WASHINGTON — Laden with 1,615 kilograms of trash from the international space station, Orbital Sciences Corp.’s uncrewed Cygnus space freighter completed a planned destructive reentry into Earth’s atmosphere Aug. 17, marking the end of the second of eight cargo delivery-and-disposal missions the Dulles, Virginia, company owes NASA under its $1.9 billion Commercial Resupply Services contract.

Cygnus decoupled from station Aug. 15 after a 31-day stay, Orbital said in an Aug. 18 press release. It reentered the atmosphere east of New Zealand at approximately 9:15 a.m. Eastern time Aug. 17. Cygnus was launched July 13 by Orbital’s Antares rocket from the Mid-Atlantic Regional Spaceport at NASA’s Wallops Flight Facility in Virginia.

In two missions, Orbital has delivered 4,793 kilograms of cargo to the station, 1,664 kilograms of which went up on the mission just completed, according to the company’s website. Orbital’s Commercial Resupply Services contract, which was signed in 2008 and helped pay for development of Cygnus and Antares, calls for delivery of 20,000 kilograms of cargo by 2017.

The two-stage Antares combines a Ukrainian-built core stage powered by Russian-made engines refurbished by Aerojet Rocketdyne of Sacramento, California, with a solid-fueled upper stage provided by the company Orbital is in the process of merging with, ATK of Magna, Utah.

For its third paid cargo mission to station, slated to launch Oct. 21, Orbital will replace the ATK Castor 30B Antares used for its latest launch with an ATK Castor 30XL. The upgrade will allow Cygnus to carry about 2,290 kilograms of cargo to station — an increase of nearly 40 percent by mass, compared with the second mission, according to Orbital’s Aug. 18 press release.

The Castor 30XL is the latest in the Castor 30 series ATK developed specifically as an Antares upper stage. A pair of Antares demonstration launches in 2013, which did not count toward fulfilling the company’s delivery-and-disposal contract with NASA, used the Castor 30A. ATK has lengthened subsequent versions of the motor, squeezing more power out of it by packing it full of more solid fuel.