Space Ops 101

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Video in TIB AV-Portal: Space Ops 101

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Space Ops 101
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An introduction to Spacecraft Operations
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CC Attribution 4.0 International:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor.
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2018
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English

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Abstract
After launching a spacecraft into orbit the actual work for mission control starts. Besides taking care of the position and speed of the spacecraft this includes e.g. detailed modeling of the power usage, planning of ground station contacts, payload operations and dealing with unexpected anomalies. In this talk we will see many examples of problems particular to space crafts and how they influence the way space craft mission operations works.
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[Music] it's an honor to introduce you stamp roofer who is a professional in the space business and he's going to give
you a introduction to spacecraft control under the title of space ops 101 okay
thank you very much for the kind introduction hello and welcome to space ops 101 my name is Ben PUFA I'm a
mission planning engineer at the German Space Operations Center which is a part of the dodges sent home falutin home fat and I will give you a slightly biased introduction to spacecraft control it's slightly biased because first of all I'm working for a particular space agency and secondly because we will look at the whole thing kind of through the lens of an mission planning engineering
unfortunately the topic is pretty well large so we won't be able to talk about everything in particular we will not
talk about launches launches are pretty
amazing I'd love to see one in real life but we can't really go into that much detail because that's a very specific in particular topic also we will not talk much about human spaceflight and neither about entry descent landing so for example landing on a another planet of course the combination of human space flight and landing on another planet would be very cool to see but I can't just talk about it right now okay so
instead we will deal with one of the
main segments of Mission Operations so in general you distinguish three parts there's one the space segment so this is
everything that actually flies up into space some particular satellite or spacecraft including its payload so whatever it is doing up there then there's the transfer segment which is well the all the launching business else and then thirdly there is the
ground segment so we will talk mostly about the ground segment so this is everything that actually takes place on earth in order to command or use the spacecraft in space okay the ground segment itself again splits into various
subsystems so one of them is the the the main player when you want to actually talk to your spacecraft those are the ground stations okay so we will definitely need to talk about those secondly we need to actually know where our spacecraft is and we're just going this is actually done or described by
the flight dynamics thirdly space is at the same time very cold and also very hot so there's the power and thermal subsystem then there is attitude and orbit control which are responsible for telling the spacecraft where it should look at and we're actually figuring out how it is orient it next we need to actually talk to the spacecraft this includes interpreting well receiving and interpreting the data so this is part of the TMT C subsystem or the data system and last but not least it's of course the most important subsystem that's the mission planning which is responsible for scheduling spacecraft activities okay so the talk will kind of follow the
lifecycle of a spacecraft we will start with the launch and early operations phase which is called ly up for short and then we will need to talk about orbits and flight dynamics as well as how to actually communicate with the spacecraft after that we will talk about how we can well test and validate our spacecraft very quickly and then we will switch to the routine face so when we do the actual operations for what of whatever the spacecraft was designed to do this includes about data analysis telemetry and tailor commands so TMT see
and also mission planning and then in the end we will talk about well the end of the mission so whatever we are going to do at the end when we want to dispose of the satellite all right so everything
starts with the launch well not quite of course before that we have a pretty lengthy phase of preparations I will not actually talk about this but this might take about something like two years in advance of the launch in order to prepare everything to make sure that everything is running smoothly once the spacecraft is strapped on to the rocket it will get well flung into space and their group is separated from the launch vehicle from this moment on then it's flying by itself and we need to actually control it however we don't really know right now where the large provider will put our spacecraft it might actually be on its final orbit and so for example if it's a rather low orbit or it might be a transfer orbit to its final target orbit if it's actually further up once this is
during this launch there's actually a second control center that's the one for the spacecraft this this is actually the control room k1 in of the German Space Operations Center and it kind of looks like you expect a control room to look so in particular there are many screens on average everybody has like four screens there are large ones for showing an overview of what's going to happen and there are many small yellow signs these yellow signs denote the various positions of the operators and the engineers at the back and the center there is one position that's called the flight director the flight directors the person who is in charge of the operations so whenever there's something that needs to be confirmed needs to be done that needs to be decided and he is the last operational person to actually confirm the decision now in principle right after the spacecraft is separated from rocket this control room actually takes over however there are few subtleties here in particular a right of the separation the spacecraft is somewhere we kind of know approximately where it is because we plant and we plant this beforehand but we don't know the precise precise position we first have to acquire a signal we have to find it in space and have to set up a connection in order to understand this we need to talk a little bit about orbital mechanics so first of all why
