Cometary probe of the Venera-Halley mission

Venera-Halley mission is to be launched to Venus in Dec. 1984. It will fly by Venus in June 1985. Separation of the cometary probe and Venera descend module will take place at that time. The gravitational swing-by at Venus will provide the encounter with the Halley comet in March 1986. The remote sensing of the inner coma (TV-imagery, spectrometry in the region from 1200 A to 12 μm, polarimetry) and of the nucleus, direct measurements of dust fluxes, dust composition, plasma and magnetic field are planned in the framework of multinational cooperation.     

The exploration of halley''s comet: An example of international cooperation

During its present appearance, Comet Halley is the focus of an unparalleled global scientific effort of exploration from the ground; from Earth orbit; from Venus orbit; from interplanetary space; and from within the comet itself.

The various activities in space are coordinated by the four space agencies — the European Space Agency (ESA), Intercosmos of the USSR Academy of Sciences, the Japanese Institute of Space and Astronautical Science (ISAS), and the National Aeronautics and Space Administration (NASA) — through the Inter-Agency Consultative Group (IACG). Coordination of the activities of the ground-based observers is provided through the International Halley Watch (IHW). The IHW was established in 1980, the IACG in 1981.

The single goal of both, IHW and IACG is to maximize the overall scientific results of all efforts in the exploration of Comet Halley from the ground and from space. The obvious success of this unique endeavor might serve as example for future cooperative scientific programs.     

Empirical model of the composition of the Venus ionosphere: Repeatable characteristics and key features not modeled

In-situ measurements of positive ion composition of the ionosphere of Venus are combined in an empirical model which is a key element for the Venus International Reference Atmosphere (VIRA) model. The ion data are obtained from the Pioneer Venus Orbiter Ion Mass Spectrometer (OIMS) which obtained daily measurements beginning in December 1978 and extending to July 1980 when the uncontrolled rise of satellite periapsis height precluded further measurements in the main body of the ionosphere. For this period, measurements of 12 ion species are sorted into altitude and local time bins with altitude extending from 150 to 1000 km. The model results exhibit the appreciable nightside ionosphere found at Venus, the dominance of atomic oxygen ions in the dayside upper ionosphere and the increase in prominence of atomic oxygen and deuterium ions on the nightside. Short term variations, such as the abrupt changes observed in the ionopause, cannot be represented in the model.     

一种针对金星探测器的姿态指向设计

摘要： 金星探测需要超长距离低码率传输,因而金星探测器需要保持其数传天线指向地球.相对于地球轨道飞行器来说,金星探测器距离太阳更近,需要固定散热面来维持探测器内的温度.提供一种基于在金星探测器偏置安装天线的姿态指向设计,能够保证从金星向地球传输数据并且维持散热面远离太阳.而此设计旨在减少数传天线的数量至一根同时将两个固定平面作为散热面.还提供两种详细方案来控制姿态机动来保证在数传天线始终指向地球的同时在特定节点切换散热面.     

Analysis of NASA’s DSN Venus Express radio occultation data for year 2014

The Venus Express Radio Science Experiment (VeRa) was part of the scientific payload of the Venus Express (VEX) spacecraft and was targeted at the investigation of Venus’ atmosphere, surface, and gravity field as well as the interplanetary medium. This paper describes the methods and the required calibrations applied to VEX-VeRa raw radio occultation data used to retrieve vertical profiles of Venus’ ionosphere and neutral atmosphere. In this work we perform an independent analysis of a set of 25 VEX, single-frequency (X-band), occultations carried out in 2014, recorded in open-loop at the NASA Deep Space Network. Our temperature, pressure and electron density vertical profiles are in agreement with previous studies available in the literature. Furthermore, our analysis shows that Venus’ ionosphere is more influenced by the day/night condition than the latitude variations, while the neutral atmosphere experiences the opposite. Our scientific interpretation of these results is based on two major responsible effects: Venus’ high thermal inertia and the zonal winds. Their presence within Venus’ neutral atmosphere determine why in these regions a latitude dependence is predominant on the day/night condition. On the contrary, at higher altitudes the two aforementioned effects are less important or null, and Venus’ ionosphere shows higher electron density peaks in the probed day-time occultations, regardless of the latitude.     

