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Success Stories

SPHERE Flight Computer Mk-I

SPHERE Flight Computer Mk-I represents the first validated step toward a scalable, indigenous rocket avionics platform. The objective was straightforward but demanding: build a flight computer that behaves like real avionics deterministic, state-aware, and reliable under non-ideal conditions.

At its core, Mk-I is driven by an ESP32, selected for its real-time performance and its ability to manage sensing, control, data storage, actuation, and safety logic concurrently. The system integrates a barometric pressure sensor for altitude estimation and an IMU for attitude and motion awareness. The complete avionics unit was assembled on a perfboard, requiring deliberate attention to grounding, power integrity, and signal routing.


Hardware Built to Be Understood:

Building Mk-I on perfboard forced every electrical decision into the open. There were no hidden ground planes or automated routing assumptions, every connection was deliberate, inspected, and tested.

The system was validated across a −40 °C to +80 °C operating temperature range, representative of realistic aerospace environments. Power stability, sensor behavior, timing consistency, and actuator reliability were evaluated throughout this range.

Hard testing included repeated power cycling, extended runtime operation, mechanical handling stress, and continuous verification of sensing and actuation paths. The goal was not to demonstrate success, but to expose failure modes early and remove them through iteration.


Mission Oriented Software Architecture:

The flight software is structured around a clean, mission oriented architecture. Sensor acquisition, estimation, control, actuation, data logging, and safety logic are clearly separated. This places SPHERE Mk-I well above demonstration level flight codes that only read sensors and move outputs.

The system operates through clearly defined mission phases:

BOOT / INITIALIZATION

ARMED

ASCENT

APOGEE DETECTION

DESCENT

LANDED / RECOVERY

Each phase enables only the logic relevant to that state, ensuring predictable and constrained behavior throughout the mission.


Robust Data Logging for Real Analysis:

One of SPHERE Mk-I’s strongest technical characteristics is its robust data logging implementation.

Each mission automatically generates a uniquely indexed SD card file (FLIGHT001.CSV through FLIGHT999.CSV), eliminating the risk of accidental data overwrites. A single header row is written at file creation, followed by timestamped data throughout the flight.

Logged parameters include IMU measurements, barometric altitude, servo positions, and MOSFET states. This produces complete, structured datasets suitable for genuine post flight analysis rather than reconstruction from partial logs.


Practical Sensor Fusion and Attitude Estimation:

Sensor fusion is implemented using a complementary filter with a high blending factor, balancing gyro stability with accelerometer correction. The approach is computationally efficient, stable, and appropriate for real time embedded execution on the ESP32.

The result is usable attitude estimation intended for control and analysis not raw sensor visualization.


Control Logic with Flight Awareness:

Control behavior is explicitly phase aware. Closed loop control is active only during the ASCENT phase. During DESCENT, control surfaces are disabled and centered, preventing unnecessary actuation, oscillations, and power waste.

Integral windup is constrained, and servo output smoothing is applied to reduce aggressive corrections and structural stress details that materially influence flight reliability.

State Gated Actuation and Safety Discipline

Critical events are governed by state and conditions, not single-sensor triggers.

Maximum altitude is tracked continuously. Descent recognition is based on altitude trend behavior. MOSFET-controlled actuation is permitted only during the DESCENT phase and is constrained by a fixed time limit of five seconds, eliminating runaway conditions. This layered gating approach reflects real aerospace safety philosophy. 


Landing Detection and Recovery Behavior:

Landing is detected through altitude stability over time, after which the system transitions to RECOVERY behavior. Audible and visual locator signals are activated to support physical retrieval in field conditions.

Distinct post landing behavior provides unambiguous confirmation of mission completion.

Hardware–Software Integration Discipline

SPHERE Mk-I reflects a safety first integration mindset:

  • MOSFET outputs default LOW on boot

  • Servo limits enforced in software

  • Direct I²C sensor access to reduce abstraction overhead

  • Audible and visual indicators for operator awareness

These decisions reduce failure impact and simplify diagnosis under real operating conditions.


A Stable Foundation for Growth:

The most important outcome of SPHERE Flight Computer Mk-I is that it establishes a stable, extensible baseline. Additional capabilities telemetry, navigation, redundancy, or advanced state machines can be integrated without restructuring the core system.

SPHERE Mk-I succeeds not by feature count, but by disciplined execution and verifiable behavior.