Was Einstein right? Scientists provide first public peek at Gravity Probe B results (Forwarded)

News Service
Stanford University
Stanford, California

Contact:
Bob Kahn, Stanford Gravity Probe B
(650) 723-2540

Buddy Nelson, Lockheed Martin
(510) 797-0349

Comment:
Francis Everitt, GP-B Principal Investigator
(650) 725-4104

April 14, 2007

Was Einstein right? Scientists provide first public peek at Gravity Probe
B results
BY Bob Kahn

For the past three years a satellite has circled the Earth, collecting
data to determine whether two predictions of Albert Einstein's general
theory of relativity are correct. Today, at the American Physical Society
(APS) meeting in Jacksonville, Fla., Professor Francis Everitt, a Stanford
University physicist and principal investigator of the Gravity Probe B
(GP-B) Relativity Mission, a collaboration of Stanford, NASA and Lockheed
Martin, will provide the first public peek at data that will reveal
whether Einstein's theory has been confirmed by the most sophisticated
orbiting laboratory ever created.

"Gravity Probe B has been a great scientific adventure for all of us, and
we are grateful to NASA for its long history of support," Everitt said.
"My colleagues and I will be presenting the first results today and
tomorrow. It's fascinating to be able to watch the Einstein warping of
space-time directly in the tilting of these GP-B gyroscopes -- more than a
million times better than the best inertial navigation gyroscopes."

The GP-B satellite was launched in April 2004. It collected more than a
year's worth of data that the Stanford GP-B science team has been poring
over for the past 18 months. The satellite was designed as a pristine,
space-borne laboratory, whose sole task was to use four ultra-precise
gyroscopes to measure directly two effects predicted by general
relativity. One is the geodetic effect -- the amount by which the mass of
the Earth warps the local space-time in which it resides. The other
effect, called frame-dragging, is the amount by which the rotating Earth
drags local space-time around with it. According to Einstein's theory,
over the course of a year, the geodetic warping of Earth's local
space-time causes the spin axes of each gyroscope to shift from its
initial alignment by a minuscule angle of 6.606 arc-seconds (0.0018
degrees) in the plane of the spacecraft's orbit. Likewise, the twisting of
Earth's local space-time causes the spin axis to shift by an even smaller
angle of 0.039 arc-seconds (0.000011 degrees) -- about the width of a
human hair viewed from a quarter mile away -- in the plane of the Earth's
equator.

GP-B scientists expect to announce the final results of the experiment in
December 2007, following eight months of further data analysis and
refinement. Today, Everitt and his team are poised to share what they have
found so far -- namely that the data from the GP-B gyroscopes clearly
confirm Einstein's predicted geodetic effect to a precision of better than
1 percent. However, the frame-dragging effect is 170 times smaller than
the geodetic effect, and Stanford scientists are still extracting its
signature from the spacecraft data. The GP-B instrument has ample
resolution to measure the frame-dragging effect precisely, but the team
has discovered small torque and sensor effects that must be accurately
modeled and removed from the result.

"We anticipate that it will take about eight more months of detailed data
analysis to realize the full accuracy of the instrument and to reduce the
measurement uncertainty from the 0.1 to 0.05 arc-seconds per year that
we've achieved to date down to the expected final accuracy of better than
0.005 arc-seconds per year," said William Bencze, GP-B program manager.
"Understanding the details of this science data is a bit like an
archeological dig. A scientist starts with a bulldozer, follows with a
shovel, and then finally uses dental picks and toothbrushes to clear the
dust away from the treasure. We are passing out the toothbrushes now."

The two discoveries

Two important discoveries were made while analyzing the gyroscope data
from the spacecraft: one, the "polhode" motion of the gyroscopes dampens
over time; two, the spin axes of the gyroscopes were affected by small
classical torques. Both of these discoveries are symptoms of a single
underlying cause: electrostatic patches on the surface of the rotor and
housing. Patch effects in metal surfaces are well known in physics and
were carefully studied by the GP-B team during the design of the
experiment to limit their effects. Though previously understood to be
microscopic surface phenomena that would average to zero, the GP-B rotors
show patches of sufficient size to measurably affect the gyroscopes'
spins.

