"Mid-February is looking to be a reasonable timeframe to do that," said Preston Burch, the Hubble manager at Nasa's Goddard Space Flight Center where telescope operations are overseen.

Nasa says the problem is in a box known as the Science Instrument Command and Data Handling (SIC&DH) Unit, and affects the functions carried out by its Science Data Formatter - Side A.

The glitch arose on Saturday and all attempts to correct have proved fruitless. The assessment is that the formatter has totally failed and will not be recoverable.

The anomaly prevents Hubble from formatting the data gathered by its instruments ready for sending to scientists on the ground. The malfunction also stops that data being stored locally on the telescope's solid state recorders for later transmission.

Hubble has a back-up - Side B - and if systems can be switched over, the observatory should return to normal operations. Engineers say it is a complex procedure but they hope to have Hubble functioning at its previous level of performance within a couple of weeks.

In the meantime, a spare SIC&DH Unit on the ground will be prepared for flight, to be included as an additional servicing task on the forthcoming Atlantis mission.

Ed Weiler, Nasa's associate administrator for science, said it was important Hubble had redundancy for Side B going into the future

"If we just go to Side B, we would be left with a system that had several single point failures, and that would be a risk to the [Hubble] mission for the long duration," he explained.

"By going ahead and accepting a delay of perhaps several months, we can get our full-up spare tested and ready to go - and if we could put that in [Hubble] sometime in the winter, we would have an observatory that was again doubly redundant; that is, it would have back-up systems."

Rescue readiness

The 62kg (136lb) box requires no new tools be developed for astronauts to fit it inside Hubble. However, time will have to be found in an already tight spacewalk schedule to get the job done.

Setting a new date for the mission is complicated by Nasa's strict flight rules introduced after the Columbia disaster.

Because Atlantis cannot get to the safety of the space station from Hubble's orbit if something goes wrong, a second shuttle must be put on the launch pad ready to fly a rescue mission if required.

For the planned 14 October launch opportunity, the back-up was supposed to be the Endeavour orbiter. But this ship is also needed for a space station mission on 16 November.

The Atlantis delay means Endeavour's mission may now be brought forward by a couple of days, and Atlantis slotted into the shuttle manifest in February or April next year when another orbiter would take up the rescue-readiness role.

The upcoming mission to Hubble is the fifth and final flight designed to keep the great observatory serviceable.

Hubble's batteries and gyroscopes, which are used to point the telescope, are degrading and they now need to be replaced.

The shuttle crew is also tasked with installing two new instruments: the Wide Field Camera 3 (WFC3), and the Cosmic Origins Spectrograph (COS). The new instruments will improve significantly Hubble's ability to probe distant, faint objects in the early Universe.

The Atlantis astronauts must also repair two instruments that have failed in recent years - the Advanced Camera for Surveys (ACS) and the Space Telescope Imaging Spectrograph (STIS).

If the work is carried out successfully, it should allow Hubble to keep operating into the next decade.

Ed Weiler said everyone should think it was lucky that the Data Formatter broke just before Atlantis set off on its servicing mission rather than just after it.

"Hubble has a habit of coming back from adversity; and the Hubble team works miracles," he added.

"I'm not too concerned about this. We'll find a way to get this fixed. This particular failure was anticipated and we have spare hardware ready to go."

adversity : 逆境
anomaly : 異常
anticipate : 預期
arise : 出現
astronaut : 太空人
attempt : 試圖做
complex : 複雜
complicated : 錯綜複雜
distant : 遠
endeavor : 努力
forthcoming : 即將要來
fruitless : 不成功
gather : 聚集
glitch : 故障
malfunction : 故障
manifest : 明白
meantime : 其間
observatory : 天文台
orbit : 軌道
orbiter : 軌道飛行器
oversee : 監督
prevent : 防止
probe : 探查
readiness : 願意
reasonable : 合理
recoverable : 可取回
redundancy : 過剩
rescue : 援救
spare : 節省
strict : 嚴格
supposed : 認為
telescope : 望遠鏡
tight : 緊
timeframe : 時間範圍
upcoming : 即將到來

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