You’re sitting in a chair on the open deck of a small rocket, 96 kilometers above Earth. “Space Diver One, you are go!” crackles1 a voice in your ear. You undo your harness2, breathe deeply, and leap, somersaulting3 into the void4.
The mother planet below is gorgeous5. You can barely perceive that you’re rushing toward it at 4,025 kilometers an hour, faster than anyone has ever gone without a vehicle.
Hurtling to Earth from space without the protective shroud6 of a space vehicle seems like sheer lunacy7. But believe it or not, the physics actually computes. Now, two veterans of the space industry, Rick Tumlinson and Jonathan Clark, are trying to make the idea real. They’ve begun to develop the space suit needed to return people from the heavens without a vehicle. They plan to demonstrate a record-breaking 37-kilometer jump by 2009 and a truly unprecedented8 96-kilometer space dive by 2011.
Mishap9 Expert
Clark and Tumlinson run a company called Orbital Outfitters10. Clark, who was a flight surgeon for NASA, the U.S. space agency, has a particularly unique understanding of the extremes of spaceflight survival and the need for safe jumps from space. His wife, astronaut Laurel Clark, died when the space shuttle Columbia broke apart on reentry11 in 2003.
Clark has studied almost every high-altitude mishap in history. He’s an encyclopedia12 of “all the ways you can die in space and on the way down from it,” he says.
The highest skydive on record is 31 kilometers, set by U.S. Air Force Capt. Joseph Kittinger, who leapt from a balloon in 1960. Whoever undergoes the 37-kilometer dive will require the same equipment Kittinger had: an oxygen supply for breathing, a drogue parachute13 to prevent runaway spins that can rip14 the body apart, a main chute to land at a survivable15 speed, and a pressurized suit. The air pressure at high altitudes is very low, and at any altitude above 19 kilometers, human blood turns to a gas. People refer to that as blood “boiling”.
Sky High
Jumping from 96 kilometers will introduce several new dangers and require extra gear16 to deal with them. The first danger is disorientation17. Once you’ve separated from the rocket, you might have difficulty orienting yourself so that you’re falling in the correct position, says Tomas Svitek, a NASA consultant working on the project. He envisions18 a simple jet pack built into the suit.
The next danger is crushing19 g-forces. Whenever your body accelerates20—that is, changes speed or direction—you experience a force. When the acceleration is extreme, the body can experience a force equal to or even greater than the downward force exerted21 by gravity. Such an extreme force caused by acceleration is called a g-force (g is short for gravity). During a space launch, astronauts are pinned to their seats by a force equivalent to three times the force of gravity—3 g’s. A drop from 96 kilometers could generate 4.4 g’s—high but still manageable even without a protective suit.
The third danger is the searing22 heat generated when air friction slows you from 4,025 kilometers per hour at the top of the atmosphere to 193 kilometers per hour in the thicker, lower air. That friction can raise the temperature of reentry to 240 degrees Celsius, hot enough to broil23 a roast. A space suit tailored24 from Nomex25, a heat-resistant fiber used in the suits of NASCAR drivers, should withstand such a cookout26.
The least understood danger comes from transonic27 speeds—what happens when you cross the sound barrier (1,235 kilometers per hour). Are there shock waves at such speeds that can injure you or send you into an unstoppable spin? No one knows because no one has ever gone that fast outside a vehicle. A space-suited human could withstand transonic shocks. In 1966, pilot Bill Weaver survived a fall from 23.6 kilometers with no lasting damage when his jet broke up. He had been flying at more than three times the speed of sound.
Higher Still
As astounding28 as a free fall from 96 kilometers may seem, that feat doesn’t come close to Clark and Tumlinson’s eventual plan. “Our ultimate goal,” says Tumlinson, “is to have human beings return from orbit alive.” That’s a drop from 240 kilometers or more, turning divers into human meteorites29.
The energy of the descent30 velocity of 29,000 kilometers per hour gets translated into 8.2 g’s and extreme heat. Although 8.2 g’s are survivable, the heat is not. At more than 1,650 degrees Celsius, a heat shield would be an absolute must31. Svitek envisions a blunt cone32 made of carbon or glass fibers proved to withstand such temperatures.
Once the suit is designed and made, one final question remains: Will anybody be crazy enough to give this ultimate thrill33 ride a go? Would you?
