P. von Allmen

Distribution of water around the nucleus of comet 67P/Churyumov-Gerasimenko at 3.4 AU from the Sun as seen by the MIRO instrument on Rosetta

The Microwave Instrument on the Rosetta Orbiter (MIRO) has been observing the coma of comet 67P/Churyumov-Gerasimenko almost continuously since June 2014 at wavelengths near 0.53 mm. We present here a map of the water column density in the inner coma (within 3 km from nucleus center) when the comet was at 3.4 AU from the Sun. Based on the analysis of the H 2 O and H18 2 O (110-101) lines, we find that the column density can vary by two orders of magnitude in this region. The highest column density is observed in a narrow region on the dayside, close to the neck and north pole rotation axis of the nucleus, while the lowest column density is seen against the nightside of the nucleus where outgassing seems to be very low. We estimate that the outgassing pattern can be represented by a Gaussian distribution in a solid angle with FWHM ≈ 80◦.

Evolutionary computation technologies for space systems

The Evolvable Computation Group, at NASAs Jet Propulsion Laboratory, is tasked with demonstrating the utility of computational engineering and computer optimized design for complex space systems. The group is comprised of researchers over a broad range of disciplines including biology, genetics, robotics, physics, computer science and system design, and employs biologically inspired evolutionary computational techniques to design and optimize complex systems. Over the past two years we have developed tools using genetic algorithms, simulated annealing and other optimizers to improve on human design of space systems. We have further demonstrated that the same tools used for computer-aided design and design evaluation can be used for automated innovation and design. These powerful techniques also serve to reduce redesign costs and schedules

Dark side of comet 67P/Churyumov-Gerasimenko in Aug.-Oct. 2014. MIRO/Rosetta continuum observations of polar night in the southern regions

The high obliquity (similar to 50 degrees) of comet 67P/Churyumov-Gerasimenko (67P) is responsible for a long-lasting winter polar night in the southern regions of the nucleus. We report observations made with the submillimeter and millimeter continuum channels of the Microwave Instrument onboard the Rosetta Orbiter (MIRO) of the thermal emission from these regions during the period August-October 2014. Before these observations, the southern polar regions had been in darkness for approximately five years. Subsurface temperatures in the range 25 50 K are measured. Thermal model calculations of the nucleus near-surface temperatures carried out over the orbit of 67P, coupled with radiative transfer calculations of the MIRO channels brightness temperatures, suggest that these regions have a thermal inertia within the range 10-60 Jm(-2) K-1 s(-0.5). Such low thermal inertia values are consistent with a highly porous, loose, regolith-like surface. These values are similar to those derived elsewhere on the nucleus. A large difference in the brightness temperatures measured by the two MIRO continuum channels is tentatively attributed to dielectric properties that differ significantly from the sunlit side, within the first few tens of centimeters. This is suggestive of the presence of ice(s) within the MIRO depths of investigation in the southern polar regions. These regions started to receive sunlight in May of 2015, and refinements of the shape model in these regions, as well as continuing MIRO observations of 67P, will allow refining these results and reveal the thermal properties and potential ice content of the southern regions in more detail.

Low-thrust mission trade studies with parallel, evolutionary computing

New mission concepts are increasingly considering the use of ion propulsion for fuel-efficient navigation in deep space. The development of new low-thrust mission concepts requires efficient methods to rapidly determine feasibility and thoroughly explore trade spaces. This paper presents parallel, evolutionary computing methods to assess a trade-off between delivered payload mass and required flight time. The developed methods utilize a distributed computing environment in order to speed up computation, and use evolutionary algorithms to approximate optimal solutions. The methods are coupled with the Primer Vector theory, where a thrust control problem is transformed into a co-state control problem and the initial values of the co-state vector are optimized. The developed methods are applied to two mission scenarios: i) an orbit transfer around Earth and ii) a transfer between two distant retrograde orbits around Europa. The solutions found with the present methods are comparable to those obtained by other state-of-the-art trajectory optimizers. The required computational time can be up to several orders of magnitude shorter than that of other optimizers thanks to the utilization of the distributed computing environment, the significant reduction of the search space dimension with the primer vector theory, and the efficient and synergistic exploration of the remaining search space with evolutionary computing

Evolutionary computation technologies for the automated design of space systems

The Evolvable Computation Group, at NASAs Jet Propulsion Laboratory (JPL), is tasked with demonstrating the utility of computational engineering and computer optimized design for complex space systems. The group is comprised of researchers over a broad range of disciplines including biology, genetics, robotics, physics, computer science and system design, and employs biologically inspired evolutionary computational techniques to design and optimize complex systems. Over the past two years we have developed tools using genetic algorithms, simulated annealing and other optimizers to improve on human design of space systems. We have further demonstrated that the same tools used for computer-aided design and design evaluation can be used for automated innovation and design, and be applied to hardware in the loop such as robotic arms and MEMS micro-gyroscopes. These powerful techniques also serve to reduce redesign costs and schedules.

