共查询到20条相似文献,搜索用时 31 毫秒
1.
《Acta Astronautica》2008,62(11-12):995-1001
A mission to the surface of Venus would have high scientific value, but most electronic devices and sensors cannot operate at the 450 °C ambient surface temperature of Venus. Power and cooling systems were analyzed for Venus surface operation. A radioisotope power and cooling system was designed to provide electrical power for a probe operating on the surface of Venus. For a mission duration of substantial length, the use of thermal mass to maintain an operable temperature range is likely impractical, and active refrigeration may be required to keep components at a temperature below ambient. Due to the high thermal convection of the high-density atmosphere, the heat rejection temperature was assumed to be at a 500 °C radiator temperature, 50 °C above ambient. The radioisotope Stirling power converter designed produces a thermodynamic power output capacity of 478.1 W, with a cooling power of 100 W. The overall efficiency is calculated to be 23.36%. The mass of the power converter is estimated at approximately 21.6 kg. 相似文献
2.
Venus remains one of the great unexplored planets in our solar system, with key questions remaining on the evolution of its atmosphere and climate, its volatile cycles, and the thermal and magmatic evolution of its surface. One potential approach toward answering these questions is to fly a reconnaissance mission that uses a multi-mode radar in a near-circular, low-altitude orbit of ∼400 km and 60–70° inclination. This type of mission profile results in a total mission delta-V of ∼4.4 km/s. Aerobraking could provide a significant portion, potentially up to half, of this energy transfer, thereby permitting more mass to be allocated to the spacecraft and science payload or facilitating the use of smaller, cheaper launch vehicles.Aerobraking at Venus also provides additional science benefits through the measurement of upper atmospheric density (recovered from accelerometer data) and temperature values, especially near the terminator where temperature changes are abrupt and constant pressure levels drop dramatically in altitude from day to night.Scientifically rich, Venus is also an ideal location for implementing aerobraking techniques. Its thick lower atmosphere and slow planet rotation result in relatively more predictable atmospheric densities than Mars. The upper atmosphere (aerobraking altitudes) of Venus has a density variation of 8% compared to Mars' 30% variability. In general, most aerobraking missions try to minimize the duration of the aerobraking phase to keep costs down. These short phases have limited margin to account for contingencies. It is the stable and predictive nature of Venus' atmosphere that provides safer aerobraking opportunities.The nature of aerobraking at Venus provides ideal opportunities to demonstrate aerobraking enhancements and techniques yet to be used at Mars, such as flying a temperature corridor (versus a heat-rate corridor) and using a thermal-response surface algorithm and autonomous aerobraking, shifting many daily ground activities to onboard the spacecraft. A defined aerobraking temperature corridor, based on spacecraft component maximum temperatures, can be employed on a spacecraft specifically designed for aerobraking, and will predict subsequent aerobraking orbits and prescribe apoapsis propulsive maneuvers to maintain the spacecraft within its specified temperature limits. A spacecraft specifically designed for aerobraking in the Venus environment can provide a cost-effective platform for achieving these expanded science and technology goals.This paper discusses the scientific merits of a low-altitude, near-circular orbit at Venus, highlights the differences in aerobraking at Venus versus Mars, and presents design data using a flight system specifically designed for an aerobraking mission at Venus. Using aerobraking to achieve a low altitude orbit at Venus may pave the way for various technology demonstrations, such as autonomous aerobraking techniques and/or new science measurements like a multi-mode, synthetic aperture radar capable of altimetry and radiometry with performance that is significantly more capable than Magellan. 相似文献
3.
Nuclear Electric Propulsion (NEP) is a technology conceptually proposed since the 1940s by E. Stuhlinger in Germany. The JIMO mission originally planned by NASA in the early 2000s produced at least two designs of ion thrusters fed by a 20–30 kW nuclear powerplant. When compared to conventional (chemical) propulsion, the major advantage of NEP in the JIMO context was recognized to be the much higher Isp (lab-tested at up to 15,000 s) and the capability for sustained power generation, up to 8–10 years when derated to Isp about 8000 s.The goal of this paper is to show that current or near term NEP technology enables missions far beyond our immediate interplanetary backyard. In fact, by extending the semi-analytical approach used by Stuhlinger, with reasonable ratios α≡power/mass of the propulsion system (i.e., 0.1– 0.4 kW/kg), missions to the Kuiper Belt (40 AU and beyond) and even the so-called FOCAL mission (at 540 AU) become feasible with an attractive payload fraction and in times of order 10–15 years.Further results regarding missions to Sedna’s perihelion/aphelion, and to Oort’s cloud will also be presented, showing the constraints affecting their feasibility and mass budget. 相似文献
4.
