Update from MEX Spacecraft operations Engineer Simon Wood at ESOC
The commands to run next week’s observations are now all confirmed on board Mars Express!
To give an idea of what these commands are and what they look like, here is a screen shot from the mission control system showing the commands on board for the first observation orbit on Monday, 25 May.
Uploading command stack to Mars Express
In essence, they are broken down into three groups: turning the spacecraft away from Earth (we call this a ‘slew’), the observation itself and then the slew back to pointing at Earth.
For the first group, the slew away, we first have a command to set what we call the ‘out of Earth timeout’; this starts a timer by the end of which the spacecraft must be back to Earth pointing. If it is not Earth pointing when the timer expires, then the spacecraft will put itself in safe mode.
This is a precaution that is taken for every pointing we do; in the event of a problem, the spacecraft won’t get stuck pointing the wrong way.
There are then the commands to update the mode in which the attitude and orbit control system (AOCS) is in and to tell the craft to start to slew. Finally, there are commands to update the position of the solar arrays to ensure that when the spacecraft has turned to its new attitude, that sufficient power is being generated.
Once in position, we can then start the observation.
Here we have the command to start the on-board control procedure (OBCP), which is a small computer program that runs on board the spacecraft and that controls the VMC camera. This program switches on and initialises the camera (this takes around two minutes) and then it enters into the programmed observations.
For the VMC Schools Campaign, this is means taking approximately 1 image per minute, cycling through 3 exposure settings. As this is a long-duration observation, there are also a group of commands that will keep updating the AOCS such that it keeps turning the spacecraft to keep Mars in the view of VMC.
The final group is the end of observation activities. Here we start another OBCP, which switches VMC off. Then the solar arrays are commanded to rotate again to optimise the power output and AOCS is then commanded to turn the spacecraft so the antenna is pointing at Earth.
After that, the transmitter will then switch on and the on-board computer will begin sending the VMC images back to Earth.
Several of the VMC Schools Campaign participants have asked, “What can we do with the images?” There’s no better way to answer this that to provide some links to past projects that have been done by schools, astronomy clubs and even individuals – all of which are very good and some of which are brilliant!
22 May – Start 11:00 EDT / 15:00 GMT / 17:00 CEST http://goo.gl/Yw8P5p
Prior to flying the campaign orbits on 25/26 May, this will be the final interactive Q&A session with the Mars Express flight control team for participants in the VMC Schools Campaign. Priority for questions will go to school/club participants. Questions can be posted in the ESA G+ channel or via Twitter using the #VMCSchools hashtag.
These three animations give you an accurate visualisation of the three orbits that will be dedicated to the VMC Schools campaign next week. We’ll Ask the MEX team to explain these in detail during Friday’s ESAHangout. They are posted below in the order in which they’ll be flown.
What you see in them is VMC’s view of Mars during the observations.
Video 1 – DOY 145 (25 May) Orbits 14456,14457 14458 Starting at 05:25 to 21:00
Thank you to everyone who replied to the Doodle poll!
Friday, 22 May, 15:00GMT – 16:30 GMT appears to be the best time slot for the most VMC School campaign participants, so let’s go with that. Go ahead and block that slot in your calendars (as will the MEX team). We’ll post details here in the blog later this week on how to join the #ESAHangout and how to post questions.
Mars Express Spacecraft Operations Engineer Simon Wood adds that, by Friday at 15:00GMT, the command stack that will trigger the VMC observations during ‘your’ three orbits next week should already be on board Mars Express!
The imaging plan with the overall target list for the VMC Schools Campaign is complete!
The MEX team have done a great job reconciling the proposed targets with all the conflicting requirements of the spacecraft, the mandated technical testing that MEX must do, the communication slots, pointing restrictions, etc.
Before you scroll down to the list below, please note several points:
For targets in the northern hemisphere and for equatorial targets (e.g. Tharisis, Valles Marineris, etc.), we will conduct imaging at (mostly) 8000-10 000km altitude.
For targets in the southern polar regions (Cavi Angusti, Phillips crater) we will be able to acquire images from much lower, at about 2000 km.
Irrespective of height, the proposals in green are the ones we believe we can do and get optimum results.
The ones in yellow are possible, but the VMC cannot be pointed directly at them and so the images won’t be centred on the target. While this is not ideal, it’s still pretty good. The green and yellow targets will be programmed into the Mars Express mission plan for the last week in May.
There are three requested observation targets that are, after a great deal of analysis, highly problematic or impossible.
