The China’s Tianwen-1 successfully landed on the Utopia Plain on May 15, 2021 at 7:18 a.m. Beijing time. Mars missions have a success rate of about 50%, with most failures occurring during entry, descent, and landing (EDL) steps.
Why Are Parachutes Important For Steps Of EDL?
Supersonic low-density parachutes play an important role in the Mars EDL and directly determine the success of the entire mission. In a research paper recently published in the journal Space: Science & Technology, Mingxing Huang of the Beijing Institute of Space Mechanics and Electricity led the design, development and validation of the Tianwen-1 Mars parachute, which could serve as a starting point for future exploration. of Mars. parachute.
Difference Between Parachutes Of Earth And Mars
Initially, the authors focused on the analysis and selection of types of Martian parachutes. Compared to Earth-operated parachutes, Mars lander parachutes face more challenges. Meanwhile, the open flight of the Mars parachute is characterized by supersonic speed, low density and low dynamic pressure.
On the other hand, atmospheric phenomena such as Martian vortex activity and dust storms can lead to harsh parachute deployment conditions. Therefore, the difficulties of the parachute’s unstable opening and reduced drag coefficient must be taken into account when designing a parachute.
Why Is DGB Often Used?
Most of the successful landings achieved in MARS have used DGB parachutes (Disk Gap Band) with good stability in superworthy and authoring environments and excellent inflation performance.
High ranking characteristics and technical risk of DGB parachute are selected as candidates for Tianwen1 Mars Probe by design modification. Depending on the percentage of the entire canopy of the area, the DGB parachute can be divided into two types-Viking Type and Type MPF (Mars PathFinder).
Significance Of Viking Type And MPF DGB Parachutes
The Viking Type DGB Parachute has a high resistance coefficient and weak stability, but the enhanced parameters of MPF and DGB are highly stable.
In addition, two ideas have been adopted to optimize and improve the existing structure of the DGB parachute. One of them is to increase the drag coefficient.
Therefore, the disc part is modified into a structure with a higher drag coefficient. Another part is to increase the area of the band to increase the stability of the parachute, such as adding a tapered band to the canopy skirt.
Therefore, five DGB parachute designs were selected as candidates, including the MPF, Viking, hemisflo, triconic and conical designs.
Subsonic, transonic, and supersonic wind tunnel tests were then performed on five DGB parachutes to optimize the design of the Mars parachute to obtain drag coefficients and vibration angles.
Combined with the wind tunnel test results at various Mach numbers to select the parachute with the best deceleration and stability characteristics, the DGB conical chute proved to be the best drag suit for Tianwen1.
Tests Conducted For The Parachutes
In April 2018, four high-altitude flight tests were performed using a sounding rocket to demonstrate the performance of a full-fledged DGB conical parachute under Mars flight conditions.
The first phase of the flight burned at an altitude of about 17-20 km, respectively, the payload section culminating between 49 km and 64 km. When the payload reaches the specified dynamic pressure and Mach number, the parachute opens.
All tests targeted a specific dynamic pressure while the parachute was opened to apply the desired load to the parachute when the parachute was fully opened. The parachute was used for mortar firing at dynamic pressures of 100-950 Pa and Mach numbers of 2.05-2.35.
In comparison, the Tianwen1 parachute opens stably within the range of Ma1.6~Ma2.3 and the dynamic pressure range of 250Pa~850Pa. In high-altitude discovery tests performed on Earth and in actual operation on Mars, the two Reynolds numbers are on the order of 2×10^6.
The results of the tests showed that the drag coefficient of the DGB conical parachute changed from 0.39 to 0.70 as the Mach number increased from 0.2 Ma to 2.4 Ma and reached a maximum value of 0.7 at 1.5 Ma.
The maximum angle of attack after opening the parachute is about 20°, demonstrating that the performance of the DGB converging parachute can meet the deceleration requirements of the Tianwen1 Mars probe.