NASA Edge | NASA Edge Visits JPL for the Latest in Supersonic Deceleration
FRANKLIN: Welcome to NASA.
BLAIR: An inside and outside look at all things NASA.
CHRIS: We’re here at the NASA Jet Propulsion Laboratory in Pasadena, California to talk about the Low-Density Supersonic Decelerator.
BLAIR: Also known as LDSD.
FRANKLIN: Which is part of the entry, decent, and landing portfolio.
CHRIS: Over the course of the show, we’re going to be talking to a number engineers and researchers. They’re going to provide us the status update on the project.
BLAIR: And we’ll learn about the future of this technology demonstration mission.
FRANKLIN: So, like LDSD, slow down, relax, and enjoy the show.
CHRIS: Watch out for the deer too.
BLAIR: Yeah, they run the place out here.
CHRIS: Ian, it’s great having you on the show again.
IAN: Thanks for having me.
CHRIS: I guess you’re just recovering from an open house here at JPL.
IAN: Yeah, Saturday and Sunday we had 45,000 people come through JPL to hear about all the things going on here. It was really nice because we got to share some of the enthusiasm. Show them some videos from LDSD talking about the future and all the cool things that we’re going to do.
CHRIS: Plus, all the noise going on, they’re cleaning up from the event. You had all these tents and chairs. It’s pretty big.
IAN: Yeah, it’s definitely a pretty big production. It’s going take a couple days to clean up.
CHRIS: The last time we had a chance to talk with you, you were talking about upcoming tests at China Lake.
CHRIS: In fact, you probably had a number tests since then. Before we actually get to the results of those tests, take us through what Low-Density Supersonic Decelerator is all about.
IAN: A couple of years ago, we put the Curiosity Rover on the surface of Mars. This was a one ton, nuclear powered laser equipped rover. It was the largest, most massive thing we’ve ever landed on another planet. The capability to put down on the surface of Mars was basically using technologies that we’ve had for decades, going back to the Viking program and the early and mid-1970s. As we look to the future and we want to do more exciting, more capable, more bold science missions and as we cast our eyes to the horizon, we start thinking about putting humans on the surface of Mars. We’re going to need new technologies that allow us to take those very large, very massive payloads and slow them down adequately enough to put them safely on the surface of Mars. That’s what LDSD is about. We’re developing the next generation of decelerators that will allow us to land these very large, very massive payloads that you’re going to need as we look into the future.
CHRIS: That’s one of the challenges, entry, decent and landing for any planetary surface but especially Mars.
IAN: For anybody with an atmosphere, absolutely, is the entry, decent and landing. Mars is particularly challenging in the solar system because the atmosphere so thin. Earth, we’ve got a very nice, thick atmosphere. It’s a relatively cush to decelerate in. There’s a lot of air, a lot of things to react against the surface. At Mars, the atmosphere is extremely thin. It’s about 1% the thickness of Earth’s atmosphere which means that you don’t have a lot of atmosphere to react against the body which means you need really big bodies to react against what atmosphere you have.
CHRIS: Looking at the LDSD project, take us through the different aspects of LDSD.
IAN: Well, it starts with the technologies. We’re developing two new flavors of supersonic decelerators. A device we call Supersonic Inflatable Aerodynamic Decelerators or SIADs and extremely large parachutes that can be used at Mach numbers, at speeds much higher than we’ve been able to use in the past. From there it goes into the idea that before we use these technologies at Mars, we need to make sure that they work the way that they need to, that we understand how they work and we get the performance that we need from them. That means we have to test them. That’s actually one of the hardest aspects of this entire project, is that the size of the devices that we’re developing and the conditions in which we’re going to be using them are things beyond whatever test capabilities we’ve had. It’s really the dawn of the space age. For 50 years, we’ve outgrown all the tools, infrastructure and capabilities that we got for doing testing on these size devices. We had to come up with new techniques. That means things like rocket sleds out in the desert or high-altitude supersonic flight test, like what we conducted last year, and what we’ll be conducting again next year.
CHRIS: Let’s go back. We interviewed you here at JPL about a year and half ago and you had an up coming sled test. Take us through that test and what were the results?
