Space Ops 101
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00:00
Manufacturing execution systemSemiconductor memoryControl flowSpacetimeMusical ensembleSpacetimeOperator (mathematics)Game controllerMereologyPlanningDiagramLecture/ConferenceMeeting/InterviewComputer animation
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SpacetimeComputer clusterCombinational logicGradient descentVideo gameOperator (mathematics)MereologySpacetimeMeeting/InterviewLecture/ConferenceComputer animation
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SpacetimePlanningAerodynamicsPower (physics)WärmestrahlungWorkstation <Musikinstrument>SatelliteHeat transferComputer wormSpacetimeOrder (biology)Dynamical systemComputer animationPanel paintingLecture/Conference
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Dynamical systemTelecommunicationPower (physics)MereologyPhysical systemScheduling (computing)WärmestrahlungPlanningEuler anglesMultiplication signSpacetimeGame controllerVideo gameCycle (graph theory)Lecture/Conference
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Operations researchPhase transitionSoftware testingOrbitAerodynamicsWorkstation <Musikinstrument>PlanningComputer fontDynamical systemData analysisPhase transitionOperator (mathematics)SatellitePlanningComputer animationLecture/ConferenceMeeting/Interview
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Flow separationOrbitSpacetimeHeat transferInternet service providerOrder (biology)Phase transitionGroup actionMoment (mathematics)Heat transferInternet service providerSpacetimeRight angleSmoothing
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Control flowSpacetimeFlow separationFormal verificationTask (computing)Order (biology)Decision theoryBitConnected spaceOperator (mathematics)Sign (mathematics)Touchscreen2 (number)SpacetimeRight anglePosition operatorGame controllerMechanism design1 (number)AverageFlow separationComputer animation
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SpacetimeFrequencyHeat transferEccentricity (mathematics)ApproximationOrder (biology)FrequencyType theoryArithmetic meanBitSatelliteHeat transferEllipseRevision controlDistanceState observerNewton's law of universal gravitationPoint (geometry)CircleDirection (geometry)Internet service providerMultiplication signRotation2 (number)SpacetimePosition operatorCASE <Informatik>
10:56
OrbitCoefficient of determinationAerodynamicsTask (computing)CalculationWorkstation <Musikinstrument>Dynamical systemTask (computing)Physical systemCalculationConcentricMathematicsNatural numberOrder (biology)Programming languageDeterminantNumeral (linguistics)SatelliteCore dumpPropagatorPoint (geometry)Direction (geometry)NP-hardMultiplication signPosition operatorArithmetic mean2 (number)Computer animation
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AerodynamicsTask (computing)Numerical analysisCalculationOrbitCoefficient of determinationWorkstation <Musikinstrument>Control flowFlow separationSpacetimeLibrary (computing)Dynamical systemConnected spaceSatellitePosition operatorSoftwareDescriptive statisticsProfil (magazine)Flow separationState of matterArithmetic meanMoment (mathematics)QuicksortDistanceTranslation (relic)HorizonDirection (geometry)Multiplication signComputer wormRight angleComputer animation
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FrequencyFrequencyArithmetic meanBitSatelliteNumberScaling (geometry)Range (statistics)CASE <Informatik>CirclePole (complex analysis)2 (number)
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FrequencyRange (statistics)Level (video gaming)Graph (mathematics)Order (biology)TelecommunicationFrequencyLevel (video gaming)Line (geometry)MereologyProjective planeSlide ruleSatelliteSpektrum <Mathematik>QuicksortRange (statistics)Water vaporMagnetic stripe cardDistortion (mathematics)CircleBit rateTrailRotationMessage passingMappingPosition operatorComputer animation
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TelecommunicationSatelliteMusical ensembleFrequencyRange (statistics)Computer wormSpacetimeOrder (biology)FrequencyLevel (video gaming)FehlererkennungMaxima and minimaSatelliteLocal ringRange (statistics)Water vaporMusical ensembleCommunications protocolCartesian coordinate systemLatent heatBit rateStandard deviationCharge carrierComputer wormSpacetimeRight angleError messageComputer animation
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Control flowTask (computing)Heat transferOrbitMereologySatelliteRight angleDatabaseOrder (biology)FrequencyTask (computing)Flow separationPower (physics)Connectivity (graph theory)Musical ensembleDirection (geometry)Different (Kate Ryan album)Multiplication signRotationComputer wormPosition operatorQuicksortCASE <Informatik>Computer animation
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Group actionSatelliteArray data structureFunction (mathematics)SatelliteInformationFunction (mathematics)FrequencyBus (computing)Software testingFlow separationBitPower (physics)AngleCASE <Informatik>RoutingMusical ensembleAdditionSource codeDatabase normalizationDegree (graph theory)Right angleComputer animation
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Data recoveryRotationFrequencyResonanceOrder (biology)Function (mathematics)ResonanceBitForcing (mathematics)Power (physics)Data recoverySatelliteQuicksortCASE <Informatik>Polar coordinate systemAcoustic shadowBlack boxPrincipal idealPulse (signal processing)Computer animation
