Anyone even remotely familiar with landing spacecraft and payloads on other worlds can respect how difficult such a feat really is, and it only gets more difficult as the spacecraft get larger and heavier. Mars rovers Spirit and Opportunity, each roughly the size of a golf cart, had to parachute in and land while cocooned inside a set of very sophisticated airbags, bouncing along the surface until coming to a stop. The rover Curiosity, which landed on Mars in August 2012, is the size of a SUV and carried out what is arguably the riskiest landing attempt of any spacecraft to date, touching down via a “sky-crane” which hovered thanks to rockets to lower the rover onto the surface.
Thing is, with the current landing technology available Curiosity is about as big a payload as we can land on Mars, and if mankind ever wants to land larger payloads, such as larger vehicles with crews or large amounts of supplies, then new technologies need to be developed to get the job done.
The space agency is also currently very restricted on where they can land, because the Martian atmosphere is so thin that current deceleration technologies do not allow for the time needed to slow down enough to land at higher elevations. NASA needs a new approach to make future missions to land on Mars possible, and the Low-Density Supersonic Decelerator (LDSD) will open up many more options for future locations by enabling landings at regions that cannot be currently accessed.
The first flight test of the LDSD was scheduled to take place earlier this month from the U.S. Navy’s Pacific Missile Range in Kauai, Hawaii, but mother nature did not want to cooperate, despite two years of research showing that the Kauai area had the proper wind conditions to carry the balloon out over the ocean for LDSD to launch. All six days of launch attempts were called off for unfavorable weather conditions.
“We needed the mid-level winds between 15,000 and 60,000 feet to take the balloon away from the island,” said Mark Adler, LDSD Project Manager from NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “While there were a few days that were very close, none of the days had the proper wind conditions.”
Now, after working with the Pacific Missile Range Facility and looking at weather conditions predicted for later in the month, NASA and the U.S. Navy are aiming to try again to fly the LDSD test article on June 28. If the LDSD cannot fly on June 28, then backup launch attempts are scheduled for June 29, June 30, July 1, and July 3.
“What folks may not realize is the variability of the weather in Kauai,” said Jody Davis, NASA Langley LDSD lead. “The island has many different types of terrain and is very mountainous, so there’s a lot of localized rain and storms. This test is very dependent on the wind direction and rain is bad for the test vehicle, so we can only launch the balloon in certain conditions.”
Landing Bigger on Mars
“If we’re going to explore an asteroid and eventually put people on the surface of Mars then we need sustained and significant investment in new space technologies. Without those investments we won’t be able to take people in any sustained way beyond low-Earth orbit,” said Jeff Sheehy, Senior Technical Officer of Space Technology Mission Directorate from NASA Headquarters. “Assume we can land something twice as big as Curiosity, what could we do with that? Where could we explore? How much MORE could we explore? How much more could we learn? We’re looking forward to sample returns from Mars and putting enough cargo on Mars to support human exploration, and the LDSD project aims at providing the technologies for entry, descent, and landing, which is one of the major challenges for sustained exploration of Mars.”
The current technology used for decelerating from a high speed atmospheric entry to the final stages of landing on Mars dates back to NASA’s Viking Program in 1976, and the same basic parachute design has been used ever since. LDSD brings a much needed upgrade; the heavier landers of the future will instead use atmospheric drag as a solution, which will save rocket engines and fuel for final maneuvers and landing procedures. LDSD will also give NASA the capability to land payloads of up to 3 tons, twice what can currently be landed, while also improving landing accuracy from the current margin of 10 kilometers to a mere three kilometers.
“We have been using the same Viking parachute design and the same supersonic Viking parachute test data from 1972 to qualify and validate the operation of our parachutes on all of our Mars missions,” said Adler. “We’ve been pushing the limits of what we can squeeze out of that data, and we’re pretty much there, we’re at the limit. That would be fine if that’s all we wanted to do, but we want to go bigger, we keep getting bigger, we went from Sojourner to MER to Curiosity but that’s not good enough, we want to land bigger things, and we want to land them at higher altitudes and land more accurately.”
“The fundamental problem we have is things start going faster and faster through the Mars atmosphere as they get larger, and so we have to slow them down at higher altitudes and higher speeds,” added Adler. “Today we slow things down at about Mach 2, we’re going to have to go up to Mach 3 or Mach 4 and higher to start slowing bigger things down and that’s what this project is all about, developing new supersonic decelerators to slow things down at higher speeds.”
The LDSD project team has already completed three successful rocket sled tests of the “SIAD-R,” one of two Supersonic Inflatable Aerodynamic Decelerators that make up the three innovative deceleration systems now in development under the LDSD project (two SIADs of different sizes and an advanced parachute system). The tests on the balloon-like pressure vessel, which is designed to inflate around a vehicle and slow its entry, went well, despite the fact the test team put the SIAD-R through aerodynamic loads 25 percent greater than it will face during atmospheric entry at Mars.
“We inflated the SIAD-R on a rocket sled going about 250 mph to show that it could take the loads at Mars, so we simulated the loads this thing will actually experience when it actually lands at Mars,” said Adler. “We had to show that it would survive, that it inflated properly and wouldn’t rip off and show that it had the right characteristics that we would expect in a Mars flight. That all worked out great.”
The Flight Test
Once mother nature decides to cooperate, the LDSD will launch from the U.S. Navy’s Pacific Missile Range Facility in Kauai, Hawaii. A 34-million-cubic-foot helium balloon will lift the solid-rocket powered LDSD test vehicle to an altitude of 120,000 feet, at which point the vehicle will fire a large Star-48 rocket motor to accelerate to supersonic speeds and reach 180,000 feet, where the atmosphere of Mars can be simulated.
“We get to the altitudes of Mars in terms of density that we would be at when we conduct our flights there, then we fly horizontally at Mach 4. At about Mach 3.75 we will deploy the SIAD, which is where it has to deploy at Mars to start slowing us down at higher speeds,” said Adler. “Shortly after that we will deploy the parachute deployment device at Mach 2.75, then the parachute will come out at about Mach 2.5, then the whole thing comes down. So the whole test occurs in this horizontal phase at high altitude and we get all our data. We have tons of cameras, GPS, temperature sensors, pressure sensors, load cells and so on to give us information about these articles in flight so we can measure the dynamics, their performance, and so on to prove to ourselves that it will work at Mars if we did this there.”
Two SIADs, which were inspired by a puffer fish’s ability to change its size rapidly without changing its mass, are being developed to serve two different purposes. A 20-foot-diameter (6-meter) SIAD will serve for landing smaller robotic payloads, and a 26-foot-diameter (8-meter) SIAD is being developed for landing larger payloads, including crews. The 100-foot-diameter parachute is also new; it’s twice as big as the parachute Curiosity used to land on Mars. It’s so big that it can’t even be tested in the world’s largest wind tunnel at AMES Research Center, instead the LDSD team had to conduct scale model tests to design the parachute for the actual flights. All three devices will be the largest of their kind ever flown at speeds several times greater than the speed of sound.
A series of flight tests are scheduled to take place in Hawaii through 2015, and the technology that comes from the LDSD project will be ready to support the missions it is designed for as soon as 2018. However, it may have to wait several more years before NASA has a reason to use it, because the space agency won’t be launching anyone anywhere until at least 2021, when the Space Launch System (SLS) and Orion spacecraft are scheduled to conduct the first crewed “deep-space” mission beyond low-Earth orbit. And if Congress continues to under-fund NASA, then it could be even longer before the missions that will need LDSD come to reality.