Todd Ely

Initial Results of Rover Localization and Topographic Mapping for the 2003 Mars Exploration Rover Mission

This paper presents the initial results of lander and rover localization and topographic mapping of the MER 2003 mission (by Sol 225 for Spirit and Sol 206 for Opportunity). The Spirit rover has traversed a distance of 3.2 km (actual distance traveled instead of odometry) and Opportunity at 1.2 km. We localized the landers in the Gusev Crater and on the Meridiani Planum using two-way Doppler radio positioning technology and cartographic triangulations through landmarks visible in both orbital and ground images. Additional high-resolution orbital images were taken to verify the determined lander positions. Visual odometry and bundleadjustment technologies were applied to overcome wheel slippages, azimuthal angle drift and other navigation errors (as large as 21 percent). We generated timely topographic products including 68 orthophoto maps and 3D Digital Terrain Models, eight horizontal rover traverse maps, vertical traverse profiles up to Sol 214 for Spirit and Sol 62 for

Constellations of elliptical inclined lunar orbits providing polar and global coverage

Prior results have developed a methodology for selecting a long-lived constellation of three satellites that provide persistent, stable coverage to either the North or South Pole with no requirement for stationkeeping under the influence of only gravitational perturbations. In the present study, the sensitivity of this coverage in the presence of nongravitational forces is determined, and a design strategy is formulated that minimizes any potential sensitivity to these accelerations. The class of orbits and methods are extended to the search for global coverage constellations of six satellites. Two constellations are designed that provide 99.999% global coverage for a ten-year period also without the need for any deterministic orbit maintenance.

Real-Time Navigation for Mars Missions Using the Mars Network

A NASA Mars technology program task is developing a prototype, embedded, real-time navigation system for Mars final approach and entry, descent, and landing using the Mars Network’s Electra ultrahigh frequency transceiver. The Mars Network is ideally situated to provide spacecraft-to-spacecraft navigation via the Electra ultrahigh frequency transceiver, which is a versatile telecommunications payload that is capable of providing autonomous on-orbit, real-time trajectory determination using two-way Doppler measurements between a Mars approach vehicle and a Mars Network orbiter. A set of analyses based on the 2010 encounter at Mars between the MarsScienceLaboratory and theMarsReconnaissanceOrbiter demonstrate that the navigation system is capable of achieving a 300m or better atmosphere entry knowledge error and that the resulting technology is a key component to enabling pinpoint landing. The development approach, software design, and test results from an engineering development unit are presented.

Expected EDL navigation performance with spacecraft to spacecraft radiometric data

Pinpoint landing (defined for the purpose of this discussion as landing within 1km of a preselected target) is a key Advanced Entry, Descent and Landing (EDL) technology for future Mars landers. Key scientific goals for Mars exploration, such as the search for water and characterization of aqueous processes on Mars, the study of mineralogy and weathering of the Martian surface and the search for preserved biosignatures in Martian rocks, require placing landers at pre-defined locations of greatest scientific interest. The capability to land within 1 km of a pre-defined landing site will improve safety and enable landing within roving range of sites of scientific interest while avoiding hazardous areas. A critical component of the closed-loop guidance, navigation and control (GN&C) system required for pinpoint landing is position and velocity estimation in real time. Spacecraftto-spacecraft navigation will take advantage of the UHF link between two spacecraft (i.e. to an orbiter from an approaching lander for EDL telemetry relay) to build radiometric data, specifically the total count carrier phase of the Doppler shifted 2-Way coherent UHF signal, that are processed to determine position and velocity in real time. The improved onboard state knowledge provided by spacecraft-to-spacecraft navigation will reduce the landed position error and improve the performance of entry guidance. Results from the first of two years planned for this effort are documented here, including selection and documentation of prototype algorithms that will go forward into flight code along with analysis results used to define the algorithm set.

Altair Navigation During Trans-Lunar Cruise, Lunar Orbit, Descent and Landing

The Altair lunar lander navigation system is driven by a set of requirements that not only specify a need to land within 100 m of a designated spot on the Moon, but also be capable of a safe return to an orbiting Orion capsule in the event of loss of Earth ground support. These requirements lead to the need for a robust and capable on-board navigation system that works in conjunction with an Earth ground navigation system that uses primarily ground-based radiometric tracking. The resulting system relies heavily on combining a multiplicity of data types including navigation state updates from the ground based navigation system, passive optical imaging from a gimbaled camera, a stable inertial measurement unit, and a capable radar altimeter and velocimeter. The focus of this paper is on navigation performance during the trans-lunar cruise, lunar orbit, and descent/landing mission phases with the goal of characterizing knowledge and delivery errors to key mission events, bound the statistical delta V costs for executing the mission, as well as the determine the landing dispersions due to navigation. This study examines the nominal performance that can be obtained using the current best estimate of the vehicle, sensor, and environment models. Performance of the system under a variety sensor outages and parametric trades is also examined.

