Propulsive Deceleration Research Articles

Unsteady Aerodynamics of the Retropropulsion Reentry Burn of Vertically Landing Launchers

During the vertical descent and landing of a launcher first stage with the aid of retropropulsion, commonly two main propulsive deceleration maneuvers are performed: the reentry burn in high altitudes at hypersonic to supersonic speeds and the landing burn shortly before touchdown at transonic to subsonic speeds. In the frame of the EU-funded H2020 project Retro Propulsion Assisted Landing Technologies (RETALT), the unsteady aerodynamics of those retropropulsion phases were studied. This paper presents results of experiments performed in the Hypersonic Wind Tunnel Cologne on the hypersonic reentry burn. The exhaust plume was simulated with pressurized air. Proper orthogonal decomposition was performed on high-speed schlieren videos, and spectral analyses of the time histories of the resulting modes were compared to the frequency content found in high-frequency pressure measurements. Dominant frequencies were found in the proper orthogonal decomposition modes for one and for three active engines. In the pressure measurements, dominant frequencies could only be observed for three active engines. The normalized pressure fluctuations are in the range of 0.002–0.012. Additionally, a good scaling of the pressures on the base area and in the wake of the configuration with the total pressure downstream of the bow shock could be confirmed, in the sense that the ratio of the local surface pressure to the total pressure downstream of the bow shock match for varying freestream Mach numbers.

Investigations of Peripheral Propulsive Deceleration Jets on a Mars Science Laboratory Aeroshell

The objective to send more massive landed missions to the surface of Mars necessitates further research and development for ways to adequately decelerate the lander, such as propulsive deceleration. Experimental measurements using planar laser-induced iodine fluorescence provide qualitative visualizations and quantitative propulsive decelerator jet mole fraction measurements over a 0.22% scaled Mars Science Laboratory aeroshell. Peripheral (off-centerline) sonic and supersonic propulsive decelerator jet models, with jet exit velocities of Mach 1.0 and 2.66, were studied in Mach 12 flow and compared with numerical results obtained using computational fluid dynamics. Experimental visualizations were obtained for various thrust coefficients ranging from 0.5 to 3.0 in increments of 0.5. Experimental results indicate that, for both sonic and supersonic jets, the bow shock is preserved between the peripheral jets and, as thrust coefficient increases, the bow shock is pushed farther from the aeroshell forebody, with the supersonic jets having a greater shock standoff distance than sonic models at thrust coefficient greater than 2.0. Comparisons of the experimental visualizations to computed streamlines and shock locations show good agreement. Computed propulsive decelerator jet mole fractions for both sonic and supersonic thrust coefficient of 1.5 closely match experimental results through the jet cores and in cross-sectional cuts.

Numerical Investigation of Multinozzle Propulsive Deceleration Jets for Mars Entry Aeroshells

The effects of peripheral propulsive decelerator jets on the deceleration performance of Mars entry aeroshells are examined using computational fluid dynamics. The study considers a 70 deg blunt-cone aeroshell with four peripheral jets in Mach 12 flow of iodine-seeded nitrogen gas. Sonic and supersonic peripheral decelerator jets are considered in this study. The results show that the peripheral jets increase the standoff distance and change the profile of the bow shock around the aeroshell. The results also show that decelerator jets obstruct the flow around the aeroshell, which creates a low-pressure region on the surface behind the jets. The level of obstruction increases with thrust, which expands the low-pressure region. As a result, the aerodynamic drag coefficient of the aeroshell is inversely proportional to the thrust. The jet Mach number, however, has a small effect on the deceleration performance, with a maximum difference of less than 2% in the axial force between sonic and supersonic peripheral jets. The study also compares the deceleration performance of peripheral jets to previously published results for central jets. The results show that the peripheral jets provide three to seven times more drag than central jets due to higher surface pressures.

Propulsion Deceleration Studies Using Planar Laser-Induced Iodine Fluorescence and Computational Fluid Dynamics

Future high-mass spacecraft entering the thin Martian atmosphere will exceed the capabilities of supersonic and subsonic parachutes and will incorporate other means of deceleration. Propulsive deceleration is one technology that is being considered. The interaction of the spacecraft aerodynamics with the propulsion deceleration jets has been shown to cause a decrease in drag coefficient with increasing thrust coefficient, which is not desirable for deceleration. Planar laser-induced iodine fluorescence images for a single-propulsion deceleration jet showed a lifting of the vehicle bow shock away from the aeroshell. Flowfield calculations showed that this lifting provided a shielding effect, preventing the freestream mass and momentum flux from reaching the aeroshell surface, creating a low-pressure region between the jet boundary and the aeroshell. With four peripheral propulsive deceleration jets, planar laser-induced fluorescence images and computational fluid dynamics calculations showed that the vehicle bow shock is maintained between the jets as the thrust coefficient is increased. This bow shock is responsible for greater drag preservation with the peripheral jets. The calculations also showed that high pressure is maintained between the peripheral jets. These results suggest that using a few peripheral propulsion-deceleration jets located near the aeroshell shoulder would provide the greatest drag preservation when using propulsive deceleration.

Analysis of a terminal landing on Mars

This study consists of a preliminary performance and sensitivity assessment of trajectory and guidance capabilities of a Mars terminal landing phase. The phase begins with the end of the entry phase, which is at parachute deployment. Therefore, the trajectory investigated in this study starts at parachute deployment and continues through parachute jettison and finally propulsive deceleration and maneuvering to a specified landing site. Various landing navigation maneuver schemes and environmental conditions for the lander are investigated and their performance analyzed. Effects of atmospheric density and surface wind deviations on landing guidance are investigated using stochastic wind and density models. Simulation shows that the lander guidance is robust to wind and density dispersions. Density dispersions are found to be more critical for a precision landing than wind dispersions. Also, because of the aerodynamic characteristics of current aeroshell vehicle designs, very little terminal maneuvering is allowed for navigation.