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Task (computing)SpacetimeComputer wormFormal verificationTelecommunicationType theoryCategory of beingPhase transitionSoftware testingState of matterSatelliteConnectivity (graph theory)State observerArray data structureMultiplication signComputer wormPattern languageComputer animation
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Phase transitionMedical imagingBitSatelliteState observerDatabase normalizationTransmissionskoeffizientDigital photographyPhase transitionInformationTelecommunicationQuicksortOperator (mathematics)File formatMetreClosed setMappingService (economics)Lecture/Conference
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Phase transitionTask (computing)Operations researchSpacetimeComputer wormOrder (biology)Phase transitionResultantVideo gameGravitationSoftwareFault-tolerant systemContingency tablePower (physics)SatelliteOperator (mathematics)DistanceChannel capacityMultiplication signBounded variationComputer wormDecimalLecture/ConferenceComputer animation
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SpacetimeParameter (computer programming)Time seriesPlotterData analysisCategory of beingState of matterBinary codeMereologyPhysical systemNumberParameter (computer programming)Error messagePredictabilityMultiplication signVideo gameInformationTask (computing)MeasurementComputer animation
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Parameter (computer programming)MetreSpacetimeDatabaseMassCore dumpDatabaseState of matterInformationSoftwareNumberQuicksortView (database)TimestampMultiplication sign9K33 OsaComputer animation
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SpacetimeLatent heatOperations researchState of matterMereologyTask (computing)Procedural programmingArithmetic meanSatelliteQuicksortOperator (mathematics)Condition numberMultiplication signStack (abstract data type)Structural loadCurvatureComputer animation
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SpacetimeAsynchronous Transfer ModeDynamical systemSequenceSubject indexingState of matterProcedural programmingBitOperator (mathematics)CASE <Informatik>Asynchronous Transfer ModePoint (geometry)Set (mathematics)Direction (geometry)Multiplication signComputer worm2 (number)Right anglePosition operatorComputer animation
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PlanningSimultaneous localization and mappingSpacetimeRevision controlDynamical systemOrder (biology)FeedbackContingency tablePhysical systemSatelliteScheduling (computing)Revision controlPlanningOperator (mathematics)Point (geometry)Multiplication signFreewareTelecommunicationQuicksortComputer animation
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PlanningInformationSoftwareLine (geometry)Physical systemResultantSatelliteRevision controlPlanningOperator (mathematics)Point (geometry)Special unitary groupCondition numberMultiplication sign
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OrbitCharacteristic polynomialSatelliteGeometryOrder (biology)InfinitySatelliteCASE <Informatik>Point (geometry)View (database)Multiplication signPosition operatorFinitismusComputer animation
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Musical ensembleWaveInternetworkingStatement (computer science)TwitterLecture/ConferenceComputer animationMeeting/Interview
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Software testingSatelliteTelecommunicationMultiplication signLecture/ConferenceComputer animation
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TelecommunicationPhysical systemNumberAreaInternetworkingExterior algebraCommunications protocolEncryptionComputer wormInformation securityMusical ensembleExpressionLecture/ConferenceMeeting/Interview
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Maxima and minimaMathematical analysisTime seriesTopological vector spaceCategory of beingAverageDecision theoryLimit (category theory)MereologyProjective planeSatelliteNumberOperator (mathematics)Process (computing)Software bugPoint (geometry)Multiplication signMessage passingPrice indexLecture/ConferenceComputer animation
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SoftwareMatrix (mathematics)Level (video gaming)Binary codeBitOrientation (vector space)SatelliteVirtual machineNumberServer (computing)CASE <Informatik>Compilation albumDistortion (mathematics)Communications protocolNeuroinformatikRotationMeeting/Interview
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BitSatelliteSpacetimeMereologyProjective planeNumberEmailAdditionCollision1 (number)Computer animationLecture/ConferenceMeeting/Interview
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NumberShift operatorSatellitePopulation densityRadiusMiniDiscKepler conjecture2 (number)SpacetimeHeat transferHidden Markov modelLecture/ConferenceMeeting/Interview
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Term (mathematics)SatelliteNumberInternetworkingPoint (geometry)InformationSoftwareTelecommunicationFrequencyBus (computing)Flow separationCausalityBitLaserMoment (mathematics)Projective planeQuicksortCASE <Informatik>RoutingLecture/ConferenceComputer animation
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Semiconductor memoryCartesian closed categorySicRoundness (object)Computer animation
Transcript: English(auto-generated)
00:18
It's an honor to introduce you Sven Prufer, who is a professional in the space business
00:23
and he's going to give you an introduction to spacecraft control under the title of Space Ops 101. Thank you very much for the kind introduction, hello and welcome to Space Ops 101.
