The X-37B, the US Air Force’s experimental, Orbital Test Vehicle (OTV) has come back down to Earth after 780 days. It landed at the Kennedy Space Center Shuttle Landing Facility on Oct. 27, 2019, at 3:51 a.m. after breaking its own record for time in space. The X-37B has now spent 2,865 total days in orbit.
Currently, commercial air travel accounts for 4 to 9% of the anthropogenic greenhouse gases that contribute to climate change. What’s worse, airplane emissions are on the rise thanks to rising populations and the increasingly globalized nature of our economy. Hence why NASA has been pursuing the development of electric aircraft these past few decades.
Much like reusable spacecraft and infrastructure, electric aircraft are part of NASA’s pursuit to make aerospace cheaper, more efficient and less harmful to the environment. Their efforts bore fruit in the form of the X-57 Maxwell – the first all-electric experimental aircraft – which was recently delivered to the NASA Armstrong Flight Research Center (AFRC) in Edwards, California.
To the scientifically uninitiated, it might seem like a frivolous idea: That those slight, wispy clouds that trail behind jet aircraft at such high altitudes could contribute to climate change. But they do.
Scientists love to measure things, and when they measured these contrails, which is short for condensation trails, they found bad news. Though they look kind of beautiful and ephemeral on a summer day, they pack an oversize punch when it comes to their warming effect.
A dramatic week in space launcher politics has left NASA’s Space Launch System (SLS) with a vastly reduced launch manifesto and casts doubt on the prospects of future upgrades to the massive launch vehicle.
On Monday the White House’s budget request laid out the administration’s plans for NASA’s coming years. For SLS there were three significant changes.
The one drawback of these spacecraft was the fact that it still took two rocket boosters and a huge external fuel tank to put them into orbit. This is where the Synergetic Air Breathing Rocket Engine (SABRE) comes into play. With the help of the European Space Agency (ESA) and the UK Space Agency (UKSA), this revolutionary hypersonic engine recently took a big step towards fruition.
After more than 10 years of hard work, NASA has reached another milestone. We’re accustomed to NASA reaching milestones, but this one’s a little different. This one’s all about a type of photography that captures images of the flow of fluids.
When Elon Musk of SpaceX tweets something interesting, it generates a wave of excitement. So when he tweeted recently that SpaceX might be working on a way to retrieve upper stages of their rockets, it set off a chain of intrigued responses.
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon
SpaceX has been retrieving and reusing their lower stages for some time now, and it’s lowered the cost of launching payloads into space. But this is the first hint that they may try to do the same with upper stages.
Twitter responders wanted to know exactly what SpaceX has in mind, and what a “giant party balloon” might be. Musk hasn’t elaborated yet, but one of his Twitter followers had something interesting to add.
If you're proposing what I think you are, an ultra low ballistic entry coefficient decelerator, then you and @SpaceX should come see what we have at the @UofMaryland . We've been working on this for awhile and just finished some testing pic.twitter.com/nJBvyUnzaK
Universe Today contacted Mr. Kupec to see if he could help us understand what Musk may have been getting at. But first, a little background.
An “ultra low ballistic entry coefficient decelerator” is a bit of a mouthful. The ballistic coefficient measures how well a vehicle can overcome air resistance in flight. A high ballistic coefficient means a re-entry vehicle would not lose velocity quickly, and would reach Earth at high speeds. An ultra low ballistic entry coefficient decelerator would lose speed quickly, meaning that a vehicle would be travelling at low, subsonic speeds before reaching the ground.
To recover an upper stage booster, low speeds are desirable, since they generate less heat. But according to Kupec, there’s another problem that must be overcome.
“What happens when these things slow down to landing velocities? If your center of gravity is offset significantly behind your center of drag, as would be the case with a returning upper stage, it can get unstable. If the center of gravity of the re-entry vehicle is too high, it can become inverted, which is obviously not desirable.”
So the trick is to lower the speed of the re-entry vehicle to the point where the heat generated by reentry isn’t damaging the booster, and to do it without causing the vehicle to invert or otherwise become unstable. This isn’t a problem for the main stage boosters that SpaceX now routinely recovers; they have their own retro-rockets to guide their descent and landing. But for the upper stage boosters, which reach orbital velocities, it’s an obstacle that has to be overcome.
“My research is specifically focused on how high you can push the center of gravity and still maintain the proper flight configuration,” said Kupec.
But what about the “giant party balloon” that Musk tweeted about?
Musk could be referring, in colorful terms, to what’s called a ballute. The word is a combination of the words balloon and parachute. They were invented in the 1950’s by Goodyear Aerospace. They can arrest the descent of entry vehicles and provide stability during the descent.
“…the balloon would have to be 120 ft. in diameter, and made of a high-temperature fabric…” – Professor Dave Akin, University of Maryland
Universe Today contacted Professor Dave Akin of the University of Maryland for some insight into Musk’s tweet. Professor Akin has been working on reentry systems for over 2 decades.