在离地球96公里的高空，你坐在一枚小型火箭的露天平台的座椅上。“太空跳伞员一号，出发！”一个声音在你的耳边脆响。你解开安全带，深吸一口气，然后纵身一跃，翻腾着坠入茫茫太空。
下面的地球母亲美极了！你几乎意识不到自己正以4,025公里的时速向它飞奔，这是人在不借助运载工具的情况下所能达到的最快速度。
没有航天器这层护罩的保护，从太空呼啸着直奔地球，这似乎是天方夜谭。但信不信由你，有人真的在做相关的物理学运算。如今，两位航天业的资深专家里克·汤姆林森和强纳森·克拉克正在努力把这一设想变为现实。他们已经着手开发在不使用运载工具的条件下把人们从高空送回地球所需的特殊宇航服。他们计划在2009年前展示一次破纪录的37公里高空坠落，到2011年实现真正史无前例的96公里太空跳伞。
空难专家
克拉克和汤姆林森经营着一家名叫“太空轨道用品”商店。曾担任美国宇航局（太空总署）外科医生的克拉克对航天飞行的极端生存状况以及从太空安全坠落的必要性有着独到的理解。他的妻子——宇航员劳雷尔·克拉克于2003年因哥伦比亚号航天飞机重返大气层时发生爆炸解体而遇难。
克拉克研究了历史上的几乎每一起高空事故。他称自己是熟知“人在太空及返航途中所有可能遭遇的死亡方式”的百科全书。
有案可查的最高跳伞纪录是31公里，由美国空军上尉约瑟夫·吉廷格于1960年从一只气球上坠落时创造。无论谁实施未来的37公里跳伞，都必须配备吉廷格当年所携带的装备：一个用来呼吸的氧气罩，一顶用于防止失控旋冲（可将人体撕裂）的减速小伞，一顶用于把着陆速度控制在非致命范围的主降落伞，以及一套增压服。高空的气压非常低，在19公里以上的任何高度，人的血液将变成气体状态。人们称之为“血沸”。
堪比天高
从96公里的高空坠落将带来几个新的危险，需要额外的装备加以应对。第一个危险是迷失方向。参与该计划的美国宇航局顾问托马斯·斯维特克说，一旦人与火箭分离，就可能在确定正确的降落方位时遇到困难。他的设想是在太空服里加入一个简易的喷气动力背包。
第二个危险是巨大的g力。每当身体加速时——即改变速度或方向——人就会受到一股力的作用。当加速达到极限时，身体将受到一股等同甚至大于向下的地心引力的反应力。这种由加速导致的极限力被称为g力（g是地心引力的缩写）。在航天器发射阶段，宇航员被一股相当于地心引力三倍的力量（即3 g）固定于座椅之上。从96公里的高空坠落可能产生4.4 g的巨大作用力，但即使没有保护装置也仍在可控制范围。
第三个危险是当空气摩擦将你的时速从大气层顶端的4,025公里降至较稠密低空中的193公里时所产生的灼烫热量。这种摩擦可使重返大气层时的温度升至摄氏240度，足以做一顿美味烧烤。用Nomex这种抗热纤维特制的太空服应该能抵挡这种炙烤，它也被用作全美汽车赛车协会参赛选手的服装材料。
最不为人们了解的危险来自于超音速——即当你越过声音障碍（时速1,235公里）时的状态。在这种速度下，会不会有冲击波对人体造成伤害或迫使其不停地旋转呢？无人知道，因为无人在运载工具之外达到过如此快的速度。穿太空服的人也许能够承受超音速的冲击。1966年，当其喷气式飞机解体时，飞行员比尔·韦弗从23.6公里的高度坠落后生还，并未造成持久伤害。他当时的降落速度是音速的三倍多。
更上层楼
从96公里的高度做自由落体似乎骇人听闻，但这一壮举离克拉克和汤姆林森的最终计划还相差很远。“我的终极目标，”汤姆林森说，“是让人类从太空轨道上平安返回。”这意味着从240公里或更高的地方坠落，把跳伞者变成人体陨石。
每小时29,000公里的下降速度所产生的能量被转换为8.2 g力和极大的热量。虽然8.2 g力尚可承受，但灼热却是致命的。在摄氏1,650度的高温下，防热保护装置绝对必不可少。斯维特克预想的方案是用碳和玻璃纤维制成的钝锥，这种材料被证明可以承受如此高的温度。
一旦这种太空服研制成功，那么还剩下最后一个问题：有谁愿意玩命来尝试这项极限体验？你愿意吗？
1. crackle v. 发劈啪声
2. harness n. 安全带；降落伞背带
3. somersault v. 翻筋斗
4. void n. 空间；真空
5. gorgeous adj. 非常漂亮的；绚丽的
6. shroud n. 覆盖物；护罩
7. lunacy n. 疯狂，精神错乱
8. unprecedented adj. 空前的，前所未有的
9. mishap n. 不幸事故；灾难
10. outfitter n. 旅行（运动）用品商店
11. reentry n. 火箭或航天器重返大气层
12. encyclopedia n. 百科全书
13. drogue parachute 小降落伞
drogue n. 锥形物
parachute n. 降落伞
14. rip [rip] v. 撕破，扯裂
15. survivable adj. 非致命的，免于死亡的
16. gear n. 设备，装备
17. disorientation n. 迷失方向
18. envision v. 预想，想象
19. crushing adj. 压倒的；毁灭性的
20. accelerate v. 加速
21. exert v. 施加；运用
22. searing adj. 烧灼的，灼热的
23. broil v. 烧烤；炙
24. tailored adj. 定做的，特制的
25. Nomex n. 高熔点芳香族聚酰胺
26. cookout n. 野炊，野餐
27. transonic adj. 超音速的
28. astounding adj. 令人惊骇的
29. meteorite n. 陨石，陨星
30. descent n. 降落，下降
31. must n. 必需的东西
32. blunt cone 钝锥 blunt [bl?蘧nt] adj. 钝的
33. thrill n. 激动，刺激