Another day, another five-year low for Sirius XM Radio (NASDAQ:SIRI) shareholders.

Shares traded as much as 20% lower this morning, as investor confidence in the satellite-radio provider continues to wane. 

The market's fear -- as Sirius goes from falling off McMarket's dollar menu to also being booted from Taco Bell's $0.79 value menu, too -- is that three debt-repayment milestones next year will be tricky. With bankers, investment banks, and lenders falling like flies these days, it may take more than the hope of next year's positive operating cash flow projections to keep the company from defaulting if it can't refinance.

This doesn't mean Sirius and XM airwaves will go silent. Filing for Chapter 11 bankruptcy protection would just be the company's way to get its creditors to ease up on the company. Unfortunately, the same can't be said for shareholders whose investments would probably be wiped out.

Hearing CEO Mel Karmazin discuss privatization also isn't helping, even if that solution would at least let shareholders walk away with something.

It's definitely been a hard month to be a Sirius XM investor. As low as the stock was heading out of what should have been a cork-popping August given the completion of the merger between Sirius and XM, things have only gotten worse. The stock has shed nearly half of its value this month alone.

Sirius has always been a low-priced stock, but now it's trading at a per share price even lower than overseas peer 1worldspace (NASDAQ:WRSP), albeit at more than six times the market cap.

If there is any consolation for investors, it's knowing that Karmazin is probably the last person on the planet who would want the company to file for bankruptcy protection. After soaring to prominence at Viacom (NYSE:VIA), the last thing the broadcasting legend would want is satellite radio's insolvency on his resume. He also bought another 2 million shares last month -- at twice today's price -- so he has real money to lose if Sirius goes under.

Another option, of course, is for a media giant such as News Corp. (NYSE:NWS), Viacom, or DirecTV (NYSE:DTV) to acquire the company, but shareholders may not be desperate enough to accept the pittance they are likely to offer.

Ultimately, this is a failure of confidence more than of fundamentals. Sirius XM hasn't necessarily done anything wrong, beyond putting out disappointing revenue and subscriber targets for 2009 earlier this month. The viability of third-party creditors and the country's flagging economy are weighing on the company these days. That isn't enough to take the stock to zero, unless shareholders let it happen.

Here are some other Sirius XM Radio programming notes:

Longtime Fool contributor Rick Munarriz is such a big satellite radio fan that he subscribes to both XM and Sirius. He does not own shares in any of the companies in this story. He is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.