IAN: We were out in the desert at China Lake. We were doing some testing on SIAD-R We wanted to take SIAD-R up to loading conditions, aerodynamic loadings, similar to what we would see if we were using it at Mars. We built a 20-foot tall, 40 ton welded steel siege tower with a mock aero shell on the front of it. We took some surplus rocket motors and lit those. We got from 0 to 300 mph in a few seconds. Once we got up to those speeds, we deployed the SIAD. We saw it inflate in a fraction of a second. We saw how it emerged from a very tightly compact stowed state into a fully deployed, fully inflated state. We got a feel for how much inflation pressure was necessary to see this thing act as a rigid structure. We got to load it aerodynamically, put all the pressure and forces that are going to be on it if it were used at Mars. We got to see how it did under all those conditions. It did flawlessly. It was inflated beautifully. It held the inflation. It held the shape much longer, much better than we thought it would and it survived all the loads just great. It was interesting for those kinds of tests. I say we were going 300 mph. We were only going 300 miles an hour because when we use these devices at Mars, they’re going to be going several times faster than that.
IAN: To replicate the aerodynamic loading because the density is so much higher here in the surface of Earth than it is at Mars, you don’t have to go as fast to get that same load.
CHRIS: That’s true. That makes sense. Was that a full-scale?
IAN: It was the full-scale. Yep. The full-scale aero shell 4.7 meters and a 6-meter diameter SIAD-R.
CHRIS: So now you have worked to the next level? You want to do an altitude test where you drop it vertically?
IAN: Yep. That was really aerodynamic loading. We got to see some initial deployment data. We really want to see how these things fly. Do they deploy in a free body sense? In other words, once this thing is flying through the sky and it begins inflating, what are the motions of the device like? Does it inflate on one side more than the other and begin to tumble the aero shell. What are the aerodynamics in a supersonic environment? To get all that kind of information, you have to take a full-scale device to conditions that are analogous to what it would see at Mars. That means going several times faster than the speed of sound, and that means doing it in a very, very thin atmosphere. There is such a place on Earth; you just have to go half way to the edge of space to find it.
IAN: Half way to the edge of space is about 50 km or almost 180,000 feet. What we did was build a test vehicle that looks very similar to the entry vehicle that lands Curiosity on Mars. We took it up to an altitude of 120,000 feet using a balloon the size of the Rose Bowl. The test vehicle itself weighs 7000 pounds. Once we got up to that altitude, we released from the balloon and we lit a giant solid rocket motor. That rocket motor took our test vehicle from an altitude of 120,000 feet to an altitude of 180,000, and got us going to over four times the speed of sound. Once we got those conditions, the motor burned out and we began our test. We got to inflate the SIAD. We saw that inflate in a fraction of a second at over four times the speed of sound, nearly 3000 miles an hour. We watched it decelerate the vehicle. We deployed another device, a ballute, a balloon parachute at nearly 3 times the speed of sound, over 2000 miles an hour. We saw this device works flawlessly. We used that device to help pull the parachute off the back the test vehicle and get it out behind the test vehicle at about 2 1/2 times the speed of sound. We then tried to take 100 pounds of nylon and Kevlar and get it to inflate properly at a 2000 mph wind. What we saw was that it didn’t inflate the way that we wanted to. It got damaged in the process but now we get to use that data; data that we didn’t think we actually get this year, data that we thought we would have to wait till next year but because we had all these technologies ready a year ahead of schedule we get this date early. We get to take this data, learn from it, and now we’re applying that knowledge to building stronger better parachutes that we’ll be testing next year.
FRANKLIN: That was some great information that Ian Clark gave us on how the LDSD project is developing.
BLAIR: I had a chance to sit down with John Gallon who works on the parachutes for LDSD. He talked about the recent test in Hawaii and the challenges they faced but he also talked about some of the challenges they faced during recovery of the test vehicle.
BLAIR: So John, earlier Ian mentioned that the test was a success. Were you able to see this real time? Where were you during the test? That would be a good place to start.
JOHN: During this test, I was actually out on the recovery boat. We were out in the Barking Sands of the Pacific missal range in the water that they control to the west of Hawaii. We were just outside of where the predicted landing elipse would be where the test vehicle could actually splash down at. From that point, we actually had a beautiful view of the test article. It was a very small misguide but we were able actually to see the balloon as it got to its float altitude. Then through the radio system, we were able actually to hear the countdown and watch. We could see the contrail of the rocket shoot across the sky.
