NASA to Rewrite Onboard Memory of Mars Orbiter

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NASA's Mars Reconnaissance Orbiter (MRO). (Credit: NASA, JPL)

NASA’s Mars Reconnaissance Orbiter (MRO).
(Credit: NASA, JPL)

It’s time for NASA to do some house cleaning concerning its Mars Reconnaissance Orbiter (MRO). The spacecraft’s flash memory contains tables that assist it to locate Earth and the Sun. The data is now 10 years old, so locations of the Earth and the sun in relationship to MRO have changed. As a result, there is a need for NASA to update the data. The spacecraft’s flash memory is being used because it is “nonvolatile,” which means that it retains the information even when the power of the spacecraft is off.

The original tables were loaded before the spacecraft was launched on August 12, 2005. They cover location data July 12, 2016. The mission team plans to begin updating this week. Performing the task will require the intentional rebooting of the onboard computer during a one-week suspension of MRO’s science observations and communication relay duty. Both NASA’s active Mars rovers will use a different NASA Mars orbiter, Odyssey, for relaying their data to Earth while MRO is out of service.

MRO has experienced unplanned reboots 16 times since it was launched. These reboots relied on the stored tables for recovery of the spacecraft. Managers anticipate that such events will continue to happen in coming years.

To update the location tables, engineers will have to rewrite the entire contents of the flash memory on the spacecraft. The orbiter has two identical computers for redundancy, with only one of them active at a time. Each computer has its own nonvolatile memory unavailable to the other, so the rewrite needs to be done twice. The “side B” computer has been active since an unplanned side swap in April 2015. The plan is to rewrite the computer’s memory starting on Monday, November 2. The procedure for “Side A” will follow in early 2016.

The contents of each computer’s 256 megabytes flash memory include backup copies of vital computer-operation files. “It’s the fundamental operating system of the spacecraft. That’s what adds to the risk,” explained MRO project manager Dan Johnston at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Just like with your home computer. If you mess with the operating system, the computer won’t work.”

The mission team has rewritten the flash memory just once since MRO was launched. That was in 2009. The side B rewrite being performed this week will follow procedures similar to those used successfully in 2009, but with an added safeguard. After a partial rewrite, an intentional reboot will be commanded to confirm that the newly recorded information is usable. If it is not, sufficient information from the 2009 rewrite would still be available as backup for a successful reboot. After confirmation that the partial rewrite is successful, the rest of the memory contents will be replaced.

Although it is already in its fourth mission extension, MRO could remain a cornerstone of NASA’s Mars Exploration Program fleet for years to come. The longevity of the mission has given researchers tools to study seasons and longer-term changes on Mars, including recently discovered seasonal activity of salty liquid water. Among other current activities, the orbiter is examining possible landing sites for future missions to Mars and relaying communications to Earth from Mars rovers.

One of the future missions for which NASA is examining landing sites is the ExoMars 2018 mission. This mission will include the landing of a rover and surface platform. It is the second of two missions making up the ExoMars program, a joint venture between the European Space Agency and Russia’s Roscosmos. The launch is planned for May 2018, with touchdown on Mars in January 2019.

The first of the two missions, the Trace Gas Orbiter and Schiaparelli entry, descent and landing demonstrator module will be launched in March 2016 and arrive at Mars about October 2016.

The search for a suitable landing site for the second mission began in December 2013, when the science community was asked to propose candidates. In October 2014, the Landing Site Selection Working Group chose four sites – Aram Dorsum, Hypanis Vallis, Mawrth Vallis and Oxia Planum. The last year has been spent evaluating these sites, taking into account the engineering constraints of descent and landing, and the best possible scientific return of the mission.

The main goal for the rover is to search for evidence of Martian life, past or present, in an area with ancient rocks where liquid water was once abundant. A drill will be included that is capable of extracting samples from up to 2 meters below the surface. This is crucial, because the present surface of Mars is a hostile place for living organisms owing to the harsh solar and cosmic radiation. By searching underground, the rover has more chance of finding preserved evidence.

Scientists believe that primitive life could have gained a foothold when the surface environment was wetter, more than 3.6 billion years ago. Buried or recently exhumed layered sedimentary deposits thus offer the best window into this important period of Mars history.

All four sites under study show evidence of having been influenced by water in the past, and are likely representative of global processes operating in the Red Planet’s early history.

All locations offer the opportunity of landing at a scientifically interesting site or finding one within 1 kilometer drive from the touchdown point, with numerous targets accessible along a typical 2 kilometer traverse planned for the mission of 218 Martian days (each 24 hours 37 minutes).

The sites must also conform to strict engineering constraints to ensure the safe entry, descent and landing of the entry module. These include the need for a relatively low-lying site, so that the module can pass through enough atmosphere for the completion of key events such as parachute opening and deceleration.

The horizontal and vertical wind speeds expected during the descent must also be considered because the module will land at the end of the planet’s global dust storm season in 2019.

Knowledge of how the terrain slopes over various scales is important, because the lander uses radar to monitor its velocity and altitude. Slopes can alter the degree of certainty in the measured distance to the ground, with implications for fuel consumption and landing.

Steep slopes and boulders taller than 35 centimetres – the clearance beneath the landing module – need to be avoided, although the rover will be able to navigate around local hazards after egress.

Taking into account these requirements and the individual science cases put forward for each site, the Landing Site Selection Working Group has recommended that Oxia Planum be the primary focus for further detailed evaluation for the 2018 mission.

A further recommendation was made to also consider Oxia Planum as one of the two candidate landing sites for the backup launch opportunity in 2020, with a second to be selected from Aram Dorsum and Mawrth Vallis.

Oxia Planum contains one of the largest exposures of rocks on Mars that are around 3.9 billion years old and clay-rich, indicating that water once played a role there.

The site sits in a wide catchment area of valley systems with the exposed rocks exhibiting different compositions, indicating a variety of deposition and wetting environments.

A period of volcanic activity may have covered early clay and other aqueous deposits, offering preservation for biosignatures against the planet’s harsh radiation and oxidation environment, and have only been exposed by erosion within the last few hundred million years.

ESA and Roscosmos will select the final landing site six months before launch.

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