Cometary constraints on the planet forming environment.

Molecular elemental and isotopic abundances of comets provide sensitive diagnostics for models of the primitive solar nebula. New measurements of the N2, NH and NH2 abundances in comets together with the in situ Giotto mass spectrometer and dust analyzer data provide new constraints for models of the comet forming environment in the solar nebula. An inventory of nitrogen-containing species in comet Halley indicates that NH3 and CN are the dominant N carriers observed in the coma gas. The elemental nitrogen abundance in the gas component of the coma is found to be depleted by a factor approximately 75 relative to the solar photosphere. Combined with the Giotto dust analyzer results for the coma dust component, we find for comet Halley Ngas + dust approximately 1/6 the solar value. The measurement of the CN carbon isotope ratio from the bulk coma gas and dust in comet Halley indicates a significantly lower value, 12C/13C = 65 +/- 9 than the solar system value of 89 +/- 2. Because the dominant CN carrier species in comets remains unidentified, it is not yet possible to attribute the low isotope ratio predominantly to the bulk gas or dust components. The large chemical and isotopic inhomogeneities discovered in the Halley dust particles on 1 mu scales are indicative of preserved circumstellar grains which survived processing in the interstellar clouds, and may be related to the presolar silicon carbide, diamond and graphite grains recently discovered in carbonaceous chondrites. Less than 0.1% of the bulk mass in the primitive meteorites studied consists of these cosmically important grains. A larger mass fraction (approximately 5%) of chemically heterogeneous organic grains is found in the nucleus of comet Halley. The isotopic anomalies discovered in the PUMA 1 Giotto data in comet Halley are probably also attributable to preserved circumstellar grains. Thus the extent of grain processing in the interstellar environment is much less than predicted by interstellar grain models, and a significant fraction of comet nuclei (approximately 5%) may be in the form of preserved circumstellar matter. Comet nuclei probably formed in much more benign environments than primitive meteorites.     

Technology development for a long duration,mid-cloud level Venus balloon

This paper describes the results of ongoing technology development activities for a Venus spherical superpressure balloon capable of flying for long durations (30 days) in the middle cloud layer at an altitude of 55.5 km. Data is presented from a successful aerial deployment and inflation flight experiment on a 5.5 m diameter prototype balloon conducted at a 2.5 km altitude above the Earth. Although the balloon in that test was not released for free flight, all other steps in the deployment and inflation process were successfully executed. Experimental and computational results are also presented from an investigation of the stress concentration phenomenon at the junction of the metal end fitting and fabric end cap of the prototype Venus balloon. Good agreement was found between the simulation and experimental results and a stress concentration factor of 1.55 determined for this end cap design compared to the expectations of thin membrane theory. Finally, results are presented for a new, second-generation Venus balloon material utilizing Aclar™ film instead of Teflon. Optical property and sulfuric acid tolerance data are presented for this material based on laboratory testing of samples.     

Lower and upper limits to comet p/halley solid material loss rate

A radiative hydrodynamic model of comet P/Halley is used to investigate quantitatively the constraints imposed onto the Comet loss rate in solids by both the in-situ data and the remote sensing data. In particular, for the first time, the in-situ data are used to fit composite spectra extending from near-IR wavelengths to the microwave region. Also, for the first time the uncertainty affecting the ejection velocity of large grains is taken into account. The results suggest that only future rendez-vous studies of the grain density in the vicinity of a comet would be able to provide definitely reliable values of the comet loss rate.     

The properties of the low altitude magnetic belt in the Venus ionosphere

When the solar wind dynamic pressure is high, the Venus ionosphere usually contains a belt of steady magnetic field at the very lowest altitudes to which Pioneer Venus probes. The current layer that flows on the high altitude side of this low altitude belt is centered at an altitude which ranges from 170 to 190 km with a most probable altitude of 182 km. This altitude is independent of solar zenith angle and hence the current system is flowing horizontally rather than vertically as proposed by Cloutier and co-workers. The lower edge of the magnetic belt was probed only on the lowest altitude passes of Pioneer Venus. This boundary is even more stable in location. The belt has decayed to 90% of its maximum strength usually by 162 km and to 50% of its maximum strength by 155 km. We interpret these data to indicate that the observed magnetic structure of the Venus ionosphere is a product of temporal evolution rather than of spacecraft motion through a spatially varying static structure.     

