Pre-flight Model Research Articles

Postflight Analysis of Atmospheric Properties from Mars 2020 Entry, Descent, and Landing

The Mars 2020 spacecraft landed the Perseverance rover and Ingenuity helicopter successfully in Jezero crater on Feb. 18, 2021. The entry, descent, and landing (EDL) sequence of the spacecraft largely leveraged the previous 2012 Mars Science Laboratory (MSL) mission. The atmospheric modeling approach for Mars 2020 was also borrowed from MSL. It consisted of two mesoscale atmospheric models of the target site and a statistical model of the pressure, density, temperature, and winds based on the mesoscale model data. This paper briefly describes the preflight atmospheric models used for Mars 2020, but focuses on the postflight assessment of these models and comparison to near-landing day orbiter sounder and other onboard atmospheric measurements. Observations from postflight analysis showed that density was underpredicted in the upper atmosphere, but within the altitudes covered by the mesoscale models, the preflight modeling matched postflight results, including for quantities like wind velocities. Potential improvements to address the upper atmosphere and other deficiencies of the Mars 2020 preflight model are also discussed.

BepiColombo: A Platform for Improving Modeling of Electric Propulsion-Spacecraft Interactions

This article provides the first results of a long-term study aimed at improving the validity of numerical modeling techniques for Electric Propulsion induced Spacecraft Charging using the Spacecraft Plasma Interaction System software. The preflight numerical model of the European Space Agency’s BepiColombo mission and its outputs are presented as a benchmark example of the present capabilities and limitations of the model. It is demonstrated that the code can obtain the spacecraft charging equilibrium by simulating the dynamic interactions between the electric propulsion system, the thruster-generated plasmas, and spacecraft systems exposed to space. The importance of including a physical description of the electron cooling in the freely expanding thruster plasmas is shown by comparing simulations with different polytropic indexes. It particularly highlights the inadequacy of treating the entire plasma as isothermal. The reported variability of the simulation outputs with numerical and physical parameters paves the way for future improvements in preflight design modeling and increased understanding of plasma thruster-induced charging processes through future comparison with available flight telemetries.

Advanced Supersonic Parachute Inflation Research Experiment Preflight Trajectory Modeling and Postflight Reconstruction

The Advanced Supersonic Parachute Inflation Research Experiment (ASPIRE) was a series of sounding rocket flights aimed at understanding the dynamics of supersonic parachutes that are used for Mars robotic applications. Although the 2012 Mars Science Laboratory (MSL) had a successful deployment of a supersonic parachute, postflight analysis and the results of the Low-Density Supersonic Decelerator project called into question some of the assumptions underlying MSL’s parachute qualification program. The ASPIRE project was a key part of the risk-reduction program undertaken by Mars 2020, the follow-on to MSL. The first sounding rocket (SR01) flight of ASPIRE occurred near Wallops Island, Virginia on 4 October 2017, and demonstrated the successful deployment and inflation of an MSL build-to-print parachute in flight conditions similar to the 2012 MSL mission. ASPIRE SR02 and SR03 were successful follow-on flights on 31 March 2018 and 7 September 2018 that demonstrated the new, strengthened supersonic parachute designed for the Mars 2020 project. The SR02 and SR03 parachutes were targeted to 100 and 140% of the expected flight limit load for Mars 2020 to confirm new margins expected from the strengthened parachute. Prior to all flights, a multibody flight dynamics simulation was developed to predict the parachute dynamics and was used, in conjunction with other tools, to target Mars-relevant flight conditions. After each flight, the onboard data were used to reconstruct the flight trajectory and to validate the preflight dynamics simulation. Postflight analysis showed that all three tests achieved their targeted conditions and preflight modeling bounded the key performance metrics for the parachute. This paper describes the flight mechanics simulation, postflight reconstruction, and the reconciliation process used to validate the flight models.

