Engineers plan to test small modifications to a payload shroud on a European Ariane 5 rocket launch Friday from French Guiana, gathering data on changes introduced to meet stringent criteria for the launch of the $10 billion James Webb Space Telescope in late 2021.

The Ariane 5 rocket is set for launch from the Guiana Space Center on the northeastern coast of South America during a 46-minute window Friday opening at 5:30 p.m. EDT (2130 GMT). It will mark the 109th flight of an Ariane 5 rocket since 1996, and the third Ariane 5 flight this year after Arianespace’s launch schedule suffered delays stemming from the coronavirus pandemic.

The rocket will carry three commercial satellites into geostationary transfer orbit, an elliptical transfer loop around Earth, on the way to final positions more than 22,000 miles (nearly 36,000 kilometers) over the equator. The payloads include Northrop Grumman’s second robotic satellite servicing vehicle, and two communications satellites.

The Ariane 5’s payload fairing, made by the Swiss company RUAG Space, protects satellites during the first few minutes of launch, while the rocket is climbing through the thickest layers of Earth’s atmosphere. Once in space, the shroud jettisons in two pieces, exposing the satellites for separation from the rocket once in orbit.

The European Space Agency is providing the launch of JWST aboard an Ariane 5 rocket through its partnership with NASA, which is the lead agency developing the new space-based observatory. The Canadian Space Agency has also contributed to the mission.

“We’re preparing for James Webb, and we have introduced a slightly modified fairing which has an impact on the pressurization under the fairing for the requirement by NASA, and we worked out the solution and we will fly it,” said Daniel Neuenschwander, ESA’s director of space transportation. “So I’m really keen to see that. We really had an excellent exchange at a technical level between NASA and ESA.”

The fairing is nearly 56 feet (17 meters) tall and measures 17.7 feet (5.4 meters) in diameter, containing room for multiple large satellites, or a large observatory like the James Webb Space Telescope.

JWST will fold up origami-style to fit under the Ariane 5 rocket’s payload shroud, then unfurl solar panels, antennas, a segmented mirror array, and a thermal sunshield the size of a tennis after separating from the Ariane 5 on the way to an observing post nearly a million miles (1.5 million kilometers) from Earth.

Once in position, JWST’s telescope — the largest ever flown in space — and four science instruments will peer into the distant universe, studying the turbulent aftermath of the Big Bang, the formation of galaxies and the environments of planets around other stars.

Delays in readying the spacecraft have forced delays and ballooned JWST’s cost to some $10 billion.

ESA, Arianespace and RUAG have modified the design of vents on the Ariane 5’s payload shroud to address a concern that a depressurization event could damage the Webb observatory when the fairing jettisons after liftoff. Engineers were concerned residual air trapped in Webb’s folded sunshield membranes could cause an “over-stress condition” at the time of fairing separation.

The sunshield is made of five thin silver layers of Kapton, a lightweight material with special thermal properties. After JWST is in space, the thermal barrier will expand to block heat from the sun from reaching the observatory’s instrument module, which must remain chilled to super cold temperatures to detect faint infrared light sources in the distant universe.

Data gathered on past Ariane 5 flights indicated some residual pressure remained inside the fairing as the rocket climbed into space. Engineers were concerned that the pressure could suddenly release when the fairing jettisons a few minutes after liftoff, potentially damaging the sensitive sunshield.

European teams developed new hardware to ensure that vents around the base of the payload fairing remain fully open the Ariane 5’s flight into space, allowing pressure to equalize before the shroud falls away from the rocket.

“What we are doing is introducing venting ports on the fairing,” Neuenschwander said in an interview with Spaceflight Now. “All of what we’re doing is going toward the launch of James Webb, and we are successfully testing a number of points.”

On an Ariane 5 launch earlier this year, engineers flew a payload fairing with the new vents, according to Eric Smith, NASA’s program scientist for JWST. That showed some improvement in the fairing’s internal air pressure, and Smith said the vents on the next Ariane 5 flight, scheduled for Friday, will test vents with a larger opening.

“What we expect is a confirmation of what we have already flown,” Neuenschwander said. “We have flown the new venting ports, and we wait for a confirmation.”

Neuenschwander said ESA will be ready for the launch of JWST when the observatory arrives in French Guiana. Engineers at a Northrop Grumman facility in Southern California are continuing with tests of the fully-assembled observatory to ensure it can withstand the rigors of launch.

NASA announced earlier in July that the launch of JWST would be delayed to Oct. 31, 2021, a seven-month slip from its previous target launch date in March 2021. Officials blamed the coronavirus pandemic, which slowed testing at Northrop Grumman, and other technical issues for the delay.

“We are ready with Ariane 5 waiting for James Webb,” Neuenschwander said last week.

The Ariane 5 launch scheduled for Friday will also debut two other upgrades.

One of the changes involves the rocket’s vehicle equipment bay, which contains the Ariane 5’s avionics, guidance system and other key components. The new vehicle equipment bay design is lighter, increasing the Ariane 5’s payload capacity by 187 pounds (85 kilograms), according to Arianespace.

That brings the Ariane 5’s total payload capacity to geostationary transfer orbit, a target orbit favored by many commercial satellite operators, up to 22,487 pounds, or 10.2 metric tons, Arianespace said.

