Ep. 304: Death of a Spacecraft

In the end, everything dies, even plucky space robots. Today we examine the last days of a series of missions. How do spacecraft tend to die, and what did in such heroes as Kepler, Spirit, and Galileo (the missions… not the people).

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    Astronomy Cast episode 304 for Monday, April 29, 2013 – Death of a Spacecraft
    Fraser: Welcome to Astronomy Cast, our weekly facts based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.
    My name is Fraser Cain, I’m the publisher of Universe Today. With me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville, and the director of Cosmoquest.
    Hi Pamela, how are you doing?
    Pamela: It is morning. We don’t record in the mornings! You’re catching me on my first cup of coffee on this recording.
    Fraser: I think you can absolutely tell I’m the morning person of this team. I’m bouncing off the walls, I had my cup of coffee and I’m going a little crazy.
    Pamela: Do you remember the threat I gave you on the cruise last year?
    Fraser: Don’t wake me up in the morning? Don’t let the kids wake me up?
    Pamela: It was any child that knocked on the door before 9am might be returned dismembered or at least tied up.
    Fraser: Throw them overboard, yes. It was everything I can do because my kids are morning people too. We’re all up at like 6.
    Pamela: We’ll we’re planning on going to Hawaii this year in January so hopefully that will be my native timezone and things will go better.
    Fraser: So should we make another reminder that we’re going to be doing this all-you-can-eat CosmoQuest-a-thon?
    Pamela: Yes. On June 15th and 16th starting at noon eastern which is GMT minus five, we’re going to do at least 24 hours of continuous science, science demonstration, science speakers and panels. Basically an online celebration of science that we’re tying to a fundraiser to help pay for what we do with CosmoQuest. As any of you in the US know we are getting hit hard with governmental sequestration which is the fancy word in the US they use to say austerity measures. We’re also facing severe funding cuts due to restructuring of how education is done in the US and all of this potentially means that all of the things that we do and all of the things that great NASA teams do is going to get defunded… which means we’re out of work and the science stops. We’re going to say “If you think this is important to donate, we think it’s important so we’re going to work our butts off to show you what we’re capable of doing for 24 hours”.
    Fraser: And what’s that date again?
    Pamela: It’s June 15th and 16th and all announcements for this are going up on CosmoQuest and on the CosmoQuest page on Google+
    Fraser: Yeah so definitely check it out on Google+. Alright lets get rolling.
    Fraser: In the end, everything dies, even plucky space robots. Today we examine the last days of a series of missions. How do spacecraft tend to die, and what did in such heroes as Kepler, Spirit, and Galileo (the missions… not the people).
    Pamela: Kepler is not quite dead yet!
    Fraser: Not dead yet! (Laughs) There are so many stories because most of the time if you look back in the missions, they mostly die. If you look back at sending missions to Venus or sending missions to Mars, its just disaster after disaster. I think we have a lot of material here. Spacecraft is a dangerous, complicated, and risky venture and we pay the price in human lives unfortunately as well but definitely in robot lives.
    Pamela: It’s important to remember that mostly dead is not the same thing as totally dead. Mostly dead, you can sometime recover from.
    Fraser: Maybe that’s another show… amazing spacecraft recoveries.
    Pamela: You actually have that one on the list.
    Fraser: Do I have that one? That would be clever me because that would be awesome. That’s going to take a little more research because those stories are a little more obscure. Let’s wind this back and start at the beginning. What goes into planning and launching a spacecraft and how can things go wrong?
    Pamela: It’s more a matter of what things can you count on not to go wrong. Anything can go wrong.
    Fraser: Of course, of course but what kind of things have gone wrong for spacecraft in the past?
    Pamela: Well the initial phase of danger is can you make it all the way to orbit in an orbit that is actually useful. So you have problems ranging from failure to make it off the launch pad but that’s pretty rare now-a-days; we’ve gotten pretty good at getting off the ground.
    Fraser: Have you seen those classic videos where the rocket just kind of goes up for 20 feet and then collapses down on itself?
    Pamela: (Laughs) Yes
    Fraser: …and BOOM it detonates on the launch pad. I wouldn’t want to be on the top of that spacecraft.
    Pamela: We’ve moved past that form of failure for the most part. The next form of failure is when you had the initial stage of the rocket successfully fire but then other stages of the rocket said “no, not going to work” and either fired wrong or failed to fire and so the spacecraft didn’t make it to the intended orbit or got steared wrong. You’re then left with a misplaced spacecraft and have to figure out if you can rescue it from there.
    Fraser: And this happens a lot. We’re still once a year reporting on a spacecraft or a package of satellites that didn’t make it to their intended orbit.
    Pamela: Yeah and the Russians had a whole string of these last year where either a fairing didn’t come undone correctly or something didn’t fire correctly and things just didn’t make it.
    Fraser: So then what do you do? It’s in orbit, it’s working, in theory it’s functioning properly but it hasn’t reached its intended orbit.
    Pamela: It depends on what the spacecraft was designed for. In some cases having it in the wrong orbit, eh, you’ll live. You may not be able to do everything you had had intended but you can do most of what you intended.
    Fraser: And I guess it can shorten the lifespan as well because it might be so low that it …
    Pamela: Experiencing a drag
    Fraser: Yeah interacting with the atmosphere and it’s just a matter of time before it reenters.
    Pamela: Then there were missions like Phobos Grunt which didn’t make it where it intended and then came back to earth instead of making it to other planets in the solar system.
    Fraser: That was not the plan.
    Pamela: That was not the plan. When you’re interplanetary spacecraft doesn’t make it to a high enough orbit it is very hard to rescue yourself. If it’s a communication satellite you may not be able to do the intended communications. If it’s a space observatory you just change how you get the signals back and forth.
    Fraser: Sometimes the price is a shorter mission. Normally you would be using all of your propellant for reorienting your spacecraft and moving to different places during the mission but if you have to use up all of that propellant to get to the proper orbit then you’re not going to be able to use it later on in the mission.
    Pamela: Right there is always the options of firing all of the engines and get close to where you intended to be. There are lots of things you can do but the question is whether or not it allows your mission to keep going. In the case of Phobos Grunt which came back to earth, no, no it didn’t but in other cases they have been able to get spacecraft pretty much where they needed to go. Sometimes what’s interesting is the changes in orbit are actually due to realizing that the intended launch vehicle won’t work. The Chandra orbiting observatory ended up not getting launched on the launch vehicle it was intended so it didn’t end up in the orbit that was intended. It’s a great mission that continues to return great science so you just make things up as you go sometimes.
    Fraser: Okay so we’ve got this situation where the rocket either detonates on launch or for some reason the upper stage doesn’t fire properly or it gets pushed into the wrong orbits. Let’s say it survives all that, there have been situations where they haven’t detached properly, the fairings haven’t come off?
    Pamela: Yeah, so when the fairings haven’t come off it means your mass isn’t quite right which means when the thrusters that you have for maneuvering fire are not strong enough, are not in the right place anymore to be useful and there is drag if you’re in earth orbit. If you’re trying to get out of earth orbit that extra mass is a problem so that’s another way to kill a spacecraft.
    Fraser: So let’s say we’ve successfully made it into space, we get on to our intended trajectory, let’s say we’re going to Mars…
    Pamela: Because Mars kills things.
    Fraser: (Laughs) Yeah because Mars is where spacecraft go to die.
    Pamela: (Laughs)
    Fraser: So what are the ways that spacecraft can die en route?
    Pamela: You can lose communication and end up permanently orbiting the sun basically as a new asteroid… just a man made asteroid.
    Fraser: Yeah we’ve had that situation right, where we lost all communication although the rocket works fine, the thrusters work great, it’s on the proper trajectory and it just can’t talk to it.
    Pamela: Yeah we just don’t know where the expletive it is. It disappeared from all radio contact and we can’t find it because they are tiny. Yeah… zombie spacecraft.
    Fraser: We had a partial problem with that with Galileo but because its main antenna failed but it still had its secondary antenna so they were still able to communicate with it they just weren’t able to send back great big high-resolution images.
    Pamela: That one didn’t kill it and that one didn’t cause it to get lost. It’s when they simply go dark when it’s a problem. What’s crazy to think about is with a lot of these missions they are preprogrammed in advance so you can lose communication with it for months on end and suddenly it will pop up completely fine, functioning somewhere else. That generally doesn’t happen but it is theoretically possible so we keep looking when we lose communications.
    Fraser: Once we’ve lost communication with a satellite, the search for that spacecraft can go on for months sometimes.
    Pamela: Yeah there are a lot of preprogrammed in things like: when you see the sun here, the earth will be here so send a message. There are a lot of what are sometimes called Lazarus modes where the spacecraft will go into an extremely low power shut-down mode and then periodically when conditions are met will send a signal back and that would allow us to resurrect it from the dead.
    Fraser: You get these situations where they go into the safe mode right? Can they bring it back from safe mode?
    Pamela: That’s pretty much where Kepler is right now and this gets us to that great rotating problem in the sky which is your gyroscopes.
    Fraser: Bring more gyroscopes! Why won’t anyone listen to me?!
    Pamela: They take, like, six quite often!
    Fraser: Maybe they just don’t report on enough of these stories to see that it’s always the gyros.
    Pamela: But they know it’s always going to be the gyroscopes this is why they build redundancy into the system but the issue is it takes…
    Fraser: Well why are these gyros? I think it’s important to understand what these things are.
    Pamela: They are spinning wheels. They are often basically fly wheels and because they are spinning they are very hard to rotate so they maintain their orientation. If you want to experiment this with yourself go find a bicycle tire and attach two methods of holding it to the axis in the center, set it spinning and if you try and rotate it, it will resist. Quite often if you’re sitting in a rotating chair or wearing roller skates, I don’t know why you would be doing that, but you will move instead of the gyroscope. In spacecraft they will use these spinning gyroscopes to maintain their orientation and to keep track of their orientation. When the gyroscopes fail, when they stop spinning basically, you lose your sense of orientation in the sky and you lose your ability to spin about a given axis. Ideally you want three of these suckers so you can keep yourself oriented in the x, y and z axises. Pitch roll and yaw, the things that we worry about rolling about with the spacecraft where you have to worry about the pitch around the one access, the roll around the other and the yaw back and forth. You need all of these gyroscopes going. You can make due with two, fuse a spacecraft that was orbiting the earth, figure out how to make due with one by using its magnetometer, it’s ability to measure the earth’s magnetic field to figure out its orientation. With Kepler though, this mission that did go up with back up gyroscopes, these things that weigh a lot and require energy, it had the back up just not as many as Fraser wanted.
    Fraser: Eight, Twelve, always more gyros.
    Pamela: (Laughs) It is now down to two. They are trying to figure out “Okay we have a mission that requires absolute perfect pointing, we need to keep the stars exactly on the right pixels on our detector to be able to get the science we need to do done with this mission.” They don’t currently have the ability to do that so they have the mission in a shut-down mode. It is still functioning and responding; they have it such that they’ll pitch it over to look at the sun… not look at the sun but point it towards the sun and the solar radiation will flip it back over. It’s basically moving in a known way so they can check out the systems. They’re communicating with it once a day but it’s not returning science… this is highly frustrating. They have to figure out if they can get it doing science again, finding exoplanets again. Or… this is where “or’s” suck given the current economy, can they design a new science mission that it’s useful for. Yes, probably, but once they figure out that new science mission that it’s capable of, will there be the money to do that and the answer is probably no.
    Fraser: We need a Kepler II… we need five more of them. It’s one of the most important missions launched in recent times. Theoretically this thing will find another earth.
    Pamela: Yeah that’s cool but at this point we don’t have the ability to do that much with the information. Look at what James…
    Fraser: I know but it’s a target for later on, for the next mission that is a terrestrial planet finder, that’s all. Scouting out locations for the terrestrial planet finder. We are going to be bringing it back from the dead, we will be resurrecting that mission with our clout in this industry.
    Pamela: One of the frustrations is you want to have a whole suite of instruments that are capable of a whole portfolio of different science. You want missions like Hubble and James Webb that are capable of numerous different projects and we can’t even imagine what we’re fully going to be able to discover with them until we try. We know James Webb will be capable of studying the earliest galaxies and studying atmospheres of exoplanets. It’s going to be this great mission for doing targeted science. We know we need things like the LSST which is a survey ground-based telescope so it won’t die in space. We need this whole suite of things and yes we do need the planet finder. You can’t say it’s the most important mission, it’s one of the components to a complete portfolio.
    Fraser: Anyway they won’t bring enough gyros so it won’t matter. We’ve gone down bit of a rabbit hole here. Lets go back to our spacecraft that is hurtling towards Mars for example and it’s made the journey. Obviously it can get hit by micrometeorites.
    Pamela: Zotted by radiation
    Fraser: This has taken out spacecraft as well. The hardest part is the landing; lets talk about how that goes poorly.
    Pamela: Mars seems to be this giant red planet eating target of death. We’ve run into all manner of difficulty from things like the polar lander that had a unit conversion issue so it didn’t fire things when it should have and landed… would be a generous term, at a velocity far greater than intended.
    Fraser: Hard landing?
    Pamela: I think crash is an accurate word.
    Fraser: So you have a situation where you’re coming in too hot and you just smash into the planet.
    Pamela: Yeah. Occasionally we have mystery forms of death. The Beagle lander that failed to make a very large dent on the surface. The folks with the highrise mission have pointed at potential crash sites but it’s not really confirmed although they’ll talk about it in the bar. Yeah, Mars eats things.
    Fraser: You can come in too hot and just smash the planet but you can also come in at the wrong angle.
    Pamela: Yes. You have to worry about if you can inject into the orbit that you need and if you can break on the atmosphere the way you want. All of these things start to matter. You can actually fly past the planet; we’re pretty good at not doing that anymore. That was a problem in the 60’s, we just missed planets.
    Fraser: In preparing for this show you look at all the missions to Mars. Aim towards Mars and… missed.
    Pamela: Now it’s solar orbit.
    Fraser: Didn’t we discuss in the last show that a grade show kid was able to do the math to work out the trajectories?
    Pamela: There is difference between doing the math and having your spacecraft actually obey because of a software glitch or radiation eating a one that needed to be there. Math is slow and tedious.
    Fraser: He couldn’t hit the broad side of a planet.
    Pamela: (Laughs) That has been true before.
    Fraser: So they’ll skip off the atmosphere, come in at the wrong angle, or just miss entirely. Let’s say they do make it down, land on the surface, how do they die now?
    Pamela: You can end up with everything from radiothermal generators, the RTG’s dying prematurely. That happened with one of the Viking landers. They can get stuck in the dirt. Spirit lived far longer than anyone thought it would. We have no complaints for how long it lived but it did die a sad death. It was basically happily going along and happily doing science, returning great results and then rolled across sand that was softer than anticipated. Just like you’ll be walking along in the woods and suddenly the trail eats your boot off your foot, well in this case it wasn’t like Spirit could lift its foot and leave it’s wheel behind. It just got stuck.
    Fraser: Can you imagine Spirit chewing its own robotic leg off somehow?
    Pamela: (Laughs)
    Fraser: If it used it’s rat tool on it’s leg and just ground it away until it could keep moving. I don’t know if anyone has thought of this, I’m pitching this to NASA right now.
    Pamela: (Still laughing) Somewhere there is a web comic getting written about this.
    Fraser: As you said Spirit was already suffering pretty badly. It was dragging it’s leg.
    Pamela: No that is Opportunity. Opportunity is still dragging its frozen-ish leg behind. I think it actually has it lifted up.
    Fraser: He should chew it off. (Laughs)
    Pamela: (Laughs)
    Fraser: At the end of the day these things are mechanical machines, these things are out on the surface of Mars, there is no repair coming, they are going to wear down so you get mechanical failure. Maybe it could have pulled itself out of the sand if it had more…
    Pamela: No, it was just stuck. This was a mission where they figured out that it was stuck. They tried, so long they tried. There was the whole free spirit movement to get it unstuck but they just couldn’t do it. When they realized that it was stuck, they turned it into a non-mobile science platform. They pointed the cameras up, they did some astrometry work, they did all sorts of neat weather work, but then it froze to death. That is often the fate of things on Mars.
    Fraser: Let’s talk about this.
    Pamela: Computers, servos, pretty much anything that is mechanical or electronic has a preferred operating temperature. They don’t like to be too hot, that’s how Venus kills things. They also don’t like to be too cold because when batteries get too cold they stop charging and stop being able to give you electricity. Anyone who has been outside at night too long knows that your headlamp will start to freeze if you don’t put your battery packet inside your jacket. With Spirit the system simply got too cold. In previous Martian winters they were able to park it on inclined hills so it was maximizing the amount of sunlight that it got. They were able to keep its temperatures above -40 F, it’s not pleasant to experience but a human will survive. They think that the final winter when it was stuck in the sand at a non-preferred angle that it probably got down to about -55 F and just wasn’t able to come back out. When the Martian summer came back it just wasn’t sufficient enough to thaw things out and the ability to charge things back up just wasn’t there anymore.
    Fraser: I think a more severe example of that would be what happened to the Phoenix lander.
    Pamela: That one they kind of knew it was going to happen.
    Fraser: It was a suicide mission.
    Pamela: Yeah, this was the robotic version of one way to Mars and one summer on Mars. They landed it in one of the polar regions. They knew it would shut down, they knew it would get stormed on and they figured it would get too cold but it had a built in Lazarus mode just in case it managed to stay warm enough and conserve enough power through the winter. And it didn’t.
    Fraser: It must have gotten snowed on during the Martian winter, near the poles at -100 F+. It must have been really devastating on the spacecraft so it wasn’t a surprise they weren’t able to reach it again come summer. They tried though. We’ve talked about mechanical failure and you talked about the RTG not working but with something like Curiosity, how will it probably die?
    Pamela: With Curiosity it could, unfortunately, have any manner of unnatural deaths. Anywhere ranging from getting over-inclined, rolling over because it got over-inclined. They have lots of safety modes to avoid that but who knows, it’s Mars. It’s never happened on Mars but It could get impacted from space which would be cool if random rock from space ate random spacecraft on Mars. Highly improbably. Most likely it’s just going to hit either a mechanical failure where it locks up and can’t move anymore or it’s going to hit a power failure where it’s no longer able to get enough battery signal going to communicate with space or rove its way across the surface. That is kind of its planned form of death.
    Fraser: It’s got this RTG power plant in it which could last it for a long time; years and years.
    Pamela: The plan on this was at least hundreds of Martian days hopefully more than that. Hope for thousands of Martian days, I don’t think anyone goes quite that far, but eventually it’s going to be lack of power that is going to kill Mars Curiosity lander unless it gets itself stuck or rolls itself over. Those are the two fundamental ways it can die is a wheel getting stuck, a mechanical failure or it over-inclines. The built in measures to keep it from getting over-inclined are huge.
    Fraser: What about spacecraft like New Horizons. I guess what is similar are the Pioneers and the Voyagers; they don’t seem to ever die. How long has the Voyager been going for?
    Pamela: I think it’s been going for longer than I’ve been alive at this point. These are again spacecraft that have RTG’s, are nuclear powered, and have the potential to get it’s constantly diminishing amounts of energy as they go through their half-life of their fuel source but at their shutting off of instruments as they’re going into low power modes where they simply ping back to earth every once in a while they are capable of lasting an extremely long time. With New Horizons we have to fundamentally worry that we don’t know what all is orbiting Pluto. We’re finding that there is more and more stuff that is orbiting Pluto than I think anyone imagined when they launched the spacecraft. There is a very real low probability but still very real possibility that this spacecraft is going to impale itself on a small moon, debris or something else that will just destroy it. Other than that its limitation is one of maneuvering thrusters more than end of life so it’s going to just keep flying just for quite some time just as the Voyager missions have.
    Fraser: Until they’re not able to communicate with it if they get a power failure or if they just can’t orient it anymore. Could have a situation with the Voyagers where they get too far away to where we just can’t communicate with them anymore?
    Pamela: That is much more an issue of their signal being too weak to coherently make out. That eventually will become a problem unless there are major breakthroughs in radio technology which we can hope for. Imagine trying to hear your cell phone signal from Mars. We’re going to hit that point eventually and, heck, my cell phone gets sad if it’s in a farm field too far from a cell tower.
    Fraser: Is that the final escape? That the spacecraft got too far away and nothing went wrong. It launched fine, it traveled fine, it did it’s mission and it was so successful and it got so far away we just couldn’t talk to it anymore.
    Pamela: I would not be surprised if that was the final fate of Voyager. It’s an amazingly built mission.
    Fraser: Yeah. Well thanks a lot Pamela.
    Pamela: It’s been my pleasure.
    This transcript is not an exact match to the audio file. It has been edited for clarity.

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