每天一篇经济学人 | Reusable rockets 可重用火箭（202...

As technological feats go, recovering and relaunching the first stage of a space rocket ranks pretty high on the scale of difficulty. So far, only SpaceX, an American giant, has pulled it off. But another outfit now seems close to doing so—albeit on a rather smaller scale. Shortly after the local weather calms (and thus after this story was published), a firm called Rocket Lab plans to dispatch a mission dubbed “There and Back Again”. 

在技术上的壮举中，恢复和重新发射太空火箭的第一级是相当困难的。到目前为止，只有美国巨头SpaceX实现了这一目标。但另一家公司现在似乎也在这么做——尽管规模较小。当地天气平静后不久(也就是本文发表后不久)，一家名为火箭实验室(Rocket Lab)的公司计划派遣一项名为“去而复返”的任务。

There and Back Again will start with the lift-off of one of the company’s two-stage Electron launchers from its spaceport on New Zealand’s North Island. (The mission’s name is a sly allusion to New Zealand’s role as a set for Peter Jackson’s filmed version of “The Hobbit”, the original book of which bore the phrase as part of its subtitle.) Minutes later, the attempt to recover the Electron’s spent first stage will begin. SpaceX, which first did this sort of thing in 2015, uses thrusters to set the descending first stages of its Falcon 9 launch vehicles gently upright on a landing pad. Rocket Lab, by contrast, will employ a helicopter to try to catch its parachuting first stage in flight.

该公司的两级电子发射装置中的一个将从位于新西兰北岛的航天港发射升空开始。（该使团的名字暗指新西兰在彼得·杰克逊的电影版《霍比特人》中扮演的角色，原著的副标题中有这个短语。）几分钟后，恢复电子第一级的尝试将开始。SpaceX公司于2015年首次采用这种方式，利用推进器将Falcon 9运载火箭的下降第一级轻轻竖立在着陆台上。相比之下，火箭实验室将使用一架直升机试图捕捉其在飞行中的第一级跳伞。

It promises to be quite an operation, even if, at 12.4 metres, an Electron’s first stage is less than a third of the height of a Falcon 9’s. Rocket Lab has designed a grappling mechanism attached to a long line which will dangle from a twinengined Sikorsky helicopter. The trick will be to manoeuvre the chopper so that this cord first makes contact with, and then slides smoothly along, the incoming stage’s taut parachute line. When that line reaches the grappler, it will snap shut like a gin trap, seizing the line in its jaws. 

即使在12.4米的高度上，电子的第一级还不到猎鹰9号的三分之一高度，这也将是一项相当艰巨的任务。火箭实验室设计了一种抓斗装置，连接在一根长绳上，该长绳将悬挂在一架双引擎西科斯基直升机上。诀窍是操纵直升机，使绳索首先与进入平台的拉紧降落伞线接触，然后沿着降落伞线平稳滑动。当钓索碰到抓钩者时，它会像捕兽夹一样啪的一声合上，用嘴咬住钓索。

This sounds both hard and risky. But, in a number of tests, the capture team has successfully grabbed the parachute line of a dummy rocket stage dropped from a second helicopter. As for keeping the whole shebang out of the helicopter’s rotors, a radio in the stage helps to do this by transmitting its position continuously to the flight crew. 

这听起来既困难又危险。但是，在一系列的测试中，捕获小组成功地抓住了从第二架直升机上落下的假火箭段的降落伞线。为了不让所有的东西进入直升机的旋翼，平台上的无线电设备通过不断地向机组人员传送设备的位置来帮助做到这一点。

The trickiest technical challenge, therefore, is not the actual process of capture, but rather the manoeuvring of the stage that takes place minutes earlier, while the helicopter is still hovering on standby near the catch zone, some 280km from shore. If all goes well, about 150 seconds after launch the first stage’s nine kerosene-powered engines will switch off. The stage will then separate. As the second stage continues upward to loft 34 small satellites into orbit around Earth, the first, by now about 80km up, will arc back downward. This is when things get really dicey. With the first stage hurtling along at 2.35km a second, atmospheric friction will soon—and quite suddenly—generate tremendous heat. “It just goes whack, like that,” says Peter Beck, Rocket Lab’s boss. His engineers refer to this first stretch of progressively thickening air as the Wall. 

