By Robbie Citrino for Kapitall. Musk’s brainchildren have climbed to a combined $50 billion in market value since Paypal’s inception in 1998. This has paid dividends for investors to the tune of 875% for those who bought Solar City (SCTY) in 2013 and 1,400% for Tesla (TSLA) owners since its IPO in mid 2010 (depending of course on when you bought in). Musk’s next ‘company of the future,' SpaceX, is a space transportation company whose end purpose is to shuttle humans between Earth and Mars. While the company has had a significant amount of funding, and seen quite a few achievements as the first privately-owned company to launch and recover spacecraft, Musk claims that there is no IPO in the company’s near future. So, how can investors cash in on the ideas of a genius without a stock? Look to its competitors. Lockheed Martin (LMT), Alliant (ATK), and Boeing (BA) all have manned spacecraft in the works, and some may be prepared for launch as early as 2015. And, while they are not operating as a delivery service, they could be the production side for a new era of travel, building the ships for a variety of companies to use in their transportation services. Do you think space stocks represent a sensible investment? Use the list below to begin your analysis and let us know what you think in the comments. Click on the interactive chart to view data over time. 1. Alliant Techsystems Inc. ( ATK): Engages in the supply of aerospace and defense products to the United States government, allied nations, and prime contractors. Market cap at $4.27B, most recent closing price at $133.77.