Featured image credit: 空天逐梦
Lift Off Time | October 8, 2022 – 23:43 UTC October 9, 2022 – 07:43 BJT |
|---|---|
Mission Name | Advanced Space-based Solar Observatory, also nicknamed Kuafu-1, the first Chinese solar observatory |
Launch Provider | China Aerospace Science and Technology Corporation (CASC) |
Customer | The Chinese Academy of Science (CAS) |
Rocket | Long March 2D |
Launch Location | Site 9401 (SLS-2), Jiuquan Satellite Launch Center, China |
Payload mass | 888 kg (2,200 lbs) |
Where did the satellites go? | A Sun-synchronous orbit (SSO) at 720 km in altitude and 98.275 degrees inclination |
Did they attempt to recover the first stage? | No, first stage recovery is not a capability of the Long March 2D |
Where did the first stage land? | It crashed on land in central China |
Did they attempt to recover the fairings? | No, fairing recovery is not a capability of the Long March 2D |
Were the fairings new? | Yes |
This was the: | – 67th launch of a Long March 2D – 133rd orbital launch attempt of 2022 |
Where to watch | Unofficial Replay |
How Did it Go?
A Long March 2D carrying the Advanced Space-based Solar Observatory (ASO-S) was launched by the China Aerospace Science and Technology Corporation (CASC) on October 8, 2022 at 23:43 UTC from Site 9401 (SLS-2) belonging to the Jiuquan Satellite Launch Center, located in the Gobi Desert, China. The vehicle achieved the targeted Sun-synchronous orbit (SSO) at approximately 720 km in altitude and 98.25 degrees of inclination, for which it first had to complete all of the flight’s phases nominally. Once the solar observatory was correctly deployed, the mission was declared fully successful.
What Is The Advanced Space-based Solar Observatory?
Equipped with three payloads, the Advanced Space-based Solar Observatory (abbreviated ASO-S) is a spacecraft set to study the star in our system — the Sun. Also known as Kuafu-1, a giant in Chinese mythology who chased the Sun, it will study its objective almost 24 hours a day along its 4-year lifetime. To do this, it is outfitted with two solar arrays supplying its systems with 898 W of electrical energy. Attitude control allows it to point its field of view with a 0.01 degree accuracy, and a stability of 0.0005 degrees per second.
China is carrying out such a dedicated scientific mission for the first time. Although CHASE did aim to study the Sun, it was only provided with a single instrument, and more focused on testing a scientific bus, or platform. ASO-S, on the other hand, will attempt to discover relationships between the solar magnetic field, solar flares, and coronal mass ejections (CMEs). All of this will be carried out during the maximum of the 25th solar cycle.
Its first conceptual studies kicked off in 2011 — though it was proposed back in 2010 — after which other phases of the project continued with its development. This solar observatory derived from a conjoint project between China and France under the name of SMESE (SMall Explorer for Solar Eruptions). When the latter abandoned the effort, it was the Chinese Academy of Science (CAS) that breathed new life into it, becoming the base for ASO-S.
Science by the Solar Observatory
Two types of eruptions from the Sun are the most energetic ones: solar flares and CMEs. These events — believed to be driven by the star’s magnetic field — powerfully affect our environment and space weather, with potentially disastrous results. Because of this, the following relationships should and will be explored by this Solar Observatory.
Solar Flare-Magnetic Field
Being the largest explosive events in our solar system, flares are bursts of radiation coming from a relatively small area of the Sun. They are related to an existing phenomenon called magnetic reconnection, which causes large releases of energy. When this happens, it is manifested in the form of thermal energy, and also in other kinds. It takes place reconfiguring the topology of the field. A magnetic field can be pictured as lines going from one pole (North) to the other (South). When reconnection occurs, the magnetic field lines get divided, and the resulting parts are then reattached to other spliced field lines, unleashing energy.
Understanding how this process is triggered, how it is related to other magnetic properties, how the magnetic field evolves through time when this happens, among other issues, could provide answers about the magnetic field-flares cause-and-effect relationship. Therefore, this research could produce the physical foundations of solar flare occurrence prediction.