Experimental Investigation and Simulation of Aircraft Tire Wear

ABSTRACT Not only in the automotive sector, but also in the field of aircraft tires, the topic of abrasion is of great importance. The aircraft tire manufacturers provide criteria for the permissible degree of wear. If these limits are exceeded, the tire must be replaced or retreaded. By this time, the tire should withstand as many takeoff and landing cycles as possible. Abrasion models should help to predict the wear behavior in preflight modeling. At the Institute of Dynamics and Vibration Research, quasi-steady abrasion tests are performed using tread block samples from an aircraft tire. For various pressures and sliding speeds, the abrasion is determined by recording the mass loss of the rubber sample. Based on these measurement data, a wear model is derived as a function of coefficient of friction, contact pressure, and sliding speed for different ambient temperatures. The well-known brush model forms the basis for the wear simulations. With parameters validated on the aircraft tire, such as contact length, stiffness, and friction coefficient, the resulting mechanical forces within the contact area are calculated. Finally, the classic brush model is extended by the abrasion calculation. The tire wear is determined during unsteady load and slip conditions by use of the quasi-steady wear maps derived from our experiments. Within a measurement campaign on the complete tire, the tread depth is measured after various driving maneuvers and is in good agreement with the simulation results.

Evaluation of the Dr. William Thornton’s Skylab BMMD

The characteristics of a pre-flight model of the Skylab BMMD (Body Mass Measurement Device), which was made around 1970 by the team led by Dr. William Thornton, are accurately evaluated using an optical interferometer on ground. The calibration of the BMMD is conducted using metal block weights in the range of the total mass of 4.134 kg to 100.131 kg, in which the RMS value of the differences between the regression line and the calibrated values are 0.018 kg. Using this calibration result, the BMMD estimates the masse values of human subjects in the range of 33.16 kg to 95.79 kg with the standard uncertainty of 0.21 kg, which corresponds to 0.2% of the maximum value of the mass of the human subjects. It is found that the oscillation of BMMD seat is disturbed even with quiet breathing of the subject human. This is considered to be caused by the relative change of the center of mass of the human body due to the movement of internal organs.

Development of Supersonic Parachute for Japanese Mars Rover Mission

For landing a rover on the Mars ground, supersonic parachute has been developed in JAXA. Key technologies are categorized in aerodynamic performance, mechanical strength, ejection system, and validation method of the design for pre-flight model. So far, we have performed experiments in low-speed, transonic, and supersonic wind tunnels in Chofu aerospace center and ISAS. From these experiments, we have investigated aerodynamic performance such as drag coefficients, opening load factor, and stability of the parachute. We have also evaluated the mechanical strength in these wind tunnel tests. In addition, ejection system with automobile airbag inflator has been developed and a vertical ground test is performed in Noshiro Rocket Testing Center.

Reconstruction of the Mars Science Laboratory Parachute Performance

The Mars Science Laboratory used a single mortar-deployed, disk-gap-band parachute of 21.35 m nominal diameter to assist in the landing of the Curiosity rover on the surface of Mars. The parachute system’s performance on Mars was reconstructed using data from the onboard inertial measurement unit, atmospheric models, and terrestrial measurements of the parachute system. In addition, the parachute performance results were compared against the end-to-end entry, descent, and landing simulation created to design and operate the entry, descent, and landing system. Mortar performance was nominal. The reconstructed aerodynamic portion of the first peak inflation force was 153.8 kN; the median value for this parameter from an 8000 trial Monte Carlo simulation yielded a value of 175.4 kN: 14% higher than the reconstructed value. Aeroshell dynamics during the parachute phase of entry, descent, and landing were evaluated by examining the aeroshell total rotation rate and total rotational acceleration. The peak values of these parameters were and , respectively, which were well within the acceptable range. The entry, descent, and landing simulation was successful in predicting the aeroshell dynamics within reasonable bounds. The average parachute total force coefficient for Mach numbers below 0.6 was 0.636, which is close to the preflight model nominal drag coefficient of 0.615.

