SpaceX’s Next Frontier: Landing a Rocket on Earth

By KENNETH CHANGJAN

In rocketry, what goes up usually comes down in pieces.

The cost of getting to orbit is exorbitant, because the rocket, with its multimillion-dollar engines, ends up as trash in the ocean after one launching.

Elon Musk, the chief executive of the Space Exploration Technologies Corporation, better known as SpaceX, likens the waste to throwing away a 747 jet after a single transcontinental flight.

“Reusability is the critical breakthrough needed in rocketry to take things to the next level,” Mr. Musk said in October during a talk at the Massachusetts Institute of Technology.

On Tuesday, his company hopes to upend the economics of space travel.

At 6:20 a.m. Eastern time, one of SpaceX’s Falcon 9 rockets is scheduled to lift off from the Cape Canaveral Air Force Station in Florida on what is otherwise a routine unmanned cargo run to the International Space Station.

But this time, the company will attempt to land the first stage of the rocket intact on a barge floating in the Atlantic Ocean. After the booster falls away and the second stage continues pushing the payload to orbit, its engines will reignite to turn it around and guide it to a spot about 200 miles east of Jacksonville, Fla.

SpaceX has attempted similar maneuvers on three earlier Falcon 9 flights, and on the second and third attempts, the rocket slowed to a hover before splashing into the water.

“We’ve been able to soft-land the rocket booster in the ocean twice so far,” Mr. Musk said. “Unfortunately, it sort of sat there for several seconds, then tipped over and exploded. It’s quite difficult to reuse at that point.”

The first rocket stage, Mr. Musk noted, is as tall as a 14-story building. “When a 14-story building falls over, it’s quite a belly flop,” he said. “What we need to do is to be able to land on a floating platform.”

So SpaceX built a floating platform, 300 feet long and 170 feet wide, for the rocket stage to land on.

A new addition to the rocket is a set of “grid fins” that will fold out after separation to help steer the rocket toward the platform. No people will be aboard the barge during the landing attempt.

If SpaceX’s gamble succeeds, the company plans to reuse the rocket stage on a later flight.

Mr. Musk put the chances of success at 50 percent or less. But, he added, over the dozen or so flights scheduled for this year, “I think it’s quite likely, 80 to 90 percent likely, that one of those flights will be able to land and refly.”

Eventually, SpaceX would like to land the first stage back at the launch site. A longer-term goal is to recover and reuse the second stage as well, and Mr. Musk has predicted that a fully reusable rocket could cut launch costs to a hundredth of what they are now.

This NASA cargo mission, SpaceX’s fifth, is carrying more than 5,000 pounds of supplies and equipment, including an IMAX movie camera, a laboratory habitat for studying fruit flies, and an instrument to measure the distribution of clouds as well as particles of dust, smoke and air pollution. After four weeks docked to the space station, the SpaceX cargo capsule will carry experiments, trash and other items back to Earth.

This flight is also attracting scrutiny because the Orbital Sciences Corporation, the other company that NASA has hired to ferry cargo to the space station, suffered a catastrophic failure in October when its Antares rocket fell back to the ground moments after liftoff.

Among the items destroyed in the explosion were 18 student experiments, part of a program run by the National Center for Earth and Space Science Education.

Some of the students had traveled to the Orbital’s launching site in eastern Virginia and left crestfallen.

But Jeff Goldstein, the director of the center, and NanoRacks, the company that made arrangements for the experiments on the space station, were already working to juggle the manifests on future cargo flights.

Three weeks later, 17 of the 18 student teams had recreated their experiments and shipped them to Houston for NASA to add them to the SpaceX payload, then scheduled for launching on Dec. 19.

“It was nuts,” Dr. Goldstein said. “NASA moved heaven and earth for this.”

The 18th team, Dr. Goldstein said, decided to modify its experiment, requiring a new safety review.

The launching was subsequently postponed after a test firing of the Falcon 9’s nine engines was cut short. After a later successful test firing, the launch date was set for Jan. 6.

火箭重複用 平價太空旅行有影

穆斯克旗下太空事業開發的獵鷹九號（Falcon 9）火箭因機件狀況延後發射，他計劃讓火箭返航的創舉，也被迫延期。若火箭能重複使用，可大大減低太空飛行的成本。

發射火箭升空的成本高昂，推進器造價數百萬美元的火箭僅使用一次，即成為海上垃圾。SpaceX創辦人穆斯克認為，若能讓火箭發射進入平流層後，返航降落在漂浮在海上駁船上，SpaceX便可讓人負擔得起太空旅行。

原本SpaceX的獵鷹九號火箭計劃在美東時間6日上午6時20分，從佛州卡納維拉角太空中心運載Dragon號貨物太空船升空，執行國際太空站補給任務。SpaceX正試圖創造歷史，讓已發射的推進器能夠垂直降落在太西洋上的無人船上，而非在重返地球大氣層時焚毀。

然而，獵鷹九號火箭在倒數計時最後1分鐘時取消發射，原因是第二節火箭推進引導的發動機出現問題。SpaceX最快將於9日上午再度發射火箭。

太空火箭通常只能發射一次，這意味像SpaceX這樣的業者就必須支付5,400萬美元。穆斯克在SpaceX官網上表示：「若有人能想出如何像飛機那樣有效重複使用火箭，飛到太空的成本最多可降一百倍。」

SpaceX在大西洋的駁船，長90公尺寬30公尺，對有14樓高的火箭算是很小的目標。SpaceX已為火箭設計重新推進功能，協助火箭慢慢垂直降落。火箭也有小型導向翼和降落架，協助火箭安全觸及目標。

SpaceX表示，已成功引導火箭在海上軟著陸兩次，不過穆斯克向紐約時報表示，這兩次火箭短暫在海面滯空，都出現傾斜並爆炸。

財星雜誌（Fortune）去年夏季報導SpaceX如何透過大幅降低太空發射服務的價格，來挑戰民間太空業的競爭對手。若SpaceX成功實現重複使用火箭的目標，可望享有更大的價格優勢。

原文參照：
http://www.nytimes.com/2015/01/05/science/space/next-frontier-for-spacex-and-elon-musk-landing-a-rocket-on-earth.html

2015-01-07．經濟日報．A8．國際．編譯鍾詠翔