UXS-016 — the outward arc: the scale ladder, the new tiers, and a science lens on every shell

Status · Draft v0.1 Extends · UXS-014 (navigating the known universe — the nav/breadcrumb/warp/lens contract stands; this adds the outward tiers, the scale ladder, the surface-completeness look, and the lens-everywhere UX) Related · PRD-034 (the three-pillar epic) · RFC-039 (the build contract) · #258 (scale picker, shipped) · #410 (message-objects, shipped) Visual fidelity · Signature moments get a visual anchor gating their slice (per "visual anchor before UX commit"). Two anchors already mocked: the 8-rung scale rail and the enriched Milky Way (Milestone 1). On the operator's Desktop.

Why this UXS exists

UXS-014 pinned how it feels to move through the four shells. Since then two things shipped — the #258 scale picker (a persistent scale control UXS-014 didn't have) and #410 message-objects — and PRD-034 decided to (a) extend the ladder to 8 tiers, (b) level the thin existing shells, and (c) put a science lens on every shell. This spec owns the UX of those three, so they aren't designed ad-hoc per tier. UXS-014's rules (you-always-know-where-you-are, warp-teaches-distance, honest-schematic-badging, lens-never-hides-the-exit) carry through unchanged.

1 · The scale ladder is the canonical scale control (8 rungs)

The #258 ExploreScalePicker becomes the one scale control for the whole arc — grown from 4 to 8 rungs (decision: PRD-034 §UX, direction A). It reads outermost→innermost so "zoom out is up":

Cosmic Web            ~14 Gpc
Laniakea              ~160 Mpc
Virgo Supercluster    ~33 Mpc
Local Sheet           ~10 Mpc
Local Group           ~3 Mpc
Milky Way             ~30 kpc
Stellar Neighbourhood ~50 pc
Solar System          ~100 AU     ← active rung highlighted

• Desktop: always-on vertical rail, lower-right, each rung = shell name + scale label; active rung highlighted (cyan), sub-view takeovers hide it (as #258 already does).
• Mobile: the same collapse-to-"Scale ▾" chip → popover; the popover now lists 8 rungs (auto-closes on pick). If 8 rungs prove too tall on a small viewport, the RFC-039 fallback (the C-hybrid spectrum) is a contained swap — same control, different presentation.
• Every rung is a warp (UXS-014): picking a distant rung drives the existing multi-step contextDeepLinkFn walk, each crossing captioned with the distance it teaches ("65 million light-years to the Virgo Cluster…"). The breadcrumb extends in lockstep: Solar System › … › Local Group › Local Sheet › Virgo.

2 · The four new outward tiers — how they read

Each new tier follows the Local Group shell's visual grammar (schematic sprites + labels + a "you are here" anchor for the shell one level in), and must carry the honest-schematic badge (UXS-014 · PRD-030 principle 2) — now with a learn-more link (fixing the LG badge's missing one):

• Local Sheet — the Local Group as a blob among the M81 group, Centaurus A, Sculptor; anchor = "Local Group ⌾".
• Virgo Supercluster — the Virgo Cluster (M87 as the highlighted BCG) + Fornax; our supercluster plane; anchor = "Local Sheet ⌾".
• Laniakea — the flow-basin toward the Great Attractor (Norma), Coma, Perseus-Pisces; velocity-flow streamlines under the Hubble-flow lens; anchor = "Virgo Cluster ⌾".
• Cosmic Web — filaments, walls, voids → the observable-universe / CMB boundary. The most schematic tier: heaviest "this is a model" badging, no implied precision.

Selecting a cluster/galaxy opens a panel (the LocalGroupPanel family, extended with member count / BCG / recession velocity / a learn-more link). Two doors in, per UXS-014: wander, or jump via ?context=<tier> / a gallery/index ?goto=.

