The questions that youngsters ask about science aren’t at all times simple to reply. Sometimes, their little brains can result in huge locations that adults neglect to discover. That is what impressed our series Science Question From A Toddler, which makes use of youngsters’ curiosity as a jumping-off level to analyze the scientific wonders that adults don’t even assume to ask about. The solutions are for adults, however they wouldn’t be attainable with out the marvel that solely a toddler can convey. I would like the toddlers in your life to be part of it! Send me their science questions, and so they could function the inspiration for a column. And now, our toddler …
How many cups of sugar would it not take to get to the moon? — Jacob P., age four.5
I’m going to be upfront right here: I selected this specific query as a result of I assumed it will be sort of enjoyable to troll some rocket scientists. I figured that asking them this query could be like asking a bunch of engineers concerning the variety of cats that might be required to construct the Verrazano-Narrows Bridge.
So you may think about my shock when Mason Peck, a professor of mechanical and aerospace engineering at Cornell University, began cheerfully telling me concerning the sugar-based gasoline used to launch do-it-yourself rockets. “There are a number of newbie rocketry folks around the globe which can be thinking about wacky propellants,” Peck informed me. “Anything with some sort of hydrocarbon in it really works fairly properly. So clearly sugar would work. Pepperoni works, and it smells scrumptious by the best way.” Yes, seriously.
Rockets don’t fly on sugar (or pepperoni) alone, thoughts you. Instead, the sugar is mixed with potassium nitrate — a mineral substance that’s also used to preserve food and make gunpowder — to create a pliable mass that may be molded right into a form to suit the rocket earlier than it hardens. The sugar burns and offers the rocket its oomph, and the potassium nitrate feeds oxygen to the sugar that it must burn. If you’ve seen the film “October Sky,” then you definately’ve watched fictionalized variations of future NASA rocket scientists build exactly this kind of “candy” powered rocket. (Since studying that sugar actually is related to rocketry, we at FiveThirtyEight have begun to wonder if we’re, actually, those being trolled and Jacob P. is secretly a 45-year-old newbie rocketry fanatic.)
Regardless, this toddler’s query brings up some attention-grabbing points. So, since sugar can launch a rocket, may it truly ship an object to the moon? The reply to that query isn’t any, mentioned Katie Robinson, a postdoctoral fellow with the Lunar and Planetary Institute, a NASA-supported analysis heart in Houston. Or, reasonably, it’s so impractical as to grow to be functionally unimaginable. And the “why” behind that seems to be deeply related — each to latest advances in area science and our desires of interplanetary journey.
That’s as a result of we resolve how one can energy our rockets primarily based not solely on a gasoline’s means to burn, but additionally on how a lot of it’s wanted to speed up a rocket out of Earth’s ambiance. When we launch something off the floor of the Earth, the overwhelming majority of what we’re launching is the huge quantity of gasoline essential to create the pressure to interrupt the surly bonds of our planet’s robust gravitational discipline. “It’s grossly inefficient,” mentioned Richard Vondrak, a consulting scientist for lunar science and exploration in NASA’s photo voltaic system exploration division. “You’re accelerating a whole lot of gasoline, however burning it up within the course of.”
Consider the Apollo program, the NASA venture to place a person on the moon. When we despatched people from Earth to the moon, we launched them utilizing the Saturn V — a skyscraper doubling as a flamethrower that’s nonetheless the tallest, strongest rocket to ever fly. When we launched people from the moon to ship them again to Earth, alternatively, we did it with the lunar module — a scrappy little car that’s the useful (and close to literal) equal of a wart on Saturn V’s face. The distinction within the dimension of these two automobiles is the mandatory results of the distinction within the gravitational forces on Earth and the moon. Remember, the pressure of gravity on the moon is about one-sixth what it’s on Earth. Astronauts bounce there. Rocketships soar.
The nice misfortune of Earthling area journey is that we to have to start out our journey from Earth. It means we have to carry a whole lot of gasoline, which provides a whole lot of weight — and a whole lot of expense.. It costs about $10,000 to place one pound of payload — the folks, machines, objects and provides a rocket carries — into Earth’s orbit. For context, the biggest payload the space shuttle system ever carried was the 50,000-pound Chandra X-ray Observatory, in 1999. Vondrak estimates that it’s in all probability six instances dearer to ship one thing to the moon. “So a quart bottle of water is $60,000 — a greenback for the water and $60,000 for the transportation,” he mentioned.
