As SpaceX prepared to launch its first commercial resupply mission to the International Space Station in October 2012, there was a rather curious aspect about the mission. While the Dragon spacecraft was advertised as being able to carry 3,310 kg of cargo, the ship was only loaded with 450 kg of cargo — less than 14 percent of maximum capacity.

SpaceX and NASA, which was paying for the flight, had an answer for that question at a press conference on the day before the Oct. 7 launch.

However, both NASA and SpaceX attributed the low mass to the selection of cargo it’s carrying. “The cargo up that we’re taking is not quite as dense as some of the cargo that we will be taking on successive missions,” said SpaceX president Gwynne Shotwell at a pre-launch press conference on Saturday. She added that SpaceX’s CRS contract with NASA requires it to carry at least 20 metric tons of cargo to the station over 12 flights; she estimates that SpaceX will carry a combined 60 metric tons up to and down from the station on those missions.

This answer does not appear to be entirely correct, however. Yes, the flight certainly carried cargo with less mass; however, the shortfall had nothing to do with the bulkiness of the equipment and supplies being sent up. Instead, it reflected the limitations of the SpaceX’s booster and supply ship at that time.

A NASA Inspector General report published in June found

The first two missions carried smaller loads because the empty cargo vehicles were heavier than expected and the Falcon 9 rocket did not meet its planned lift capability. SpaceX has since addressed both of these issues with an upgrade to its Falcon 9 rocket.

With the exception of SpaceX’s first two missions (SPX-1 and SPX-2), which delivered 450 kg and 865 kg to the ISS, respectively, NASA has generally loaded Dragon 1’s pressurized module to its volumetric limit.

The small cargo loads on the first two flights put SpaceX behind on its contractual obligation to fly up to 20 metric tons of cargo to the space station, although the company later reached that total on the eighth flight. The loss of the seventh resupply mission in June 2015 when its Falcon 9 rocket exploded in flight destroyed 2,478 kg of cargo worth $118 million. Under its contract with SpaceX, NASA must pay for the replacement and re-flight of that cargo.

NASA and SpaceX also experienced mass shortfalls on other Dragon flights due to limits packing limitations and a shortage of cargo for the spacecraft’s unpressurized trunk. SpaceX has become better at packing the Dragon with supplies. The shortage of equipment for the truck also has been addressed.

NASA has extended SpaceX’s Commercial Resupply Services 1 (CRS-1) contract, ordering eight more flights for a total of 20. The contract also has been extended until the CRS-2 take effect in 2019.

SpaceX and Orbital Sciences Corporation (now Orbital ATK) were awarded CRS-1 contracts. NASA awarded CRS-2 contracts to both companies and Sierra Nevada Corporation that run from 2019 to 2014.

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