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China Space - Astronomy

Taiji gravitational wave

CAS has announced the research program "Taiji" that will study gravitational waves from the merging of binary black holes and other celestial bodies. The satellite has been named Taiji-1. As a Chinese term for the "supreme ultimate," Taiji is well-known as the black and white circular symbol representing yin and yang. The pattern of Taiji also resembles a binary star system composed by objects like neutron stars or black holes. CAS set a three-step strategy to implement the Taiji program. It took the research team about one year to develop Taiji-1, the first satellite of the program. It is expected to launch another two satellites in the second step after 2023, and three more satellites in the third step around 2033.

The firsst satellite, sent into orbit on 31 August 2019, is China's first such kind of satellite, and has completed its first stage tests in orbit, laying a solid foundation for future gravitational wave observation in space, said Xiangli Bin, vice president of CAS. "This is the first step of China's space-based gravitational wave detection. But there is still a long way to go to realize detecting gravitational waves in space. Chinese scientists will continue to contribute Chinese wisdom to the exploration and human progress," Xiangli said.

Gravitational waves are "ripples" in space-time caused by some of the most violent and energetic processes in the universe. Albert Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity. The strongest gravitational waves are produced by catastrophic events such as colliding black holes, supernovae, coalescing neutron stars or white dwarf stars and possibly even the remnants of gravitational radiation created by the birth of the universe itself. The first discovery of gravitational waves by the LIGO Collaboration in 2015 has opened a new window to observe the universe and encouraged scientists worldwide to accelerate their research.

Unlike the LIGO research conducted from a ground-based observatory, Taiji will conduct space-based detection on the gravitational waves with lower frequencies to observe celestial bodies with greater mass or located farther away in the universe, said Wu Yueliang, chief scientist of the Taiji program and an academician of CAS. However, the gravitational wave signals from those celestial bodies are extremely weak, posing great challenges for detection. Scientists need to break through the limit of current precise measurement and control technology.

Taiji-1 aims to test the key technologies such as high-precision and ultra-stable laser interferometer, gravitational reference sensor, ultra-high precision drag-free control and ultra-stable and ultra-static satellite platform. Taiji-1 has realized China's most accurate space laser interference measurement and the first in-orbit drag-free control technology test. It also carried out electric propulsion technology experiments. The first-stage in-orbit test showed that the accuracy of displacement measurement of the laser interferometer on Taiji-1 could reach a 100-picometer order of magnitude, equivalent to the size of an atom.

Hard X-ray Modulation Telescope (HXMT)

The Hard X-ray Modulation Telescope (HXMT), or Insight, satellite has been launched succesefully at 11 a.m. on 15 June 2017 from Jiuquan, China. Li Tipei, the CAS academician who first proposed the satellite in the early 1990s, said Chinese scientists could have made many great scientific discoveries if it had been launched within 10 years of first being mooted. Even so, he is confident the satellite can make new findings. "Our satellite has advantages in detecting transient phenomena and X-ray explosions of celestial bodies. And its functions have expanded, as its developers added more detectors so it can cover a broader range of energy," Li said.

Gu Yidong, a CAS academician, said China still lags behind advanced levels in space science. "We should have a sense of urgency. We will make efforts to upgrade China's space science to advanced levels within two decades."

The PRC since the year 2000 has had under development a new space telescope designed to observe high-energy astronomical bodies and high energy radiation phenomena as well as “black holes” and neutron stars in deep space. Though originally planned for launch in 2010 its launch has been delayed due to project financing short falls. This was the second five year plan (2000-2005 & 2006-2010) it had been under and it would not be launched until the third five year plan (2011-2015) of the program as it is planned.

With a 100-cm optical lens and a group of X-ray equipped telescopes on it, the 2-ton-weight telescope, called "Space Solar Telescope", is designed with a service term of three to five years. With the cost of over RMB 2 billion yuan, by 2002 the Space Solar Telescope was China's most expensive space explorer. Differing from Hubble, China's Space Solar Telescope will focus on diversification of solar magnetic field, as well as solar activities and the space climate.