因此，最棘手的技术挑战不是实际的捕获过程，而是几分钟前进行的阶段操纵，而直升机仍在距离海岸约280公里的捕获区附近悬停待命。如果一切顺利，发射后约150秒，第一级的九个煤油发动机将关闭。然后平台将分离。随着第二阶段继续向上，将34颗小型卫星送入环绕地球的轨道，到目前为止，第一阶段大约在80公里以上，将向下延伸。这是事情变得非常危险的时候。随着第一级以每秒2.35公里的速度飞驰，大气摩擦很快就会突然产生巨大的热量。火箭实验室的老板彼得·贝克（PeterBeck）说：“事情就是这样发展起来的。”。他的工程师们把这第一段逐渐增厚的空气称为墙。

To survive the Wall intact, the first stage will use thrusters to flip itself over, so that it is travelling tail first. The bottom part of the stage is already designed to handle the intense heat of the engine’s exhaust, so it makes sense to take advantage of its heatresistance to slice a pathway through the air. The friction of re-entry will nevertheless create a bow wave of superheated air molecules surrounding the stage, which Mr Beck describes as “a hot knife of plasma” . This renders the margin for error slim. Were the stage to tip slightly, and touch this plasma knife, he says, it would be cut through almost as if it were butter. 

为了使墙完好无损地存活下来，第一级将使用推进器翻转自身，使其先尾部移动。该级的底部已经设计用于处理发动机排气的高热，因此利用其耐热性在空气中切割出一条通道是有意义的。然而，重返大气层的摩擦将在平台周围产生过热空气分子的弓形波，贝克先生将其描述为“等离子的热刀”。这使得误差的幅度很小。他说，如果平台稍微倾斜，然后触摸这把等离子刀，它就会像切黄油一样被切穿。

Friction from passing through the Wall will slow the stage, but not enough for it to deploy its main parachute immediately. Instead, at an altitude of about 13km, a pneumatic mortar will shoot out a smaller drogue chute. Only when the descending stage has reached an altitude of 6km will the big parachute be released. Even then, a circular “reefing” cord will restrict its opening to a quarter of its maximum surface area. Roughly a minute later, that cord will be severed, to permit the parachute to inflate fully. This will slow the stage’s descent to just ten metres a second. As the earlier trials have shown, at that speed the helicopter’s pilot is able to snag the spent stage with neither great difficulty nor a dangerous downward yank on the aircraft. 

穿过墙壁的摩擦力会减慢平台的速度，但不足以使其立即展开主降落伞。相反，在大约13公里的高度，气动迫击炮将射出一个较小的drogue滑道。只有当下降阶段达到6公里的高度时，大降落伞才会被释放。即便如此，圆形“卷绕”绳索也会将其开口限制在最大表面积的四分之一以内。大约一分钟后，绳子将被切断，以使降落伞充分充气。这将使平台的下降速度减慢到每秒10米。正如早期的试飞所显示的那样，在这种速度下，直升机的飞行员既不太困难，也不需要对飞机进行危险的向下猛拉，就可以抓住已用完的阶段。

Rocket Lab is not the only company which hopes to emulate SpaceX’s feat of recycling. Quilty Analytics, a firm that advises the space industry, is aware of at least five others—though none is as far advanced as Rocket Lab. As to how much money the firm might save if all this proves successful, Mr Beck remains coy. However, Chris Quilty, Quilty Analytics’ founder, reckons the Electron’s first stage may well account for more than two-thirds of the launcher’s cost, so reusing it will cheapen things considerably. It is a fair bet, then, that Rocket Lab’s competitors will be almost as keen as the firm itself to see just how well the operation succeeds.

火箭实验室并不是唯一一家希望效仿SpaceX回收技术的公司。为航天行业提供咨询的Quilty Analytics公司知道至少还有五家公司，但没有一家公司比火箭实验室更先进。至于如果这一切都成功的话，该公司能节省多少钱，贝克先生仍然很腼腆。然而，Quilty Analytics的创始人克里斯·奎尔蒂（Chris Quilty）认为，电子的第一阶段可能占发射器成本的三分之二以上，因此重复使用它将大大降低成本。因此，火箭实验室的竞争对手几乎和公司本身一样渴望看到运营的成功程度，这是一个公平的赌注。