Countdown Meets Perfect Storm
|Florida radar of cloud patterns during the planned MESSENGER launch on early Monday morning
"We are scrubbing for the night," announced the flight controller of Monday’s planned MESSENGER launch from Cape Canaveral, Florida. "We have two weather violations."
The next attempt for this first orbital mission to the inner planet Mercury would be at 2:15:56 AM EDT on Tuesday morning, if a twenty-four hour turnaround is possible.
The weather team forecasts the probability of favorable Tuesday weather as remaining at thirty-percent, just as what was the chance for the Monday launch when tropical storms still covered the northeast part of Florida radar maps.
The launch window for the Mercury-bound mission is what planners call an ‘instantaneous’, meaning that a mere 12 seconds is available to get the Delta rocket off the pad.
Getting to Mercury is considered a complex event to time for launch planners owing to greater than six flybys of Earth, Venus and finally Mercury. These close approaches are gravity assists to slow-down the relative motion of MESSENGER in preparation for orbit. To get to the inner planet, a successful probe has to brake most of the way inwards. This roundabout trajectory also extends the mission time and fuel requirements.
When fully fueled, MESSENGER carries fifty-five percent fuel, which is the same proportion needed by the much larger Cassini probe that travelled a billion miles to Saturn. The MESSENGER trajectory will not enter orbit of Mercury until 2011 because of this roundabout tour. The Mercury probe will travel a circuitous five billion miles before entering a year-long orbit of the innermost planet.
|Flight controllers reach a countdown hold with only 4 minutes left before scrubbing for the day
Residuals of tropical storm Alex still hung around the launch pad as the rocket powered up inside of 4 minutes to take-off. Alex is the first of the season and has hovered over the Florida, Georgia and South Carolina coast most of the week. While weather had threatened the Florida coast earlier in the afternoon, the early morning hours appeared to break and a lone ‘anvil-shaped’ cloud drifted across the east coast. This type of cloud formation breaks off of larger storms in a highly charged state prone to discharging lightning. Lightning yielding clouds must be at least one-hour away to satisfy Cape Canaveral’s launch rules.
The spring and summer weather patterns over Florida begin with cloud formation on the west coast, then drifting patterns like this anvil can violate launch rules and scrub activities at Cape Canaveral. The most dramatic example of such weather risks was the 1969 launch of Apollo 12 to the moon (see banner image).
|MESSENGER held in the nosecone while gaseous oxygen vents from the lower stages.
Seconds after launch, the hearts of Apollo 12 ground controllers skipped a beat when a lightning bolt hit the Saturn V rocket and jolted its electrical circuitry. The enormous rocket –comparable to the size of an aircraft carrier –passed through the storm and reset its ground communication. Since Apollo 12 strict weather rules govern tracking of potentially charged cloud patterns.
Next steps for MESSENGER’s launch operators will be to drain the liquid oxygen from the first stage of the Delta rocket. Tomorrow’s weather during the day is expected to remain dominated by tropical storm Alex, but should allow launch workers to ready the mission to Mercury back to following its standard countdown.
Three decades ago, the last mission to Mercury was a flyby, Mariner 10. About half of the global map of Mercury, a relatively nearby planet, is still unknown to scientists partly because of the difficult planning required to get so close to the Sun. New materials and better navigation methods now have presented and lighter mission profile and the new orbital mission was prioritized as part of NASA’s Discovery program.
"A mission to Mercury…is our closest model to what happens during planet formation around a star," said Sean Solomon, MESSENGER Principal Investigator . "It is about how to make a planet."