Douglas S. Adams

Deployment Analysis of the Lenticular Jointed Antennas Onboard the Mars Express Spacecraft

DOI: 10.2514/1.36890 Extensive analytical and experimental activities were carried out that culminated in successful deployments in May and June of 2005 of three lenticular, jointed booms that formed a first of its kind of ground penetrating radar antenna onboard the Mars Express spacecraft. These activities went well beyond the normal required tasks due to a postlaunch realization that the stowed booms retained a high level of stored energy. This high level of stored energy resulted in an uncontrolled boom deployment rather than a predictable boom deployment. Experimentally measured straight section properties and hinge properties were incorporated into specialized modeling techniques that were then used to simulate the boom lenticular joints. System level models were exercised to understand the boom deployment dynamics and spacecraft level implications including spacecraft attitude control and possible entanglement. Discussion includes a comparison of deployment simulation results to measured flight data taken during the three boom deployments. Important parameters that govern lenticular joint behavior are outlined and a short summary of lessons learned and recommendations is included to better understand future applications of this technology.

Lenticular Jointed Antenna Deployment Anomaly and Resolution Onboard the Mars Express Spacecraft

During the summer of 2005, ESAdeployed a series of three lenticular jointed antenna booms that formed afirst-ofits-kind ground-penetrating radar antenna onboard the Mars Express spacecraft. The booms were each released from their cradles with a high level of stored energy and allowed to deploy in a chaotic manner with no direct control over their speed or range of motion until their final geometries were achieved. Despite careful preparations, an unforeseen anomaly occurred during the release of thefirst boom that resulted in apartially deployed state. Theflight team was able to determine the boom’s intermediate geometry with a high degree of accuracy and to recommend a corrective spacecraft maneuver. This determination, the measured boom properties, and the on-orbit environment that led to the irregularity are discussed, along with the subsequent resolution of the situation and the ultimately successful deployment. Experience gained from the first boom was used to develop a new spacecraft maneuver that was designed tomitigate the chances of another anomaly occurring during the deployment of the second boom,which took place successfully several weeks later. These activities are summarized and the resulting flight data are presented for both dipole booms, which demonstrate a fully deployed and healthy antenna.

Landing site dispersion analysis and statistical assessment for the Mars Phoenix Lander

The Mars Phoenix Lander launched on August 4, 2007 and successfully landed on Mars 10 months later on May 25, 2008. Landing ellipse predicts and hazard maps were key in selecting safe surface targets for Phoenix. Hazard maps were based on terrain slopes, geomorphology maps and automated rock counts of MROs High Resolution Imaging Science Experiment (HiRISE) images. The expected landing dispersion which led to the selection of Phoenixs surface target is discussed as well as the actual landing dispersion predicts determined during operations in the weeks, days, and hours before landing. A statistical assessment of these dispersions is performed, comparing the actual landing-safety probabilities to criteria levied by the project. Also discussed are applications for this statistical analysis which were used by the Phoenix project. These include using the statistical analysis used to verify the effectiveness of a pre-planned maneuver menu and calculating the probability of future maneuvers.

Analysis of the Lenticular Jointed MARSIS Antenna Deployment

This paper summarizes important milestones in a yearlong comprehensive effort which culminated in successful deployments of the MARSIS antenna booms in May and June of 2005. Experimentally measured straight section and hinge properties are incorporated into specialized modeling techniques that are used to simulate the boom lenticular joints. System level models are exercised to understand the boom deployment dynamics and spacecraft level implications. Discussion includes a comparison of ADAMS simulation results to measured flight data taken during the three boom deployments. Important parameters that govern lenticular joint behavior are outlined and a short summary of lessons learned and recommendations is included to better understand future applications of this technology.