CME-Magnetic Field
Coronal Mass Ejections are much larger events, which originate in the upper portion of the Sun’s atmosphere — the corona. Strong magnetic fields give structure to this layer of our star, but at specific points where they are closed — e.g., over sunspots — they can violently expel colossal lumps of matter and magnetic fields in an instant. Once these “break free” from the gravitational attraction to the scorching giant, they can reach our planet, interacting with our magnetosphere, and even damaging our electrical power grids on rare occasions.
Given our present technical capabilities, our measurements of the magnetic fields are only reliable in the photosphere — a layer that is found below the corona and the chromosphere. This is why the reliability of these measurements must be increased beyond its current state, so as to adequately extrapolate them into the corona. Only then it will be possible to grasp the mechanisms behind the CME-magnetic field interaction, and behind many other related processes. With this knowledge, CME occurrence prediction could be potentially achieved.
Solar Flare-CME
With the apparent common trigger between these two physical processes being the magnetic field of the star, further study is still needed to further what we know regarding heliophysics. What is more, these two events’ interaction could lead to deeper insight on how effects derived from small-scale and large-scale magnetic fields work simultaneously. Nevertheless, understanding of how one phenomenon could trigger the other one, or if any of them could exist without the other one, or a more thorough comprehension of their emissions, among others, are relevant topics that still require study.
Summarized Objectives
The following is a list of the main four objectives — as explicitly exposed in this paper — the Advanced Space-based Solar Observatory will try to accomplish:
- To simultaneously acquire non-thermal images of solar flares in hard X-rays and the initiations of CMEs in the Ly waveband, in order to understand the relationships between flares and CMEs.
- To simultaneously observe the full-disk vector magnetic field, the energy build-up and release of solar flares, and the formation of CMEs, in order to understand the causality among them.
- To record the response of the solar atmosphere to eruptions, in order to understand the mechanisms of energy release and transport.
- To observe solar eruptions and evolution of the magnetic field, in order to provide clues for forecasting space weather
ASO-S’ Instruments
When speaking of payloads, it may mean the cargo that is being transported by the rocket — presently, the Long March 2D — which tends to be a spacecraft of some kind. Nevertheless, when it is mentioned in reference to a satellite, like this observatory, then it usually means a carried instrument intended to perform a specific task. As previously noted, the Advanced Space-base Solar Observatory features three of them installed in it.
FMG
One of them is the Full-disk vector MagnetoGraph, which presents six subsystems: optical imaging, polarization, electronics, thermal control, imaging stability, and data processing. Together in action, they ensure the working wavelength always remains at 532.42 nm, and an image stability better than 0.25′′/30 s. In this way, it will take measurements of the vector magnetic field in the entire solar disk.
It consists of an optics package, an electronics box, a harness connecting the first two to the satellite, and a thermal control system. In the first one, sunlight enters through a window, travels through an optical path, to finally reach an imaging detector — a camera — with a resolution of 4096 x 4096 pixels. The electronic box contains the circuitry for carrying out the following tasks: control, power supply and distribution, active temperature control, data acquisition and processing, image stabilization, polarization analysis, among others. The thermal control keeps all components at the correct temperatures by radiating any excess heat. For reference, the optics package operates at 22 ± 2 °C, while the detector at about -30 °C.
LST
This payload will image the Sun, and the inner corona up to 2.5 mean solar radius, using a high resolution in time and space. Its objectives will be mainly solar flares, CMEs and filaments or prominences, observing them in the Lyα and visible wavebands.
Its abbreviated name stands for Lyα Solar Telescope, an instrument made out of another three: the Solar Disk Imager (SDI), and the Solar Corona Imager (SCI), with the suppression of stray light being the most critical technology in the latter. Both of them will observe CMEs in all of the space going from the initiation of the solar disk to a few solar radii outward. They will record flares and other activities as well. Finally, the White-light Solar Telescope (WST), serving calibration purposes, will also be used in the observation of white-light flares.
HXI
The Hard X-ray Imager will conduct observations of the full solar disk, but in a high energy range going from about 30 keV to 200 keV. Similarly to the previous two instruments, this is expected to be achieved with a high angular and temporal resolution. It will use indirect imaging of spatial modulation, by means of a collimator and solar aspect subsystem, a calorimeter subsystem, and an electronics subsystem. A total of 91 pairs of grids — many different subcollimators — with different pitches and orientations, provide image reconstruction. Key for this payload functioning is the accurate alignment between front and rear grids. Additionally, HXI also takes measurements of the total flux and charged particle background.
