> For the complete documentation index, see [llms.txt](https://yasmin.gitbook.io/grace/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://yasmin.gitbook.io/grace/grace.md). # Grace Designing & Building Two-Stage Flight Computer with Yasmin(VGEC Rocketry's Senior Avionics Engineer) **The Beginning of the Madness** After wrapping up our first ever flight computer, we officially became part of our college's rocketry team. A month later, we had *that* meeting. You know, the one with the chaotic "WHAT’S NEXT?" vibe. It was less of a meeting and more of a parliament debate. Some of us wanted to dive into liquid propulsion (ambitious, I know), others were hyped about boosters. But given our resource constraints, we all found common ground on one thing—let’s go for a two-stage rocket. And because being realistic is boring sometimes, we didn't settle at 1 km or 3 km. Nah—we shot for **8 km**. Why? Because we were *high* on dreams (and maybe caffeine). So, we began our research and designed our test rocket, lovingly named **"Venessa."** A two-stage beauty. But this time, she wasn't just pretty—she was smart. Two brains smart: **"GRACE"** and **"NERVE"**—redundant flight computers because we *did* learn from our first crash-and-burn attempt. This blog is about my GRACE—because this one’s close to heart. ## Two-Stage Rockets: A Quick Layman Drop So what *is* a two-stage rocket? It’s basically a rocket stacked on top of another rocket. The first stage gets you going and gains altitude; once it burns out, the second stage lights up and pushes you higher. This technique increases efficiency by ditching dead weight mid-flight. Most hobby projects go with **passive ignition** for stage two—meaning the second motor lights up automatically after a delay, regardless of what's actually going on mid-flight. We said nope to that. We wanted **active control**. Because with active control, we decide when (and *if*) it should fire, based on real flight data—not hope and timing. ## Logic Abstract: What Makes GRACE Smart? In a single-stage rocket, you mostly worry about one event—**apogee**, the highest point. Detect it? Pop the chute. Simple. But a two-stage system? It’s a whole new level of complication. For **Venessa**, we didn’t rely on preset timers because we were using *in-house solid fuel*, not fancy commercial motors with precise burn durations. So how do we detect when the first stage is done burning? **Physics to the rescue.** We observed **acceleration data**. While the motor burns, acceleration increases. When it burns out? A *sudden drop*. That’s our first cue. But that’s not enough—we also check the **pitch angle** to ensure the rocket is still pointing mostly upward (within a 30° vertical cone). If both conditions are met? Boom—Stage 2 lights up. Otherwise? Abort the second stage and deploy the parachute. No missiles today, thanks. ## Hardware: Choices with Reason GRACE’s brain is an **Arduino Nano**, wired up with **BMP280** for altitude and **MPU6050** for acceleration and pitch. We added: * Two **pyro channels** controlled via transistor switches: * One for **stage 2 ignition**. * One for **parachute ejection**. * A single **state-indicating LED**. * A **3.7V LiPo** for power. * And since Nano doesn’t have fancy storage? We used **EEPROM** to log max altitude and pitch at burnout.

### But why these components? **Custom PCB vs Off-the-Shelf:** We went with a **custom PCB**—yes, it takes more time and effort, but it gave us control over component placement and reduced dead weight. Nothing unnecessary. **Arduino Nano:** Low power, compact, and perfect for our payload constraints. Sure, it lacks Wi-Fi or massive memory like ESP8266, but that’s where “NERVE” comes in. GRACE focuses on control logic. **BMP280 :** Cheaper, reliable, and accurate *enough* for our altitude readings. We didn’t need barometric overkill. **MPU6050** MPU6050 is cost-efficient and gives us just what we need—acceleration. No need for magnetometers in this mission. **In-House PCB Manufacturing:** It gave us flexibility and iterative testing. We learned *a lot* from soldering, designing, redesigning—and burning our fingers.