Suicide Burn
A suicide burn (or “hover slam”) is an orbital landing maneuver where a spacecraft performs a single, continuous engine burn to cancel all downward velocity exactly at the landing site — with essentially zero margin for error. If the burn starts too early, the spacecraft runs out of fuel. Too late, and it crashes.
The Mathematics
For a simple case (constant gravity, no atmosphere):
v_target = -sqrt(2 * a_available * altitude_above_ground)
Where a_available is the net upward acceleration the engines can provide (thrust/mass - gravity).
In AEGIS
AEGIS implements a sqrt glideslope profile (ADR-022) that generalizes the suicide burn:
v_target = -sqrt(2 * a_avail * alt_above_floor)Where a_avail is the vessel’s actual TWR-derived net upward acceleration, computed each tick. This replaces older linear profiles that saturated at high altitude.
Phases
| Phase | Description |
|---|---|
DEORBIT_BURN | Initial deceleration from orbit |
HYPERSONIC_COAST | Unpowered descent through atmosphere |
POWERED_DESCENT | Main engine burn begins |
HOVER_TARGETING | Near-surface horizontal alignment |
TERMINAL_DESCENT | Final vertical landing |
Key Challenge: Engine Failure
If an engine fails during the burn:
- Total thrust decreases → less
a_avail - Asymmetric thrust → torque
- The glideslope must be recomputed in real-time → Control Allocator remaps thrust
Related Concepts
- Powered Descent — The broader category of engine-assisted landing
- Control Allocation — Remapping thrust after engine failures
- Glideslope Profile — The trajectory to follow
- Hohmann Transfer — Orbital mechanics for approach
- SpaceX Landing — Real-world implementation (Falcon 9, Starship)
Sources
- AEGIS Project (
src/guidance/controller.py,src/mission/flight_control.py)