Comet Encounter Challenges

Comet-Siding-SpringThe encounter with Comet Siding Spring on 19 October at 18:33 UTC brought unprecedented challenges to spacecraft around the planet Mars.

The Mars Reconnaissance Orbiter spacecraft started the day before a very complex on board sequence defined to mitigate the risks associated with hitting dust particles (predicted to be in the order of units per cubic kilometre) and also to perform a score of observations of the comet itself. This sequence had been carefully crafted in the previous weeks (related activities started in August) by the POST and SOT (Payload Operations Support Team, Science Operations Team) at JPL, and the MRO FET (Flight Engineering Team) at Lockheed Martin. The sequence has been compiled multiple times (to adjust with newer and newer orbital predictions, and changing spacecraft constraints) and rehearsed and tested on the ground on a spacecraft test bed before being loaded and committed for execution on board.

The management of the special CSS Encounter sequence is part of the so-called Background Sequence that manages the S/C while typical science observations are managed with a science-related timeline called Integrated Targeting Load, or ITL. The HiRise camera observations of the comet were part of the special Background Sequence, together with risk mitigation activities and many other things, because imaging of the comet is done in a completely different way from the typical imaging done of the surface of Mars. For one thing the camera needs to target a deep-space object, and then it has to be slewed not only to compensate the relative motions but also to scan the imaging area because of the way HiRise works.

But HiRise, which was expected to get very grainy images of the comet’s nucleus, is not the only instrument doing observations. Basically also all other instruments on MRO are also performing observations, including MCS, CTX, MARCI and CRISM (please check the JPL page on MRO to learn more about them). In particular SHARAD, the Italian SHAllow RADar (and the only European instrument on board MRO), is already performing a suite of 128 observations of the surface of Mars to try and assess subtle variations in the ionosphere that may be deducted by analyzing differences in the radar returns. SHARAD observations were performed in portions of ITL timeline that were allowed during the special sequences running during the encounter phase.

Targeting, planning and commanding the operations of multiple instruments, along with taking care of a very complex spacecraft as MRO is, has been a very exciting and intense activity. The spacecraft teams had to keep working on the nominal flow of science observations, scheduled roughly on a two weeks basis, while also working to devise and prepare the special sequences. In the main sequence running from last Friday until the Monday morning were more than 800 spacecraft activities and events, not including the actual commands for the instruments to perform their observations.

This is an engineering aspect that it is seldom discussed, or mentioned, in public outreach events, but that it is indeed a very inspiring one to new generations or to technically-minded people. Going into space does not mean only being an astronaut, a multi-talented, highly disciplined, operator. It also means to be working, for instance, on managing a deep-space mission with all its intricacies, and challenges and risks. This is a very rewarding and engaging career that can offer many more job opportunities than one might think, not only in the US, but also in Europe.

Other spacecraft also performed measurements related of the comet, including Mars Express, MAVEN, and presumably the latest newcomer MOM from India. We decided to concentrate on MRO just because we have a good insight on what’s going on there. Please read also about their activities. The Comet Siding Springs encounter may be considered a once in a lifetime event and worthy the attention of all space enthusiasts.

Fabrizio Bernardini

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