ISS Risk Mitigation

Shuttle-Mir Alignment Stability Experiment (SMASE)


The SMASE experiment was designed to characterize the relative alignment stability of Shuttle and Mir navigation bases while docked. Characterization of this stability will enable mission planners to determine the feasibility of transferring attitude data between vehicles in the event that either vehicle is unable to maintain an accurate estimate of attitude. This technique will be applicable to ISS since it may be necessary in Phase 2 and/or 3 to transfer sensor data between Russian and U.S. segments.

Shuttle-Mir Missions
STS-71, STS-74, STS-76, STS-79

Shuttle and Mir vehicle attitude data were collected during multiple three-hour data collection periods while the two vehicles were docked. Navigational-dependent events were attitude thruster firings, Inertial Measurement Unit (IMU) alignments, and star tracker data takes. The experiment required no astronaut crew involvement; the Mir star trackers were activated during periods of time while the Orbiter was docked to Mir. Data transfer was made by ground controllers and evaluated postflight.

Results have shown that the measured transformation between the Shuttle and the Mir Space Station was within 0.3 degrees of preflight predictions. For STS-74, the measured bias of 0.95 degrees about the Orbiter pitch axis agreed very well with the JSC Structures and Mechanics Division prediction of 0.9 degrees. The maximum attitude variation between Shuttle and Mir did not exceed 0.61 degrees, but this maximum attitude value did occurred on STS-71. For STS-74 and STS-76, the maximum values were 0.20 and 0.47, respectively. During any three hour period, the relative stability between Shuttle and Mir did not exceed 0.12 degrees RMS. Typically, the relative stability between Shuttle and Mir was about 0.6 degrees RMS. The stability was excellent, considering attitude time tag errors were as large as 2.5 seconds. Shuttle attitude data was utilized to reduce Mir attitude errors from 2-3 degrees to 1 degree on STS-76.

Analysis of experiment results provided validation of analytical tools that will used to predict the transformation between U.S. segments. Very good stability during a mission indicates that Russian attitude data will meet the U.S. segment accuracy requirements of 0.5 degrees/axis. Additionally, very good stability within data periods indicates low noise on Russian segment attitude data. Transferring attitude data between U.S. and Russian segments is feasible and will certainly benefit ISS.

Lofton R, Conley C. International Space Station Phase 1 Risk Mitigation and Technology Demonstration Experiments. 48Th International Astronautical Congress; 1997 Oct 6-10; Turin, Italy; International Astronautical Federation.

Principal Investigators
Russell E. Yates
NASA/Johnson Space Center

S. Shitov, Ph.D.

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Page last updated: 07/16/1999

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