TGO in orbit Options

[Habukaz]

The latest and greatest on the plans for the CaSSIS imaging instrument:

After ExoMars TGO has reached its Mars Capture Orbit, the intention is to switch on CaSSIS in the week from November 21 to 28 and acquire images of Mars for the first time. A media release is planned on 1 December 2016 when ESA’s Ministerial Council is being held in Lucerne.

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The highly elliptical orbit is not ideal. When we approach Mars, the orbital speed is much higher than in our science orbit and the timing will be difficult to get right. Our aim is to get something – we do our best – and learn from what we get.

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When should the image be acquired, do we have enough time to rotate the instrument to get the 2nd half of a stereo pair, do we have enough time to get the data out of the instrument before the next image should be acquired? That planning process costs a lot of time and we don’t have many people to help do it. The hard part in MCO is that the speed over the surface at periapsis is much quicker than in the circular orbit so there is a good chance to mess it up.

http://nccr-planets.ch/getting-ready-tricky-task/

[bobik]

A recent paper (full text available) on CaSSIS science planning contains some info about the rotation mechanism problems (#10) and especially about the consequences for science operations:

Another important event that triggered software changes at all levels were the motor issues CaSSIS experienced at the start of 2019. Although CaSSIS did recover part of the motor movement, at the time of writing the first 100 degrees of the full 360° rotation are not being used. Also the motor is being moved less frequently, with the end result that more images are acquired with a fixed motor position. In order to minimize the impact on the science, the tools were updated to take into account this fixed motor position. The CaSSIS team then identifies on a weekly basis a motor position that allows acquisition of many targets with a maximum of 20° misalignment with the spacecraft ground track. This provides almost full overlap of the colours in the CaSSIS focal plane so that colour imaging is efficient.

The tools were also updated to allow for stereo images and aligned single images that use the motor on an individual basis. As the CaSSIS teams has gained confidence the number of images allowed with these methods has been slowly increased to the point that is almost indistinguishable from the operations before the motor issues.

[volcanopele]

Yep, we are taking 5 stereo images per week to help reduce wear and tear on the motor mechanism. We are also taking up to 30 "aligned" images, where the motor is rotated to align with the image groundtrack. Otherwise a fixed motor position is used.