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Gravity Probe B
Processing Activities
11 July 2003
Gravity Probe B arrived at Vandenberg Air Force Base (VAFB)
from the Lockheed Martin Plant in Sunnyvale, Calif.
12 July 2003
Gravity Probe B was taken to NASA
spacecraft processing hangar 1610
located on North Vandenberg Air
Force Base. The spacecraft was unloaded
from its transporter, placed on
an assembly and test stand then
the soft shipping cover was removed.
Mechanical and electrical ground
support equipment is being set up
and the necessary connections made
with the spacecraft. Battery charge/discharge
cycles are underway as part of the
battery conditioning process.
23 July 2003
Functional testing of Gravity Probe
B and the initial liquid helium
cyrogenic servicing are being performed.
The telescope stray-light test is
also being performed.
2 Aug 2003
Download and verification of the
new flight/mission software was
completed.
15 Aug 2003
The Compatibility Test Van (CTV),
which contains equipment to simulate
NASA’s ground network of tracking
stations and the Tracking and Data
Relay Satellite System completed
testing with the spacecraft.
27 Aug 2003
The electromagnetic interference
(EMI) test has been successfully
completed. The Gas Management Assembly
(GMA) "rate of rise" testing
is under way and is successful to
date. At this time there are three
days of testing remaining. Certification
testing of the pump module in preparation
for conditioning the dewar was successfully
completed.
3 Sept 2003
In processing activities this week,
the initial filling of the dewar
with cryogenic helium has been performed.
This prepared the dewar for the
upcoming series of about 6 -7 cycles
of pumping down the tank to a near
vacuum, then refilling as necessary,
to achieve the superfluid conditions.
The first pump-down began today.
17 Sept 2003
The pumping down of the dewar which is filled with cryogenic
liquid helium continues. This brings the environment within
the dewar to a near vacuum. It will then be refilled to the
level necessary to achieve and maintain superfluid conditions.
24 Sept 2003
Conditioning of the dewar to a superfluid
state has been completed. Conditioning
is the process of taking liquid
helium at a temperature of about
4 Kelvin (-452 degrees F) to a colder
state, known as superfluid, which
will allow the helium to last throughout
the duration of the mission. Filling
the dewar with superfluid helium
is a slow and repetitive process.
The dewar is now 95% full of superfluid
helium at a temperature of 1.65
Kelvin (-456 degrees F) and it will
be maintained in this state from
now until launch.
In upcoming spacecraft activities,
electrical testing is scheduled
for Oct. 8.
16 Oct 2003
Testing of the Super Quantum Interference
Device (SQUID) readouts are under
way this week. The SQUID are ultra-sensitive
magnetometers that can detect a
change in the tilt of a spinning
gyroscope to an angle of 0.1 milliarc-seconds,
equivalent to viewing the width
of a human hair at 100 miles. A
test to verify the reliability of
the SQUID is scheduled for Friday,
Oct. 17. The electrical system testing
that was under way last week has
been completed succesfully. Ordnance
installation is scheduled for Oct.
20-24, and solar array installations
is scheduled to begin Oct. 27.
Gravity Probe B will be transported from the spacecraft hangar
to Space Launch Complex 2 on Nov. 18 and hoisted atop the
second stage. Then the final major test before launch, the
Flight Program Verification, will be conducted on Nov. 20.
This is an integrated test conducted after the Gravity Probe
B spacecraft is mated atop the second stage of the launch
vehicle. The Delta II fairing will be installed around the
spacecraft on Nov. 25 as part of final preparations for launch.
29 Oct 2003
Solar array installation began on Tuesday. There are four
arrays to be installed and tested. The first array is now
installed and testing of it is under way today. Solar array
installation activities are targeted for completion on Nov.
7. the Delta II launch vehicle/payload adapter will be delivered
to the spacecraft processing facility on Nov. 10.
Marshall Space Flight Center's equivalent of a Mission Readiness
Review is scheduled to be held in Huntsville on Nov. 12.
5 Nov 2003
Solar array installation began last week. Two of the four
arrays are now installed, and installation of the third solar
array is in progress. Installing each array is a 3-day process
and includes a functional deployment test.
The spacecraft's cryogenic dewar was sealed prior to beginning
solar array installation at a temperature of 1.648 K. The
temperature is rising very slowly, but is expected to remain
less than 1.88 K by the time launch occurs. The current temperature
is 1.695 K, which is well within the expected rate of rise.
The dewar will be topped off at the pad prior to launch.
14 Nov 2003
The installation of the four solar arrays, deployment testing
and lighting tests have been successfully completed. The Delta
II payload adapter was mated to the GP-B spacecraft on Thursday,
Nov. 13.
