The Space Accessibility Index — Methodology & Intellectual Lineage
1. What SAI Measures
The Space Accessibility Index (SAI) is a 0–100 composite measuring how accessible space is — to capital, to cargo, and to operators — updated every pipeline tick (sub-hourly for launch-derived metrics; per-30-day refresh window for the three static-cadence inputs: space_workforce, ground_station_sites, gov_space_budgets).
One sentence of positioning that frames everything below:
The Kardashev scale measures a civilization's command of energy on civilizational timescales. SAI measures its command of access on investable timescales.
Most space data products tell you what happened. SAI tells you where the system is on the single transition that defines this era of the space economy: the shift from a planetary civilization that visits space to one that operates there.
2. Intellectual Lineage
SAI did not invent the idea of scoring civilizational capability. It industrializes a sixty-year lineage of scales — and fixes the parts that made them unusable for allocators.
Kardashev (1964). Nikolai Kardashev's "Transmission of Information by Extraterrestrial Civilizations" proposed ranking civilizations by total energy command: Type I (planetary), Type II (stellar), Type III (galactic). Built for SETI detectability, not economics — but it established the core move: reduce "advancement" to a measurable physical quantity.
Sagan (1973). Carl Sagan replaced the three buckets with a continuous formula: K = (log₁₀P − 6) / 10, with P in watts and Type I normalized at 10¹⁶ W. Humanity's ~20 TW of consumption puts us near K ≈ 0.73 today. Two design lessons SAI inherits directly: a continuous score beats discrete types, and log scaling is mandatory when the underlying quantity spans many orders of magnitude. Sagan also proposed a second, information-based axis — establishing that civilizational progress is multi-dimensional.
Barrow (1998). John Barrow's scale in Impossibility runs the other direction: civilizations ranked by mastery of the very small (objects → genes → molecules → atoms → nuclei → spacetime). The space-economy translation is immediate: a smallsat doing the work of a school-bus-sized predecessor is Barrow-progress, not Kardashev-progress. Any honest access index must count sophistication, not just tonnage.
Zubrin (1999). Robert Zubrin's Entering Space re-typed civilizations by domain mastered: Type I (full planetary), Type II (interplanetary), Type III (interstellar). This is the frame SAI lives in. The entire commercial space economy is the Type I → Type II transition, and SAI is its live gauge.
The maturity scales. NASA's Technology Readiness Levels (developed from the 1970s, now ISO 16290) and Steve Blank's Investment Readiness Level score individual technologies and ventures on 1–9 ladders. They grade things; civilizational scales grade systems. SAI sits at the system level — and AstraVeris's company-level counterpart, ARI, sits at the thing level (see §6).
The Space Sustainability Rating. Developed through the World Economic Forum and operated by the EPFL Space Center, SSR grades missions on debris behavior. Its core insight is SAI's corrective to Kardashev: mass on orbit is not progress if it degrades the orbital commons (see §7).
SAI synthesizes the lineage: Sagan's mathematical discipline, Zubrin's domain framing, Barrow's inward axis, TRL/IRL's institutional vocabulary, and SSR's sustainability stance — rebuilt as a finance-grade instrument.
3. The Three Axes
SAI's seventeen sub-metrics group into three axes that map directly onto the lineage:
Outward Capacity — the Kardashev axis. How much, how often. Raw throughput of the access system: launch cadence, mass delivered, vehicle availability.
Inward Sophistication — the Barrow axis. How well. Doing more with less: reusability, reliability, capability density per kilogram.
Economic Depth — the finance axis. How cheaply, how fundably. The axis the academic scales never built: cost per kilogram, capital formation, market access.
