打个例子吧，现在非洲森林中有某个原始民族，而且是非常古老的那种，即便全世界都不知道它的存在，它的族人也应该知道自己的存在吧。

检索了一下电子书：
“太空族”这个词第一次出现：
（第一次看的时候真没注意这里）
“No, by Black Space, no! My grandfather was a blood-poor son-of-a-spacer who died heaving coal at starving wages before the Foundation took over. I owe nothing to the old regime. But I was born in Smyrno, and I’m not ashamed of either Smyrno or Smyrnians, by the Galaxy. Your sly little hints of treason aren’t going to panic me into licking Foundation spittle. And now you can either give your orders or make your accusations. I don’t care which.”
“不对，太空啊，大错特错！我的祖父出身卑微，他是‘太空族’的后裔，是一个赤贫的矿工，一生仅靠挖煤糊口。在基地接管司密尔诺之前他早已去世，我并未受到以前那个政权的任何荫庇。但我的确生于司密尔诺，银河在上，我并不会因此自卑。你狡猾地暗示我是叛徒，这可吓不倒我，我不会因此对基地卑躬屈膝地讨饶。现在你可以命令我，也可以指控我，反正我都不在乎。”
（1951）
第二次出现：
（这里我注意到了，所以我还以为这个“太空族”是阿西莫夫发明的感叹词来着，类似“银河在上”这样的。所以第一反应是以为杜尔想说“the son-of-a-bitch”……）
“Snake Sutt?” Jaim Twer grew excited. “A trick. The son-of-a-spacer is getting rid of you. Mallow--”
“毒蛇瑟特吗？”杜尔激动起来，“那是诡计。那个太空族的**想把你支开，马洛……”
（1951）
之后五册书都没再提到过这个词。
第七册再次出现：
“Important? I doubt it,” said Deniador faintly. “Perhaps amusing, however. Earth is not the only planet whose position is a mystery. There are the worlds of the first group of Settlers; the Spacers, as they are called in our legends.Some call the planets they inhabited the ‘Spacer worlds’; others call them the ‘Forbidden Worlds.’ The latter name is now the usual one.
“In their pride and prime, the legend goes, the Spacers had lifetimes stretching out for centuries, and refused to allow our own short-lived ancestors to land on their worlds. After we had defeated them, the situation was reversed. We scorned to deal with them and left them to themselves, forbidding our own ships and Traders to deal with them. Hence those planets became the Forbidden Worlds. We were certain, so the legend states, that He Who Punishes would destroy them without our intervention, and, apparently, He did. At least, no Spacer has appeared in the Galaxy to our knowledge, in many millennia.”
“重要吗？我很怀疑。”丹尼亚多轻声说，“不过也许很有意思。地球不是唯一行踪成谜的行星，第一波殖民者——在我们的传说中，称他们为‘太空族’——他们的世界如今也不知所踪。有些人管那些世叫‘太空世界’，也有人称之为‘禁忌世界’，后者现在较为通用。
“传说是这么说的，在他们的黄金时代，太空族使寿命延长到数个世纪，并且拒绝让我们的短寿命祖先登陆他们的世界。在我们击败他们之后，情势有了一百八十度的逆转，我们不屑和他们来往，禁止我们的船舰和行商跟他们接触，要让他们自生自灭。因此那些行星变成了禁忌世界。根据传说的记述，我们确定根本无需插手，惩罚者便会毁灭他们，而他显然做到了。至少，据我们所知，已经有许多仟年，不曾见到太空族在银河出现。”
（1981）
按阿西莫夫的写作时间来说，“太空族”这个词第一次出现：
When Spacetown was first established some twenty-five years earlier, there was a
strong tendency to make a showplace out of it. The hordes of the City herded in that direction.
The Spacers put a stop to that. Politely (they were always polite), but without any compromise with tact, they put up a force barrier between themselves and the City. They established a combination Immigration Service and Customs Inspection. If you had business, you identified yourself, allowed yourself to be searched, and submitted to a medical examination and a routine disinfection.
且说大约二十五年前，太空城建立之初，曾有一股很强的力量，想推动它成为观光胜地。于是，一群群的纽约人蜂拥而至。
太空族及时阻止了这股风潮。他们以圆滑的手腕，客客气气（这种态度从无例外）却毫无妥协地在两城之间建造了一道力场关卡。然后，他们成立了一个兼顾“移民”和“海关”的联合机构。如果你要去太空城办事，必须以真实身份提出申请，并且默许他们对你进行搜身、健康检查以及例行的消毒。
（1950）
所以，阿西莫夫写《基地》的时候已经提出“太空族”的完整概念了，而《基地与地球》是间隔了三十多年才写出来的想想吧，大概率是老阿随口在《基地》里提了一句然后几十年后忘了这个设定了。