Molecule Indexes

Space Science Reviews -     

Rosina – Rosetta Orbiter Spectrometer for Ion and Neutral Analysis

The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) will answer important questions posed by the mission’s main objectives. After Giotto, this will be the first time the volatile part of a comet will be analyzed in situ. This is a very important investigation, as comets, in contrast to meteorites, have maintained most of the volatiles of the solar nebula. To accomplish the very demanding objectives through all the different phases of the comet’s activity, ROSINA has unprecedented capabilities including very wide mass range (1 to >300 amu), very high mass resolution (m/Δ m > 3000, i.e. the ability to resolve CO from N₂ and ¹³C from ¹²CH), very wide dynamic range and high sensitivity, as well as the ability to determine cometary gas velocities, and temperature. ROSINA consists of two mass spectrometers for neutrals and primary ions with complementary capabilities and a pressure sensor. To ensure that absolute gas densities can be determined, each mass spectrometer carries a reservoir of a calibrated gas mixture allowing in-flight calibration. Furthermore, identical flight-spares of all three sensors will serve for detailed analysis of all relevant parameters, in particular the sensitivities for complex organic molecules and their fragmentation patterns in our electron bombardment ion sources.     

Rare Atoms,Molecules and Radicals in the Coma of P/Halley

We have searched for rare molecules and radicals in the coma of P/Halley using the ion data obtained by IMS-Giotto. Whereas our established methods were used in the ionosphere, a new model was developed for the interpretation of the ion data in the outer coma. Ne/H₂O < 1.5 × 10^-3 was determined in the coma of the comet. Upper limits for the production of Na were derived from the very low abundance of Na⁺. Methyl cyanide and (probably) ethyl cyanide were identified with abundances of CH₃CN/H₂O = (1.4 ± .6) × 10^-3 and C₂H₅CN/H₂O = (2.8 ± 1.6) × 10^-4. These results and upper limits for other N-bearing species confirm that nitrogen is depleted in the Halley material. C₄H was identified and a point source strength of C₄H/H₂O = (2.3 ± .8) × 10^-3 was derived. Our upper limit for C₃H is lower than the abundance of C₄H. This is in agreement with the enhanced abundances of C_nH species with even numbers of C-atoms found in interstellar molecular clouds, suggesting that the C₄H in Halley was synthesized under molecular cloud conditions. Thus, C₄H and other organics with unpaired electrons may turn out to be indicators for a molecular cloud origin of cometary constituents. This revised version was published online in June 2006 with corrections to the Cover Date.     

New Centroid Algorithm Based upon Amplitude-Angle Signature

A method of estimating the centroid location of a target utilizing radar scan return amplitude versus angle information is presented. The method is compared with three thresholding estimators and a first moment estimator in a computer-simulated automatic landing system. This new method is the most robust and accurate during periods of low signal-to-noise ratio. In periods of high signal-to-noise ratio the method has less error than the thresholding methods and is similar in accuracy to the first moment estimator. Furthermore, the number of pulse transmissions required to obtain a desired level of performance in noise is much less than that needed for the thresholding methods and the first moment estimator employed in this simulation.     

Frequency-Agility Processing to Reduce Radar Glint Pointing Error

A technique to reduce radar pointing errors due to glint using frequency agility and amplitude weighting is presented. The reduction in rms tracking error is developed into an equation dependent upon the original glint tracking error, ?g, and the number of returns weighted, N. The rms tracking error is thereby reduced approximately by a factor of N. Finally, the equation formulated allows one to evaluate the reduction in glint error versus the number of frequencies chosen for frequency agility.