火箭固态发动机的工作原理

Design is future

固体火箭最特别之处就是它的燃烧是从内侧到外侧，而不是从下向上。

  燃料和氧化剂再加一些粘合剂(掺在一起合称推进剂)被做成固体，装在固体火箭外壳内。其中例如阿丽亚娜5号的固体火箭助推器推进剂成分为：14%丁二烯，18%铝粉和68%的高氯酸铵。

  它的截面形状被根据飞行任务设计。下面具体说

  阿丽亚娜5号运载火箭的助推器

  首先固体火箭的点火装置在最上面，有不同的点火方式。比如可以用电来打着一块固体燃料，制造出来的高热高速气体吹入火箭主体。

  假如推进剂截面形状为均匀圆形的话，那刚点火时推力最低，因为燃烧面积最小。越烧面积越大也就推力越大。而火箭刚点火时最重，需要相对较高的推力。

  这时工程师想到一个解决方案，将推进剂截面形状做成例如星星状。

  这样在刚开始燃烧时，燃烧面积最大，当星星状的突出部被烧完了，燃烧面积变小。

  航天工程师可以通过推进剂截面形状来设计推力相对时间的曲线。

  但是当这一切都完成时，它的行为也就完全预先设计好了。固体火箭一旦点火就必须飞了，没有熄灭推迟再发一次的可能性。其内部几乎没有活动部件。

  不同于液体火箭燃烧室比较小，固体火箭整个都是燃烧室，很高，会导致上下方向的压力振荡，燃烧不稳定。而液体火箭的燃烧室上下振荡远远不如这么剧烈。

  所以芯体为液体火箭，助推器为固体的火箭发射时，都是芯体先点火，工程师检查液体火箭工况一切正常，才会再将固体火箭助推器点火。

  虽然固体火箭比冲不大，但是推力非常高，这也是它被用来做助推器的原因。而由于它的推力远高于主火箭，假如左右助推器的推力过于不对称，这个偏向很难被修正回来，所以固体火箭助推器的生产需要非常非常高精度(当然上天的东西，都挺精密的)。阿丽亚娜5号主火箭1390kN推力，单个助推器7080kN(GS, ECA, ES子型号)。

  额外，不像液体火箭发射时需要准备并加注燃料，固体火箭可以长期待命，说发就发。这对军事用途非常友好，但是比冲略低，投射能力低于液体火箭。结构简单，设计和制造要求也低于液体火箭。包括军用飞机的弹射座椅也使用固体火箭。

The advance of technology is based on making it fit in so that you don't really even notice it, so it's part of everyday life.

B. Johnso

Computer inside

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