On February 18, 2021, NASA's Mars 2020 Rover “Perseverance” conducted the Entry, Descent, and Landing (EDL) sequence to land safely on the surface of Mars at Jezero Crater. Due to the criticality of the EDL sequence, redundant telecommunications strategies were utilized to observe the event. The rover transmitted an X-band (8.4 GHz) signal encoded with Multiple Frequency Shift Keying tones direct-to-Earth and a UHF (401.5 MHz) signal with 8 kbps encoded telemetry to orbiters, which relayed the signal back to Earth at X-band. NASA's Deep Space Network complexes at Goldstone, California and Madrid, Spain received the direct-to-Earth X-band signal. Two of the largest steerable radio telescopes in the world, the 100-meter Green Bank Telescope in West Virginia and the Effelsberg 100-meter Radio Telescope in Germany also received the UHF carrier signal on Earth. During the EDL event, full spectrum recordings of the UHF and X-band signals were captured at these observatories using open-loop receivers. Real-time and post-processing signal analysis to determine power level, received frequency, and Doppler shift allowed determination of the spacecraft's health and safety state during critical sequences, including event detection such as atmospheric entry, plasma blackouts, and parachute deployment. Simultaneous observations of the UHF and X-band radio links allow for redundancy in the event of a fault and greatly improve confidence in Doppler event detection.

The Mars 2020 (M2020) mission utilized Multiple Frequency Shift Keying (MFSK) tones for direct-to-Earth (DTE) communications during Entry, Descent, and Landing (EDL). DTE communications at X-band frequencies were complementary to relay EDL communications to the Mars orbiter network at UHF frequencies. The MFSK tones communications technique enables downlink communication of the spacecraft health and status during challenging scenarios such as the large Doppler shifts that take place during EDL. The M2020 EDL X-band DTE signals were received by the Deep Space Network (DSN) 70-m antennas and recorded by the DSN open-loop receiver (OLR) at the Goldstone and Madrid complexes. The M2020 MFSK signals were tracked through Doppler variations with tones detected in near real time by the EDL Data Analysis (EDA) software. The configuration and performance of the EDA software are discussed in comparison with expected signal parameters and theoretical detection models. Preparations for EDL included testing with the M2020 system testbed, with the flight system during system testing, and an in-flight end-to-end test during cruise. The EDA system was stress tested to characterize the signal power required for correct tone detection, which is valuable for future missions planning DTE communications during critical events.

The Mars Science Laboratory (MSL) mission landed the Curiosity Rover on the surface of Mars on August 6, 2012, beginning a one Martian year primary science mission. The UHF relay link from Curiosity to the Mars Reconnaissance Orbiter (MRO) incorporates new features enabled by the Electra and Electra-Lite software-defined radios on MRO and Curiosity, respectively. Specifically, the Curiosity-MRO link has for the first time utilized frequency-agile operations, increased data rates from 256 kbps up to 2048 kbps, employed suppressed carrier modulation and a new Adaptive Data Rate algorithm in which the return-link data rate is varied to match the observed channel condition. During the first 200 sols, the telecom operations team has been able to tune the radio and protocol parameters to maximize return-link data volume, which is now averaging roughly 500 Mbits per sol or twice the design requirement of 250 Mbits per sol. The telecom team has also derived new predict models that reduce data volume prediction errors and that quantify the impact of operational modes and link parameters, providing further planning insight for MSL mission operations team.

This paper discusses the Mars Science Laboratory telecommunications configuration for ultrahigh-frequency relay data and direct-to-Earth X-band semaphore tones during entry, descent, and landing, as well as the configuration of the Mars Reconnaissance orbiter, Mars Odyssey orbiter, and the Deep Space Network. Actual link performance will be compared with a priori predictions, including signal strength, Doppler shift, plasma blackout, and the range and angles between the Mars Science Laboratory and orbiting relay assets. Predictions were generated using telecom link budgets and models developed at the Jet Propulsion Laboratory. These data were also integrated into the mission's primary end-to-end entry, descent, and landing performance simulation, Program to Optimize Simulated Trajectories II which enabled telecom predictions based on Monte Carlo results of entry, descent, and landing simulations.

Mars Science Laboratory (MSL) undergoes extreme heating and acceleration during Entry, Descent, and Landing (EDL) on Mars. Unknown dynamics lead to large Doppler shifts, making communication challenging. During EDL, a special form of Multiple Frequency Shift Keying (MFSK) communication is used for Direct-To-Earth (DTE) communication. The X-band signal is received by the Deep Space Network (DSN) at the Canberra Deep Space Communication complex, then down-converted, digitized, and recorded by open-loop Radio Science Receivers (RSR), and decoded in real-time by the EDL Data Analysis (EDA) System. The EDA uses lock states with configurable Fast Fourier Transforms to acquire and track the signal. RSR configuration and channel allocation is shown. Testing prior to EDL is discussed including software simulations, test bed runs with MSL flight hardware, and the in-flight end-to-end test. EDA configuration parameters and signal dynamics during pre-entry, entry, and parachute deployment are analyzed. RSR and EDA performance during MSL EDL is evaluated, including performance using a single 70-meter DSN antenna and an array of two 34-meter DSN antennas as a back up to the 70-meter antenna.

