Thursday, 13 June 2013

Solar Power Satellite IV

Satelit Sel Surya, Teknologi Penyuplai Sumber Energi Terbarukan Di Masa Depan: 

Tenaga surya yang dikumpulkan di luar angkasa dapat digunakan untuk menyediakan energi terbarukan di masa depan. Hal tersebut kemungkinan dapat terjadi berkat penelitian inovatif yang dilakukan oleh para insinyur di University of Strathclyde di Glasgow. 

Para peneliti dari University of Strathclyde telah menguji peralatan ruang angkasa yang akan menyediakan platform untuk panel surya yang akan mengumpulkan energi dan kemudian ditransfer ke bumi ditransfer kembali ke bumi melalui gelombang mikro atau laser.

Panel Surya tersebut akan menjadi sumber energi yang dapat diandalkan dan memungkinkan mengirimkan energi ke daerah terpencil di dunia, misalnya seperti memberikan daya ke daerah bencana atau daerah terpencil yang sulit dijangkau dengan cara tradisional. 


Launch costs 

Without doubt, the most obvious problem for the SPS concept is the current cost of space launches. Current rates on the Space Shuttle run between $3,000 and $5,000 per pound ($6,600/kg and $11,000/kg) to low Earth orbit, depending on whose numbers are used. Calculations show that launch costs of less than about $180-225 per pound ($400-500/kg) to LEO (Low Earth orbit) seem to be necessary.

However, economies of scale for expendable vehicles could give rather large reductions in launch cost for this kind of launched mass. Thousands of rocket launches could very well reduce the costs by ten to twenty times, using standard costing models. This puts the economics of an SPS design into the practicable range. Reusable vehicles could quite conceivably attack the launch problem as well, but are not a well-developed technology.

Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at acceptable cost. Examples include ion thrusters or nuclear propulsion. They might even be designed to be reusable.

Power beaming from geostationary orbit by microwaves has the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption and even potential beam blockage by rain or water droplets.

Because of the thinned array curse, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.

To give an idea of the scale of the problem, assuming an (arbitrary, as no space-ready design has been adequately tested) solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons, all of which would, in current circumstances, be launched from the Earth.

Very lightweight designs could likely achieve 1 kg/kW, meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. This would be the equivalent of between 40 and 80 heavy-lift launch vehicle (HLLV) launches to send the material to low earth orbit, where it would likely be converted into subassembly solar arrays, which then could use high-efficiency ion-engine style rockets to (slowly) reach GEO (Geostationary orbit).

With an estimated serial launch cost for shuttle-based HLLVs of $500 million to $800 million, total launch costs would range between $20 billion (low cost HLLV, low weight panels) and $320 billion ('expensive' HLLV, heavier panels).

Economies of scale on such a large launch program could be as high as 90% (if a learning factor of 30% could be achieved for each doubling of production) over the cost of a single launch today. In addition, there would be the cost of an assembly area in LEO (which could be spread over several power satellites), and probably one or more smaller one(s) in GEO. The costs of these supporting efforts would also contribute to total costs.

So how much money could an SPS be expected to make? For every one gigawatt rating, current SPS designs will generate 8.75 terawatt-hours of electricity per year, or 175 TW•h over a twenty-year lifetime. With current market prices of $0.22 per kW•h (UK, January 2006) and an SPS's ability to send its energy to places of greatest demand (depending on rectenna siting issues), this would equate to $1.93 billion per year or $38.6 billion over its lifetime.

The example 4 GW 'economy' SPS above could therefore generate in excess of $154 billion over its lifetime. Assuming facilities are available, it may turn out to be substantially cheaper to recast on-site steel in GEO, than to launch it from Earth. If true, then the initial launch cost could be spread over multiple SPS lifespans.

"Ilmu Pengetahuan dan Teknologi Canggih dapat kita kuasai bersama asal kita dapat bekerja bersama-sama"

Extraterrestrial materials

Gerard O'Neill, noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the Moon. Launch costs from the Moon are about 100 times lower than from Earth, due to the lower gravity. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial up front capital investment to establish mass drivers on the Moon.

Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than terrestrial materials for a system of as few as thirty Solar Power Satellites of 10GW capacity each.

In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al published another route to manufacturing using lunar materials with much lower startup costs This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under telepresence control of workers stationed on Earth. Again, this proposal suffers from the current lack of such automated systems on Earth, much less on the Moon.

Asteroid mining has also been seriously considered. A NASA design study evaluated a 10,000 ton mining vehicle (to be assembled in orbit) that would return a 500,000 ton asteroid 'fragment' to geostationary orbit. Only about 3000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine; which could be arranged to be the spent rocket stages used to launch the payload.

Assuming, likely unrealistically, that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition. There has been no such survey. Once built, NASA's CEV should be capable of beginning such a survey, Congressional money and imagination permitting.

"Kita harus kembali ke dasar pembangunan, BACK TO BASIC!, untuk penghematan Energi, jangan segan kembali ke hal-hal bermanfaat yg sudah disediakan oleh pemerintah sebelumnya. Pernah dibuat prototipe kapal yg memanfaatkan energi angin, energi sinar matahari, jangan disia-siakan."

Kunjungi Juga:

Indonesian Space Sciences & Technology School

Indonesian University Space Research Association

Semoga Bermanfaat

To Be Continued

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