From 748a3099950cb37d338830b0b15928639dfea075 Mon Sep 17 00:00:00 2001 From: cinnaboot Date: Mon, 19 Jan 2026 10:35:00 -0500 Subject: [PATCH] Move implementation session summary to session summaries - Extract Implementation Session Summary from mission_planning.md - Create new session summary: 2026-01-18-mission-planning-leo-impulse-burn.md - Keep Current Issue Identified section in mission_planning.md - Session summary includes: Phases 0-4 work, test results, delta-v bug analysis, next steps --- docs/mission_planning.md | 100 ------ ...01-18-mission-planning-leo-impulse-burn.md | 289 ++++++++++++++++++ 2 files changed, 289 insertions(+), 100 deletions(-) create mode 100644 docs/session_summaries/2026-01-18-mission-planning-leo-impulse-burn.md diff --git a/docs/mission_planning.md b/docs/mission_planning.md index 199d356..f220189 100644 --- a/docs/mission_planning.md +++ b/docs/mission_planning.md @@ -463,106 +463,6 @@ TODO: Future config file format improvements: ### Functions Removed - `spawn_spacecraft_on_transfer()` - Still present in code but no longer used - ---- - -## Implementation Session Summary - -### Date: January 18, 2026 -### Branch: mission-planning -### Duration: ~2 hours - -### Completed Work - -#### Phase 0: Git Workflow ✅ -- Stashed debug changes on main branch -- Switched to mission-planning branch -- Applied debug printf statements to mission-planning branch -- All debug output from spacecraft parent investigation preserved - -#### Phase 1: Configuration File ✅ -- Added Spacecraft body to `tests/configs/earth_mars_simple.toml` -- Configured with placeholder position/velocity (set at runtime) -- Parent set to Earth (index 1) -- Initial semi-major axis placeholder: 6.571e6 m (Earth radius + 200km) - -#### Phase 2: Mission Planning Module ✅ - -**Function Declarations Added:** -```cpp -void initialize_spacecraft_leo(CelestialBody* spacecraft, CelestialBody* parent, - double altitude_m); -void apply_transfer_burn(SimulationState* sim, int spacecraft_idx, - int departure_idx, TransferParameters* params); -double calculate_phase_angle(SimulationState* sim, int departure_idx, int arrival_idx); -``` - -**Function Implementations:** - -1. **`initialize_spacecraft_leo()`** - Sets circular LEO orbit at specified altitude - - Calculates orbital radius = Earth radius + altitude - - Positions spacecraft radially outward from Sun - - Calculates LEO velocity: v = sqrt(G * M_earth / r) - - Sets prograde orientation (tangential to Earth-Sun line) - - Verified to produce correct LEO velocity (~7788 m/s at 200km altitude) - -2. **`calculate_phase_angle()`** - Computes phase angle between two bodies - - Calculates angular positions relative to Sun - - Returns phase difference normalized to [0°, 360°) - - Used for launch window verification - -3. **`apply_transfer_burn()`** - Applies impulse burn for Hohmann transfer - - Calculates required heliocentric velocity magnitude from transfer parameters - - Calculates prograde direction (tangential to Earth-Sun line) - - Computes delta-v vector: Δv = v_target - v_current - - Applies impulse to spacecraft velocity - - Updates local velocity relative to departure body - -#### Phase 3: Comprehensive Test Case ✅ - -**Test Structure:** -``` -1. Load config with 4 bodies (Sun, Earth, Mars, Spacecraft) -2. Initialize spacecraft in 200km LEO around Earth -3. Verify LEO orbit stability (parent, position, velocity, energy) -4. Calculate Hohmann transfer parameters -5. Wait for Earth-Mars launch window (within 1°) -6. Verify phase angle accuracy -7. Apply impulse burn for transfer -8. Verify post-burn energy >= 0 (escape trajectory) -9. Simulate transfer for 110% of expected duration -10. Track SOI transitions (Earth→Sun→Mars) -11. Verify final parent and energy conservation -12. If Mars SOI entry, verify distance -``` - -**Test Results (Current Status):** - -✅ PASSED (8 assertions): -- Config loading (4 bodies loaded) -- Spacecraft loaded correctly -- Spacecraft parent = Earth (index 1) -- LEO position within expected radius (<1km error) -- LEO velocity matches expected (<10 m/s error) -- LEO total energy negative (bound to Earth) -- Launch window opened after ~94 days -- Phase angle error < 1° - -❌ FAILED (1 assertion): -- Post-burn heliocentric energy >= 0.0 (expected) - - Actual: -3.5e8 J (negative, still bound) - - Expected: ≥ 0 J (positive, escape trajectory) - -#### Phase 4: Build System ✅ -- Makefile already configured for mission_planning.o -- Test executable builds successfully -- All warnings noted (unused variables, harmless) - -#### Phase 5: Cleanup ⏸️ -- Not yet started (waiting on test fix) - ---- - ## Current Issue Identified ### Problem: Incorrect Delta-V Direction After Multi-Day Wait diff --git a/docs/session_summaries/2026-01-18-mission-planning-leo-impulse-burn.md b/docs/session_summaries/2026-01-18-mission-planning-leo-impulse-burn.md new file mode 100644 index 0000000..9fc45e8 --- /dev/null +++ b/docs/session_summaries/2026-01-18-mission-planning-leo-impulse-burn.md @@ -0,0 +1,289 @@ +# Session Summary: Mission Planning - LEO Spacecraft and Impulse Burn + +**Date:** January 18, 2026 +**Session Length:** ~2 hours +**Branch:** mission-planning +**Goals:** +1. Replace dynamic spacecraft spawning with config-based LEO spacecraft +2. Implement patched conics impulse burn for Hohmann transfer +3. Add comprehensive test verification + +--- + +## Work Completed + +### Phase 0: Git Workflow ✅ +- Stashed debug changes on main branch +- Switched to mission-planning branch +- Applied debug printf statements to mission-planning branch +- All debug output from spacecraft parent investigation preserved + +### Phase 1: Configuration File ✅ +**File:** `tests/configs/earth_mars_simple.toml` + +**Changes:** +- Added Spacecraft body to config +- Configured with placeholder position/velocity (set at runtime) +- Parent set to Earth (index 1) +- Initial semi-major axis placeholder: 6.571e6 m (Earth radius + 200km) + +### Phase 2: Mission Planning Module ✅ + +**Function Declarations Added:** +```cpp +void initialize_spacecraft_leo(CelestialBody* spacecraft, CelestialBody* parent, + double altitude_m); +void apply_transfer_burn(SimulationState* sim, int spacecraft_idx, + int departure_idx, TransferParameters* params); +double calculate_phase_angle(SimulationState* sim, int departure_idx, int arrival_idx); +``` + +**Function Implementations:** + +1. **`initialize_spacecraft_leo()`** - Sets circular LEO orbit at specified altitude + - Calculates orbital radius = Earth radius + altitude + - Positions spacecraft radially outward from Sun + - Calculates LEO velocity: v = sqrt(G * M_earth / r) + - Sets prograde orientation (tangential to Earth-Sun line) + - Verified to produce correct LEO velocity (~7788 m/s at 200km altitude) + +2. **`calculate_phase_angle()`** - Computes phase angle between two bodies + - Calculates angular positions relative to Sun + - Returns phase difference normalized to [0°, 360°) + - Used for launch window verification + +3. **`apply_transfer_burn()`** - Applies impulse burn for Hohmann transfer + - Calculates required heliocentric velocity magnitude from transfer parameters + - Calculates prograde direction (tangential to Earth-Sun line) + - Computes delta-v vector: Δv = v_target - v_current + - Applies impulse to spacecraft velocity + - Updates local velocity relative to departure body + +### Phase 3: Comprehensive Test Case ✅ + +**Test Structure:** +``` +1. Load config with 4 bodies (Sun, Earth, Mars, Spacecraft) +2. Initialize spacecraft in 200km LEO around Earth +3. Verify LEO orbit stability (parent, position, velocity, energy) +4. Calculate Hohmann transfer parameters +5. Wait for Earth-Mars launch window (within 1°) +6. Verify phase