Sub-metric mapping
| Sub-metric (production label) | Axis | Weight | Primary data source | Update cadence |
|---|---|---|---|---|
| Satellite Manufacturing Revenue | Economic Depth | 7.66% | SIA + external benchmarks | Annual / per tick |
| Government Space Budgets | Economic Depth | 12.18% | OECD / Euroconsult / NASA CBJ / ESA | Annual (~30-day refresh) |
| Commercially Available Launch Vehicles | Inward Sophistication | 7.81% | launch_events DISTINCT vehicle_id | Per pipeline tick |
| Commercial Ground Station Sites | Inward Sophistication | 7.06% | ground_stations table | Per pipeline tick |
| Successful Orbital Launches | Outward Capacity | 3.71% | launch_events count | Per pipeline tick |
| Active Launch Providers | Inward Sophistication | 7.09% | launch_events DISTINCT operator_id | Per pipeline tick |
| Lowest Launch Cost to LEO | Economic Depth | 2.70% | Vehicle registry MIN($/kg) | Per pipeline tick |
| Spacecraft Deployed to Orbit | Outward Capacity | 3.28% | launch_events payload count | Per pipeline tick |
| Mass Delivered to Orbit | Outward Capacity | 3.14% | launch_events SUM(payload_mass_kg) | Per pipeline tick |
| Launch Reusability Rate | Inward Sophistication | 5.46% | launch_events booster_reuse_count | Per pipeline tick |
| Rideshare Missions | Inward Sophistication | 2.91% | launch_events distinct operators ≥ 2 | Per pipeline tick |
| Commercial Crew Missions | Outward Capacity | 3.01% | launch_events crew_onboard / crew-payload | Per pipeline tick |
| Controlled Reentry Missions | Inward Sophistication | 3.00% | launch_events event_category='reentry' | Per pipeline tick |
| Operational Spaceports | Outward Capacity | 8.62% | launch_events DISTINCT launch_site | Per pipeline tick |
| Private Space Investment | Economic Depth | 2.97% | deals table SUM(VC types) | Per pipeline tick |
| Government Commercial Space Grants | Economic Depth | 7.75% | gov_grants table SUM | Per pipeline tick |
| Space Industry Workforce | Inward Sophistication | 14.67% | StartUs / BEA / Space Foundation | Annual (~30-day refresh) |
Axis weight subtotals (presentation only — the composite math is unchanged): Outward Capacity 21.76% · Inward Sophistication 48.00% · Economic Depth 33.26%.
4. K_access — The Kardashev Companion Stat
SAI is multi-factor and weighted; weighting involves judgment. To check that judgment, AstraVeris publishes a single-factor, judgment-free physical derivative alongside it:
K_access = log₁₀(M) / 9, where M is trailing-12-month payload mass delivered to orbit, in kilograms.
Anchors.
- M = 1 kg/yr → K_access = 0.00. The pre-spaceflight floor.
- M = 10⁹ kg/yr (one megatonne) → K_access = 1.00. The interplanetary logistics threshold: the order of magnitude implied by permanent off-world settlement and industrial-scale in-space activity — the onset of Zubrin Type II. Nine orders of magnitude, deliberately echoing the decade-spanning structure of Sagan's formula.
Worked example (illustrative figures only — live values come from the Tracker pipeline). At roughly 3,000 tonnes/yr to orbit: log₁₀(3×10⁶) ≈ 6.48, so K_access ≈ 0.72. The resonance with Sagan's energy value of ~0.73 is coincidence, not physics — but it is a useful mnemonic: humanity's access to space currently tracks its command of energy.
Live value: Humanity's current K_access is 0.73, computed from 4,108 tonnes delivered to orbit over the trailing twelve months. K_access is computable end-to-end from the launch dataset. The current implementation uses each launch's vehicle-registry LEO throw-weight as the per-launch mass (a consistent capacity-proxy upper bound) — measured per-mission mass is on the v1.1 roadmap. Each annual bucket carries a method flag (mixed / estimated / insufficient) so chart viewers see exactly which years are well-populated and which are not.
