Why Are there Holes in the James Webb Sunshield? (Explained by My Dad) - Smarter Every Day 270

Destin attempts to interview his father at his work facility after two years of trying. The facility is unmarked and difficult to locate, and accessing it requires special clearance from security personnel.

Destin's dad is a metrologist who previously worked in the auto industry making new ways to measure car parts as they came off assembly lines. He now works on the James Webb Space Telescope project.

Upon arriving at the facility, Destin discovers his father is working on the bottom layer of the James Webb Space Telescope sunshield. Destin is amazed that it was harder to get into this room than it was to meet the President of the United States.

The sunshield protects the telescope's optics from heat and light from the sun, Earth, and moon, as well as from electronics on the bottom side. It consists of five layers that unfold like origami ten days after launch as the telescope travels to L2, the second Lagrangian point.

• The room is divided into dirty and clean sides with specific protocols for entering • Workers must wear special protective gear including hoods to prevent spit and facial hair from contaminating equipment • The clean side has positive air pressure blowing dust outward, requiring workers to pass through multiple barriers

The core measurement group consists of Destin's dad (Darrell), Bobby Thorn (who has worked together with Darrell for 25 years combined), and Mark, a specialist on the shield who has worked on the program for many years and holds a patent on one of their innovations.

• The layers are extremely thin: the thickest layer is only two-thousandths of an inch thick • One layer is just one-thousandth of an inch thick, similar to a potato chip sack • The material is Kapton, a durable polyimide film used in space applications

The sunshield is held up by a verification structure with yellow pulley blocks that simulate the tension cables pulling on the heat shield in space. These blocks are positioned within five-thousandths of an inch precision and flex under load to simulate the shape the shield will take in space.

Destin observes numerous holes in the sunshield and asks why there would be holes in a heat shield designed to block the sun. This seems counterintuitive to the shield's primary function.

• The holes are vent holes designed for deployment during launch in the Ariane 5 rocket • The sunshield is folded up and stowed inside the rocket for launch • Air trapped in the folded sunshield must escape during ascent to prevent pressure buildup

Each of the five layers has vent holes, but they are strategically offset so that holes in layer two are not aligned with holes in layer one, layer three holes are offset from layer two, and so on. This prevents direct sunlight from passing through all holes simultaneously.

After deployment in space, the vent holes serve no purpose and are essentially wasted space. As the atmosphere expands during rocket ascent, the holes prevent the folded sunshield from inflating like a balloon. Once in the vacuum of space, there is no air conveyance, making the holes irrelevant.

Destin's dad uses a Pharoah Focus 3D laser scanner, which is fundamentally different from coordinate measuring machines (CMMs) he previously used. The reason he took this job was to work with this advanced 3D laser scanning device.

• A laser comes out of the scanner, bounces off a rapidly rotating mirror • The laser is not eye-friendly and requires a 35-foot safety distance • It captures 975,000 X-Y-Z points per second, creating plane-by-plane scans • As the mirror rotates, multiple planes are taken to scan the entire room

The team uses nine calibration spheres placed around the room. At least three spheres must be visible from any scanning position to serve as reference points. When they perform a scan, they want to see as many spheres as possible to anchor the data to the external coordinate system more accurately.

• Laser scanner: paints a wide area with laser to get a broad point cloud of the surrounding space • Laser tracker: precisely measures individual hard points to a high degree of accuracy • Together, they provide both comprehensive coverage and precise measurements for validation

Four monuments (holes drilled in the floor) serve as solid reference points. These determine the frame of reference relative to the structure and rim pulley block points, allowing the team to take measurements from different spots and maintain consistency across measurements.

• The laser tracker uses corner reflectors (spherical mounted retroreflectors) to locate precise points • Seven points are taken around each reference sphere to calculate its exact center • Measurements are taken on the north pole, around the hemisphere, and at the equator of each sphere • The software waits for stable measurements before acquiring each point

The measurements achieve accuracy within 0.003 inches (three mils), which is very tight tolerance when measuring a large plastic surface like the sunshield. The data shows sphere centers positioned within less than three mils of their actual location.

