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  "title": "Orbital optical links and contact budgets",
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  "topic": "Frontier infrastructure",
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      "title": "Orbital optical links and contact budgets",
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      "title": "What changes when a link is available only one quarter of the time?",
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    {
      "title": "Explore in Atlas",
      "url": "https://semiaifoundry.com/ai-atlas/#orbital-link-contacts"
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    {
      "title": "NASA’s Record-Breaking Laser Demo Completes Mission",
      "url": "https://www.nasa.gov/directorates/somd/space-communications-navigation-program/nasas-record-breaking-laser-demo-completes-mission/"
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    {
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      "url": "https://arxiv.org/html/2511.19468v2"
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      "title": "Optical transceiver and fiber link",
      "url": "https://semiaifoundry.com/learn/atlas/optics/"
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      "url": "https://semiaifoundry.com/learn/atlas/orbital-evidence-status/"
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  "content": "Frontier infrastructure · Atlas v1.3.0\n\n# Orbital optical links and contact budgets\n\nSeparates inter-satellite exchange from ground-data delivery and sustained useful service.\n\n[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#orbital-link-contacts)Spacecraft to proposed constellation; orbital geometry schematic\n\nLearning objectiveCompare peak link rate, delivered contact volume and end-to-end latency.\n\n## The mechanism\n\nOrbital compute needs at least two communication budgets: exchanges inside a distributed cluster and transfers to or from ground users. Optical links require acquisition, pointing, sufficient received power and an available path. Ground links add weather and contact-window constraints. NASA’s TBIRD demonstrated high-rate orbital downlink during particular passes, while Suncatcher’s disclosed high-rate result was a short ground bench path. Peak bit rate cannot be multiplied by a full day unless the link is actually usable for that whole interval. Data placement matters: processing a space-generated image locally may avoid much more traffic than serving a ground-resident training dataset.\n\n1.  Separate intra-cluster traffic from ground ingress, outputs and operational telemetry.\n2.  Calculate link power and pointing requirements for the actual range and apertures.\n3.  Model contact windows, weather and payload efficiency before integrating delivered bytes.\n4.  Add propagation, routing, queueing and processing to the latency path.\n5.  Check whether the workload’s data generation and consumption rates fit both communication budgets.\n\n## Science and assumptions\n\n### Contact payload and propagation\n\n$$\nQ\\le\\frac{\\eta R t_{\\mathrm{contact}}}{8},\\qquad T_{\\mathrm{prop}}=\\frac{d}{c}\n$$\n\nContact payload is bounded by efficiency times bit rate times contact duration divided by eight. One-way propagation time is path length divided by light speed.\n\nSymbols and units\n\nQ\n\nContact payload bound\n\nbytes\n\nη\n\nUseful payload efficiency\n\nfraction\n\nR\n\nPhysical link bit rate\n\nbits/s\n\nt\\_contact\n\nUsable contact duration\n\ns\n\n8\n\nBits per byte\n\nbits/byte\n\nT\\_prop\n\nOne-way propagation time for the selected path\n\ns\n\nd\n\nActual signal path length\n\nm\n\nc\n\nSpeed of light along the modeled free-space path\n\nm/s\n\nR is bits/s, tcontact seconds, η payload efficiency, Q bytes, d meters and c≈3×10⁸ m/s.\n\nAssumptions Use actual contact availability and path length; pointing, weather, coding and queueing are separate effects.\n\n## Engineering example\n\nSynthetic continuous 200 Gbit/s for 300 s has a 7.5 TB raw upper bound. NASA’s 4.8 TB demonstrated pass is a measured delivered quantity and must remain separate from that ideal calculation.\n\n## Distinctions and tradeoffs\n\nA five-minute burst demonstration does not establish continuous daily service at its peak rate.\n\nCloser inter-satellite spacing can help link budgets but constrains formation flying; more ground stations can improve contact coverage while adding infrastructure.\n\nDistributed training needs sustained exchanges, while compact inference outputs can tolerate much smaller ground-data budgets.\n\n## Specifications and interfaces\n\nRates and volumes\n\nBits/s, bytes/contact and contact duty cycle\n\nPeak, bidirectional aggregate and sustained payload are distinct.\n\nLatency path\n\nActual slant range and route\n\nAltitude alone is only a special geometric lower-bound input.\n\n### Interfaces\n\nSpacecraft or ground data Input\n\nDatasets, activations, prompts and telemetry\n\nAvailable optical path Output\n\nDelivered useful bytes with pointing and contact constraints\n\n## Check your understanding\n\n### What changes when a link is available only one quarter of the time?\n\n1.  Its peak bit rate must quadruple automatically\n2.  A byte becomes four bits\n3.  Its long-term average delivery bound falls unless other links fill the gaps\n\nAnswer and reasoning\n\nIts long-term average delivery bound falls unless other links fill the gaps\n\nContact duty cycle reduces integrated delivery independently of the instantaneous rate while the link is active.\n\n## Evidence and scope\n\nTBIRD was an orbital communication demonstration; Suncatcher’s 800 Gbit/s one-way result was on a ground bench. Neither alone qualifies a fleet-scale compute network.\n\nClose a bounded payload solar, eclipse-energy, radiator and communications scenario; radiation, structural design and lifecycle costs remain unmodeled.\n\n## Sources\n\n-   [NASA’s Record-Breaking Laser Demo Completes Mission](https://www.nasa.gov/directorates/somd/space-communications-navigation-program/nasas-record-breaking-laser-demo-completes-mission/)\n-   [Towards a future space-based, highly scalable AI infrastructure system design, v2](https://arxiv.org/html/2511.19468v2)\n\n[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/orbital-link-contacts-b56332aa7bb64d28.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)\n\n## Continue exploring\n\n### Foundations\n\n-   [Optical transceiver and fiber link](https://semiaifoundry.com/learn/atlas/optics/)\n-   [Orbital computing evidence ladder](https://semiaifoundry.com/learn/atlas/orbital-evidence-status/)\n\n### Related lessons\n\n-   [Radiation effects, detection and recovery](https://semiaifoundry.com/learn/atlas/orbital-radiation-recovery/)"
}