An analysis is performed on four typical materials (aluminum, liquid hydrogen, polyethylene, and water) to assess their impact on the length of time an astronaut can stay in deep space and not exceed a design basis radiation exposure of 150 mSv. A large number of heavy lift launches of pure shielding mass are needed to enable long duration, deep space missions to keep astronauts at or below the exposure value with shielding provided by the vehicle. Therefore, vehicle mass using the assumptions in the paper cannot be the sole shielding mechanism for long duration, deep space missions. As an example, to enable the Mars Design Reference Mission 5.0 with a 400 day transit to and from Mars, not including the 500 day stay on the surface, a minimum of 24 heavy lift launches of polyethylene at 89,375 lbm (40.54 tonnes) each are needed for the 1977 galactic cosmic ray environment. With the assumptions used in this paper, a single heavy lift launch of water or polyethylene can protect astronauts for a 130 day mission before exceeding the exposure value. Liquid hydrogen can only protect the astronauts for 160 days. Even a single launch of pure shielding material cannot protect an astronaut in deep space for more than 180 days using the assumptions adopted in the analysis. It is shown that liquid hydrogen is not the best shielding material for the same mass as polyethylene for missions that last longer than 225 days. 相似文献
5.
Beyond the Earth's atmosphere, galactic cosmic radiation (GCR) and solar energetic particles (SEPs) are a significant hazard to both manned and robotic missions. For long human missions on the lunar surface (months to a year) a radiation shelter is needed for dose mitigation and emergency protection in case of solar events. This paper investigates the interaction of source protons of solar events like those of February 1956 that emitted many fewer particles with energies up to 1000 MeV and of the October 1989 event of lower protons energy but higher fluence, with the lunar regolith and aluminum shielding of a lunar shelter. The shelter is 5 m in diameter and has a footprint of 5×8 m and a 10 cm thick aluminum support structure, however, actual thickness could be much smaller (~1–2 cm) depending on the weight of the regolith shielding piled on top. The regolith is shown to be slightly more effective than aluminum. Thus, the current results are still applicable for a thinner aluminum structure and increased equivalent (or same mass) thickness of the regolith. The shielding thicknesses to reduce the dose solely due to solar protons in the lunar shelter below those recommended by NASA to astronauts for 30 day-operation in space (250 mSv) and for radiation workers (50 mSv) are determined and compared. The relative attenuation of incident solar protons with regolith shielding and the dose estimates inside the shelter are calculated for center seeking, planar, and isotropic incidence of the source protons. With the center seeking incidence, the dose estimates are the highest, followed by those with isotropic incidence, and the lowest are those with the planar incidence. 相似文献
6.
