Category: Other Worlds and Tech

It’s been an eventful week for Mars-related activities. After suffering a software reset on November 7th, as reported on in my last MSL update, the rover Curiosity experienced a second problem on November 17th.

This was caused by an unexpected voltage change being detected in the vehicle, described as a “soft” short, meaning that electricity is unexpectedly passing through something that is partially conductive, and in difference to a “hard” short, such as one electrical wire contacting another.

The short was first noted as a voltage difference between the chassis and the 32-volt power bus that distributes electricity to systems throughout the rover. Data indicating the change were received on Sunday November 17th, Curiosity’s 456th Martian day. Prior to the short occurring, the voltage level had been a consistent 11 volts; however, the data received indicated it has dropped to 4 volts.

While there was no immediate danger, as the rover’s electrical system is designed with the flexibility to work properly across a range of voltages – a design feature called “floating bus” – the decision was taken to suspend science operations while matters were investigated.

This was actually the second soft short Curiosity has experienced.  The first occurred on the very day it arrived on Mars – August 5th/6th 2012 – when the bus-to-chassis voltage dropped from about 16 volts to about 11 volts. This was thought to be related to explosive-release devices used for deployments shortly before and after the landing, but did it not and has not interfered with the rover’s operational capacity or capabilities.

Although the voltage change did not pose any immediate threat, and the vehicle did not enter a safe mode status, nor was it related to the earlier software reset, such soft shorts can reduce the robustness of the rover’s electrical systems for tolerating other shorts in the future. Further, they can indicate a possible problem in whichever component is the site of the short. Hence the decision to suspend science operations and take time to check some of the possible root causes for the voltage change.

Subsequent analysis revealed that the voltage drop occurred intermittently three times in the hours before it became persistent. Some six days were spent in root cause analysis using data returned by the rover, which saw a number of potential causes suggested by mission engineers eliminated. This resulted in the most likely cause being identified as an internal short in Curiosity’s power source, the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG or RTG for short).

Due to resiliency in the RTG design, this type of short does not affect operation of the power source or the rover. In fact, similar generators on other spacecraft, including NASA’s Cassini at Saturn, have experienced shorts with no loss of capability, and testing of an Earth-based RTG over many years found no loss of capability despite the presence of these types of internal shorts.

As a result of these findings, the rover was commanded to re-start science activities on November 23rd, and data returned from Curiosity’s onboard monitoring systems indicated that voltage levels had successfully returned to levels prior to that of the November 17th incident, a sign which is again indicative of an internal short within the RTG systems.

The resumption of science activities was marked by the rover delivering a further sample of rock cutting gathered some 6 months ago from an outcrop dubbed “Cumberland” in the “Yellowknife Bay” area of Gale Crater. A number of samples from the outcrop have already been analysed by the Sample Analysis at Mars (SAM) suite of instruments, which has the flexibility to be able to carry out such analyses a number of different ways, allowing significantly more data to be gathered on samples of the same rock gathered and stored by the rover.

Continue reading “Of volts and launches and looking for answers in the air” →

It’s been fairly quiet as the Mars Science Laboratory (MSL) rover Curiosity continues driving towards the point at which it is hoped the rover can traverse between a line of low-lying sand dunes and start exploring the lower slopes of Aeolis Mons, which NASA has dubbed “Mount Sharp”.

However, Thursday November 7th saw an unexpected hiccup in proceedings as Curiosity unexpectedly performed a “warm reset” (software reboot).  This occurred around four and a half hours after the new flight software uploaded to the rover (see my last mission report) had been temporarily loaded into memory as a part of the uploading and commissioning of the software, and while the rover was also transmitting data to the Mars Reconnaissance Orbiter (MRO) for later transmission to Earth.

A warm reset is executed when the flight software identifies a problem with one of the operations it is executing which may adversely affect the rover’s operations, and is a standard fault protection mode on all automated craft operated by NASA. It resets the software to its initial state, preventing further issues occurring. While there have previously been problems with Curiosity’s on-board computers, this was actually the first time since the rover’s arrival on Mars 16 months ago that a fault-related software warm reset had been executed.

