{"id":"orbital-replacement-mass","level":"infrastructure","name":"Launch, replacement and end-of-life mass","shortName":"Launch, replacement and end-of-life mass","role":"Accounts for a computing fleet’s support mass and continuing lifecycle logistics.","description":"An orbital payload launches with solar arrays, radiators, structure, communications, control and other support equipment. The relevant mass therefore includes far more than accelerator boards. Hardware degrades, fails or becomes obsolete, and physical repair may be limited by the mission design. A fleet needs spares, replenishment flights and a planned retirement path. NASA’s deorbit guidance describes physical disposal approaches whose suitability depends on orbit and spacecraft capabilities. Replacement cadence affects both sustained useful capacity and recurring launch demand. A low launch price per kilogram does not remove the need to manufacture, integrate and deploy every replacement system.","specs":[{"label":"Mass basis","value":"kg per usable payload kW or system","context":"Specify what support equipment is included."},{"label":"Lifetime","value":"Years of useful service","context":"Technical survival and economical software usefulness can differ."}],"interfaces":[{"name":"Spacecraft bill of materials","direction":"in","signal":"Payload, power, thermal, link and control mass"},{"name":"Fleet lifecycle flow","direction":"out","signal":"Initial deployment, replacement, spares and retirement"}],"tradeoff":"Larger support systems can improve power or thermal margins while increasing launch demand; longer service life reduces replacements but can retain obsolete hardware.","whyAI":"Orbital compute economics depend on replacing the entire supported payload, not merely comparing chip power against a terrestrial electricity bill.","related":["orbital-radiator-budget","orbital-solar-storage","orbital-lifecycle-economics"],"sources":[{"title":"Small Spacecraft State of the Art: Deorbit Systems","url":"https://www.nasa.gov/smallsat-institute/sst-soa/deorbit-systems/"},{"title":"Towards a future space-based, highly scalable AI infrastructure system design, v2","url":"https://arxiv.org/html/2511.19468v2"}],"scale":"Payload electronics to fleet and lifecycle; conditional scenarios","kind":"architecture","branch":"Frontier infrastructure","subbranch":"Orbital reliability and lifecycle economics","mechanism":["Build a mass budget that includes all support systems required by the workload.","Define useful life, expected degradation and replacement policy.","Translate desired sustained capacity into initial and recurring launched mass.","Account for launch availability, deployment failures and spare capacity.","Plan retirement or disposal using the actual orbit and vehicle capability, preserving jurisdiction-specific requirements for separate review."],"misconception":"Accelerator mass alone is not spacecraft mass, and reaching orbit once does not establish a sustainable replacement cadence.","check":{"question":"If total fleet mass stays fixed and useful life halves, what happens to ideal annual replacement mass?","options":["It becomes independent of mass","It doubles","It halves"],"answer":1,"explanation":"A steady fleet needs the same total mass replaced over half the interval."},"science":[{"title":"Replacement-flow model","equation":"Mfleet = Ppayload m; Mreplace/year ≈ Mfleet / L","explanation":"Ppayload is kW, m kg/kW and L years; mass flows are kg/year.","assumptions":"Steady fleet with uniform lifetime; failures, spare inventory, growth and disposal hardware add requirements."}],"prerequisites":["orbital-solar-storage","orbital-radiator-budget"],"learningObjective":"Estimate full-system deployment and replacement mass with explicit lifetime assumptions.","workstream":"W12","visualFamily":"orbital-system","engineeringExample":"Synthetic 1 MW payload at 20 kg per payload kW implies 20,000 kg supported fleet mass. A five-year useful life gives about 4,000 kg/year steady replacement before failures, spares or growth.","evidenceNotes":"Mass and lifetime are hypothetical, not current spacecraft specifications. No present launcher capability or regulatory disposal deadline is asserted.","labId":"library","scope":"Browse the numerical library; no current calculator directly models this lesson’s central mechanism.","labScope":"Browse the numerical library; no current calculator directly models this lesson’s central mechanism."}