外文翻译--太空电梯的经济学

Space elevator economics Space elevator economics compared and contrasted with the economics of alternatives, like rockets.Costs of current systems (rockets)The costs of using a well-tested system to launch payloads are high. Prices range from about $4,300/kg for a Proton launch1 to about US$40,000/kg for a Pegasus launch (2004).23 Some systems under development, such as new members of the Long March CZ-2E, offer rates as low as $5,000/kg, but (currently) have high failure rates (30% in the case of the 2E). Various systems that have been proposed have offered even lower rates, but have failed to get sufficient funding (Roton; Sea Dragon), remain under development, or more commonly, have financially underperformed (as in the case of the Space Shuttle). (Rockets such as the Shtil-3a, which offers costs as low as $400/kg rarely launch but has a comparatively small payload, and is partially subsidised by the Russian navy as part of launch exercises.) Geosynchronous rocket launch technologies deliver two to three times smaller payloads to geosynchronous orbit than to LEO. The additional fuel required to achieve higher orbit severely reduces the payload size. Hence, the cost is proportionately greater. Bulk costs to geosynchronous orbit are currently about $20,000/kg for a Zenit-3SL launch. Rocket costs have changed relatively little since the 1960s, but the market has been very flat.3 It is, however, quite reasonable to assume that rockets will be cheaper in the future; particularly if the market for them increases. At the same time, it is quite reasonable to assume the market will increase, particularly if rockets will become cheaper. Rocket costs are significantly affected by production volumes of the solid parts of the rocket, and by launch site costs. Intuitively, since propellant is by far the largest part of a rocket, propellant costs would be expected to be significant, but it turns out that with hydrocarbon fuel these costs can be under $50 per kg of payload. Study after study has shown that the more launches a system performs the cheaper it becomes. Economies of scale mean that large production runs of rockets greatly reduce costs, as with any manufactured item, and reuseable rockets may also help to do so. Improving material and practical construction techniques for building rockets could also contribute to this. Greater use of cheap labour (globalisation) and automation is practically guaranteed to reduce manpower costs. Other costs, such as launch pad costs, can be reduced with very frequent launches. Cost estimates for a space elevatorFor a space elevator, the cost varies according to the design. Dr. Bradley Edwards, who has put forth a space elevator design, has stated that: The first space elevator would reduce lift costs immediately to $100 per pound ($220/kg).4 However, as with the initial claims for the space shuttle, this is only the marginal cost, and the actual costs would be higher. Development costs might be roughly equivalent, in real terms, to the cost of developing the shuttle system. The marginal or asymptotic cost of a trip would not solely