Atlantis’ legacy continues as healthy Hubble finds primitive galaxies
One of the jewels in NASA’s crown – the Hubble Space Telescope – is continuing to expand our understanding of the universe, with new findings uncovering a previously unseen population of seven primitive galaxies that formed more than 13 billion years ago. However, the discovery was made via an instrument delivered by Shuttle Atlantis during her STS-125 mission, as her legacy lives on long after her retirement.
Hubble And Shuttle:
The association between the Space Shuttle fleet and Hubble began at the point of the telescope’s departure from Earth, under the protection of Shuttle Discovery, as she lofted HST into orbit in her cargo bay on STS-31.
That early morning launch over 22 years ago always promised a new era of discovery, but it was the Shuttle fleet’s unmatched versatility that would prove to be the key for ensuring Hubble would fulfil its role. After all, Hubble – much to the shock of its team – was launched with a major fault.
The fault was only discovered after scientists first started to receive imagery from the telescope, revealing the main mirror had been ground incorrectly, effectively compromising Hubble’s eyesight.
Discovery’s younger sister came to the rescue of Hubble in 1993, as Endeavour launched on only her fifth mission to carry out a critical service mission, with the main goal of correcting the telescope’s impaired vision.
With STS-61’s five EVAs successfully installing a corrective optics package – along with new solar arrays – during the highly complex 11 day mission, Hubble was back to full health and started to provide the stunning images of the cosmos that have fascinated the entire human race ever since.
Discovery would return to Hubble in 1997, as STS-82’s mission upgraded the telescope’s scientific instruments, and increased its research capabilities. Discovery would visit her favourite telescope once again on the third servicing mission in 1999, replacing all six of Hubble’s gyroscopes – three of which had failed – along with replacing a Fine Guidance Sensor (FGS) and the telescope’s computer.
In what was Columbia’s penultimate mission prior to her tragic loss, STS-109 carried out the fourth servicing mission in 2002.
The five EVA mission installed the Advanced Camera for Surveys (ACS), new rigid Solar Arrays (SA3), a new Power Control Unit (PCU) and a new Cryocooler for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). Columbia also provided Hubble with a farewell push, as the orbiter reboosted the telescope to a higher orbit.
Due to Columbia’s loss the following year, NASA managers were left with a dilemma. Hubble was next scheduled to be serviced in 2005, yet NASA’s own Return To Flight (RTF) rules insisted on the “safe haven” requirement, allowing for an orbiter, damaged during launch, to fly to the International Space Station (ISS) for its crew to await another shuttle to bring them home safe.
With this “safe haven” requirement impossible for a mission to Hubble, the final Shuttle servicing mission was cancelled. However, with a robotic mission deemed not to be viable, pressure grew both at the public and political level to review the cancellation.
In 2005, incoming NASA administrator Mike Griffin eventually approved SM-4 for Atlantis and STS-125, after the Space Shuttle Program (SSP) started to prove its new safety measures were working – such as the increasing mitigation of External Tank foam loss and advances in Thermal Protection System (TPS) inspection and repair techniques – during the opening salvo of post-RTF missions.
The best possible crew were assigned to Atlantis for the final rendezvous between the world-famous vehicles, led by commander Scott Altman, assisted by six crewmembers that included John Grunsfeld and Mike Massimino.
Endeavour would also receive a co-star role by standing by as the STS-400 rescue mission, seeing her sat on Pad 39B ready to launch at short notice in the event Atlantis’ launch – from Pad 39A – suffered a major issue during the ride uphill on what proved to be a delayed launch date, as Hubble itself worked through problems on orbit.
That contingency wasn’t required, as Atlantis and her crew conducted a flawless launch and rendezvous with Hubble in May, 2009 – no easy task even under nominal conditions, as the orbiters used up nearly half of their prop capability just to reach the “height” of the telescope’s orbit and can endure higher MMOD risks.
The 14 day mission involved five back-to-back EVAs, including its own challenges – highlighted by Massimino literally using brute force to pull off the STIS hand rail from the telescope (see L2 video) during EVA-4.
However, the mission achieved all of its primary goals, including the installation of two new instruments, namely the the Cosmic Origins Spectrograph (COS) and the Wide Field Camera 3 (WFC 3), leaving Hubble in a great condition to continue its role for many years to come.
One such example of the legacy Atlantis and STS-125 provided was seen via a NASA release on Wednesday, relating observations made by WFC 3 – an instrument that is much more capable than the WFPC2 (Wide Field and Planetary Camera 2) which it replaced.
Thanks to its additional imaging sensor that works in the near infra-red – something the older camera was not capable of – astronomers announced they have seen further back in time than ever before and have uncovered a previously unseen population of seven primitive galaxies that formed more than 13 billion years ago, when the universe was less than three percent of its present age.
These deepest images to date from Hubble yield the first statistically robust sample of galaxies that tells how abundant they were close to the era when galaxies first formed.
The results are from an ambitious Hubble survey of an intensively studied patch of sky known as the Ultra Deep Field (UDF). In the 2012 campaign, called UDF12, a team of astronomers led by Richard Ellis of the California Institute of Technology in Pasadena used Hubble’s Wide Field Camera 3 (WFC 3) to peer deeper into space in near-infrared light than any previous Hubble observation.
Without STS-125’s delivery of the WFC 3 to Hubble, the latest results would have been extremely difficult to obtain.
The observations were made during six weeks in August and September, and the first scientific results now are appearing in a series of scientific papers.
“Our study has taken the subject forward in two ways,” Ellis explained. “First, we have used Hubble to make longer exposures. The added depth is essential to reliably probe the early period of cosmic history. Second, we have used Hubble’s available color filters very effectively to more precisely measure galaxy distances.”
The team estimated the galaxy distances by studying their colors through a carefully chosen set of four filters at specific near-infrared wavelengths.
“We added one filter, and undertook much deeper exposures in some filters than in earlier work, in order to convincingly reject the possibility that some of our galaxies might be foreground objects,” said team member James Dunlop of the Institute for Astronomy at the University of Edinburgh in Scotland.
Astronomers have long debated whether hot stars in such early galaxies could have provided enough radiation to warm the cold hydrogen that formed soon after the big bang. This process, called “reionization,” is thought to have occurred 200 million to 1 billion years after the birth of the universe. This process made the universe transparent to light, allowing astronomers to look far back into time. The galaxies in the new study are seen in this early epoch.
“Our data confirm reionization was a gradual process, occurring over several hundred million years, with galaxies slowly building up their stars and chemical elements,” said Brant Robertson of the University of Arizona in Tucson. “There wasn’t a single dramatic moment when galaxies formed. It was a gradual process.”
So while Atlantis is now long retired since completing her STS-135 mission, and is preparing to go on display to the public in her new facility at KSC’s Visitor Center, she – and her crew – can be proud of the legacy one of her many missions is continuing to provide to the public they served.
(Article images via L2, L2 Historical, NASA and Ed Cheung)
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