angle accuracy +7. Apply impulse burn for transfer +8. Verify post-burn energy >= 0 (escape trajectory) +9. Simulate transfer for 110% of expected duration +10. Track SOI transitions (Earth→Sun→Mars) +11. Verify final parent and energy conservation +12. If Mars SOI entry, verify distance +``` + +**Test Results (Current Status):** + +✅ PASSED (8 assertions): +- Config loading (4 bodies loaded) +- Spacecraft loaded correctly +- Spacecraft parent = Earth (index 1) +- LEO position within expected radius (<1km error) +- LEO velocity matches expected (<10 m/s error) +- LEO total energy negative (bound to Earth) +- Launch window opened after ~94 days +- Phase angle error < 1° + +❌ FAILED (1 assertion): +- Post-burn heliocentric energy >= 0.0 (expected) + - Actual: -3.5e8 J (negative, still bound) + - Expected: ≥ 0 J (positive, escape trajectory) + +### Phase 4: Build System ✅ +- Makefile already configured for mission_planning.o +- Test executable builds successfully +- All warnings noted (unused variables, harmless) + +### Phase 5: Cleanup ⏸️ +- Not yet started (waiting on test fix) + +--- + +## Test Status + +### Before Session +- Previous mission planning implementation with spacecraft spawning + +### After Session +- Test framework complete with LEO spacecraft initialization +- 8/9 assertions passing in Hohmann transfer test +- 1 assertion failing: post-burn energy validation + +--- + +## Code Statistics + +### Files Modified (3) +- `tests/configs/earth_mars_simple.toml` - Added spacecraft body (+13 lines) +- `src/mission_planning.h` - Added function declarations (+3 lines) +- `src/mission_planning.cpp` - Implemented new functions (~100 lines) +- `tests/test_hohmann_transfer.cpp` - Added comprehensive test (~175 lines) + +### Net Changes +- **~+291 lines** (estimated, not yet committed) + +--- + +## Documentation + +### Updated +- `docs/mission_planning.md` - Implementation plan for LEO spacecraft approach + - Added test configuration reference + - Added future work section + - Added notes and references + +--- + +## Current Issue + +### Problem: Incorrect Delta-V Direction After Multi-Day Wait + +**Symptom:** +- Spacecraft enters LEO orbit correctly with negative energy (bound to Earth) +- Waits 94 days for Earth-Mars launch window +- During wait period, spacecraft completes ~6.3 LEO orbits +- LEO orbit phase changes significantly over 94 days +- After wait, `apply_transfer_burn()` applies delta-v assuming spacecraft is at Earth's current orbital phase +- Result: Delta-v applied in wrong direction, resulting in retrograde burn +- Post-burn energy remains negative (spacecraft still bound to Earth) + +**Root Cause Analysis:** + +The `apply_transfer_burn()` function calculates: +1. Required heliocentric transfer velocity magnitude: `v_transfer = 32,697 m/s` +2. Prograde direction based on Earth's current position: `transfer_dir = prograde(t_current)` +3. Target velocity: `v_target = v_transfer * transfer_dir` + +However, after 94 days: +- Earth has moved to different orbital phase +- Spacecraft in LEO is still orbiting Earth +- Spacecraft's current heliocentric velocity includes Earth's motion + LEO motion +- The calculated transfer direction is based on Earth's instantaneous position, not spacecraft's actual heliocentric velocity vector +- This results in delta-v that doesn't account for spacecraft's phase in LEO + +**What Should Happen:** +1. Calculate spacecraft's current heliocentric velocity vector: `v_current` +2. Calculate required heliocentric velocity for transfer orbit: `v_transfer` +3. Apply delta-v: `Δv = v_transfer - v_current` (vector subtraction, not magnitude-based) + +**What Currently Happens:** +1. Assumes spacecraft starts at Earth's orbital position (ignores LEO phase) +2. Calculates transfer direction based on Earth's current prograde vector +3. Applies magnitude-based delta-v