LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator)
LOFTID is demonstrating a truly crosscutting technology for atmospheric entry. One of the challenges NASA faces is how to deliver heavy payloads (experiments, equipment, and/or people) to destinations with an atmosphere. This technology enables a variety of proposed NASA missions to destinations such as Mars, Venus, Titan, and return to Earth. 1) 2)
When a spacecraft enters an atmosphere, aerodynamic forces act upon it. Specifically, aerodynamic drag helps to slow it down, converting its kinetic energy into heat. Utilizing atmospheric drag is the most mass-efficient method to decelerate a spacecraft. The atmosphere of Mars is much less dense than that of Earth, and provides an extreme challenge for aerodynamic deceleration. The atmosphere is thick enough to account for some drag, but too thin to decelerate the spacecraft as quickly as it would in Earth's atmosphere. LOFTID acts as a giant brake by deploying a large inflatable aeroshell (a deployable structure protected by a flexible heatshield) before entering the atmosphere. The large aeroshell creates more drag and begins slowing down in the upper reaches of the atmosphere, allowing the spacecraft to decelerate sooner while experiencing less intense heating.
LOFTID is demonstrating a large aeroshell entry from orbit, and it is applicable to any destination with an atmosphere. Benefits of using the inflatable decelerator design for a variety of space applications include:
• Landing more mass
• Landing at higher altitude locations
• Enabling better utilization of the full volume of a launch vehicle fairing by stowing forward of the spacecraft (rather than encapsulating it within a rigid aeroshell) at launch
• Enabling more access to spacecraft while integrated in the launch vehicle stack.
The inflatable decelerator technology should be scalable to both crewed and larger robotic missions to Mars. Potential commercial applications include (in order of increasing scale):
• LEO (Low-Earth Orbit) return (free flyer, in-space manufactured materials)
• International Space Station down mass (without Shuttle, the U.S. has no large-scale down mass capability)
• Lower cost access to space through launch vehicle asset recovery.
The LOFTID project is a part of the Technology Demonstration Missions Program sponsored by NASA's Space Technology Mission Directorate. The project is managed by NASA's Langley Research Center in Hampton, Virginia.
Figure 1: Technology to deliver people, and their associated large payloads, safely to Mars is being developed and tested right now. Engineers are working to overcome the challenges of landing heavier cargos than ever before on other planets, and as well as returning things to Earth, using a Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technique. The Low-Earth Orbit Flight Test of an Inflatable Decelerator, or LOFTID, will demonstrate the next generation of HIAD technology. Learn more about the latest in NASA’s cutting-edge entry, descent and landing technology in this episode of NASA X (video credit: NASA)
Figure 2: Artist's illustration of the deployed LOFTID in orbit (image credit: NASA)
LOFTID project overview
LOFTID is a public-private partnership between NASA’s Space Technology Mission Directorate and United Launch Alliance (ULA). The LOFTID project is poised to revolutionize the way NASA and industry deliver payloads to a planet’s surface or into orbit, utilizing aerodynamic forces instead of propulsion. Since NASA’s inception in 1958, the agency has relied heavily on retro-propulsion (rockets) and rigid heat shields to decelerate people, vehicles, and hardware during orbital entry, descent, and landing (EDL) operations. — After more than a decade of development of the Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technology, including two suborbital flight tests, the LOFTID orbital flight test is the next logical step. Return from orbit provides an entry environment relevant to many potential applications, paving the way for its use on future missions. 3) 4)
HIAD technology can enhance, and even enable, larger missions to higher elevations at Mars. It can also be applied at Earth, providing capability for International Space Station (ISS) down-mass, or even enabling return for free-flying orbital manufacturing. Recovery of spent launch vehicle assets for reuse, such as ULA’s plan to recover their first stage booster, can reduce the overall cost of access to space.
Enabling Mass Efficient and Cost Effective Payload Delivery Solutions
For destinations with a sensible atmosphere, aerodynamics (specifically atmospheric drag) provides the most mass-effective way to decelerate a payload to a soft landing, or capture it into orbit. Larger aerodynamic decelerators, or aeroshells, provide more drag force, and therefore allow larger masses to be delivered to any elevation. HIAD overcomes packaging limitations of current rigid systems by utilizing inflatable soft-goods materials that can be stowed within the launch vehicle shroud. The aeroshell is deployed outside the atmosphere prior to atmospheric entry. HIAD technology enables a lower mass solution for slowing a spacecraft during EDL. Ultimately, increased payload mass fraction means cost savings.
Vehicles entering an atmosphere from outer space are traveling so fast that they create a high-energy pressure wave. This pressure wave entraps and rapidly compresses atmospheric gases, resulting in drag forces that decelerate the vehicle coupled with intense thermal loads that heat its surface. The HIAD design consists of an inflatable structure that maintains the aeroshell shape against the drag forces, and a protective FTPS (Flexible Thermal Protection System) that withstands the thermal loading. The term “flexible” refers to the FTPS being foldable, packable, deployable, and tailorable as opposed to being stretchable.
