Computer Science – Performance
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.462g&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Performance
Scientific paper
Seen the efforts to find alternative actuation systems to the pyrotechnic devices, our department is developing and testing release mechanisms, for microsatellites, actuated by Shape Memory Alloy (SMA) wires. Following up increasing interest on SMA actuated mechanisms, the author has been developing, in the last few years, a mechanism of which a prototype version has been presented in the last IAF congress. The present work describes the test phase of the mechanism, aimed at proving the capability of the parts of withstanding the severe space environmental conditions. The mechanism task is to open a steel rope loop, replacing a pyrotechnic guillotine. It is activated by three SMA wires that, shrinking, pull a sleeve and separate the two parts of the mechanism where the extremities of the rope are fixed. In the paper, after a short review of the past design and realization activities, we describe the tests conducted and their results. After the room condition tests, the mechanism has been set up for thermo-vacuum tests. In high vacuum condition, 10-10 bar, we validate the thermodynamic model for the SMA alloy. In room condition, free convection around the wires subtracts a large amount of the energy provided to the wires due to Joule effect, and then we have been obliged to actuate the mechanism with a power greater than that needed in vacuum, providing a constant current of 5 Amperes. In the thermo-vacuum chamber of the University we can simulate space environment and we can power the mechanism exactly with the current (3A) that will be actually employed during the mission. Moreover, the environmental control of the chamber allowed us to test the real capability of the mechanism, and of the SMA wires, to operate correctly at different temperatures. Inside the chamber a set of lamps irradiate energy toward the mechanism and heat it, simulating the solar and albedo radiation. Cooling the internal surface of the chamber with liquid nitrogen, we can simulate the eclipse condition, in witch the satellite and the mechanism are no more heated by the sun and they cool radiating energy toward the open space. The mechanism is lightweight and the SMA wires are 0.4 millimetres in diameter, making the system very sensible to the environmental changes and making it reach the equilibrium temperature in a few seconds. After solving the problems connected to the temperature measurement of a thin and light wire, we have simulated the thermal excursion expected during a typical LEO microsatellite mission, and we have observed the performance of the mechanism at high and low temperature, validating the mathematical model. It is needed that the mechanism does not open accidentally for excessive heating when it is not powered, and we have to prove that the mechanism will open, when powered, even if it is very cold. It is clear that when the wires are heated by solar radiation, it will be needed a minor amount of energy to cause the transition of the SMA wires from martensitic to austenitic phase and, when the wires are cold, the power system has to feed the mechanism for a longer time. We have compared the experimental data with the numeric prediction of the actuation times and we will see if the power needed is compatible with the power availability of a microsatellite. After the thermo-vacuum tests we are interested in the capability of the mechanism to bear the vibration of a space launch system. Since it is mounted on a steel rope, the system acts like a vibrating rope with masses applied on it. We have to see if the oscillations of the rope will not open the mechanism. Moreover, the SMA wires themselves can be modelled as vibrating ropes; we have to verify that their oscillation will not act like a shrinking of the wires, opening the mechanism. Using the shaker in our structure laboratory we will show that the mechanism will not accidentally open when it is shaken along different directions. We will compare the numeric predicted critical frequencies with the experimental observations. In this paper we will prove that the devised mechanism can pass the qualification tests and that it is a valid device for space applications.
No associations
LandOfFree
Thermo Vacuum and Vibration Tests on a Shape Memory Alloy (SMA) Actuated Release Mechanism for Microsatellite does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Thermo Vacuum and Vibration Tests on a Shape Memory Alloy (SMA) Actuated Release Mechanism for Microsatellite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermo Vacuum and Vibration Tests on a Shape Memory Alloy (SMA) Actuated Release Mechanism for Microsatellite will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1331714