INSAT-I series outcome: Of the four INSAT-I satellites planned by India, which one was (initially) the successful operational satellite?

Introduction / Context:
India’s INSAT-I series was an early backbone for telecommunication, meteorology, and broadcasting. Understanding which missions succeeded helps track the program’s maturation.

Given Data / Assumptions:

• Four satellites: INSAT-1A, 1B, 1C, 1D (launched across the 1980s–1990).
• Question style reflects the period when INSAT-1B emerged as the first successful operational satellite after 1A’s failure.
• We answer consistent with the classic exam framing.

Concept / Approach:

INSAT-1A experienced early failure and did not fulfill its operational life. INSAT-1B entered service successfully and became the program’s first sustained success. Later, INSAT-1D was also successful, but the question’s conventional answer points to 1B as the first proven success in the series.

Step-by-Step Solution:

Verification / Alternative check:

ISRO mission summaries document 1B’s long operational service supporting telephony, TV, and weather payloads.

Why Other Options Are Wrong:

• INSAT-1A: did not achieve sustained service.
• INSAT-1C: issues limited operational effectiveness.
• INSAT-1D: successful but later; the classic “first successful” identification is 1B.

Common Pitfalls:

• Answering 1D as “the only success”; multiple in the series ultimately worked, but 1B is the early, well-known success.

Final Answer:

INSAT-IB