John A. Christian

Extension of Traditional Entry, Descent, and Landing Technologies for Human Mars Exploration

The human exploration of Mars presents many challenges, not least of which is the task of entry, descent, and landing. Because human-class missions are expected to have landed payload masses on the order of 40 to 80 t, significant challenges arise beyond those of current robotic missions. This study uses parametric trade studies to provide insight into the feasibility of using Viking and Apollo heritage technologies to enable a human-class mission to Mars. The challenges encountered with human-class missions, as well as potential solutions, are highlighted through the results of parametric studies on vehicle size and mass. To populate the trade space, aerocapture, and entry-from-orbit analyses of 10 and 15-m diam aeroshells with a lift-to-drag ratio of 0.3 and 0.5 were investigated. The methodology developed to perform these trade studies represents a significant advancement in human Mars entry, descent, and landing system sizing. Numerous comparisons are made with past missions, both real and conceptual, and sources of discrepancies are discussed. Results indicate that in the limit, a crew capsule used only for entry from orbit could have an arrival mass as low as 20 t. For larger landed payloads, such as a 20-t surface power system, a vehicle with an arrival mass on the order of 80 t may be required. Finally, no feasible entry, descent, and landing systems were obtained with the capability to deliver more than approximately 25 t of landed payload to the Mars surface for arrivalmasses less than 100 t. This suggests that extension of traditional entry, descent, and landing technologies used for robotic exploration may be insufficient for human Mars exploration.

A Survey of LIDAR Technology and Its Use in Spacecraft Relative Navigation

This paper provides a survey of modern LIght Detection And Ranging (LIDAR) sensors from a perspective of how they can be used for spacecraft relative navigation. In addition to LIDAR technology commonly used in space applications today (e.g. scanning, flash), this paper reviews emerging LIDAR technologies gaining traction in other non-aerospace fields. The discussion will include an overview of sensor operating principles and specific pros/cons for each type of LIDAR. This paper provides a comprehensive review of LIDAR technology as applied specifically to spacecraft relative navigation. HE problem of orbital rendezvous and docking has been a consistent challenge for complex space missions since before the Gemini 8 spacecraft performed the first successful on-orbit docking of two spacecraft in 1966. Over the years, a great deal of effort has been devoted to advancing technology associated with all aspects of the rendezvous, proximity operations, and docking (RPOD) flight phase. After years of perfecting the art of crewed rendezvous with the Gemini, Apollo, and Space Shuttle programs, NASA began investigating the problem of autonomous rendezvous and docking (AR&D) to support a host of different mission applications. Some of these applications include autonomous resupply of the International Space Station (ISS), robotic servicing/refueling of existing orbital assets, and on-orbit assembly.1 The push towards a robust AR&D capability has led to an intensified interest in a number of different sensors capable of providing insight into the relative state of two spacecraft. The present work focuses on exploring the state-of-the-art in one of these sensors - LIght Detection And Ranging (LIDAR) sensors. It should be noted that the military community frequently uses the acronym LADAR (LAser Detection And Ranging) to refer to what this paper calls LIDARs. A LIDAR is an active remote sensing device that is typically used in space applications to obtain the range to one or more points on a target spacecraft. As the name suggests, LIDAR sensors use light (typically a laser) to illuminate the target and measure the time it takes for the emitted signal to return to the sensor. Because the light must travel from the source, to

Q-Method Extended Kalman Filter

A new algorithm is proposed that smoothly incorporates the nonlinear estimation of the attitude quaternion using Davenport’s q-method and the estimation of nonattitude states through an extended Kalman filter. The new algorithm is compared to an existing one and the various similarities and differences are discussed. The validity of the proposed approach is confirmed by numerical simulations.

Cooperative Relative Navigation of Spacecraft Using Flash Light Detection and Ranging Sensors

Autonomous rendezvous and docking of a spacecraft with a cooperative target vehicle is critical for a wide array of future mission applications, and flash light detection and ranging sensors are one of the most promising sensors for achieving this task. This paper presents an end-to-end assessment of how these sensors may be used for relative navigation. Within a unified framework, detailed discussions are provided on the topics of navigation architecture, flash light detection and ranging sensors measurements and image processing, reflector identification, and the estimation of relative position and attitude.