The gyroscope's polhode motion is akin to the common "wobble" seen on a
poorly thrown American football, though it shows up in a much different
form for the ultra-spherical GP-B gyroscopes. While it was expected that
this wobble would exhibit a constant pattern over the mission, it was
found to slowly change due to minute energy dissipation from interactions
of the rotor and housing electrostatic patches. The polhode wobble
complicates the measurement of the relativity effects by putting a
time-varying wobble signal into the data.

The electrostatic patches also cause small torques on the gyroscopes,
particularly when the space vehicle axis of symmetry is not aligned with
the gyroscope spin axes. Torques cause the spin axes of the gyroscopes to
change orientation, and in certain circumstances, this effect can look
like the relativity signal GP-B measures. Fortunately, the drifts due to
these torques have a precise geometrical relationship to the misalignment
of the gyro spin/vehicle symmetry axis and can be removed from the data
without directly affecting the relativity measurement.

Both of these discoveries first had to be investigated, precisely modeled
and carefully checked against the experimental data before they could be
removed as sources of error. These additional investigations have added
more than a year to the data analysis, and this work is still in process.
To date, the team has made very good progress in this regard, according to
its independent Science Advisory Committee, chaired by relativistic
physicist Clifford Will of Washington University in St. Louis, Mo., that
has been monitoring every aspect of GP-B for the past decade.

In addition to providing a first peek at the experimental results at the
APS meeting, the GP-B team has released an archive of the raw experimental
data. The data will be available through the National Space Sciences Data
Center at the NASA Goddard Space Flight Center beginning in June.

Conceived by Stanford Professors Leonard Schiff, William Fairbank and
Robert Cannon in 1959 and funded by NASA in 1964, GP-B is the longest
running, continuous physics research program at both Stanford and NASA.
While the experiment is simple in concept -- it utilizes a star, a
telescope and a spinning sphere -- it took more than four decades and $760
million to design and produce all the cutting-edge technologies necessary
to bring the GP-B satellite to the launch pad, carry out this "simple"
experiment and analyze the data. On April 20, 2004, GP-B made history with
a perfect launch from Vandenberg Air Force Base in California. After a
four-month initialization and on-orbit check-out period, during which the
four gyroscopes were spun up to an average of 4,000 rpm and the spacecraft
and gyro spin axes were aligned with the guide star, IM Pegasi, the
experiment commenced. For 50 weeks, from August 2004 to August 2005, the
spacecraft transmitted more than a terabyte of experimental data to the
GP-B Mission Operations Center at Stanford. One of the most sophisticated
satellites ever launched, the GP-B spacecraft performed magnificently
throughout this period, as did the GP-B Mission Operations team, comprised
of scientists and engineers from Stanford, NASA and Lockheed Martin, said
Stanford Professor Emeritus Bradford Parkinson, a co-principal
investigator with John Turneaure and Daniel DeBra, also emeritus
professors at Stanford. The data collection ended on Sept. 29, 2005, when
the helium in spacecraft's dewar was finally exhausted. At that time, the
GP-B team transitioned from mission operations to data analysis.

Over its 47-year lifetime, GP-B has advanced the frontiers of knowledge,
provided a training ground for 79 doctoral students at Stanford (and 13 at
other universities), 15 master's-degree students, hundreds of
undergraduates and dozens of high school students who worked on the
project. In addition, GP-B spawned more than a dozen new technologies,
including the record-setting gyroscopes and gyro suspension system, the
SQUID (for Superconducting QUantum Interference Device) gyro readout
system, the ultra-precise star-pointing telescope, the cryogenic dewar and
porous plug, the micro-thrusters and drag-free technology, and the Global
Positioning System-based orbit determination system. All of these
technologies were essential for carrying out the experiment, but none
existed in 1959 when the experiment was conceived. Furthermore, some
technologies that were designed at Stanford for use in GP-B, such as the
porous plug that controlled the escape of helium gas from the dewar,
enabled and were used in other NASA experiments such as COBE (the COsmic
Background Explorer, which won this year's Nobel prize), WMAP (for
Wilkinson Microwave Anisotropy Probe) and the Spitzer Space Telescope.