In an e-mail exchange, Professor Akin told us, “There have been concepts proposed for deploying a large balloon on a cable that is towed behind you on entry. The balloon lowers your ballistic coefficient, which means you decelerate higher in the atmosphere and the heat load is less.” So the key is to scrub your speed before you get closer to Earth, where the atmosphere is thicker and generates more heat.
But according to Professor Akin, this won’t necessarily be easy to do. “To get the two orders of magnitude reduction in ballistic coefficient that Elon has been talking about the balloon would have to be 120 ft. in diameter, and made of a high-temperature fabric, so it’s not going to be all that easy.”
But Musk’s track record shows he doesn’t shy away from things that aren’t easy.
Retrieving upper rocket stages isn’t all about lowering launch costs, it’s also about space junk. The European Space Agency estimates that there are over 29,000 pieces of space junk orbiting Earth, and some of that junk is spent upper stage boosters. There have been some collisions and accidents already, with some satellites being pushed into different orbits. In 2009, the Iridium 33 communications satellite and the defunct Russian Cosmos 2251 communications satellite collided with each other, destroying both. If SpaceX can develop a way to retrieve its upper stage boosters, that means less space junk, and fewer potential collisions.
There’s a clear precedent for using balloons to manage reentry. With people like Professor Akin and Quinn Kupec working on it, SpaceX won’t have to reinvent the wheel. But they’ll still have a lot of work to do.
Musk tweeted one other thing shortly after his “giant party balloon” tweet:
One of the technological hurdles of our age is to get people and equipment into space more cheaply. SpaceX gets a lot of the headlines around that, with their reusable rockets. And so does Blue Origin, to some degree. Now a small start-up affiliated with Purdue University is tackling the problem and making some headway.
The company is called Leo Aerospace LLC and they’re using balloons to lower the cost of putting micro-satellites into orbit, rather than reusable rockets. The balloons will be reusable, but the rockets won’t.
Leo Aerospace plans to revive a decades-old method of putting satellites into space. They’re using hot air balloons to lift the rocket and its micro-satellite payload 18 km (11 miles) above Earth. At that altitude, there’s 95% less atmosphere. This means much less drag on the rocket, which translates into smaller rockets with less fuel. This is an intriguing idea, if not for the unfortunate name.
The rockoons will be used to launch rockets into sub-orbital and orbital flights. Sub-orbitals are often used by researchers because it gives them access to zero gravity and to vacuum, both of which are necessary for some experiments. According to Leo Aerospace, there’s something revolutionary about their plans.
“We’re targeting the microsatellites by saying, ‘You don’t have to ride-share with anyone. We can guarantee you will be our only payload and we will be focused on you.’” – Drew Sherman, Leo Aerospace’s Head of Vehicle Development.
They intend on targeting micro-satellite developers. Micro-satellites are often hitch-hikers on larger payloads, which basically means they’re second-class customers. They have to wait until there’s room for their micro-satellite on a traditional rocket carrying a larger payload. This can mean long delays of several months, and that micro-satellite developers have to compromise when it comes to the orbits they can obtain. It can also make micro-satellite missions difficult to plan and execute efficiently and economically. Micro-satellites are becoming more and more capable, so having a launch system tailor-made for them could indeed be revolutionary.
“We’re targeting the microsatellites by saying, ‘You don’t have to ride-share with anyone. We can guarantee you will be our only payload and we will be focused on you,’” said Drew Sherman, Leo Aerospace’s head of vehicle development. “‘We will work with you exclusively to get you into orbit. You won’t have to worry about other payloads or getting dropped off in the wrong spot.’”
The flexibility of the rockoon system that Leo Aerospace is developing will be intriguing for micro-satellites. Rockoons will give micro-satellites the flexibility they need to operate efficiently. The launch can be scheduled and adapted to the needs of the individual satellite. “Our goal is to give people access to space. The only way to do that right now is to help people get their satellite into orbit. That’s where we want to leave our mark,” said Abishek Murali, Head of Mission Engineering at Leo Aerospace.
“Our goal is to give people access to space.” – Abishek Murali, Head of Mission Engineering at Leo Aerospace
The rockoon itself is a hybrid of a balloon and a rocket. The hybrid design takes advantage of physics by using the balloon to float the rocket 18 km high before launching the rocket. The rockoon has Leo Aerospace’s own patent-pending technology to control the pitch and angle of the launch, allowing for precision launches.
Rockoons were first used by the US Air Force back in the 1950s. But this next generation of rockoons, coupled with modern micro-satellites, will be much more capable than the 1950s technology.
Currently, Leo Aerospace is in the development and funding phase. They’ve obtained some funding from the National Science Foundation, and from a venture capital firm. They have about half of the $250,000 they need. They plan to conduct their first sub-orbital flight in 2020, and to launch their first micro-satellite into orbit in 2022. They intend to use existing approved launch sites.
Leo Aerospace was founded by five then-students at Purdue University. Leo started as a club, but the former students have turned it into a business. And that business seems to have a bright future. They conducted a customer discovery and market validation study and found a large demand for a better way to launch micro-satellites.