consist of the electricity required to lift the elevator payload. Maintenance, and one-way designs (such as Edwards) will add to the cost of the elevators. The gravitational potential energy of any object in geosynchronous orbit (GEO), relative to the surface of the earth, is about 50 MJ (15 kWh) of energy per kilogram (see geosynchronous orbit for details). Using wholesale electricity prices for 2008 to 2009 (7.1 NZ cents per kWh) and the current 0.5% efficiency of power beaming, a space elevator would require USD 220/kg just in electrical costs. By the time the space elevator is built, Dr. Edwards expects technical advances to increase the efficiency to 2% (see power beaming for details). It may additionally be possible to recover some of the energy transferred to each lifted kilogram by using descending elevators to generate electricity as they brake (suggested in some proposals), or generated by masses braking as they travel outward from geosynchronous orbit (a suggestion by Freeman Dyson in a private communication to Russell Johnston in the 1980s). For the space elevator, the efficiency of power transfer is just one limiting issue. The cost of the power provided to the laser is also an issue. While a land-based anchor point in most places can use power at the grid rate, this is not an option for a mobile ocean-going platform. A specially built and operated power plant is likely to be more expensive up-front than existing capacity in a pre-existing plant. Up-only climber designs must replace each climber in its entirety after each trip. Some designs of return climbers must carry up enough fuel to return it to earth, a potentially costly venture. Contrasting rockets with the space elevatorGovernment funded rockets have not historically repaid their capital costs. Some of the sunk cost is often quoted as part of the launch price. A comparison can therefore be made between the marginal costs of fully or partially expendable rocket launches and space elevator marginal costs. It is unclear at present how many people would be required to build, maintain and run a 100,000 km space elevator and consequently how much that would increase the elevators cost. Extrapolating from the current cost of carbon nanotubes to the cost of elevator cable is essentially impossible to do accurately. Space elevators have high capital cost but presumably low operating expenses, so they make the most economic sense in a situation where they would be used to handle many payloads. The current launch market may not be large enough to make a compelling case for a space elevator, but a dramatic drop in the price of launching material to orbit would likely result in new types of space activities becoming economically feasible. In this regard they share similarities with other transportation infrastructure projects such as highways or railroads. In addition, launch costs for probes and craft outside Earths orbit would be reduced, as the components could be shipped up the elevator and launched outward from the counterweight satellite. This would cost less in both funding and payload, since most probes do not