Further information on structure of the atmosphere of Venus derived from the VEGA Venus balloon and Lander mission

Continued analysis of the pressure and temperature data returned by the two Vega mission balloons has revealed an apparently significant difference in mean atmospheric static stability between the two data sets. Furthermore, the stability is time dependent within each data set, as reported earlier. The 6.5K temperature contrast between the two balloons remains, and appears to have a counterpart in the contrast between two of the Pioneer Venus probes at these levels, which has been attributed to planetary scale waves. Comparisons of the Vega 2 Lander data with those of the Pioneer Venus Large Probe shows relatively close agreement in the state properties and in the atmospheric static stability profiles as well.     

Dust modelling of fast-flyby missions: Implications of in situ measurements

Using the Divine approach to modelling of cometary dust distributions within the dust envelope, together with the Reference Model parameters established by the Comet Halley Environment Working Group, predicted flux and fluence values are presented for each of the Giotto Dust Impact Detection System (DIDSY) subsystems. Implications for returned DIDSY data is discussed with particular reference to mass-size distribution and particle fluence as a fuction of time. It is also shown that the first particle impact event recorded by any of the DIDSY subsystems is likely to be of sufficient mass to penetrate the front shield of the Giotto spacecraft.     

Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude

From a critical comparison and synthesis of data from the four Pioneer Venus Probes, the Pioneer Venus Orbiter, and the Venera 10, 12, and 13 landers, models of the lower and middle atmosphere of Venus are derived. The models are consistent with the data sets within the measurement uncertainties and established variability of the atmosphere. The models represent the observed variations of state properties with latitude, and preserve the observed static stability. The rationale and the approach used to derive the models are discussed, and the remaining uncertainties are estimated.     

In-situ photopolarimetric measurements of dust and gas in the coma of Halley''s comet

The Halley Optical Probe Experiment (HOPE) on board the Giotto spacecraft has provided the first in-situ measurements, both of the dust and of some gaseous species, from inside the coma of the comet. The instrument has already been described /1/, together with first results /2/. The purpose of this note is to show how optical measurements can lead to in-situ information, how those were obtained during the 13–14 march 1986 Halley fly-by, and what is the status of the data analysis.     

Comparative atmospheric dynamics for terrestrial planets

A review is presented of theoretical ideas on the general circulations in the atmospheres of Earth, Mars and Venus and also of results of their theoretical modelling. The role of various factors is discussed in the formation of the circulations. These results are compared with observational data obtained by different means. Data of direct local measurements of meteorological parameters in the atmospheres of Venus and Mars are discussed including those obtained at their surfaces.     

Comparative study of the dust emission of 19P/Borrelly (Deep space 1) and 1P/Halley

Images obtained by the Miniature Integrated Camera and Imaging Spectrometer (MICAS) experiment onboard the Deep Space 1 spacecraft which encountered comet 19P/Borrelly on September 22nd 2001 show a dust coma dominated by jets. In particular a major collimated dust jet on the sunward side of the nucleus was observed. Our approach to analyse these features is to integrate the observed intensity in concentric envelopes around the nucleus. The same procedures has been used on the Halley Multicolour Camera images of comet 1P/Halley acquired on March 14th 1986. We are able to show that at Borrelly the dust brightness dependence as a function of radial distance is different to that of Halley. At large distances both comets show constant values as the size of the concentric envelopes increases (as one would expect for force free radial outflow). For Halley the integral decreases as one gets closer to the nucleus. Borrelly shows opposite behaviour. The main cause for Halley's intensity distribution is either high optical thickness or particle fragmentation. For Borrelly, we have constructed a simple model of the brightness distribution near the nucleus. This indicates that the influence of deviations from point source geometry is insufficient to explain the observed steepening of the intensity profile close to the nucleus. Dust acceleration or fragmentation into submicron particles appear to be required. We also estimate the dust production rate of Borrelly with respect to Halley and compare their dust to gas ratios.     