Normally, soft-goods materials would not be considered for the loads and environments that a spacecraft would encounter during atmospheric entry. Materials advancement is the key. The inflatable structure is constructed with a stack of pressurized concentric tubes, or tori, that are strapped together to form an exceptionally strong blunt cone-shaped structure. The tori are constructed from braided synthetic fibers that are 15 times stronger than steel. While the inflatable structure has the capability to withstand temperatures beyond 400 ºC, the HIAD relies on the FTPS to survive entry temperatures.
The FTPS, which covers the inflatable structure and insulates it from the searing heat of atmospheric entry, can be separated into three functional layers: an exterior ceramic fiber cloth layer that can maintain integrity at surface temperatures in excess of 1600º C, protecting the underlying plies from the aerodynamic shear forces; a middle layer of high temperature insulators that inhibit heat transmission; and an interior impermeable gas barrier layer that prevents hot gas from reaching the inflatable structure.
The LOFTID Reentry Vehicle (RV) is a secondary payload hosted on an Atlas V launch vehicle, and will be delivered to its reentry state by the Centaur, the Atlas V second stage. The RV is stowed within a primary payload adapter on the Centaur, such that the primary payload adapter can be released and separated to expose the stowed aeroshell for deployment while the RV is attached to the Centaur. The RV is inactive and powered off during the launch and delivery of the primary payload. After the primary payload has been delivered to orbit, the Centaur performs a deorbit burn to reenter the Earth’s atmosphere. After the payload adaptor is jettisoned, the RV is then powered on, the packing restraint is released, and the aeroshell inflation is initiated. The inflation system begins a “soft start” and then full inflation, delivering nitrogen inflation gas from pressurized tanks provided by ULA.
When the aeroshell is fully inflated, the Centaur attitude control system spins up the spacecraft and performs a final pointing adjustment before releasing the RV on its spin-stabilized reentry trajectory. The Centaur then performs a divert maneuver to avoid re-contact with the RV as the Centaur burns up on reentry.
The RV reenters the atmosphere on the prescribed trajectory, and decelerates from hypersonic down to subsonic flight. Throughout the RV flight, a real-time beacon transmits minimal data packets to a satellite network, while data from instrumentation, cameras, and other subsystems is acquired and processed, sending duplicate comprehensive data to both an Internal Data Recorder (IDR) and an Ejectable Data Recorder (EDR). After reentry, the RV ejects the EDR, which is buoyant and provides a GPS locator signal for physical recovery from the ocean surface. As a secondary means of recovery provided by ULA, the RV deploys a parachute to enable a soft splash down and boat retrieval of the RV from the ocean surface.
• Orbital reentry flight demonstration of advanced inflatable aeroshell
• Validates structural and thermal performance against mission relevant flight conditions
• Largest blunt body atmospheric entry ever, 6m diameter.
• Able to withstand temperatures in excess of 1600ºC (2900ºF).
Table 1: Mission specifics
• July 1, 2019: An inflatable decelerator technology that could one day help humans land on Mars will fly on the same Atlas V rocket as the JPSS-2 (Joint Polar Satellite System) satellite. 5)
- The Apollo lunar landers fired retro rockets to land humans on the Moon. The space shuttle relied on drag from the atmosphere to act like a brake during re-entry to Earth. But firing rockets requires hauling lots of fuel. And the Martian atmosphere, which is roughly 100 times thinner than our own, is too thin to produce enough drag to slow a spacecraft as easily as we can on Earth.
- The 2,000-pound Curiosity Rover, which landed on Mars in 2012, is the biggest thing we’ve ever sent to the Red Planet, and close to the weight limit for existing deceleration technology.
- “Right now, heat shields are rigid, and the maximum size is constrained by the size of the launch vehicle,” said Barry Bryant, project manager for LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) at NASA/LaRC (Langley Research Center).
- Delivering humans and their cargo to Mars will require much bigger payloads. Humans need lots of food, water, air, insulation, radiation protection and life support systems - rovers don't.
- “To take humans to Mars, we have to deliver a small house,” said Neil Cheatwood, senior engineer for planetary entry, descent and landing at NASA’s Langley Research Center. “You need an aeroshell much larger than you can fit inside a rocket.”
- But in order to one day deliver that payload, engineers need to first demonstrate that the decelerator can survive the incredible heat and speeds of reentry.
- Enter LOFTID, a partnership between NASA’s Space Technology Mission Directorate and United Launch Alliance. It’s the latest step in a kind of technology known as HIAD (Hypersonic Inflatable Aerodynamic Decelerator).