Marshall Space Flight Center's Mission Readiness Review was
held on Wednesday, Nov. 12. This review, chaired by MSFC,
is intended to certify readiness of Gravity Probe B for flight,
the readiness of the spacecraft operations team and readiness
of mission personnel and ground stations to achieve the science
objectives.
The GP-B test results during the period that the spacecraft
has been undergoing activities in processing facility 1610
are now having a final assessment prior to an engineering
review to be held on Monday, Nov. 17. This review will determine
the readiness of GP-B to go to the pad. It will also cover
the readiness of the Delta II launch vehicle for spacecraft
erection and for proceeding with final prelaunch activities.
Gravity Probe B will be placed into a transportation canister
on Tuesday Nov. 18 and transported to Space Launch Complex
2 the following day on Nov. 19.
20 Nov 2003
After a final review of test data before going to the launch
pad, spacecraft management made a decision to reschedule the
launch of Gravity Probe B. They want to address an issue of
electronic noise on one of the two output channels of the
No. 1 experiment gyro. This problem was found during testing
and could compromise the quality of the data from the gyro.
While a work around of the problem was considered, engineers
decided that fixing the problem will provide the greatest
chance of success over the planned 16-month life of the mission.
This repair will restore full redundancy to the output of
the experiment gyro.
In preparation for the repair, the payload attach fitting
used in mating to the Delta II is being removed today from
the base of the spacecraft.
Meetings are set to begin at Vandenberg Air Force Base on
Friday. These will determine the approach to be taken for
repair and thus how long the launch postponement will be;
however, launch cannot occur during December. The difficulty
has been found to be within the spacecraft's experiment control
unit (ECU).
25 Nov 2003
The solar arrays are beginning to be removed from around the
spacecraft for access to the experiment control unit (ECU).
Yesterday, one of the four solar arrays was taken off, and
a second array was removed today. A third array will be removed
if time permits: otherwise, the third and fourth arrays will
be removed next Monday and Tuesday after the spacecraft team
returns from the Thanksgiving holidays.
A decision has been made that the cryogenic helium will not
need to be off-loaded from the spacecraft to remove the ECU
for rework. Because decisions remain to be made on what will
be necessary to restore Gravity Probe B to flight readiness,
it is not possible at this time to determine a new launch
date.
3 Dec 2003
The ECU is expected to return to the factory on or about Dec.
15. While no new launch date has been established, a Flight
Planning Board meeting is planned for mid-December and the
outcome could determine a possible target date, or at least
a new launch time frame.
17 Dec 2003
On Monday this week, the Flight Planning Board met and set
April 20, 2004 as the new launch date for Gravity Probe B.
A launch time hasn't been set.
The Experiment Control Unit (ECU) was returned to Palo Alto,
Calif. late last week. Two associated circuit boards contained
in the ECU are being removed and replaced with ones slightly
different in circuit design.
No further status reports are planned to be issued on Gravity
Probe B until January.
14 Jan 2004
The Gravity Probe B spacecraft is awaiting the return of the
reworked Experiment Control Unit (ECU). The state of battery
charge is monitored on a constant basis. The temperature of
the dewar's main tank is 1.864 K and has warmed from 1.648
K since the solar arrays were installed over the cryogenic
access ports, after the last helium servicing. The temperature
is targeted to be no warmer than 1.880 K at launch. However,
since the solar arrays have been removed because of the stand-down,
there is planned to be another cryogenic serving of liquid
helium in mid-February.
The ECU was returned to Palo Alto, Calif. in December and
is in the Lockheed Martin Facilities there. The reworking
of the circuit board is complete and it is currently undergoing
thermal vacuum testing.This is scheduled to be finished late
next week.
22 Jan 2004
The reworking of the circuit board was completed last week.
The functional testing and thermal vacuum testing of the ECU
were completed earlier this week as planned. Vibration testing
is now underway.
30 Jan 2004
The reworking of the circuit board, installation into the
ECU and functional testing is complete. Final thermal vacuum
chamber testing is under way. The ECU containing the associated
circuit board will be returned for installation into the GP-B
spacecraft by Feb. 10.
4 Feb 2004
The reworking of the circuit board, installation into the
ECU, functional testing and thermal vacuum chamber testing
are all complete. The work has gone better than expected and
the ECU will be returned to Vandenberg Air Force Base tomorrow,
Thursday, Feb. 5. Meanwhile this week, GP-B spacecraft team
members have been returning to Vandenberg in preparation for
the arrival of the ECU.
In other planned spacecraft processing, battery reconditioning
is scheduled for Feb. 6-8. The ECU will be reinstalled Feb.
9. Cryogenic servicing of liquid helium is scheduled for Feb.
16. Operations to reinstall the solar arrays are planned for
Mar. 7-19. The spacecraft is currently scheduled to be transported
to Space Launch Complex 2 on Apr. 1 and mated to the Delta
II rocket.