The laser scanner-derived sphere centers are compared to laser tracker measurements. The tracker provides the most accurate data that never moves, serving as a temporary datum to anchor the scanner data to the coordinate frame for the rest of the system.

• Photons are emitted from the laser and reflected back to a detector • Time-of-flight calculation: knowing the travel time and speed of light, the distance to the object is calculated • Azimuth (left-right) and elevation (up-down) angles allow trigonometry to calculate 3D coordinates • Repeated measurements create a point cloud defining the surface shape

The ideal scanning angle is orthogonal (90 degrees) to the object surface to achieve good laser return. Scanning at shallow angles causes the light beam to reflect off the shiny surface rather than return to the detector. The team positions the scanner as close to 90 degrees as the confined room allows.

• Specular reflection: shiny, reflective surfaces like the Kapton material bounce light away • Diffuse reflection: scatter light in all directions, allowing the laser scanner to detect the surface better • The team uses flash breaker tape targets with diffuse properties to help the scanner locate reference points

The team has a 3D model of the shield loaded into their software. They can turn surface features on and off and colorize them. This allows them to label features and point to specific locations, with the software knowing what the shield is supposed to look like.

After the measurement team collects data, they hand it off to Naveen, a data analyst with a Ph.D. in nuclear fusion. The measurement team describes themselves as the measurement monkeys, while Naveen processes the data into usable formats.

• Naveen uses MATLAB and programming software for data processing • The technique is called photogrammetry, similar to topographical surveying • Each scanner location produces a different point cloud depending on the scanning position • Coordinate transformation is required to align all clouds into a single reference frame

Naveen uses the sphere positions as anchor points for coordinate transformation. He takes whatever the scanner detected at those sphere locations and transforms the data so all point clouds align properly, then cleans the data for comparison with the final model.

The combined point cloud from all scanning locations used to be approximately ten gigabytes of data containing millions of X, Y, Z coordinate points. This comprehensive dataset represents the entire three-dimensional geometry of the sunshield as it physically exists.

When measuring the Kapton, the team had to shut down all air conditioning and HEPA filters. They walked very slowly through the room because even slight air movement could cause the material, which is like a big kite, to ripple and affect measurements.

• All testing was conducted in the middle of the night to minimize external disturbances • Only one or two people were allowed to enter the clean room at a time • Walkers moved very slowly to avoid creating air currents that would disturb the Kapton

When a helicopter flew over the building, the vibrations were transmitted through the structure and caused visible ripples in the Kapton that the laser scanner could detect. The team noted these times in their logs so that when reviewing the point cloud data, they could account for these vibration-caused ripples.

The laser scanner's extreme accuracy (0.003 inch tolerance) meant it could detect even tiny vibrations and movements. This sensitivity required exceptional care in controlling the measurement environment to ensure data quality and validity.

The sunshield must be measured in Earth's gravity (1G environment), but it will operate in the zero-gravity environment of space. The team measures the shape with one Jeep (unit load) pulling the material down, which is not the weightless environment it will experience in space.

• Measured data in 1G is compared to finite element analysis models • The team measures at 1G and 3G load conditions to validate the models • Models predict how the shape will look under different gravity conditions • This comparison shows how good the model predictions are for zero-G conditions

The sunshield not only blocks incoming light and heat from the sun and Earth, but it also manages heat generated by the telescope instruments in the box underneath. The shape of the Kapton layers is critical for radiating this internal heat outward into space.

The five layers function like a heat pipe with reflective surfaces bouncing heat between layers. Heat bounces back and forth between reflective materials in specific patterns, radiating outward to the sides rather than back to the instruments. The shape is critical for directing this heat flow correctly.

A catenary curve is the natural shape a chain or string assumes when suspended from both ends. It is mathematically described by a hyperbolic sine function. This same curve appears in the sunshield design where the membrane is suspended under tension.

