Ever since the beginning of the Space Age, the inner planets and the Earth-Moon system have received the lion’s share of attention. That makes sense; it’s a whole lot easier to get to the Moon, or even to Mars, than it is to get to Saturn or Neptune. And so our probes have mostly plied the relatively cozy confines inside the asteroid belt, visiting every world within them and sometimes landing on the surface and making a few holes or even leaving some footprints.
But there’s still one place within this warm and familiar neighborhood that remains mysterious and relatively unvisited: the Sun. That seems strange, since our star is the source of all energy for our world and the system in general, and its constant emissions across the electromagnetic spectrum and its occasional physical outbursts are literally a matter of life and death for us. When the Sun sneezes, we can get sick, and it has the potential to be far worse than just a cold.
While we’ve had a succession of satellites over the last decades that have specialized in watching the Sun, it’s not the easiest celestial body to observe. Most spacecraft go to great lengths to avoid the Sun’s abuse, and building anything to withstand the lashing our star can dish out is a tough task. But there’s one satellite that takes everything that the Sun dishes out and turns it into a near-constant stream of high-quality data, and it’s been doing it for almost 15 years now. The Solar Dynamics Observatory, or SDO, has also provided stunning images of the Sun, like this CGI-like sequence of a failed solar eruption. Images like that have captured imaginations during this surprisingly active solar cycle, and emphasized the importance of SDO in our solar early warning system.
When I was a kid, the solar system was simple. There were nine planets and they all orbited in more-or-less circles around the sun. This same sun-and-a-handful-of-planets scheme repeated itself again and again throughout our galaxy, and these galaxies make up the universe. It’s a great story that’s easy to wrap your mind around, and of course it’s a great first approximation, except maybe that “nine planets” thing, which was just a fluke that we’ll examine shortly.
What’s happened since, however, is that telescopes have gotten significantly better, and many more bodies of all sorts have been discovered in the solar system which is awesome. But as a casual astronomy observer, I’ve given up hope of holding on to a simple mental model. The solar system is just too weird.
Reaching orbit around Earth is an incredibly difficult feat. It’s a common misconception that getting into orbit just involves getting very high above the ground — the real trick is going sideways very, very fast. Thus far, the most viable way we’ve found to do this is with big, complicated multi-stage rockets that shed bits of themselves as they roar out of the atmosphere.
Single-stage-to-orbit (SSTO) launch vehicles represent a revolutionary step in space travel. They promise a simpler, more cost-effective way to reach orbit compared to traditional multi-stage rockets. Today, we’ll explore the incredible potential offered by SSTO vehicles, and why building a practical example is all but impossible with our current technology.
A Balancing Act
The SSTO concept doesn’t describe any one single spacecraft design. Instead, it refers to any spacecraft that’s capable of achieving orbit using a single, unified propulsion system and without jettisoning any part of the vehicle.
The Saturn V shed multiple stages on its way up to orbit. That way, less fuel was needed to propel the final stage up to orbital velocity. Credit: NASA
Today’s orbital rockets shed stages as they expend fuel. There’s one major reason for this, and it’s referred to as the tyranny of the rocket equation. Fundamentally, a spacecraft needs to reach a certain velocity to attain orbit. Reaching that velocity from zero — i.e. when the rocket is sitting on the launchpad — requires a change in velocity, or delta-V. The rocket equation can be used to figure out how much fuel is required for a certain delta-V, and thus a desired orbit.
The problem is that the mass of fuel required scales exponentially with delta-V. If you want to go faster, you need more fuel. But then you need even more fuel again to carry the weight of that fuel, and so on. Plus, all that fuel needs a tank and structure to hold it, which makes things more difficult again.
Work out the maths of a potential SSTO design, and the required fuel to reach orbit ends up taking up almost all of the launch vehicle’s weight. There’s precious mass left over for the vehicle’s own structure, let alone any useful payload. This all comes down to the “mass fraction” of the rocket. A SSTO powered by even our most efficient chemical rocket engines would require that the vast majority of its mass be dedicated to propellants, with its structure and payload being tiny in comparison. Much of that is due to Earth’s nature. Our planet has a strong gravitational pull, and the minimum orbital velocity is quite high at about 7.4 kilometers per second or so.
