May 26, 1998
"The design and construction of the GP-B probe was an enormous engineering challenge precisely because the experiment to be carried out will be measuring extremely minute changes in the orientation of gyroscopes housed within it," says Gary Reynolds, probe engineer at the ATC. "This was a custom job from start to finish. We had to work hand-in-hand with vendors to acquire the right materials, and we developed new construction methods and engineering processes to meet the very strict demands for this important experiment."
The requirements of the GP-B experiment for stability and freedom from outside forces are extremely demanding. The ATC team has provided Stanford an enclosure within which the scientific instrument can operate at a temperature near absolute zero, and in a pressure that is 10 times lower than the vacuum pressure in space in which the spacecraft will be flying. The magnetic field is less than one millionth of the Earth's magnetic field and the experimental apparatus inside the probe will operate in a very quiet, low acceleration environment.
"GP-B has been very fortunate to have the outstanding team at Lockheed Martin that has developed and built the flight probe," says John Turneaure, Stanford co-principal investigator and hardware manager for GP-B. "The flight probe was designed and built to very demanding requirements for which there was little flight engineering heritage. The delivery of this critical piece of hardware is a big step forward as we proceed to the integration and test of the science payload."
The experimental apparatus, under development at Stanford University, comprises a quartz-block structure, including the reference telescope and four superconducting gyroscopes, all to be enclosed in the heart of the probe -- a cylindrical chamber just 10 inches in diameter and 90 inches long. Eighty-one electrical cables, 85 instrumentation wires and 15 plumbing lines, that together serve to operate and monitor the experiment, had to be painstakingly installed around the inner circumference of the probe to provide a clear line of sight for the reference telescope. Additionally, all had to be custom-designed to operate flawlessly in near-Absolute Zero temperatures for the life of the mission.
The experiment and probe will together reside inside the Science Mission Dewar, a massive thermos bottle, and the key structural component around which the GP-B spacecraft will be built. The dewar also was designed and fabricated at the ATC, and was delivered to Stanford in November 1996. In December 1984, Stanford University selected Lockheed Martin Missiles & Space to build the GP-B payload. Missiles & Space was selected by Stanford and NASA in 1993 to build the GP-B spacecraft.
"Completion of the flight probe is an exceptional engineering achievement and a key milestone for Gravity Probe B," says Rex Geveden, GP-B program manager at NASA Marshall Space Flight Center. "Stanford and Lockheed Martin are to be congratulated for their teamwork and intense efforts."
The Lockheed Martin Missiles & Space Advanced Technology Center (ATC) is a world-class provider of advanced scientific and space technologies, prototypes, and research for physical, electronic, information/computing, materials, engineering, and electro-optical applications. The development of numerous sophisticated systems and programs -- ranging from submarine-launched ballistic missiles to satellite telescopes used to measure solar phenomena -- originated at ATC.
University of Arizona News Services
February 9, 1998
Optical scientists at The University of Arizona in Tucson have successfully polished a 75-pound quartz block that is a critical piece in a science mission to test two remarkable predictions of Albert Einstein's general theory of relativity. The quartz block is for the Gravity Probe B experiment that Stanford University and NASA will fly. The predictions are that massive bodies such as Earth warp space and time, and that such bodies drag space-time with them as they rotate.
Martin J. Valente, manager of the Optical Sciences Optics Laboratory, will deliver the block to scientists from Stanford University and the Naval Research Labs next Thursday, Feb. 12, in Tucson. The block then will be shipped to the W.W. Hansen Experimental Physics Labs at Stanford for integration into the space experiment, in development for launch in 2002.
First conceived 40 years ago, Gravity Probe B is NASA's longest running astrophysical development program.
Valente, UA senior optician Scot Sumner and others from the UA Optics Shop earlier polished and delivered another identical quartz block, the flight backup quartz block for the Gravity Probe B experiment. The experiment will check, very precisely, tiny changes in the direction of spin of four gyroscopes contained in an Earth satellite orbiting at 400-mile altitude directly over the poles. The 22-inch long, 7 1/4-inch diameter quartz block is the stable mechanical structure within which the four, perfectly spherical gyroscope "rotors" will spin. The block will be married to a quartz telescope fabricated by Tucson Optical Research Corp., a Tucson firm owned by Joseph Appels, a scientist formerly with UA Optical Sciences. The quartz block and telescope will be contained in a helium-cooled dewar.
The telescope will point at a distant, seemingly fixed-position reference star, and the gyroscopes will be set spinning with their axes pointed at this object. According to Einstein's theory, a massive body (Earth, in this case) spinning in space would drag space and time around with it. This "frame-dragging effect" should be most noticeable close to the rotating Earth. Researchers will measure the extremely slight change in the direction predicted for the spinning gyroscopes. Scientists predict the change in gyroscope spin during one year will be 42 thousandths of an arc second, or the width of a single human hair seen from a quarter mile away.
The experiment will measure both how space and time are warped by Earth's mass and how Earth's rotation drags space-time around with it.
Stanford awarded UA Optical Sciences the job of polishing the quartz block and its backup twin after two previous polishing attempts at other facilities failed. It took the UA researchers 14 months to grind and polish the blocks to incredibly exacting specifications. The block face to which the telescope will be mounted has been polished to within 2.5 millionths-of-an-inch, peak to valley. The other block faces were polished to a smoothness of 7 millionths-of-an-inch, Valente said.
But the greatest challenge was to hold very tight angular tolerances between faces of the block, Valente said. Sumner had to control extremely small angles between block faces in two planes: Two side surfaces had to be within 5 arc seconds of each other and within one arc second of the front face. (An arc second is one-3,600th of a single angular degree; there are 360 angular degrees in a circle.)
The UA team achieved this precision by measuring angles with a strange-looking, reflective device called an autocollimator and some auxiliary optics called optical squares.
The polishing had to be done by hand because machines are not precise enough. Sumner used polishing tools as small as 1/4-inch in diameter to stroke seemingly imperceptible bumps to smoothness. Temperatures in the lab are kept to within a single degree Fahrenheit during polishing operations.
The fused quartz material used in the blocks presented no unknown challenges to the team, Valente said. Previously, the Optical Sciences Optics Shop had collaborated with UA optical scientist Steven Jacobs in supplying test pieces of the fused quartz material for the Stanford experiment.
Valente's group is currently involved in other spaceborne projects. Given their success with the Gravity Probe B science mission blocks, "I really want to pursue more projects like this," he said. "There is definitely a need out there. Now that we've done this successfully, we realize that we're the ones developing this technology."
Polished Quartz for Gravity Probe B
Senior Optician Scot Sumner of the UA Optical Sciences Center in Tucson gently lowers the quartz block for Gravity B Probe into its padded shipping box. Gravity B Probe, being developed by Stanford University and NASA for launch in 2002, will test predictions about space and time postulated 80 years ago by Einstein in his Theory of Relativity. Sumner hand polished the quartz block, as well an identical, flight backup block to incredibly exacting specifications. Two previous polishing attempts at facilities elsewhere failed. Demand for UA optics fabricating and finishing expertise for spaceborne as well as ground based projects is growing.