Marc Studer Gesine Bradacs Andre Hilliger Eva Hürlimann Stephanie Engeli Cora S. Thiel Peter Zeitner Beat Denier Markus Binggeli Thomas Syburra Marcel Egli Frank Engelmann Oliver Ullrich 《Acta Astronautica》2011,68(11-12):1729-1741
Long-term sensitivity of human cells to reduced gravity has been supposed since the first Apollo missions and was demonstrated during several space missions in the past. However, little information is available on primary and rapid gravi-responsive elements in mammalian cells. In search of rapid-responsive molecular alterations in mammalian cells, short-term microgravity provided by parabolic flight maneuvers is an ideal way to elucidate such initial and primary effects. Modern biomedical research at the cellular and molecular level requires frequent repetition of experiments that are usually performed in sequences of experiments and analyses. Therefore, a research platform on Earth providing frequent, easy and repeated access to real microgravity for cell culture experiments is strongly desired. For this reason, we developed a research platform onboard the military fighter jet aircraft Northrop F-5E “Tiger II”. The experimental system consists of a programmable and automatically operated system composed of six individual experiment modules, placed in the front compartment, which work completely independent of the aircraft systems. Signal transduction pathways in cultured human cells can be investigated after the addition of an activator solution at the onset of microgravity and a fixative or lysis buffer after termination of microgravity. Before the beginning of a regular military training flight, a parabolic maneuver was executed. After a 1 g control phase, the parabolic maneuver starts at 13,000 ft and at Mach 0.99 airspeed, where a 22 s climb with an acceleration of 2.5g is initiated, following a free-fall ballistic Keplerian trajectory lasting 45 s with an apogee of 27,000 ft at Mach 0.4 airspeed. Temperature, pressure and acceleration are monitored constantly during the entire flight. Cells and activator solutions are kept at 37 °C during the entire experiment until the fixative has been added. The parabolic flight profile provides up to 45 s of microgravity at a quality of 0.05g in all axes. Access time is 30 min before take-off; retrieval time is 30 min after landing. We conclude that using military fighter jets for microgravity research is a valuable tool for frequent and repeated cell culture experiments and therefore for state-of-the art method of biomedical research. 相似文献
7.
A new and innovative type of gridded ion thruster, the “Dual-Stage 4-Grid” or DS4G concept, has been proposed and its predicted high performance validated under an ESA research, development and test programme. The DS4G concept is able to operate at very high specific impulse and thrust density values well in excess of conventional 3-grid ion thrusters at the expense of a higher power-to-thrust ratio. This makes it a possible candidate for ambitious missions requiring very high delta-V capability and high power. Such missions include 100 kW-level multi-ton probes based on nuclear and solar electric propulsion (SEP) to distant Kuiper Belt Object and inner Oort cloud objects, and to the Local Interstellar medium. In this paper, the DS4G concept is introduced and its application to this mission class is investigated. Benefits of using the DS4G over conventional thrusters include reduced transfer time and increased payload mass, if suitably advanced lightweight power system technologies are developed.A mission-level optimisation is performed (launch, spacecraft system design and low-thrust trajectory combined) in order to find design solutions with minimum transfer time, maximum scientific payload mass, and to explore the influence of power system specific mass. It is found that the DS4G enables an 8-ton spacecraft with a payload mass of 400 kg, equipped with a 65 kW nuclear reactor with specific mass 25 kg/kW (e.g. Topaz-type with Brayton cycle conversion) to reach 200 AU in 23 years after an Earth escape launch by Ariane 5. In this scenario, the optimum specific impulse for the mission is over 10,000 s, which is well within the capabilities of a single 65 kW DS4G thruster. It is also found that an interstellar probe mission to 200 AU could be accomplished in 25 years using a “medium-term” SEP system with a lightweight 155 kW solar array (2 kg/kW specific mass) and thruster PPU (3.7 kg/kW) and an Earth escape launch on Ariane 5. In this case, the optimum specific impulse is lower at 3500 s which is well within conventional gridded ion thruster capability. 相似文献
8.
In this paper we calculate the effect of atmospheric dust on the orbital elements of a satellite. Dust storms that originate in the Martian surface may evolve into global storms in the atmosphere that can last for months can affect low orbiter and lander missions. We model the dust as a velocity-square depended drag force acting on a satellite and we derive an appropriate disturbing function that accounts for the effect of dust on the orbit, using a Lagrangean formulation. A first-order perturbation solution of Lagrange's planetary equations of motion indicates that for a local dust storm cloud that has a possible density of 8.323×10−10 kg m−3 at an altitude of 100 km affects the orbital semimajor axis of a 1000 kg satellite up −0.142 m day−1. Regional dust storms of the same density may affect the semimajor axis up to of −0.418 m day−1. Other orbital elements are also affected but to a lesser extent. 相似文献
9.
