Lesson 1 of 4 · From regional service to global navigation
From regional service to global navigation
6 minute lesson · 3 checks along the way
Your goal for this lessonDistinguish BeiDou’s development stages and the change from active to passive positioning.
In this lesson 3 sections · 3 checks
Using archive links & definitions
Follow a linked name to explore its archive card. “Back to your lesson” brings you to the same part of the reading.
Read & understand
A service built in stages
BeiDou, or BDS, is China’s satellite-navigation program. BDS-1 began serving China in 2000; BDS-2 extended service to the Asia-Pacific region in 2012. BDS-3 was formally commissioned for global services on July 31, 2020. These milestones describe service development, not the launch dates of three individual spacecraft.
The archive’s Beidou DJW entry identifies an early satellite, also called Beidou-1 G1. Compare that individual object with the whole program: a satellite can be launched before a service is ready, and a service can continue while its satellites are replaced. A useful timeline therefore gives separate rows to launches, commissioning and later replacement.
Check 1 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
Two different paths to a position
CNSA’s 2003 description explains BDS-1 active positioning: a user terminal transmitted through satellites to a ground center, which calculated a position and returned it. The two-satellite method depended on additional constraints and ground processing. It was not the same four-unknown, receive-only calculation introduced in the next lesson.
BDS-2 added passive positioning. In this mode, a compatible receiver processes satellite broadcasts without transmitting a location request back through the constellation. In a paper exercise, draw arrows for both arrangements. The early arrangement needs an outgoing terminal link and a return path; passive positioning needs usable incoming broadcasts and a receiver calculation.
BeiDou-3 exhibit model at Hong Kong’s InnoTech Expo, December 13, 2022. Photograph by AKAMGO yalms; published extraction by Shujianyang, CC BY-SA 4.0. This is a display model, not an identified flight article. Atlas retains the selected source’s complete frame; display copies are resized and compressed.
Look closely
Can this exhibit photograph establish the accuracy of an operating BeiDou receiver?
See what to notice
No. The model illustrates spacecraft hardware; receiver performance needs measurements under documented conditions. The photograph does not identify a specific flight article.
Check 2 of 3
10 pointsUse the reading above. You can try again without losing points.
Read & understand
What a development milestone proves
China’s white papers connect the program to independent infrastructure, national security and economic and social uses. Those are stated policy goals. To evaluate a particular application, ask what service was available, to whom, when, and with what equipment. A government’s goal is a different kind of evidence from a receiver test.
Imagine a historian finds a 2016 forecast for completion in 2020 and a 2022 account of the July 2020 commissioning. Cite the forecast when explaining the plan and the later account when reporting the milestone. Neither alone establishes whether a particular satellite is transmitting today. This distinction keeps a historical course useful as the operational fleet changes.
Check 3 of 3
10 pointsUse the reading above. You can try again without losing points.
Put it together
Your lesson progress
Each check connects to a part of the story. Complete all 3 to earn your 25-point lesson bonus.
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