Space Telescopes Maneuver like CATS - Smarter Every Day 59

Space telescopes produce awesome science, but the engineering behind making them work is equally impressive.

• The James Webb Space Telescope uses a sun shield to maintain stable operating environment • The instrument operates at about 45 degrees Kelvin with intense heat from the sun on the other side • A 3D laser scanner ensures the sun shield is perfect for precise instrument operation

Understanding how space telescopes point at and observe specific stars and nebulae.

Two main methods exist to apply external force on satellites to make them turn and maneuver.

Rockets can point space telescopes at desired stars and celestial objects in orbit.

• Rockets use fuel which clouds up the area around the satellite • Fuel is a finite resource and can run out, ending the mission • This method is not sustainable for long-term space telescope operations

Scientists need alternative methods that don't rely on rocket fuel.

A more elegant approach using electromagnetic principles and torque rods is needed.

• A compass needle interacts with Earth's magnetic field • Scaling this up creates a torque rod with a coil of wire • Applying voltage to the wire generates an electromagnetic field • The electromagnetic field interacts with Earth's magnetic field to create rotation

Scientists use three torque rods positioned in three different axes on spacecraft, applying or removing voltage as needed to rotate based on Earth's magnetic field position.

This is an elegant solution with no moving parts.

• Only works in places with an external magnetic field like Earth • Doesn't work in deep space or on Mars where magnetic fields are very weak • Alternative methods needed for distant space missions

Space telescopes in deep space use the same physics principles as a cat flipping 180 degrees from rest by rotating against itself.

• Cats and space telescopes change their rotation state without violating conservation of angular momentum • This ability has been studied extensively by applied mathematicians, neuroscientists, robot builders, and astrophysicists

• A ping pong ball in a block returns to initial state when the block returns to its starting position via the same path • If the block returns along a different path, the system doesn't return to the initial state • The path taken determines the final state of the system

Systems where angular momentum never changes but final rotation can be altered are called Nonholonomic systems, which enable cats to flip and space telescopes to maneuver.

Reaction wheels are devices that keep space telescopes pointed at particular stars.

• Multiple reaction wheels spin inside the spacecraft • Engineers calculate which wheel should be sped up or slowed down at specific times • This precise control achieves rotation in the needed axis

Momentum management is used on the space station and any system flying in space to point and focus at nebulae or stars for telescope observations.

Engineers are essentially brokers of momentum, managing the amount of momentum in the system to enable precise pointing and focusing.

Control Moment Gyros (CMGs) are more advanced than reaction wheels, featuring the ability to rotate their axis itself.

CMGs have two axes of rotation, allowing more complex control than single-axis reaction wheels.

• The added capability of rotating the CMG's axis creates significantly more complex mathematics • Specialized engineers calculate precise satellite pointing trajectories from one point to another • Advanced mathematics ensures smooth transitions along specific paths

• CMGs can reach singularity points where rotation becomes blocked and no further movement is possible • When singularity occurs, external energy inputs like magnetic torquers or propulsion jets are needed to escape the blocked position

NASA's attitude control components lab tests spacecraft control systems to ensure they will function properly in orbit.

• The Chandra X-Ray Telescope reaction wheel undergoes life testing to determine longevity • Life tests assess how long components will last in space • Failed components can be analyzed and replaced if issues are discovered

• Chandra was built in the early 1990s and uses hardware from that era • Test equipment must match the actual hardware flying on the telescope • Components cannot be updated or modernized after launch

Once a spacecraft is launched, it is locked in time with the components built at that moment, requiring continued use of identical hardware for testing and operation, similar to the space station and shuttle programs.