Mohamed S. El-Genk 《Acta Astronautica》2009,64(9-10):833-849
The history of the deployment of nuclear reactors in Earth orbits is reviewed with emphases on lessons learned and the operation and safety experiences. The former Soviet Union's “BUK” power systems, with SiGe thermoelectric conversion and fast neutron energy spectrum reactors, powered a total of 31 Radar Ocean Reconnaissance Satellites (RORSATs) from 1970 to 1988 in 260 km orbit. Two of the former Soviet Union's TOPAZ reactors, with in-core thermionic conversion and epithermal neutron energy spectrum, powered two Cosmos missions launched in 1987 in ~800 km orbit. The US’ SNAP-10A system, with SiGe energy conversion and a thermal neutron energy spectrum reactor, was launched in 1965 in 1300 km orbit. The three reactor systems used liquid NaK-78 coolant, stainless steel structure and highly enriched uranium fuel (90–96 wt%) and operated at a reactor exit temperature of 833–973 K. The BUK reactors used U-Mo fuel rods, TOPAZ used UO2 fuel rods and four ZrH moderator disks, and the SNAP-10A used moderated U-ZrH fuel rods. These low power space reactor systems were designed for short missions (~0.5 kWe and ~1 year for SNAP-10A, <3.0 kWe and <6 months for BUK, and ~5.5 kWe and up to 1 year for TOPAZ). The deactivated BUK reactors at the end of mission, which varied in duration from a few hours to ~4.5 months, were boosted into ~800 km storage orbit with a decay life of more than 600 year. The ejection of the last 16 BUK reactor fuel cores caused significant contamination of Earth orbits with NaK droplets that varied in sizes from a few microns to 5 cm. Power systems to enhance or enable future interplanetary exploration, in-situ resources utilization on Mars and the Moon, and civilian missions in 1000–3000 km orbits would generate significantly more power of 10's to 100's kWe for 5–10 years, or even longer. A number of design options to enhance the operation reliability and safety of these high power space reactor power systems are presented and discussed. 相似文献
10.
M.A. Kolosov O.I. Yakovlev A.I. Efimov S.S. Matyugov T.S. Timofeeva E.V. Chub A.G. Pavelyev A.I. Kucheryavenkov I.E. Kalashnikov O.E. Milekhin 《Acta Astronautica》1980,7(2):219-234
Using the Venera-9 and 10 satellites radio occultation measurements of the atmosphere and bistatic radar measurements of the surface of the planet Venus were realized from October 1975 to March 1976. The altitude dependence of the molecular number density, pressure and temperature on the night and day sides were derived.An analysis is made of the stratified structure and turbulence in the atmosphere of Venus. The results of pressure measurements on the surface by the method of bistatic radar are presented. The diagrams and the tables of the parameters of the atmosphere are given. 相似文献
11.
Potential encore-mission scenarios have been considered for the Cassini mission. In this paper we discuss one of the end-of-life scenarios in which the Cassini spacecraft could perform a Saturn escape via gravity assists from Titan. It is shown that such satellite-aided escape requires a small deterministic maneuver (e.g., Δv<50 m/s), but provides enough energy for the Cassini spacecraft to reach a range of targets in our Solar System, as close to the Sun as the asteroid belt or as far as the Kuiper belt. The escape sequence could be initiated from an arbitrary point during the on-going Cassini mission. Example tours are presented in which the final Titan flyby places the spacecraft into ballistic trajectories that reach Jupiter, Uranus, and Neptune. After years of heliocentric flight, the spacecraft could impact on the target gas giant or perform a flyby to escape from the Solar System (if not to another destination). The concept can be generalized to a new kind of missions, including nested-grand tours, which may involve satellite-aided captures and escapes at more than one planet. 相似文献
12.
On 14 May 2009 the European Space Agency launched 2 space observatories: Herschel (with a 3.5 m mirror it is the largest space telescope ever) will collect long-wavelength infrared radiation and will be the only space observatory to cover the spectral range from far-infrared to sub-millimetre wavelengths, and Planck will look back at the dawn of time, close to the Big Bang, and will examine the Cosmic Microwave Background (CMB) radiation to a sensitivity, angular resolution and frequency range never achieved before. This paper will present the Flight Dynamics, mission analysis challenges and flight results from the first 3 months of these missions.Both satellites were launched on the same Ariane 5 and travelled to the L2 Lagrange point of the sun–earth system 1.5 million km from the earth in the opposite direction of the sun. There they were injected to a quasi-halo orbit (Herschel) with the dimension of typically 750,000 km×450,000 km, and a Lissajous orbit (Planck) of 300,000 km×300,000 km.In order to reach these Lissajous orbits it is mandatory to perform large trajectory correction manoeuvres during the first days of the mission. Herschel had its main manoeuvres on the first day. Planck had to be navigated on the first day and by a mid-course correction manoeuvre, the L2 orbit insertion manoeuvre was planned on day 50. If these slots were missed, fuel penalties would rapidly increase.This posed a heavy load on the operations teams because both spacecrafts have to be thoroughly checked out and put into the correct modes of their attitude control systems during the first hours after launch.The sequence of events will be presented and explained and the orbit determination results as well as the manoeuvre planning will be emphasised. 相似文献
13.
