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<\/p>\nThis December, an Ariane 5 rocket will launch from Kourou, French Guiana carrying the most complicated telescope ever developed \u2014 the joint NASA\/ESA\/CSA James Webb Space Telescope. However, when the telescope launches, it will not immediately be ready for scientific observations. In fact, the telescope won\u2019t perform any observations until about six months after launch.<\/p>\n
Following separation from the Ariane 5 second stage, James Webb will spend the next month deploying all of its instruments, mirrors, and structural systems that will be used for scientific observations. Once the telescope reaches its orbit at Earth-Sun Lagrange Point 2 (L2), it will spend up to six months performing tests and calibrating systems for observations.<\/p>\n<\/p>\n
This entire deployment and testing process is called commissioning and it is a vital part of a spacecraft\u2019s life and ultimately determines if a spacecraft will be able to properly function as expected. For James Webb, commissioning is an extremely important process that the entire telescope team will monitor.<\/p>\n
To gain insight into James Webb\u2019s commissioning process and what the process will be like for the team, NASASpaceflight spoke with Keith Parrish, James Webb\u2019s Observatory Manager and Commissioning Lead.<\/p>\n
\u201cCommissioning actually starts when the rocket leaves the ground. So once Ariane 5 takes off, that\u2019s when we say commissioning is starting,\u201d Parrish said.<\/p>\n
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Artist\u2019s depiction of Ariane 5 fairing seperation during the launch of JWST. (Credit: ESA)<\/p>\n
\u201cSo commissioning really starts with that first day of activities, which is getting safely on orbit. That\u2019s our entire goal. We\u2019re completely focused on just getting the observatory on orbit safely. We define \u2018safe\u2019 as Webb is talking to the ground, its solar arrays are deployed and generating power, and we\u2019re on our way to L2. It\u2019s a really fast compressed time period from the time that James Webb leaves the ground to it getting on orbit.\u201d<\/p>\n
\u201cSo now we\u2019re on orbit. Now we do a mid-course correction phase. That\u2019s where we will actually use Webb\u2019s thrusters to take out any of the errors that Ariane 5 gave us. We tell the Ariane 5 team to send us in a certain direction at a certain velocity, and they\u2019ll get us really, really close to that target. We\u2019re talking [40,200 km\/h], though, so we may have to put in a few meters per second of velocity [to get to the exact velocity and direction]. So we\u2019re talking little tiny puffs from our onboard thruster system.\u201d<\/p>\n
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\u201cWe do in that first day, about 12 and a half hours after launch. We\u2019ll see how that first mid-course correction went and then about two days later we\u2019ll do another small correction. The corrections will start getting smaller and really narrowing us down so that we\u2019re right on that track to get to L2.\u201d<\/p>\n
After this, perhaps the most critical aspect of James Webb\u2019s mission is up next \u2014 deployments.<\/p>\n
\u201cAbout three or four days after launch is actually when we go into our deployments phase.<\/p>\n
\u201cWe\u2019ll start our deployment phases with our sunshield deployment. We have very large pallets that are 20 to 30 feet tall that hold all of our membrane material [for the sunshield]. We have five small and very thin membranes that constitute our sunshield, and we have to unfold all that material and get it pulled into place. We start by lowering the front and back pallets down, and that takes about a day. Then over the next two to three days, we start releasing all of our release devices [on the sunshield and pallets]. We have about 170 released devices that we fire to actually release all this material and structures over the sunshield\u2019s deployment phase. Between day three and day six, we actually get the sunshield fully deployed.\u201d<\/p>\n
\u201cAlso in that period, we start to see rapid cooling of our telescope and its instruments once we get that sunshield out.\u201d<\/p>\n
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James Webb\u2019s sunshield fully deployed. (Credit: NASA\/Chris Gunn)<\/p>\n
Next up is the deployment of James Webb\u2019s 6.5 m diameter mirror \u2014 one of the largest mirrors ever flown into space, and the most complex space telescope mirror ever built.<\/p>\n
\u201cSo our telescope consists of our primary mirror, which is made of eighteen individual mirror segments. For launch, we fold back six of the segments so Webb will fit inside the launch vehicle. Then, we have a secondary mirror. That secondary mirror is actually what takes in all the light that gets collected by the main mirror and puts the light down into our cameras and our instrument systems. The secondary mirror is kind of mounted on a tripod that is broken up into different links and folded back onto the primary mirror. So we fold the secondary mirror out and then we fold out the two wings of the primary mirror.\u201d<\/p>\n
\u201cSomewhere around the 10 to 14-day range, we feel like we will have the primary and secondary mirror fully deployed,\u201d Parrish said.<\/p>\n
NASASpaceflight recently spoke with James Webb\u2019s Optical Telescope Element Manager about the mirror\u2019s systems and complexity.<\/p>\n<\/p>\n