The satellite radio company’s shares are up more than 3.6% in pre-market trading this morning after it beat its own projections, and analysts’, for subscriber growth in Q2. Sirius XM says it added 622,042 net subscribers — a 38% improvement from the same period last year when it picked up 452,147. All told, it has gained 1M customers in the first half of 2012, giving it a total of more than 22.9M. The company now expects to end the year with 1.6M new customers, and about $3.4B in revenue. It left unchanged the projection for free cash flow, the metric that CEO Mel Karmazin watches most closely. That stays at $700M. “Our second quarter subscriber gains mark a record quarter of net additions since the merger of Sirius and XM in July 2008,” he says. He attributed the improvement to “our unparalleled programming lineup” in the midst of “a weak US economic outlook.” But last week one analyst, Lazard Capital Markets’ Barton Crockett, predicted that sub numbers would be strong based on the pickup in car sales — one of the main sources of satellite radio customers. Auto sales were up 22.2% in June vs the same month last year, and +2.5% in May. “If new car sales stay near current levels, we see 2M sub adds as possible” this year for Sirius XM, he says this morning.