The James Webb Space Telescope reached L2 the other day. How do they KNOW it’s there?


With JWST being so far out there, how do they know it reached the correct location and made it into stable orbit? What are they measuring/referencing to verify it’s where it needs to be?

In: 6

It’s in constant radio communication with Earth.

From the radio signal alone we can get a good estimate of its location and distance from Earth.

But in addition, James Webb is making its own measurements of its position, orientation, and velocity relative to the Earth and the Sun using a variety of sensors, and transmitting that data back. That information can all be correlated with what we can observe independently to give us an even more accurate estimate.

They use radio to locate it. Ground stations can precisely locate the origin of its signals in the sky. By timing how long it takes for radio signals to get there and back the distance can be determined, which is all that is required to get its location.

Do that more than once at different times and you can tell its speed.

JWST communicates with ground stations on the Earth, and the delay in sending signals back and forth can be used to measure the distance to the telescope. Small shifts in the frequency of a signal can be used to measure its velocity (thanks to the Doppler effect).

Operators here on Earth use that info, called telemetry, to calculate the telescope’s trajectory and can send commands to make the telescope move as needed.

It communicates and says it has arrived.

You can also tell which direction a signal from space is coming from when you use a dish to pick it up as the dish will gets the best signal when pointing directly at what is giving off the signal.