实测阶段进入第4周的时候，3号陀螺出现故障而进入安全（保护）模式。实验必须在10个时间内完成，否则引力探测器上的氦气将泄露完而不能继续。

GRAVITY PROBE B MISSION UPDATE

GP-B had an eventful week. We began the 4th week of science with all four gyroscopes in the science mode. Then on Thursday we had an anomaly with gyro #3.

At 830 PM local time on Thursday, the drag-free gyro #3 transitioned to analog mode resulting in safemode that stopped the timeline. The GP-B vehicle and science gyros were safe. Gyro's #1, #2 and #4 remained in the digital suspension science mode. A preliminary assessment by the science team indicated minimal impact to any experiment accuracy. An investigation is under way to determine the cause of the drag-free gyro #3 transition to analog mode and safemode activation. The operations and engineering teams did an excellent job working through the night to safe the vehicle and quickly develop a recovery plan.

By Friday afternoon the spacecraft was back in science collecting mode with gyro #1 performing the drag free operation. On Saturday the operations team successfully transitioned Gyro #3 from analog suspension to the digital suspension science mode. All other spacecraft systems are in excellent health. The spacecraft is rolling at a rate of 0.775 rpm (one revolution every 77.5 seconds). The Attitude and Translation Control (ATC) system is maintaining a drag-free orbit around gyro #1, and it is properly tracking the guide star, IM Pegasi. The Dewar temperature is nominal (1.82 Kelvin), and the flow of helium, venting from the Dewar through the micro thrusters has remained within expected limits.

During the week the team performed a heat pulse test on the spacecraft Dewar to obtain further information to help predict lifetime. Early indications are that the helium in the Dewar will last another 10 months, which should be sufficient to satisfy the mission requirements.