AST SpaceMobile (ASTS 1.75%) stock enjoyed a second straight day of strong stock price gains on Friday. After shooting up 24.5% Thursday, the stock gained a further 13.4% through 12:20 p.m. ET Friday. Even better news for shareholders, there's a reason behind this rally:

This start-up space communications company is just about ready to start launching satellites.

AST SpaceMobile's big news

AST SpaceMobile announced yesterday it has completed construction and testing of its first five Bluebird communications satellites -- operational units, as opposed to the prototype sats launched previously. Next, the company plans to ship its satellites to Cape Canaveral in August, so that SpaceX can launch them into orbit in September.

Once in orbit, AST says the satellites will provide "U.S. nationwide non-continuous service with over 5,600 cells in premium low-band spectrum, with a planned 10-fold increase in processing bandwidth" over time. Starting slow, the company eventually hopes to build a global constellation of 168 satellites to provide direct cellphone-to-cellphone service all around the globe -- with no need for cell towers in the mix.

And as the company described before its 2021 initial public offering (IPO), AST's ultimate goal is to provide this service to as many as 5 billion mobile subscribers, staking out for itself a large share of the "$1 trillion global mobile wireless services market."

Is AST stock a buy?

So far, so good -- but not all the news is good. Building a 168-satellite constellation isn't cheap, and at last report, AST had only $210 million on its balance sheet.

Giant telecom customers including AT&T and Verizon Communications have offered to help out with that, signing contracts worth hundreds of millions of dollars to AST. But the company is still burning cash at the rate of more than $300 million a year. AST will need to ramp up operations -- and revenue -- quickly, if it's to make a go of this business.

On that score, make sure to tune back in on Aug. 14, when AST will hold a conference call to tell investors how much cash it has left.