According to a Chinese astronomer, with the capability of suppressing interference from the aerosphere, the space astronomical telescope may provide a higher resolution ration. With no equipment of this kind in hand, China has to submit the application and research project schedule in advance if it wants to use Hubble. And the research project will be permitted only after it is approved by concerned institutions.

Hard X-ray band is a key waveband for high energy astrophysics study. Exploring various kinds of black holes is a major frontier of physics and astronomy in the new century. Hard X-rays originate mostly from regions closest to black holes and are highly penetrative, and are therefore important tools for studying the physical processes in the extreme conditions such as high matter density, high energy density, high electric-magnetic field, and high gravitational field. As a hard X-ray telescope with the highest sensitivity and spatial resolution, Hard X-ray Modulation Telescope (HXMT) will have the following observational targets:

  • All-sky hard X-ray survey. To draw a high precision hard X-ray sky map and to discover about 1000 new hard X-ray sources including possible new types of objects.
  • Active galactic nuclei (AGN). The energy source of AGNs remains a mystery. It is probably from the interaction of massive black holes with the surrounding materials. HXMT will systematically study the hard X-ray emission properties and mechanism of various types of AGNs, especially the type II AGNs that are thought to be extremely absorbed.
  • X-ray binaries. An X-ray binary involves a compact object(a black hole or a neutron star) and a normal star. HXMT will observe the hard X-ray spectra and temporal variability of X-ray binaries, study the formation and evolution of accretion disks, jets and black holes, and further test various general relativistic effects.
  • Supernova remnants (SNRs). SNRs are longly thought to be the producer of cosmic-rays up to the 1015 eV. HXMT will study the nonthermal X-ray emission properties of SNRs and explore the particle acceleration at the shock front.
  • Soft Gamma-ray burst Repeater (SGR). SGR are thought to be high energy transient sources associated with young highly magnetized neutron stars. The bursts are probably corresponding to the sudden magnetic energy release caused by the cracking of the neutron star crusts. HXMT can study the structure of magnetars, the matter state equation in strong magnetic field and with high density.
  • Clusters of galaxies. Clusters of galaxies are the largest systems that are bounded gravitationally in the universe. HXMT will study the hard X-ray emission of clusters of galaxies and explore their origin.
  • Gamma-ray bursts (GRBs). GRBs are the most violent explosion is the universe. Their origin is a serious challenge to astrophysics. GRBs can be also used to explore the early universe. HXMT can be used to observe GRBs.

It was assumed that the development of the prototype Hard X-ray Modulation Telescope (HXMT) and the key technical hurdles that had to be resolved for the project to move forward was the major factor eating up the space telescope satellites program funding. Li Tipei the Chief Scientist of the project for the Chinese Academy of Sciences (CAS) stated July 23, 2009 that “So far, the ground prototype of the HXMT is completed, with all the key technical difficulties being overcome.” This certainly indicates that the approximately 1 metric ton space telescope plus its spacecraft bus combination is still not built for its 500 kilometer circular orbital launch. It is assumed to be waiting on the next Five Year Plan’s funding starting on January 1, 2011 to complete preparation and testing of the final satellite design and its ultimate launch in 2012. Li Tipei did indicate the primary issue holding back HXMT Space Telescope program progress was the financing without providing details.

In excess of 1 billion yuan ($146.4 million) for the two five year plans 2001-2010 two budgets would no doubt exceed its original projected total budget but was it considered a high priority Astrophysics Science & Technology project for the State. It had been designed to combine three or four single telescopes into one with none optical individual hard X-ray detectors under the leadership of CAS, with the Ministry of Science and Tsinghua University, school of engineering.

