SpaceX Capsule to Deliver New Parking Spot for Space Station

Besides food and experiments, the Dragon cargo ship ordered up by NASA holds a new docking port, or parking place, for future commercial crew capsules.

Liftoff is scheduled for 10:21 a.m. Sunday. Good flying weather is forecast for SpaceX's unmanned Falcon rocket.

This shipment is especially critical because the space station has lost two deliveries since fall.

A Russian supply ship spun out of control shortly after liftoff in April and burned up on re-entry with all its contents. In October, an Orbital Sciences Corp. cargo carrier was destroyed in a Virginia launch explosion.

Once again, SpaceX is picking up the slack. This will be the eighth station supply run for the California-based company; the first was in 2012.

"Dragon has been super reliable," SpaceX's Hans Koenigsmann told reporters Friday.

Nearly 5,300 pounds of gear is packed for the trip, including replacements for science experiments lost in the Orbital launch accident, some of them designed by students.

Stored in the capsule's unpressurized trunk is the first of two new docking rings for the station. Spacewalking astronauts will hook up the 1,160-pound port built by Boeing later this summer.

The twin ports eventually will be used by astronauts arriving in new American-built capsules. NASA is paying billions of dollars to SpaceX and Boeing to develop the crew capsules. The SpaceX version is a souped-up Dragon. Boeing's model is the CST-100, short for Crew Space Transportation; the 100 represents the beginning of space at 62 miles up, or 100 kilometers.

Here’s why I think there will be a successful landing tomorrow:

From The why and how of landing rockets.

http://www.spacex.com/news/2015/06/24/why-and-how-landing-rockets

A description of the last landing attempt and what went wrong:

Last-second tilt aside, the landing attempt happened pretty much exactly as planned. Shortly after stage separation (when the second stage leaves the first stage behind and goes on to carry Dragon to orbit), cold gas thrusters fired to flip the stage to reorient it for reentry. Then, three engines lit for a “boostback burn” that slows the rocket and brings it toward the landing site.

The engines then re-lit to slow the stage for reentry through Earth’s atmosphere, and grid fins (this time with much more hydraulic fluid) extended to steer the lift produced by the stage. Our atmosphere is like molasses to an object traveling at Mach 4, and the grid fins are essential for landing with precision. The final landing burn ignited, and together the grid fins, cold gas thrusters and steerable engines controlled the vehicle, keeping the stage within 15 meters of its target trajectory throughout the landing burn. The vehicle’s legs deployed just before it reached our drone ship, “Just Read the Instructions”, where the stage landed within 10 meters of the target, albeit a bit too hard to stay upright. Post-launch analysis has confirmed the throttle valve as the sole cause of this hard landing. The team has made changes to help prevent, and be able to rapidly recover from, similar issues for the next attempt, which will be on our next launch—the eighth Falcon 9 and Dragon cargo mission to the space station, currently scheduled for this Sunday.

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