Historical series. K_access is computed annually from 1957 using the historical launch database. Where actual payload masses are unavailable for early years, vehicle-class capacity estimates are used and flagged per year — the chart legend distinguishes measured from estimated. The arc is the story: the climb from Sputnik (~84 kg), the Apollo-era peak, the long plateau of the 1980s–2010s, and the reusability-driven reacceleration. The lost decades are visible in the data.
Why two numbers. K_access is the headline — one physical quantity, one public formula, reproducible by anyone. SAI is the instrument — multi-factor, weighted, opinionated. K_access deliberately ignores cost, reliability, sustainability, and who gets to fly. That is SAI's job. A single-axis scale presented alone misleads — that is the Kardashev scale's core weakness, and AstraVeris does not repeat it.
5. Slope Over Level
For allocators, the level of SAI matters less than its derivative. A K_access of 0.72 is trivia; the rate at which it is rising is an investment thesis. Every SAI release therefore publishes ΔSAI (QoQ and YoY) and the K_access gradient alongside the levels. The gradient is where the investable story lives — and the recurring editorial segment built on it is The Kardashev Gradient (see Intelligence/newsletter integration).
6. SAI and ARI — Division of Labor
The literature splits cleanly into civilizational scales (Kardashev, Sagan, Zubrin, Barrow) and maturity scales (TRL, IRL). AstraVeris mirrors that split:
- SAI is the system-level instrument — the finance-grade descendant of the civilizational scales. It scores the state of access itself.
- ARI is the company-level instrument — functionally a TRL × IRL composite, decomposed across
11factors. It scores individual operators' technical and capital maturity within the system SAI describes.
Full ARI factor decomposition and scoring is part of the Intelligence tier. ``
7. The Sustainability Stance — Kardashev's Blind Spot
The classic critique of Kardashev is that it rewards consumption regardless of efficiency or externality: a civilization burning energy wastefully scores identically to one using it well. SAI takes an explicit position:
Orbital mass that degrades the operating environment is not access. It is a liability against future access.
Debris is upmass too — and it counts against the system, not for it. The Catalog module (object census, debris tracking, decay) is the data spine for this stance.
The v1.0 composite does not yet include a sustainability adjustment; it is the first item on the methodology roadmap. The Catalog tracks object census, debris, and decay, and a v1.1 weighted penalty on mass-on-orbit-that-degrades-orbital-commons will be published with the next methodology bump.
8. Transparency Commitments
1. Versioned methodology. This page carries a version number (1.0) and a public changelog. Weight or formula changes are announced before they take effect, never silently. 2. Reproducibility. K_access is reproducible by any reader from the public formula and the published upmass figure. 3. Sourced data. Every datapoint feeding SAI and K_access carries a source reference. Where data is estimated (early-era payload masses), the estimate is flagged, not blended. 4. No synthetic values. If an input is unavailable, the affected output displays an explicit insufficient-data state. AstraVeris does not backfill with fabricated numbers.
Appendix A — Energy-Equivalent Variant
For readers who want strict Sagan units: delivering mass to low Earth orbit imparts roughly 33 MJ/kg of mechanical energy. At an illustrative 3,000 t/yr, that is ~10¹⁴ J/yr ≈ 3×10⁶ W of continuous power — which plugs into Sagan's formula as K ≈ 0.05. In pure energy terms, space logistics is a K-0.05 activity inside a K-0.73 civilization. That gap is the growth thesis.
Appendix B — References
- Kardashev, N. (1964). "Transmission of Information by Extraterrestrial Civilizations." Soviet Astronomy.
- Sagan, C. (1973). The Cosmic Connection. (Continuous K formula; information axis.)
- Barrow, J. (1998). Impossibility: The Limits of Science and the Science of Limits. (Inward manipulation scale.)
- Zubrin, R. (1999). Entering Space: Creating a Spacefaring Civilization. (Planetary / interplanetary / interstellar typology.)
- NASA Technology Readiness Levels; ISO 16290.
- Blank, S. Investment Readiness Level.
- Space Sustainability Rating — World Economic Forum / EPFL Space Center (eSpace).