# FAR Project Overview
###### tags: `System`

## 1. Abstract
This project is for the FAR(Friends of Amateur Rocketry) competition. In this project, we are going to build a launch viechle that can carry a 3U cubesat with a rover and a glider in it to 10000ft. AGL(above ground level). The rocket motor is a KNSB solid-state motor. After deploying the cubsat, the cubesat can deploy the rover and glider on its own. The goal of this project is to demonstrate the feasibility of deploying cubesats from sounding rockets. The result will also be demonstrated through the FAR competition.

## 2. Introduction
We are ISP(Institute of Space Propulsion). ISP is a club from NCKU(National Cheng Kung University) from Taiwan. ISP consists of talented students from different department, and we all love rocketry. We have three main divisions, propulsion, avionics, structure. These three divisions cover the 90% of the reseach and development of our rockets.
The prjoect can be divided into 5 phases and 3 parts. Phase 1~5 are the feasibility and risk assessment, design and test at small scale, design and test at nominal scale, import less important subsystem, final fix and test. Three parts are building the project main subject, the testing environment, and the competition affair.
The project main subject, the sounding rocket, is capable of carrying a 3U, 8 pounds cubesat, and sending it to 10000ft. AGL. It requires a M-class solid-state motor. There are two de-spin mechanism on the rocket, yoyo de-spin, reaction wheel. De-spin control is for creating a good attitude to deploy a cubesat. Therefore it will be initiated near apogee. We will use black powder to generate small explosion to push out the cubesat, and after complete deployment, the second explosion will release the rocket parachute. If the first parachute got jammed or failed to release, the backup parachute will be released. The cubesate also has two parachute, the main one and the backup one. It will release parachute after deployment, and it carries a rover, a glider, a reaction wheel for controlling heading. Carrying a rover and a glider is a rule from FAR competition, it really doesn't matter what is inside the cubsat. The cubesat will deploy the glider below 400ft. and the glider can return to control room through remote control. After the cubesat landing, it will deploy a rover. The rover needs to drive at least 10ft. away by itself. Every individual is capable of video transmition and romote control. They are also equipped with GPS, IMU sensors to tell us where and what attitude they are.
The following chapters will show the detail of our rocket system.

## 3. System architecture overview

### Propellent
We use KNSB as our propellent. The propellent is made from 65% potassium nitrate and 35% sorbitol. The propellent will be heated up to about 170 Celsius and filled to a paper tube. The propellent will be shaped into a tube 100mm in outer diameter, 20mm in inner diameter and in 100mm length. 8 sessions in total, the overall weight of propellent is about 10.5kg.

### Motor
Our motor is a solid-state motor. There are two main parts in it, combustion chamber and nozzle. The conbustion chamber is 105mm in diameter and 840mm in length. The nozzle's throat is 19.14mm in diameter. It has an expansion ratio of 8. The maximum chamber pressure will be 80.3bar. The esimate maximum thrust will come to 3452N, and the average thrust is 2529N. The total burn time is 5.431 seconds, and the total impulse is at 13733Nxsec. The motor is at N class. The motor is made of 6061 aluminum and the nozzle is made of graphite using CNC to manufacture.
### Airframe
火箭長約2300mm、直徑約150mm，穩定度2.0；火箭於點火後0.32秒離架，離架速度為28.6m/s；第3.91至5.49秒超音速，期間高度上升512m，其中最高速達353.7m/s，約等於1.04馬赫，故鼻錐選用穿音速階段(0.8~1.0馬赫)較佳且1.0~1.2馬赫時阻力相對較小的LD-Haack (Von Kármán)形狀。

### Avionics
The avionics system has two parts, rocket and payload. Both need the ability to measure the attitude, altitude and location. They can also communicate with ground station with more than 10km distance.
#### Inertial Measurement Unit
Inertial measuremnet unit, IMU, consists of an accelerometer and a gyroscope. We also add a magnetometer in it to read its heading. We can use these data to calculate its poses and traveling distance. Most of the purpose is to check if it is flying at a right pose and tell the controller what should do next. For example, when the rocket is at apogee, its pose will be horizontal to earth, then it should deploy the payload.
#### Barometer
Barometer can read air pressure, and it can be converted to height. We can use a barometer simply to read height directly without any integration, therefore it is rather accurate than IMU to measure altitude. It can also measure vertical velocity by differentiating height.
#### Global Positioning System
Global positioning system(GPS) can locate the rocket position for recovery. The rocket might land at a place too far to see, therefore, the GPS can tell where it lands.
#### Communcation
The communication system can be divided into two parts, data transmission and video transmission.
##### Data Transmission
We will use LoRa(Long Range) as our commuication protocol. It is a protocol for sub GHz commuication. It can provide a stable link with low energy cost. We can grab every data we need during the flight.
##### Video Transmission
We will use 2.4Ghz RF for out video transmission. The reason we can not use LoRa to transmit video is because of its low bandwidth. Therefore, we use higher frequency to get better video quality.