does the spacecraft not fall down well if you look at the ISS so the International Space Station it flies at an altitude of about 300 to 400 kilometers where the gravitational force of the earth is still about 90 percent of the one at ground this means that you really need some horizontal speed in order to not fall down to earth so you need to go really fast 7.9 kilometers per second says the speed that you actually need in order to not fall down on the ground so if you are a bit higher and in some orbit then you need a bit less speed actually okay because you're farther away from the from the earth okay so we need to go very fast good thing to know secondly we need to know at which distances we will actually be flying our spacecraft so this is Earth obviously in particular at the following picture will actually be to scale approximately so one thing one possible place where you can put your spacecraft is low-earth orbit so that's the reason region below about 2,000 kilometers altitude above ground however mm sorry pretty high so very common are altitudes of 600 kilometers 500 700 this is a place where you mostly do scientific experiments and particular observation okay so there are many many satellites science scientific satellites that actually try to take pictures at various frequencies of the earth and also this is a place where I do reconnaissance okay then there are actually bit higher altitudes for example there's a medium Earth orbit so the the drawn circle is actually at an altitude of 20,000 kilometers and this is mainly used for navigational satellites so thank DPS or Galileo the European version and then there's another very common type of orbit that's the geostationary orbit this is at an altitude of about or pretty much precisely thirty five thousand seven hundred eighty six kilometers above ground this is chosen in such a way that the orbital period so the the time it takes you to fly once around the earth is 24 hours this has the advantage that the the movement of the satellites actually synced up what they are synchronized with the rotation of the earth meaning that your satellite is kind of always at the same position as when seen from Earth this is particularly important for TV satellites because well imagine you would have to actually move around your TV satellite dish all the time just because the satellite is moving instead you only have to fix it once and then it's pointing in the right direction okay and this is also a very common place for communication satellites for the same reason because we actually want to have a fixed position in which we have to look okay in order to get there for example a new session your orbit it's possible that the launch provider will actually put us in some kind of transfer of it yeah they usually then don't look like circles but rather like ellipses and and that in such a case we would need to do additional maneuvers yeah so we are on the red circle we will fly outwards but at some point will touch the geostationary orbit so the black one but in order to not well kind of fly back to earth we will have to accelerate so this is a maneuver that we have to execute somewhat at the beginning of the mission in order to well reach our geostationary orbit okay so
the the system that actually deals with these concentrations calculations etc that's the flight dynamics department so their tasks are in particular orbit
determination they're very various ways to do this for example very often you can actually ask the satellite where it is because it has GPS onboard at least if it's a Leo so a satellite in low-earth orbit so it actually knows where it is or you can do ranging which we'll talk about in a few seconds and from this you can calculate the orbit once you have to orbit you also want to know where the satellite is going to be located in the future so you will do orbit propagation next thing well we have to we might have to execute some maneuver to actually stay where we want to be or to get where we want to be so we need to calculate which direction we have to thrust whether we have to turn on our thrusters for how long this is also done by flight dynamics and the fourth point is well we have to talk to the satellites so we actually need to see it in order to do this and flight dynamics can actually calculate the the times and the positions or the directions rather where the satellites going to be and you can see all of these tasks are pretty numerical in nature it's really it's hard core mathematics numerix meaning that you actually want to use some tools that are very well battle-tested so to speak and well one of the most common programming languages for numerical calculations is of course Fortran okay so that's really a place where Fortran is still being used
actively being used because these libraries are just working the way they're supposed to work so nobody really wants to switch from there because they're just very good ok now
let's go back to the control room we have talked to our flight dynamics department they've told us well the satellites going to be at a certain position at a certain time or at least that's where we expected so the next thing we need to do is we need to establish the connection to the satellite and for this for this we need