00:46
My name is Sven Prufer, I'm a mission planning engineer at the German Space Operations Center, which is a part of the Deutsches Centrum für Luften Romfahrt 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
01:03
and secondly because we will look at the whole thing kind of through the lens of mission planning engineering. Unfortunately, the topic is pretty large, so we won't be able to talk about everything. In particular, we will not talk about launches.
01:22
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 and particular topic. Also we will not talk much about human space flight and neither about entry descent landing, so for example landing on another planet.
01:41
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.
02:02
So in general you distinguish three parts. There's one, the space segment, so this is everything that actually flies up into space, so in particular a satellite or a spacecraft, including its payload, so whatever it is doing up there. Then there's the transfer segment, which is, well, all the launching business.
02:22
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.
02:44
So one of them is 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 where it is going.
03:02
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
03:22
where it should look at and actually figuring out how it is oriented. Next we need to actually talk to the spacecraft. This includes receiving and interpreting the data, so this is part of the TMTC subsystem or the data system.
03:41
And last but not least, that'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 life cycle of a spacecraft. We will start with the launch and early operations phase, which is called LEOP for
04:02
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 test and validate our spacecraft very quickly, and then we will switch to the routine phase, so when we do the actual operations of whatever the spacecraft was designed to do.
04:25
This includes data analysis, telemetry, and telecommands, so TMTC, and also mission planning. And then in the end we will talk about the end of the mission, so whatever we are going to do at the end when we want to dispose of the satellite.
04:41
Alright, 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
05:01
everything is running smoothly. Once the spacecraft is strapped onto the rocket it will get, well, flown into space and there it will be separated from the launch vehicle. From this moment on then it's flying by itself and we need to actually control it.
05:22
However, we don't really know right now where the launch provider will put our spacecraft. It might actually be on its final orbit. 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.
05:43
During this launch there's actually a second control center. That's the one for the spacecraft. This is actually the control room K1 of the German space operation center. And it kind of looks like you expect the control room to look.
06:02
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 in the center there is one position that's called the flight director.
06:25
The flight director is the person who is in charge of the operation. So whenever there's something that needs to be confirmed, needs to be done, that needs to be decided, then he is the last operational person to actually confirm the decision.
06:40
Now in principle, right after the spacecraft is separated from the rocket, this control room actually takes over. However, there are a few subtleties here. In particular, right after separation, the spacecraft is somewhere. We kind of know approximately where it is because we planned this beforehand,
07:01
but we don't know the 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,
07:21
it flies at an altitude of about 300 to 400 kilometers where the gravitational force of the Earth is still about 90% 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.
07:41
7.9 kilometers per second is the speed that you actually need in order to not fall down on the ground. So if you are a bit higher in some orbit, then you need a bit less speed actually because you are farther away from the Earth. Okay, so we need to go very fast.
08:00
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, the following picture will actually be to scale approximately. So one possible place where you can put your spacecraft is low Earth orbit.
08:21
So that's the region below about 2,000 kilometers altitude above ground. However, 2,000 is already pretty high, so very common are altitudes of 600 kilometers, 500, 700. This is a place where you mostly do scientific experiments, in particular, Earth observation. So there are many, many scientific satellites
08:43
that actually try to take pictures at various frequencies of the Earth. And also, this is a place where you do reconnaissance. Okay, then there are actually a bit higher altitudes. For example, there's a medium Earth orbit. So the drawn circle is actually at an altitude of 20,000 kilometers,
09:03
and this is mainly used for navigational satellites. So think GPS 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 35,786 kilometers above ground.
09:25
This is chosen in such a way that the orbital period, so the time it takes you to fly once around the Earth, is 24 hours. This has the advantage that the movement of the satellite is synchronized with the rotation of the Earth,
09:42
meaning that your satellite is kind of always at the same position 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,
10:01
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, on geostationary orbit,
10:21
it's possible that the launch provider will actually put us in some kind of transfer orbit. They usually don't look like circles, but rather like ellipses. And in such a case, we would need to do additional maneuvers. So we are on the red circle, we will fly outwards, but at some point we will touch the geostationary orbit,
10:41
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 system that actually deals with
11:02
these considerations, calculations, the SITRA, that's the flight dynamics department. So their tasks are in particular orbit determination. There are 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,
11:23
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 the orbit, you also want to know where the satellite is going to be located in the future. So you will do orbit propagation.