BLAIR: Were you able to recover everything or did you only get the test vehicle or the black box if you will?
JOHN: We were actually able to recover everything that we set out to recover and even more. We came amongst some other stuff we were able to recover that we didn’t even think we are going to see, namely this ballute system that was used to deploy the parachute. On the way to get to the test vehicle, we actually found it floating in the ocean. We were able to real-time make some decisions on if we wanted to attempt to recover it even though it wasn’t on our list of top priority recovery items. We all put our heads together and said, yeah we’re going to try to cover this ballute. We put a time limit on it of 15 minutes. If we can’t get it out of water within 15 minutes, we’re just going to leave it and go straight to the main objective. This wasn’t something we even talked about recovering and the fact that it actually could have a live pyrotechnic still on board, I needed to brief the EOD, the Explosive Ordinance team, how are you going to recover this? What are you going to look out for? So in real time, I gave them a complete briefing; told them of the hazards; how much ordinance was on board; where would they would look to see if it had fired or not. This all happen in the course of about 15 minutes by the time we said we were going to recover the ballute and the point that we actually got the boat to the ballute.
BLAIR: I would have said this isn’t on our list, too bad. It seems like you scored a huge victory in being able to recover some pretty important data.
JOHN: It was. It was because we needed to know how well the ballute worked. If we thought we would have ever recovered it, would it have gotten put on the list? It definitely would have.
BLAIR: So, you got the ballute and that’s great. How did it go once you actually got to the test vehicle?
JOHN: Once we got to the test vehicle, we had two boats. One was called the fast boat. It actually was able to get to the test vehicle before the big crane boat that we actually would use to pick the test article out of the water. The first boat got there. It had two Navy EOD divers on board as well as two of the JPL employees to basically evaluate the situation. They couldn’t pull the vehicle out of the water but at least they could get there. The Navy guys had some buoys. They had all of their dive gear and stuff to be able to go in and get on the vehicle and start to pull off critical data like this little black box item, which would have all the critical data in it. Then it went on to securing the test vehicle. We wanted to make sure we recovered as many of the test assets off of the vehicle. Unfortunately when we got there the parachute had totally sunk. It was actually straight underneath the test vehicle and it was actually kind of pulling at the test vehicle a little bit. Basically, they cut the parachute free and were able to transfer that structural load over to the boat. The boat was actually able to move away from the test vehicle basically holding the parachute, keeping it from sinking as well as making sure that the test vehicle remained afloat and wasn’t getting yanked underwater by this parachute. Shortly thereafter, the EOD guys actually stayed and sat on the test article until the large crane boat was able to come over. At that point we started the recovery efforts of getting the test vehicle out of the water. When the day was done, we recovered all the items that we set out to do, plus the ballute.
CHRIS: You know, Franklin, it seems like John had great time being on the recovery team on the flight test out in Hawaii.
FRANKLIN: Yes. He was also out there with Rob Manning who is the chief engineer for LDSD. We sat down and talked about the design challenges that he had to address through testing. Rob, you’re the chief engineer for LDSD.
FRANKLIN: You’ve worked with Mars missions prior to what maybe LDSD might be used for down the road. You’ve had missions that have gone to Mars where you didn’t test these parachutes like that.
ROB: That’s correct.
FRANKLIN: What’s the difference between then; say for instance what you did with Curiosity, Pathfinder, and even Viking to moving forward to LDSD to where you are know? What’s the difference?
ROB: I think the biggest difference, those parachutes were all designed to conform to an architecture and design principles that were tested at high altitude in the 1960s and early 1970s. There were three test programs where high altitude balloon would lift up a parachute with a simulant of an entry vehicle and launch it way up into the upper atmosphere just like we’re doing above New Mexico and test out these parachutes to see how well they work, especially how well they inflated in those conditions. We’ve been counting on those test results for 40 years. That test program has given us confidence that the parachutes we designed will inflate. We still have to make sure that the parachutes were designed to be strong enough. What we can do is inflate them in earth conditions in giant wind tunnels and get the strength tested that way. We can’t reproduce the high-speed inflation part we are counting on those test results from the past. My team said, let’s build a Rover, like Curiosity. What’s the biggest parachute that was ever tested in the 1960s and 1970s. There was one parachuted tested that was just about the size of Curiosity’s. We said, okay, we’re using that test result. We analyzed the video. Looked at the test results, watched how it opened, watched how it balanced.