land anywhere. Also, almost all the probes that do land somewhere have no need to carry fuel for launch away from their destination. Most probes are on a one-way journey. Funding of capital costsNote that governments generally have not historically even tried to repay the capital costs of new launch systems from the launch costs. Several cases have been presented (space shuttle, ariane, etc), documenting this. Russian space tourism does partially fund ISS development obligations, however. It has been suggested that governments are not usually willing to pay the capital costs of a new replacement launch system. Any proposed new system must provide, or appear to provide, a way to reduce overall projected launch costs. This was the nominal impetus behind the Space Shuttle program. Governments tend to prefer to cut costs in many cases. Spending more money is something they are usually loath to do. Alternatively, according to a paper presented at the 55th International Astronautical Congress5 in Vancouver in October 2004, the space elevator can be considered a prestige megaproject and the current estimated cost of building it (US$6.2 billion) is rather favourable when compared to the costs of constructing bridges, pipelines, tunnels, tall towers, high speed rail links, maglevs and the like. It is also not entirely unfavourable when compared to the costs of other aerospace systems as well as launch vehicles.6 Total cost of a privately funded Edwards Space Elevator A space elevator built according to the Edwards proposal is estimated to cost $20 billion ($40B with a 100% contingency)7. This includes all operating and maintenance costs for one cable. If this is to be financed privately, a 15% return would be required ($6 billion annually). Subsequent elevators would cost $9.3B and would justify a much lower contingency ($14.3B total). The space elevator would lift 2 million kg per year per elevator and the cost per kilogram becomes $3,000 for one elevator, $1,900 for two elevators, $1,600 for three elevators. For comparison, in potentially the same time frame as the elevator, the Skylon, 12,000 kg cargo capacity spaceplane (not a conventional rocket) is estimated to have an R&D and production cost of about $15 billion. The vehicle has about the same $3,000/kg price tag. Skylon would be suitable to launch cargo and particularly people to low/medium Earth orbit. An early space elevator can move only cargo although it can do so to a much wider range of destinations.8 References1. Space Transportation Costs: Trends in Price Per Pound to Orbit 1990-2000 (PDF). Retrieved on 2006-03-05.2. Pegasus. Encyclopedia Astronautica. Retrieved on 2006-03-05.3. The economics of interface transportation (2003). Retrieved on 2006-03-05.4. What is the Space Elevator?. Institute for Scientific Research, Inc. Retrieved on 2006-03-05.5. 55th International Astronautical Congress. Institute for Scientific Research, Inc. Retrieved on 2006-03-05.6. Raitt, David; Bradley Edwards. THE SPACE ELEVATOR: ECONOMICS AND APPLICATIONS (PDF). 55th International Astronautical Congress 2004 - Vancouver, Canada. Retrieved on 2006-03-05.7. 