Figure 3: LOFTID is the next flight mission of the HIAD (inflatable heat shields) technology. HIAD is on the cutting-edge cusp of heat shields and NASA Langley researchers recently tested the LOFTID HIAD by doing a blow down test to measure gas intake (video credit: NASA)
Figure 4: Engineers prepare for the flexible heat shield installation on the inflatable structure. The view is from the bottom side, the heat shield is on top. The gold straps hanging from the black triangles will be attached to the inflatable structure strapping and tensioned (image credit: NASA/LaRC)
- LOFTID will fly as a rideshare with the JPSS-2 polar-orbiting satellite of NOAA in March 2022.
- This flight will not carry a payload, but will test the vehicle’s ability to survive re-entry to Earth from space, produce the desired atmospheric drag and, Cheatwood said, “exhibit adequate aerodynamic stability to keep us pointed forward and not just come in tumbling.”
- JPSS-2, to be renamed NOAA-21 after entering orbit, is a continuation of the Joint Polar Satellite System series of satellites, which provide data that inform seven-day forecasts and extreme weather events. Instruments from the JPSS satellites also tell us about wildfires, volcanoes, atmospheric ozone, ice loss and ocean health.
- “Our JPSS-2 mission is literally focused on the Earth,” said Greg Mandt, director of the JPSS Program. “To think that we could share some of the excess capacity from our Atlas launch vehicle to test technologies that will support human exploration of Mars is a tremendous bonus.”
- LOFTID will get folded and packed down tight during launch and then inflated just before re-entry. The inflatable structure is made of synthetic fibers, braided into tubes that are 15 times stronger than steel. The tubes are coiled so that when they’re inflated, they form the shape of a blunt cone. The thermal protection system that covers the inflatable structure is designed to survive searing entry temperatures and able to withstand 1600ºC. The aeroshell built for the flight demonstration will reach 6 m in diameter when deployed, nearly five times its size when stowed and the length of a mini school bus. Engineers believe it can be scaled up to accommodate large payloads.
Figure 5: Artist rendering of the LOFTID aeroshell and payload. For this flight experiment, the payload consists of the inflation system (large green tanks), instrumentation throughout the flexible heat shield and inflatable structure, data handling, internal data recorder, ejectable data recorder and parachute( image credit: NASA/LaRC)
- “If you look at fuel efficient cars, they’re streamlined to minimize drag,” said Cheatwood, who is also the principal investigator for LOFTID. “Part of their efficiency is coming from low mass, and part is the aerodynamic shape. We’re looking for the opposite. We want to maximize the drag.”
- After the JPSS-2 satellite is delivered to its orbit, the Centaur, the rocket’s second stage, will do a deorbit maneuver to a lower orbit. The Centaur will point the LOFTID vehicle toward its desired atmospheric entry point and allow the aeroshell to inflate. The Centaur then will spin the vehicle up to give it gyroscopic stability, eject it, and then perform a divert maneuver. As LOFTID reenters the Earth's atmosphere, it will slow from hypersonic to subsonic speeds, deploy a parachute and then land, likely in the Pacific Ocean near Hawaii. It is expected to reach speeds as fast as 8 km/s.
- Getting humans to the surface of Mars is just one of many possible applications for LOFTID. United Launch Alliance is interested in its potential to recover booster engines after launch. The technology could also be used to haul equipment back from the International Space Station or to return materials like fiber optic cables manufactured in space.
- “ULA is excited to work with NOAA and NASA to demonstrate this critical technology,” said Michael Holguin, senior program manager for the LOFTID mission for United Launch Alliance. “Not only for recovery of engines for the Vulcan Centaur program engine reuse, but also for the entire space program, re-entry of space vehicles to Earth as well as other planetary bodies.”
1) ”Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID),” NASA, June 25, 2019, URL: https://www.nasa.gov/mission_pages/tdm/loftid/index.html
R. A. Dillman, J. M. DiNonno, R. J. Bodkin, S. J. Hughes, F. M.
Cheatwood, H. Blakeley, R. L. Akamine, & A. Bowes, ”Planned
Orbital Flight Test of a 6m HIAD,” 2018 International Planetary
Probe Workshop Boulder, Colorado, USA, June 11-15, 2018, URL: https://www.colorado.edu/event/ippw2018/sites/default/files
3) ”Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID),” NASA Fact Sheet, June 2019, URL: https://www.nasa.gov/sites/default/files/atoms/files/loftid_fact_sheet_june2019.pdf
4) Stephen J. Hughes, Dr. F. McNeil Cheatwood, Dr. Anthony M. Calomino, Henry S. Wright, Mary Elizabeth Wusk and Monica F. Hughes, ”Hypersonic Inflatable Aerodynamic Decelerator (HIAD) Technology Development Overview,” NASA, URL: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130013167.pdf
Marder , ”Inflatable Decelerator Will Hitch a Ride on the JPSS-2
Satellite,” NASA Feature, 01 July 2019, URL: https://www.nasa.gov/feature/goddard/2019
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).