The experiment's final result is expected upon completion of the data
analysis this December. Asked for his final comment, Everitt said: "Always
be suspicious of the news you want to hear."

NASA's Marshall Space Flight Center manages the GP-B program and
contributed significantly to its technical development. NASA's prime
contractor for the mission, Stanford University, conceived the experiment
and is responsible for the design and integration of the science
instrument, as well as for mission operations and data analysis. Lockheed
Martin, Stanford's major subcontractor, designed, integrated and tested
the spacecraft and built some of its major payload components, including
the dewar and probe that housed the science instrument. NASA's Kennedy
Space Center in Florida and Boeing Expendable Launch Systems of Huntington
Beach, Calif., were responsible for the launch of the experiment aboard
the Delta II rocket.

[Bob Kahn is the public affairs coordinator for Gravity Probe B at
Stanford.]

-30-

Editor Note:

Everitt will present the experiment's preliminary results at the American
Physical Society meeting in Jacksonville, Fla. His plenary is scheduled
for 8:30 a.m. Eastern Time on Saturday, April 14, at the Hyatt Regency
Jacksonville Riverfront, 225 East Coast Line Dr., Jacksonville, Fla.
32202. In addition, beginning at 8:30 a.m. Eastern Time on Sunday, April
15, Gravity Probe B co-principal investigators John Turneaure and Bradford
Parkinson and GP-B Chief Scientist Mac Keiser will present back-to-back
invited talks. Also on Sunday, in a poster session from 2 p.m. to 5 p.m.
Eastern Time, members of the GP-B team will make 22 poster presentations
covering all aspects of the experiment and technologies.

Photos and graphics are available from GP-B's Image Gallery at
http://einstein.stanford.edu/content/pict_gal/main_index.html
Select high-resolution images are located at
http://einstein.stanford.edu/pix/hires_graphics

Relevant Web URLs:

* Stanford's Gravity Probe B page
http://einstein.stanford.edu/
* NASA's Gravity Probe B page
http://www.nasa.gov/mission_pages/gpb/index.html
* Putting relativity to the test, NASA's Gravity Probe B experiment is one
step away from revealing if Einstein was right [Stanford Press Release,
Oct. 3, 2005]
http://news-service.stanford.edu/pr/2005/pr-gpbempty-100505.html
* T-minus 45 years: Gravity Probe B finally launches [Stanford Report,
April 21, 2004]
http://news-service.stanford.edu/news/2004/april21/gpbshort-421.html

*****

[http://news-service.stanford.edu/pr/2007/pr-aps_side-041807.html]

News Service
Stanford University
Stanford, California

Contact:
Bob Kahn, Gravity Probe B
(650) 723-2540

Comment:
Bill Bencze, GP-B Program Manager
(650) 725-5691

April 16, 2007

Beyond theory, space mission pushes frontiers of human possibility,
engineering

BY Annie Jia

When Gravity Probe B (GP-B) was conceived in 1959, much of the technology
needed to conduct the experiment did not exist. An unprecedented level of
technological precision was needed to measure the curvature of space, and
it took more than three decades for scientists and engineers to create
more than a dozen technologies needed to make their vision a reality.

"The number of new technologies that has spawned spinoffs on this
experiment is astounding, but probably the most important spinoff is the
over 90 PhD theses that have been sponsored by this experiment, because
that represents education," said Brad Parkinson, the mission's
co-principal investigator and co-inventor of the Global Positioning System
(GPS).

Following are just a few examples of the technologies GP-B research has
spawned.

Gyroscopes steadier than an owl's eyes

To create wobble-free gyroscopes, scientists produced the world's most
perfect spheres. Enlarged to the size of the Earth, the spheres would have
mountains no more than 8 feet high. The gyroscopes are now recorded in the
Guinness Database of World Records as the roundest manmade objects. They
are surpassed in roundness by only one type of object in the entire
universe: dense neutron stars.