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft, launched in August 2004 under NASA's Discovery Program, was inserted into orbit about the planet Mercury in March 2011. MESSENGER's three flybys of Mercury in 2008–2009 marked the first spacecraft visits to the innermost planet since the Mariner 10 flybys in 1974–1975. The unprecedented orbital operations are yielding new insights into the nature and evolution of Mercury. The scientific questions that frame the MESSENGER mission led to the mission measurement objectives to be achieved by the seven payload instruments and the radio science experiment. Interweaving the full set of required orbital observations in a manner that maximizes the opportunity to satisfy all mission objectives and yet meet stringent spacecraft pointing and thermal constraints was a complex optimization problem that was solved with a software tool that simulates science observations and tracks progress toward meeting each objective. The final orbital observation plan, the outcome of that optimization process, meets all mission objectives. MESSENGER's Mercury Dual Imaging System is acquiring a global monochromatic image mosaic at better than 90% coverage and at least 250 m average resolution, a global color image mosaic at better than 90% coverage and at least 1 km average resolution, and global stereo imaging at better than 80% coverage and at least 250 m average resolution. Higher-resolution images are also being acquired of targeted areas. The elemental remote sensing instruments, including the Gamma-Ray and Neutron Spectrometer and the X-Ray Spectrometer, are being operated nearly continuously and will establish the average surface abundances of most major elements. The Visible and Infrared Spectrograph channel of MESSENGER's Mercury Atmospheric and Surface Composition Spectrometer is acquiring a global map of spectral reflectance from 300 to 1450 nm wavelength at a range of incidence and emission angles. Targeted areas have been selected for spectral coverage into the ultraviolet with the Ultraviolet and Visible Spectrometer (UVVS). MESSENGER's Mercury Laser Altimeter is acquiring topographic profiles when the slant range to Mercury's surface is less than 1800 km, encompassing latitudes from 20°S to the north pole. Topography over the remainder of the southern hemisphere will be derived from stereo imaging, radio occultations, and limb profiles. MESSENGER's radio science experiment is determining Mercury's gravity field from Doppler signals acquired during frequent downlinks. MESSENGER's Magnetometer is measuring the vector magnetic field both within Mercury's magnetosphere and in Mercury's solar wind environment at an instrument sampling rate of up to 20 samples/s. The UVVS is determining the three-dimensional, time-dependent distribution of Mercury's exospheric neutral and ionic species via their emission lines. During each spacecraft orbit, the Energetic Particle Spectrometer measures energetic electrons and ions, and the Fast Imaging Plasma Spectrometer measures the energies and mass per charge of thermal plasma components, both within Mercury's magnetosphere and in Mercury's solar-wind environment. The primary mission observation sequence will continue for one Earth year, until March 2012. An extended mission, currently under discussion with NASA, would add a second year of orbital observations targeting a set of focused follow-on questions that build on observations to date and take advantage of the more active Sun expected during 2012–2013. MESSENGER's total primary mission cost, projected at $446 M in real-year dollars, is comparable to that of Mariner 10 after adjustment for inflation. 相似文献
14.
Akira Kakami Shinji Beppu Muneyuki Maiguma Takeshi Tachibana 《Acta Astronautica》2011,68(7-8):1228-1233
The present paper describes thrust measurement results for an arcjet thruster using Dimethyl ether (DME) as the propellant. DME is an ether compound and can be stored as a liquid due to its relatively low freezing point and preferable vapor pressure. The thruster successfully produced high-voltage mode at DME mass flow rates above 30 mg/s, whereas it yielded low-voltage mode below 30 mg/s. Thrust measurements yielded a thrust of 0.15 N and a specific impulse of 270 s at a mass flow rate of 60 mg/s with a discharge power of 1300 W. The DME arcjet thruster was comparable to a conventional one for thrust and discharge power. 相似文献
15.
