Dec 8, 2025
Inside the SpaceX Internal Design Tool
Pari Singh
The Bill of Design (BOD) is how SpaceX turns requirements, ownership, and testing into a single operating system for speed and rigor.
SpaceX’s killer internal tool - Bill of Design (BOD) – is the backbone for their design culture. It’s the tactics of how they combine speed + rigour.
BOD is critically different to a traditional BOM (Bill of Materials). How?
BOM is focused on what (parts) whereas BOD is focused on needs (Requirements/Design Criteria).
Modern hardware teams think differently:
Parts → Design units (flexible, not tied to instances that can be deleted)
Requirements → Design Criteria (flexible, changing, open to push back from the engineers).
Engineering executors → Responsible Engineers
Deep Dive on mindset:
#1. Design Units not Parts
Starship went from Landing legs → Tower catch.
Elon repeats one thing to his teams: “kill the part or process step.” But that is almost impossible when you treat your BOM as sacred. You get attached to parts and justify their existence. It creates psychological resistance to elimination.
The BOD changes that psychology. It uses Design Units. A Design Unit is defined by its Design Criteria (the why), not its CAD model (the what).
Once you break that mental link, engineers can actually kill things. Combine them. Remove steps. Challenge what exists without the emotional baggage of a part list.
#2. Responsible Engineers (REs) Own the Requirements
SpaceX has Responsible Engineers. They set a their own design criteria, flexible, challengeable requirements, by talking directly to their peers (crazy idea).
RE ↔ RE collaboration drives the whole machine. REs are ultimate owners of their hardware.
Every engineer becomes a systems engineer because they have to. Systems Engineers work for engineers, not shouting requirements at engineers. This keeps the design process fast.
#3. Automated verification
It needs to be obvious if a design is a go/no go.
How do we move fast, and make sure we're good to fly? Test aggressively and often. Test all the time–continuously.
An RE picks a design unit type. The system infers the rigor level and the verification needs. Simple automation that speeds up sign-offs:
• Automatic verification paths
• Clear pass or fail signals
• A go or no-go status anyone can read
Most modern space/automotive/robotics companies are moving from their own Jira build BOD → Flow. We couldn't be more happy to serve you. ❤️