Mars Science Laboratory Entry Atmospheric Data System Trajectory and Atmosphere Reconstruction

On 5 August 2012, the Mars Science Laboratory entry vehicle successfully entered Mars’s atmosphere and landed the Curiosity rover on its surface. The entry vehicle carried a system of heat shield instrumentation that measured the aerodynamic and aerothermal environment during entry. Included in these sensors were seven pressure transducers linked to ports across the entry vehicle forebody that recorded the local surface pressures during entry. These measured surface pressures were used to generate estimates of atmospheric quantities based on computationally modeled surface pressure distributions. Angle of attack, angle of sideslip, dynamic pressure, Mach number, atmospheric conditions, and vehicle aerodynamics were reconstructed from the measured pressures. Three data reduction algorithms using subsets of the available data were used to assess data quality and interpret the entry performance. A Kalman filter algorithm was used to combine all available data for a final, complete reconstruction. The reconstruction results indicate that the data quality was good, and aerodynamic performance was within the uncertainties of preflight models. The three independent reconstructions are in overall good agreement, with several small anomalies that were reconciled using reasonable corrections within known sources of error. The combined Kalman filter reconstruction identified winds that are reasonable compared with preflight atmospheric models.

Retrieving lunar topography from multispectral LROC images

A technique for retrieving information about the lunar topography from any individual multispectral LROC Wide Angle Camera (WAC) image has been developed. This technology is possible, since images acquired at different wavelengths correspond to different viewing angles and the influence of color differences between the images on the parallax assessments is small. This method provides the precision of Digital Elevation Models (DEMs) comparable to the global lunar 100m raster DTM retrieved from the LROC WAC stereo model (GLD100). It potentially allows one to obtain maps of the elevations with better horizontal resolution than those of the GLD100. An empirical model of the distortion for LROC WAC has been developed and used for correction of the initial WAC images. In contrast to the standard pre-flight model, our model allows for compensation of the radial distortion, decentering the optics, and tilt of the CCD array almost fully. The DEMs obtained using our approach exhibit real morphological details in some cases that are invisible in GLD100 maps. Thus, our method suggests additional independent information about the lunar topography. The fact that our elevation maps have the same projection as the initial images allows valid corrections of these images to account for topographic effects (i. e. orthorectification) in contrast to the use of the GLD100 that may have slightly different coordinates referencing in comparison to individual WAC images.

Status of the Hard X-ray Modulation Telescope Project

The Hard X-ray Modulation Telescope (HXMT) is China's first astronomical satellite. It will perform a broad band (1-250keV) scan survey and do pointed observations of X-ray sources to study their spectra and multi-wavelength temporal properties. The pre-flight models of the satellites have been finished, and the flight models are in production. The expected launch date of HXMT is in late 2015.

The Genesis Solar Wind Concentrator: Flight and Post-Flight Conditions and Modeling of Instrumental Fractionation

The Genesis mission Solar Wind Concentrator was built to enhance fluences of solar wind by an average of 20x over the 2.3 years that the mission exposed substrates to the solar wind. The Concentrator targets survived the hard landing upon return to Earth and were used to determine the isotopic composition of solar-wind—and hence solar—oxygen and nitrogen. Here we report on the flight operation of the instrument and on simulations of its performance. Concentration and fractionation patterns obtained from simulations are given for He, Li, N, O, Ne, Mg, Si, S, and Ar in SiC targets, and are compared with measured concentrations and isotope ratios for the noble gases. Carbon is also modeled for a Si target. Predicted differences in instrumental fractionation between elements are discussed. Additionally, as the Concentrator was designed only for ions ≤22 AMU, implications of analyzing elements as heavy as argon are discussed. Post-flight simulations of instrumental fractionation as a function of radial position on the targets incorporate solar-wind velocity and angular distributions measured in flight, and predict fractionation patterns for various elements and isotopes of interest. A tighter angular distribution, mostly due to better spacecraft spin stability than assumed in pre-flight modeling, results in a steeper isotopic fractionation gradient between the center and the perimeter of the targets. Using the distribution of solar-wind velocities encountered during flight, which are higher than those used in pre-flight modeling, results in elemental abundance patterns slightly less peaked at the center. Mean fractionations trend with atomic mass, with differences relative to the measured isotopes of neon of +4.1±0.9 ‰/amu for Li, between −0.4 and +2.8 ‰/amu for C, +1.9±0.7‰/amu for N, +1.3±0.4 ‰/amu for O, −7.5±0.4 ‰/amu for Mg, −8.9±0.6 ‰/amu for Si, and −22.0±0.7 ‰/amu for S (uncertainties reflect Monte Carlo statistics). The slopes of the fractionation trends depend to first order only on the relative differential mass ratio, Δm/m.