• Force vectors applied at specific points along the rim define the catenary curve shape • Two main tension points create the curve that suspends the entire membrane • The curve keeps the center of the sunshield tight, like the head of a drum under tension

Darrell's dad emphasized that he is a measurement specialist, not a structural engineer. He measures the actual shape that the catenary forces create, but the engineers determine the optimal force and curve design. The measurement validates whether the actual shape matches the design predictions.

An assembly table with a gantry system is used for inspecting, attaching, and laying out components. Technicians can lay on belly boards and slide along the gantry, reaching different spots on the shield. The laser tracker is positioned to pinpoint precise locations where holes or components must be attached.

Northrop Grumman provides the design specifications for hole positions. Pro/E (a CAD software) can flatten the curved sunshield structure and determine where holes should be positioned on the initially flat material before it is formed into its final curved shape.

• Laser tracker marks initial hole locations within 30 thousandths of an inch precision • Technicians come through and fine-tune positions to within ±0.003 inches • After holes are punched, the team measures again to verify the punches did not move during production • Multiple safeguards and double-checks ensure cuts are clean and accurate

Creating a curved structure using planar tools and flat material is a complex problem. The team developed procedures to ensure holes land in exactly the right positions. If a mistake occurred, patches could theoretically be applied, though the team aimed to avoid this through careful measurement and verification.

The rim surface where the telescope will interface is held flat within 0.005 inches tolerance. Achieving this flatness required two and a half days of shimming and torquing bolts, but once accomplished, the team became proficient at repeating the process. This is described as measure twice, cut once philosophy.

The layers are joined together using a proprietary thermal bonding process developed and patented by Mantech NeXolve. This is the secret sauce of the sunshield manufacturing, and Mantech is the only company capable of performing this specialized process.

The James Webb Space Telescope sunshield was manufactured in Huntsville, Alabama because Mantech NeXolve, the only company with the proprietary thermal bonding technology, is located there. This geographic concentration of expertise was essential to the project.

• Darrell started work on the project in November 2010 and worked for six years on the final phase • Before the five flight layers, the team made five test layers to practice and develop the manufacturing process • So the team worked on ten total layers of this size before completing the final flight hardware

Bobby mentions that he has only been involved for two years, whereas Darrell has been there for six years. Bobby worked on all five layers and was involved in assembly and setup work. Both team members expressed being tired after the intensive work, but Bobby particularly wanted to see the telescope fly despite physical strain.

Destin takes a moment to stand at the center of the sunshield where the telescope will be positioned. This is the exact spot where the telescope will make historic astronomical observations and glimpse the deepest reaches of time and space. It represents a significant and important location in the project.

Destin reflects on the emotional weight of the moment. After his father has worked six years on this project, the family gets to document this moment together. A selfie taken at the center of the sunshield becomes a meaningful keepsake of this achievement.

The final layer acceptance shape test takes place at 4 a.m. after an all-nighter of laser scanning work. Before deployment, the team builds a cradle to protect the folded membrane. The folded layer will be purged of oxygen to prevent contamination and damage during storage and transport.

Watching the team fold up the sunshield for shipment to California is described as a beautiful and complex origami dance. This final process represents the culmination of the entire James Webb Space Telescope program as a technological collaboration.

The Ariane 5 rocket launches with the James Webb Space Telescope. As the rocket ascends, the vent holes that the team spent years positioning perform their critical function by allowing air trapped in the folded sunshield to escape, preventing the membrane from inflating like a balloon.

The telescope successfully separates from the launch vehicle and moves gently away from the Ariane 5 rocket. Images from the upper stage camera show the James Webb Space Telescope departing on its journey to the L2 point.

• The James Webb Space Telescope involved 10,000 stories like Darrell's, each representing someone who worked on the project • Mirror components were manufactured in Coleman, Alabama by ordinary people • The sunshield was manufactured in Huntsville, Alabama • Thousands of people from all over the world collaborated to make the telescope a reality

Naveen, a collaborator on the project, grew up in a small town in India without television or telephone. His first knowledge of NASA came from a dictionary. He never imagined he would work on a telescope now in space. The project demonstrates how extraordinary things are accomplished by ordinary people with dedication and faith in teamwork.