A Proposed Discovery Mission
Photo: NASA/JPL [Larger 99K GIF]
Photo: NASA/JPL [Larger 99K GIF] | NOTE: The following information was provided to the Astrobiology Web by the Prinicpal Investigator on this proposed mission with their permission to distribute it freely as we deemed appropriate. This is not an official NASA or JPL website and, as such, the information presented here is in no way endorsed or validated by NASA or JPL. Neither the Astrobiology Web or Reston Communications has any contractual or bidding relationship with NASA, JPL, or any of the proposing parties. We just think these are exciting ideas and wanted to share what we have learned with our readers. |
D. SCIENCE
D.4.6. Particle Collector (PC)
The Particle Collector consists of a small box comprising several cells of the collecting plate area with a total area of 25 cm2. (See figure on pullout). The box is capped with a thin metal film. As particles impact on the film they penetrate leaving microscopic holes. After entering the box particles will largely vaporize as they impact the far wall of the collection chamber. The small holes represent a negligible leak and the vapor is essentially trapped for the duration of the encounter. After encounter a metal lid with a low temperature Indium Gallium metal seal is thermally activated to emplace a metal - to - metal seal preventing any further loss of gas.
The expected mass in particles intercepted by the spacecraft is computed to be over 0.01 ug m- 2 (see figure on pullout), or for a 10 cm radius collector. Since the mean particle size is expected to be 1 um, this implies capture of about 70 particles. To determine the loss rate of gas in the collection box during the encounter we assume that the entrance film receives 100 punctures of 1 um radius. The pressure of 0.3 nanograms of mass in the 0.5 liter volume is ~10- 13 atms (for an intial gas temperature of 500 K) and the mean free path is of vastly larger than the size of the container. Thus leakage from the collector will occur only when molecules chance to impact the puncture sites. The loss rate is therefore the hole area divided by the total container area multiplied by the collision rate with the walls. Due to the extremely small area insignificant leakage occurs over the timescale of the encounter (the timescale to deplete by a factor of e is about 14 hours and the encounter lasts only 10 minutes). After encounter the container is closed with the metal lid and sealed with the low current solder system for return to Earth.