When it comes to building a second income, investing in Space Exploration Technologies (NASDAQ: SPCX) might not be the obvious place to start. It may be that years down the line it generates substantial spare cash and chooses to start paying a dividend. To target a £10k annual second income at that level, someone would need to invest well over £3m. At that level, a £10k+ second income would need a portfolio worth at least around £167k. One income share to considerIts business is more mundane than SpaceX's, but one dividend share I think investors should think about for its income potential is 5.8%-yielding British American Tobacco (LSE: BATS).