North Pole: For the two observations proposed for imaging the North Pole, we will only see that area when it is about 90% in shadow, so you really wouldn’t see much. As an alternative – and if the proposers (HTBLA Kaindorf, Austria, and Aspiration Creation, USA, can accept) – we will be going over the South Pole under pretty good illumination conditions, and you could get images of that area. Just let us know!
Phobos: Imaging of Phobos (requested by School for Tomorrow, USA) will just not be possible – on the two occasions when Phobos crosses the disk of Mars (and so would be visible), we have an unavoidably higher-priority radio science pass.
The MEX team are now preparing a final mission plan, and we will have an animation and further details for you early next week.
We would also like to schedule a Google+ Hangout on 20, 21 or 22 May to provide interactive answers to as many of the teams as possible. We’ve set up a Doodle poll to determine which date/time is best for the most. PLEASE COMPLETE THE DOODLE HERE to let us know.
Today’s update compiled from inputs by several of the Mars Express team at ESOC. Thank you Simon, Andy and our Spacecraft Operations Manager Michel – Ed.
In the weeks since we announced which entries had made it through to the final round, we’ve been busy working out how many of the observations would be possible.
Even before we announced the VMC Schools Campaign, and assuming we might get, say, a handful of submissions, our original plan was to select as many of the requested targets as possible and then command Mars Express to turn and point VMC at each of them as it orbited the planet.
As you know, we ultimately received 25 excellent proposals (thank you!) and so the MEX team have been working hard to revise our strategy to accommodate this large number of requests.
The VMC webcam provides images of Mars having about the same quality as those provided by the ESA/NASA HUbble telescope. Image credit: ESA/Mars Express/VMC/ Humboldt Gymnasium, Vaterstetten
Mars Express was designed for performing steady observations and not rapidly turning to point at different science targets (we call these “pointings”).
And, as a safety feature, Mars Express is programmed to return to Earth-pointing between each science pointing (and it doesn’t slew, or rotate, very fast anyway – only about 10 degrees/min). Even a very short observation can take up to two hours, out of which 45 minutes are required for the move from Earth to the target pointing, and another 45 min to move back . As the spacecraft orbits Mars every seven hours, this restricts us to about three pointings per orbit.
Also, even though science will be turned off during the upcoming conjunction period, we must still allow time for communicating with Earth, which can take up to eight hours at a time. With the antenna and all the instruments rigidly fixed to the body of Mars Express, we cannot use communication periods for conducting observations with VMC. We also have other spacecraft tests that must be conducted in the week of 25-29 May.
All this reduces the number of orbits we have available for the VMC Campaign to four.
We also noticed that quite a few of the requested targets are close to each other. This causes a problem in that if we were to slew the spacecraft to point at any one first, by the time we have done this, then pointed back to Earth and then moved on to the next (nearby) target, it may well have moved out of view.
Together, these constraints mean that we might only observe about five of the proposed targets. Clearly, with so many excellent requests and so few discrete pointings available, we needed to devise Plan B.
When the cosmos hands you lemons, make lemonade
Of course, being Mars Express engineers, if we’re told that something is difficult or impossible, we take that as a personal challenge! We suspected that we could improve on this situation, and started working on ideas for a better plan.
First, note that, at 45 degrees, the field of view of the VMC camera is much larger than that of our main science camera. After a series of simulations, it became clear that by simply pointing VMC straight down and then flying the orbits, many of the requested targets would pass into view of the camera.
This wouldn’t be quite as good as performing individual pointings, but it would still be pretty good and remove the need for the time-consuming slews.
The trouble is, pointing VMC ‘straight down’ is not quite as simple as it may sound. What we actually do is called a ‘spot pointing’ in which Mars Express’ attitude control system aims an instrument at a specific point on Mars (such as Olympus Mons, for example) and then the spacecraft continuously adjusts its orientation to keep the instrument fixed on that spot.
In order to point down continuously, we would in fact need to conduct many of these spot pointings in a row – but then this means many slews and we’d be faced again with the multiple 45-minute slew delays!
That ‘a-ha’ moment
What we need is a single point on (or ‘in’) Mars that is ‘down’ no matter where we are over the surface; as it happens, there is such a point: The very centre of the planet.
The result is that VMC will continuously track the planet itself, keeping it in the camera’s field of view during the entire way around the orbit; by taking pictures at regular intervals we can then capture far more of the requested targets as they pass into view.
Indeed, at least one, or even, with some luck, several of the images thus acquired will be the closest to each of the requested targets. The MEX team at ESOC will download all the images, identify which picture(s) taken at which time(s) match the requested target, and parcel them out accordingly.