18. The Space Elevator - Chapter 7: Destinations. Retrieved on 2006-03-05.太空电梯的经济学太空电梯经济学和火箭经济学的对比与比较。目前（火箭）系统的成本使用完善的测试系统发射有效载荷的成本是很高的，2004年其价格范围是从约4300美元每千克发射一个质子到40,000美元每千克发射一个飞马座。一些处于发展中的系统，如长征系列的新成员长征CZ-2E，其提供的价格低至5000美元每千克，但是它（目前）具有较高的失败率（2E的失败率为30 ）。各种被推荐的系统，有的甚至提供更低的价格，但是未能获得足够的资金支持（如roton ;海龙），仍然处于发展之中，或更为普遍，没有财政补助（如太空中的穿梭机一样）。像shtil-3A型火箭，其成本低至400美元每千克，很少发射，但其有一个相对较小的有效载荷，得到了俄罗斯海军的部分资助，他们将其用于发射演习。地球同步轨道火箭发射技术向地球同步轨道提供的有效载荷比向狮子宫提供的有效载荷小了两至三倍，实现更高的轨道所需要的额外燃料，严重降低了有效载荷的大小。因此，成本是按比例增大的，发射天顶-3SL地球同步轨道火箭的批量成本目前约为20,000美元每千克。自20世纪60年代以来，火箭的成本改变不大，但火箭的市场需求却一直很平稳。然而，我们可以作相当合理的假设，火箭的成本在将来将会更加便宜，尤其是市场对它们达需求增加时；同时，假定市场对火箭的需求也会增加亦是合理的，尤其是当火箭的成本变得更低的时候。火箭的成本受火箭固定部分生产量和发射场费用的影响显著。凭直觉，既然火箭推进剂，是迄今为止火箭最大的一个组成部分，那么火箭推进剂的成本预计将很高，但结果表明，与碳氢燃料相比，这些费用却在50美元每公斤的有效载荷之下。经过不断研究表明，一个火箭执行发射的次数越多，那么它将变得更加便宜。规模经济意味着火箭的大批量生产，将大大降低其成本，对于任何配件项目制造，重复使用火箭也可以极大的降低其成本。改进制造火箭的材料和实际施工技术也可以对降低成本做出贡献；更多地使用廉价劳工（全球化）和自动化，也能减少人力资源成本。其他费用，像发射架上的成本，可以通过频繁的火箭发射来减少其成本。太空电梯的成本估算太空电梯的费用依不同设计而变。布拉德利爱德华兹博士，提出了太空电梯的设计，他表示：“首先，太空电梯能够立即使电梯费用减少至100美元每镑”即（220美元/kg）。然而，这只不过是边际成本，如果加上先前的航天飞机成本，实际成本将会更高。以实质计算，其开发成本可能相当于，开发穿梭机系统的成本。边际或渐近的成本不仅仅是由支撑太空电梯有效载荷所需要的电力成本构成，维修成本和单向的设计（如爱德华兹）亦将增加电梯的成本。处在地球同步轨道上的任何物体相对于相对地球表面所具有的引力势能，约50兆焦耳（15千瓦时）每千克。2008至2009年，使用的电力批发价格为（7.1美分，新西兰元每千瓦时），以及当前的0.5的工作效率，太空电梯在电气成本方面将需要220美元每千克，到太空电梯建成之时，博士爱德华兹预计技术进步，将使其工作效率提高至2。此外，通过使用太空电梯来发电，或通过他们脱离地球同步轨道时所产生的大量制动，也可以恢复一些能量转移到每公斤当中，因为他们可以制动。（20世纪80年代弗里曼戴森和罗素庄士敦在一次私人访谈中建议）。太空电梯能量转换的效率只是其中一项限制性的问题，提供给激光的能源成本亦是一个限制性问题。而陆基定位点在大多数地方能够以网格率的形式使用能源，这对于远洋移动平台来说，不是一种选择。一个专门兴建和营运的电厂很可能是比较昂贵的先前行动，比现有的已存在的一个事物更加昂贵，在每一个飞船完成它们的行程之后，飞船的设计都必须改变，一些返回舱的设计还必须能够携带足够的燃料，以使其能够返回地球，这是一种潜在的风险成本。火箭与太空电梯的比较政府资助的火箭在历史上并没有偿还他们的资本成本，部分的沉没成本是经常引用的一部分发射成本。因此，在完全或部分消耗性火箭发射的边际成本和太空电梯的边际成本之间作一比较，虽然目前还不清楚需要多少人来建立，维持和运行这一距离地球10000公里的太空电梯，以及随后的太空电梯成本会增加多少，但从目前的碳纳米管成本，和电梯电缆成本推算，基本上是不可能得到准确的对比。太空电梯具有较高的资本成本，但据推测其营运成本比较低，所以他们作出比较经济的意识，即在一个情况下，它们将被用于处理很多的有效载荷。目前火箭发射市场还不足够大以至不能为太空电梯作出一个令人信服的理由。但随着发射材料价格的急剧下降，这将使得新类型的空间活动在经济上成为可行。在这方面，他们与其他交通基础设施项目，如公路或铁路有着非常的类似。此外，随着配件从太空电梯中发运，并离开卫星发射，地球轨道之外的探头和工艺的发射费用也将会减少，这将使得资金和有效载荷的成本减少，因为大多数探针并不着落。此外，几乎所有在某处需要着落的探针并没必要携带燃料发射，从而远离自己的目的地，大多数探针只是一个单向的征程。资金的资本成本请注意，各国政府普遍没有在历史上，甚至试图从发射费用中偿还新的发射系统的资本成本。已提交的几起案件（航天飞机，阿丽亚娜等），说明了这一点。俄罗斯太空旅游是否部分上是基金发展国际空间站的义务。曾有人认为，各国政府通常不会愿意为更换一个新的发射系统而付出资本成本。任何新系统的建议必须提供，或出现一种方法，以减少整体预计发射成本。这是航天飞机发射计划背后，名义象征性的动力。在许多情况下，各国政府往往倾向于降低成本。他们通常不愿意花费更多的钱这样做。另外，根据2004年10月在温哥华举行的第55届国际宇航大会5提交的论文，太空电梯被视为大的可信项目，它目前的估计建设成本为62亿美元，相比建设桥梁，管道，隧道，水塔，身高，高速铁路等的成本，它处于有利的地位。相比其他航天系统以及运载火箭的成本费用，它的成本也是可以接受的。私人资助的爱德华兹太空电梯总成本根据爱德华兹的建议，建造一架太空电梯估计要花费成本200亿美元，这包括一条光缆的全部运营和维修费用。如果这些资助由私人来提供的话，那么每年将要给他们15的回报即60亿美元。接着，电梯将要耗资9.3亿美元和证明有一个更低更合理的临时费用。太空电梯中每一部电梯每年将载重200万千克，因此，对于每一部电梯来说，每一千克的费用也就变成了3000美元，对两部电梯来说是1900美元，三部则是1600美元。比较一下，假如在同一时间、同一空间范围内，像斯科隆太空飞船，一架有着12，000公斤货运能力的太空飞船（不是常规的火箭），据估计其研发和生产成本约为150亿美元。这样的运输工具有着大约3000公斤的载重量。斯科隆太空飞船比较适合运送货物，尤其是在低/中等地球轨道上比较适合载人，早期的太空电梯只是用来运送货物，虽然也可以这样做，以达到更为广泛的目的地。参考文献1.空间运输费用：每磅轨道的价格趋势 1990-2000年（ PDF）.2006-03-05.2.飞马座.宇航百科全书. 2006-03-05.3.界面运输经济学（2003）. 2006-03-05.4.什么是太空电梯？科研公司研究所.2006-03-05 .5.第55届国际宇航大会.科研公司研究所.2006-03-05.6.国宝;布拉德利爱德华兹.太空电梯：经济学和应用（PDF）.第55届国际宇航大会2004 年-加拿大温哥华.2006-03-05.7.同1.8.太空电梯-第7章：目的地. 2006-03-05.