Chasing Black Holes: An Insider's View of a Space Astronomy Mission by Bradt Hale

Author:Bradt, Hale
Language: eng
Format: epub
Publisher: Van Dorn Books
Published: 2021-08-30T00:00:00+00:00

A dedicated-spacecraft study and another painful scrubbing, April 1990

As the instrument teams began their design efforts, in 1990, the XTE was still to fly on the Explorer Platform with a change-out of instruments (EUVE to XTE) to take place in the Shuttle bay. The risks associated with this complex operation were becoming apparent upon closer examination. Also, the 1986 loss of the Challenger and subsequent 2.7-year hiatus of Shuttle flights made clear that our dependence on an operational Shuttle carried substantial risk of additional large delays.

An alternative plan was thus revived, namely the fabrication of a dedicated spacecraft designed for XTE, which would be launched by a Delta II rocket. This would completely free the XTE project from the Shuttle, the Explorer Platform, the EUVE project, and the (expensive) manned space program. Goddard would design and build the spacecraft and integrate the experiments into it, making use of its own expert in-house team of engineers and technicians.

A study by Goddard of this plan yielded a cost for the spacecraft. In the same time frame, new costs were generated by the three instrument teams. The total program then underwent a review led by George Newton of NASA Headquarters. As usual, the total cost had come to a higher value than was deemed acceptable, and there was again great pressure on both the spacecraft people and the instrument teams to bring that cost down. If we were to escape from the risky Explorer Platform, it was essential that the dedicated spacecraft plan be made attractive to NASA Headquarters. Again, the mission was at a critical juncture!

I remember sitting around a big table, possibly in April 1990 at Goddard, with Dr. Newton and his staff from NASA Headquarters, managers and engineers from the Goddard spacecraft group, and my fellow scientists from UCSD and Goddard. From my team, there was Al Levine, Bill Mayer, and Ron Remillard who was new to such meetings. Everyone was put on the spot to give up something to get the cost down. It was made clear again that smoke-and-mirrors savings such as reductions in man-hour estimates were not acceptable. Only giving up real hardware or complete tasks would count.

At stake were the integrity of the science experiments and the spacecraft systems that we desired for an effective mission. The latter included rapid maneuverability, nearly continuous telemetry at a high rate, and (nearly) all-sky all-year pointing of the PCA. If the ASM saw a spectacular flareup of a source, we wanted to be able to reorient XTE to bring it into the PCA narrow field of view and collect data from it, no matter the time of year or where the source was on the sky.

This required rotatable (not fixed) solar panels for electrical power and two antennas, one of which would be kept continuously pointed toward one of NASA’s two TDRSS telemetry relay satellites. The two antennas would allow XTE to download data and to upload commands from almost any point in the XTE orbit regardless of XTE’s orientation.

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