FRANKLIN: But it’s also based on the weight of the vehicle, right?
ROB: It turns out because the inflation process is so fast, the weight of the thing that’s pulling on isn’t playing a very big role.
ROB: Weight doesn’t play a very big role instead the size of the vehicle plays a role, because what that does produces a supersonic wake the flows back to the parachute. So, what we really need is not so much something that is that heavy but something that doesn’t slow down too fast during the inflation process. Because the inflation process is so fast on Mars, it doesn’t have to be exactly the same way weight. Back then, the weight wasn’t that high but the size of the fore body the heat shield of the wake was about right. Again, we could take advantage of that. On Earth, weight does play a role because it takes such a long time for the parachute to open. So, by the time the parachute has opened, you have already slowed down to half your speed. On Mars, it goes from nothing to something in a matter of a half a second.
FRANKLIN: Okay. So in LDSD, you have your supersonic parachute but that’s only half of what you’re working with. You have the SIAD that deploys.
ROB: That’s right. We did a “two for.” We did two tests in one chance last June. What’s so nice about a SIAD is it doesn’t weigh a lot and it’s pretty easy to pack around the aft body of the space capsule. We can pack it there and with a pretty small gas strainer we can inflate it, “boom,” and add to the diameter of the heat shield. The cool thing about that is that now we can get a bigger vehicle that would otherwise have to inflate its parachute at three times the speed of sound. Instead, we can use it to slow down from say Mach 4 down to Mach 2 without losing too much altitude. The problem here is that you’re running out of space but if you wait too long with your parachute, you hit the ground. In our case with LDSD, we said if we could try out this SIAD technology, we could even go to bigger systems, bigger than Curiosity. If you add to this a new supersonic parachute that’s twice the area of Curiosity’s parachute then we will have really pushed the envelope and allowed future designers, future mission designers to land things that right now I can’t land because the largest parachute ever tested successfully was back in 1972.
FRANKIN: What’s the difference between the speed of, say for instance, when Curiosity entered Mars atmosphere versus what you’ll send to Mars 10 to 20 years from now after the SIAD has been deployed?
ROB: In all cases, we don’t want to test parachutes much above Mach 2. The reason is that we go to Mach 3, the temperature, the friction of the atmosphere at those speeds will melt the fabric. In all cases, we’re trying to get the whole vehicle down to a velocity, an altitude where the parachute will work. That’s around about Mach 2 to Mach 2 ½.
FRANKLIN: That’s what you’ve managed in the past.
ROB: We’ve managed in the past. What a SIAD does, it allows you to have bigger vehicles to take you into that realm without getting too close to the ground.
FRANKLIN: It’s almost like down shifting your car.
ROB: It is, exactly. It’s like a transmission. You’ve got to get in the next velocity regime and altitude regime to use your equipment safely. That’s why a SIAD and this parachute really do go together for bigger vehicles.
FRANKLIN: Looking at the data you’ve received from the Hawaii test and your helicopter test, what are your design challenges going for to develop the supersonic parachute?
ROB: The first design challenges is to figure out what were the actual stresses on the fabric during inflation? Is it possible that we underestimate how much force is applied to these parachutes under supersonic conditions or was there something about that parachute that made it weaker than we expected. That’s a primary question. The other question is what happened in this test where it actually failed well below our expectations. It could tell us that maybe it’s not something about supersonic because we’ve never had this kind of failure. If you look back at all the previous supersonic flights in the 1960s and 70s, they never had this kind of failure. We’re thinking that maybe there was something about how the manufacturing tolerances stack up when you make something this large. That might be at a potential cause but there may be other causes. Our biggest challenge is how strong do I make the next parachute? I could make the parachute a lot stronger. We can put much more Kevlar on it. We can just go to town making a stronger and heavier and harder to use. If I make the parachute to massive then nobody is going to want to use because it’s just not paying for itself anymore. The right thing is to find the right balance between making it strong but not too heavy. That’s the real challenge. Can we come up with computer simulations and models that make accurate predictions of the stresses in that fabric and structure during a supersonic inflation? That’s what we’re doing now. If we can do that, we will win this game.
