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:
Earlier this week, the island nation of New Zealand accomplished a historic first. On Wednesday, May 24th at 16:20 p.m. NZST – 00:20 a.m. EDT; May 23rd, 21:20 p.m. PDT – the country joined the small club of nations that have space launch capability. Taking off from a launch pad located on the Mahia Peninsula (on the North Island), the test flight was also a first for the US/NZ-based company Rocket Lab.
With the successful launch of their test rocket, Rocket Lab has become the latest aerospace firm to join a burgeoning market, where private companies are able to provide regular launch services to Low-Earth Orbit (LEO). Whereas other companies like SpaceX are looking to restore domestic heavy-launch capability, companies like Rocket Lab are looking to fill a niche market which would make space more accessible.
The launch was originally pushed back to this past Wednesday, which was the fourth day in a ten-day launch window (running from May 21st to May 30th), due to bad weather. And while no spectators or media outlets were permitted to witness the event, the company recorded the launch and posted it to their website and official Twitter account (shown below).
Though the rocket did not quite reach orbit, it successfully flew along the trajectory that future launches will follow. This test launch was the first of three planned, and carried sensor equipment rather than a conventional payload in order to let engineers on the ground gather data on the flight. As chief executive Peter Beck said in a statement after the rocket took off from Rocket Lab’s Launch Complex 1:
“It was a great flight. We had a great first stage burn, stage separation, second stage ignition and fairing separation. We didn’t quite reach orbit and we’ll be investigating why, however reaching space in our first test puts us in an incredibly strong position to accelerate the commercial phase of our program, deliver our customers to orbit and make space open for business.”
The rocket in question was a prototype disposable vehicle known as the Electron rocket. This two-stage rocket is composed of carbon fiber, which allows for durability and reduced weight, and is manufactured in-house. It also relies on a “plug-in payload” design that allows for the separation of the main assembly and payload integration processes.
In short, in the future, customers will be able to load the payload fairing themselves at their own facilities. This is especially useful wherever environmentally-controlled or sealed cargo is involved. They will then be able to have the second stage transported to the Rocket Lab facility for integration. This design is also intended to allow for flexibility, where the launch vehicle can be tailored to meet specific mission requirements.
The first stage of the vehicle is powered by nine Rutherford engines – an oxygen/kerosene pump-fed engine designed and built by Rocket Lab – while the second stage is powered by a single Rutherford. In addition to reducing mass, the engine is also the first oxygen/kerosene engine to make use of 3-D printed components. Each engine offers a liftoff thrust of 18 kilo Newtons, or 4000 pound-force (lbf), and a peak thrust (in vacuum) of 22 kN (41,500 lbf).
Once testing is complete, Rocket Lab intends to maintain a fleet of these rockets, which will be capable of launching payloads of between 150 and 225 kg (330 to 496 lbs) to a 500 km Sun-synchronous orbit. With these parameters in mind, Rocket Lab is clearly aiming to cater to telecommunications companies, internet providers, research institutions and universities.
In short, small satellites are a fast-growing market, but the current space launch environment can be prohibitive to small companies and researchers. As it stands, booking a space launch is a complicated matter, subject to flight schedules, the availability of cargo space, and costs that are outside of many customers’ price range. By developing rockets that are relatively cheap and can be built quickly, those looking to launch small satellite will have increased options.
“We’re one of a few companies to ever develop a rocket from scratch and we did it in under four years. We’ve worked tirelessly to get to this point,” said Beck. “We’ve developed everything in house, built the world’s first private orbital launch range, and we’ve done it with a small team.
New Zealand was selected as the location of the company’s launch facility for a number of reasons. Compared to the US and other potential launch sites, New Zealand has less air traffic, which ensures that air carriers don’t need to reroute their flights during a launch. The country is also well-situated to get satellites into a north-to-south orbit around Earth, and launches take place over open water (away from population centers).
On top of that, Rocket Lab CEO and founder Peter Beck is a native of New Zealand. In the coming weeks, the company he founded will be looking over its test flight data to prepare for its second test launch, which will take place in a few months. This launch will attempt to reach orbit and maximize the payload the rocket can carry. All told, Rocket Lab has three test flights scheduled for 2017.
Once the company reaches full production, they hope to be conducting a record-setting 50 to 120 launches a year. If possible, this will significantly reduce the costs associated with small payload launches.
“We have learnt so much through this test launch and will learn even more in the weeks to come,” said Beck. “We’re committed to making space accessible and this is a phenomenal milestone in that journey. The applications doing this will open up are endless. Known applications include improved weather reporting, Internet from space, natural disaster prediction, up-to-date maritime data as well as search and rescue services.”