3 · Milestone 1 — the enriched Milky Way (the first build, mock-gated)

The Milky Way shell today is 2 clickable objects and no lens (RFC-039 §4). The enriched look (mocked, on the operator's Desktop) adds, on the existing gorgeous spiral:

• The galactic bar — a subtle elongated core glow, labelled (the science article already claims a barred spiral).
• A globular-cluster halo — the ~30 globulars already in the data, pinned above/below the disc; headliners labelled (ω Centauri, 47 Tuc, M13). Clickable → panel + article.
• The Magellanic Clouds — LMC + SMC as fuzzy companions at the disc edge (they're gravitationally MW, conceptually in-shell).
• Arm interactivity — each arm label becomes a clickable chip → arm panel/article (today they're dead sprites).
• The scale HUD — un-suppressed: a kpc scale bar + "Milky Way · ~30 kpc across" (today the MW shell shows no distance reference at all).
• The first MW science lens — chips for Rotation curve, Dark-matter halo, Stellar populations (§4). This proves the per-shell lens pattern the rest of the epic reuses.

Interaction stays within UXS-014's model (click-a-pin, breadcrumb, lens-toggle). This look is mock-gated before the slice (anchor delivered).

4 · A science lens on every shell + the chip taxonomy (the UX)

PRD-034 pillar 3 / RFC-039 Contract D, as felt by the user:

• The lens is the single home for "this teaches you something." Every shell — including the Milky Way and Local Group, which have none today — gets a science-lens surface (the ScienceLayersPanel or the neighborhood's inline lens-chip pattern, unified).
• Two visually distinct chip families:
  • Service chips (always-on, no lens gate) — pure visibility toggles: PLANETS, DWARFS, COMETS, INTERSTELLAR, PATHS. Neutral/slate styling.
  • Teaching chips (inside the science lens) — DEEP-SKY, CONSTELLATIONS, HR-diagram, light-cones, and the new cosmology lenses (distance-ladder, Hubble-flow, dark-matter-web, redshift). Cyan "lens" styling; each carries a → science learn link into its article.
• Turning the lens on reveals the teaching chips for the active shell and nothing meaningless (only context-relevant lenses show — UXS-014). Turning it off leaves the service chips + the honest scene. The breadcrumb + exit are never hidden.
• New cosmology lenses read as overlays on the same scene, never separate screens (UXS-014): distance-ladder draws the parallax→Cepheid→SN Ia rungs; Hubble-flow draws recession vectors; dark-matter-web tints the filament mass; redshift colours galaxies by z.

5 · The learning surface, surfaced (the cosmology articles)

Every new tier and lens links out to a backing /science article (the see_in_app ↔ learn-link loop, UXS-014). The new cosmology set (Big Bang, nucleosynthesis, carbon/CNO, distance ladder, redshift/Hubble, dark matter/energy, CMB, large-scale structure — RFC-039 §6) is reachable from the lens chips and the tier badges, so the atlas always answers "how do we know?" No tier ships without its story.

6 · Responsive, a11y, honesty (carried from UXS-014)

• Mobile parity on core nav (ladder popover, warp, select, breadcrumb, lens); density adapts to the device budget; heaviest cosmology shaders desktop-first with a legible mobile tier.
• A11y: the object/tier index is keyboard-reachable via the DOM mirror + ?context=/?goto=; warps announce destinations; reduced-motion shortens the crossings.
• Honesty: every super-galactic tier is schematic and badged; the Cosmic Web tier's badge is the loudest. Culture-door / fiction badging unchanged.

7 · Signature moments that get a visual anchor before their slice

1. The enriched Milky Way (Milestone 1) — ✅ mocked.
2. The 8-rung scale rail (desktop + mobile popover) — ✅ mocked (direction A).
3. Each outward boundary crossing — the collapse-and-rebase (Local Group → Local Sheet, etc.) + distance caption, per tier.
4. A new cosmology lens toggle — the scene re-rendered through physics (Hubble-flow vectors / dark-matter web).

3 and 4 are mocked/prototyped on real frames and gated on the operator's approval before their slices ship.

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UXS-016 · draft · 2026-08-08 — the outward arc's interaction spec: the 8-rung ladder, the new tiers, the Milky-Way-first enrichment, and the science-lens-everywhere + chip taxonomy. Extends UXS-014.