High energy-density propulsion—reducing the risk to humans in planetary exploration

The potential benefits to humankind of space exploration are tremendous. Space is not only the final frontier but is also the next marketplace. The orbital space above Earth offers tremendous opportunities for both strategic assets and commercial development. The critical obstacle retarding the use of the space around the Earth is the lack of low cost access to orbit. Further out, the next giant leap for mankind will be the human exploration of Mars. Almost certainly within the next 30 years, a human crew will brave the isolation, the radiation, and the lack of gravity to walk on and explore the Red planet. Both of these missions will change the outlook and perspective of every human being on the planet. However, these missions are expensive and extremely difficult. Chemical propulsion has demonstrated an inability to achieve orbit cheaply and is a very high-risk option to accomplish the Mars mission. An alternative solution is to develop a high performance propulsion system. Nuclear propulsion has the potential to be such a system. The question will be whether humanity is willing to take on the challenge.     

相位检测误差对核磁共振陀螺输出频率的影响

针对核磁共振陀螺中采用相位检测方案时可能引起额外频率误差的问题,提出了通过控制电子顺磁共振失谐量及静磁场扰动来抑制额外频率误差的方案。基于Bloch方程,推导了惰性气体原子系综输出频率的表达式,并将相位检测的过程包含在内。建立了考虑相位检测误差的核磁共振陀螺频率误差方程,给出了相位检测引入的额外频率误差表达式并进行了数值仿真。仿真结果表明,通过设定合适的共振失谐量,其额外频率误差至少可以抑制1个数量级,而通过精确地抑制静磁场的一阶及二阶扰动,可以进一步抑制1～3个数量级,将额外频率误差降低到nHz量级。     

核热推进地面试验技术研究

核热推进具有比冲高、推力大等特点,在载人深空探测和星际货运任务上具有广阔应用前景。核热推进技术的研发需要进行大量地面试验。首先回顾了美国与俄罗斯的核热推进地面试验技术的发展,对地面试验技术进行分类总结。然后基于一种小型核火箭方案,研究了燃料元件非核试验、燃料元件辐照考验试验和带核整机地面试验等关键地面试验技术,并提出了初步试验方案。最后对我国核热推进地面试验的发展提出了一些建议。     

New trade tree for manned mars missions

Recent studies on human missions to Mars suggest revisiting the parameters that have the most important impact on the complexity, the initial mass in low Earth orbit, the risks and the development costs for the first journey to the red planet. In the last NASA reference mission, a trade tree is proposed.     

Nuclear fragmentation database for GCR transport code development

A critical need for NASA is the ability to accurately model the transport of heavy ions in the Galactic Cosmic Rays (GCR) through matter, including spacecraft walls, equipment racks, etc. Nuclear interactions are of great importance in the GCR transport problem, as they can cause fragmentation of the incoming ion into lighter ions. Since the radiation dose delivered by a particle is proportional to the square of (charge/velocity), fragmentation reduces the dose delivered by incident ions. The other mechanism by which dose can be reduced is ionization energy loss, which can lead to some particles stopping in the shielding. This is the conventional notion of shielding, but it is not applicable to human spaceflight since the particles in the GCR tend to be too energetic to be stopped in the relatively thin shielding that is possible within payload mass constraints. Our group has measured a large number of fragmentation cross sections, intended to be used as input to, or for validation of, NASA’s radiation transport models. A database containing over 200 charge-changing cross sections and over 2000 fragment production cross sections has been compiled. In this report, we examine in detail the contrast between fragment measurements at large acceptance and small acceptance. We use output from the PHITS Monte Carlo code to test our assumptions using as an example ⁴⁰Ar data (and simulated data) at a beam energy of 650 MeV/nucleon. We also present preliminary analysis in which isotopic resolution was attained for beryllium fragments produced by beams of ¹⁰B and ¹¹B. Future work on the experimental data set will focus on extracting and interpreting production cross sections for light fragments.     

Extension of INCL4 between 2 and 15 GeV

The intranuclear cascade model INCL4 has been shown to be very successful for describing, without adjustable parameters, a whole set of data for p-induced reactions in the 40 MeV–2 GeV energy range. In view of its possible application to cosmic ray interactions, the INCL4 code has been extended to the 2–15 GeV energy range, so covering a large part of the spectrum of the incident energy of the cosmic rays.     

核磁共振陀螺中内嵌碱金属磁力仪研究

核磁共振陀螺利用核自旋的闭环磁共振实现角速度的测量,其磁共振信号一般由内嵌碱金属磁力仪测出。为了提高磁力仪性能,对描述磁力仪的Bloch方程,采用微扰迭代法和级数展开法,求出了各磁矩分量的近似解,然后讨论了线性测量范围随纵向与横向弛豫时间的变化规律以及频率响应特性。利用数值仿真,对上述近似解析解进行了验证。结果表明,磁力仪的线性测量范围随纵向、横向弛豫时间的增大而减小,其频率响应为一阶低通,截止频率仅与横向弛豫时间有关。上述研究对核磁共振陀螺的优化有一定的参考意义。     

核磁共振陀螺仪中共振磁场强度优化研究

核磁共振陀螺中,共振磁场的幅值直接影响原子核自旋磁矩进动信号的强度,进而影响陀螺信号的信噪比.基于核磁共振陀螺Bloch方程,从理论和实验两方面研究了共振磁场幅值对宏观原子核自旋磁矩的影响.结果表明,随着共振磁场幅值的增加,宏观核自旋磁矩进动信号的强度先增大后减小,进动信号的强度与共振磁场的幅值呈色散关系.共振磁场幅度...     

防护超高速碰撞破坏的材料设计

概述了超高速碰撞对空间飞行器的破坏效应，简述了防护超高速碰撞的薄板屏蔽方法。从冲击波传播规律出发，阐述了抗超高速碰掸破坏的防护材料的理论设计方法，提出了防护材料的基本结构模型。