without considering spacecraft's actual velocity direction +4. Results in incorrect burn direction + +### Solution Required + +Modify `apply_transfer_burn()` to: + +1. **Calculate spacecraft's actual heliocentric velocity:** +```cpp +Vec3 v_current_helio = spacecraft->velocity; // Already in global frame +``` + +2. **Calculate required heliocentric transfer velocity:** +```cpp +double v_transfer_mag = params->departure_velocity; // ~32,697 m/s + +// Direction: prograde to Sun (same as Earth's orbital direction) +Vec3 sun_to_earth = vec3_sub(departure->position, sun->position); +Vec3 sun_to_earth_norm = vec3_normalize(sun_to_earth); +Vec3 transfer_dir = (Vec3){-sun_to_earth_norm.y, sun_to_earth_norm.x, 0.0}; +Vec3 v_transfer_helio = vec3_scale(transfer_dir, v_transfer_mag); +``` + +3. **Calculate delta-v as vector difference:** +```cpp +Vec3 delta_v = vec3_sub(v_transfer_helio, v_current_helio); +``` + +4. **Apply impulse:** +```cpp +spacecraft->velocity = vec3_add(spacecraft->velocity, delta_v); +spacecraft->local_velocity = vec3_sub(spacecraft->velocity, departure->velocity); +``` + +**This approach:** +- Accounts for spacecraft's actual heliocentric velocity (includes LEO phase) +- Uses vector subtraction instead of magnitude-based calculation +- Produces correct delta-v direction regardless of LEO phase +- Should result in positive post-burn energy (escape trajectory) + +--- + +## Next Steps + +### High Priority +1. **Fix Delta-V Direction Bug** + - Modify `apply_transfer_burn()` to use vector subtraction + - Test with actual spacecraft heliocentric velocity + - Verify post-burn energy becomes positive + - Estimated time: 30 minutes + +2. **Complete Full Transfer Test** + - Verify Mars SOI entry after fix + - Validate energy conservation during transfer + - Confirm SOI transitions (Earth→Sun→Mars) + - Estimated time: 1 hour + +### Medium Priority +3. **Phase 5: Cleanup** + - Remove `spawn_spacecraft_on_transfer()` function + - Update documentation + - Estimated time: 20 minutes + +--- + +## Technical Decisions + +### 1. Config-Based vs Dynamic Spawning +- **Decision:** Use config-based LEO spacecraft initialization +- **Rationale:** Cleaner approach, spacecraft in config from start +- **Result:** Spacecraft loaded with placeholder position/velocity, set at runtime + +### 2. Single-Impulse vs Patched Conics +- **Decision:** Single impulse as initial approximation +- **Rationale:** Simpler to implement, adequate for initial testing +- **Future:** Can refine to two-impulse burn for higher accuracy + +### 3. LEO Orbit Phase +- **Issue:** Spacecraft LEO phase changes during multi-day wait +- **Impact:** Delta-v must account for spacecraft's actual heliocentric velocity +- **Fix:** Use vector subtraction with spacecraft's actual velocity + +--- + +## Achievements + +1. ✅ Config-based LEO spacecraft initialization +2. ✅ Three new functions in mission planning module +3. ✅ Comprehensive test framework with SOI transition tracking +4. ✅ LEO orbit validated (position, velocity, energy) +5. ✅ Launch window detection working +6. ✅ Root cause identified for delta-v direction bug +7. ✅ Clear solution path defined + +--- + +## Risks and Blockers + +### Current Blockers +1. **Delta-V Direction Bug** - Blocks completion of transfer test + - Impact: Can't validate full Hohmann transfer + - Severity: Low - solution is clear and simple + - Mitigation: Fix identified, implementation straightforward + +--- + +## Conclusion + +Session focused on implementing config-based LEO spacecraft initialization and impulse burn for Hohmann transfer. Core implementation complete, test framework working. One bug identified (delta-v direction) with clear solution path. + +**Session Outcome:** Productive with clear fix required for final test validation. + +**Estimated Time to Complete:** 1.5-2 hours (fix bug, complete test, cleanup)