While this solution may seem obvious, remember that as the main instruments are only ever pointed at specific targets, this kind of observation was never catered for in the planning and control systems, and so we have had to do some deft programming to ‘fool’ the system (thanks for avoiding the word ‘hacking’ in our public blog posts – Ed.), but just by a little.
We think it’s an elegant solution to a perplexing problem and we think most if not all proposals can be met.
Making space movies
This solution, as hinted at the start of this post, uses the same technique we used for the Mars full orbit movies. The difference is that then, we collected a batch of images (about 600) during a single continuous orbit of seven hours.
This time, we will be performing the pointing in three segments for a total of 28 hours over a three-day period. This allows the best compromise between the requested VMC observations and the required communication periods and subsystem tests that we must do.
Reaction wheel on board Mars Express Credit: ESA
Currently, this plan is in the final stages of checking; our Flight Dynamics team are performing the required detailed calculations on the effects this will have on the spacecraft
For example, we cannot expose certain sides to the Sun for too long, nor can we allow our reaction wheels – the devices which turn the spacecraft to point in the desired direction – to build up too much speed.
The good news is that their analysis is almost complete and we expect the results shortly.
Once we have these, we can then use their output to generate a final simulation of the three-day observation period and can then give a final confirmation of which targets will be observed.
Information for schools, astronomy clubs, science centres and any other eligible group wishing to take part. Official hashtag: #vmcschools
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft successfully entered Mars’ orbit at 04:24 CEST on 22 September 2014. This image was acquired by the low-resolution VMC camera on board Mars Express at 14:50 CEST on 20 September, when MAVEN was an estimated 312,000 km from Mars. Credit: ESA/MEX/VMC
Mars is approaching solar conjunction where it will be on the opposite side of the Sun from Earth; this will affect communication with the spacecraft for a period of about five weeks and so science observations have to be stopped.
For this particular Solar conjunction, running for about five weeks between 28 May and 1 July, the Mars Express team will be stopping science four days earlier than usual for operational reasons. Part of this time is to be used to run tests on spacecraft subsystems, but we have an exciting plan with what to do with the remainder! (See details via Why conjunction frees up VMC time?)
How would you like to be a scientist on a Mars mission?
We would like to offer the opportunity for about eight (final number depends on the proposed targets) schools or other youth clubs/organisations to propose observations to be performed with the VMC camera (in principle, almost any large feature on the martian surface can be imaged) and then complete and submit a project report with their results; we’ll publish them here in the MEX blog. (See official announcement plus link to terms, conditions and the registration form here.)
The closing date for proposals is 12:00 CET on 27 March 2015 – which is not far off, so you’ll need to work quickly if you wish to be involved.
So what do you need to know?
First of all, you need to understand a bit about the VMC camera. It is our most basic instrument, being basically a low-resolution webcam that was originally only to be used to record the release of the Beagle 2 lander. Since then, we have used it to take some very impressive images of Mars, its moons and atmosphere as well as other planets. Although lacking the extreme resolution of the professional HRSC camera on board Mars Express, it does allow the entire martian disk to be observed in a single image. Go through our Flickr library to get a good idea of what we can do with it.
The VMC webcam provides images of Mars having about the same quality as those provided by the ESA/NASA HUbble telescope. Image credit: ESA/Mars Express/VMC/ Humboldt Gymnasium, Vaterstetten
In fact, VMC provides images of Mars having about the same resolution and quality as those obtained by the ‘professional’ ESA/NASA Hubble orbiting observatory!
Next, you need to know a bit about the orbit of Mars Express. We don’t expect you to attempt any of the incredible mathematics that our Flight Dynamics team here at ESOC perform on a routine basis, do but you need to understand that Mars Express has a highly elliptical orbit, which – combined with the rotation of Mars – means that not all of the planet’s surface will be visible to the camera during the available observing slots during 25-27 May.
Take a look at the VMC full-orbit animation, derived from Celestia, which is a great way to visualise what VMC can see during 25-27 May.
You will also need to know a bit (but not too much!) about Mars Express. Keep in mind that although we are inviting you to point Mars Express at a target of your choice (the VMC camera is fixed in position, so to point it, we slew the entire craft), we have many rules and restrictions for ensuring the safety of the spacecraft that cannot be violated.
We will take care of this within the MEX flight control team here at ESOC for you, but there are a few obvious things that you need not request, such as pointing toward the Sun or asking for two targets in quick succession (we avoid turning the spacecraft too quickly). Also, as Mars (and hence Mars Express) is almost at its furthest distance from Earth, the amount of data we can return is very limited (which is why the professional instrument payload is being switched off in the first place), and so we will not accept any long observation proposals (this also enables a larger number of short observation slots, giving as many schools or clubs as possible an opportunity to carry out observations).
