One of the launches we’ve been expecting for a while now is CRS-25, SpaceX’s latest resupply mission to the International Space Station (ISS). CRS-25 was originally slated to launch on June 10 but was delayed first to July 10 and then later. As of recording this episode, it is expected to launch during our hiatus at 00:44 UTC on July 15. The drone ship left Port Canaveral several days ago to catch the first stage.
The cause of the month-long delay was a leak in the valves that control propellant flow to the spacecraft’s Draco thrusters. The leak was detected during the pre-launch fueling of the system. Monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) can cause degradation of different components if exposed, so to be extra careful, SpaceX replaced several components, including the affected valves and the spacecraft’s parachutes.
Once in orbit, CRS-25 will take its usual two days to reach the ISS, docking to the zenith or space-facing port on Node 2 of the ISS. Then the astronauts of Expedition 67 will unload over 2.6 metric tons of cargo from onboard the Dragon and its trunk.
The largest single experiment by mass is EMIT or Earth Surface Mineral Dust Source Investigation. This large experiment is located in the trunk and will be removed by the Canadarm and mounted on the outside of the station. EMIT will study the composition of different mineral dust – sand basically – that is blown into the air to get a better understanding of the effects on the climate.
For example, massive dust storms blowing off of the Sahara and traveling west across the Atlantic, deposit dust on the U.S. and affect the chance of storms and air quality. Generally, darker particles will cause warming, and lighter particles cause cooling. The precise mix of particles is not well known, and EMIT will use its imaging spectrometer to provide data for further analysis.
CRS-25 will also carry five CubeSats for deployment from the ISS. You can read about those satellites and the rest of the experiments at a link in our show notes.
NASA press release