Evolutionary Computational Methods for the Design of Spectral Instruments

We have developed a technique based on evolutionary computational methods (ECM) that allows for the automated optimization of complex computationally modeled systems. We have demonstrated that complex engineering and science models can be automatically inverted by incorporating them into evolutionary frameworks and that these inversions have advantages over conventional searches by not requiring expert starting guesses (designs) and by running on large cluster computers with less overall computational time than conventional approaches. We have applied these techniques to the automated retrieval of atmospheric and surface spectral signatures from Earthshine observational data. We have demonstrated that in addition to automated spectral retrieval, ECM can also be used to evaluate the discriminability of scientific results as a function of requirements placed on the spectral model. An important application of this technique is for the optimization of design parameters for spectral instruments.

Spatially resolved evolution of the local H2O production rates of comet 67P/Churyumov-Gerasimenko from the MIRO instrument on Rosetta

Aims. Using spectroscopic and continuum data measured by the MIRO instrument on board Rosetta of comet 67P/ChuryumovGerasimenko, it is possible to derive and track the change in the water production rate, to learn how the outgassing evolves with heliocentric distance. The MIRO data are well suited to investigate the evolution of 67P, in unprecedented spatial and temporal detail. Methods. To obtain estimates of the local effective Haser production rates we developed an efficient and reliable retrieval approach with precalculated lookup tables. We employed line area ratios (H16 2 O/H 18 2 O) from pure nadir observations as the key variable, along with the Doppler shift velocity, and continuum temperature. This method was applied to the MIRO data from August 2014 until April 2016. Perihelion occurred on August 13, 2015 when the comet was 1.24 AU from the Sun. Results. During the perihelion approach, the water production rates increased by an order of magnitude, and from the observations, the derived maximum for a single observation on August 29, 2015 is (1.42 ± 0.51) × 1028. Modeling the data indicates that there is an offset in the peak outgassing, occurring 34 ± 10 days after perihelion. During the pre-perihelion phase, the production rate changes with heliocentric distance as r−3.8±0.2 h ; during post-perihelion, the dependence is r −4.3±0.2 h . The comet is calculated to have lost 0.12 ± 0.06 % of its mass during the perihelion passage, considering only water ice sublimation. Additionally, this method provides well sampled data to determine the spatial distribution of outgassing versus heliocentric distance. The time evolution is definitely not uniform across the surface. Preand post-perihelion, the surface temperature on the southern hemisphere changes rapidly, as does the sublimation rate with an exponent of ∼−6. There is a strong latitudinal dependence on the rh exponent with significant variation between northern and southern hemispheres, and so the average over the comet surface may only be of limited importance. We present more detailed regional variation in the outgassing, demonstrating that the highest derived production rates originate from the Wosret, Neith and Bes regions during perihelion.

Fault Injection Campaign for a Fault Tolerant Duplex Framework

Software based fault tolerance may allow the use of COTS digital electronics in building a highly reliable computing system for spacecraft. In this work we present the results of a fault injection campaign we conducted on the Duplex Framework (DF). The DF is a software developed by the UCLA group [1], [2] that allows to run two copies (or replicas) of the same program on two different nodes of a commercial off-the-shelf (COTS) computer cluster. By the means of a third process (comparator) running on a different node that constantly monitors the results computed by the two replicas, the DF is able to restart the two replica processes if an inconsistency in their computation is detected. In order to test the reliability of the DF we wrote a simple fault injector that injects faults in the virtual memory of one of the replica process to simulate the effects of radiation in space. These faults occasionally cause the process to crash or produce erroneous outputs. For this study we used two different applications, one that computes an encryption of a input file using the RSA algorithm, and another that optimizes the trade-off between time spent and the fuel consumption for a low-thrust orbit transfer. But the DF is generic enough that any application written in C or Fortran could be used with little or no modification of the original source code. Our results show the potential of such approach in detecting and recovering from radiation induced random errors. This approach is very cost efficient compared to hardware implemented duplex operations and can be adopted to control processes on spacecrafts where the fault rate produced by cosmic rays is not very high.