PARIS — The investment company that took mobile satellite services operator Iridium Communications public in 2009 is selling all its shares despite the stock’s decline in recent months, saying it will use the proceeds to shore up its own depressed stock.

Greenhill & Co. Inc. of New York, which is a major Iridium owner, will be selling its 9.8 million shares of Iridium stock on a daily basis over the coming months, with the daily sell-off ebbing and flowing with Iridium’s share price.

In an Oct. 4 announcement, Greenhill said that it will be selling 15,000 Iridium shares per day if the stock trades at less than $8.50 per share, which has been the case recently. At between $8.50 and $9.50 a share, the daily sell-off will be 20,000 shares a day, and will reach 25,000 shares per day if the stock closes at a price greater than $9.50 a share.

“We continue to believe strongly in the value of Iridium as a global communications company,” Greenhill Chief Executive Scott Bok said in an Oct. 4 statement. “We’ve made the decision today to sell our stake … primarily to fund the repurchase of Greenhill’s own attractively valued common stock.”

The Greenhill decision came at a time when Iridium stock has been trading near its 52-week lows. It closed at $5.94 Oct. 5 in trading on the U.S. Nasdaq exchange. But Greenhill’s stock has also collapsed in recent months, falling from around $80 per share in late 2010 to around $30 per share recently.

In response to Space News inquiries, McLean, Va.-based Iridium issued the following statement Oct. 5:

“Greenhill became a stakeholder when they brought Iridium public in 2009 through their SPAC [special-purchase acquisition company], and they continue to be confident about our potential and value as a global communications company. Scott Bok of Greenhill has kept his personal stake, remaining a shareholder and serving as a senior member on our Board.

“Otherwise, it’s business as usual here. Greenhill decided on the most beneficial path forward — a 10b5-1 sales plan — which is the least disruptive path by automatically selling small daily amounts (less than 5 percent of our current daily trading volume) over approximately two years. Greenhill is an investment banking firm versus an investment company, and we expected they would eventually sell. This is a measured and thoughtful path parallel to our expectation from day one of our relationship.”

Iridium said its bank financing, which is backed by the French export-credit agency, Coface, will not be affected by the Greenhill move. Iridium is building a $3 billion second-generation constellation of 66 low-orbiting satellites, called Iridium Next, which is expected to be launched over two years beginning in 2015.

For the first six months of 2011, Iridium reported revenue of $187.2 million, up 13 percent from a year earlier. Operational earnings before interest, taxes, depreciation and amortization were 49 percent of revenue, up from 42 percent in the same period last year.

Peter B. de Selding was the Paris bureau chief for SpaceNews.