This paper discusses the MSL telecommunications configuration for UHF relay data during EDL, as well as the configuration of NASA's Mars Reconnaissance Orbiter and Mars Odyssey. Actual link performance will be compared to a priori predictions including signal strength, Doppler shift, UHF plasma blackout, and the range and angles between MSL and UHF relay assets. Predictions were generated using telecom link budgets and models developed at JPL. These data were also integrated into MSL's primary end-to-end EDL performance simulation, NASA Langley's Program to Optimize Simulated Trajectories II (POST2), which enabled telecom predictions based on Monte Carlo results of EDL simulations.

During the Entry, Descent, and Landing (EDL) of NASA's Mars Science Laboratory (MSL), or Curiosity, rover to Gale Crater on Mars on August 6, 2012 UTC, the rover transmitted an X-band signal composed of carrier and tone frequencies and a UHF signal modulated with an 8kbps data stream. During EDL, the spacecraft's orientation is determined by its guidance and mechanical subsystems to ensure that the vehicle land safely at its destination. Although orientation to maximize telecom performance is not possible, antennas are especially designed and mounted to provide the best possible line of sight to Earth and to the Mars orbiters supporting MSL's landing. The tones and data transmitted over these links are selected carefully to reflect the most essential parameters of the vehicle's state and the performance of the EDL subsystems for post-EDL reconstruction should no further data transmission from the vehicle be possible. This paper addresses the configuration of the X band receive system used at NASA / JPL's Deep Space Network (DSN) to capture the signal spectrum of MSL's X band carrier and tone signal, examines the MSL vehicle state information obtained from the X band carrier signal only and contrasts the Doppler-derived information against the post-EDL known vehicle state. The paper begins with a description of the MSL EDL sequence of events and discusses the impact of the EDL maneuvers such as guided entry, parachute deploy, and powered descent on the frequency observables expected at the DSN. The range of Doppler dynamics possible is derived from extensive 6 Degrees-Of-Freedom (6 DOF) vehicle state calculations performed by MSL's EDL simulation team. The configuration of the DSN's receive system, using the Radio Science Receivers (RSR) to perform open-loop recording for both for nominal and off-nominal EDL scenarios, is detailed. Expected signal carrier power-to-noise levels during EDL are shown and their impact on signal detection is considered. Particular attention is given to the selection of the appropriate RSR processing bandwidths and to its configuration for real-time signal detection. The X-band carrier frequency obtained through post-processing of the open-loop recorded spectrum is given. Detection of spacecraft status and completion of key vehicle events through their Doppler signature is discussed and illustrated. This Doppler-derived information is compared against the very accurate vehicle data obtained post-EDL via MSL's UHF radio subsystem. The paper concludes with a discussion on the advantages and disadvantages of transmitting the X-band carrier and tone signal in the general context of EDL communications and lessons learned for future missions with EDL sequences are given.

The Mars Science Laboratory (MSL) mission landed the Curiosity Rover on the surface of Mars on August 6, 2012, beginning a one-Martian-year primary science mission. An international network of Mars relay orbiters, including NASA's 2001 Mars Odyssey Orbiter (ODY) and Mars Reconnaissance Orbiter (MRO), and ESA's Mars Express Orbiter (MEX), were positioned to provide critical event coverage of MSL's Entry, Descent, and Landing (EDL). The EDL communication plan took advantage of unique and complementary capabilities of each orbiter to provide robust information capture during this critical event while also providing low-latency information during the landing. Once on the surface, ODY and MRO have provided effectively all of Curiosity's data return from the Martian surface. The link from Curiosity to MRO incorporates a number of new features enabled by the Electra and Electra-Lite software-defined radios on MRO and Curiosity, respectively. Specifically, the Curiosity-MRO link has for the first time on Mars relay links utilized frequency-agile operations, data rates up to 2.048 Mb/s, suppressed carrier modulation, and a new Adaptive Data Rate algorithm in which the return link data rate is optimally varied throughout the relay pass based on the actual observed link channel characteristics. In addition to the baseline surface relay support by ODY and MRO, the MEX relay service has been verified in several successful surface relay passes, and MEX now stands ready to provide backup relay support should NASA's orbiters become unavailable for some period of time.

A compact set of tools have evolved for engineering analysis of Mars UHF relay telecommunications performance at NASA's Jet Propulsion Laboratory. The tools model all telecom variables from the RF layer up through the protocol link layer. The tools can solve for point solutions, analyze dynamic performance based on link geometry and can generate a variety of multi-day performance statistics. The telecom parameters and models in the tool set have been derived from or vetted against laboratory and Mars in-situ telecom performance measurements. The tool set and underlying models feed forward into mission specific flight operations software tools, proving to be invaluable for UHF telecom systems engineering analysis at all phases of mission life cycles.

