SpaceX's (News - Alert) attempt to demonstrate a rendezvous and berthing with the International Space Station (ISS) has been put on hold (again). A launch date was set for April 30, but has been postponed for at least a week, apparently due to issues in the software.

"After reviewing our recent progress, it was clear that we needed more time to finish hardware-in-the-loop testing and properly review and follow up on all data," said a SpaceX spokesperson via email. "While it is still possible that we could launch on May 3rd, it would be wise to add a few more days of margin in case things take longer than expected. As a result, our launch is likely to be pushed back by one week, pending coordination with NASA."At about the same time on Monday afternoon, SpaceX founder and CEO Elon Musk (@elonmusk) tweeted the following: "Am pushing launch back approximately a week to do more testing on Dragon docking code. New date pending coordination with NASA"

Spaceflight Now attributes the delay to more detailed software reviews, a perennial problem that seems to have plagued the company. Launch attempts in late 2011 and 2012 were set and then scrubbed due in part to software testing and validating issues.

A new target date has not officially been set, but now SpaceX runs into availability issues at Cape Canaveral and parking coordination at ISS. A U.S. Air Force communications satellite is scheduled to launch on May 3. If there's a delay, this ripples through to SpaceX, since the Air Force needs to reconfigure its systems from the Air Force launch.

May 10 might also be available, but the SpaceX Dragon capsule would have one shot to rendezvous and berth by May 13. A new three-person crew is scheduled to launch from Kazakhstan on May 13. Once the launch occurs, ISS operations shift to preparing for Soyuz docking and crew rotation. 

This would leave Dragon literally "floating around" in orbit while the Soyuz delivers its crew. SpaceX hasn't said how long they can remain in orbit. A second rendezvous attempt hinges on the amount of fuel available for another rendezvous attempt and the overall health of the Dragon vehicle.

This latest news is a glass half-empty or half-full, depending on where you sit. NASA still doesn't have a demonstration flight for COTS/CRS under its belt, and software continues to be the big devil in the details – something Musk should know about, doing that PayPal (News - Alert) thing a while back.   On the other hand, safety and success of the ISS COTS mission are obviously paramount here and SpaceX appears to be in no hurry to launch until every piece of code is just right.