Gravity Probe B Mid Way Through Orbit Checkout

TECH SPACE

Gravity Probe B's orbit

Los Angeles (JPL) May 31, 2004
At five weeks past launch, the Gravity Probe B mission is now about half way through the Initialization and Orbit Checkout (IOC) phase of the mission. Thus far, the team has successfully transmitted over 5,000 commands to the spacecraft, which remains healthy on orbit. All spacecraft subsystems are continuing to perform well.

The spacecraft's orbit is stable, meeting our requirements for next month's transition into the science phase of the mission. All four gyros are now digitally suspended, and the team is in the process of locking the on-board telescope onto the guide star, I'm Pegasi.

This past week, the team began spinning up the gyros. During this complex and delicate process, which spans the entire second half of IOC, each of the four gyros undergoes a series of spin-up and testing sequences, the first of which gets the gyros spinning-but at a very slow speed.

Because the correctperformance of the gyros is critical to the success of the experiment, theteam is proceeding through the spin-up process slowly, painstakingly monitoring and checking the performance of the gyros throughout the process.

In preparation for spin-up, the digital suspension system for each gyro was first tested. This was accomplished by suspending each gyro in the center of its housing, electrically "nudging" it slightly off center in one of eight directions (the corners of a cube), and monitoring its automatic re-centering. This checkout was first performed under low voltage conditions (fine control) and then under high voltage conditions (secure hold).

To begin the actual spin-up process, ultra-pure helium gas was flowed over gyros #1 and #4 for 15 seconds, which started them spinning at approximately 0.125 Hz (7.5 rpm). While these gyros were slowly spinning, the suspension test was repeated under high voltage conditions on gyros #2 and #3.

Duringthis high voltage suspension test on gyro #3, the team discovered an errorin its command template, which turned off the high voltage amplifier to gyro #1 and caused it to lose suspension. There was no damage to gyro#1.

More than 1,000 commands have now been sent to the Gyro Suspension System (GSS), and this was the first error found. Discovering an error in these numerous, intricate command templates was exactly the kind of situation that the painstaking gyro spin-up process was designed to identify; it enabled the team to correct the command template for gyro #2 without serious consequences.

Also, as a further precaution, the team has thoroughly reviewed the command templates for the remaining three gyros. Gyros #2 and #3 have now been spun-up to 0.26 Hz (15 rpm) and 0.125 Hz (7.5 rpm) respectively without incident, and gyro #1 is currently being spun-up, as well.

Over the past week, much progress has been made towards the goal of locking the spacecraft's on-board telescope onto the guide star. The pointing error of the spacecraft has been reduced to within 385 arc-seconds (0.11 degrees). This allows the on-board telescope to see the guide star over a portion of a spacecraft roll cycle.

The team is in the process of fine-tuning the spacecraft's attitude by adjusting the navigational gyroscope in the Attitude and Translation Control (ATC) system, so that the telescope will be able to see the guide star throughout the entire spacecraft roll cycle, and the team hopes to lock onto the guide star by the beginning of next week.

TECH SPACE

Gravity Probe B Rollout Continues

Stanford - May 10, 2004
As of Mission Day #17, the Gravity Probe B spacecraft continues to perform well, and we are expecting a smooth and successful transition into the science phase of the mission.

Thanks for being here; We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain. With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords. Our news coverage takes time and effort to publish 365 days a year. If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor $5 Billed Once credit card or paypal		SpaceDaily Monthly Supporter $5 Billed Monthly paypal only

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.