11:41
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, we have to turn on our thrusters for how long. This is also done by flight dynamics. And the fourth point is,
12:01
well, we have to talk to the satellite, so we actually need to see it in order to do this. And flight dynamics can actually calculate the times and the positions or the directions, rather, where the satellite's going to be. And you can see all of these tasks are pretty numerical in nature, yeah?
12:21
It's really, it's hardcore mathematics numerics, 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.
12:40
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. Okay. Now, let's go back to the control room. We have talked to our flight dynamics department,
13:02
they've told us, well, the satellite's going to be at a certain position at a certain time, or at least that's where we expect it. So the next thing we need to do is we need to establish a connection to the satellite. And for this, we need a ground station. The picture you see here is actually a ground station
13:22
in Weilheim, that's in Bavaria. That's sort of the main ground station that we use. And, well, it knows where to expect the satellite, so at a certain direction it should appear at a certain time above the horizon and then it tries to establish a contact. This first acquisition
13:41
it 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, it needs to downlink some data. So, download, but it's called downlink. This includes telemetry, so descriptions of
14:01
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 was that the satellite was supposed to
14:21
measure or to take. And then it will also uplink some stuff. So, for example, commands, because we want to tell the satellite to do something. But this might also include, for example, software updates. Right. And one other thing that the ground station can do is
14:40
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 signal or to that packet and then the answer will fly, well, will go back to the ground station.
15:02
And if you measure the time and if you know how long the satellite takes to actually react to such a packet, you can calculate the distance from the ground station. If you do this several times, then you get kind of like a radial distance profile. And from this, you can really deduce the orbit of the satellite.
15:23
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
15:41
is 600 kilometers above the ground. This is actually to scale. Now, the signals of the ground station, they actually have to pass through the atmosphere, meaning they are attenuated quite a bit. So, you have a finite range of the ground station signal. And this is drawn here.
16:01
So, the red circle is an approximate range of the ground station. And this intersects the orbit of the satellite only at a certain time interval. Or a certain interval 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
16:21
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. So, this means we would expect to see the satellite every 90 minutes for 10 minutes. And this is when we have to do all the
16:41
downlink and uplink. Unfortunately, it's a bit more complicated because Earth actually rotates. This map of Earth actually shows the ground track of the satellite. So, that's the projection of the satellite onto the ground. So, that's the red line. And the problem is that after 90 minutes
17:01
the satellite returns to the position where it was before. However, Earth has actually rotated by some amount, like 90 minutes divided over 24 hours. This is why the ground tracks actually don't close up. So, instead you get these kinds of stripes.
17:20
Over Europe, you see WHM, that's the Walheim station. It has a certain range. That's the circle-like black line. And you can see that usually you have two contacts with the satellite per rotation.
17:42
The third pass will already be outside of the range of the ground station. So, we 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 there are
18:00
actually circles, so all the distortions that you've seen on the earlier slide was due to the projection that was used for the map. This is sort of what it actually looks like if you look from above the Earth. The other one is the typical maps that you see. We have found our
18:21
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. First of all, we noticed that there is, for example, water vapor in the atmosphere, which absorbs parts of the electromagnetic spectrum.
18:41
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 frequency usage to actually lower
19:01
frequencies in order to get a higher range, but then we also have maybe less data rate. In spacecrafts, you usually use actually the lower part of the graph that's shown here, usually even below what is shown at all. This starts at 10 gigahertz, and
19:21
you use even less frequencies or lower frequencies. For example, you might use UHF, so amateur radio at 430 megahertz. You might use L-band, 1 to 2 gigahertz. In particular, the main carrier frequency of GPS
19:41
satellites is in this range. Then there is S-band, so that's a very typical frequency range from 2 to 4 gigahertz, which is used for the actual commanding of the satellite. This is an important frequency for us, or band for us. Then there is also the X-band. X-band is
20:01
higher frequency, so we expect even higher data rates. This is usually then used for payloads. If you have a lot of data that you want to downlink, for example a picture that you just took from your satellite. Also, this is being used for deep space missions. Then there is Ku-band. Ku-band is used for TV satellites.