The Red Planet
Some knowledge of Mars is also important – as we assume that is at what you will be pointing VMC. In principle, you could request to point VMC away from Mars, but, as it is a low-resolution device, we don’t think you’ll see that much (we did get a misty shot of Earth one time!). We will leave this for you to research on your own. There are many sources of information on the Main ESA website, the Internet and in your library that you will want to look in to in order to come up with a good proposal.
Emily Lakdawalla, from the Planetary Society, has posted online a series of excellent tutorials on working with space images, including the VMC. And you can find all archived VMC images for practice via the Mars Webcam blog and Flickr.
... and the fine print
Mars Express is an operational mission, and considerations of spacecraft safety and the primary professional science mission always come first. We may have to amend, change, or cancel the VMC Imaging Campaign at any time, or there may be some other reason why we can’t carry out your requested observation(s). But the slots on 25-27 May are looking good and we will do our best!
Tweet with the hashtag #vmcschools or post a query in the blog
So, what can you propose?
What do you think you can do? Would you like to get a close-up image of a certain feature (Olympus Mons?), or observe the whole of Mars? Are you going to work with raw VMC data or use the processed images? Can you identify certain features or landforms and explain what is going on? What caused them? We aren’t necessarily looking for the cleverest or most innovative observation proposals, but we will select eight (or so) good ones that we can fit together in to our observation window and that provide the best scientific, artistic or educational merit.
So, if you would like to take part in this extremely rare opportunity to briefly ‘take charge’ of a spacecraft around another world, make a plan and submit your proposals. Time is short and we know that there are many enthusiastic people – teachers, students, artists, young amateur astronomers and many more – out there with great ideas. Best of luck and we look forward to hearing from you!
Editor’s note: Thanks to Andy Johnstone & Michel Denis for this post
19 March – #ESAHangout via Google+ – Mars Express mission team will provide a tutorial on the VMC and how its images are planned & acquired
27 March – Deadline for registered groups to submit final proposal (12:00 CET)
8 May – #ESAHangout via Google+ – the Mars Express mission team will announce accepted observation targets
25-27 May – VMC imaging!
28 May (+/-) – VMC images downloaded and delivered to participant groups
End of current academic year or 31 July, which ever comes first – All participant groups must submit project report
We asked Michael Khan, working at ESA’s Mission Analysis Office at ESOC, what he would select as targets for VMC. His comments and some very useful charts are below – Ed.
Potential observation targets
Here are a series of charts that indicate when/where MEX will be in relation to a selection of nine surface features (click for full size). These indicate the ground track, time, the range and the elevation for Mars Express (and hence the VMC) with respect to nine select features.
The ground track of the Mars Express spacecraft from 25 through 27 May. Where the red line is vertical, the spacecraft is passing its closest point to Mars, at around 250 km over the surface. Conversely, where the line is canted, the spacecraft is near the farthest point out on its elliptical orbit. This diagram shows the entire ground track – however, some of the ground track also passes over the Martian night, when the regions directly below are dark. Credit: ESA/M. Khan
The local solar time is the current actual time at a given Mars location. In late May, it just so happens that the orbit is oriented such that most passes occur in the local morning hours, with very few passes (those that occur when the spacecraft is closest to Mars) in the late afternoon. Credit: ESA/M. Khan
For the nine sample locations, the range (distance from the location to Mars Express) is shown for 25-27 May. Ideally, to obtain bright, high-resolution images, the elevation (see http://bit.ly/1MbUteQ) should be high and the range should be low, though this combination may be difficult to obtain. Credit: ESA/M. Khan
For nine sample locations on Mars, the elevation at which the spacecraft passes overhead, 25-27 May, is shown. Only those overflights where the Sun is up at each of the respective locations are taken into account. The higher the elevation, the better the observation conditions. For 90-deg elevation, Mars Express would be directly overhead. Credit: ESA/M. Khan
Two proposals from my side, based on my results:
Eos Chasma on 2015/5/28, around 07:00 UTC at <2000 km range and up to 65 deg elevation. Arguably, pretty!
Elysium Planitia and Elysium Mons on 2015/5/26 around 16:00 at <1200 km range and up to 45 deg elevation, and again on 2015/5/27 at 18:00 UTC at <2000 km range and up to 55 deg elevation. This area is the one where Mars Express saw the ‘frozen sea’ 10 years ago. It is also the landing region of NASA’s Insight Spacecraft in September 2016.