Solar wind interaction with comet Halley

In March 6 and 9, 1986 the spacecrafts ‘Vega-1’ and ‘Vega-2’ have flown through the coma of comet Halley and have carried measurements of plasma, energetic particles, magnetic field and plasma waves along its trajectory. A short review of these measurements and its comparison with theoretical models of solar wind interaction with comets are given.

The spacecrafts ‘Vega-1’ and ‘Vega-2’ have studied the solar wind loading by cometary ions, the structure of cometary bow shock and the processes in the inner coma of comet Halley. Exactly in this sequence we discuss the results of measurements and compare them with the theory.     

Hydrogen coma of comet P/Halley

The main molecular processes to produce the hydrogen comae of comets are now well known: Water, the main constituent of cometary atmospheres, is photodissociated by the solar ultraviolet radiation to form the high (20 km s⁻¹) and low (8 km s⁻¹) velocity components of the atomic hydrogen. The hydrogen clouds of various fresh comets have been observed in 1216Å by a number of spacecrafts. Ultraviolet observations of short period comets are, however, rather rare. Consequently Comet P/Halley in this apparition is a good object to obtain new physics of the hydrogen coma. Strong breathing of the hydrogen coma of this comet found by “Suisei” provides just such an example. The rotational period of Comet Halley's nucleus, its activity in the form of outbursts alone, and the position of jet sources etc. are determined from the breathing phenomena. Atomic hydrogen from organic compounds with a velocity of 11 km s⁻¹ play an important role in that analysis. The time variations of the water production rate of Comet Halley during this apparition observed by various spacecrafts appear to be in agreement with each other and are about 1.5–2 times larger than the standard model. The difficulty of the calibration problem was emphasized.     

Development of the Infrared Telescope in Space: IRTS

Infrared Telescope in Space (IRTS) is a cryogenically cooled small infrared telescope aboard the small space platform, SFU (Space Flyer Unit). IRTS has a telescope of 15 cm diameter, which is rather small compared with other big space missions. IRTS, however, is optimized to observe extended diffuse sources with four focal plane instruments which have wide wavelength coverage from the near infrared to the submillimeter region.

All instruments have been calibrated with a test cryostat, and integrated into the flight cryostat. Cooling tests of the whole IRTS system have confirmed that instruments and cryostat will perform as expected. Integration of the IRTS on the SFU will soon begin and the ground tests of the SFU system will be conducted in the coming year.

The launch of the SFU will be in early 1995. The IRTS will survey the 10% of the sky during the three week mission and provide significant scientific results on cosmology, galactic structure, interstellar matter, stars, and solar system.     

SAX overview

Information is given concerning the satellite for X-Ray Astronomy SAX, a project of the Italian Space Agency in collaboration with the Netherlands Agency for Aerospace Programs, due for launch at end 1993.

The scientific objectives and the payload are described, together with the ground system structure and organization.     

Planetary environment protection ID no: F3.3-M.1.05 implications for the development of a network of surface stations on Mars.

The European Space Agency's studies of a Comet Nucleus Sample Return mission (ROSETTA) as its Planetary Cornerstone in its long-term programme 'Horizon 2000' and the Marsnet mission, a potential contribution of the Agency to an international network of surface stations on Mars, has revived the interest in the present state of Planetary Protection requirements. MARSNET was one of the four candidate missions selected in April 1991 for further Design Feasibility (Phase A) Studies. Furthermore, of all space agencies participating in planetary exploration activities only the United States National Aeronautics and Space Administration had a well established Planetary Protection Policy on Viking and other relevant planetary missions, whereas ESA is considering the feasibility and potential impact of a planetary protection policy on its Marsnet mission, within the framework of a tight budgetary envelope applicable to ESA's medium (M) class missions. This paper will discuss in general terms the impact of Planetary Protection measures, its implications for Marsnet and the issues arising from this for the implementation of the mission in ESA's scientific programme.     

Phobos-Grunt: Russian sample return mission

As an important milestone in the exploration of Mars and small bodies, a new generation space vehicle “Phobos-Grunt” is planned to be launched by the Russian Aviation and Space Agency. The project is optimized around a Phobos sample return mission and follow up missions targeted to study some main asteroid belt bodies, NEOs and short period comets. The principal constraint is use of the “Soyuz-Fregat” rather than the “Proton” launcher to accomplish these challenging goals. The vehicle design incorporates innovative SEP technology involving electrojet engines that allowed us to increase significantly the mission's energetic capabilities, as well as highly autonomous on-board systems. Basic criteria underlining the “Phobos-Grunt” mission scenario, scientific objectives and rationale including Mars observations during the vehicle's insertion into Mars orbit and Phobos approach maneuvers, are discussed and an opportunity for international cooperation is suggested.     

Project overview and highlights of Suisei and Sakigake

ISAS's (Institute of Space and Astronautical Science) project for the exploration of comet Halley consists of two spacecraft, Sakigake and Suisei, launched on 7 January 1985 and 18 August, respectively.