20:23
And Ka-band. This is now slightly above the local water vapor absorption maximum. This is pretty cool. There you really have high data rates. It's been used for various applications whenever you need a high data rate. However, there are
20:40
some mechanical difficulties because you have directional antennas, 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
21:00
level of error correction, etc. So I will not talk about this but in principle there are very specific standards for space that are being used in order to assure that signals that you send or that you receive actually get received. Okay. Right. So we can now
21:20
talk 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 there are a few things that are left to do, actually.
21:41
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 new power. So for this you need to deploy solar panels. This is done during the LEOP. Also you might need to deploy antennas.
22:00
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 X-band. For this you need an additional antenna so this needs to be deployed. Also this is the time when you do all the other
22:20
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. Star trackers are essentially cameras that just take pictures of the sky of the stars and they compare them to some onboard database of
22:41
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 the spacecraft you can then choose 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
23:01
need something like a star tracker. Another thing that you would kind of switch on or actually spin up during a LEOB 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 this stabilizes
23:20
the spacecraft because you actually want to control the rotations in most cases. Okay. So now we hope that everything was working perfectly we launched the spacecraft but unfortunately not always everything goes perfectly.
23:41
So let's maybe dig into some example. This is TV Set 1 well I don't have a picture but it was a TV satellite from 1987 and everything worked as we described. So we got the first acquisition we got some telemetry from the spacecraft but unfortunately the solar arrays turned out to be
24:00
only partially deployed. That's of course a problem and we need to diagnose this and we need to fix it if possible. So the first thing you have to know is that you kind of can't really necessarily trust all the data that you get. You have to confirm that whatever you're seeing is actually the case
24:22
so you have to use 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
24:42
deployment command again. It's possible that the automatic solar panel deployment didn't work so we just tried again. Unfortunately this did not work. So it still seemed undeployed. Now you start thinking
25:00
well what are we going to do? And you consult usually the satellite manufacturer. The satellite manufacturer actually also sits in the control room during the LEOP because there happen to be many questions so you need somebody on hand. And they suggested or the people who operated the satellite they suggested various tests to figure out
25:22
what was wrong with TVSAT 1. 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 sunlight and then you start rotating it. If you do this carefully
25:40
and you measure the power output of the solar arrays you can actually estimate the angle that the solar array was deployed. So they did that and they figured out well they're completely not deployed. So less than two degrees actually. Okay so
26:00
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 actual stirrups so the black boxes in the picture which keep the solar array attached to the satellite during the launch that they
26:20
might still be there. In principle they should have been kind of fired off or removed and then the solar array should 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 stirrups will
26:41
cause a small shadow over the solar array. This will reduce the power output again just a tiny little bit so you might be able to measure this and this way you confirm that the stirrups are still there. Turns out this was not actually really well measurable
27:00
so this didn't work. However they were still able to reduce it was probably the stirrups that are still there. Once you have diagnosed 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
27:20
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 loosen the stirrups. Another thing you can try to do you can use your main engine to actually
27:40
accelerate the spacecraft in the pulsed way in order to excite resonance frequencies of the stirrups. Okay so hopefully this will this might actually loosen the stirrups. Another thing you can try to do is you can command the spacecraft to heat up and to cool down in some ways and this way
28:00
actually also loosen the stirrups. And the last thing you can try is 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
28:20
that the force actually pushes the solar array open. Yeah unfortunately none of those worked and this was an unsuccessful recovery of a satellite. So in particular the main problem was that well this was a TV satellite so it really needs the antenna but the antenna
28:40
couldn't deploy because of the stuck solar array. So in this case this did not work but usually of course this works and people are coming up with very creative and very interesting solutions to all kinds of problems and get things running. Alright so
29:00
once we have our spacecraft in some kind of safe state we kind of conclude the LEOB and we start testing the actual properties of the spacecraft. This is called the commissioning phase or in-orbit testing of the payload. So this usually takes longer than a LEOB might take several months depends on
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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. So in the picture you see a geostationary communication satellite so its main payload
29:40
are the communication arrays or the antennas in particular so for example you might want to actually verify that the antennas are working properly after the launch so during launch they all get shaped up and its 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
30:02
point the satellite at your ground station, you measure the strength of the signal that you receive then you move it slightly you measure again the strength and this way you kind of get a pattern of the antenna and this is a property of this particular
30:21
antenna that you might use later another thing that you do during this time is you check out redundant components of the satellite so for example if you have an earth observation mission 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
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you obviously have a large problem because now suddenly you don't know where you are taking photos or images so usually there's quite a bit of redundancy on satellites so there are two GPS transmitters and then you can actually
31:00