Optical Navigation Plan and Strategy for the Lunar Lander Altair; OpNav for Lunar and other Crewed and Robotic Exploration Applications

This paper reviews the currently planned Altair Optical Navigation (OpNav) system. The discussion includes description of the OpNav camera manifest. The Altair OpNav plan envisions one, OpNav camera assembly, with perhaps a functional backup that includes a wide angle-imager (of 40 deg to 60 deg field of view - FOV), and a narrow angle imager (of 1 to 3 deg FOV) co-mounted on a 2-degree-of-freedom gimbal. Both imagers are assumed to be relatively wide aperture and large dynamic range to provide excellent short-exposure images at mid-latitudes, and adequate images of longer-exposure near the poles. Landmark modeling and tracking methodology is discussed, including the stereophotoclinometry method assumed to be used to obtain high-accuracy terrain maps at lunar landing sites of 1 - 2 m, and 50 - 100 m elsewhere, using the images expected to be obtained from the Lunar Reconnaissance Orbiter (LRO). Characteristics of the OpNav navigation system are discussed and architecture and results from landing simulations presented, showing expected landing accuracies of better than 10m.

Real-Time EDL Navigation Performance Using Spacecraft to Spacecraft Radiometric Data

A two-year task sponsored by NASAs Mars Technology Programs Advanced Entry, Descent and Landing (EDL) work area includes investigation of improvements to EDL navigation by processing spacecraft-to-spacecraft radiometric data. Spacecraft-to-spacecraft navigation will take advantage of the UHF link between two spacecraft (i.e. to an orbiter from an approaching lander for EDL telemetry relay) to build radiometric data, specifically the velocity between the two spacecraft along the radio beam, that are processed to determine position and velocity in real time. The improved onboard state knowledge provided by spacecraft-to-spacecraft navigation will improve the performance of entry guidance by providing a more accurate state estimate and ultimately reduce the landed position error. A previous paper documented the progress of the first year of this task, including the spacecraft definitions, selection and documentation of the required algorithms and analysis results used to define the algorithm set. The final year of this task is reported here. Topics include modifications to the previously selected algorithm set for implementation, and performance of the implemented algorithms in a stand-alone filter, on an emulator of the target processor and finally on a breadboard processing unit.

Expected Performance of the Electra Transceiver for Mars Missions

The Electra UHF Transceiver, developed at NASA’s Jet Propulsion Laboratory, will provide accurate trajectory determination for future Mars missions. Autonomous on-orbit navigation and guidance will enable maneuvers such as aerocapture and surface landings within 1 km. In order for the Electra to perform its function, it must be able to acquire and track a 2-way signal under a wide range of vehicle dynamics and signal strengths as a vehicle approaches Mars. In anticipation of the testing of two Engineering Development Units of the Electra, a standard approach trajectory is deflned using Mars Science Laboratory as an example. This trajectory demonstrates the dynamic operating environment that the tracking loops will encounter during a planetary approach. A detailed link analysis is presented for a variety of receiver design and system model parameters. It is determined that the current hardware design should be able to establish a measurement link at a range of 100,000 km from an orbiting vehicle. This initial acquisition range may be extended with future algorithm enhancements.

Mercury Ion Clock for a NASA Technology Demonstration Mission

There are many different atomic frequency standard technologies but only few meet the demanding performance, reliability, size, mass, and power constraints required for space operation. The Jet Propulsion Laboratory is developing a linear ion-trap-based mercury ion clock, referred to as DSAC (DeepSpace Atomic Clock) under NASAs Technology Demonstration Mission program. This clock is expected to provide a new capability with broad application to space-based navigation and science. A one-year flight demonstration is planned as a hosted payload following an early 2017 launch. This first-generation mercury ion clock for space demonstration has a volume, mass, and power of 17 L, 16 kg, and 47 W, respectively, with further reductions planned for follow-on applications. Clock performance with a signal-to-noise ratio (SNR)*Q limited stability of 1.5E - 13/τ1/2 has been observed and a fractional frequency stability of 2E-15 at one day measured (no drift removed). Such a space-based stability enables autonomous timekeeping of Δt <; 0.2 ns/day with a technology capable of even higher stability, if desired. To date, the demonstration clock has been successfully subjected to mechanical vibration testing at the 14 grms level, thermal-vacuum operation over a range of 42 °C, and electromagnetic susceptibility tests.

Advancing Navigation, Timing, and Science with the Deep Space Atomic Clock

NASAs Deep Space Atomic Clock mission is developing a small, highly stable mercury ion atomic clock with an Allan deviation of at most 1e-14 at one day, and with current estimates near 3e-15. This stability enables one-way radiometric tracking data with accuracy equivalent to and, in certain conditions, better than current two-way deep space tracking data; allowing a shift to a more efficient and flexible one-way deep space navigation architecture. DSAC-enabled one-way tracking will benefit navigation and radio science by increasing the quantity and quality of tracking data. Additionally, DSAC would be a key component to fully-autonomous onboard radio navigation useful for time-sensitive situations. Potential deep space applications of DSAC are presented, including orbit determination of a Mars orbiter and gravity science on a Europa flyby mission.