	December 31,
	2019			2018
Land	$	381		$	381
Satellite network		198,746			195,886
Capitalized software		83,320			67,509
Computer hardware		6,528			5,850
Other		7,787			5,610
Assets under construction		13,832			12,489
		310,594			287,725
Less: accumulated depreciation and amortization		(165,041	)		(127,655	)
	$	145,553		$	160,070

During the years ended December 31, 2019, 2018 and 2017, the Company capitalized internal costs attributable to the design, development and enhancement of the Company’s products and services that have not yet been placed into service and internal-use software in the amounts of $13,945, $12,817 and $12,776, respectively.

Depreciation and amortization expense for the years ended December 31, 2019, 2018 and 2017 was $37,717, $36,609 and $33,889, respectively, including amortization of internal-use software of $3,117, $3,433 and $6,186 for the years ended December 31, 2019, 2018 and 2017, respectively.

For the years ended December 31, 2019, 2018 and 2017, 45%, 47% and 61% of depreciation and amortization expense, respectively, relate to cost of services and 7%, 9% and 8%, respectively, relate to cost of product sales, as these assets support the Company’s revenue generating activities.

As of December 31, 2019 and 2018, assets under construction primarily consisted of costs associated with acquiring, developing, enhancing and testing software and hardware for internal and external use that have not yet been placed into service.

One OG2 satellite that was launched in December 2015 experienced a solar array anomaly in July 2016 that resulted in the satellite entering a safe mode and being taken out of commercial service. This satellite had previously been intermittently providing AIS service and regularly communicating with the ground infrastructure. In April 2017, communication was lost with this OG2 satellite. The Company’s satellite engineering team developed and uploaded new software designed to prevent a similar solar array anomaly from occurring on other OG2 satellites.

In June 2017, there was a loss of communication with the prototype OG2 satellite that was launched in December 2015, and in July 2017 there was a loss of communication with an OG2 satellite that was launched in July 2014. The Company recorded a non-cash impairment charge of $31,224 in the quarter ended September 30, 2017 to write-off the net book value of the three OG2 satellites. In addition, the Company decreased satellite network and other equipment by $39,576 and the associated accumulated depreciation by $8,352 to remove the assets as of September 30, 2017.

In October 2018, the Company experienced a communication issue with an additional OG2 satellite. The Company remains in operational control of this satellite and is developing new software in an attempt to restore AIS and/or messaging services.