World's best protractor

The width of a human hair viewed from a quarter of a mile away -- that is
the tiny angle by which space-time around Earth was predicted to tilt
GP-B's gyroscopes. To measure these minuscule angles, engineers had to
develop sensors of astounding precision. The Superconducting QUantum
Interference Device (SQUID) magnetometers use a superconducting niobium
loop to measure tiny changes in magnetic field that result from the
gyroscopes' shift. The devices are so sensitive that they can detect a
magnetic field 10 trillion times smaller than Earth's.

Giant thermos

A minivan-sized dewar, or thermos, filled with liquid helium surrounds the
gyroscope assembly and keeps it at a cryogenic temperature near absolute
zero. To maintain the experimental apparatus at a temperature of 1.8
Kelvin for 16 months in space, the dewar employed advanced technology to
insulate, block space radiation and cool by evaporation.

Porous plug

Despite the dewar's incredible insulating abilities, a small amount of
heat seeps in and turns some liquid helium into gas. A porous plug allows
this "warm" gas to escape while keeping the liquid helium inside to cool
the assembly through evaporation, just as sweating cools a person's skin.
What's more, the porous plug helps fine-tune the position of the
spacecraft. Escaping helium gas is directed through micro-thrusters that
puff out amounts one-fiftieth the size of a person's breath to minutely
shift and turn the spacecraft to achieve perfect alignment with its guide
star. The porous plug has since been used in other NASA flights, including
this year's Nobel Prize-winning COBE (for COsmic Background Explorer)
mission.

World's best star tracker

Scientists chose a distant star as the fixed reference point for measuring
the small angles of deflection of GP-B's gyroscopes. Because of the
minuteness of the angles, the telescope's focus on the guide star had to
be precise to one 10-millionth of an inch. A telescope lens alone would
provide an image 10,000 times too rough, so GP-B engineers created a
device to split the incoming telescope image of the star into two separate
images, one for the horizontal alignment and one for the vertical. Each
image was again divided in two. Then delicate sensors measured the amount
of light in each half image, and the spacecraft's orientation was adjusted
until the two halves were perfectly balanced, indicating that the star's
perfect center had been found.

Gyro suspension system

With the gyroscopes spinning at 4,000 rpm, their suspension system used
electrostatic fields to hold each rotor in a vacuum a mere paper's width
from the walls of its housing. Any contact of the rotors with the walls
would destroy the equipment. The gyro suspension system adjusts the
rotors' positions 220 times a second to continually ensure perfect
suspension.

Drag-free orbit

It is customary to track the path of an orbiting spacecraft, not the path
of the equipment inside it. GP-B's drag-free technology flips that
paradigm and instead tracks the path of the equipment inside the
spacecraft. Like gnats swarming around a person, the GP-B spacecraft
"chases" one of four gyroscopes, which serves as the experiment's central
mass. The spacecraft's body shields the gyroscope from outside
disturbances, such as friction and magnetic fields, so that the gyroscope
is affected only by gravity and orbits the Earth in perfect free-fall. The
spacecraft itself, constantly disturbed by the harsh forces of space,
adjusts its own position 10 times a second, based on information from the
gyro suspension system, to remain perfectly centered around the drag-free
gyroscope. Stanford's Aeronautics and Astronautics Department pioneered
drag-free satellite technology in the early 1960s.

Precision GPS

Scientists needed an accurate method to map GP-B's orbit because the
distortion of space-time varies with location. Hence they adapted
conventional GPS technology for GP-B's high speeds and rotating motion. In
the process they discovered a way to enhance the standard GPS receiver to
measure position down to the centimeter level. Precision GPS has since
been adopted in automated tractors, aircraft landing systems and vehicles
used in mining and building roads. "[Robotic farm tractors have] launched
a market now valued at well over $100 million and growing," Parkinson
said. "The productivity enhancements are startling, and clearly benefit
many with less expensive food."

[Annie Jia is a science-writing intern at the Stanford News Service.]

-30-

Editor Note:

This is a sidebar to a story about the presentation of Gravity Probe B's
first results. Science-writing intern Annie Jia wrote this release.
High-resolution images are posted at
http://einstein.stanford.edu/pix/hires_graphics/

Relevant Web URLs:

* Gravity Probe B
http://einstein.stanford.edu/


.