### De-spin control
The de-spin control is the most special part in this project. In order to deliver all kinds of payload, it is important to control rocket attitude. Most of the model rocket will spin fast after launch, because of the misalignment of fins. Without active stable control, there is no chance for a model rocket to deliver a payload equipped with directional antenna or other deivces. We have two mechanisms for reducing spin, yoyo de-spin and reaction wheel.
#### Yoyo de-spin
Yoyo de-spin as its name implies, the mechanism is just like a yoyo. When the rocket is at a high angular veocity, it pushes out two masses with string tied to in opposite direction. The centrifugal force will throw out them. The rocket's moment of inertial increase and the angular velocity of entire system will decrease due to the conservation of angular momentum. After that, we cut out the string and the rocket will spin in a much slower speed. Figure? shows the concept of this mechanism. However, the rocket is still spinning, the next part will introduce how to stop the rocket spinning.
#### Reaction Wheel
Reaction wheel is a wheel with quite mass. Spinning it up will cause a counter force because of the conservation of angular momentum. We can use this property to control the entire rocket roll action. A feedback system is indispensable for controlling a reaction wheel. We must know the angular velocity of the rocket and use PI controller to reduce it to zero or control it to a desired value. Figure? shows the block diagram of the control system. But why don't we just use the reaction wheel for this mission, if it can control the rolling speed? If a rocket spin too fast or its mass is too large, the moment of inertia will also be large. It is either raising the wheel speed or its mass. Neither of them is ideal for any of rockets. It will cost too much energy. But we can only increase the length of string for yoyo de-spin to handle the high moment of inertia condition. It is much simpler and cost effcient for reducing spinning.

### Payload
Our payload is a 3U cubesat equipped with IMU, barometer, GPS, communication system. It carries two cargos, a glider and a rover. This is a part of FAR challenge. It will also have a reaction wheel on it because it need to deploy a glider below 400ft. If the payload is spinning, there is no chance for a glider taking off.
The cubesat have three chambers. The top chamber carries a parachute. The middle chamber carries a glider. The bottom chamber carries a rover. The reaction wheel is a flat wheel hiding between the glider and the rover. Figure? shows the design of the cubesat.
### Glider
The glider need to have the capability to return to a FAR designated location autonomously or by remote control. Therefore it needs a guidance system, like GPS. And we will control it remotely, so it also needs video tranmission ability. Since we will load the glider into the cubsat, its wing span can only be smaller than 10cm.
### Rover
The rover has to travel a minimum of 10ft on its own with live video after cubesate touchdown. Therefore, it also needs video transmission ability.

### Parachute
應用理論：Drag equation:Drag=Weight=Cd*r*v^2/2A，其中r為air density=1.225kg/m^3，v為降落終端速度，A為降落傘表面積。首先製作已知A與酬載重量之降落傘，另終端速度v=5m/s，Cd=1.75，將其裝載航電板並量測其實際終端速度，再代回Drag equation計算傘布之Cd。
設計：以ripstop nylon為傘布材料，製作由12片布塊縫製而成的圓頂狀降落傘。傘布以french fell seam方式縫合，傘繩材料為Kevlar ，共12條，利用眼扣將其綁在降落傘邊。傘繩中後段集結成一束，再與金屬掛鉤結合，掛鉤將固定於箭身中。
製作流程：1.得已知傘布之Cd後，另終端速度為5m/s帶入，求得傘布表面積A並推算降落傘半徑。
2.使用Parachute generator繪製每片傘布形狀，再列印得模板，裁剪出12塊傘布。
3.將傘布縫合收邊，綁上傘繩與掛鉤固定後便完成。

## Mission concept of operations overview

- Phase 1: Ignition & Lift-off
- Phase 2: Feul Burns Out & Goes Supersonic
- Phase 3: De-spin & Reach apogee & deploy payload
- Phase 4: Deploy Parachutes
- Phase 5: Cubsat Deploy Glider
- Phase 6: Landing & Deploy Rover

## Test equipment
### Thrust test stand
In order to test our SRAD motor for identifying thrust curve, we need a thrust test stand. Since there is no commercial thrust test stand for rocket motor in Taiwan, it is inevitable for us to build our own thrust test stand.
The stand needs to have the ability to test different scale of motor. Our final motor might have a peak thrust at 300kgf. The safety factor must be at least 2, therefore, our test stand needs to take at least 600kgf thrust. Figure? shows our thrust test stand design.
### Test flight launch pad
Before the competition, we plan to have several test flight for testing our rocket. We need a strong enough launch pad for us to launch our rocket. We have already build two type of launch pad. Figure? shows the launch pad for early stage test flight. Figure? shows the launch pad for our final rocket.
## Schedule

## Budget