**Memorandum of Understanding**

**between**

**The Gravity Probe-B Mission**

**and**

**The National Space Science Data Center**

# January 15, 2006

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**Ed Grayzeck, Francis Everitt**

**Head, National Space Science Data Center Principal Investigator,
Gravity Probe-B**

**NASA Goddard Space Flight Center Stanford University**

**Approved by:**

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**Joseph Bredekamp Alan Smale**

**Program Manager, NSSDC Program Executive, Gravity Probe-B**

**NASA Headquarters NASA Headquarters**

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**Tony Lyons Tom Langenstein**

**Program Manager Gravity Probe B Deputy Program Manager**

**NASA Marshall Space Flight Center Stanford University**

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**Jennifer Spencer**

**Data Processing Lead, Gravity Probe-B**

**Stanford University**

Memorandum of Understanding

between

The Gravity Probe-B Mission

and

The National Space Science Data Center

1\. Introduction

This is a Memorandum of Understanding (MOU) between the National Space
Science Data Center (NSSDC) at Goddard Space Flight Center (GSFC) and
the Gravity Probe-B mission (GP-B) at Stanford University. It documents
the roles of those organizations in the acquisition, management,
dissemination and preservation of data from the Gravity Probe B space
mission. This MOU supersedes any prior agreements between the NSSDC and
GP-B regarding the archiving and dissemination of relevant data.

The NSSDC was created in 1966 as NASA\'s only archive for space and
Earth science data. The NSSDC\'s data management role has evolved with
the emergence of a series of active archives in both space and Earth
science. Presently it has permanent archiving responsibility for NASA
space science mission data. It has active archiving responsibilities in
certain space science discipline areas. It has additional roles not
germane to this MOU. The NSSDC home page is at
<http://nssdc.gsfc.nasa.gov/>.

Gravity Probe-B was begun in 1959, funded by NASA since 1963
(retroactively from 1964). The purpose of the Gravity Probe B Relativity
Mission satellite is to measure two relativistic effects on nearly
perfect gyroscopes. Einstein's General Theory of Relativity precisely
predicts both of these effects; the spacecraft measurements are an
experimental test of the General Theory of Relativity.

The two measured relativistic effects are the geodetic effect, which is
due to the gravitational interaction of the spinning gyroscope and its
orbital angular momentum about the earth, and the motional or
frame-dragging effect which is due to the gravitational interaction
between the spinning gyroscope and the angular momentum of the earth.
The geodetic effect is predicted to cause a drift rate of 6.6 arc
seconds per year in the plane of the orbit for a gyroscope in a \~640 km
circular orbit, and the motional effect is predicted to cause a drift of
the 41 milli-arc seconds per year in a direction perpendicular to the
plane of the orbit.

The requirement for the overall accuracy of the Gravity Probe B
Experiment is to measure the drift rate of each of the four gyroscopes
to an accuracy of 0.5 milli-arc-seconds per year. At this level, the
frame dragging effect will be measured to an accuracy of 1%, and the
geodetic effect will be measured to an accuracy of 1 part in 10,000. A
measurement of the drift rate of the gyroscopes at this level of
accuracy will be the most accurate non-null experimental test of the
General Theory of Relativity. Present estimates of the overall accuracy
of the experiment indicate that it will be possible to measure the drift
rates significantly better than 0.5 milli-arc-seconds per year.

The telemetry from the satellite contains the essential information to
determine the gyroscope drift rate as well as the health and safety of
the satellite and its subsystems. The Gravity Probe B "Stanford
Post-Processing Operations for Science Mission Data" document (S0401D)
describes the method for processing and storing this information.

Inconsistencies between current practices and MOU statements, or future
modifications to this MOU, will be addressed and agreed to by the
Directors of the NSSDC and GP-B, with involvement of relevant NASA
program managers when needed. This MOU will be consistent with the GP-B
Data Management Plan

2\. GP-B and NSSDC

GP-B has interfaces with NASA Headquarters, NASA-funded spaceflight
missions, and with other relevant programs designated by NASA. NASA
agencies are involved in the creation of the Data Management Plan (DMP),
and Data Archive Plan. These documents specify what data and supporting
material will be delivered to NSSDC and the delivery schedule.

The NSSDC will ensure that the data and supporting material are
effectively accessible by potential users from NASA, other research
communities, and by the public. It is expected that some user access
will be electronic, but the NSSDC will also satisfy occasional requests
for data to be sent offline. The GP-B team will provide supporting
documentation and other material to ensure the data is usable.

GP-B will provide copies of its data to the NSSDC for permanent
archiving in formats acceptable to GP-B and the NSSDC (and/or it will
ensure a parallel flow of data and supporting material directly to the
NSSDC\-\--what does this mean, exactly? Examples?). As GP-B releases new
products to the public, these products will be transmitted to the NSSDC
in a mutually agreed upon manner. For data releases on CD, DVD, or
similar media, GP-B shall provide the NSSDC with a set of these volumes.
For data to be sent electronically, the details of such transfer shall
be devised and agreed upon by GP-B and the NSSDC. Data transferred
electronically will be subject to quality assurance by the NSSDC and
remote storage of backup copies will be provided by the NSSDC.

3\. NSSDC as Permanent Archive

The NSSDC will receive NASA-sanctioned GP-B data and supporting material
from GP-B, and it will ensure their long-term preservation against both
media deterioration and technology obsolescence. The NSSDC permanent
archive is not electronically accessible outside the NSSDC. The NSSDC
assumes that the data and supporting material provided by GP-B is
correct. It is the responsibility of GP-B to ensure this correctness
when the data are delivered to the NSSDC.

Upon request from GP-B, the NSSDC will provide copies of data and/or
supporting material in the same format it was provided by GP-B at the
time of the initial delivery.

[Upon request from GP-B or the research or public user
community]{.underline}, the NSSDC will replicate and mail data volumes
to requesters. It will charge end users a fee just sufficient to cover
the incremental cost of satisfying the request.

The NSSDC will point users to the appropriate web page as the source of
GP-B data for researchers.