NASA and United Launch Alliance, builder of the RBSP mission's Atlas 5 booster, hope to make another attempt Saturday at 4:07 a.m. EDT (GMT-4), the opening of a 20-minute launch window, assuming the transponder issue can be resolved in time.
The preliminary forecast called for a 60 percent chance of acceptable weather Saturday, with scattered clouds at 2,000 and 22,000 feet, isolated coastal showers and winds gusting to 16 mph.
Today's countdown proceeded smoothly until the final few minutes.
"Toward the end of the countdown we did get a reading that the C-band tracking beacon on the launch vehicle, the frequency of that C-band tracking beacon, was drifting from the range systems that are picking that up," said launch director Tim Dunn. "Now that's a mandatory safety item so we can track the vehicle in flight.
"With our very limited window, we did not have enough time to evaluate the cause and if we were OK. The reason that C-band beacon is so important is in flight, we really only have a few tracking sources. We can skin track with the radar, we can track the telemetry coming back from the launch vehicle, we have optical tracking and then we have this C-band beacon. If we were to lose one of these mandatories, we would be down into a situation where it might not be acceptable to pass through certain times of flight, such as staging events.
The launch team, Dunn said, decided "to err on the side of conservatism. Tomorrow or the day after are fine days to launch. We've tentatively set up for a 24-hour recycle ... however, we do need to clear this issue."
Engineers did not immediately know if the problem was an issue "we can live with, was it the range equipment that was giving erroneous readings or was it truly the launch vehicle C-band transmitter that had an anomaly," Dunn said. "If that's the case, we may have to access the launch vehicle and change out that piece of hardware."
Replacing the transponder would require rolling the rocket back to its processing building, likely delaying launch to early next week.