trends we expect mst 2019s 2015 net sales to be comparable to 2014 net sales , with the increased volume from new program starts , specifically space fence and the combat rescue and presidential helicopter programs , offset by a decline in volume due to the wind-down or completion of certain programs . operating profit is expected to decline in the mid single digit percentage range from 2014 levels , driven by a reduction in expected risk retirements in 2015 . accordingly , operating profit margin is expected to slightly decline from 2014 levels . space systems our space systems business segment is engaged in the research and development , design , engineering and production of satellites , strategic and defensive missile systems and space transportation systems . space systems is also responsible for various classified systems and services in support of vital national security systems . space systems 2019 major programs include the space based infrared system ( sbirs ) , aehf , gps-iii , geostationary operational environmental satellite r-series ( goes-r ) , muos , trident ii d5 fleet ballistic missile ( fbm ) and orion . operating profit for our space systems business segment includes our share of earnings for our investment in ula , which provides expendable launch services to the u.s . government . space systems 2019 operating results included the following ( in millions ) : .

Table: 2014 2013 2012 net sales $ 8065 $ 7958 $ 8347 operating profit 1039 1045 1083 operating margins 12.9% ( 12.9 % ) 13.1% ( 13.1 % ) 13.0% ( 13.0 % ) backlog at year-end $ 18900 $ 20500 $ 18100

2014 compared to 2013 space systems 2019 net sales for 2014 increased $ 107 million , or 1% ( 1 % ) , compared to 2013 . the increase was primarily attributable to higher net sales of approximately $ 340 million for the orion program due to increased volume ( primarily the first unmanned test flight of the orion mpcv ) ; and about $ 145 million for commercial space transportation programs due to launch-related activities . the increases were offset by lower net sales of approximately $ 335 million for government satellite programs due to decreased volume ( primarily aehf , gps-iii and muos ) ; and about $ 45 million for various other programs due to decreased volume . space systems 2019 operating profit for 2014 was comparable to 2013 . operating profit decreased by approximately $ 20 million for government satellite programs due to lower volume ( primarily aehf and gps-iii ) , partially offset by increased risk retirements ( primarily muos ) ; and about $ 20 million due to decreased equity earnings for joint ventures . the decreases were offset by higher operating profit of approximately $ 30 million for the orion program due to increased volume . operating profit was reduced by approximately $ 40 million for charges , net of recoveries , related to the restructuring action announced in november 2013 . adjustments not related to volume , including net profit booking rate adjustments and other matters , were approximately $ 10 million lower for 2014 compared to 2013 . 2013 compared to 2012 space systems 2019 net sales for 2013 decreased $ 389 million , or 5% ( 5 % ) , compared to 2012 . the decrease was primarily attributable to lower net sales of approximately $ 305 million for commercial satellite programs due to fewer deliveries ( zero delivered during 2013 compared to two for 2012 ) ; and about $ 290 million for the orion program due to lower volume . the decreases were partially offset by higher net sales of approximately $ 130 million for government satellite programs due to net increased volume ; and about $ 65 million for strategic and defensive missile programs ( primarily fbm ) due to increased volume and risk retirements . the increase for government satellite programs was primarily attributable to higher volume on aehf and other programs , partially offset by lower volume on goes-r , muos and sbirs programs . space systems 2019 operating profit for 2013 decreased $ 38 million , or 4% ( 4 % ) , compared to 2012 . the decrease was primarily attributable to lower operating profit of approximately $ 50 million for the orion program due to lower volume and risk retirements and about $ 30 million for government satellite programs due to decreased risk retirements , which were partially offset by higher equity earnings from joint ventures of approximately $ 35 million . the decrease in operating profit for government satellite programs was primarily attributable to lower risk retirements for muos , gps iii and other programs , partially offset by higher risk retirements for the sbirs and aehf programs . operating profit for 2013 included about $ 15 million of charges , net of recoveries , related to the november 2013 restructuring plan . adjustments not related to volume , including net profit booking rate adjustments and other matters , were approximately $ 15 million lower for 2013 compared to 2012. .

Question: what was the change in millions in backlog at year-end between 2013 and 2014?
Answer: -1600
Calculation: subtract(18900, 20500)