a ground station the picture you see here is actually the ground station in vial hime that's in Bavaria that's sort of the main translation that we use and well it knows where to expect the satellite so it's a certain direction it should appear at a certain time above the horizon and then it tries to establish your contact this first acquisition is called is the first contact of the spacecraft after the separation and this is of course a crucial moment now once it has established a connection it tries to do various things so first of all needs to downlink some data so download but it's called downlink this includes telemetry so descriptions of the state of the spacecraft because we want to make sure that well the spacecraft is actually still working after the launch and then later this also includes downlink of payload data for example so think pictures or whatever it is was that the satellite was supposed to to measure or to take and then it will also uplink some stuff so for example commands because we want to tell their satellite to do something but this might also include for example software updates okay right and one other thing that the grant station can do is ranging ranging means that well you send a package or a packet to the satellite from the ground station this travels with a speed of light then the satellite will actually reply to that to that signal or to that that packet and then the answer will fly well we'll go back to the ground station and if you measure the time and if you know how long the satellite takes to actually react to to such a packet you can calculate the distance from the ground station if you if you do this several times then you get kind of like this like a radio this distance profile and from this you can really did use the orbit of
okay so let's look again to earth there's a ground station it's actually located at the North Pole here so that's on top and there's a satellite the satellite is not to scale just in case you were wondering and it's actually flying on an orbit which is 600 kilometers above the ground this is actually to scale now the the signals of the ground station they actually have to pass through the atmosphere meaning they're attenuated quite a bit so you have a finite range of the ground station second signal and this is drawn here so the red circle is an approximate range of the ground station and this intersects the orbit of the satellite only at certain time interval okay or a certain interval of the of the orbit in particular we can look at some numbers here if you have a satellite at 600 kilometers altitude you get a 90 minutes period approximately 90 minutes period around the earth and the portion of the orbit that you actually see the satellite from one given ground station is 10 minutes long okay so this means we would expect to see the satellite every 90 minutes for 10 minutes okay and this is when we have to do all the downlink and uplink unfortunately it's a bit more complicated because earth actually
rotates this map of Earth actually shows the the ground track of the satellite so that's the projection of the satellite onto the ground so that's a red line and the problem is that after 90 minutes the satellite returns to the position whereas before however Earth has actually rotated yeah by some amount like 90 minutes divided over 24 hours this is why the the ground tracks actually don't close up yeah so instead you get these these kinds of stripes over Europe's you see wh em that's the wild ham station it has a certain range that's the the the circle like black line and you can see that usually you have two contacts with the satellite pure well pure rotation okay so the third pass will already be outside of the range of the the of the ground station okay so you actually have even less contacts than what I said earlier this picture actually shows the same situation from the top so from North Pole you can see that actually there are actually circles so all the distortions that you've seen on the earlier slide was due to the protection that was used for the map you know so this is sort of what it actually looks like if you look from above the earth but the other one is the typical maps that you see okay so now we want to we have found our spacecraft we want to talk to it so we need to actually send a signal there now let's think about which kinds of frequencies we might use for this communication well first of all we noticed that there is for example water vapour in the atmosphere which absorbs parts of the electromagnetic spectrum so for example here at around 23 gigahertz there is an absorption peak due to water and the higher frequencies we use the more actually gets absorbed this means that we kind of want to restrict our frequencies frequency usage to actually lower frequencies in order to get a higher range but then we also have well maybe less data rate so in spacecrafts you usually use actually the lower part of the graph that's shown here usually even we know what is what is shown at all so this starts at 10 gigahertz and you use even less frequencies or in
lower frequencies for example you might use UHF so amateur radio at 430 megahertz you might use L bands one to two gigahertz in particular the the main carrier frequency of of GPS satellites is in this range okay then there's s band so that's a very typical frequency range from two to four gigahertz which is used for the actual commanding of the satellite yeah so this is an important frequency for us or band for us then there's also the X band so X band is higher higher frequency so we expect even higher data rates and this is usually then used for payloads okay so if you have a lot of data that you want to down link for example a picture that you just took from your satellite also this is being used for deep space missions then there's K U band K u band is used for TV satellites and ka band so this is now slightly above the the local water vapour absorption maximum so this is pretty cool there you really have high data rates it's been useful various applications whenever you need a high data rate however there are some mechanical difficulties you know because if ya direct directional antenna so this is slightly non-trivial but it's being used more and more often now if you fix such a frequency and you talk to the satellite you of course need to modulate some signal on top of that you need some protocols which do some level of error correction etc so I will not talk about this but in principle there are very specific standards for space that they're being used in order to assure that signals that you send or that you receive actually get received okay right
so we can now talk to the to our satellite we have acquired a signal so we switch back to the control room in the control room we are now very happy so we have done the first acquisition this is actually when people hear applause and then afterwards you there are a few things that aren't left to do actually now the work starts so for