“We want to be part of the space market,” Murali said. “People are interested in space and creating technologies that not only can operate in space but also help people back on Earth. What we’re trying to do is help them get there.”
But they still need a better name than “rockoons.”
NASA has a lot of experience when it comes to developing supersonic aircraft. In fact, testing supersonic craft was how NASA got its start, back when it still known as the National Advisory Committee for Aeronautics (NACA). Beginning with the Bell X-1, the tradition of using X-planes and other experimental aircraft continues, and has progressed to hypersonic scramjets and spaceplanes (like the X-37).
And now, for the first time in decades, NASA is looking to develop a new supersonic aircraft. But whereas previous aircraft were developed for the sake of breaking speed records, the purpose of this latest X-plane is to create a Quiet Supersonic Transport (QueSST). NASA hopes that this craft will provide crucial data that could enable the development of commercial supersonic air travel over land.
To that end, NASA awarded a $247.5 million contract to Lockheed Martin Aeronautics Company on April 2nd to build the X-plane and deliver it to the agency’s Armstrong Flight Research Center in California by the end of 2021. As Jaiwon Shin, NASA’s associate administrator for aeronautics, indicated in a recent NASA press release, this project is like revisiting the old days of NASA research.
“It is super exciting to be back designing and flying X-planes at this scale,” he said. “Our long tradition of solving the technical barriers of supersonic flight to benefit everyone continues.”
In the past, supersonic commercial flights were available, for people who could afford them at least. These included the British-French Concorde (which operated until 2003) and the Russian Tupolev Tu-144 (retired in 1983). However, these craft were incapable of conducting supersonic flights over land because of how breaking the sound barrier would generate a sonic boom – which are extremely loud and potentially harmful.
As a result, current Federal Aviation Administration (FAA) regulations ban supersonic flight over land. The purpose of this latest aircraft – known as the Low-Boom Flight Demonstrator – is to conduct supersonic flights that create sonic booms that are so quiet, they will be virtually unnoticeable to people on the ground. The key is how the X-plane’s uniquely-shaped hull generates supersonic shockwaves.
With conventional aircraft designs, shockwaves coalesce as they expand away from the airplane’s nose and tail, resulting in two distinct sonic booms. In contrast, the X-plane’s hull design sends shockwaves away from the aircraft in a way that prevents them from coming together. Instead, much weaker shockwaves are sent to the ground that would be heard as a series of soft thumps.
Since the 1960s, NASA has been testing the idea using vehicles like the F-5E Tiger II fighter jet. This aircraft, which flew test flights in 2003-2004 as part of NASA’s Shaped Sonic Boom Demonstration program, had a uniquely-shaped nose and demonstrated that boom-reducing theory was sound. More recent flight testing, wind-tunnel testings, and advanced computer simulations tools have also indicated that the technology will work.
As Peter Coen, NASA’s Commercial Supersonic Technology project manager, stated:
“We’ve reached this important milestone only because of the work NASA has led with its many partners from other government agencies, the aerospace industry and forward-thinking academic institutions everywhere.”
The X-plane’s configuration will be based on a QueSST design that Lockheed Martin developed in 2016 in partnership with NASA, and which completed testing in a wind tunnel at NASA’s Glenn Research Center in 2017 . The proposed aircraft will measure 28.65 meters (94 feet) long, have a wingspan of about 9 meters (29.5 feet), and have a takeoff weight of 14,650 kg (32,300 lbs).
Based on the company’s design, the X-plane will be powered by a single General Electric F414 engine, the same used by F/A-18E/F fighters. It will be flown by a single pilot and have a top speed of Mach 1.5 (1590 km; 990 mph) and a speed of Mach 1.42 (1513 km; 940 mph) at a cruising altitude of 16764 meters (55,000 feet).
As Shin indicated, the development of the X-plan is a joint effort involving all of NASA’s aeronautics research centers:
“There are so many people at NASA who have put in their very best efforts to get us to this point. Thanks to their work so far and the work to come, we will be able to use this X-plane to generate the scientifically collected community response data critical to changing the current rules to transforming aviation!”
The program is divided into three phases which are tentatively scheduled to run from 2019 to 2025. Phase One, which will run from 2019 to 2021, will consist of a critical design review in preparation for construction. If successful, construction will begin at Lockheed Martin’s Skunk Work‘s facility in Palmdale, followed by a series of test flights and culminating with the delivery of the craft to NASA.
Phase Two, scheduled to begin in 2022, will consist of NASA flying the X-plane in the supersonic test range over Edwards Air Force Base in southern California to see if it is safe for operations in the National Airspace System. Phase Three, running from 2023 to 2025, will consist of the first community response test flights (staged from Armstrong Air Force Base) followed by further test flights over four to six U.S. cities.
The data gathered from these community response tests will then be delivered to the FAA and the International Civil Aviation Organization (ICAO) – currently targeted for delivery in 2025 – so they can adopt new rules based on perceived sound levels. If the Low-Boom Flight Demonstrator should prove to be effective, commercial supersonic flights over land may finally become feasible.
And be sure to enjoy this video of the X-plane’s development, courtesy of NASA: