The Bandwidth Ladder — and where orbital breaks it
Four figures tracing the communication hierarchy. Every figure traces to AI Compute Bandwidth Ladder.xlsx. Current = B200 / NVLink 5 / HBM3e / 800G (mid-2026); Forward = Rubin / NVLink 6 / HBM4 / NVL576 (2026–27). Not investment advice.
FIG 1The bandwidth ladder
Per GPU or per link, log scale. Each rung down is ~an order of magnitude slower than the one above. The orbital rung sits below terrestrial cross-rack — the whole thesis in one row.
Current (B200-gen)Forward (Rubin-gen) reachThe two cliffs that matter
~1,600× drop from on-die SRAM to a satellite laser link. Notice the ratios barely move from Current to Forward — faster silicon moves the whole staircase up; it doesn't flatten the cliffs.
FIG 2The scissors: model size vs. the rack
Frontier total parameters (left, log) against the NVLink scale-up domain (right) — the 8 → 72 → 576 staircase. Models got bigger because the coherent fast domain got bigger.
The 8→72 step (GB200 NVL72, 2025) is a 9× expansion of the coherent domain — and it lands the same year ultra-sparse trillion-parameter MoE models became routine. Cause and effect, not coincidence.
FIG 3The orbital cliff — terrestrial vs. orbital
Two ladders, identical down to the scale-up rung. Terrestrial bottoms out at ~100 GB/s cross-rack; orbital drops a further rung to ~3–25 GB/s sat-to-sat laser. On Earth a model spilling the rack drops once; in orbit it drops twice.
The inversion: on Earth the constraint has migrated down toward power. In orbit power is abundant (continuous solar) — and networking becomes the wall. Orbital compute makes the bottom rung the whole story.
FIG 4Why orbital training is gated — the causal chain
It isn't one bottleneck; it's a chain. Keeping it honest: physical limits on the satellite cap the fast domain, which forces the model across the slow link.
The steelman: a tight ~1 km formation with DWDM optics (Google's Project Suncatcher, ~1.6 Tbps bench) rebuilds the DC fabric in orbit — turning the bandwidth problem into a formation-flying problem. The constraint changes disciplines; it doesn't vanish.