Teams working at the Northrop Grumman spacecraft plant in southern California have connected for the first time the spacecraft and scientific modules of the James Webb Space Telescope, an important step for engineers preparing for to check if the sun visor of the observatory was well set and to begin acoustic tests in the coming months.
On August 23, technicians at Northrop Grumman's facility in Redondo Beach, California, assembled the JWST telescope with its space bus. Since then, the workers have finalized the mechanical and electrical connections between the two main elements of the observatory, the most powerful space telescope ever built.
"This is an important step for us," said Eric Smith, JWST program scientist at NASA's headquarters in Washington. "It's a program that debuted in people's minds about 30 years ago. Some of the original contracts were concluded in 2001 and 2002, and seeing it in this clean room is now breathtaking. Many people have waited a long time for this. It is wonderful to see. "
Scheduled for the launch of French Guiana aboard a European Ariane 5 rocket in March 2021, the James Webb Space Telescope will cost more than $ 10 billion by the end of its mission, including contributions from NASA, of the European Space Agency and the Canadian Space Agency.
NASA bears the brunt with about $ 9.7 billion. ESA provides instrument equipment and a launcher to Webb, and Canada has built the precision guidance sensor and a spectrograph for the observatory.
"It's an exciting time to see all Webb parties finally gathered in one observatory for the very first time," said Gregory Robinson, webb program director at NASA headquarters. "The engineering team has taken a big step forward and we will soon see incredible new views of our amazing universe."
Webb's scientific and scientific modules have been individually tested at various assembly stages over the last decade. Now is the time to test the entire observatory in one piece.
A crane lifted the Webb telescope element over the spacecraft's bus and sun visor and carefully lowered it. There are six mechanical attachment points between the scientific module, which includes Webb's telescope and scientific instruments, and the spacecraft bus, as well as a dozen cable bundles, each carrying many data cables. and electric, said Smith
Once the connections are complete, the teams will deploy the sun visor the size of an observatory's tennis court, a thermal barrier designed to keep Webb's sensitive infrared detectors cool.
Consisting of five Kapton membranes, as thin as a human hair, the sun visor is designed to deploy in its open configuration once Webb is in the space. The membranes are coated with aluminum and treated silicon to evacuate the heat from the observatory, keeping Webb instruments as cold as minus 370 degrees Fahrenheit or minus 223 degrees Celsius. Internal coolers will cool some of the telescope's sensors even colder.
The engineers discovered seven rips on the sunscreen membranes during a previous deployment test, and a tension system used to keep the membrane in its shape developed too soft during the test, creating thus a risk of snagging, said NASA.
Since the discovery and repair of solar tears, ground crews have subjected the spacecraft element that holds the sun visor to a series of vibration, acoustic and thermal vacuum tests to expose the material to unstable environments. , noisy, cold and airless he meets when launching in space.
"They will now deploy the sun visor to make sure it's behaving as expected after launch (environments)," Smith said. "They will release all the diaphragm devices, push back the arrows of the sunshade and tend the membranes.
"That's one of the things they're definitely going to look for, is to review the environments, what's the shape of the sunshade coming out of it?" Smith said. "Did the procedures put in place to correct some of the things that caused the tears, the last time, work as expected? This is really part of this deployment test.
"They also had to make some adjustments to the so-called tension system of the diaphragm, the pulley system that actually tightens the visor," Smith said in an interview with Spaceflight Now. "Then they made these adjustments, and we'll see that we also did what we needed."
Northrop Grumman's test team will also deploy other structures on the telescope, and then subject the entire observatory to electrical, vibratory and acoustic tests. Once these checks are complete, the technicians will again deploy the full observatory to ensure that all mechanisms have survived the launch environment tests.
Then the technicians will put the observatory in launch configuration.
The observatory folds like origami to fit under the veil of the payload of the rocket Ariane 5. According to your account, Webb will perform more than 300 deployments after separating from the top floor of the launcher Ariane 5. According to NASA, the Mars Curiosity rover had about 70 deployments in a similar way.
