Last night, our country successfully launched the first solar exploration science and technology test satellite "Xihe" at the Taiyuan Satellite Launch Center, marking our country’s entry into the era of "sun exploration". The full name of "Xihe" is the solar H α spectral detection and double super platform science and technology test satellite. What is H α? What does "double super" mean? What mysteries can this satellite detect about the sun? Jiefang Daily Shangguan News reporter interviewed Shi Wei, director of the Shanghai Planetarium Network Science Department.
The radiation that jumps from the third floor to the second floor is Hα
Hα, pronounced the "hydrogen alpha coefficient," refers to a spectral line of a hydrogen atom with a wavelength of 656.281 nanometers, which lies in the red range of visible light. What is a hydrogen atomic spectral line? According to the Bohr model of the atom, electrons do not move around the nucleus in a specific orbit within the atom, Shi Wei explained, but in an "orbit" with a quantized distribution of energy.
The so-called quantum is the inseparable smallest unit of a physical quantity. A physical quantity is quantized if it cannot be changed continuously and can only take some discrete values. It is like taking a staircase, we can only climb one step, not half. Scientists have found that many physical quantities in the microscopic world are quantized. For example, the energy of electrons in hydrogen atoms can only take one basic value – 13.6 electron volts or its 1/4, 1/9, 1/16, 1/25, etc., but not 2 times or 1/2, 1/3.
There are countless energy levels outside the nucleus of a hydrogen atom, and each energy level can be regarded as an orbital, and the energy levels are discontinuous and uneven. Although a hydrogen atom has only one electron, it can appear at any energy level and can transition between energy levels. Electrons jump from energy level "n = 3" to "n = 2", releasing light of a specific energy, which is the Hα emission line.
Electrons jump from energy level n = 3 to n = 2, releasing light of a specific energy, which is the H alpha emission line. (Source: Wikipedia)
"You can think of the orbit of an electron outside the nucleus of a hydrogen atom as the various floors of a building. The ground is the nucleus, and each floor is an energy level. From the bottom to the top, it is marked with n = 1, n = 2, n = 3, and so on." Physicists refer to the spectral lines emitted by electrons that jump from the third floor and above to the second floor as the "Balmer system" (named after the physicist John Balmer), Shi Wei said. The radiation that jumps from the third floor to the second floor is called Hα, from the fourth floor to the second floor is called Hβ, from the fifth floor to the second floor is called Hγ, and so on.
Red light H α is the brightest hydrogen spectral line in the visible spectrum. By observing this band of light, astronomers can understand the atmospheric characteristics of the solar spherical and chromospheric layers, as well as atmospheric activities such as solar prominences, and analyze the changes in atmospheric temperature, speed and other physical quantities during solar outbursts, so as to deeply study the dynamic process and physical mechanism of solar outbursts.
Full-time faces in the Hα band (Photo by Alan Friedman)
Double super platform technology has broad application prospects
The "Xihe" satellite adopts a "dual super" satellite platform design with ultra-high pointing accuracy and ultra-high stability, which greatly improves the pointing accuracy and attitude stability of the load.
In this regard, Shi Wei explained that a satellite generally consists of a platform and a load. The satellite platform is responsible for the system service and guarantee of the entire satellite, including control, propulsion, thermal control and other systems. The load is the detector that performs scientific tasks, such as CCD cameras, particle detectors, magnetometers, etc. Traditional satellite designs directly connect the load to the platform, and the directivity and stability of the load are completely realized by the platform. However, the platform is "dynamic" and the load is "static" – when the satellite is in orbit, the micro-vibration of the platform cannot be avoided, and the load needs to be accurately pointed at the target at all times, so the pointing accuracy and stability of the load are always restricted by the vibration of the platform.
In order to solve this contradiction, the satellite development team made an innovation in design, dividing the satellite platform into two cabins – the platform cabin and the payload cabin. The platform cabin contains the structure subsystem, the integrated electronic subsystem, the measurement and control subsystem, the data transmission subsystem, the power subsystem, the attitude and orbit control subsystem, the electric flotation control subsystem and the cabin connection unlocking subsystem. The payload cabin contains the structure of the payload cabin, the integrated electronics of the payload cabin and the load. The effect of "dynamic and static isolation and leader/follower coordination" is achieved by using electric flotation control between the two cabins.
Dual Supersatellite Load Design (Source: School of Astronomy and Space Sciences, Nanjing University)
Using this "airframe anti-shake" technology, the directivity and stability of the payload are improved by 1-2 orders of magnitude compared with traditional satellites, which will make the "Xihe" more accurate and stable when "taking pictures" in space, and obtain higher-quality images.
In the future, the dual super platform technology will be widely used in space missions such as high-resolution ground detailed investigation, large-scale three-dimensional mapping, and exoplanet discovery, which is expected to promote the leap-forward development of space science and technology implementation in our country.
