Lesson49
Rockets and artificial satellites can go far above the ionosphere, and even escape from the Earth. Yet they are complex and expensive, and in their present stage of development they cannot lift massive telescopes, keep them steady while the observations are being carried out, and then return them safely. Balloons are much easier to handle, and are also vastly cheaper. Their main limitation is that they are incapable of rising to the ionosphere. A height of between 80,000 and 90,000 feet is as much as can reasonably be expected, and so balloon-borne instruments can contribute little to either ultra-violet astronomy or X-ray astronomy.
All the same, the balloon has much to be said in its favour, since it can at least carry heavy equipment above most of the atmospheric mass--thus eliminating blurring and unsteadiness of the images. Moreover, water-vapour and carbon dioxide in the lower air absorb most of the infra-red radiations sent to us from the planets. Balloon ascents overcome this hazard with ease.
Hot-air balloons date back to the year 1783, and within a few months of the first flight a French scientist, Charles, went up two miles in a free balloon. Yet there is little resemblance between these crude vehicles and a modern scientific balloon, which has by now become an important research tool.
The main development has been carried out by M. Schwarlschild and his team at Princeton University in the United States, in collaboration with the United States Navy, the National Science Foundation, and the National Aero-nautics and Space Administration. The 'Stratoscope' flights of 1959, concerned mainly with studies of the Sun, were remarkably successful, and the project has
now been extended. With Stratoscope II, the overall height from the telescope to the top of the launch balloon is 666 feet, the balloons together weigh over two tons, and another two tons of ballast are carried for later release if height has be maintained during the night. The telescope, plus its controls weighs three-and-a-half tons. Two large parachutes arc also carried; in case of emergency, the instruments and their records can be separated from the main balloon system, and brought down gently. Many of the radio and electronic devices used are similar to those of artificial satellites.
PATRICK MOORE Balloom Astronomy from The Listener
参考译文
火箭和人造卫星能远远升越电离层，甚至逃逸出地球。不过它们既复杂又昂贵，而且处于目前发展阶段，它们还不能运载巨型望远镜，且不能在进行观察时保持其稳定并让其安全返回地面。气球则较易于操纵，而且
便宜得多。它们的主要局限性是无法上升至电离层。它们可望升到的最大高度为80，000至90，000英尺，因此球载仪器无法对紫外文学或X射线天文学作出贡献。不过气球仍有很多长处，这是因为它至少能把笨重的仪器
带到大部分大气团以上，从而消除了成像的模糊和不稳定。此处，大气低层的水蒸气和二氧化碳会把从各行星发射来的大部分红处辐射吸收掉。升空的气球能轻而易举地克服这一困难。
热气球可追溯至1783年，在首次飞行后几个月，法国科学家Charles乘自由气球上升至2英里高处。不过这种原始运载工具同现代科学气球极少相似之处，后者现已成为重要的研究工具。
主要研制工作是由美国普林斯顿大学的M.Schwarzschild和他的小组完成的，协作单位有美国海军、国家科学基金会以及国家宇航局。主要用来研究太阳的1959年历次“同温层观察仪”飞行取得巨大成功，该项规划现
已予以扩充。在同温层观察仪2号上，望远镜到发射气球顶部的总高度为600英尺；气球总重超过2吨，另外还带有2吨压舱物，以便于夜间保持高度时抛掉。望远镜加上控制设备共重3吨半。还带上两顶大降落伞；遇有紧急
情况，仪器及其记录可从主气球系统分离徐徐下降。气球上的许多无线电和电子器件同人造卫星上使用的相类似。
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