Rocket Lab is joined by companies like ARCA, which is seeking to lower the costs of small-payload launches through the development of single-stage-to-orbit (SSTO) rockets. Their SSTO rocket concept, known as the Haas 2CA, was unveiled in March and is scheduled to begin launch testing next year.
Be sure to check out this video of the launch as well, courtesy of Rocket Lab:
Is there a better way to get to space? Current traditional methods using expendable rockets launching from the surface of the Earth are terribly inefficient. About 90% of the bulk and mass of what you see on the launch pad is expended in the first few minutes of the mission, just getting the tiny payload above the murk of Earth’s atmosphere and out of the planet’s gravity well.
One idea that’s been out there for a while is to loft a launch platform into the upper atmosphere, and simply start from there. One Spanish-based company named Zero2infinity plans to do just that.
Recently, on May 20th, 2016, Zero2infinity lofted Aistech’s first satellite into the upper atmosphere, aboard its Sub-Orbital Platform in Near Space balloon system. Zero2infinity uses these Near Space balloons to carry client payloads up above 99% of the Earth’s atmosphere. This is a cheap and effective way to get payloads into a very space-like environment.
These near Space Balloon platforms typically reach an altitude of 28 kilometres (17 miles) above the surface of the Earth. For reference, the Armstrong Line (where the boiling point of water equals human body temperature) starts 18 kilometers up, and the Kármán line — the internationally recognized boundary where space begins — starts at an altitude of 100 kilometers, or 62 miles up.
Most satellites in Low Earth Orbit (LEO) go around the Earth 300 to 600 kilometers up, and the International Space Station resides in a 400 by 400 kilometer standard orbit.
The mission of Aistechsat-1 is to “provide thermal images of the Earth and also help with maritime and aeronautical tracking,” Zero2infinity representative Iris Silverio told Universe Today via email. Zero2infinity plans on conducting another balloon test with Aistechsat-1 later this month on an as yet to be announced date. The final decision all hinges on the weather and the wind speeds aloft.
Aistech envisions a constellation of 25 such nanosatellites encircling the planet.
Zero2infinity also has a grander vision: eventually launching satellites into Low Earth Orbit via balloon. Known as Bloostar, this system would loft a three stage rocket with the company’s existing and proven Near Space balloon technology. The ‘launch’ would occur high in the upper atmosphere, as the engines take over to get the payload into orbit.
The idea is certainly attractive. Dubbed a ‘shortcut to space,’ the three engine booster rings depicted are a fraction of the size of typical rocket stages. The toroid ring-shaped stages are simply nestled one inside the other, like Russian dolls. Zero2infinity also envisions scaling its ‘Bloon’ platform for micro and nano payloads… and I’ll bet that a Bloostar atmospheric launch will be an interesting spectacle to watch with binoculars from the ground, especially around dawn or dusk.
Another possible advantage includes a much more spacious payload nose cone, meaning no more folding of satellites for launch and unfolding them in orbit. More than a few payloads have suffered setbacks because of this, including the Galileo mission to Jupiter, whose main antenna failed to unfurl completely in 1990.
According to an email discussion with Zero2infinity representative Silverio, the first commercial Bloostar launch is set for 2019, with possible orbital trials starting as early as 2018. Bloostar deployments will occur off the coast of the Canary Islands in the Atlantic. The initial Bloostar launcher will deploy payloads up to 75 kilograms in a 600 kilometer orbit around the Earth.
Rise of the Rockoons
The idea of conducting launches via balloon, known as a ‘rockoon,’ has been around for a while. Thus far, only sub-orbital launches have been conducted in this manner.
The first balloon-based launch of a rocket occurred on August 9th, 1953, when a Deacon rockoon successfully carried out a sub-orbital launch high over the Atlantic Ocean. Though several companies have kicked around the idea of launching an orbital satellite via balloon-based platform, Zero2infinity might just be the first to actually accomplish it. The United States Department of Defense has considered the idea of launching satellites (and satellite-killing missiles) via the U.S. Air Force’s high flying F-15 Eagle aircraft. Orbital Sciences does currently use its Pegasus-XL rocket carried aloft by a L1011 aircraft to place satellites in orbit. That’s how NASA’s NuSTAR X-ray telescope got into space in 2012.
There is one main problem facing balloon-based space launches: weather. Unlike aircraft, balloons are often at the whims of the winds aloft, and sometimes stubbornly refuse to go where you want them to. Often, an orbital launch will need to target a precise azimuth heading, a tricky sort of pointing to do from underneath a balloon. Still, we’ve already seen precedent for overcoming this in the effective pointing of balloon-based telescopes, such as the BLAST telescope.
Bloostar might just provide an innovative and cost-effective way to head into orbit, very soon.
-Check out this 2014 article from Universe Today on Zero2Infinity.
If new rocket engines being developed by the European Space Agency (ESA) are successful, they could revolutionize rocket technology and change the way we get to space. The engine, called the Synergistic Air-Breathing Rocket Engine (SABRE), is designed to use atmospheric air in the early flight stages, before switching to conventional rocket mode for the final ascent to space. If all goes well, this new air-breathing rocket could be ready for test firings in about four years.
Conventional rockets have to carry an on-board oxidizer such as liquid oxygen, which is combined with fuel in the rocket’s combustion chamber. This means rockets can require in excess of 250 tons of liquid oxygen in order to function. Once this oxygen is consumed in the first stages, these used up stages are discarded, creating massive waste and expense. (Companies like SpaceX and Blue Origin are developing re-usable rockets to help circumvent this problem, but they’re still conventional rockets.)
Conventional rockets carry their own oxygen because its temperature and pressure can be controlled. This guarantees the performance of the rocket, but requires complicated systems to do so. SABRE will eliminate the need for carrying most on-board oxygen, but this is not easy to do.
SABRE’s challenge is to compress the atmospheric oxygen to about 140 atmospheres before introducing it into the engine’s combustion chambers. But compressing the oxygen to that degree raises its temperature so much that it would melt the engines. The solution to that is to cool the air with a pre-cooling heat exchanger, to the point where it’s almost a liquid. At that point, a turbine based on standard jet engine technology can compress the air to the required operating temperature.
This means that while SABRE is in Earth’s atmosphere, it uses air to burn its hydrogen fuel, rather than liquid oxygen. This gives it an 8 x improvement in propellant consumption. Once SABRE has reached about 25 km in altitude, where the air is thinner, it switches modes and operates as a standard rocket. By the time it switches modes, it’s already about 20% of the way into Earth orbit.
Like a lot of engineering challenges, understanding what needs to be done is not the hard part. Actually developing these technologies is extremely difficult, even though many people just assume engineers will be successful. The key for Reaction Engines Ltd, the company developing SABRE, is to develop the light weight heat exchangers at the heart of the engine.
Heat exchangers are common in industry, but these heat exchangers have to cool incoming air from 1000 Celsius to -150 Celsius in less than 1/100th of a second, and they have to do it while preventing frost from forming. They are extremely light, at about 100 times lighter than current technology, which will allow them to be used in aerospace for the first time. Some of the lightness factor of these new heat exchanges stems from the wall thickness of the tubing, which is less than 30 microns. That’s less than the thickness of a human hair.
Reaction Engines Limited says that these heat exchangers will have the same impact on aerospace propulsion systems that silicone chips had on computing.
A new funding agreement with the ESA will provide Reaction Engines with 10 million Euros for continued development of SABRE. This will add to the 50 million Pounds that the UK Space Agency has already contributed. That 50 million Pound investment was the result of a favorable viability review of SABRE that the ESA performed in 2010.
IN 2012, the pre-cooler and the heat exchangers were tested. After that came more R&D, including the development of altitude-compensating rocket nozzles, thrust chamber cooling, and air intakes.
Now that the feasibility of SABRE has been strengthened, Reaction Engines wants to build a ground demonstrator engine by 2020. If the continued development of SABRE goes well, and if testing by 2020 is successful, then these Air Breathing rocket engines will be in a position to truly revolutionize access to space.
In ESA’s words, “ESA are confident that a ground test of a sub-scale engine can be successfully performed to demonstrate the flight regime and cycle and will be a critical milestone in the development of this program and a major breakthrough in propulsion worldwide.”
While NASA has had a long and storied history of building and testing experimental aircraft – called X-planes — it has been almost a decade since the space agency has developed any new aircraft. But an initiative announced earlier this year as part of the new budget has NASA back designing, building and flying a new series of X-planes, with the goal of creating more “green” aviation technologies that can then be utilized by the aeronautics industry.
NASA unveiled the first plane in the new X series, an electric aircraft with 14 motors integrated into a new wing design. This experimental airplane has been designated the X-57, with the nickname of “Maxwell,” to honor James Clerk Maxwell, the 19th century Scottish physicist who did groundbreaking work in electromagnetism.
“With the return of piloted X-planes to NASA’s research capabilities – which is a key part of our 10-year-long New Aviation Horizons initiative – the general aviation-sized X-57 will take the first step in opening a new era of aviation,” said NASA Administrator Charlie Bolden, speaking at an annual forum of theAmerican Institute of Aeronautics and Astronautics (AIAA).
Other new X-plane designs include larger transport-scale aircraft that will use less fuel and create less noise, and a business-jet-sized supersonic vehicle that burns low carbon bio-fuels and generates only quiet sonic booms that people on the ground will barely hear. The main goals of the new X-planes will be to demonstrate how airliners can burn half the fuel, saving airline companies money, while generating 75 percent less pollution during each flight as compared to now. They’ll also be much quieter than today’s jets.
The X-57 Maxwell has newly designed long, skinny wings embedded with 14 electric motors – 12 on the leading edge for take offs and landings, and one larger motor on each wing tip for use while at cruise altitude. The idea is that distributing electric power across a number of motors integrated with an aircraft will result in a five-time reduction in the energy required for a private plane to cruise at 175 mph.
NASA’s first X-plane was the X-1, which in 1947 became the first airplane to fly faster than the speed of sound. It was flown by Chuck Yeager and was featured in the book and movie “The Right Stuff.” While many of the aircraft were well known — like the X-15 that became the fastest piloted aircraft of the X-plane program — other aircraft were developed clandestinely. Other experimental aircraft included research on lifting bodies and other wing designs or unique engines like the scramjet. Other experimental aircraft didn’t carry the “X” designation, like the Navy’s D-558-II Skyrocket, but was flown by Scott Crossfield in 1953 to become the first airplane to travel twice the speed of sound, or Mach 2.
“Dozens of X-planes of all shapes, sizes and purposes have followed – all of them contributing to our stature as the world’s leader in aviation and space technology,” said Jaiwon Shin, associate administrator for NASA’s Aeronautics Research Mission Directorate. “Planes like the X-57, and the others to come, will help us maintain that role.”
Here on Earth, we tend to take air resistance (aka. “drag”) for granted. We just assume that when we throw a ball, launch an aircraft, deorbit a spacecraft, or fire a bullet from a gun, that the act of it traveling through our atmosphere will naturally slow it down. But what is the reason for this? Just how is air able to slow an object down, whether it is in free-fall or in flight?
Because of our reliance on air travel, our enthusiasm for space exploration, and our love of sports and making things airborne (including ourselves), understanding air resistance is key to understanding physics, and an integral part of many scientific disciplines. As part of the subdiscipline known as fluid dynamics, it applies to fields of aerodynamics, hydrodynamics, astrophysics, and nuclear physics (to name a few).
By definition, air resistance describes the forces that are in opposition to the relative motion of an object as it passes through the air. These drag forces act opposite to the oncoming flow velocity, thus slowing the object down. Unlike other resistance forces, drag depends directly on velocity, since it is the component of the net aerodynamic force acting opposite to the direction of the movement.
Another way to put it would be to say that air resistance is the result of collisions of the object’s leading surface with air molecules. It can therefore be said that the two most common factors that have a direct effect upon the amount of air resistance are the speed of the object and the cross-sectional area of the object. Ergo, both increased speeds and cross-sectional areas will result in an increased amount of air resistance.
In terms of aerodynamics and flight, drag refers to both the forces acting opposite of thrust, as well as the forces working perpendicular to it (i.e. lift). In astrodynamics, atmospheric drag is both a positive and a negative force depending on the situation. It is both a drain on fuel and efficiency during lift-off and a fuel savings when a spacecraft is returning to Earth from orbit.
Calculating Air Resistance:
Air resistance is usually calculated using the “drag equation”, which determines the force experienced by an object moving through a fluid or gas at relatively large velocity. This can be expressed mathematically as:
In this equation, FD represents the drag force, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and CD is the the drag coefficient. The result is what is called “quadratic drag”. Once this is determined, calculating the amount of power needed to overcome the drag involves a similar process, which can be expressed mathematically as:
Here, Pd is the power needed to overcome the force of drag, Fd is the drag force, v is the velocity, p is the density of the fluid, v is the speed of the object relative to sound, A is the cross-section area, and Cd is the the drag coefficient. As it shows, power needs are the cube of the velocity, so if it takes 10 horsepower to go 80 kph, it will take 80 horsepower to go 160 kph. In short, a doubling of speed requires an application of eight times the amount of power.
Types of Air Resistance:
There are three main types of drag in aerodynamics – Lift Induced, Parasitic, and Wave. Each affects an objects ability to stay aloft as well as the power and fuel needed to keep it there. Lift induced (or just induced) drag occurs as the result of the creation of lift on a three-dimensional lifting body (wing or fuselage). It has two primary components: vortex drag and lift-induced viscous drag.
