|This article contains information about a rocket launch which is scheduled to occur in the next 9 hours.
Details may change rapidly as the countdown and ascent progress.
Artist rendering of the SpaceX Dragon spacecraft being berthed to ISS
|Mission type||ISS resupply|
|Start of mission|
|Launch date||20 September 2014 (planned)|
|Rocket||Falcon 9 v1.1|
|Launch site||Cape Canaveral SLC-40|
|Berthing at ISS|
|Berthing port||Harmony nadir|
SpaceX CRS-4, also known as SpX-4, is a cargo resupply mission to the International Space Station, contracted to NASA, and is currently manifested for launch on September 20, 2014. It will be the sixth flight for SpaceX's uncrewed Dragon cargo spacecraft, and the fourth SpaceX operational mission contracted to NASA under a Commercial Resupply Services contract. The mission will bring equipment and supplies to the space station, including the first 3D printer to be tested in space, and small satelites to be launched from the station.
NASA has contracted for the CRS-4 mission and therefore determines the primary payload, date/time of launch, and target orbital parameters. Among other NASA cargo, the ISS-RapidScat, a Scatterometer that will support weather forecasting, will be launched as an external payload to be attached on the end of the station's Columbus laboratory. Also CRS-4 will include the Space Station Integrated Kinetic Launcher for Orbital Payload Systems (SSIKLOPS). This launcher will provide still another means to release other small satellites from the ISS. SpaceX CRS-4 also will carry a new permanent life science research facility to the station. The Bone Densitometer (BD) payload, developed by Techshot, will provide a bone density scanning capability on ISS for utilization by NASA and the Center for the Advancement of Science in Space (CASIS). The system measures bone mineral density (and lean and fat tissue) in mice using Dual-Energy X-ray Absorptiometry (DEXA). 
SpaceX has the primary control over manifesting, scheduling and loading secondary payloads. However there are certain restrictions included in their contract with NASA that preclude specified hazards on the secondary payloads, and also require contract-specified probabilities of success and safety margins for any SpaceX reboosts of the secondary satellites once the Falcon 9 second stage has achieved its initial low-Earth orbit (LEO).
The CRS-4 mission will carry the 3D Printing in Zero-G Experiment to the ISS, as well as two small satellites as secondary payloads that will be deployed from the ISS: Arkyd-3 and SPINSAT.
3D Printing in Zero-G Experiment
The 3D Printing in Zero-G Experiment will demonstrate the use of 3D printing technology in space. 3D printing works by the process of extruding streams of heated material (plastic, metal, etc.) and building a three-dimensional structure layer-upon-layer. The 3D Printing in Zero-G Experiment will test the 3D printer specifically designed for microgravity, by Made In Space, Inc., of Mountain View, California. Made In Space’s customized 3D printer will be the first device to manufacture parts away from planet Earth. The 3D Printing in Zero-G Experiment will validate the capability of additive manufacturing in zero-gravity. This experiment on the International Space Station is the first step towards establishing an on-demand machine shop in space, a critical enabling component for deep-space crewed missions and in-space manufacturing.
Planetary Resources has packaged a number of the non-optical satellite technologies of its larger Arkyd-100 telescope satellite—essentially the entire base of the Arkyd-100 satellite model revealed in January 2013, but without the space telescope—into a "cost-effective box" of 'Arkyd 3, or A3, for early in-space flight testing as a subscale nanosatellite. The Arkyd 3 testbed satellite will be packaged in a 3U CubeSat form-factor of 10×10×30 centimetres (0.33×0.33×0.98 ft). The company has contracted with NanoRacks to take the A3 to the ISS where it will be released from the airlock in the Kibo module.
The subsystems to be tested include the avionics, attitude determination and control system (both sensors and actuators), and integrated propulsion system that will enable proximity operations for the Arkyd line of prospectors in the future.
SPINSAT will also be a technology demonstrator for electric solid propellant (ESP) thrusters from Digital Solid State Propulsion (DSSP). DSSP's technology utilizes electric propulsion to enable small satellites to make orbital maneuvers that have generally not been possible in the very small, mass-constrained satellites such as CubeSats and nanosats. This will be DSSP's first flight and will be deployed from the Kibo module airlock. NASA safety experts approved the mission—which by its nature must start with the satellite inside the habitable volume of the ISS—because the satellite's 12 thruster-clusters burn an inert solid fuel, and then only when an electric charge is passed across it.
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