Identification of the Transonic Aerodynamic Model for a Re-entry Vehicle

The development of flight control systems for aerospace vehicles requires the availability of reliable aerodynamic models. Pre-flight models, obtained by means of wind tunnel tests and computational fluid dynamics analyses, are usually to be refined using test flight data in order to reduce the level of uncertainty on aerodynamic coefficients. In this paper we present a methodology for the estimation of the lateral-directional aerodynamic model of a re-entry vehicle in subsonic, transonic and supersonic regimes. The identification is formulated as a nonlinear filtering problem and solved through a multi-step approach using the Unscented Kalman Filter. The exploitation of all the available a priori information for the stochastic characterization of the filter models and sensors noises and a rigorous management of all the uncertainties involved in the system identification process allow to obtain reliable figures of estimation accuracy, that are of paramount importance for the design of guidance, navigation and control (GNC) system. The methodology is applied to the simulated data of the CIRA Dropped Transonic Flight Test 2 mission, that will be performed by the end of 2009, with the objective of refining the lateral-directional aerodynamic model.

Measurements of molecular absorption spectra with the SCIAMACHY pre-flight model: instrument characterization and reference data for atmospheric remote-sensing in the 230–2380 nm region

Using the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometer, gas-phase absorption spectra of the most important atmospheric trace gases (O 3, NO 2, SO 2, O 2, OClO, H 2CO, H 2O, CO, CO 2, CH 4, and N 2O) have been measured in the 230–2380 nm range at medium spectral resolution and at several temperatures between 203 and 293 K. The spectra show high signal-to-noise ratio (between 200 up to a few thousands), high baseline stability (better than 10 −2) and an accurate wavelength calibration (better than 0.01 nm) and were scaled to absolute absorption cross-sections using previously published data. The results are important as reference data for atmospheric remote-sensing and physical chemistry. Amongst other results, the first measurements of the Wulf bands of O 3 up to their origin above 1000 nm were made at five different temperatures between 203 and 293 K, the first UV-Vis absorption cross-sections of NO 2 in gas-phase equilibrium at 203 K were recorded, and the ultraviolet absorption cross-sections of SO 2 were measured at five different temperatures between 203 and 296 K. In addition, the molecular absorption spectra were used to improve the wavelength calibration of the SCIAMACHY spectrometer and to characterize the instrumental line shape (ILS) and straylight properties of the instrument. It is demonstrated that laboratory measurements of molecular trace gas absorption spectra prior to launch are important for satellite instrument characterization and to validate and improve the spectroscopic database.

Viking Satellite Orbit Determination

During the summer of 1976, the two Viking spacecraft, each consisting of an orbiter-lander combination, were inserted into orbit about Mars. The paper describes the experiences of the Viking Satellite Orbit Determination Team in determining Mars centered ephemerides of the orbiters and positions of the landers from the two-way Doppler and range data, and synthesizes the different phases of the navigation plan which involves pre-flight modeling and error analysis for all Viking navigation functions from launch through landing. The problem of initial orbit convergence is solved by using DPODP's (Double Precision Orbit Determination Program) square-root batch data filter, and gravity models for both Viking I and Viking II were produced from the combination of short arc estimates. The importance of synchronous Viking orbits (with the rotational period of Mars) is stressed and future extended missions of the spacecraft are outlined.