12 Feb 2004
After final thermal vacuum chamber testing at Lockheed Martin
in Sunnyvale, Calif., the ECU was shipped to Vandenberg and
arrived there Feb. 4. The ECU was reinstalled into the Gravity
Probe B spacecraft over the weekend. Testing of the spacecraft
with the ECU installed is now underway.
In other planned spacecraft processing, servicing of the
Gas Management Assembly (GMA) is underway today. The GMA provides
the helium gas required to spin up the gyroscopes. It also
performs magnetic flux reduction, of "flux flushing,"
to minimize noise or reduce the trapped magnetic field within
each gyro's housing.
Filling the dewar with liquid helium in preparation for cryogenic
servicing of the spacecraft is planned for Feb. 13. The actual
servicing of the spacecraft is scheduled to begin Feb. 16.
18 Feb 2004
The dewar with cryogenic liquid helium is connected to the
ground support equipment, in preparation for servicing that
will return the helium to a superfluid state. The filling
of the spacecraft with helium begins today.
Operations to reinstall the solar arrays are planned to
begin in mid-March. The spacecraft is currently scheduled
to be transported to Space Launch Complex 2 on Apr. 1 and
mated to the Delta II rocket.
25 Feb 2004
Powered-on testing of the spacecraft with the reworked ECU
installed continues without problems.
Reconditioning of the spacecraft's cryogenic helium dewar
back to a temperature of 1.65 Kelvin has been underway. This
is essentially a topping off process that also cools the helium
in the tank to a superfluid state near absolute zero. The
topping continued until 95% of the helium in the dewar was
in a superfluid condition. The dewar has now been closed out,
so the launch nominally needs to occur within about 90 days.
A final top-off is planned to occur at the launch pad to assure
the helium will last the planned 16-month duration of the
mission.
In other planned spacecraft processing, the Gas Management
Assembly (GMA) is undergoing "rate of rise" testing
that checks for leakage rates.
3 March 2004
Powered-on testing of the spacecraft with the reworked ECU
reinstalled is complete and a detailed data analysis is now
underway. The ECU appears to be performing fully as intended.
Functional testing of the remainder of the spacecraft continues
and is on schedule. No problems have been revealed.
The Gas Management Assembly (GMA) "rate of rise"
testing has been completed satisfactorily. This testing checked
leakage rates and amounts.
Reconditioning of the spacecraft's cryogenic helium dewar
back to a temperature of 1.65 Kelvin has been completed and
the dewar was sealed.
Operations to reinstall the solar arrays will begin on March
8.
10 March 2004
The first of four solar arrays has been installed and testing
has been completed. The second solar array will be installed
March 11. Solar array installation activities are targeted
for completion on March 18.
Powered-on testing of the spacecraft with the reworked Experiment
Control Unit (ECU) reinstalled is complete. A detailed data
analysis is confirming that the ECU is performing as desired.
Installation of small ordnance inside the Forward Equipment
Enclosure (FEE) has been completed. The FEE surrounds the
electronics of the Science Mission Dewar, which has valves
that are opened on-orbit by these pyrotechnics to equalize
pressure.
17 March 2004
Three of four solar arrays have been installed and tested.
The remaining array will be installed tomorrow. After each
solar array is installed, a "walk-out test," which
is an unfolding, is performed to ensure that the array deploys
properly. The spacecraft is then rotated for installation
of the next solar array.
24 March 2004
All four solar arrays have been installed and were tested
successfully.
The spacecraft will be mated to the payload attach fitting
(PAF) on March 25. Closeouts to Gravity Probe B in preparation
for going to the launch pad will then be performed on March
29. The following day, it will be installed into the transportation
canister. The spacecraft will be transported to Space Launch
Complex 2 on April 1 and mated to the Boeing Delta II rocket.
31 March 2004
The spacecraft was mated to the payload attach fitting (PAF)
on March 25. Closeouts to Gravity Probe B in preparation for
going to the launch pad have been completed. Today the spacecraft
is being installed into the transportation canister in preparation
for being moving to Space Launch Complex 2 on Thursday, April
1 and mated to the Boeing Delta II rocket.
8 April 2004
The launch of the Gravity Probe B spacecraft has been postponed
to no earlier than Monday, April 19. The additional time is
necessary to allow engineers to troubleshoot an apparent short
in launch pad ground support equipment. It is associated with
a spacecraft battery monitoring circuit. Without this circuit,
the battery voltage on the spacecraft cannot be remotely monitored
from the pad during certain essential operations. The launch
time for Monday, April 19 is 10:01:20 PDT. Should the launch
be postponed 24 hours for any reason, the launch time is 9:57:24
a.m. PDT.
15 April 2004
Gravity Probe B is proceeding forward with a launch date of
Monday, April 19, at 1:01:20 p.m. EDT.
20 April 2004
Gravity Probe B launches successfully.
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