switch between them and during this phase you will test that they are working properly ok so let's suppose we have done this and everything is working as expected then we start with the routine phase the routine phase is sort of the main phase of the operation so that's when you actually do the science experiments
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or you start offering communication services or whatever it is you're doing this picture is a picture of the mission Terraza tandem X so those are two radar satellites flying in low earth orbit and they can actually make
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three dimensional maps of the ground by sending a radar signal and then receiving it and because they're flying in close formations or something like a few hundred meters apart from each other they actually get this kind of stereographical 3D information ok and during the routine phase a scientist
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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 or the command center would command this data take it gets down linked and then the result will actually give them to the scientist
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ok so this is the main phase of spacecraft life so where we do the payload operations by the way this picture is a picture of a joint American-German mission that's the GRACE follow on mission two satellites that have a microwave or a laser link between them
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and they measure the distances in order to well variations of the distances in order to deduce the gravitational field of the earth last year at 34C3 there was actually a talk about the predecessor mission here actually probably in this room ok so this is
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this is the time when we do our science experience furthermore we actually monitor the spacecraft of course because we 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
33:21
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 so its total capacity actually
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gets smaller over time so you need to adapt to that for example if there is less power available then you can actually do fewer data takes something like that and you need to monitor this and react accordingly ok so how does the monitoring work well that's part of
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the TCTM and the data subsystem or system and the idea is that the spacecraft actually measures various properties that describe the state all the time so we have a time series of binary data and also numerical values
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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 live we only get this once we actually downlink it and then we get a huge part of the data at once ok
34:40
so this describes the state of the spacecraft and there can be lots of parameters so for example 20,000 telemetry parameters for one spacecraft is 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
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do a lot of data analysis time series analysis with that you can do anomaly detection telemetry prediction detecting errors or problems within this data also what you need to do is
35:20
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 spacecraft so this is an example for a telemetry view so this is one software that we use
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it's called GECOS you can see here a number of telemetry packets so for example there are a few confirmations that some checksum was correct that some ping was actually received and was being worked on so it was executed it's time stamped and you get some additional information and this is sort of the most
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basic thing 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 via telecommands and on the picture here you can see some commands that have
36:20
been executed and also some that are still to be executed so for example 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 a few telecommands
36:41
on the manual command stack prepare them and then execute them very quickly this is the lower part notice that these telecommands 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 somehow
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understand all the possible things you can do in particular you very often don't really want to do very atomic things but instead you want to achieve a certain task for this you bundle the telecommands you can add for example telemetry checks so conditions
37:20
on the telemetry and you call this a flight operations procedure so this will be sort of a bundled thing that will execute it on the spacecraft for the purpose of achieving a specific goal another thing that's important as I've mentioned various times you don't see the
37:40
spacecraft all the time meaning you cannot really command it all the time but instead what you do is you send telecommands but you make them time tagged and then they get executed for example when you don't see the spacecraft and these kinds of telecommands are called TTC let's look at an example so this might be
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a set of time tagged telecommands for a maneuver so at time T0 we want to execute some maneuver so we want to turn on the thrusters of course this time and the position and the duration of the burn they were calculated by the flight dynamics departments of course but one hour before that we actually need to
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check for example that the spacecraft is in some fixed state some prepared safe state eight 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
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automatically command the switch on some additional telemetry so this is kind of like you turn on the debug mode you just tell the spacecraft to actually tell you to give you more data then because the burn will actually make the spacecraft shake quite a bit
39:00
there will be lots of alarms going off so at some point before the burn you will turn off these alarms to safeguards just because the direction of the spacecraft is 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
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additional safeguard stop command just to make sure that in case the other one didn't get executed you stop nevertheless and then you kind of reverse the whole procedure to return to a mode where you can proceed with your payload operations and this would be a sequence of time tech commands that are
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uploaded to the spacecraft during an uplink and then executed whenever T0 was actually taking place alright so there's one other thing that I want to describe and this is mission planning so it's probably
40:01
one of the lesser known subsystems and this is sort of at the point where you have to wait between 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
40:21
