Does astro means space or stars
Astro comes from the greek άστρο which not only means star but has a more general meaning that includes any small dot in the night sky (see https://en.wiktionary.org/wiki/%CE%AC%CF%83%CF%84%CF%81%CE%BF#Greek for details)

In today's language it still has a quite broad meaning:

Oxford English dictionary (https://www.oed.com/view/Entry/12240?isAdvanced=false&amp;result=2&amp;rskey=LlaQB9&amp;): 


  Forming terms relating to stars, other celestial objects, or outer space.


Merriam Webster (https://www.merriam-webster.com/dictionary/astr-)


  : star : heavens : outer space : astronomical 


Conclusion: Sheldon and Raj are right