The derivation of Halley parameters from observations

A set of nominal model parameters for P/Halley is derived from its light curve and spectra. In those cases where Halley observations are not sufficient, the average value derived from a large set of other comets has been used, or data from comet Bennett, Halley's best analogue has been taken. The derived parameters include nucleus mass, size, density, albedo, rotation period, axial inclination, and surface temperature, the composition of the parent molecules, the total gas and dust production rates, distributions for the dust size and bulk density as well as various other parameters.     

Thermal modeling of Halley's comet

The comet thermal model of Weissman and Kieffer is used to calculate gas production rates and other parameters for the 1986 perihelion passage of Halley's Comet. Gas production estimates are very close to revised pre-perihelion estimates by Newburn based on 1910 observations of Halley; the increase in observed gas production post-perihelion may be explained by a variety of factors. The energy contribution from multiply scattered sunlight and thermal emission by coma dust increases the total energy reaching the Halley nucleus at perihelion by a factor of 2.4. The high obliquity of the Halley nucleus found by Sekanina and Larson may help to explain the asymmetry in Halley's gas production rates around perihelion.     

Planet-A mission to Halley

Looking at the chance of the next apparition of the Halley comet in 1986, ISAS decided to send a first Japasanese interplanetary spacecraft for the study of cometary hydrogen coma and solar wind. The Planet-A spacecraft which carries VUV imaging camera and solar wind plasma analyser will be launched in August 1985 and flyby the Halley comet in early March 1986 with the distance of several million kilometers from the comet nucleus. This mission is not only self-consistent but collaborative with other space mission as well as earth-bound observations. In the present paper, the Planet-A mission to Halley is described with brief explanation of the spacecraft.     

Composition of the Venus atmosphere below 100 km altitude

Our current knowledge on the composition of the Venus atmosphere in the altitude range from the surface to 100 km is compiled. Gases that have been measured, and whose mixing ratios are assumed to be constant with altitude, are CO₂, N₂, He, Ne, Ar, and Kr. Gases that have been identified in the lower and/or middle atmosphere, but whose mixing ratios may depend on altitude, latitude and/or local time, are CO, H₂O, HCl, HF, and SO₂. Conflicting data or only upper limits exist on some important trace gases, such as O₂, H₂, and Cl₂. The latter two are key constituents in the photochemistry of the middle atmosphere of Venus. The chapter concludes with a listing of the isotopic abundances of elements measured in the Venus atmosphere.     

Venus atmospheric circulation: Observations and implications of the thermal structure

Continued analysis of Pioneer Venus imaging and polarimetry data indicates that the average cloud-top level circulation is mainly zonal (east to west) with a small meridional component. Presence of planetary scale waves and a possible sun-related component are evident in the data. If the tracked features refer to the same vertical level, then some variability of the circulation would have to be present to account for the Pioneer and Mariner 10 cloud-tracking results. However, the implied balanced flow from the observed thermal structure analysis strongly suggests that at least some of the variations in these observations is due to apparent cloud-top variations and that the circulation itself is relatively stable.Direct cyclostrophic calculations based on the observed thermal structure of the atmosphere yield a balanced zonal circulation with distinct mid-latitude jets (peak velocities about 110–120 ms^?1) located between 50 and 40 mb in each hemisphere of the planet near 45° latitude. The calculations which extend to about 40 km altitude from 80 km above the surface agree well with the observed entry probe zonal components and indicate breakdown of the balance condition near the upper and lower boundaries at low latitudes.The balanced flow results are consistent with the Mariner 10 and Pioneer cloud tracked estimates of the zonal circulation provided the effective altitude of the tracked features is slightly different at different observation periods. The features in the Pioneer Venus data would then lie on a sloping surface that extends from about 68 km (40 mb) at low latitudes to about 75 km (10 mb) in mid-latitudes. The polarization features would occur on a roughly parallel surface that is 1–2 km above the effective cloud-height surface, and Mariner 10 features would have effective altitudes somewhat lower than the Pioneer ultraviolet features. A slight asymmetry is evident in the balanced zonal circulation arising out of an asymmetry in the thermal field.Finally, the solenoids formed by intersecting isobaric and isosteric (constant specific volume) surfaces deduced from the Pioneer Venus radio occultation data show distinct evidence of a direct meridional circulation that may be important in sustaining the Venus atmospheric circulation.