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 has been taken care of by the 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
40:40
the telecommand operators to actually execute 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
41:01
being needed for example due to those contingencies so what the mission planning system internally does is it schedules activities and it tries to do this in some consistent and conflict free manner so imagine for example for a data take
41:21
you need to actually take the picture before you want to downlink it so those are two activities and they should actually take place in some order from these kind of activities that were requested by some scientists the system
41:41
creates a timeline which is then provided to everybody who needs to know what the spacecraft is going to do at some point so here is one example one software that we use so it's called Pinta and it shows on the x axis the time
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and up on the top you see these black white things and these are actually eclipses so whenever the spacecraft is not in the sun or is in the sun you can see this there and below that there are a few experiments planned but one of them is partially planned during an eclipse
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but it has the condition that it must not take place during an eclipse so this gives a conflict and the mission planning system is responsible for identifying these kind of conflicts and actually supplying that information to the scientist or the operator to be resolved one other thing you can see
42:41
is this thing that we talked about at the beginning so you need to downlink the information from the experiment so you need some scheduled downlinks downlink opportunities and you can see two of them actually as the green lines above the blue ground so this is the next time when the satellite actually sees the ground station
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and it can downlink the results of the prior experiments ok 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
43:21
so there is also the end of the mission that you have to consider so in general the mission time of a spacecraft might depend for example on the mission goal imagine 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
43:40
so if you have a spacecraft in an altitude of 300 to 400 kilometers it will actually descend into the atmosphere within less than a year if you have a satellite at an altitude above say 700 kilometers it will take more than 25 years to actually get down if you are in a geostationary
44:00
orbit you will actually never come down so another thing is and this is mainly for geostationary orbit geostationary satellites is that you have a finite amount of fuel so at some point you can't really keep your spacecraft at the position where it is
44:21
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
44:42
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 in order to actually take it to a lower orbit such that it
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de-orbits and disintegrates in the atmosphere within something like 25 years these 25 years they are nowadays pretty much mandated by for example the FCC and also the ESA so you really need to kind of dispose of your spacecraft at most 25 years after the end of your mission
45:22
so you can de-orbit leo satellites but usually there is not enough fuel to de-orbit a geostationary satellite in that case you will actually raise the altitude by something like 500 km and put them on the so called graveyard orbit because that's a place where they are not disturbing
45:41
anybody anymore so you can put them there and well kind of forget about them ok well and then you can look back at your mission you have spent quite a few years on that and well hopefully everything was working correctly you produce a lot of scientific
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data you are happy and with this I also want to end my talk so thank you very much and enjoy the rest of the conference
46:22
there is about 10 to 50 minutes left for Q&A this works pretty simple you walk to a microphone you wave your hand and you may end up with the opportunity to ask a question this gets me to the asking questions bit Q&A is for questions not about statements or how nice to speak etc.
46:40
keep it short the first question goes to the internet to the signal angel who has been diligently monitoring IRC and twitter on the hashtag whole c so signal angel do we have a question? yes yes hello yes yes yes no mic hello
47:00
hello hello hello need mic on the signal angel hello check check you need to use the microphone get the microphone I will get the question first with this microphone over here hi hello is this on? nope microphone 2 please it's not on is it on now?
47:23
ok great test test would it be feasible to put like 4 satellites in geostationary orbits as communication relays so we have uplink all the time and why is it not done? yeah so this is feasible
47:41
and this is actually being done so for example the ISS as far as I know actually does most of its communication via some relays relay satellite in geostationary orbit by NASA but there are also for example European alternatives ok so there is a European data relay system for example that you can also use for this
48:00
this is being used however it's always I mean money is always an important issue ok so if you're using somebody else's communication relay system then you of course have to pay for that so you very often actually try to well find a minimal solution to
48:20
to your communication needs thank you ok next question goes to microphone number 2 yes this is a question from the internet which would like to know about the security of the protocols in particular encryption or anything like that ok so I mean I can't really give too many details about this because it's not my particular
48:42
area of expertise but in principle the telecommanding 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
49:00
encrypted for example very famously known are the weather satellites you can just receive the data and it's transmitted and clear and you can just receive them ok thank you ok next question is from microphone number 1
49:57
ok so the decision making process is kind of involved
50:01
I haven't been part of any mission yet that fails so I kind of don't really know the details of that but in principle there's not just the flight director so for example I mentioned the flight director but that's actually the person in charge during the actual operations but there's also for example the project investigators or the PI who's doing the scientific
50:22
who's 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 ok so this is a non-trivial decision and regarding the other question the so I mean they could still for TVSAT 1
50:41
they could still control the satellite so they were actually able as far as I know to lower the orbit to actually have it burn up at some point I think they even tried 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 mentions somebody
