On New Year's Day 2022, the Tianwen-1 Mars rover sent blessings from mars orbits nearly 400 million kilometers away from Earth, sending back a set of beautiful images, including a spectacular selfie with Mars as a backdrop. Many people may wonder when they see this photo: in the vast space, who took pictures of the orbiter and Mars? In fact, this is not the first space selfie of Tianwen-1.
Tianwen-1 orbiter poses with Mars
As early as the National Day in 2020, Tianwen-1 completed the first space "selfie" on the way to Mars, and the five-star red flag on the orbiter was dazzling and shining.
2020 National Day Tianwen-1 first space "selfie"
After the successful landing on Mars, on the surface of Mars, the lander and Zhu Rong rover also completed a selfie group photo.
Take a group photo
It is reported that the two space "selfies" are separated monitoring tasks developed by the Eighth Academy of Aerospace Science and Technology Group under the control of the separation measurement sensor under ground control.
After the separation measurement sensor is detached from the orbiter, in the process of slowly moving away, the two wide-angle lenses installed on both sides of the sensor are used to take an image per second, and then the image is transmitted back to the Tianwen-1 probe through Wi-Fi transmission, and finally the Arctic ice sheet, the local close-up of the orbiter, and the picture of the orbiter and Mars are presented in front of our eyes.
These two "selfies" are disposable, but they are not just show selfies, mainly to do a good job of visual monitoring of the orbital working status of the Mars rover.
Surrounder local close-up
If you use a selfie stick in space, it takes up to 15 meters, which is obviously unrealistic, not only consumes large resources, but also has certain security risks.
To this end, the Eighth Academy Mars Orbiter Engineering Measurement Subsystem Team proposed a "separation monitoring scheme", designed a set of monitoring systems composed of multiple separated measurement sensors, and completed the deep space "selfie" of the probe by throwing them away.
The separation measurement sensor is a product designed according to the concept of small satellites of surveillance cameras, which needs to be locked and unlocked within the total mass of 1kg, separated and released, and the functions of self-power supply, automatic photography, And Wi-Fi communication after separation are quite difficult to develop.
At the beginning of the design, the stand-alone development team formulated the goal of "locking firmly, separating, supplying, filming well, and transmitting back" according to the characteristics of the task.
In the separation between launch vehicle stages, satellite release and other links, fireworks are used to achieve the requirement of "locking firmly and separating", but this is the first time in space photoelectric products. The team used a pyrotechnic pin to secure the separation measurement sensor to the whole device, and then achieved on-orbit separation through a separation switch.
Pyrotechnics, also known as firearms, is a general term for single-use components and devices that are equipped with gunpowder or explosives, which are stimulated by the outside world to produce combustion or explosion, in order to ignite gunpowder, detonation explosives or do mechanical work.
The North Pole Ice Sheet of Mars
After the separation measurement sensor is separated, it is powered by the lithium battery carried by the sensor itself and transmits data via Wi-Fi.
However, using Wi-Fi in outer space is not so simple. In order to verify the actual situation of communication under high and low temperature conditions, the R & D team repeatedly tested the product for a wide range of temperature adaptability, measured and analyzed the key signals, and obtained the circuit status data under the actual temperature shock change.
Subsequently, the team made several rounds of iterative improvements to the relevant circuits, and continuously modified and improved the software protocol, and finally realized the stable Wi-Fi data transmission of the flying process after separation.
In addition, the R&D team simulated the lighting conditions of the Mars orbit on the ground, carried out hundreds of tests and verifications of different shooting angles, different light intensities, and different shooting positions, and finally formulated a strategy of segmented automatic exposure in the Martian background, and adjusted the exposure time according to the number of cells occupied by Mars in the field of view to ensure that Mars and orbiters could be clearly photographed in the Martian background.
In addition, because the separation measurement sensor does not have the attitude adjustment function, in order to enable the sensor to be separated according to the predetermined trajectory, the research team carefully designed the separation switch, so that the mechanical conditions of the separation process meet the demanding photographic requirements, ensuring that both the close-up of the probe can be taken, and the state of the orbiter in the background of Mars can be photographed, and a perfect picture is constructed.