MAXIMA II - Spring 1999

The National Scientific Balloon Facility at Palestine, Texas

Hoisting the Receiver : 5/14/99

The MAXIMA 2 field campaign began officially on April 22, 1999. Adrian, Brad, Bahman, and Celeste, with the much appreciated help of the NSBF riggers, unloaded all the MAXIMA hardware from a 48' rig that made the trek from Berkeley in under 60 hours.

After setting up lab in the High Bay, we reassembled the various components of the experiment. Brad and Bahman completed the structural assembly of the gondola . Shaul and Brad wired up the Data Acquisition System (DAS). Bahman wired up the various sensors in the Attitude Control System (ACS). Adrian re-tuned the primary mirror chopper.

The receiver required the most attention. We learned in Berkeley that we could significantly minimize the receiver sensitivity to Radio Frequency Interference (RFI) by installing surface mount LC filters on the wires entering the bolometer cavities. Everyone participated in the painstaking task of rewiring all bolometers. We were happy to learn in subsequent tests that these radical efforts did not compromise any of our detectors!

By early May, we were ready to begin receiver tests. We inserted the detector array in the cryostat , buttoned up the various shells, then cooled the receiver down to 100 mK (all in all, a 3 day process). Once "cold", we performed various diagnostics: we measured the cryogenic hold-times of the various refridgeration stages in the cryostat, we determined the optical responsivity of our 16 optical channels, we investigated spectral leaks in all optical channels with the use of switchable thick-grill high pass filters, we measured the RF sensitivity of all bolometers with a many-Gigahertz output RF sweeper, and we investigated detector noise.

Meanwhile, we continued to work on the gondola. We cover the gondola with almuminzed foam (Celotex (tm)) baffles, which shield the receiver from RF and from hot sources, like the sun, earth, and moon, during flight. We are also incorporating NSBF transmitters and receivers on the paylod, which enable us to send commands to and receive data from the experiment during flight.

Between keeping the cryostat cold and finishing these preparations, there's just enough time to stop and smell the flowers.

On May 14, we installed the receiver in the gondola. We did a rough alignment of the primary mirror and the receiver. We determined the beam patterns of all detectors by measuring each bolometer's response as a function of azimuth and elevation to a signal emitted by our artificial planet.

On June 2, we calibrated the magnetometer, which is our azimuth sensor in flight. The magnetometer measures the relative strength of the eartg's magnetic field, and thus must be calibrated in magnetically clean environment. Marty, the rigger, drove the gondola outdoors on the forklift to the A-frame (which is made largely of wood). After calibrating the magnetometer, we observed Polaris and Venus through the CCD cameras.

On June 6, we measured the sidelobe response of the receiver. This entails measuring the bolometers' response to a 150 GHz chopped source as a function of the source's angular position. We mounted the source to the top of the NSBF cherry picker, which allowed us great flexibility in positioning the source above the experiment. Here's Brad's view of the gondola.

We need to carry this measurement in a reflection-free environment. We drove the payload and the cherry picker out to the launch-pad, and measured the near and far sidelobe response as a function of azimuth and elevation. Here's a nice picture of the set-up. Here's Bahman recording a measurement. Brad spent 4 hours in the cherry picker that afternoon. Here are some cool views from the cherry picker.

The MAXIMA 2 flight may extend into daytime hours. Paul and Brad paint the gondola with optically reflective white paint, which will keep the payload from heating up after sunrise.

On June 16, 1999, at 7:30 P.M. Central Time, the MAXIMA 2 payload was succesfully launched. The scientific team proudly stands below the payload right before launch.

Given the variabilty of East Texas weather in the spring, a launch attempt can be cancelled at any given moment. In 1998, the MAXIMA I campaign was prolonged for two months given El Ni~no (this is the truth!). MAXIMA II proved much luckier: we launched within one week of being "flight ready". The moment the balloon box is opened and the balloon is rolled out onto the launch pad, the scientific team can breath a sigh of relief: the launch is imminent.

Pre-launch activities send everyone in a fury. The scientific team must cycle and replenish all cryogenics, engage battery power, position telemetry antennaes, uncover optics, and complete the gondola baffling. The NSBF riggers attach ballast and crush padding to the gondola, rig the flight line, set-up and inflate the balloon. The NSBF Electronics staff, in coordination with the scientists, test all telemtry-related systems. The NSBF weather staff are on standby, keeping Operations informed of last-minute weather changes. At 7 PM, all activies come to a screeching halt; the payload is ready for launch.

At 7:30 PM, the balloon is released from its tether. A crane-operator maneuvers Tiny Tim under the ascending balloon so that the flight line is absolutely vertical when the payload is released from the crane's jaws. This entire operation takes no more than a minute. Observers on the ground can maintain visual contact with the payload for the next hour as it slowly ascends over Palestine.

The balloon achieved float altitude (125,000 ft.) roughly 3 hours after launch. During the 12 hour duration of the flight, the scientific team and NSBF Operations succesfully maneuvered the payload through its observations. The MAXIMA 2 data includes 6 hours of fully cross-linked CMB scans, an observation of Mars, and a measurement of the CMB dipole. The Mars and dipole observations provide calibration for the detector response and beam-size.

Once the payload leaves telemetry range (350 miles from Palestine; usually near Midland/Odessa, TX), the flight is terminated. The payload is cut-down from the balloon via command sent from aircraft. The payload free-falls until there is enough atmospere to engage the parachute. The payload then drifts to the ground. Once aircraft establishes visual contact with the payload on the ground, another command is sent to disengage the parachute.

While most of Operations remain in Palestine during the night, a recovery team of riggers and scientists pursue the payload by land vehicles. After a long night's drive, they must get to work clearing the payload, parachute, and balloon from the landing site. The surreal quality of this activity is heightened by the West Texas landscape.

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