Neuenschwander said the Ariane 5 flight Friday, designated VA253, will also mark the first launch with a new autonomous location system developed by CNES, the French space agency, in partnership with ESA.

“It’s a system which allows it to be autonomous on the launcher side,” Neuenschwander said. “You will depend less on ground means in terms of telemetry during the first minutes of the launch, when you are under the overall safety conditions linked around the launch range. This is a crucial point … It will help a lot for future tracking of launchers.”

Eventually, the autonomous locator will be part of an automatic flight termination system, which would be activated to destroy the rocket if it flew off course and threatened populated areas. The current Ariane 5 flight termination system can only be triggered manually from the ground, where experts track the rocket’s course using radars.

The autonomous range safety system has been introduced on U.S. rockets, such as SpaceX’s Falcon 9 launcher. Europe’s next-generation Ariane 6 rocket will use similar technology, and the system’s demonstration on the Ariane 5 flight Friday is a step in that direction.

“We are developing this system in different incremental steps,” Neuenschwander said. “We are introducing new functions progressively. That is an end goal, but it is not achieved right now.”

The launch Friday from French Guiana is Arianespace’s first mission since the company paused launch campaigns at the European-run spaceport in March, when the number of coronavirus cases began rising across Europe and in communities around the launch base in South America.

Preparations for launches resumed in May at the Guiana Space Center, and Arianespace attempted to launch a light-class Vega rocket in June on a rideshare mission with 53 small satellites for commercial and international customers. Strong winds at high altitude over the spaceport were unfavorable for several weeks, preventing the launch from happening and finally forcing Arianespace to stand down from the mission in order to recharge batteries on the Vega rocket and on its 53 small satellite payloads.

Arianespace plans to try again to launch the Vega mission later this month. The French launch services provider is in charge of launch operations in French Guiana with the heavy-lift Ariane 5, the medium-class Russian Soyuz rocket, and the Vega launcher designed for smaller payloads.

The Ariane 5 typically launches on commercial missions with two large geostationary communications satellites, but Friday’s launch will carry three spacecraft in one go.

The rocket flies with a carbon fiber structure inside its payload fairing, giving the rocket upper and lower berths inside the nose shroud.

Two of the satellites launching Friday will fit together inside the larger upper section of the Ariane 5 payload fairing, while the third spacecraft will ride below in the lower berth.

The end user for two of the satellites is Intelsat, which operates one of the largest fleets of commercial geostationary communications satellites. The owner of the other payload is B-SAT, a Japanese communications satellite operator.

Intelsat’s 7,270-pound (3,298-kilogram) Galaxy 30 video broadcast satellite and Northrop Grumman’s second Mission Extension Vehicle — with a launch weight of 6,338 pounds (2,875 kilograms) — will launch together inside the upper compartment of the payload fairing. The 7,782-pound (3,530-kilogram) BSAT-4b television broadcast satellite will ride into orbit in the lower berth.

MEV-2 is Northrop Grumman’s second autonomous satellite servicing spacecraft, following launch of the MEV-1 mission in October 2019 aboard a Russian Proton rocket.

The MEV-1 mission docked with the Intelsat 901 in February, locking onto the satellite after accomplishing the first docking between two commercial satellites, and the first-ever linkup between two objects in geostationary orbit. Intelsat 901 was launched in 2001 and was running low on fuel. The Mission Extension Vehicle is designed to take over attitude control of a client satellite and extend its useful life.

Intelsat purchased life-extension services for two of its satellites from Space Logistics, a subsidiary of Northrop Grumman that manages the commercial robotic servicing program. Intelsat 901 resumed commercial communications service in April.

The MEV-2 mission will perform a similar docking and mission extension service beginning in early 2021 for the Intelsat 10-02 communications satellite, which launched in 2004.

An Intelsat communications satellite will accompany MEV-2 into orbit. Named Galaxy 30, the Northrop Grumman-built satellite will provide commercial video and television broadcast services across the United States.

Galaxy 30 will also provide broadband connectivity, and it hosts a Wide Area Augmentation System payload for the Federal Aviation Administration to support navigation services for civil aviation in the United States, including precise altitude and position data for airplanes departing and arriving at busy airports.

The BSAT-4b satellite, made by Maxar, will be positioned over the Asia-Pacific region, and it will broadcast direct-to-home 8K and 4K ultra-high-definition television services for the Japanese operator B-SAT. The new satellite will be a backup for BSAT-4a, which launched in 2017.

The Ariane 5 rocket will deliver the three commercial payloads into their targeted geostationary transfer orbit around 25-and-a-half minutes after liftoff, following burns by the launcher’s twin solid-fueled boosters, and a hydrogen-fueled core stage and upper stage.

Galaxy 30, the uppermost satellite in the triple-payload arrangement, will deploy first from the Ariane 5’s upper stage at Plus+27 minute, 47 seconds. The MEV-2 spacecraft, connected with Galaxy 30 during launch, will separate next at Plus+34 minutes, 22 seconds.

Then the carbon fiber Sylda adapter structure covering BSAT-4b will jettison at Plus+35 minutes, 52 seconds, setting the stage for separation of BSAT-4b at Plus+47 minutes, 39 seconds.

The satellites will use their own thrusters to reach their final operational positions in circular geostationary orbits, where their speeds will match the rate of Earth’s rotation over the equator.

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