Task 374: Add Brachistochrone Velocity Profile Charts to EP01 and EP04

Status: DONE

Motivation

EP03 has a brachistochrone velocity profile time-series chart showing velocity evolution during the Saturn→Uranus transfer. EP02 has a velocity profile for the trim-thrust transfer. EP05 has a nozzle life chart. EP04 has a radiation dose chart.

However, EP01 (Mars→Ganymede, 72h brachistochrone) and EP04 (Titania→Earth, 65% thrust) lack velocity profile charts despite involving significant brachistochrone transfers. CLAUDE.md says "More figures are better than fewer" and "Concrete values need visualization."

Changes

1. EP01 velocity profile chart (ep01-chart-velocity-profile):

- 72h brachistochrone at 299t, 9.8 MN → peak 4,248 km/s (1.42% c)

- 21 data points with midpoint flip annotation

- Error bands: mass ±10% (269-329t)

1. EP04 thrust comparison chart (ep04-chart-thrust-comparison):

- Compares 100% thrust (9.8 MN, 160h, peak 9,431 km/s) vs 65% thrust (6.37 MN, 199h, peak 7,604 km/s) at 300t

- Shows +24% transit time increase and -19% peak velocity reduction from thrust limitation

- Error bands on 65% profile for mass ±10%

- Dual midpoint flip annotations

1. TDD tests in article-content-validation.test.ts:

- EP01: 3 new tests (chart presence, peak velocity, axis labels)

- EP04: 2 new tests (chart presence, 100%/65% comparison)

Total: +5 new content validation tests, all 2,499 TS tests pass, 398 Rust tests pass.

Non-goals

• Changing existing charts in other episodes
• Adding new orbital diagrams