Following the reset, the rover resumed communications, but the mission team initiated a root cause analysis for the reset using the ground testbed unit (essentially, Curiosity’s Earthside “twin”). This revealed an error in a catalogue file for the existing onboard software was triggered when the catalogue file was executed by the newly uploaded flight software, causing the reset.  As a result of this analysis, the flight software team were able to determine the steps required to recover the rover to its operating state prior to the reboot. These were successfully uploaded to Curiosity, and on Sunday November 10th, the rover set confirmation to mission controllers that it has successfully transitioned back to a nominal surface operations mode.

“We returned to normal engineering operations,” software and systems engineer Rajeev Joshi from the Curiosity team at JPL reported following the transition. “We are well into planning the next several days of surface operations and expect to resume our drive to Mount Sharp this week.”

Following the successful reinstatement of normal operations for the rover, the mission science team resumed planning for the next stage of Curiosity’s surface activities, which were due to restart on Thursday November 14th.

Continue reading “Resets, safe modes, and the journey so far” →

No, this isn’t a return to coverage of Wars of the Worlds in  SL. November marks the start of the next round of missions to Mars, with two new orbiters about to depart Earth as a part of our efforts to better understand the Red Planet and its atmosphere. Meanwhile, and despite a lack of headline news, NASA’s Mars Science Laboratory (MSL) continues its own explorations of the Red Planet, as does its little cousin Opportunity, half a world away.

Driving Forward

During the last week of October, the MSL rover Curiosity chalked up another achievement making its first pair of back-to-back autonomous drives using its on-board capabilities rather than relying on assistance from Earth.

I’ve covered the benefits of Curiosity’s ability to “self navigate” and how it works in previous MSL reports. However, up until now the system has only been used after the rover has initially traversed a course carefully plotted by the drive team on Earth using images taken by the rover and from overhead passes of the Mars Reconnaissance Orbiter (MRO).

This was the case with the rover’s drive on Sunday 27th October, when it completed an autonomous drive after a plotted drive. However, on Monday 28th October Curiosity immediately resumed its autonomous drive without any input from Earth, heading for the next waypoint along the route which will eventually bring it into the lower slopes of “Mount Sharp”.

This waypoint, dubbed “Cooperstown”, is a rocky outcrop which had been identified as a candidate for examination by the rover in MRO images of the route to “Mount Sharp”. It is anticipated that Curiosity will spend no more than a day examining the outcrop, which is liable to be done predominantly using the instruments mounted on the turret at the end of the rover’s robot arm.

“What interests us about this site is an intriguing outcrop of layered material visible in the orbital images,” said Kevin Lewis of Princeton University and a participating scientist for the mission responsible for planning the “Cooperstown” activities. “We want to see how the local layered outcrop at ‘Cooperstown’ may help us relate the geology of ‘Yellowknife Bay’ to the geology of ‘Mount Sharp’.”

“Yellowknife Bay” is an area of Gale Crater which, alongside that of “Glenelg”, the rover spent some 6-months examining various rock formations and gathering samples for analysis.

The planned duration of the “Cooperstown” stop is in marked contrast to the rover’s last waypoint stop, and coupled with the testing of back-to-back autonomous drives, is aimed at accelerating Curiosity’s progress towards the desired destination of “Mount Sharp”. So far, the rover has traversed around one-third of the 8.6 kilometres (5.3 miles) separating the “Yellowknife Bay” area, which it left in July 2013, from the entry point to the lower slopes of “Mount Sharp”.

The ability for the rover to safely store data necessary for it to resume self-navigation in its onboard memory is also vital for future planning for Curiosity’s progress over the upcoming holidays, when it is hoped that multi-day operations for the rover can be planned and uploaded, allowing the rover to continue in a range of activities, including driving, rather than necessarily spending the entire holiday periods parked-up and performing static science.

The next key activity for the rover is the uploading of the third new version of the on-board software. Such uploads are periodically needed in order to both prepare the rover for upcoming aspects of the mission and to improve its capabilities. This next update will see improvements in the information the rover is able to store overnight for the purposes of autonomous driving, updates to the software controlling the robot arm which should further increase the ability to use the arm when the rover is parked on a slope – something which is likely to be needed once Curiosity starts exploring “Mount Sharp”.

Continue reading “A Martian invasion” →