Stage Fright
Historically, we’ve cheated the rocket equation through smart engineering. The trick with staged rockets is simple. They shed structure as the fuel burns away. There’s no need to keep hauling empty fuel tanks into orbit. By dropping empty tanks during flight, the remaining fuel on the rocket has to accelerate a smaller mass, and thus less fuel is required to get the final rocket and payload into its intended orbit.
The Space Shuttle sheds its boosters and external fuel tank on its way up to orbit, too. Credit: NASA
So far, staged rockets have been the only way for humanity to reach orbit. Saturn V had five stages, more modern rockets tend to have two or three. Even the Space Shuttle was a staged design: it shed its two booster rockets when they were empty, and did the same with its external liquid fuel tank.
But while staged launch vehicles can get the job done, it’s a wasteful way to fly. Imagine if every commercial flight required you to throw away three quarters of the airplane. While we’re learning to reuse discarded parts of orbital rockets, it’s still a difficult and costly exercise.
The core benefit of a SSTO launch vehicle would be its efficiency. By eliminating the need to discard stages during ascent, SSTO vehicles would reduce launch costs, streamline operations, and potentially increase the frequency of space missions.
Pushing the Envelope
It’s currently believed that building a SSTO vehicle using conventional chemical rocket technology is marginally possible. You’d need efficient rocket engines burning the right fuel, and a light rocket with almost no payload, but theoretically it could be done.
Ideally, though, you’d want a single-stage launch vehicle that could actually reach orbit with some useful payload. Be that a satellite, human astronauts, or some kind of science package. To date there have been several projects and proposals for SSTO launch vehicles, none of which have succeeded so far.
Lockheed explored a spaceplane concept called VentureStar, but it never came to fruition. Credit: NASA
One notable design was the proposed Skylon spacecraft from British company Reaction Engines Limited. Skylon was intended to operate as a reusable spaceplane fueled by hydrogen. It would take off from a runway, using wings to generate lift to help it to ascend to 85,000 feet. This improves fuel efficiency versus just pointing the launch vehicle straight up and fighting gravity with pure thrust alone. Plus, it would burn oxygen from the atmosphere on its way to that altitude, negating the need to carry heavy supplies of oxygen onboard.
Once at the appropriate altitude, it would switch to internal liquid oxygen tanks for the final acceleration phase up to orbital velocity. The design stretches back decades, to the earlier British HOTOL spaceplane project. Work continues on the proposed SABRE engine (Syngergetic Air-Breathing Rocket Engine) that would theoretically propel Skylon, though no concrete plans to build the spaceplane itself exist.
The hope was that efficient aerospike rocket engines would let the VentureStar reach orbit in a single stage.
Lockheed Martin also had the VentureStar spaceplane concept, which used an innovative “aerospike” rocket engine that maintained excellent efficiency across a wide altitude range. The company even built a scaled-down test craft called the X-33 to explore the ideas behind it. However, the program saw its funding slashed in the early 2000s, and development was halted.
McDonnell Douglas also had a crack at the idea in the early 1990s. The DC-X, also known as the Delta Clipper, was a prototype vertical takeoff and landing vehicle. At just 12 meters high and 4.1 meters in diameter, it was a one-third scale prototype for exploring SSTO-related technologies
It would take off vertically like a traditional rocket, and return to Earth nose-first before landing on its tail. The hope was that the combination of single-stage operation and this mission profile would provide extremely quick turnaround times for repeat launches, which was seen as a boon for potential military applications. While its technologies showed some promise, the project was eventually discontinued when a test vehicle caught fire after NASA took over the project.
McDonnell Douglas explored SSTO technologies with the Delta Clipper. Credit: Public domain
Ultimately, a viable SSTO launch vehicle that can carry a payload will likely be very different from the rockets we use today. Relying on wings to generate lift could help save fuel, and relying on air in the atmosphere would slash the weight of oxidizer that would have to be carried onboard.
However, it’s not as simple as just penning a spaceplane with an air-breathing engine and calling it done. No air breathing engine that exists can reach orbital velocity, so such a craft would need an additional rocket engine too, adding weight. Plus, it’s worth noting a reusable launch vehicle would also still require plenty of heat shielding to survive reentry. One could potentially build a non-reusable single-stage to orbit vehicle that simply stays in space, of course, but that would negate many of the tantalizing benefits of the whole concept.
Single-stage-to-orbit vehicles hold the promise of transforming how we access space by simplifying the architecture of launch vehicles and potentially reducing costs. While there are formidable technical hurdles to overcome, the ongoing advances in aerospace technology provide hope that SSTO could become a practical reality in the future. As technology marches forward in materials, rocketry, and aerospace engineering in general, the dream of a single-stage path to orbit remains a tantalizing future goal.
Since the dawn of the industrial revolution, humans have been searching for more energy. Especially lately, there has been a huge interest in wind, solar, geothermal, and other ways to capture and harness power. However, we have a huge power plant just eight light minutes away: our sun. Oh sure, we toy with solar power, but the amount of sunlight hitting the Earth or even Earth orbit is a tiny fraction of Sol’s total output. But what if you could capture nearly all of the sun’s output? Scientists think that maybe — just maybe — they’ve detected 60 new extraterrestrial civilizations doing just that. At least, that’s what it could be.
[Freeman Dyson] popularized the idea of a Dyson sphere, an artificial sphere surrounding a sun to capture the maximum amount of energy, back in 1960. However, the idea is older and usually credited to [Olaf Stapledon]’s 1937 novel Star Maker. While most people think the sphere would be solid, [Dyson] himself thought it would be a swarm of disjointed collectors owing to the difficulty in creating a solid shell of the required size.
Both SETI and Fermilab have searched for what is thought to be telltale infrared radiation that scientists think would emanate from a star surrounded by spheres or swarms. Several have been located, but there is no conclusive evidence.
The new 60 were identified by analyzing data from the Gaia satellite. Again, the evidence is not conclusive, but small and dim stars that are very bright in infrared can’t be explained by conventional explanations. One way to explain at least some of the stars would be if about 16% of the star was obscured by something like a swarm of Dyson sphere collectors.
There are, of course, more jejune explanations possible. For example, the star might happen to be in front of some more distant IR source. Still, it is tantalizing to think there may be more than 60 high-tech civilizations out there either waiting to meet us or, perhaps, waiting to eat us, depending on how paranoid you are.
There have been all kinds of wild ideas to get spacecraft into orbit. Everything from firing huge cannons to spinning craft at rapid speed has been posited, explored, or in some cases, even tested to some degree. And yet, good ol’ flaming rockets continue to dominate all, because they actually get the job done.
Rockets, fuel, and all their supporting infrastructure remain expensive, so the search for an alternative goes on. One daring idea involves using airships to loft payloads into orbit. What if you could simply float up into space?
[Jon Petter Skagmo] claims that the spaceship simulator he’s working on is for his daughter, but we think there’s an excellent chance he’s looking to fulfill a few childhood dreams of his own. But no matter what generation ends up getting the most enjoyment out of it, there’s no question it’s an impressive build so far, complete with a very realistic-looking instrument display and joystick.
This is only the first in a series of builds, but our inner child is already intensely jealous. So far, [Jon] has built the instrument panel and controller that lights all buttons and runs the displays, which shows telemetry from a Falcon 9 launch. The video below goes into a lot of detail about how he built this SPI-driven instrument panel and why he made the whole thing modular, so it can be easily expanded without turning into a spaghetti-like mess.
It’s a great intro to thinking before you build, showing how he planned and built the system for maximum expandability and flexibility. Before the end, we wouldn’t surprised if he’s got quite a Kerbal Space Program controller on his hands for when the kid goes to bed.
Once upon a time, when the earliest spy satellites were developed, there wasn’t an easy way to send high-quality image data over the air. The satellites would capture images on film and dump out cartridges back to earth with parachutes that would be recovered by military planes.
It all sounds so archaic, so Rube Goldberg, so 1957. And yet, it’s still a viable method for recovering big globs of data from high altitude missions today. Really, you ask? Oh, yes indeed—why, NASA’s gotten back into the habit just recently!
