CUBIC status

This page gives the latest status of the CUBIC instrument on the SAC-B satellite.

Present CUBIC location:

Low Earth Orbit

The SAC-B satellite carrying the CUBIC instrument was launched into low earth orbit on November 4, 1996 by a Pegasus XL rocket. Unfortunately, the Pegasus failed to separate from the satellite, leaving the CUBIC instrument as an orbiting memorial tribute to our friend Mario Gulich, the original SAC-B Project Manager, who died two years ago. More information is available on our SAC-B Launch Date page.

[Pegasus]

SAC-B Launch Date ...

Status as of October 2, 1996:

We continue to monitor the CUBIC pressure, which was less than 10**-5 Torr on 9/4/96, 9 Torr on 9/18/96, and 17 Torr on 9/30/96. The pressure rise is consistent with a constant leak rate of about 640 mTorr per day. We expect that the pressure at launch (10/21/96) will be about 30 Torr at the current rate.

The pressure is primarily a concern because of the possibility of acoustic damage to the thin Al/Ti filter inside the CUBIC camera. Last week an identical filter survived a protoflight-level acoustic test at NASA/Goddard Space Flight Center with 100 Torr in the camera. Based on this test, which found no damage to the filter, we expect the flight filter to survive launch without damage.

Status as of September 1, 1996:

The SAC-B satellite arrived at Vandenberg Air Force Base on August 25, 1996, for final testing and integration into the Pegasus XL launch vehicle. It will remain at Vandenberg until October 17, 1996, when it will be flown to NASA's Wallops Flight Facility in preparation for launch from that site.

Status as of August 20, 1996:

The CUBIC pumps were disconnected from CUBIC on July 30, 1996, in preparation for mounting the Italian instrument, ISENA, next to CUBIC on the SAC-B satellite, and for shipping the satellite to the US for integration into the launch vehicle. At that time, the internal pressure was still in the 5 microtorr range. The pumps will be reattached at Vandenberg Air Force Base on August 28, 1996 in order to determine the pressure rise per week and to pump out the camera again.

Status as of September 10, 1996:

The CUBIC pumps were reconnected to CUBIC on August 29, 1996. After approximately one month without pumping, we found that the pressure inside CUBIC had risen to about 60 Torr. We now believe that this pressure rise is due to an undetected leak at the rate of about 2 Torr per day. The instrument was pumped out to about 6 microtorr for testing, and was extensively tested for over 12 hours. All systems appear to be working correctly. The camera was then vented to atmosphere and a pressure test was performed on the relief valve, which was shown to operate at about 20 Torr differential pressure. Pending results of an acoustical test to be performed this week at Goddard Space Flight Center, we now expect to launch CUBIC with about 80 Torr inside. During launch, this will vent through the relief valve, so that the pressure on orbit will be 20 Torr or less when the door is opened. We have previously demonstrated that the filters will not break if the door is opened in this way.

The camera was then pumped out to 7 microtorr again and the pumps were removed for the final time. Last week the thermal paint on the radiation plate was touched up and the pump port was closed. The satellite is undergoing final battery checks before installation onto the Pegasus XL launch vehicle in about two weeks.

Status as of August 20, 1996:

Status as of April 8, 1996:

The CUBIC camera pressure is dropping slowly, with the current pressure ~ 5-6 microtorr.

Status as of February 15, 1996:

CUBIC & SAC-B sit quietly under a clean tent inside the class 10,000 clean room at INPE-LIT. CONAE & INPE personnel are back from their summer vacations, and reports via e-mail are that all is well. The CUBIC camera continues to be pumped with the ion pump, and the camera pressure is ~ 6-7 microtorr.

Status as of December 22, 1995:

Every other month the SAC-B satellite is turned on to spin up the momentum wheels and test the satellite status. During such a test in early December, one of the DC-DC converters for the Attitude Control System failed. The tests were completed with the backup ACS electronics. Last week, the failed converter was removed and replaced with a backup. Following this change, a complete set of Basic Functional Tests (BFT) was run on the satellite and all instruments. CUBIC passed its BFT with flying colors, as did the rest of the satellite. The satellite is back in storage now awaiting launch. Meanwhile, the failed converter is being sent back to the manufacturer for tests to determine the cause of the failure.

Status as of November 1995:

The CUBIC (Cosmic Unresolved Background Instrument using CCDs) experiment was fabricated in the Penn State High Energy Astrophysics Laboratory for flight on the US/Argentine SAC-B minisat. CUBIC is designed to make measurements of the spectrum of the diffuse X-ray background from 0.2 - 10 keV, with energy resolution comparable to the ASCA SIS instrument.

CUBIC hardware fabrication was completed in autumn 1994, in parallel with the preliminary calibration of the X-ray detection elements (EEV-supplied charge-coupled devices (CCDs)). The completed payload was calibrated in the X-ray group's soft X-ray calibration/thermal vacuum chamber in Osmond Laboratory on the Penn State campus . In February 1995, CUBIC was hand-carried to INVAP (the Argentine spacecraft contractor), in Bariloche, Argentina where it was electrically and mechanically integrated into the SAC-B payload. Functional tests verified 100% experiment operation following transport and integration.

In April 1995 the SAC-B payload was transported to the Brazilian Integration and Testing Laboratory, INPE-LIT (Instituto Nacional de Pesquisas Espaciais, Laboratory of Integration and Testing), in Sao Jose dos Campos (100 km NE from Sao Paulo), for environmental testing.

During May 1995 the four solar panels were installed, and SAC-B (and CUBIC) underwent extensive vibrational testing. SAC-B & CUBIC met or exceeded all vibrational design goals.

Thermal vacuum testing occurred during June and early July. CUBIC achieved a low enough temperature to operate on four separate occasions. Basic and Full functional tests were conducted, and data were taken using the integral CUBIC ⁵⁵Fe sources and LED. Both CCDs (and both amplifiers on each CCD) were deemed to be operating as well as they had been during testing at Penn State. Both Al/Ti optical blocking filters appeared to have survived the vibrational and thermal testing.

During testing at INVAP and INPE the pressure inside the CUBIC camera was measured to be rising at a rate of about 500 mT per day. We determined during thermal vac chamber testing that this pressure rise is due to outgassing inside the camera body, and not from any external leak. CUBIC is currently attached to SAC-B, and both reside in the class 10,000 cleanroom at INPE-LIT. We have attached a 40 liter per second ion pump to CUBIC, and are pumping on the camera to reduce the pressure rise. The last recorded pressure inside the CUBIC camera was ~7 x 10^-6 torr. Pumping will continue until the satellite needs to be shipped. Tests have been conducted at Penn State to determine whether this pressure rise poses any hazard to the thin optical filters inside the camera. The result of these tests shows that damage to the filter is unlikely, even if the instrument is opened on-orbit with up to 10 torr of pressure inside. (The filter was tested up to 20 torr differential pressure and sustained a few small pin-hole leaks. In the flight mounting, we expect the differential pressure across the filter to be small because of gaps between the filter housing and the CCD, so we do not anticipate any damage to the filter in flight.)

All testing having been completed, CUBIC and SAC-B await transport to the NASA Wallops Flight Facility, for integration into the Pegasus XL launch vehicle .

Get more instrument specs , see photos, and learn about the launch date.

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Last updated: October 2, 1996
Web page maintained by David Burrows ( burrows@astro.psu.edu ) and Mark Skinner
Department of Astronomy and Astrophysics
Penn State University