The vortices derive from the turbulent mixing of air of varying pressure on the upper and lower surfaces of the body. These are needed to create lift. As the lift increases, so does the lift-induced drag. For an aircraft this means that as the angle of attack and the lift coefficient increase to the point of stall, so does the lift-induced drag.
By contrast, parasitic drag is caused by moving a solid object through a fluid. This type of drag is made up of multiple components, which includes “form drag” and “skin friction drag”. In aviation, induced drag tends to be greater at lower speeds because a high angle of attack is required to maintain lift, so as speed increases this drag becomes much less, but parasitic drag increases because the fluid is flowing faster around protruding objects increasing friction. The combined overall drag curve is minimal at some airspeeds and will be at or close to its optimal efficiency.
Wave drag (compressibility drag) is created by the presence of a body moving at high speed through a compressible fluid. In aerodynamics, wave drag consists of multiple components depending on the speed regime of the flight. In transonic flight – at speeds of Mach 0.5 or greater, but still less than Mach 1.0 (aka. speed of sound) – wave drag is the result of local supersonic flow.
Supersonic flow occurs on bodies traveling well below the speed of sound, as the local speed of air on a body increases when it accelerates over the body. In short, aircraft flying at transonic speeds often incur wave drag as a result. This increases as the speed of the aircraft nears the sound barrier of Mach 1.0, before becoming a supersonic object.
In supersonic flight, wave drag is the result of oblique shockwaves formed at the leading and trailing edges of the body. In highly supersonic flows bow waves will form instead. At supersonic speeds, wave drag is commonly separated into two components, supersonic lift-dependent wave drag and supersonic volume-dependent wave drag.
Understanding the role air frictions plays with flight, knowing its mechanics, and knowing the kinds of power needed to overcome it, are all crucial when it comes to aerospace and space exploration. Knowing all this will also be critical when it comes time to explore other planets in our Solar System, and in other star systems altogether!
The invention of the rocket changed space science forever. The Universe could only be inspected from the surface of the Earth, with all that atmosphere in the way, until rockets were invented. And as far as the modern age of rocketry goes, it all started 90 years ago with Robert Goddard’s liquid-fuelled rocket.
Goddard was a dreamer. He envisioned rocket-powered spacecraft plying the solar system. Obviously, he passed away before interplanetary travel materialized, but his work on rocketry certainly laid the groundwork for that eventual achievement. The Goddard Space Flight Center is named after him, and it’s doubtful that any engineering or technology student in the world doesn’t know who he is.
Goddard’s first liquid-fuelled rocket was modest by today’s standards, of course. But he had to solve several technical challenges to achieve it, and his ability to solve these challenges led to not only this first flight, but to a total of 34 rocket flights in 15 years, from 1926 to 1941. His rockets reached the altitude of 2.6 km (1.6 miles) and speeds of 885 km/h (550 mph.) He also patented 214 inventions.
Goddard is considered the father of modern rocket science, but he is actually one of three men who are considered the main contributors to modern rocketry. Russian Konstantin Tsiolkovsky (1858-1935) and German Hermann Oberth (1894-1989) are the other founding fathers of modern rocketry.
Goddard didn’t invent rocketry, of course. The Chinese used rockets as far back as the 13th century, and rockets made appearances throughout history as weapons and fireworks. But Goddard’s success at liquid-fuelled rocketry, and the capabilities that came with it, is when rocketry really got off the ground. (Sorry.)
Nowadays, Goddard is understood to be a driven and highly-intelligent person, the type of person who is responsible for advancing science and technology. But back in his time, before he had successful flights, he and his ideas were ridiculed. Check out this criticism from the New York Times, January 13th, 1920:
“That Professor Goddard, with his ‘chair’ in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react — to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools.”
Stinging words, to be sure, but people who know anything about the history of science are familiar with this kind of condemnation of brilliant people, coming from those who lack vision.
Now of course, we have huge rockets. Great thundering beasts that lift enormous loads out of Earth’s gravity well. And we’re so accustomed to rocket launches now that they barely make news. But I always get a kick out of imagining what people like Goddard would feel if they were able to view a launch of one of today’s behemoths, like the Ariane 5. I’m sure his chest would swelled with pride, and he would be amazed at what people have accomplished.
But his vindication wouldn’t just come from the huge leaps we’ve made in rocket technology, and the huge rockets we now routinely launch. It would also come from this retraction, delivered decades too late but with class, by the New York Times, on July 17 1969, the day after Apollo 11 launched:
Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th Century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error.