CHRIS: Okay Ian, what’s next for LDSD?
IAN: We’re still going. We’ve got more testing.
IAN: We have the parachute data that we got from this year’s test. We’re taking that knowledge. We’re applying it to how to build better, stronger parachutes. We’ve got two more high altitude, supersonic flight tests in 2015.
CHRIS: Will that be in Hawaii too?
IAN: Those will be off the coast of Kauai, absolutely. We have more sled tests. Once we have this new parachute design, we’re going to go back out to the desert and we’re going to expose it to over 100,000 pounds of force and make sure the parachute is strong enough to survive the forces. It’s going to need to survive again if it’s going to be used at Mars. We’ve got more sled testing on the SIAD-E device. The device that we’re targeting for things three or more times the size of Curiosity rover. It’s the data from these tests, in particular, the data from the high altitude flight test this year and those technologies that are really going to be driving the future of the missions that we do to Mars. Hopefully one day, being used to land humans on the surface of Mars.
CHRIS: I assume at some point in the future, you’ll actually have a high altitude test with SIAD-E?
IAN: That’s our hope. Right now for 2015, the two tests are targeted with SIAD-R and parachute, and trying to get the parachute fully inflated at the test conditions we need to and maybe even trying to deploy the parachute in new way; constrain the opening diameter. Reef it, it’s called. To not generate as large of loads and maybe have a more controlled opening. That’s one of the things we’re testing.
CHRIS: How soon could you even think about having a mission, a robotic mission using SIAD or the LDSD concept going to Mars?
IAN: Well, in theory by the end of this project, these technologies, particularly the SIAD and the parachute particular will be ready for adoption by an inflight project. That means that at the end of next year, we will have all the data and we’ll have conducted most of the testing necessary for them to be incorporated onto a flight project. You just sort of look onto the horizon and see what opportunities do we have for mission to Mars. We have a couple coming up in the near term. The 2020 opportunity that is very similar to the Mars Curiosity Rover. It’s more likely that the missions coming behind that one after 2020 are going to be using these technologies. For example, the 2020 Mission has a caching component associated with it. It wants to collect a number of samples that we hope to be able retrieve and bring back to Earth. The mission that comes after that is going to have to go retrieve that sample, load it onto a rocket that takes it from the surface of Mars at least up into Mars’ orbit. That’s an enormous system and that’s a system that is going to require a minimum larger, better parachute like what we’re developing but possibly a SIAD as well.
CHRIS: That’s just awesome. Just think maybe your concept will be used when we land the first humans on Mars.
IAN: That’ll be exciting. I want to keep going. I want to go bigger. I want to develop more technologies. The technologies we’re developing we’re targeting things bigger than Curiosity but I’ve told you on the horizon is one day putting humans on the surface of Mars. I would like to be able to keep going with these kinds of technologies and develop them further to make sure that we have that set enabled for when we want to go land humans on the surface of Mars.
CHRIS: I think Ian Clark will be a name to remember for the first humans to land on Mars.
IAN: Hopefully LDSD because it’s an enormous team and a very amazing team we’ve assembled here at JPL and across NASA and across all of our industry partners. You know the Navy, the Columbia Scientific Balloon Facility, our NASA Centers, Langley, Ames, Goddard, Wallops; all across the nation. It’s just a really phenomenal team that we’ve got.
CHRIS: Ian, thanks for joining us again. I appreciate the update on LDSD. We look forward to seeing more great things about the project in the next couple years.
IAN: Thanks for having me.
FRANKLIN: Ian, John and Rob gave us a great overview of the LDSD technology demonstration mission.
CHRIS: Entry, decent and landing is one of the critical challenges we’re going to have to overcome if we’re going to land humans on Mars.
BLAIR: The challenges don’t stop with all the LDSD. We’re going to look at several EDL projects on future episodes of NASA EDGE, like THOR, for example.
CHRIS: Dropping the hammer early.
FRANKLIN: Ah. You’re watching NASA EDGE.
CHRIS: An inside and outside look…
BLAIR: At all things NASA.