Note also that really we need Dg = Ds + rλ/Ds to account for the original extent of the beam before diffraction spreads it further. So really, the one on Earth would be 660 m across.Launching a microwave dish this large should strike anyone as prohibitively difficult,Such a shop offers a great number of advantages. You'll always feel free to see closer any model of Sexy Adult Costumes and to order the one that has been loved most of all. So, a sexy lingerie shop online is an embodiment of convenience. Besides, shopping online will spend much of your precious time. Besides, you can go shopping online any time of the day or night. so let's scale back to a more imaginable Ds = 30 m (still quite impressive), in which case our ground-based receiver must be 3.6 km in diameter!

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