Property and equipment, including satellites, are stated at cost, less accumulated depreciation.  Equipment under capital leases is stated at the present value of minimum lease payments.  Depreciation is calculated using the straight-line method over the following estimated useful life of the asset:

We review long-lived assets, such as property and equipment, for impairment whenever events or changes in circumstances indicate the carrying amount may not be recoverable.  Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to estimated undiscounted future cash flows expected to be generated by the asset.  If the carrying amount of an asset exceeds the estimated future cash flows, an impairment charge is recognized for the amount by which the carrying amount exceeds the fair value of the asset.  We did not record any impairments during the years ended December 31, 2015, 2014 or 2013.

Property and equipment, net, consists of the following:

Construction in progress consists of the following:

Depreciation expense on property and equipment was $220,514, $211,407, $203,303 for the years ended December 31, 2015, 2014 and 2013, respectively.  We retired property and equipment of $43,833, $19,398 and $16,039 during the years ended December 31, 2015, 2014 and 2013, respectively, which included the retirement of our XM-1 and XM-2 satellites in 2015 and 2014, respectively.  We recognized a loss on disposal of assets of $7,384 during the year ended December 31, 2015, which related to the disposal of certain obsolete terrestrial repeaters and related parts.  We did not recognize any loss on disposal of assets during the years ended December 31, 2014 and 2013.

Satellites

We currently own a fleet of eight operating satellites.  We are in the process of de-orbiting XM-1, a satellite that is no longer in use and has also reached the end of its operational life. The chart below provides certain information on our operating satellites:

* Satellite was fully depreciated and was still in operation as of December 31, 2015.