Engineering topics

Snow, Frank

Publications and source records attributed to Snow, Frank.

6 records

NASA NTRS2004

Fixing What's Broken

We planned to launch in July 2000. Heading into March that year we were on schedule, under budget, meeting all of our performance requirements, and ready for the final testing Near the end of the day, it was time for the sign burst test. For 200 milliseconds we would put a non-feedback force on our system, which meant we couldn't adjust or halt the test in progress. Something went wrong, terribly wrong during the sign burst test. For 200 milliseconds we would put a non-feedback force on our system, which meant we couldn't adjust or halt the test in process. Something went wrong, terribly wrong during the sign burst test. As mission manager, I was standing just ten feet away from the spacecraft when this happened. It sounded like a clap of thunder. With the test stopped, we moved in closer to see what had happened - and we knew immediately that we had damaged our spacecraft. How much, we didn't know.

Snow, Frank↗

NASA NTRS2002

Two Outs, Bottom of the Ninth

It was eight months before launch when my second Flight Operations Team lead said he was leaving the project for another job. Six months earlier, the original lead had said he was leaving. I was stunned--but I remained confident that we would recover. I didn't expect to lose the second lead. After all, lightning is not supposed to strike twice in the same place. This time, with only eight months until launch, I was very much concerned. No, 'concerned' is probably too mild a word. Let's get it right: I was sweating. Losing a lead at any stage presents problems, but two losses within 6 months of each other can definitely shake the confidence of an inexperienced Flight Ops Team.

Snow, Frank↗

NASA NTRS2002

The 'Tried and True'

There was a Chinese place near Goddard Space Flight Center where members of my Advanced Composition Explorer (ACE) team often went for lunch. The food wasn't great, but after you go to a place a few times, suddenly, you've got a history there. It's where we celebrated birthdays, project milestones; it was a good place to get away during the day when things weren't going well and folks needed to blow off steam; and it was also the place to go when we needed to let someone go on the project, to mitigate any hard feelings that might linger as a result. I wouldn't want to give anyone the idea that project teams, even the successful ones, are 11 perfect families." Conflicts occur when you're dealing with engineers, scientists, technicians, and bureaucrats. We had our share on ACE. For the good of the project and everyone involved, we occasionally had to get rid of some people. I made it a policy that when someone was leaving the project because of a personality conflict, then everyone on the team, or as many as there were around, went out for lunch as a send off. End things on a nice, friendly note. If there is some bitterness, and sometimes there is, we see if we can bury that and just go on.

Snow, Frank↗

NASA NTRS1996

Enhancing the ACE control center for the multiple uses of spacecraft integration and test and mission and science operations

In relation to the mandate to reduce space mission development and operations costs, the advanced composition explorer (ACE) will use a version of the Transportable Payload Operations Control Center (TPOCC) for its mission operations. It was determined during the phase B of the ACE project that a potential existed for substantial savings if the adaptation of the TPOCC for the ACE mission operations could include its adaptation for use as the primary component in the ground support equipment for the integration and testing of the ACE spacecraft, and for use as the basic component in the ACE science center. The implementation of this approach required the enhancement of the TPOCC requirements, changes in the development schedule and changes in the allocation and activities of the personnel responsible for the development of ACE operations. It is discussed how these issues, and the problems that arose, were addressed.

Snow, Frank↗

NASA NTRS1988

Accuracy study of the Upper Atmosphere Research Satellite (UARS) definitive attitude determination

The Upper Atmosphere Research Satellite (UARS) has two definitive attitude determination requirements: the definitive attitude of the Modular Attitude Control Subsystem (MACS) and the definitive attitude of the gimbaled Solar-Stellar Pointing Platform (SSPP). The onboard computer (OBC) will compute the MACS attitude using a Kalman filter and will transform this attitude solution through the SSPP gimbals to calculate the SSPP attitude. The attitude ground support system (AGSS) will compute the MACS attitude using a batch least-squares differential corrector algorithm and will also transform this solution through the gimbals to obtain the SSPP attitude. This paper reports the results of a prelaunch study to predict the accuracy of the OBC attitude solutions and the accuracy of the AGSS attitude solutions. The OBC and AGSS solution accuracies are then compared to establish the relative quality. The effects of star observability, sensor noise, and sensor misalignment uncertainties on attitude determination accuracy are analyzed for each case.

Snow, Frank↗

NASA NTRS1988

An analysis of the Kalman filter in the Gamma Ray Observatory (GRO) onboard attitude determination subsystem

The Gamma Ray Observatory (GRO) spacecraft needs a highly accurate attitude knowledge to achieve its mission objectives. Utilizing the fixed-head star trackers (FHSTs) for observations and gyroscopes for attitude propagation, the discrete Kalman Filter processes the attitude data to obtain an onboard accuracy of 86 arc seconds (3 sigma). A combination of linear analysis and simulations using the GRO Software Simulator (GROSS) are employed to investigate the Kalman filter for stability and the effects of corrupted observations (misalignment, noise), incomplete dynamic modeling, and nonlinear errors on Kalman filter. In the simulations, on-board attitude is compared with true attitude, the sensitivity of attitude error to model errors is graphed, and a statistical analysis is performed on the residuals of the Kalman Filter. In this paper, the modeling and sensor errors that degrade the Kalman filter solution beyond mission requirements are studied, and methods are offered to identify the source of these errors.

Snow, Frank↗