Statistical Reconstruction of Mars Entry, Descent, and Landing Trajectories and Atmospheric Profiles

Accurate post-flight reconstruction of a vehicle’s trajectory during entry into a planetary atmosphere can produce a wide array of valuable information. The data collected through the reconstruction of entry, descent, and landing system performance enables the quantification of performance margins for future systems. Beyond the engineering knowledge gained through trajectory reconstruction, the results may also be used by planetary scientists to generate an accurate atmospheric profile. A computer tool was developed to facilitate the rapid analysis of data gathered during entry, descent and landing. Emphasis was placed on making the tool flexible and capable of easily incorporating different types of data. These data are used to provide an accurate reconstruction through the use of an Extended Kalman Filter (EKF). The filter propagates the mean state forward using a three degree-of-freedom dynamic model and is capable of handling data from accelerometers and altimeters. The tool is validated against previous trajectory and atmosphere reconstructions that were performed for the Mars Pathfinder mission. In addition, an improved estimate of the Mars Pathfinder parachute drag coefficient is obtained by taking into account the parachute system deceleration during terminal descent. Inclusion of this acceleration effect within the reconstruction increases the reconstructed value of the parachute drag coefficient by approximately 7 percent (CDPar = 0.4419 ± 0.0549 [3-σ]) relative to earlier estimates.

Optical Navigation Using Planet's Centroid and Apparent Diameter in Image

Recent interest in sending humans to the moon, Mars, or other destinations beyond low Earth orbit has created an increased need for autonomous spacecraft navigation. Because traditional navigation approaches rely on ground-based tracking, new onboard techniques are necessary for the crew to safely return to Earth in the event of a communication systems failure. This paper investigates how images of a planet or moon may be used to perform autonomous navigation through the centroid and apparent diameter measurement type. If a planet is modeled as a triaxial ellipsoid, then it will project to an ellipse in an image. A new approach, which allows estimation of the spacecraft position relative to the observed planet using the full set of parameters describing an ellipse that is fit to points along the planet’s lit horizon, is presented. The performances of a number of different ellipse-fitting algorithms are also evaluated. Finally, the covariance of the solution is derived, and simulation results are presented.

Sizing of an Entry, Descent, and Landing System for Human Mars Exploration

*† ‡ ‡ ‡ ‡ , The human exploration of Mars presents many challenges, not least of which is the task of entry, descent, and landing (EDL). Because human-class missions are expected to have landed masses on the order of 40 to 80 metric tons, significant challenges arise that have not been seen to date in robotic missions. This study provides insight into the challenges encountered as well as potential solutions through parametric trade studies on vehicle size and mass. Aerocapture and entry-from-orbit analyses of 10 and 15 m diameter aeroshells with a lift-to-drag ratio of 0.3 or 0.5 were investigated. Results indicate that in the limit, a crew capsule used only for descent could have an initial mass as low as 20 t. For larger landed payloads, such as a 20 t surface power system, a vehicle with an initial mass on the order of 80 t may be required. In addition, no feasible EDL systems were obtained with the capability to deliver more than approximately 25 t of landed payload to the Mars surface for initial masses less than 100 t. This suggests that an aeroshell diameter of 15 m may not be sufficient for human Mars exploration.

A Quantitative Methodology for Identifying Evolvable Space Systems

*† With the growing emphasis on spiral development, a system’s ability to evolve is becoming increasingly critical. This is especially true in systems designed for the exploration of space. While returning to the Moon is widely regarded as the next step in space exploration, our journey does not end there. Therefore, the technologies, vehicles, and systems created for near-term lunar missions should be selected and designed with the future in mind. Intelligently selecting evolvable systems requires a method for quantitatively measuring evolvability and a procedure for comparing these measurements. This paper provides a brief discussion of a quantitative methodology for evaluating space system evolvability and an in-depth application of this methodology to an example case study. Nomenclature e = event s = state vector of original mission requirements s’ = state vector of evolved mission requirements S(X) = possible state space of system SL(X) = lawful state space of system W = evolvability vector wi = difficulty rating for i-th state variable along most efficient path of evolvability

Sequential Optimal Attitude Recursion Filter

A new nonlinear attitude filter called the sequential optimal attitude recursion filter is developed. This routine is based on maximum likelihood estimation and a sequentialization of the Wahba problem that has been extended to include nonattitude states. The algorithm can accept either individual unit vector measurements or quaternion measurements. This new algorithm is compared with existing attitude filtering routines, including the multiplicative extended Kalman filter, filter QUEST, REQUEST, optimal REQUEST, and extended QUEST.

Integrated Performance of an Autonomous Optical Navigation System for Space Exploration

y-bys that occur when the Sun is between the Earth and the planet. Autonomous navigation may also help reduce the tracking demands on ground based infrastructure. Optical navigation techniques are proposed as a solution to the problem of navigating independent of ground based tracking or state updates. In this paper, a new autonomous optical navigation system designed specically for spacecraft operating in a planetary system is presented. The paper briey highlights the image processing algorithm used to extract navigation measurements from a raw image. The primary measurements obtained from this process are a line-of-sight to the planet’s centroid, an estimate of the planet’s apparent diameter, and angular measurements between the planet horizon and reference stars. This paper, however, focuses more on ltering