Recent planning for science and exploration missions has emphasized the high interest in the close investigation of small bodies in the Solar System. In particular in-situ observations of asteroids and comets play an important role in this field and will contribute substantially to our understanding of the formation and history of the Solar System.The first dedicated comet Lander is Philae, an element of ESA's Rosetta mission to comet 67/P Churyumov–Gerasimenko. Rosetta was launched in 2004. After more than 7 years of cruise (including three Earth and one Mars swing-by as well as two asteroid flybys) the spacecraft has gone into a deep space hibernation in June 2011. When approaching the target comet in early 2014, Rosetta will be re-activated. The cometary nucleus will be characterized remotely to prepare for Lander delivery, currently foreseen for November 2014.The Rosetta Lander was developed and manufactured, similar to a scientific instrument, by a consortium consisting of international partners. Project management is located at DLR in Cologne/Germany, with co-project managers at CNES (France) and ASI (Italy). The scientific lead is at the Max Planck Institute for Solar System Science (Lindau, Germany) and the Institut d'Astrophysique Spatiale (Paris).Mainly scientific institutes provided the subsystems, instruments and the complete, qualified lander system. Operations are performed in two dedicated centers, the Lander Control Center (LCC) at DLR-MUSC and the Science Operations and Navigation Center (SONC) at CNES. This concept was adopted to reduce overall cost of the project and is foreseen also to be applied for development and operations of future small bodies landers.A mission profiting from experience gained during Philae development and operations is MASCOT, a surface package for the Japanese Hayabusa 2 mission. MASCOT is a small (∼10 kg) mobile device, delivered to the surface of asteroid 1999JU3. There it will operate for about 16 h. During this time a camera, a magnetometer, a thermal monitor and an IR analytical instrument will provide ground truth and thus will even be able to support the selection of possible sampling sites for the main spacecraft.MASCOT is a flexible design that can be adapted to a wide range of missions and possible target bodies. Also the payload is flexible to some extent (with an overall mass in the 3 kg range). For example, the surface package is part of the optional strawman payload for MarcoPolo-R, a European asteroid sample return mission, proposed for ESA Cosmic Vision M-class. 相似文献
16.
D. V. Titov H. Svedhem D. McCoy J. -P. Lebreton S. Barabash J. -L. Bertaux P. Drossart V. Formisano B. Haeusler O. I. Korablev W. Markiewicz D. Neveance M. Petzold G. Piccioni T. L. Zhang F. W. Taylor E. Lellouch D. Koschny O. Witasse M. Warhaut A. Acomazzo J. Rodrigues-Cannabal J. Fabrega T. Schirmann A. Clochet M. Coradini 《Cosmic Research》2006,44(4):334-348
The first European mission to Venus (Venus Express) is described. It is based on a repeated use of the Mars Express design with minor modifications dictated in the main by more severe thermal environment at Venus. The main scientific task of the mission is global exploration of the Venusian atmosphere, circumplanetary plasma, and the planet surface from an orbiting spacecraft. The Venus Express payload includes seven instruments, five of which are inherited from the missions Mars Express and Rosetta. Two instruments were specially designed for Venus Express. The advantages of Venus Express in comparison with previous missions are in using advanced instrumentation and methods of remote sounding, as well as a spacecraft with a broad spectrum of capabilities of orbital observations. 相似文献
17.