In the past decade, an evolving network of Mars relay orbiters has provided telecommunication relay services to the Mars Exploration Rovers, Spirit and Opportunity, and to the Mars Phoenix Lander, enabling high-bandwidth, energy-efficient data transfer and greatly increasing the volume of science data that can be returned from the Martian surface, compared to conventional direct-to-Earth links. The current relay network, consisting of NASA's Odyssey and Mars Reconnaissance Orbiter and augmented by ESA's Mars Express Orbiter, stands ready to support the Mars Science Laboratory, scheduled to arrive at Mars on Aug 6, 2012, with new capabilities enabled by the Electra and Electra-Lite transceivers carried by MRO and MSL, respectively. The MAVEN orbiter, planned for launch in 2013, and the ExoMars/Trace Gas Orbiter, planned for launch in 2016, will replenish the on-orbit relay network as the current orbiter approach their end of life. Currently planned support scenarios for this future relay network include an ESA EDL Demonstrator Module deployed by the 2016 ExoMars/TGO orbiter, and the 2018 NASA/ESA Joint Rover, representing the first step in a multimission Mars Sample Return campaign.

The Phoenix spacecraft landed successfully on 25 May 2008 on the northern plains of Mars to conduct a five-month study of the Martian environment. In response to NASA's requirement to provide spacecraft communications during critical events, the Phoenix Mars Lander provided continuous telecommunications coverage during entry, descent and landing allowing NASA's mission control teams and the public to witness in real time the events that led to the successful landing. Phoenix thereby employed a number of first-time communication strategies. The paper briefly reviews the constraints and degrees of freedom in designing an entry, descent and landing communications link and presents Phoenix's novel and robust implementation approach to entry, descent, and landing communications. It then compares the actual and the predicted communications performance using data collected by the Mars Odyssey, Mars Reconnaissance, and Mars Express orbiters as well as by terrestrial ground stations. The overall lessons learned and conclusions described herein can serve as a pathfinder for the entry, descent, and landing communications architecture and implementation of future Mars landed missions.

The Phoenix Lander, first of NASA's Mars Scout missions, arrived at the Red Planet on May 25, 2008. From the moment the lander separated from its interplanetary cruise stage shortly before entry, the spacecraft could no longer communicate directly with Earth, and was instead entirely dependent on UHF relay communications via an international network of orbiting Mars spacecraft, including NASA's 2001 Mars Odyssey (ODY) and Mars Reconnaissance Orbiter (MRO) spacecraft, as well as ESA's Mars Express (MEX) spacecraft. All three orbiters captured critical event telemetry and/or tracking data during Phoenix entry, descent and landing. During the Phoenix surface mission, ODY and MRO provided command and telemetry services, far surpassing the original data return requirements. The availability of MEX as a backup relay asset enhanced the robustness of the overall relay plan. In addition to telecommunications services, Doppler tracking observables acquired on the UHF link yielded a highly accurate position for the Phoenix landing site.

The Mars Express Lander Communications subsystem (MELACOM) was initially designed as a relay for communications with the BEAGLE-2 lander. The failure of the landing over Christmas 2003 made its attempted use with BEAGLE-2 from January to February 2004 unsuccessful. However, intrinsic to the design was the capability for cross-support with other landers via the implementation of version 2 of the draft Proximity-1 protocol, CCSDS 211.0-R-2, which was designed to ensure reliable data transfer between remote autonomous communication nodes operating in close proximity. Reliability of the

The Phoenix Lander, a NASA Discovery mission which lands on Mars in the spring of 2008, will rely entirely on UHF relay links between it and Mars orbiting assets, (Odyssey and Mars Reconnaissance Orbiter (MRO)), to communicate with the Earth. As with the Mars Exploration Rover (MER) relay system, non directional antennas will be used to provide roughly emispherical coverage of the Martian sky. Phoenix lander deck object pattern interference and obscuration are significant, and needed to be quantified to answer system level design and operations questions. This paper describes the measurement campaign carried out at the SPAWAR (Space and Naval Warfare Research) Systems Center San Diego (SSC-SD) hemispherical antenna range, using a Phoenix deck mockup and engineering model antennas. One goal of the measurements was to evaluate two analysis tools, the time domain CST, and the moment method WIPL-D software packages. These would subsequently be used to provide pattern analysis for configurations that would be difficult and expensive to model and test on Earth.

The Phoenix Mars Scout Lander will launch in August 2007 and land on the northern plains of Mars in May of 2008.In a departure from traditional planetary surface mission operations, it will have no direct-to-Earth communications capability and will rely entirely on Mars-orbiting relays in order to facilitate command and control as well as the return of science and engineering data.The Mars Exploration Rover missions have demonstrated the robust data-return capability using this architecture, and also have demonstrated the capability of using this method for command and control.The Phoenix mission will take the next step and incorporate this as the sole communications link.Operations for 90 Sols will need to work within the constraints of Odyssey and Mars Reconnaissance Orbiter communications availability, anomalies must be diagnosed and responded to through an intermediary and on-board fault responses must be tolerant to loss of a relay.These and other issues pose interesting challenges and changes in paradigm for traditional space operations and spacecraft architecture, and the approach proposed for the Phoenix mission is detailed herein.I.