example the satellite was actually running on battery during the launch and afterwards but it needs of course some some new power so for this you need to deploy solar panels this is done during the layup also you might need to deploy antennas I showed you various frequency bands and usually satellites actually have several antennas and using several bands for different tasks so the commanding might be done on the S band but the actual downlink of the payload data might be on expand for this you need an additional antenna so this needs to deployed we deployed also this is the time when you do all the other maneuvers in order to reach your final orbit and you start switching on other components of the spacecraft this might include for example star trackers so star trackers are essentially essentially cameras that just take pictures of the sky sort of the stars and they compare them to some onboard database of known star positions and this way the camera can figure out in which direction it is looking if you know how the star tracker is actually mounted on a spacecraft you can then that use how the spacecraft is oriented and this is important for example if you want to take a picture then of course you need to know where have you been actually looking at so you need some something like a star tracker another thing that it would kind of switch on or actually spin up during a layup would be a reaction wheel so reaction wheels are essentially gyros that just rotate very quickly you spin them up and the idea is that well this stabilizes the spacecraft now because you actually want to control the rotations in most cases okay so um now we hope that everything was working perfectly we launched the spacecraft but
unfortunately not always everything goes perfectly so let's maybe you dig into some example this is TV set one well I don't have a picture but um there was the satellite TV satellite from 1987 and everything worked as we described so we got the first acquisition we got some telemetry from the from the spacecraft but unfortunately the solar arrays turned out to be only partially deployed that's of course a problem and we need
to diagnose this and we need to fix it if possible so it the first thing you have to know is that you kind of don't I can't really necessarily trust all the data that you get you have to confirm that whatever you are seeing is actually the case so we have to use additional additional sources for example in the case of a solar array you can actually check how much is the power output is it actually less than expected if it was deployed and it turned out yes there's not enough power and secondly once you notice this you can actually send the manual deployment command again yeah so it's possible that the automatic solar panel deployment didn't work so we just try it again unfortunately this did not work so it still seemed and deployed now you start thinking well what are we going to do and you consult the usually the satellite manufacturer the satellite manufacturer actually all also sits in the control room during the lis up yeah because there happen to be many questions so you need somebody on the hand and they suggested or already the people who operate the satellite they suggested various tests to figure out what was wrong with TV set one and I want to present just two of these things you can try one is you can orient the spacecraft or the satellite such that it is at a 45-degree angle towards the the sunlight and then you start rotating it if you do this carefully and you measure the the power output of the solar arrays you can actually estimate the the angle that the solar array was was deployed so they did that and they figure out well they're completely not deployed yeah so less than two degrees actually okay so that's a problem then they did various other tests and they came up with one possible
problem and this is that there might be the the actual stir up sort of the black boxes and the picture which keep the solar array attached to the satellite during the launch the day might still be there and principal they should have been fired off or removed and then the solar array show deploy but it looked like they were actually still there so one thing you can then try is well you can again rotate the satellite in such a way that the spirit stirrups will cause a small shadow over the solar array this will reduce the the power outage again the power output again just a tiny little bit so you might be able to measure this and this way confirmed that the stirrups are still there turns out this was not actually ready well measurable so this didn't work however they were still able to to reduce it it was probably the stirrups that are still there once you have diagnose the problem you want to solve it of course so let's see how can we recover such a situation and this is sort of where you can well just follow your creativity and come up with arbitrary solutions and see whether you can actually try them so one thing we can do is we can spin up the spacecraft if we do this very fast we will have a very strong centrifugal force so maybe an acceleration of about 1g and this way we might hope that we lose in the stirrups another thing you can try to do you can use your main engine to actually accelerate spacecraft in the Buddhist way in order to excite resonance frequencies of the stirrups okay so hopefully this will this might actually lose and disturbs another thing you can try to do is you can command the spacecraft to to well to heat up and to cool down in some ways and this way actually also loosen the stirrups and the last thing you can tries you can well kind of just try to shock the whole thing so for example you could deploy an antenna in this particular case this was the main antenna which was actually stuck beneath the solar array so you try to deploy this and hope that the force actually pushes this solar array okay yeah unfortunately none of those worked and this was an unsuccessful recovery of a satellite so in particular the the main problem was that well this was a TV satellite so it really needs the antenna but then I couldn't deploy because because of the stock solar array so in this case this did not work but usually of course this works and people are coming up with very creative very interesting solutions to all kinds of problems and get things running all right
