As the Rutgers team battled winter storm Jonas over the weekend, Challenger managed to fight her way through to some favorable currents to the east. The two models we use for piloting showed two eddies spinning in opposite directions just ahead of the glider, but as 29 approached, the currents reported began to resemble the eddy shown by Copernicus. The following images are the forecast for Copernicus (top) and RTOFS (bottom).
Since we will resume following Copernicus, the waypoint was pushed further east to 34˚30S 9˚E to take advantage of the bottom portion of this counter clockwise spinning warm eddy. With the boost from this string of eddies, the glider has returned to speeds of 20 km/day for the first time since the underwater reset and the steering issues started a few weeks ago.
As for the condition of the glider itself, power is back up to about 2.5 AH/day meaning we have about 125 days of power. The increased power is a combination of repeat call in and the tuning we are doing for the gliders flight parameters.
Our big problem right now is steering. We are in a minimum of the horizontal component of the earths magnetic field, which is located just west of South Africa. This could be a contributing factor. But our bigger fear is biofouling. The steering issues came on suddenly. For the initial months of the mission, we had excellent steering, with less than 5 degrees rms error. Around December we made a jump to about 15 degrees rms error. Then last week we made an even more sudden jump to about 50 degrees rms error and our speed made good towards Cape Town plummeted to 10 km/day. If this is biofouling, it usually effects the vertical speed, slowing us down, reducing the flow over the rudder, and we loose steering. So the fix is to increase vertical speed, but we don’t want to loose our sweet spot on the pump. So we are starting with adjustments to pitch.
We have been flying descents at 26 degrees and ascents at 22 degrees pitch. The 22 degrees helps us squeeze out a little more horizontal distance on each ascent, but it means a slower ascent. So we switched the pitch back to our standard 26 degrees for the full yo. Over the weekend we flew a couple of segments at our standard pitch to establish a baseline of performance to compare to testing done throughout the week. Meanwhile we will set up for a new series of steering diagnostics to be sent back with the science data files every surfacing.
As it looks now, if we can maintain this speed as we steer through the eddies ahead, we are still look at about 70 more days making our approach towards Cape Town.
Force Wind Sea & Honor