10 days until launch.
The cryostat is full of hydrogen!
The fairing is on the rocket!
Today was a big day for WIRE. We installed the fairing around the spacecraft, and we started a ground-hold test which demonstrates that the cryostat insulation is in good shape.
The day began with the instrument team starting the liquid helium disconnect at 6am. The liquid helium keeps the hydrogen in the cryostat frozen. As soon as the disconnect is started, the hydrogen begins to warm toward the melting point. As long as the hydrogen is frozen, it cannot get out of the cryostat, but after it is all melted, the pressure can build up to the point where the hydrogen vents. Once it starts to melt, the temperature stops rising until all of the solid is melted. Shortly after all of the hydrogen melts, if we don't get the cooling reconnected, the temperature starts to climb and the hydrogen will soon build up enough pressure to vent. We can't tell how fast the hydrogen is melting, since the temperature is constant during the melting process, so we don't know how much time we have left before melting is complete. To be safe, we established the rule that the safety vent must be connected whenever the hydrogen is not completely frozen. So we had only about 8 hours from the time the disconnect was started until we had to have the safety vent reconnected.
The disconnect took about 3 hours, and we spent another hour performing final close-outs on the spacecraft. About 10am we disconnected the safety vent and started moving the right half of the fairing into place. After half the fairing was bolted into place, we installed the quick-disconnect (QD) portion of the safety vent. The QD goes through a hole in the top of the fairing. It connects the spacecraft safety vent to the safety vent of the L- 1011 Orbital Carrier Aircraft (OCA) which carries the Pegasus rocket.
Next, we brought a portion of the OCA vent system into place over the fairing. This section is known as the load isolation system (LIS). The LIS is a flexible section of vent which allows the rocket to move some while it is still attached to the aircraft. It took some time to position the LIS with the crane, attach the vent, and temporarily attach the LIS support structure to the fairing. The LIS will ride with the fairing until the rocket is attached to the OCA next week.
Finally, we routed the building's safety vent around the left half of the fairing and attached it to the LIS's outlet. It was 1pm and the hydrogen was still frozen. We accomplished everything we had set out to do. After a lunch break, we installed the left half of the fairing.
We allowed the hydrogen to continue to warm. It reached triple point during our lunch break, at about 2pm. We will allow it to continue to melt for another day, confirming that all the solid will not melt in 24 hours. The shape of the warm-up curve indicates at what rate heat leaks into the cryostat. The heat leak rate closely matches the results of a test we ran last year. The cryostat is in good shape.
Here are two photos of the spacecraft tucked inside the right half of the
fairing, just before the left half was moved into place. The instrument
aperture shade is in place and all covers are removed from the sensors.
The left photo below shows the cryostat still partially connected to the
plumbing which is used to keep the hydrogen frozen. Liquid helium at 4 K (-
452 degrees Fahrenheit) flows from a large metal dewar into the instrument,
through cooling lines around the tanks, then back out. Whenever liquid helium
is flowing, we have a vacuum line connected to the cryostat to pump out the
small amount of helium which always leaks from the Teflon cooling lines
inside the cryostat. The vacuum helps insulate the frozen hydrogen from the
outside world, just like the vacuum in a thermos bottle. In the right photo,
the cyrostat team is moving the equipment out of the way to prepare for the
fairing installation.
Here the Orbital team brings the right half of the fairing into place. The
bag over the instrument aperture protects it from dust. It will be removed
just before the left half is moved into place. We have been very careful to
keep the spacecraft, rocket, and especially the instrument clean, since WIRE
can spot a grain of dust the diameter of a human hair 10 km away.
After the right half of the fairing was in place, Pete Rossoni installed
the quick-disconnect joint (QD) while Giulio Rosanova (on right) and Bob Light
(on left) assisted. The right photo shows Pete's hand next to the QD. The QD
connects the safety vent plumbing of the cryostat to the safety vent system
which flys on the Orbital Carrier Aircraft (OCA). The safety vent will carry
hydrogen safely away if the cryostat ever unexpectedly warms up and vents
hydrogen. When the Pegasus is dropped from the OCA, the QD breaks just below
the point where it penetrates the fairing. A rubber boot seals the fairing
around the QD, and a flapper door closes over the hole after drop.
The next three photos show the connection of the load isolation system
(LIS) to the quick disconnect joint (QD). The LIS attaches to the Orbital
Carrier Aircraft (OCA) vent and to the QD. It provides a continuous path for
the hydrogen while allowing relative movement of the rocket and aircraft of up
to 3 inches--the rocket can shake around a bit underneath the OCA. The LIS is
temporarily connected to the fairing, until the rocket is rolled out and mated
to the OCA. The metal deck which supports the LIS will be bolted to the OCA.
The vent system is suspended above the deck via springs and it uses bellows to
provide the flexibility.
These last three photos show the final closing of the fairing. The
cryostat plumbing will be connected through the fairing doors. Another door
provides access to the spacecraft test connector panel where the arming
connectors are located. Final installation of those connectors occurs on
launch day.
Previous updates:
August 18, 1997 Structure and Cryostat progress
October 20, 1997 Structure qual and harness
installation
October 31, 1997 First powerup
November 7, 1997 Transponder integration, power
long functional
November 14, 1997 WIE and pyro
box integration
November 21, 1997 RF and ACS
integration
December 5, 1997 ACS testing
December 23, 1997 Work under spacecraft
January 9, 1998 ACS testing, gyro phasing
January 16, 1998 Instrument thermal simulator
January 23, 1998 Wire tracker
January 30, 1998 Build up solar array
February 6, 1998 Ops testing, remove transponder
February 20, 1998 Move to Building 7
March 12, 1998 Cleaning and Solar Array Testing
March 23, 1998 Prep for Environmental and into EMI
April 3, 1998 EMI and Vibration
April 20, 1998 Vibration and Shock
April 25, 1998 Thermal Balance
May 29, 1998 Instrument integration and Thermal
Vacuum
June 3, 1998 Spin Balance
June 17, 1998 Astrotech Tour and Magnetic
Calibration
June 30, 1998 QD qual, fairing fit
check, comprehensive testing
July 29, 1998
Ready to ship, QD testing
August 13, 1998 Launch delay
November 23, 1998 New launch date
January 19, 1999 WIRE at launch site
January 21, 1999 WIRE turnover/on Byrd Mobile
January 26, 1999 Instrument cooling, electrical
mate
January 29, 1999 Spacecraft on the rocket
February 15, 1999 Hydrogen load in progress