Why conjunction frees up VMC time

You may be wondering why the VMC camera will be free for public imaging requests on 25-28 May – and hence why we can run the VMC Imaging Campaign. Mars Express Spacecraft Operations Engineer Andy Johnstone provided this reply.

The present conjunction period, when the Sun will block the direct line of sight between Mars and Earth, starts on Friday, 28 May, and lasts about five weeks until 1 July; the conjunction point happens on 14 June. As we’ve described before here in the blog, routine science payload observations are carefully planned well in advance.In this case, there is a boundary on the planning period (which are normally 28 days) that ends four days before 28 May, and it was decided by the operations and science planners not to conduct science during only four days.

ExoMars Trace Gas Orbiter at Mars. TGO will be launched in 2016 with Schiaparelli, the entry, descent and landing demonstrator module. It will search for evidence of methane and other atmospheric gases that could be signatures of active biological or geological processes on Mars. TGO will also serve as a communications relay for the rover and surface science platform that will be launched in 2018. Credit: ESA–D. Ducros

ExoMars Trace Gas Orbiter at Mars. TGO will be launched in 2016 with Schiaparelli, the entry, descent and landing demonstrator module. It will search for evidence of methane and other atmospheric gases that could be signatures of active biological or geological processes on Mars. TGO will also serve as a communications relay for the rover and surface science platform that will be launched in 2018. Credit: ESA–D. Ducros

So, while this frees up a rare time slot when no science will take place, and while VMC therefore may be used for this valuable public and educational outreach activity, this isn’t the only activity happening during the four days. We are spacecraft engineers, after all, and our goal is always to test, optimise and maximise the performance of our spacecraft.

We are performing other activities in this 4 day period:

  • Monday-Wednesday:  Tests with MELACOM (our UHF radio used to communicate with landers on the surface) as part of preparations for Mars Express to support ExoMars Entry Descent Module (EDM) landing next year.
  • Tuesday: A test for the Trace Gas Orbiter (TGO) mission, a partnership between ESA and Russia’s Federal Space Agency, Roscosmos. They want to prove that we can perform ground station swaps without bringing down the carrier. We are going to let them use MEX as a test vessel.
  • Wednesday: Performance tests on our solar arrays and batteries (last done just after the passage of comet Siding Spring in October 2014) and testing of redundant heater lines. We may also perform a special pointing with all instruments OFF in order to get a more accurate model of how much heating comes from the Sun, and how much is from internal components.
  • Wednesday-Thursday: Loading of the most vital commands to configure the craft for the Solar conjunction period. These relate to our attitude and orbit control system (AOCS). For this conjunction, we will be leaving our X- and S-band transmitters ON throughout as we do not have any power limitations this year.
  • Thursday:  A full performance check of the Transponders (radio transmitter/receivers) in both X- and S-band; this takes advantage of us having some long passes with no science data to be dumped. We can see how they both behave at the same distance on the same station with the same weather.

So, VMC is not the only valuable activities taking place in the run up to the conjunction period. We are using this opportunity to carry out lots of tests and it is likely that we may end up with more. But, with VMC, we are using some spare time in between operational activities to give something back to the public – especially students and teachers – who are some of our strongest supporters!

 

Mars Express, Phobos and the occult … ation

Today’s post contributed by Michael Khan, a mission analyst at ESOC and an avid amateur astronomer – Ed.

Imagine you’re playing Scrabble. The tiles on your rack don’t look as if there is much you could do with them. No vowels. Three ‘Y’s, a ‘Z’, and a ‘G’. Oh no! You might as well pass and exchange all tiles for new ones, Right?

You think you're good at online Scrabble? Well, I just put "syzygy" on the board - see if you can beat that! Credit: E. Yourdon CC BY-NC-SA

You think you’re good at online Scrabble? Well, I just put “syzygy” on the board – see if you can beat that! Credit: E. Yourdon CC BY-NC-SA

Wrong! (Don’t quit yet!)

Just look for a letter ‘S’ somewhere on the game board and you can append five of your tiles to spell the word SYZYGY (preferably such that it covers a triple word score). Thus you get rid of the ‘Z’ and the ‘Y’s and you earn heaps of points. There will be complaints around the table, but you can relax and let them complain: You really cleaned their clocks with this one. You win!

In astronomy, a syzygy defines a situation where at least three bodies are aligned. Eclipses, such as the 15 April lunar eclipse, are a perfect example of a syzygy in action.

Via Flickr E. Yourdon

In spacecraft operations, syzygies abound, and our Mars Express is no exception. Often, they are regarded as an unavoidable nuisance. When the spacecraft passes through the shadow of Mars and has to run on batteries, that is a syzygy of Mars Express, Mars and the Sun. When MEX is occulted by Mars and communications are interrupted, that is a syzygy of MEX, Mars and the Earth.

Other syzygies, however, offer real science opportunities. Stellar occultations by bodies in the Solar System have led to very important scientific discoveries.

To name but a few: