摘要立方体纳卫星始于1999年加州理工大学和斯坦福大学的一项科学研究项目。其外形为边长10cm的立方体，输出功率相当于普通的手机，重量不足1.33kg。作为卫星，其最基本的需求就是入轨后能与地面站进行数据通信。61174

本文主要介绍了微纳卫星NUJST-1的主要系统构成，各部分的主要作用。分析了AX.25通信协议的具体格式，以及AX.25通信协议在通信链路建立过程中的相关步骤。本文基于keil编译环境，运用软件编程来解决数据打包的问题。编写了基于STM32单片机的AX.25协议打包程序，同时还通过自行搭建程序验证平台来验证程序,为南理工第一颗纳卫星NJUST-1通信子系统的开发储备了一定的技术力量。

毕业论文关键词  立方体纳卫星   AX.25通信协议   STM32  通信下行程序

毕业设计说明书（论文）外文摘要

Title    The  Development  Of  Downlink  Program  for  CubeSat   

Abstract The CubeSat program is a project birthed and supported by Cal Poly and Stanford in 1999. Its appears as a cube of side length 10cm, the output power is equivalent to an ordinary cell phone, and it weighs less than 1.33kg. As a satellite, the most basic is to communicate with the ground station after getting into the orbit. 

This paper mainly describes the system constitutes and the major role on each portion. of the CubeSat ,NUJST-1 .This paper also analyzes AX.25 communication protocol specific format ,and the steps in the process of establishing the communication link with AX.25 communication protocol .This paper is based on keil compiler environment, using software to solve the problem of data packaged. Compile AX.25 protocol packaged program based on STM32 MCU, this approach not only free up more space of the CubeSat, but also reduce power consumption for the limited power budget of CubeSat. In addition, This paper also verifies the program through building verification platform. Reserve certain technical strength for the development of the communication subsystem in NJUST-1, the first CubeSat of NJUST.

Keywords:  CubeSat  AX.25 communication protocol  STM32  downlink program

1. 引言 1

1.1 立方体纳卫星标准 1

1.2 QB50项目介绍 2

2. NJUST-1双单元立方星 3

2.1 NJUST-1系统设计 3

2.2 任务分析 7

2.2.1 轨道分析 7

2.2.1 电量分析 9

2.2.2 最小波特率的计算 9

2.2.3 下行遥测链路计算 10

3. AX.25卫星通信协议 11

3.1 协议概述 11

3.2 AX.25帧格式 12

3.2.1 标志字段 12

3.2.2 地址字段 13

3.2.3 控制字段 13

3.2.4 PID字段 17

3.2.5帧校验序列 17

3.3 AX.25通信链路 18

4. 通信下行软件开发 19

4.1 AX.25打包软件 21

4.1.1数据框架说明 22

4.1.2软件打包 24

4.2 AX.25解包程序