Because of the expense, it’s necessary that any rocket gasoline we use to go away Earth pack as a lot punch-per-pound as it may well. And that’s why NASA doesn’t launch sugar rockets. Sugar may match advantageous for newbie rocketry, however in contrast with skilled rocket gasoline, it has a lot much less power in the identical quantity of area.
Robinson helpfully did the mathematics for me, evaluating the power in white sugar with the power within the liquid hydrogen and kerosene used within the Saturn V. There are a whole lot of other ways you could possibly calculate this, she informed me, relying on the assumptions you make about the best way the totally different fuels burn. But Robinson mentioned we’d want, oh, four,753,787 cups of sugar to launch the Saturn V to the moon. And as a result of that sugar doesn’t pack the identical energy-to-weight ratio punch as precise rocket gasoline, this hypothetical Saturn V must carry 285 metric tons extra gasoline than the true one. “Basically sugar has a whole lot of power, however it’s nonetheless a awful rocket gasoline,” Robinson informed me. “Liquid hydrogen is a extremely good rocket gasoline; it solely accounts for 13 p.c of the gasoline by mass on the Saturn V, however accounts for practically half the overall power produced when that gasoline is burned.”
Even with the suitable gasoline, long-distance area journey makes an already inefficient system even more so. Imagine attempting to blast off from Earth, journey to Mars, land, launch from there, and journey again once more. Now think about the additional weight and expense of carrying all of the gasoline crucial for that journey. And that’s why you hear about research into things like space elevators — a so-far-still-sci-fi system that might carry folks, components, and (sure) gasoline into Earth’s orbit by transferring a car alongside a tether between the planet and a geosynchronous area station. A area elevator wouldn’t want rockets, or rocket gasoline, and could be 100 p.c reusable. But, for now, there’s no materials robust sufficient to construct that sort of tether.
Instead, within the close to time period, our greatest guess for planet-hopping is to excellent a system that might permit us to make gasoline someplace aside from Earth. Once you will get your area gasoline in area, you wouldn’t must crush an Earth launch with further gasoline, after which all types of potentialities open up, Peck mentioned. Some concepts for the way to do that contain constructing spaceships that may create their very own gasoline on board. Peck is part of a team engaged on one among these tasks. The group’s rocket engine makes use of solar energy to create an electrical present that may separate a molecule of water into hydrogen and oxygen. Split from their H2O tangle, these parts burn very properly. In truth, the mixture of liquid hydrogen and oxygen is a standard alternative for rocket gasoline.
Peck’s group has developed a briefcase-sized craft that may fly on their engine. The catch: It has solely sufficient energy to fly in area, not launch by itself from Earth. He informed me that NASA has agreed to take it into orbit for a take a look at flight, although — in all probability someday within the subsequent couple of years. Even if it may well’t launch itself, a ship like this may make it extra possible and lots cheaper to traverse the photo voltaic system.
Another possibility, alongside the identical traces, could be to reap hydrogen and oxygen from one other object in area — the moon, as an example. Not very way back, Robinson mentioned, this may have sounded insane. When she was an undergrad — round 2007 — the thought of water on the moon was rejected out of hand. By the time she was engaged on her Ph.D., simply 4 years later, water on the moon was a proven fact. How simply this water might be was rocket gasoline is an open query, Robinson mentioned. Most of the tangled hydrogen and oxygen that has been discovered shouldn’t be in a type that almost all of us would acknowledge as water. Instead, it’s sure up with the mineral apatite — microscopic crystals making up 1 p.c or 2 p.c of a lunar soil pattern. And researchers nonetheless aren’t positive whether or not there’s sufficient of it on the moon to be a gasoline supply.
That mentioned, NASA has also found evidence suggesting that there’s ice in a number of the shadowed craters on the moon’s floor. If that’s true, splitting lunar hydrogen and oxygen into rocket gasoline could be a lot simpler. That could be the important thing to an actual, everlasting moon base, Robinson mentioned — a supply of not solely gasoline, but additionally drinkable water and breathable oxygen.
But, for now, we’re nonetheless fighting the constraints imposed by what we will carry, and that first step from the bottom to the sky stays our greatest hurdle. As lengthy as rocket gasoline weighs lots and takes up a whole lot of area, something that makes it simpler and cheaper to get into area is a breakthrough.