Google·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say

Apr 2026

Summary

Got a system design question at Google that had nothing to do with anything I'd prepped for. Space networking is not something I'd ever thought about seriously before someone put it in front of me as an interview problem.

Questions Asked (1)

How would you design a high-speed network to enable communication between Earth-based teams and team members on the Moon?

System DesignTechnical Trade-offsAdaptability & Ambiguity

Author's notes

I stared at this for a second longer than I should have.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, such as data volume, latency tolerance, and budget, since the Moon is ~384,400 km away. Then propose a hybrid architecture combining deep-space optical communication for high bandwidth and radio frequency for reliability, and discuss trade-offs and failure modes.

Pro tip: Acknowledge the ~1.3-second one-way light delay and design protocols that tolerate it, rather than trying to eliminate it. This shows you understand fundamental physics and can adapt system design accordingly.

1. Clarify Requirements and Constraints

Ask about expected data rates, latency sensitivity, reliability needs, and budget. Consider the lunar environment (no atmosphere, extreme temperatures) and Earth-based ground station limitations.

2. Propose a Hybrid Communication Architecture

Suggest using free-space optical (laser) communication for high-bandwidth downlinks and radio frequency (RF) as a backup or for control signals. Include relay satellites if needed to maintain line-of-sight.

3. Address Latency and Protocol Design

Explain that the ~1.3-second one-way delay requires protocols like Delay-Tolerant Networking (DTN) instead of TCP/IP. Discuss buffering, error correction, and autonomous operations on the Moon.

4. Discuss Trade-offs and Failure Modes

Compare optical vs. RF in terms of bandwidth, power, weather susceptibility, and cost. Outline redundancy strategies, such as multiple ground stations and fallback to RF during cloud cover.

5. Summarize and Iterate

Recap the proposed design, highlighting how it meets the key requirements. Suggest next steps like prototyping or simulation, and invite feedback to refine the approach.

Key Points to Mention

Free-space optical communication for high bandwidth (e.g., laser links)
Radio frequency (RF) as a reliable backup and for control signals
Delay-Tolerant Networking (DTN) protocols to handle high latency and intermittent connectivity
Use of relay satellites (e.g., lunar orbiters) to maintain line-of-sight and extend coverage
Trade-offs: bandwidth vs. reliability, power consumption, cost, and weather effects on Earth
Error correction, buffering, and autonomous systems on the Moon to reduce dependency on real-time communication

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.