A Rocket-borne Ion Mass Spectrometer for the Mesosphere That is Pumped by Rocket Aerodynamics

Details A Rocket-borne Ion Mass Spectrometer for the Mesosphere That is Pumped by Rocket Aerodynamics A Rocket-borne Ion Mass Spectrometer for the Mesosphere That is Pumped by Rocket Aerodynamics

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa21a0250s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA21A-0250

Physics

3311 Clouds And Aerosols, 3349 Polar Meteorology

Scientific paper

Rocket-borne mass spectrometers for ions have been flown that were evacuated by cryogenic vacuum pumps with liquid helium or neon. There have not been flights since 1993 because these instruments required expensive deliveries of cryogens and frequent refillings. Advances in (1) aerodynamic modeling, (2) mass spectrometer design, and (3) ion detection technology make possible a new approach to mass spectrometry in the mesosphere in which the spectrometer is pumped by the flow around the rocket. First, the Direct Simulation Monte-Carlo method has been applied to simulating the air flow around the rocket payload. We find that if the forward deck of the payload is supported on a stalk of smaller diameter (10 cm for example), that a low-density void is created below the forward deck by the flow around the payload, assuming that the payload is pointed in the ram direction. The air density below the deck is reduced from ambient by a factor 7 and 15 at altitudes of 80 and 90 km, respectively. The mass spectrometer is exhausted into this void which acts as a pump. In a conservative scenario, the spectrometer is kept evacuated on the upleg then opened at the apogee both at the inlet and exit. Data are acquired on the downleg to 70 km, below which the pressure in the low-density void becomes too high. Second, we use the rotating field mass spectrometer which operates at higher pressure (up to 30 mTorr) than the quadrupole spectrometer because the ion path length is shorter (2 cm) and because a larger ion acceleration potential is used that reduces the ion-neutral collision cross section. Third, we use a new design of channel electron multiplier that has been shown to operate at pressures up to 10 mTorr in the lab, corresponding to the number density at approximately 80 km in the arctic winter.

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