《韦氏高阶》head词条下的说明：

To be heading or headed somewhere is to be going or directed somewhere.

• Where are you heading? = Where are you headed? [=where are you going?]

• The ship was heading/headed out to sea.

— often + for

• We were on a plane headed for Hawaii.

 即be heading/headed +介词短语或方位副词，表示朝某个方向或地方行进、移动。

如果省略be, 则heading/headed +介词短语或方位副词，就可以做名词的后置定语。

网友的这个句子中，headed for...和 heading...分别为前面名词civil servants 和private daredevils, tourists and entrepreneurs的后置定语。

headed for far-flung government establishments 飞往遥远的政府设施（如空间站）

far-flung：adj. 遥远的

heading who knows where 飞向没人知道的地方

who knows where = no one knows where. = 地点副词（说话人杜撰出来的副词）。

又如：

He spent who knows how much momey on clothes. 他在衣服上花了不知有多少钱。

who knows how much为说话人杜撰的形容词，作定语修饰money.

还可以是He spent God knows how much money, 或 He spent no one knows how much money. 他花了鬼知道有多少钱。强调花钱很多，超出想象。