More than a month since its arrival, SpaceX’s CRS-18 Dragon cargo ship departed the International Space Station (ISS) and returned to Earth earlier today (Tuesday), bringing around 2,700 pounds (1,225 kg) of experiments and payloads back home and into the hands of eager research teams. The Dragon was released by the station’s 57.7-foot-long (17.6-meter) Canadarm2 robotic arm at 10:59 a.m. EDT, whilst flying 256 miles (412 km) over the Pacific Ocean. At the controls of Canadarm2 was Robotics Officer (ROBO) David Gruntz in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, whilst Expedition 60 astronaut Christina Koch provided monitoring of Dragon’s departure from her perch in the space station’s multi-windowed cupola. A few hours later, Dragon performed an on-time de-orbit maneuver and splashed down in the Pacific Ocean at 1:21 p.m. PDT (4:21 p.m. EDT), some 300 miles (480 km) southwest of Long Beach, Calif.
Launched on 25 July, CRS-18 is the 18th dedicated Dragon cargo mission executed under the terms of the Commercial Resupply Services agreement with NASA. These contracts were signed back in December 2008 and initially called for 12 Dragon missions to the ISS, ferrying up to 44,000 pounds (20,000 kg) of payloads and supplies. Three additional flights were secured in early 2015, followed by five more in the spring of 2016, which will see the CRS1 first round close out with the CRS-20 Dragon, currently scheduled to launch in March 2020. These “additional” Dragons—of which today’s CRS-18 is one—will bridge the gap before the second-round CRS2 contracts kick off next summer.
As the first Dragon cargo ship to fly a third mission, the vehicle being used for CRS-18 has now become the first to log almost 100 cumulative days in space. First flown on CRS-6 in April 2015 and again on CRS-13 in December 2017, all told this particular Dragon has logged more than 90 days berthed at the ISS over its career to date. Across those three missions, the venerable Dragon has delivered a combined 14,345 pounds (6,532 kg) of payloads and supplies to successive ISS crews and has returned a grand total of 9,800 pounds (4,450 kg) of scientific samples back to Earth.
In pride of place aboard CRS-18’s unpressurized trunk was the second Boeing-built International Docking Adapter (IDA-3), which was installed earlier this month onto Pressurized Mating Adapter (PMA)-3 atop the Harmony node to provide a backup interface for Commercial Crew vehicles. In co-ordination with ISS robotics, Expedition 60 spacewalkers Nick Hague and Drew Morgan labored in pressurized suits on 21 August to hook up electrical and data cables between IDA-3 and its new home on the station.
With the first piloted test flights of both Commercial Crew vehicles—SpaceX’s Crew Dragon and Boeing’s CST-100 Starliner—tentatively slated to occur before year’s end, it remains to be seen which of the two (if either) will be first to utilize the IDA-3 interface. But one thing is certain: if regular Commercial Crew operations are underway by 2020, IDA-3 should not remain idle for too long.
Returning home aboard CRS-18 today were results and samples from several key research investigations. These include Biorock, which seeks to understand the physical interactions of liquids, rocks and micro-organisms and carries applications for future space mining activities. The biofilms used in the investigation were incubated aboard the ISS, then photographed and placed into cold storage prior to its return to Earth. The samples will be handed over to the Biorock principal investigator’s team at Long Beach airport later today for post-landing fixation and subsequent analysis.
Also aboard Dragon were specimens of Physcomitrela patens—spreading earth-moss—which were being flown as part of ongoing studies of the growth, development, gene expression and photosynthetic activity of tiny, rootless plants which might someday be of use on lunar or Martian bases. And Goodyear Tire’s much-publicized experiment to understand the formation of silica fillers in microgravity will return rubber samples to Earth for analysis. Such experiments may help future applications to develop better-performing tire technologies.
After being robotically detached from Harmony by ground commanding early Tuesday, the CRS-18 spacecraft was positioned in its ready-to-depart orientation, with the departure window due to open at 10:59 a.m. EDT. Right on time, Mr. Gruntz commanded the opening of Canadarm2’s wire snares and Dragon departed smoothly and crisply into the inky blackness.
Over the next quarter-hour, the spacecraft performed three separation “burns” to depart the vicinity of the ISS. “We are very appreciative of a successful Dragon mission,” radioed Christina Koch at the completion of today’s operation, then expressed a fervent hope that more Dragons would follow in its footsteps. Indeed, current plans call for CRS-19 in December to transport Japan’s Hyperspectral Imager Suite (HISUI) remote-sensing instrument to the station, after which CRS-20 in March of next year will bring uphill the Bartolomeo commercial payloads anchor for the European Space Agency (ESA) to be installed onto the Columbus lab.