Sakigake passed the sunward side of the comet on 11 March 1986 with a miss distance of 6.99 million km. Three experiments, a plasma wave probe with dipole and search-coil antennae, a magnetometer with three axis ring core sensor on an extended boom and a four-grid Faraday cup attached to the inner side of the wall of the spacecraft, detected various phenomena caused by the comet at a distance as far as 7 million km.

The other spacecraft, Suisei, flew by the comet on its sunward side with a miss distance of 151 thousand km on 8 March 1986. It carried two experiments, an ultraviolet imager and an energy analyzer for ions. The UV imager was able to take the first image of the hydrogen cloud of comet Halley on 26 November 1985. With this experiment, the spin period of the cometary nucleus, location of jets, amount of water evaporation, distribution of hydrogen density inside cloud, etc. were clarified. The energy analyser experiment provided information on the intensive interaction between cometary and solar wind ions.     

Optical observations of ion tail structures and velocity flows in comet Halley during the period of the five spacecraft encounters

Observations of the distribution and evolution of a number of the major constituents of the neutral coma (CN, C₂, CH, O, H, Na) of Comet Halley were made during two observing periods, each of 3 weeks duration, from the Table Mountain Observatory, California. The first period was pre-perihelion, in late November/December 1985. The second period, from Feb 28 to March 22 1986, covered the five close spacecraft encounters with Halley, and when ICE flew some 20 M Km upstream of Halley. Sodium emission was recorded in early Dec 1985 from the near-nuclear region at a heliocentric distance of 1.4 AU, an observation confirmed with the UCL Doppler Imaging system. The CN coma could be detected to an outer diameter of more than 4M Km in Dec 1985, and 5 – 6M Km in early March 1986, allowing the production of heavy cometary pick-up ions to be estimated. Observations of the cometary ion coma (H₂O⁺ and CO⁺ ions) showed considerable variability from day to day, particularly during the period of the spacecraft encounters. These observations have been used, in conjuction with the neutral coma data, to map the flow field of cometary ions. In early Dec. 1985, Halley developed a traditional “type I” ion tail, which persisted until late April 1986. It has also been possible to evaluate the ion flow fields within the narrow core of the ion tail, and in the surrounding diffuse, low density, regions populated by pick-up and extracted cometary ions, and by slowed solar wind ions. Tail disconnection events were observed on several occasions, particularly between the VEGA 2 and GIOTTO encounters, and with a highly spectacular event on March 19 1986.     

火星空间环境磁场探测研究——高精度磁强计

萤火一号卫星将对火星空间环境磁场实施探测。火星磁场对火星弓激波、磁鞘、电离层、大气等绝大多数空间环境效应都具有重要影响,萤火一号对火星磁场的探测是通过搭载于其上的科学载荷磁强计来实现的。此磁强计在工作原理及具体设计上,考虑了火星轨道严酷的工作环境和科学目标所需的测量要求。通过装星前的地面标定测试,验证了萤火一号磁强计可以在-130～75℃温度范围内测量±256nT以内的磁场,分辨率可达到0.01 nT,带宽内总噪声小于0.03 nT,能够满足萤火一号对火星空间环境探测的需求。     

Cometary atmosphere (gas and dust)

There is important progress now in the identifications and measurements of primary (parent) molecules in the inner coma of Comet Halley. H₂O, CO₂ and CO are definitely in the list, CH and some complicate organic molecules are suspected. Gas production rate for water vapor is Q_H2O 10³⁰ s⁻¹. The bulk of data doesn't contradict to the Whipple model of nucleus (with clathrate modification). Pronounced spatial structure of gaseous flow in the coma was observed, but in general measured properties of neutral gas in the coma of Comet Halley are not very different from predicted. Situation for dust is different. In situ dust measurements show that size spectrum and optical properties of particles in coma are substantively declining from predicted on the base of groundbased photometry. However there are discrepancies between Vega and Giotto dust counter data. Dust in the inner coma didn't prevent the succesful imaging of nucleus by TV on Vega 1 and 2.     

Solar wind plasma flow and motion of the comet tail

The paper overwievs the bending of the ion tail of Comet Halley between the period of the first of December, 1985 and the first of April, 1986 by using the solar wind and interplanetary magnetic field data which were obtained by Japan's first interplanetary probe ‘SAKIGAKE’.     