Phoenix Landing Site Hazard Assessment and Selection

The Phoenix Mars Scout landing site hazard assessment and selection process began with a survey of the latitude band from 65–72 N to identify candidate landing regions that were accessible, safe, and suitable for meeting the mission science objectives. Four candidate landing regions were identified based upon proximity of ground ice to the surface. Thermal inertia data, visible imagery, and topographicmapswere combined tomake an initial assessment of rock abundance and slopes. Broadly distributed high-resolution images enabled refined interpretation of the lowerresolution data sets. Based upon this assessment, a broad valley to thewest ofHeimdall crater at 68.3 N, 124.6 Wwas selected as the target landing region for the Phoenix mission. A detailed evaluation of this region resulted in the identification of eight different geologic units, with each unit exhibiting characteristic terrain type and rock abundances. Targeted high-resolution images were acquired across much of the region. An autonomous rockcounting algorithm was used to develop probabilistic risk distributions. Landing ellipse placement was selected to maximize the probability of a safe landing considering rock and slope hazards, including craters. Postlanding images from the Phoenix stereoscopic imager show a landing site generally devoid of hazardous rocks and slopes, consistent with predictions.

Reconstruction of the Mars Science Laboratory Parachute Performance and Comparison to the Descent Simulation

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 has been reconstructed using data from the on-board 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 (EDL) simulation created to design, develop, and operate the EDL system. Mortar performance was nominal. The time from mortar fire to suspension lines stretch (deployment) was 1.135 s, and the time from suspension lines stretch to first peak force (inflation) was 0.635 s. These times were slightly shorter than those used in the simulation. The reconstructed aerodynamic portion of the first peak force was 153.8 kN; the median value for this parameter from an 8,000-trial Monte Carlo simulation yielded a value of 175.4 kN - 14% higher than the reconstructed value. Aeroshell dynamics during the parachute phase of EDL were evaluated by examining the aeroshell rotation rate and rotational acceleration. The peak values of these parameters were 69.4 deg/s and 625 deg/sq s, respectively, which were well within the acceptable range. The EDL simulation was successful in predicting the aeroshell dynamics within reasonable bounds. The average total parachute force coefficient for Mach numbers below 0.6 was 0.624, which is close to the pre-flight model nominal drag coefficient of 0.615.

MARSIS Antenna Flight Deployment Anomaly and Resolution

This paper summarizes the resolution of an in flight anomaly that occurred during the deployment of the first of three MARSIS antenna booms. Characteristics of this deployment are described, along with a correlation to finite element models and measured spacecraft inertias, which allowed the intermediate state of the boom to be accurately determined. Based on this information, a spacecraft maneuver was performed that warmed the stalled hinge and led to the first boom successfully locking into its designed geometry. The confirmed partially deployed boom shape was then used to develop a thermal model of the stalled hinge both in its initial solar attitude and during the successful spacecraft maneuver. Results from the hinge thermal model and component level testing were evaluated in order to determine the root cause of the anomaly and the probability of its recurrence on subsequent deployments. These conclusions were then utilized in planning mitigating actions that were implemented during the remaining two boom deployments. Final flight data are presented for both dipole booms indicating a correctly deployed and healthy antenna. The monopole boom deployment was detected but the final state of the boom is unknown.

Landing Site Dispersion Analysis and Statistical Assessment for the Mars Phoenix Lander

The Mars Phoenix Lander launched on August 4, 2007 and successfully landed on Mars 10 months later on May 25, 2008. Landing ellipse predicts and hazard maps were key in selecting safe surface targets for Phoenix. Hazard maps were based on terrain slopes, geomorphology maps and automated rock counts of MRO’s High Resolution Imaging Science Experiment (HiRISE) images. The expected landing dispersion which led to the selection of Phoenix’s surface target is discussed as well as the actual landing dispersion predicts determined during operations in the weeks, days, and hours before landing. A statistical assessment of these dispersions is performed, comparing the actual landing-safety probabilities to criteria levied by the project. Also discussed are applications for this statistical analysis which were used by the Phoenix project. These include using the statistical analysis used to verify the effectiveness of a pre-planned maneuver menu and calculating the probability of future maneuvers.