Other Chinese Science Missions
In the following table, we present a list of relatively recent scientific missions carried out by China.
| Satellite | Launch Date | Launch Vehicle | Present Orbit |
| Tianwen 1 | July 23, 2020 – 04:41 UTC | Long March 5 | Highly elliptical Mars orbit |
| Chang’e 5 | November 23, 2020 – 20:30 UTC | Long March 5 | Lunar distant retrograde orbit |
| CHASE | October 14, 2021 – 10:51 UTC | Long March 2D | Sun-synchronous orbit, ~515 km |
| Daqi-1 | April 15, 2022 – 18:16 UTC | Long March 4C | Sun-synchronous orbit, ~710 km |
| TECIS | August 4, 2022 – 03:08 UTC | Long March 4B | Sun-synchronous orbit, ~505 km |
What Is The Long March 2D?
Developed and manufactured by SAST — based on the Long March 4A — the two-stage Long March 2D purpose was to serve the SSO and LEO market segments in the lower range of the medium-lift launch vehicles. It is possible to find it mentioned in its short form “LM-2D,” or by its Chinese name “Chang Zheng 2D,” or abbreviated “CZ-2D.”
| Characteristic | Value |
| Stage quantity | 2 (3, optional) |
| Length [m] | 41.06 |
| Lift-off mass [t] | 250 |
| Mass to LEO [kg] | 3,700 |
| Mass to SSO [kg] | 1,300 |
| Fuel | UDMH (all stages) |
| Oxidizer | N2O4 (all stages) |
Originally provided with the type-A fairing — 2.90 m in diameter — a larger new one was later offered to customers — type-B, 3.35 m in diameter. Further developments included a second stage’s attitude control motors, and a passivation and deorbiting system for this same stage.
In spite of lifting off mainly from the launch center in Jiuquan, there have been Long March 2D rockets launching from the Taiyuan and the Xichang ones. Derived from the flight-proven technology of the Dong Feng 5 ICBMs, it only suffered a partial failure on December 28, 2016, otherwise keeping a flawless record since its maiden flight on August 9, 1992.
Deorbiting The Second Stage
Recent in-flight tests of a sail for increasing the orbital decay of the second stage of the Long March 2D have been reported for Yaogan 35 launches. That is, at least, apparently valid for Groups 02, 03,and 04. Such a device is a Chinese effort in reducing space debris generation.
Stages of the Long March 2D
First
Four YF-20 engines power this first stage, working under a gas generator cycle, and using hypergolic propellants (as already mentioned) with an ISP of 260 s at sea level. This group is identified as the YF-21 engine, its C version being the one installed in this stage. Further information can be seen in the comparative table.
Second
When adapted to a vacuum environment, where the second stage operates, the YF-20 engines are designated as YF-22. These feature a thrust of ~742 kN and an ISP of 300 s. Vernier engines give a stage attitude control capabilities when the main engine does not gimbal. One such vernier is the YF-23, generating ~47 kN of thrust and with an ISP of 289 s. These two engines are part of what is called the YF-24 engine, which is solely fed the hypergolic propellants listed before.
| Stage Number | Length [m] | Diameter [m] | Propellant Mass [t] | Engine Name | Thrust [kN] |
| 1 | 27.91 | 3.35 | 182.0 | YF-21C | 2,961.6 |
| 2 | 10.90 | 3.35 | 52.7 | YF-24C | ~789.1 |
Third — Optional
The China Academy of Launch Vehicle Technology (CALT) is responsible for having developed the Yuanzheng (YZ) upper stage. Adapted to ride atop the Long March 2D — its third version, YZ-3 — it adds restarting capabilities, allowing for higher energy final orbits, or circularization maneuvers. These are achieved with burns of 6.5 kN in thrust, burning the same two hypergolic propellants already indicated in this text.
Yuanzheng 3 flew only once: on December 29, 2018, stacked onto the Long March 2 Y35, and launching Yunhai-2 satellites and Hongyan-1.
