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”.?

在技術(shù)上的壯舉中，恢復(fù)和重新發(fā)射太空火箭的第一級是相當(dāng)困難的。到目前為止，只有美國巨頭SpaceX實現(xiàn)了這一目標(biāo)。但另一家公司現(xiàn)在似乎也在這么做——盡管規(guī)模較小。當(dāng)?shù)靥鞖馄届o后不久(也就是本文發(fā)表后不久)，一家名為火箭實驗室(Rocket Lab)的公司計劃派遣一項名為“去而復(fù)返”的任務(wù)。

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.

該公司的兩級電子發(fā)射裝置中的一個將從位于新西蘭北島的航天港發(fā)射升空開始。（該使團的名字暗指新西蘭在彼得·杰克遜的電影版《霍比特人》中扮演的角色，原著的副標(biāo)題中有這個短語。）幾分鐘后，恢復(fù)電子第一級的嘗試將開始。SpaceX公司于2015年首次采用這種方式，利用推進器將Falcon 9運載火箭的下降第一級輕輕豎立在著陸臺上。相比之下，火箭實驗室將使用一架直升機試圖捕捉其在飛行中的第一級跳傘。

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，電子的第一級還不到獵鷹9號的三分之一高度，這也將是一項相當(dāng)艱巨的任務(wù)?；鸺龑嶒炇以O(shè)計了一種抓斗裝置，連接在一根長繩上，該長繩將懸掛在一架雙引擎西科斯基直升機上。訣竅是操縱直升機，使繩索首先與進入平臺的拉緊降落傘線接觸，然后沿著降落傘線平穩(wěn)滑動。當(dāng)釣索碰到抓鉤者時，它會像捕獸夾一樣啪的一聲合上，用嘴咬住釣索。

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.?

這聽起來既困難又危險。但是，在一系列的測試中，捕獲小組成功地抓住了從第二架直升機上落下的假火箭段的降落傘線。為了不讓所有的東西進入直升機的旋翼，平臺上的無線電設(shè)備通過不斷地向機組人員傳送設(shè)備的位置來幫助做到這一點。

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，最棘手的技術(shù)挑戰(zhàn)不是實際的捕獲過程，而是幾分鐘前進行的階段操縱，而直升機仍在距離海岸約280公里的捕獲區(qū)附近懸停待命。如果一切順利，發(fā)射后約150秒，第一級的九個煤油發(fā)動機將關(guān)閉。然后平臺將分離。隨著第二階段繼續(xù)向上，將34顆小型衛(wèi)星送入環(huán)繞地球的軌道，到目前為止，第一階段大約在80公里以上，將向下延伸。這是事情變得非常危險的時候。隨著第一級以每秒2.35公里的速度飛馳，大氣摩擦很快就會突然產(chǎn)生巨大的熱量?；鸺龑嶒炇业睦习灞说谩へ惪耍≒eterBeck）說：“事情就是這樣發(fā)展起來的?！?。他的工程師們把這第一段逐漸增厚的空氣稱為墻。

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.?

為了使墻完好無損地存活下來，第一級將使用推進器翻轉(zhuǎn)自身，使其先尾部移動。該級的底部已經(jīng)設(shè)計用于處理發(fā)動機排氣的高熱，因此利用其耐熱性在空氣中切割出一條通道是有意義的。然而，重返大氣層的摩擦將在平臺周圍產(chǎn)生過熱空氣分子的弓形波，貝克先生將其描述為“等離子的熱刀”。這使得誤差的幅度很小。他說，如果平臺稍微傾斜，然后觸摸這把等離子刀，它就會像切黃油一樣被切穿。

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.?

穿過墻壁的摩擦力會減慢平臺的速度，但不足以使其立即展開主降落傘。相反，在大約13公里的高度，氣動迫擊炮將射出一個較小的drogue滑道。只有當(dāng)下降階段達到6公里的高度時，大降落傘才會被釋放。即便如此，圓形“卷繞”繩索也會將其開口限制在最大表面積的四分之一以內(nèi)。大約一分鐘后，繩子將被切斷，以使降落傘充分充氣。這將使平臺的下降速度減慢到每秒10米。正如早期的試飛所顯示的那樣，在這種速度下，直升機的飛行員既不太困難，也不需要對飛機進行危險的向下猛拉，就可以抓住已用完的階段。

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.

火箭實驗室并不是唯一一家希望效仿SpaceX回收技術(shù)的公司。為航天行業(yè)提供咨詢的Quilty Analytics公司知道至少還有五家公司，但沒有一家公司比火箭實驗室更先進。至于如果這一切都成功的話，該公司能節(jié)省多少錢，貝克先生仍然很靦腆。然而，Quilty Analytics的創(chuàng)始人克里斯·奎爾蒂（Chris Quilty）認為，電子的第一階段可能占發(fā)射器成本的三分之二以上，因此重復(fù)使用它將大大降低成本。因此，火箭實驗室的競爭對手幾乎和公司本身一樣渴望看到運營的成功程度，這是一個公平的賭注。