SpaceX is borrowing money for the first time, and in doing so it pulled back the curtain on just how much cash the rocket company is sitting on.

According to CNBC's Samantha Subin, SpaceX announced a senior unsecured notes offering on Monday and disclosed that it holds about $100.8 billion in cash. A senior unsecured notes offering is essentially a corporate bond sale: the company borrows from investors and promises to pay them back with interest, without pledging specific assets as collateral.

CNBC reports that the bond sale is SpaceX's inaugural one, coming just days after the company's blockbuster IPO. In other words, a firm that just raised money by selling shares to the public is now also tapping the debt markets.

The market reaction was notably cool. CNBC reports that SPCX, the company's newly public stock, dropped more than 8%. Investor's Business Daily reports that SpaceX shares fell after the bond offering and new analyst coverage, and that space stocks broadly slid toward key technical levels.

Why investors sold on news of a giant cash balance isn't spelled out in these reports, but raising fresh debt on top of an enormous cash cushion can raise questions about how a company plans to spend, and at what cost.

Why it matters: a newly public SpaceX revealing a $100.8 billion war chest while still borrowing more signals just how much capital the space economy is now absorbing — and how closely Wall Street is scrutinizing where it all goes.