An inter-comparison of zenith tropospheric delays derived from DORIS and GPS data

Doppler Orbitography Radiopositioning Integrated by Satellite (DORIS) and Global Positioning System (GPS) techniques are similarly affected by propagation delays in the neutral atmosphere (troposphere) and hence make use of similar data processing strategies for reducing this effect. We compare Zenith Tropospheric Delays (ZTDs) estimated from 52 DORIS and GPS station pairs co-located at 35 sites over the 2005–2008 period. We find an overall systematic negative mean bias of −4 mm and a median bias of −2 mm, with a large site-to-site scatter and especially stronger biases over South America, potentially linked to remaining problems related to the South Atlantic Anomaly (SAA) in the current DORIS data processing. The standard deviation of ZTD differences is in the range 4–12 mm over the globe (8 mm on average), with larger values located in the southern hemisphere. The spatial variability of differences is consistent with previous work but remains largely unexplained. DORIS is shown to be much less sensitive to instrumental changes than GPS (only the switch from Alcatel to Starec antenna at Toulouse is detected as an offset of −4 mm in the ZTD time series). On the opposite, discontinuities and spurious annual signals are found in the GPS ZTD solutions. A discontinuity of +5 mm is found on 5 November 2006, linked to the switch from relative to absolute GPS antenna models used in the data processing. The use of modified GPS antennas (e.g. at GODE) or improved antenna models is shown to reduce the spurious annual signal (e.g. from 5 mm to 2 mm at METS). Overall, the agreement between both techniques is good, though DORIS shows a significantly larger random scatter. The high stability and good spatial and temporal coverage make DORIS a potential candidate technique for meteorology and climate studies as long as reasonable time averaging can be applied (e.g. differences are reduced from 8.6 to 2.4 mm with 5-day averages) and no real-time application is considered. This technique could be considered as a potential contributor to Global Geodetic Observing System (GGOS) for climatology.     

Telerobotics: problems and research needs

With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of `telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA     

Prebiotic significance of extraterrestrial ice photochemistry: detection of hydantoin in organic residues

The delivery of extraterrestrial organic materials to primitive Earth from meteorites or micrometeorites has long been postulated to be one of the origins of the prebiotic molecules involved in the subsequent apparition of life. Here, we report on experiments in which vacuum UV photo-irradiation of interstellar/circumstellar ice analogues containing H(2)O, CH(3)OH, and NH(3) led to the production of several molecules of prebiotic interest. These were recovered at room temperature in the semi-refractory, water-soluble residues after evaporation of the ice. In particular, we detected small quantities of hydantoin (2,4-imidazolidinedione), a species suspected to play an important role in the formation of poly- and oligopeptides. In addition, hydantoin is known to form under extraterrestrial, abiotic conditions, since it has been detected, along with various other derivatives, in the soluble part of organic matter of primitive carbonaceous meteorites. This result, together with other related experiments reported recently, points to the potential importance of the photochemistry of interstellar "dirty" ices in the formation of organics in Solar System materials. Such molecules could then have been delivered to the surface of primitive Earth, as well as other telluric (exo-) planets, to help trigger first prebiotic reactions with the capacity to lead to some form of primitive biomolecular activity.     

Estimation of moving heat sources with a three-dimensional unsteady inverse method

This study aims at estimating a moving heat source with a three dimensional inverse model and a high spatial resolution. In order to cope with the large amount of computations required in the three dimensional case, a linear unsteady inverse model based on the principle of superposition has been made. Two concepts are used to reduce the computation time: the first is linked to the diffusion time of the heat, and the second to the redundancy of information. Firstly, numerical tests are presented. Then, a laboratory experiment, consisting in the estimation of the flux of a moving laser beam, is described.     

The performance of KSC Fixation Tubes with RNALater for orbital experiments: A case study in ISS operations for molecular biology

Molecular biology experiments on the International Space Station (ISS) continue to face challenges of sample harvesting and sample return to earth for post flight analysis; however, the use of Kennedy Space Center Fixation Tubes filled with RNALater has proven to be a robust solution to many of these challenges. While it is clear that one direction of future spaceflight experimentation may be towards enhanced on-orbit analytical capabilities, the rapid progress of earth-bound analytical capacity dictates that facile return of molecular biology samples from the ISS will continue to be a mainstay of space life sciences research and flight operations. In this paper we present a case study of the successful performance of KFTs and RNALater over a broad set of operational conditions of ascent configuration, on-orbit experiment use, on-orbit storage and sample return configurations that are unique to ISS current operations and constraints. We also provide observations on performance limits and discuss deployment opportunities and scenarios that are consistent with continued successful ISS molecular biology experimentation.     

The quantification of wound healing as a method to assess late radiation damage in primate skin exposed to high-energy protons.

In an experiment examining the effects of space radiations on primates, different groups of rhesus monkeys (Macaca mulatta) were exposed to single whole-body doses of 32- or 55-MeV protons. Survivors of those exposures, together with age-matched controls, have been monitored continuously since 1964 and 1965. Late effects of nominal proton doses ranging from 2-6 Gray have been measured in vitro using skin fibroblasts from the animals. A logical extension of that study is reported here, and it involves observations of wound healing after 3-mm diameter dermal punches were removed from the ears (pinnae) of control and irradiated monkeys. Tendencies in the reduction of competence to repair cutaneous wounds have been revealed by the initial examinations of animals that received doses greater than 2 Gy more than 2 decades earlier. These trends indicate that this method of assessing radiation damage to skin exposed to high-energy radiations warrants further study.     

L'avion,plateforme d'observations scientifiques

Transition between high altitude manned observatories and unmanned balloon-borne or rocket-borne experiments is achieved with high flying aircrafts, at altitudes above tropopause (>12 km), which became readily available, at reasonable cost and reliability, in the past five or ten years.This paper reviews the development of scientific uses of aircrafts, especially for astronomy and geophysics, with some emphasis placed on infrared problems, closely related to the scale height of the chief infrared absorber, i.e. telluric water vapor.Absorbers distribution vs altitude and spectral characteristics are summarized (Figures 1, 2, 3).Capabilities of various available aircrafts are compared (Table I) and the various ways to consider modifications are discussed: structural modifications or design problems to fit telescopes or light collectors on board. Tables II and III list the advantages of airborne observations, compared to other spatial carriers, and also the specific problems connected with aircrafts. Adopted solutions to these problems are exposed (Figures 4, 5, 6, 7) and costs are briefly discussed.Finally, a few examples of scientific results, gathered in the few past years from aircraft, are given, both in astronomy and in geophysics.