Engineering topics

Bell, Charles E.

Publications and source records attributed to Bell, Charles E..

4 records

NASA NTRS2010

We're Here to Help You

Air Force lore tells us that the two biggest lies you will ever hear on the tarmac are when the Inspector General steps off the plane and says to the Wing Commander, "We're here to help you," and the Wing Commander replies, "We're glad to see you." Not too surprisingly, a similar relationship is often perceived between a project manager and the mission assurance representative (especially for operations). This perception intensifies as budgets shrink and missions shorten, after all, where is the value added? That is the question we will examine for three small, short projects: Phoenix, WISE, and Grail (which is yet to launch). All have limited resources to devote to "niceties" and a very short mission to reap the benefits for their operations. We will examine how mission operations assurance evolved for each project, what worked well, what could have been improved, and how these lessons can be applied to ensure mission operations assurance is a value added function for Grail and future small missions.

Topex↗

NASA NTRS1988

The Mariner Mark II high precision scan actuator - Results of an options trade study covering pointing performance and system-wide impacts

Four actuators considered as candidates to meet the requirements of the Mariner Mark II high-precision scan platform are evaluated with respect to such criteria as the net effect on spacecraft mass, required power, cost, expected pointing performance, operational considerations, and necessary control complexity. A direct drive actuator is found to be the most suitable candidate. It is noted that for missions where reactionless actuation results in a lower spacecraft mass due to propellant savings, the option of using a platform mounted or spacecraft mounted reaction wheel for platform momentum compensation and spacecraft attitude control is attractive.

Schier, J. Alan↗

NASA NTRS1987

Soft mounted momentum compensated pointing system for the Space Shuttle Orbiter

This paper describes a potential pointing and tracking system for the Space Shuttle with possible future application to Space Station. In order to accomplish high precision pointing and tracking (at rates up to 2 deg/s) in the expected disturbance environment, a high bandwidth gimbaled pointing system is required. A soft-mounted, momentum-compensated gimbal system is suggested for this role. A momentum-compensated system is inertially reacting, decoupling the control system dynamics from the basebody structural dynamics. This allows a soft isolation stage to be added between the basebody and the articulation stage, which attenuates high frequency disturbances. In this paper, three configurations are examined: a hard-mounted system, a passive soft-mounted system, and an active soft-mounted system. Analysis demonstrates that the soft-mounted systems have superior disturbance-rejection properties. The active soft mount allows reduction of the isolation stiffness to zero, and so obtains the highest level of performance.

Sirlin, Samuel W.↗

NASA NTRS1987

Mariner Mark II - Spacecraft control for the 1990's and beyond

The Mariner Mark II reconfigurable modular spacecraft concept will incorporate a Spacecraft Attitude and Articulation Control System of novel design. Attention is presently given to key component technologies that will be used for the first time in the Mariner Mark II; these encompass CCD-based, target-referenced extended body tracking, fiber-optic rate sensing, and momentum compensation for dynamic isolation of payloads. An analysis of star and target body-tracking requirements is presented, together with an account of the precision-pointing platform disturbance rejection properties required.

Bell, Charles E.↗