Private Cygnus freighter arrives at the ISS with 4 tons of supplies (photos)

Northrop Grumman's robotic Cygnus freighter reached the International Space Station (ISS) early Tuesday morning (Aug. 6), carrying about 4 tons of supplies to the orbiting lab.

The Cygnus, which launched atop a SpaceX Falcon 9 rocket on Sunday (Aug. 4), was captured by the station's robotic arm on Tuesday at 3:11 a.m. (0711 GMT), as the duo were flying over the South Atlantic Ocean.

The freighter — named the S.S. Richard "Dick" Scobee , after the commander of the tragic STS-51-L mission of the space shuttle Challenger — delivered nearly 8,200 pounds (3,720 kilograms) of food, scientific gear and other supplies to the ISS.

Among the experiments is Rotifer-B2, which will study how spaceflight affects DNA repair mechanisms in the rotifer species Adineta vaga .

"These tiny but complex organisms are known for their ability to withstand harsh conditions, including radiation doses 100 times higher than human cells can survive," NASA officials wrote in a description of the current cargo mission , which is known as NG-21, because it's the 21st ISS flight for a Cygnus vehicle.

Rotifer-B2 "could improve the general understanding of DNA damage and repair mechanisms for applications on Earth," they added.

Related: Facts about Cygnus, Northrop Grumman's cargo ship

— SpaceX launches private Cygnus cargo craft to ISS (video, photos)

— Track the ISS: How and where to see it

— International Space Station — Everything you need to know

The S.S. Richard "Dick" Scobee didn't have a perfectly smooth ride to the ISS. Shortly after deploying from the Falcon 9's upper stage on Sunday, the freighter missed a planned engine burn. The Cygnus then aborted the rescheduled burn 50 minutes later after detecting slightly lower-than-expected pressure readings.

But Northrop Grumman engineers evaluated the data and confirmed that the pressure readings were acceptable after all, NASA officials announced in an update today (Aug. 5) . Cygnus performed two engine burns and got itself on course for its ISS rendezvous.

Editor's note: This story was updated at 3:20 a.m. ET on Aug. 6 with news of Cygnus' arrival at the ISS.