51:01
I'm not quite sure but yeah it was still usable well in that sense you could still lower the orbit so that's not a problem for the satellite ok next question from microphone number 2 you mentioned you had a temperature time series on your
51:21
on your charts I was wondering what methods do you use to find animals in this temperature time series what's the question what methods do you use to find animals in that temperature time series well
51:41
so I mean there are quite a few properties of the spacecraft that might actually deteriorate over time and there might be various indications for that and you try to look for hints that something is wrong
52:01
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 it's still below some kind of alarm limit but it's actually getting worse so you try to do time series analysis for that
52:22
yeah there are various similar issues that you want to identify moving average or ARIMA so this particular example yeah I was wondering well I'm not sure this particular example shows anything particular so this
52:41
seems to work properly I guess so ok questions for now next question is microphone microphone number 1 you spoke about sending comments these comments get sent
53:03
and interpreted by the server or there is some kind of compilation you know and you send a binary or something like that an executable do you ever have a server side server side supply side or you send a
53:21
software ok well it's kind of like an API I mean that you define that actually gets provided by the satellite manufacturer so you really send a binary command so it might be these protocols are actually very effective yeah so they do just one thing they make sure that this is actually transmitted correctly and then
53:41
it gets executed so this might be just switch one of the machines ok 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
54:01
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
54:21
somehow fix this in your internal calculations for that you need to actually upload some rotation matrix for example describing this small distortion ok so in that case you would actually upload some binary data that gets put at the correct place on the on port computer ok next question is for microphone number 4
54:41
um um about the orbits is there much garbage on these orbits and is this a problem is there a what sorry is there much garbage so all satellites or parts
55:00
get lost so you're talking about 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 um maneuvers to just well to be on the safe side to not crash into some to not
55:20
collide with some space debris um it's getting more and more in particular there was a destruction of a satellite a few years ago by the Chinese so they tried to blow up 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
55:41
same orbit as it was before hand ok so instead of large target you now have many smaller ones they are being tracked by various space agencies you can actually get this data online somewhere and I think they will even write you an email if your satellite happens to be on a collision course with something ok now as a second question
56:01
is there any idea how to remove this or so I'm not too knowledgeable about this but in principle there are people trying to do this so the ESA actually has various projects has done a few conferences on the question how to deal with space debris
56:20
but I'm not sure there's any really good and feasible solution yet but maybe in a few years hopefully thank you ok next question is for microphone number 5 yeah I would like to add to her question so she was talking about
56:42
the Kepler syndrome in the LEO right? but you also talked about the graveyard orbit so will we build a second Kepler syndrome just a little further out so I'm not sure I got the last question but so the graveyard
57:01
orbits there actually for geostationary orbits yeah because you can't deorbit a satellite from there so instead you kind of move it away from the earth so my question is will we create the same problem on the geostationary disk
57:20
I mean in principle this means that there is also space debris then there in geostationary orbit however I mean if you fix the orbit well with increasing orbit the well there is more space left ok so the density actually kind of
57:42
reduces with larger radius so you're not having the same problems as with LEO because in LEO there really you're accumulating space debris faster than you're actually deorbiting it and you have to actually go through LEO to get to
58:02
geotransfer orbits but yeah it's not such an urgent issue there and likely will never be but who knows also maybe also some comment nowadays there's kind of a shift from geostationary orbits to actually go more LEO also
58:22
for communication satellites so this might actually maybe in long term even reduce the number of geostationary satellites but I don't know ok next question goes to the internet so IRC hello yes IRC would like to know
58:42
if you're concerned with the SpaceX launching 5,000 satellites into lower orbit running at 25,000 kph pardon can you repeat that? SpaceX is talking about launching thousands of satellites how is that going to work with communications with those buzzing around in lower orbit?
59:03
so I don't know the details about this project but 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 via lasers ok so they will actually spend
59:22
sort of a laser communication network and then you just try to route your the information that you have through this network ok of course this is a lot of satellites I don't know at which altitude they will operate this will cause problems for anybody but as far as I know the FCC
59:41
in the US has already said that it's ok to proceed with this project so yeah let's see where this will lead it's hard to say at the moment next question is for microphone number 3 and this may be the last question
01:00:00
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 that were actually intended for another frequency? Especially in two scenarios if the antenna receiving instructions is compromised and cannot deploy
01:00:31
or, for example, if the telemetry antenna is somehow incapacitated.
01:00:41
On the ground, for example, an antenna might actually be able to serve another frequency. This is pretty common. For example, in Weilheim, in 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.
01:01:01
However, of course you could try to route the same kind of information through another antenna, but it depends a little bit on the satellite bus. On some satellites, the additional antennas are actually kind of separate from the satellite bus.
01:01:22
In that case, it's not feasible to actually route the telemetry through that. I guess in various cases this is indeed possible, but I'm not sure. I've never heard that this is actually being used. Okay, thank you very much. That was the last question, and this was the end of this talk.
01:01:43
A round of applause for our speaker.