Named in honor of James Webb, NASA's director from 1961 to 1968, the new observatory will be stationed at nearly one million miles (1.5 million kilometers) from Earth, at the 39, using a 6.5-meter mirror and four scientific instruments. distant universe, studying the turbulent consequences of the Big Bang, the formation of galaxies and the environments of planets around other stars.
According to Mr. Smith, NASA has about three months' margin in Webb's schedule before the mission's target launch date of March 30, 2021. This additional time could be used to resolve problems that arise during testing. ground remaining.
"You are testing this equipment in the field because if there are problems, you want to find them so that you can fix them before sending them to orbit," Smith said. "A program as large as Webb has a very large testing program and it's something we have to go through.
"The number of activities for the first time – these things we've never done before, and so maybe we do not understand as (totally) something we've done before – these numbers are decreasing, now, "he said. . "Most of this material has been exercised. Ambient (vibration) and acoustic tests are only one unit, yes, this is a first activity because we have never done it before. But that's something we'll have to do, and that's why we have an integrated planning margin to fix the problems that come up when they do it during testing. "
Last year, NASA acknowledged that Webb would not be ready for its target launch date scheduled for 2019. This delay was delayed after the announcement in 2017 that the mission would not be launched in 2018, as previously planned.
The launch time up to 2021 has resulted in an additional cost of nearly one billion dollars. It was just the latest in a series of failures in the program's tortured history.
An independent evaluation committee blamed the recent growth in costs and the latest delays for errors made by Northrop Grumman's Webb manufacturing and testing team. The panel also said that NASA was overly optimistic in its timing forecasts.
According to NASA, engineers replaced a catalyst bed heater and Webb propulsion system valves damaged by human error.
The workers misplaced the fasteners on Webb's sunshade before an acoustic test, and a number of screws, washers and nuts loosened during the acoustic test of the shuttle. After initially failing to consider all fixations, causing concern, some pieces fell into the spacecraft. The teams have now found all the material, Smith said.
Read more about the issues that caused Webb's launch delay to 2021.
Engineers have identified some other problems on the spacecraft bus that require special attention, Smith said.
"When we finished the environmental tests on the spacecraft, there were two electronic components that did not work as expected," he said. "The one was a component of a communication system. It's an amplifier. We have redundant amplifiers, but one of them did not work as expected.
"And some cards from one of the command and telemetry processors that (were also behaving in an unexpected way," he said. "So we buy new amplifiers … and we take control engineering units and telemetry processors that we already have and somehow improve them for the flight. "
The workers will replace the amplifier and the command and telemetry processor after the sunshield deployment test.
"At the same time as we are replacing this amplifier, we will be replacing one of these command and telemetry processors," Smith said. "This is a redundant system, we are just replacing one of them."
"The spacecraft has all of its electronics and avionics on the side panels, so there's a time when we basically have to put one of these panels flat to replace those two things," Smith said. "So we had to use some planning margin to accommodate that change, but that was taken into account and we still have room to go."
ESA and Arianespace officials have also agreed to change the design of the Ariane 5 rocket's payload vane vents to address concerns that a depressurization event could damage the Ariane 5 rocket. Webb observatory after taking off from the fairing.
The shell-shaped fairing will protect Webb since the Ariane 5 rockets cross the dense lower layers of the atmosphere. Once over the discernable atmosphere, the fairing relaxes to lose weight as the Ariane 5 rises into space.
Engineers were concerned that the residual air trapped in Webb's folded sunshades would cause a "surge" when the fairing was separated.
Smith told NASA to provide Arianespace, the launch operator of Ariane 5, with high-fidelity sensors allowing it to fly in two Ariane 5 missions and measure the pressure inside the aircraft. fairing during the bonnet separation sequence.
"They show that there is a problem of depressurization, which means that there would be enough residual pressure to threaten some of our equipment," Smith said. "So they agreed that to solve this problem, they would install additional equipment on their vents. These shrouds are ventilated at the base and we think the problem is that even if they open up, they may not stay fully open throughout the course.
"So, ESA and Ariane are working on a design that will essentially keep these vents open, and all calculations show that this should lower the pressure below the level required for our payload," Smith said. "So, this story is taking a good resolution."
New equipment to keep the fairing vents open will be used as part of an Ariane 5 mission before Webb to verify that the change is working.
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