This paper concerns the drag-free and attitude control (DFAC) of the European Gravity field and steady-state Ocean Circulation Explorer satellite (GOCE), during the science phase. GOCE aims to determine the Earth's gravity field with high accuracy and spatial resolution, through complementary space techniques such as gravity gradiometry and precise orbit determination. Both techniques rely on accurate attitude and drag-free control, especially in the gradiometer measurement bandwidth (5–100 mHz), where non-gravitational forces must be counteracted down to micronewton, and spacecraft attitude must track the local orbital reference frame with micro-radian accuracy. DFAC aims to enable the gravity gradiometer to operate so as to determine the Earth's gravity field especially in the so-called measurement bandwidth (5–100 mHz), making use of ion and micro-thruster actuators. The DFAC unit has been designed entirely on a simplified discrete-time model (Embedded Model) derived from the fine dynamics of the spacecraft and its environment; the relevant control algorithms are implemented and tuned around the Embedded Model, which is the core of the control unit. The DFAC has been tested against uncertainties in spacecraft and environment and its code has been the preliminary model for final code development. The DFAC assumes an all-propulsion command authority, partly abandoned by the actual GOCE control system because of electric micro-propulsion not being fully developed. Since all-propulsion authority is expected to be imperative for future scientific and observation missions, design and simulated results are believed to be of interest to the space community. 相似文献
18.
X-ray astronomy is in a privileged situation with the successful missions Chandra and XMM-Newton for more than 10 years in orbit, and Astro-H in the building phase. Over the past 10 years ESA, NASA, and YAXA studies have been made of follow-up missions, like Constellation-X, XEUS, IXO, and ATHENA. This presentation will highlight the technological challenges encountered to build X-ray optics and instrumentation for these types of missions. The optics requires an order of magnitude more collecting area (>5 m2) for a few seconds of arc spatial resolution. This drives the focal length of the telescope (∼25 m), and thereby the complexity of the spacecraft. Furthermore new technologies are required to realize such an optic within a reasonable mass. The detectors require significant improvement in field of view (number of pixels), energy resolution, and count rate ability. This tends to be possible by the use of Si-based imaging arrays with a large number of pixels, high detection efficiency, and high count rate ability at one side, and the development of modest imaging arrays of cryogenic sensors with very high energy resolution and good detection efficiency at the other side. The cryogenic detectors require further development of cooling systems based on mechanical coolers, like employed for the 1st time on Planck, and planned for Astro-H. The biggest challenge for the realization of such a mission is however not technical. That challenge is that the realization of this future X-ray astronomy mission will require coordination between scientists and Space Agencies on a Global scale. 相似文献
19.
More than 60 years after the late Nobel laureate Hannes Alfvén had published a letter stating that oscillating magnetic fields can accelerate ionised matter via magneto–hydrodynamic interactions in a wave like fashion, the technical implementation of Alfvén waves for propulsive purposes has been proposed, patented and examined for the first time by a group of inventors.Consequently improved since then, the name of the latest concept, relying on magneto-acoustic waves to accelerate electric conductive matter, is MOA2—Magnetic field Oscillating Amplified Accelerator. Based on computer simulations, which were undertaken to get a first estimate on the performance of the system, MOA2 is a corrosion free and highly flexible propulsion system, whose performance parameters might easily be adapted in operation, by changing the mass flow and/or the power level. As such the system is capable of delivering a maximum specific impulse of 13116 s (12.87 mN) at a power level of 11.16 kW, using Xe as propellant, but can also be attuned to provide a thrust of 236.5 mN (2411 s) at 6.15 kW of power. First tests—that are further described in this paper—have been conducted successfully with a 400 W prototype system at an ambient pressure of 0.20 Pa, delivered 9.24 mN of thrust at 1472 s ISP, thereby underlining the feasibility of the concept.Based on these results, space propulsion is expected to be a prime application for MOA2—a claim that is supported by numerous applications such as Solar and/or Nuclear Electric Propulsion or even as an ‘afterburner system’ for Nuclear Thermal Propulsion. However, MOA2 has so far seen most of its R&D impetus from terrestrial applications, like coating, semiconductor implantation and manufacturing as well as steel cutting. Based on this observation, MOA2 resembles an R&D paradigm buster, as it is the first space propulsion system, whose R&D is driven primarily by its terrestrial applications. Different terrestrial applications exist, but the most successful scenarios so far revolve around MOA2's unique features with respect to high throughput/low target temperature coatings on sensitive materials. In combination with its intrinsic high flexibility, MOA2 is highly suited for a common space-terrestrial application research and utilisation strategy.This paper presents the recent developments of the MOA2 R&D activities at Q2 Technologie(s), the company in Vienna, Austria, which has been set up to further develop and test the magneto-acoustic wave technology and its applications. 相似文献