Science and Technology question from JKAS Prelims, 2023 by JKPSC
Name the twin satellites orbiting Earth that track the movement of water around the planet:
Last updated May 15, 2026
Correct Answer:
Option B —
GRACE-FO
What is GRACE-FO?
GRACE-FO stands for Gravity Recovery and Climate Experiment Follow-On. Launched in 2018, it is a joint mission between NASA and the German Research Centre for Geosciences (GFZ).
The mission consists of two identical satellites orbiting Earth, one behind the other. They track the movement of water by measuring changes in Earth's gravity field. Because water has mass, its movement (as ice melts, groundwater is depleted, or sea levels rise) changes the pull of gravity in specific spots.
How the "Twins" Work
The two satellites are separated by about 220 kilometers. They use a microwave ranging system (and a laser ranger) to measure the distance between them with incredible precision—down to the width of a human hair.
When the lead satellite approaches a mass of water (like a large ice sheet), the extra gravity pulls it forward, increasing the distance between the two satellites.
As the second satellite catches up, it also gets pulled forward, closing the gap.
Scientists use these tiny "nudges" to map where water is moving across the globe.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
