Advanced Mars communications: networks, DTN and operations

Interactive beginner glossary

Use the interactive terms to understand what happens to information between generation and delivery. Each definition should clarify delay, storage, priority, reliability or radio-link performance.

• latency — Latency is the elapsed time between sending information and its useful arrival or response. For Earth–Mars links, propagation delay alone can reach many minutes.
• light time — Light time is the propagation time imposed by distance divided by the speed of light. No antenna, coding scheme or higher transmitter power can remove this geometric delay.
• bandwidth — Bandwidth is the range of frequencies available to a communication channel. It constrains achievable data rate together with received-signal condition, coding and modulation.
• data rate — Data rate is the amount of digital information transferred per unit time, commonly expressed in bit/s, kbit/s or Mbit/s.
• throughput — Throughput is the useful application data successfully delivered per unit time after accounting for coding, retransmissions, protocol overhead and unavailable contact periods.
• contact window — A contact window is an interval during which two communication nodes have suitable geometry and link conditions to exchange data.
• relay — A relay is an intermediate node that receives data and forwards it toward its destination, extending coverage or creating an alternate path when direct communication is unavailable.
• orbiter — An orbiter is a spacecraft operating around a planetary body. Around Mars it can act as a relay between surface assets and Earth while also performing science and navigation support.
• store and forward — Store-and-forward means a node can retain data locally when the next link is unavailable and transmit it later when a suitable contact becomes available.
• DTN — Delay/Disruption Tolerant Networking (DTN) is a networking approach designed for long delays and intermittent links by storing data between contacts instead of assuming a continuous end-to-end connection.
• bundle — A bundle is a self-contained unit of data used by DTN's Bundle Protocol, carrying payload and routing/lifetime information so it can survive store-and-forward transfer.
• custody — Custody is a reliability mechanism in which a DTN node accepts responsibility for retaining a bundle until another node has safely accepted it or the bundle expires.
• priority — Priority ranks traffic so limited contact time and storage are used first for information with greater operational urgency or value.
• expiration — Expiration is the time after which queued data is no longer worth forwarding, preventing obsolete bundles from consuming storage and communication capacity.
• backlog — Backlog is queued data waiting for transmission. It grows when data generation exceeds delivered throughput and shrinks only when later capacity exceeds incoming traffic.
• compression — Compression reduces the number of bits required to represent information. Lossless methods preserve all information; lossy methods trade some fidelity for a larger size reduction.
• coding — Channel coding adds structured check information so the receiver can detect or correct transmission errors, improving reliability at the cost of extra transmitted bits.
• protocol overhead — Protocol overhead is the fraction of transmitted bits used for headers, addressing, framing, acknowledgements or other control information rather than the useful payload.
• link budget — A link budget accounts for transmitter power, antenna gains, propagation losses and receiver requirements to estimate received signal level and communication margin.
• transmitter power — Transmitter power is the radio-frequency power delivered by the transmitter before antenna gain. Increasing it can improve received signal strength but costs electrical power and thermal capacity.
• antenna gain — Antenna gain describes how strongly an antenna concentrates transmitted or received energy in a direction compared with an isotropic reference.
• free-space loss — Free-space path loss is the geometric spreading of radio energy as a wave propagates over distance. It rises strongly with distance and frequency.
• pointing loss — Pointing loss is the reduction in received signal caused when transmitting or receiving antennas are not perfectly aligned with the intended direction.
• receiver noise — Receiver noise is unwanted random electrical energy in the receiving system that competes with the desired signal and limits detectability.
• signal-to-noise ratio — Signal-to-noise ratio compares useful received signal power with noise power. Higher values generally support more reliable or faster communication.
• link margin — Link margin is the amount by which the predicted received signal performance exceeds the minimum required performance after all stated gains, losses and uncertainties are included.
• ground station — A ground station is a terrestrial facility with antennas, radios, timing and network systems used to communicate with spacecraft or planetary assets.
• time-tagged command — A time-tagged command carries an execution time so a remote system can perform an approved action later without waiting for a real-time command from Earth.
• autonomy — Communication autonomy is the ability of a Mars asset to queue, prioritize, route and act on information locally when Earth contact is delayed or interrupted.
• disruption — A disruption is a temporary loss of a communication path caused by geometry, obstruction, weather, equipment state, interference or scheduled unavailability.