The Hard X-ray Modulation Telescope (HXMT) is a collimated hard X-ray (20-200 keV) telescope with the highest sensitivity and spatial resolution power in the world. It would perform an all-sky hard X-ray survey, in which about 1000 new hard X-ray sources will be discovered, and sensitive pointed observations of important cosmic X-ray sources including black holes and neutron stars.

HXMT is based on the direct demodulation (DD) method and the well developed NaI(Ti)/CsI(Na) phoswich detecting techniques. The Phase A study of the HXMT mission has been jointly supported by the Ministry of Science and Technology of China, the Chinese Academy of Sciences, and Tsinghua University since 2000. All the key technical difficulties of the telescope have been overcome, the ground prototype of HXMT has been constructed, and the balloon borne flight testing has been finished. The platform HXMT used is that of "Ziyuan II" (Earth Resource II) satellite series. This long-time tested platform meets the requirements of HXMT very well, and there is no key technical difficulty that needs to be surmounted.

Dark Matter Particle Explorer (DAMPE)

The Dark Matter Particle Explorer (DAMPE) Satellite, developed by the Chinese Academy of Sciences (CAS), was expected to be launched at the Jiuquan Satellite Launch Center in mid-December. DAMPE, the first satellite in a CAS space science program, and its carrier Long March 2-D rocket left Shanghai on 15 November 2015, heading for Jiuquan in northwest China's Gansu Province. The satellite and carrier rocket are fully prepared for blast-off after passing the inspection and approval of the CAS. It will be the 26th mission for the Long March 2-D rocket.

DAMPE is one of the first four scientific satellites employed in the CAS space program. It will observe the direction, energy and electric charge of high-energy particles in space in search of dark matter. DAMPE will have the widest observation spectrum and highest energy resolution of any dark matter probe in the world. According to experts, DAMPE is designed for increased payload, with the scientific payload weighing 1,410 kg and the whole satellite weighing 1,850 kg. The design helps cut down on the size and weight of the satellite and save launching costs.

China has launched its first space telescope that will look for signs of dark matter, a type of substance invisible to the naked eye but hypothetically constituting the whole universe’s mass.

The Dark Matter Particle Explorer (DAMPE), the first of China’s four planned missions, was laucnhed from a launch pad at the Jiuquan Satellite Launch Center in the Gobi desert on 16 December 2015.

The satellite, nicknamed “Wukong” after a character from Chinese legend, is to keep track of the direction, energy and electric charge of particles in space. Scientists believe that from space it will be easier for the instruments to detect something that may subsequently help them crack the mystery that surrounds dark matter.

“This is an exciting mission. If dark matter annihilates, as some theories predict, DAMPE has an opportunity to detect dark matter annihilation products,” David Spergel, a theoretical astrophysicist from Princeton University, said, according to Science magazine. “This is like tracking down the ‘son’ of dark matter – if you cannot find the father, you go to the son and you could learn about at least some properties of his father,” Chang Jin, leader of the project, was quoted as saying by The Hindu.

In January 2016 it was reported that the Hard X-ray Modulation Telescope (HXMT), a new exploration satellite, will be launched in 2016.

2-Meter Class Space Telescope

China planned to launch a 2-meter class space telescope in the future, and by 2010 this telescope was being designed. Its main science goals are performing a sky survey for research about dark matter and dark energy, and high resolution observations. Some experts suggest that this space telescope should be installed inside the Chinese space station. In accord with this suggestion the first configuration, i.e., to adopt a coud´e system for this telescope. This coud´e system comes from the Chinese 2.16m telescope’s coud´e system, which includes a relay mirror so that excellent image quality can be obtained. In a second configuration, the whole space telescope fly freely as an independent satellite outside the space station.

When it needs servicing, for example, changing instruments, refilling refrigerant or propellant, etc., this space telescope can fly near or even dock with the core space station. Although some space stations have had accompanying satellites, the one we propose is a space telescope that will be much larger than other accompanying satellites in terms of weight and volume. On the basis of the second configuration, we also put forward the following idea: the space station can be composed of several large independent modules if necessary.




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