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| Hubble's sense of direction boost | Hubble's sense of direction boost |
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| Two shuttle astronauts have begun the most critical repair to the Hubble Space Telescope in a second spacewalk. | Two shuttle astronauts have begun the most critical repair to the Hubble Space Telescope in a second spacewalk. |
| Mission specialists Mike Good and Mike Massimino are to replace "rate sensing units", or gyroscopes, as well as three batteries on the telescope. | Mission specialists Mike Good and Mike Massimino are to replace "rate sensing units", or gyroscopes, as well as three batteries on the telescope. |
| Currently, only three of the six gyroscopes work, and two are needed to orient the telescope properly. | Currently, only three of the six gyroscopes work, and two are needed to orient the telescope properly. |
| The replacement along with Thursday's work are the top-priority tasks to ensure Hubble five more years of life. | The replacement along with Thursday's work are the top-priority tasks to ensure Hubble five more years of life. |
| HUBBLE SPACE TELESCOPE Named after the great US astronomer Edwin HubbleLaunched in 1990 into a 600km-high circular orbit Equipped with a 2.4m primary mirror and five instrumentsLength: 15.9m; diameter: 4.2m; Mass: 11,110kg In pictures: The best of Hubble | HUBBLE SPACE TELESCOPE Named after the great US astronomer Edwin HubbleLaunched in 1990 into a 600km-high circular orbit Equipped with a 2.4m primary mirror and five instrumentsLength: 15.9m; diameter: 4.2m; Mass: 11,110kg In pictures: The best of Hubble |
| The spacewalk will be the 20th undertaken in the service of Hubble but will be Mike Good's first. | The spacewalk will be the 20th undertaken in the service of Hubble but will be Mike Good's first. |
| "Welcome to the wonderful world of working in a vacuum," Mike Massimino told him as he exited the airlock. | "Welcome to the wonderful world of working in a vacuum," Mike Massimino told him as he exited the airlock. |
| The first part of the spacewalk was to replace the three rate sensing units (RSUs), each of which contains two gyroscopes. | The first part of the spacewalk was to replace the three rate sensing units (RSUs), each of which contains two gyroscopes. |
| While the first RSU went in as planned, the second one did not seat properly on its plate. The crew opted to place the third RSU in the slot of the second. | |
| The same problem occurred when the RSU meant for the second slot was placed into the third, so the crew are now attempting to install a standby unit instead. | |
| The batteries to be replaced are the original equipment installed on Hubble 19 years ago, intended to have just a five-year lifespan. | The batteries to be replaced are the original equipment installed on Hubble 19 years ago, intended to have just a five-year lifespan. |
| On Thursday, the telescope's Wide Field Camera was replaced, giving the telescope an even deeper view into space - and thus into the history of the Universe. | On Thursday, the telescope's Wide Field Camera was replaced, giving the telescope an even deeper view into space - and thus into the history of the Universe. |
| A data processing unit that failed in 2008 was also replaced. | A data processing unit that failed in 2008 was also replaced. |
| In three further spacewalks to be undertaken in the next three days, two spectrographs will be installed and the remainder of Hubble's batteries will be replaced. | In three further spacewalks to be undertaken in the next three days, two spectrographs will be installed and the remainder of Hubble's batteries will be replaced. |