中国深空探测任务轨道控制技术综述

深空探测作为人类航天活动的重要方向,是人类探索宇宙奥秘和寻求长久发展的必然途径,也是衡量一个国家综合国力和科学技术发展水平的重要标志。深空探测轨道控制技术作为决定深空探测任务成败的关键技术之一,越来越多地受到关注并得到应用,成为各国深空探测技术研究和发展的热点。以我国探月工程各次任务为脉络,简述了历次任务轨道控制的目标和实施效果,总结了主要技术创新,在此基础上,展望了我国未来深空探测轨道控制的发展趋势。     

Investigation of magnetospheric processes with the use of a source of strong magnetic field in the ionosphere

More than 20 years ago V.P. Shabansky suggested that the magnetic system installed aboard the satellite, could be used as a physical instrument for studying the processes which occur in the near Earth space. The corresponding space scales of an artificial “magnetosphere”—“magnisphere”—are 10 m in the experiment with relatively small magnets in the ionosphere and 100 m in the solar wind. The corresponding similarity criteria are estimated. The possible scheme of the experiment with a superconducting magnet (magnetic moment 10⁵ A · m²) installed aboard the satellite is considered. The experimental complex includes a number of systems for measuring the fluxes of charged particles in a wide energy range, DC electric and magnetic fields, the electromagnetic fields in different frequency bands (from X-rays to radio). The scientific objectives are discussed in detail.     

Tail phenomena

An overview of tail phenomena is presented based on worldwide submissions to the Large-Scale Phenomena Discipline Specialist Team of the International Halley Watch. Examples of tail phenomena and science are presented along with estimates of total expected yield from the Network. The archive of this material will clearly be very valuable for studying the solar-wind/comet interaction during the 1985–1986 apparition of Halley's Comet.     

Wide field ultraviolet observations of Comet Halley with the FAUST Spacelab I instrument

The wide field (7.5°), arc minute imaging, and spectroscopic capabilities of the Far Ultraviolet FAUST telescope which will be flown on Spacelab I can provide valuable information on Comet Halley. The use of the FAUST instrument in obtaining images of the hydrogen coma at 1216 Å, and in obtaining objective grating spectroscopy from 1300–3300 Å of the comet and tail, are described. The FAUST images would provide large field of view data that are required for model calculations of gas production rates and the determination of scale lengths and lifetimes of ion species.     

Orbit Design for Twin-spacecraft Space VLBI

Space Very Long Baseline Interferometry (S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes. It can achieve much higher spatial resolution than that from the ground-only VLBI. In this paper, a new concept of twin spacecraft S-VLBI has been proposed, which utilizes the space-space baselines formed by two satellites to obtain larger and uniform uv coverage without atmospheric influence and hence achieve high quality images with higher angular resolution. The orbit selections of the two satellites are investigated. The imaging performance and actual launch conditions are all taken into account in orbit designing of the twin spacecraft S-VLBI. Three schemes of orbit design using traditional elliptical orbits and circular orbits are presented. These design results can be used for different scientific goals. Furthermore, these designing ideas can provide useful references for the future Chinese millimeter-wave S-VLBI mission.      

VEGA three-channel spectrometer experiment: Spectroscopy of comet Halley in the visible and near-ultraviolet ranges

A total of 3600 spectra of Comet Halley in the 275–710 nm were obtained on March, 8, 9, 10 and 11, 1986, from the VEGA 2 spacecraft. The emissions of OH, NH, CN, C₃, CH, C₂, NH₂ and H₂O⁺ are identified. From the OH intensity in the (0,0) band: 1.1 Megarayleigh at 5400 km from the nucleus, it can be inferred that the OH production rate was (1.4 ± 0.5)×10³⁰ molecules s⁻¹. The NH, C₃, CH and NH₂ bands became comparatively more intense at distances from the nucleus shorter than 3000km. At 06:40 U.T. when the instrument field of view was 6000×4500 km, two jets were observed. Spectra from the jets show significant differences with other spectra. Inside a jet NH, C₃ and NH₂ are comparatively more intense and the rotational distributions of OH, CN and C₂ are strongly distorted. This shows that part of the observed emissions probably comes from radicals directly produced in the excited state during the initial process of photolysis of the parent molecules.     

Origin of organic matter in the protosolar nebula and in comets.

Comet organics are traced to their origin in interstellar space. Possible sources of comet organics from solar nebula chemistry are briefly discussed. The infrared spectra of interstellar dust are compared with spectra of solar (space) irradiated laboratory organic residues and with meteorites. The spectra compare very favorably. The atomic composition of first generation laboratory organic residues compares favorably with that of comet Halley organics if divided into appropriate "volatile" (less refractory) and "refractory" (more refractory) complex organics.     

A Far Infrared Photometer (FIRP) for the Infrared Telescope in Space (IRTS)

We describe the design and calibration of the Far-Infrared Photometer (FIRP), one of four focal plane instruments on the Infrared Telescope in Space (IRTS). The FIRP will provide absolute photometry in four bands centered at 150, 250, 400, and 700 μm with spectral resolution λ/Δλ ≈ 3 and spatial resolution ΔΘ = 0.5 degrees. High sensitivity is achieved by using bolometric detectors operated at 300 mK in an AC bridge circuit. The closed-cycle ³He refrigerator can be recycled in orbit. A 2 K shutter provides a zero reference for each field of view. More than 10% of the sky will be surveyed during the ≈3 week mission lifetime with a sensitivity of <10⁻¹³ W·cm⁻²·sr⁻¹ per 0.5 degree pixel.