so once we have our spacecraft in some kind of safe state we kind of conclude the lis up and we start testing the actual properties of the spacecraft this is called the commissioning phase or in all the testing of the payload so this usually takes longer than a layup might take several months depends on what type of mission you're looking at this is when you actually start or switch on the payload and when you also verify that the payload is working as expected okay so in the picture you see a geostationary communication satellites so its main payload are the communication arrays or lydian the antennas in particular so for example you might want to actually verify that the antennas are working properly after the launch now so during launch they only get checked up and then it's really pretty intense so you want to make sure that they are working properly afterwards so for example one thing you might want to do is point the satellite on you at your ground station you measure the the strength of the signal that you receive then you move it slightly you measure again the strength and this way you you kind of get a pattern of the the antenna okay and this is a property of of this particular one this particular antenna that you might use later another thing that you do during this time as you check out redundant components of the satellite so for example if you have an
observation mission you as I already mentioned you need to know where you're looking at so you need for example GPS or star tracker now if that fails you obviously have a large problem because now suddenly you don't know where you're taking photos or images so usually there's quite a bit of redundancy on satellites and so there are two GPS transmitters or a receiver sorry and then you can actually switch between them and during this face you will test that they are working properly okay so let's suppose we have done this and
everything is working as expected then we start with the routine face the routine face is sort of the main face of the operations so that's when you actually do the science experiments or you start offering communication services or whatever it is you're doing this picture is as a picture of the the mission there's a tandem X so that those are two radar satellites flown in flying in low Earth orbit and they can actually make three-dimensional maps on of the ground by sending a radar signal and then receiving it and because they are flying in close formation so something like a few hundred meters apart from each other they actually get this kind of stereo graphical 3d information okay and during the routine phase a scientist would actually order a data take or a picture of this kind somewhere maybe online and then somehow the the mission
would actually command this order the command center would command this data
take it gets downlinked and then the result will actually give them to the scientist okay so this is the main phase
of the spacecraft life so where we do this payload operations by the way this picture is as a picture of the of a joined American German mission that's the grace follow-on mission to satellites that have a microwave or a laser link between them and they measure the distances in order to well variations of the distances in order to did use the the gravitational field of the earth last year at 34 c3 there was actually a talk about the previous decimation here actually probably in this room okay so this is so we this is a time when we do our science experience furthermore we actually monitor the spacecraft of course because all they still need to know what's happening is it working properly we will of course continue to handle contingencies but hopefully there are none anymore and we might also adapt to new mission requirements so for example well you could actually try to devise new kinds of experiments on the flying satellite and for that you might need to upload new software which is also done during this phase another issue is that a spacecraft actually ages so for example a battery might deteriorate now so it's its total capacity actually gets smaller over time so you need to adapt to that for example if there's less power available then you can actually do fewer data takes now something like that and you need to monitor this and react accordingly okay so how does the monitoring work well
that's part of the the TC TM and the data a subsystem or system and the idea is that the spacecraft actually measure measures various properties that it the task or the describes state all the times we have time series of binary data and also of a numerical values for example here the plot shows the temperature of a certain part of the spacecraft over time but remember we don't have this information available life we only get this once we actually downlink it okay and then we get a huge well part of the data at once okay so this is grabs the state of the spacecraft and there can be lots of parameters so for example 20,000 telemetry parameters for one spacecraft is as possible if you measure something once every second you do this for a few years 20,000 parameters this means that you have a lot of data so obviously you can do a lot of data analysis time series analysis with that you can do anomaly detection telemetry prediction prediction or yeah detecting errors or problems but within this data also what
you need to do is you kind of need to save this to some kind of offline database because lots of other subsystems actually need this data because they want to know what is the state of the of the spacecraft so this
is an example for for telling telemetry view so this is one software that we use it's called geckos and you can see here a number of telemetry packets so for example there is there are few confirmations that some checksum was correct and that some ping was actually received and was being worked on okay so and it was executed it's time stand and you get some additional information and this is sort of the most well basic thing you can you can really see once you know the state
of your spacecraft you actually want to command the spacecraft to do something this is done by a tiller commands and on the picture here you can see some commands that have been executed and also some that are still to be executed so for example on the upper link sorry in the upper part you see a few pings
which were not actually answered by the spacecraft but the last one was received and was replied to and the operator can for example already load of utila commands on the manual commands tech prepare them and then execute them very quickly this is the lower part notice that these two commands are very specific to the spacecraft because they really need to do something there so this is in some way provided by the satellite manufacturer and you have to yeah somehow yeah understand all the possible things you can do in particular you very often don't really want to do is like very atomic things but instead you want to achieve a certain task for this you bundle the attiny commands you can add for example also telemetry checks so conditions on the telemetry and you call this a flat operations procedure so this will be sort of a a bundled thing that will execute it on their spacecraft and wait for the purpose of achieving a specific goal another thing that's important as I've mentioned various times you don't see the spacecraft all the time meaning you cannot really command it all the time but instead what you do is use Antilla commands but you make them time tacked and then they get executed for example when you don't see the spacecraft ok and these kinds of tina commands are called TTC let's look
at an example so this might be a set of contact tina commands for a maneuver ok so at time t 0 we want to execute some maneuvers so we want to turn on thrusters at this time and the position understand the duration of the burn they were calculated by the flight dynamics departments of course but one hour before that we actually need to check for example that the spacecraft is in some some fixed state some prepared safe state 8 seconds later we might actually start heating up thrusters because the fuel needs some kind of operational temperature then 11 minutes before the burn start you will automatically command the switch or some additional telemetry so this is kind of like you turn you turn on the debug mode ok you just tell the spacecraft to actually tell you to give you more data then because the the the brain will actually make the spacecraft shake quite a bit there would be lots of alarms going off so at some point before the burn you will turn off these alarms to safeguards just because they're the direction of the spacecraft's actually expected then you start rotating in the right direction of course and at some point the burn starts now this should in principle stop automatically however you might command an additional safeguard stop command just to make sure that in case the other one well kind of did index didn't get executed you you stopped nevertheless and then you kind of reverse the whole procedure to return to a mode where you can proceed with your payload operations okay and and this would be a sequence of time tech commands that are uploaded to the spacecraft during an uplink and then executed whenever t0 was actually taking place alright so there's my other thing
that I want to describe and this is mission planning it's probably the the the yeah one of the lesser-known subsystems and this is sort of it is at the point where you have to wait between ultimate automation and manual commanding so suppose you have a scientist that actually wants to take pictures so he wants to have the satellite taking some pictures of some region so then he has to sort of ask if the satellite can do this and has to make a reservation this is being taken care of the body mission planning system which will then talk to flight dynamics to see whether this is actually possible give feedback to the scientists and this will also tell the operators or the operating well the telecom operators to actually execute some some command to take the data take however because of all these kinds of little issues problems that you can have all the time you cannot really automate everything there is some kind of some amount of manual commanding that's still being needed for example due to those contingencies so what the mission planning system internally does is it schedules activities and it to do this in some consistent and conflict-free manner as imagine for example for the for a data take you need to actually take the picture before you want to downlink it okay so the those are two activities and they should actually take place and in some order okay from this these kind of activities that were requested by some scientists they create the system creates a timeline which is then well provided to everybody who needs to know what if spacecraft is going to do at some point so here's one example so that's one one
software did we use so it's called Pinta and the chose on the x-axis the time and up on the top you see these black/white things okay so and this is these are actually eclipses so whenever the spacecraft is not in the Sun or isn't a Sun you can see this there and below that there there are a few experiments planned but one of them is partially planned during an eclipse but it has the condition that it must not take place during eclipse so this gives a conflict okay and the mission planning system is responsible for identifying these these kind of conflicts and actually supplying that information to the scientist or the operator to to be resolved one other thing you can see is this thing that we talked about at the beginning so you need to download the information from the experiment so you need some scheduled downlink downlink opportunities and you can see two of them actually as the green lines above the blue ground so this is when the next time when the satellite actually sees the ground station and can downlink the results of the prior experiments okay so now we are doing kind of semi-automated all our experiments we gather a lot of scientific data but at some point
everything has to end so there's also the the end of the mission that you have to consider in general the mission time of a spacecraft might depend for example on the mission goal imagine that the that you have one specific experiment that you want to do and this might be finished at some point in time also it might depend on the orbit itself yeah so if you have a spacecraft and an altitude of 300 to 400 kilometers it will actually descend into the atmosphere within less than a year if you have satellite at an altitude above say 700 kilometers it would take more than 25 years to actually get down if you are on a geostationary orbit you will actually never come down so another thing is and this is mainly year 4 for geostationary orbit view stationary satellites is that you have infinite amount of fuel so at some point you you can't really keep your spacecraft at the position where it is so then you have to end the mission of course for geostationary satellites this might take something like 15 years for low-earth orbit satellites a few years are pretty common but very often you can actually extend the lifetime quite considerably if you are very careful about your fuel consumption for example now what are you going to do once you reach this end of the mission well this depends again on the orbit so for example if you have a low Earth orbit satellite then you reserve some fuel you might reserve some fuel in order to actually take it to a lower lower orbit such that it the orbits and disintegrates and the atmosphere within something like 25 years these 25 years there now the nowaday is pretty much mandated by for example the FCC and also the ISA so you really need to kind of dispose of your spacecraft at most 25 years after the end of your mission so you can the orbit Leo satellites but usually there's not enough fuel to deorbit a geostationary orbit satellite in that case you will actually erase the altitude by something like 500 kilometers and put them on the so-called graveyard orbit because that's a place where they are not disturbing anybody anymore so you can put them there and we'll kind of forget about them okay well and then you can look back at at your mission you have spent quite a few years and that you know and well hopefully it was
everything was working correctly you produce a lot of scientific data you're happy and with this I also want to end my talk so thank you very much and enjoy the rest of the Congress
[Applause] [Music]
thank you there's about 10 to 15 minutes left for Q&A this works pretty simple
you walk to a microphone you wave your hand and you may end up with opportunity
ask question which gets me to the asking questions bit Q&A is for questions not about statements or how nice SP girls etc so keep it short and the first question goes to the Internet to the signal angel who has been diligently monitoring IRC and Twitter on the hashtags Hulsey so signal angel do we have a question yes yes hello yes yes
yes no Mike hello hello a little hello to little check-check you need to know to use the microphone get the microphone okay the crest refers to this microphone over here okay hi hello is this on nope microphone to please it's not on is it is it on now okay great test test would it be feasible to put like four satellites in geostationary orbits as communication relays so we
have uplink all the time and why is it yeah so this is feasible and this is actually being done so for example the the ISS as far as I know actually does most of its communication why are some relays relay satellites in geostationary orbit by NASA but they're also for some
European alternatives okay so there's a European data relay system for example you can also use for this this is being used however it's always I mean money is always an important issue okay so if you're using somebody else's communication relays system then you of course have to pay for that so you some very often actually try to well find a minimal solution to two to your communication needs thank you okay next question goes to microphone number two yes this is a question from the internet which would like to know about the security of the protocols and protects your encryption or anything like that okay so I mean I can't really give too many details about this because it's not my particular area of expertise but in principle the the till commanding and or the or at least the telemetry is usually encrypted so there's a lot of effort put into that however for the payload data this is not always encrypted for example very famously known are the be the weather satellites yeah you can just receive the data and it's transmitted and clear and you can just receive them okay thank you okay an expression is microphone number one [Music]
yeah okay so the decision-making process is kind of involved I haven't been part of any mission yet that failed so I kind of don't really know the details on that but in principle there's not just the flight director so firstly I mentioned the flight director but that's actually the person in charge during the actual operations but there's also for example the the project investigators or the the PI who is doing the the scientific was having the who's in charge of the scientific process there are other kinds of organizational people and they decide this together in some way okay so this is a non-trivial decision and regarding the other question the so I mean they could still afford TVs at one they could still control the satellite yeah so they we're actually I go as far as I know they to to lower the orbit to actually have it burn up at some point I think they even try to turn it on at some time later and I think it still worked but nowadays I think it is already burned up so at least this mentioned somebody and not quite sure but yeah it was still usable well in that sense you could still lower the orbit the orbit so that's not a problem for this satellite okay next question for microphone number two you mentioned you had a temperature time serious on your on your charts I was wondering what methods do you use to find animals this temperature time series but what's the question message sweetie use to find anomalies anomalies in that well so I mean there there are there are quite a few properties of the spacecraft that might actually deteriorate over time and there there might be various indications for that and you try to look for hints that something is wrong something that you're not noticing because nothing is failing yet but you actually want to see that for example some sliding average is actually increasing over time yeah it's it's still below some some kind of alarm limit but it's it's actually getting worse okay so you you try to do time series and analysis for that yeah there are very various similar issues that you want to identify this particular example
or well I'm not sure this this particular example shows anything particular so this seemed to work properly I guess and also questions or not so next question is marks of nom microphone number one okay well it's kind of like an API I mean that you define that actually gets provided by the the satellite manufacturer so you really send a binary command so might be these these protocols are actually very effective yes so they did do just one thing they make sure that this is actually transmitted correctly and then it gets executed so this might be just switch one of the the machines okay so there's just some binary thing that you need to transmit to the satellite there's of course some level of checking going on so for example there might be a command counter that needs to be correct or some kind of checksum but apart from that this will be executed directly however sometimes you also need to upload some kind of binary data for example imagine that for some reason one of the the things on your satellite moves a little bit then the orientation is not correct anymore and you need to somehow fix this in your internal calculations for that you need to actually upload some rotation matrix for example describing this the small distortion okay so in that case you would actually upload some some binary data that gets put at the correct place and on the on-board computer okay next question is for microphone number four about the orbits is there much garbage on this orbit is
there a what sorry and is there much garbage so so so you're talking about a space debris so stuff that's flying around and that might actually hit our satellite yes there is quite a bit so satellites actually have to do maneuvers to just well to be on the safe side to not crash into some to not collide with some space
debris it's getting more and more in particular there was a distraction of a satellite a few years ago by the Chinese so they try to upload their own satellite and for example this created a lot of additional debris this is however the debris is actually flying on the same orbit or approximately the same orbit as it was beforehand okay so instead of large target you now have many smaller ones they are being tracked by various base agencies and you can actually get there this data online somewhere and I think they will even write you an email if if your satellite happens to be on a collision course with something so I'm not too knowledgeable about this but in principle they are people trying to do this so these are actually has various projects and has has done a few conferences on the question how to deal with space debris but I'm not sure there's any really good and feasible solution yet but maybe in a few years hopefully thank you okay next question
is from microphone number five but about
grave a second Kepler's just a little further out so I'm not sure I got last question but so at the graveyard your orbits they're actually for geostationary orbits yeah because because you can't the orbit a satellite from there so instead you kind of move it away from the earth we create the same problem on the geostationary this hmm yeah I mean in principle this means that there is also specially than there and geostationary orbit however I mean the if you fix the orbit then well with increasing orbit the the well there's more space left okay so the density actually kind of reduces with larger radius so you're not having the same problems as with Leo now so because and year there really you you you're accumulating specifically faster than you're actually do orbiting it so and you have to actually go through Leo to get to zero transfer orbits but yeah it's not it's not such an urgent issue there and likely will never be but who knows also and maybe also some comment nowadays there's kind of a shift from geostationary orbits to actually go and going more Leo yeah also for
communication satellites so this might actually may be in long term even reduce
the number of geostationary satellites
but I don't know okay next question goes to the internet so IRC hello yes I would like to know if you're concerned with this SpaceX launching 5,000 satellites and to lower running at 25,000 kph point
can you repeat that SpaceX is talking about launching thousands of satellites
yeah how is that gonna work with communications with those buzzing around so I don't know the details about this project but so as far as I know they talk about something like 4,000 communication satellites in lower Earth orbit and as far as I remember they're supposed to communicate by lasers okay so they will actually spend sort of the laser communication network and then you just try to route your the information that you have through this network okay of course this is a lot of satellites I don't know at which altitude they will operate whether this will cause problems for anybody but as far as I know the FCC and the US has already said that it's okay to proceed with this project so yeah let's see where this will lead it's hard to save at the moment I guess next question is for microphone number three and this may be the last question I would like to know in regard to redundancy with antennas are the satellites built in a way that an antenna for one frequency can take over duties for that were actually intended for another frequency especially in two scenarios if antenna receiving instructions is compromised and cannot deploy or for example if the telemetry antenna is somehow incapacitated right so and on the ground for example as an antenna might actually be able to serve another frequency okay so this is pretty common for example and in white I'm one of the pictures you've seen a large antenna that can actually serve multiple frequencies on a satellite I don't think this is actually done as far as I know however of course you could try to route the same kind of information through another antenna but it depends a little bit on the bus I guess so for example of the satellite bus so on certain some satellites the the additional antennas are actually well kind of separate from the the satellite bus and in that case it's not feasible to actually route the the telemetry through that but I guess in various cases this is indeed possible but I'm not sure I've ever heard that this is actually being used okay thank
you very much that was the last question and there was the end of this talk and a round of applause for our speaker [Applause] [Music]
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