It's been a red-hot summer for this space telecommunications stock.AST SpaceMobile (ASTS -2.35%) followed a spectacular May with another strong performance in June, with the stock climbing 40% for the month, according to data provided by S&P Global Market Intelligence.Investors are increasingly getting excited about this space start-up's chances for success, and the stock is rocketing higher as a result.First customers, now cashAST is a space telecommunications company hoping to build a space-based broadban ...