# Standard Operating Procedure
**Document Number:** [GUIDANCE-SYS-001]  
**Standard Operating Procedure (SOP):** Shuttle Digital Autopilot Guidance System  
**Revision:** 1.0  
**Last Updated:** [DATE]

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## Contents

1. Introduction  
1.1 Purpose  
1.2 System Overview  
1.3 Regulatory Compliance  

2. System Specifications  
2.1 Technical Parameters  
2.2 Equipment Configuration  

3. Operational Protocols  
3.1 Standard Operating Procedures  
3.1.1 Startup Procedure  
3.1.2 Normal Operation  
3.2 Performance Optimization  
3.2.1 Monitoring Parameters  
3.2.2 Adjustment Procedures  

4. Emergency Operations  
4.1 Emergency Response Protocols  
4.2 System Recovery  

5. Maintenance Requirements  
5.1 Preventive Maintenance Schedule  
5.2 Predictive Maintenance Implementation  

6. Quality Assurance  
6.1 Performance Metrics  
6.2 Documentation Requirements  

7. Security Protocols  
7.1 Physical Access Control  
7.2 Data and System Security  

8. Environmental Considerations  
8.1 Environmental Impact  
8.2 Sustainability Measures  

9. Training Requirements  
9.1 Personnel Qualifications  
9.2 Training Programs  

10. Document Control  
10.1 Revision History  
10.2 Authorization  

11. Process Flows and State Transitions  
11.1 System States  
11.2 Operational Workflows  
11.3 Resource Management  

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## 1. Introduction

### 1.1 Purpose
Defines when the Shuttle’s digital autopilot should engage emergency (3E/O) guidance based on flight conditions.

### 1.2 System Overview
- Continuously checks key flight parameters: velocity, altitude, pitch, and pressure.
- Reacts autonomously to deviations from nominal flight conditions.
- Triggers different operational branches based on current flight mode and state.

Monitors altitude, velocity, dynamic pressure, and other sensor inputs to determine the correct abort procedure or emergency region.

### 1.3 Regulatory Compliance
Complies with NASA abort guidance protocol and on-orbit emergency safety regulations.

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## 2. System Specifications

### 2.1 Technical Parameters
- Monitors: Velocity, vertical speed, angle of attack, dynamic pressure
- Flags: `cont_3EO_start`, `RTLS_abort_declared`, `region_selected`
- Modes: `mm102` (ascent), `mm103` (coast), `mm601` (abort/RTLS)

### 2.2 Equipment Configuration
All logic runs through onboard flight control computers. Inputs sourced from IMU, barometric sensors, and mission timers.

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## 3. Operational Protocols

### 3.1 Standard Operating Procedures

#### 3.1.1 Startup Procedure
- Set all internal control flags to default or false.
- Assign `step = undef` to reset the logic flow.
- Initialize region register to `reg-1` (unset).
- Await activation via `start_cont_3eo_mode_select`.

- Initialize step to undefined  
- Clear emergency flags and assign initial region (`reg-1`)  
- Wait for `start_cont_3eo_mode_select` to trigger

#### 3.1.2 Normal Operation
- Read flight parameters from sensors (e.g., IMU, velocity meters).
- Evaluate abort conditions based on velocity and MECO.
- Assign region: `reg1–reg4` for various emergency levels, or `reg102` for early ascent.
- Set `region_selected = TRUE` upon successful region assignment.
- If no abort required, exit without engaging emergency logic.

- Step through logic using flight parameters  
- If MECO occurs or abnormal flight detected, transition to emergency mode  
- Set region and guidance flags based on matching conditions

### 3.2 Performance Optimization

#### 3.2.1 Monitoring Parameters
- Track velocity thresholds for abort triggers  
- Monitor apogee vs reference altitude  
- Check dynamic pressure for region assignment

#### 3.2.2 Adjustment Procedures
- Region logic allows dynamic transition between `reg1–4` or `reg102`  
- Abort flag resets if region not selected or emergency condition no longer exists

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## 4. Emergency Operations

### 4.1 Emergency Response Protocols
- Detect abnormal flight status post-MECO.
- Evaluate downrange distance and velocity profile.
- Assign region based on emergency type and severity.
- Activate guidance system for tank separation and pitch adjustment.

- If velocity low and MECO confirmed, set `cont_3EO_start = TRUE`  
- Determine region (RTLS, region 1–4, or fast separation)

### 4.2 System Recovery
- Execute pitch and dump maneuvers per region logic  
- Transition to MM601 after RTLS declared

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## 5. Maintenance Requirements

### 5.1 Preventive Maintenance Schedule
- Confirm thresholds and transition logic before launch  
- Validate region outputs in simulation

### 5.2 Predictive Maintenance Implementation
- Use telemetry data from past missions to refine parameter thresholds  
- Apply redundancy checks for key region signals

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## 6. Quality Assurance

### 6.1 Performance Metrics
- Region assignment accuracy under stress conditions.
- Mean time from trigger to emergency guidance activation.
- Integrity of abort sequences during regression testing.

- Accuracy of region selection  
- Time-to-decision under MECO/abort conditions

### 6.2 Documentation Requirements
- Log each invocation of `cont_3EO_start`  
- Record final region, guidance actions, and result

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## 7. Security Protocols

### 7.1 Physical Access Control
- Guidance logic secured in onboard computers with tamper detection

### 7.2 Data and System Security
- Abort logic verified pre-flight  
- Region transitions not externally modifiable during mission

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## 8. Environmental Considerations

### 8.1 Environmental Impact
- System ensures controlled reentry and tank jettison

### 8.2 Sustainability Measures
- Reduces risk of uncontrolled failure or debris

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## 9. Training Requirements

### 9.1 Personnel Qualifications
- Engineers must understand model-checking logic.
- Controllers must interpret flight mode transitions.
- All personnel must pass abort guidance simulation tests.

- Mission controllers must understand abort logic flow  
- Flight software engineers must validate logic against models

### 9.2 Training Programs
- Simulation training for all emergency conditions  
- Pre-flight briefings on region-based guidance logic

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## 10. Document Control

### 10.1 Revision History
- Rev 1.0 – Initial SOP based on guidance.txt formal specification

### 10.2 Authorization
- Authorized by Flight Software Group Lead  
- Reviewed by Mission Operations Directorate

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## 11. Process Flows and State Transitions

### 11.1 System States
- `step` variable transitions: 1 → a1 → 2... → exit  
- Conditional transitions based on altitude, speed, and pitch

### 11.2 Operational Workflows

#### 11.2.1 Workflow 1
1. Evaluate mode and velocity  
   - If `mm102`: set `reg102`  
   - If velocity above limit: exit

2. Assign region based on:
   - Apogee, q_bar, h_dot, and angle

3. Set `region_selected = TRUE` and exit

#### 11.2.2 Workflow 2
1. Engage guidance  
2. Trigger tank separation  
3. Command OMS dump  
4. Adjust pitch and attitude  
5. Finalize entry and abort state

### 11.3 Resource Management

#### 11.3.1 Resource Allocation
- Region assigned based on live telemetry  
- State transitions gated by sensor thresholds

#### 11.3.2 Synchronization Procedures
- Abort flags, separation commands, and entry orientation are interlocked  
- Once triggered, system cannot re-enter mode select unless reset