Expected EDL Navigation Performance with Spacecraft to Spacecraft Radiometric Data

Abstract

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.

Autonomous navigation method based on unbiased minimum-variance estimation during Mars entry

“…The most significant uncertainty sources, including the initial state errors at the atmospheric entry interface and the uncertainties of the atmospheric density, induce the Mars entry dynamic model errors (Prasun et al, 2006;Prince et al, 2011). Using radiometric data as a new way for Mars entry navigation is proposed by Burkhart et al (2005). Throughout EDL, UHF transmissions from Curiosity (a MSL mission) are monitored by three Mars orbiters: the Mars Reconnaissance Orbiter, the 2001 Mars Odyssey and the European Space Agency's Mars Express (Way et al, 2013).…”

Consider unobservable uncertain parameters using radio beacon navigation during Mars entry

“…The feasibility of the above navigation scheme is based on research that the ultrahigh frequency radio communication is not blocked by the plasma sheath around the entry vehicle (Morabito, 2002;Morabito and Edquist, 2005;Burkhart et al, 2005;Williams et al, 2012). The National Aeronautics and Space Administration (NASA) is developing the advanced Mars Network's Electra ultra-high frequency transceiver, which is a prototype, embedded, real-time navigation system that provides radio communication information between the entry vehicle and an orbiting satellite or a surface beacon (Lightsey et al, 2008;Williams et al, 2012).…”

Navigation strategy with the spacecraft communications blackout for Mars entry

“…Then, the Electra UHF Transceiver was designed for use on a space vehicle, which realized radio measurements between beacons and the entry vehicle (Lightsey et al, 2005). In the paper Burkhart et al (2005), the spacecraft-to-spacecraft navigation algorithm was proposed, which took 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.…”