Final Limits |Space
The current speed record has been held for 46 years. When is it struck? Adam Hadhazy asks.
People are obsessed with speed. For example, the last few months have brought news thatStudents in Germany have broken the record for the fastest accelerating electric car, and which the US Air Force plans to developHypersonic jets that would travel at more than five times the speed of sound– these are speeds over 6,100 km/h.
These planes would be unmanned, but not because humans can't travel at such high speeds. In fact, humans have flown many times faster than Mach 5. However, is there a limit beyond which falling bodies can no longer withstand the speed load?
The current human speed record is shared equally by the trio of astronauts who flew on NASA's Apollo 10 mission. Returning from a lunar orbit in 1969, the astronauts' capsule reached a top speed of 39,897 km/h (24,790 mph) relative to planet Earth. "I think a hundred years ago we probably couldn't have imagined that a human being could travel through space at almost 25,000 miles per hour," says Jim Bray of aerospace company Lockheed Martin.
Even green power cars get fast on the race track; but mankind will have to be much faster to explore the universe (Credit: Stuttgart Green Team)
But we could break this record relatively soon. Bray is project manager for the Orion crew module for the US space agency NASA. The Orion spacecraft is designed to launch astronauts into low Earth orbit, and it's a good bet for the vehicle to break the 46-year-old record for the fastest we've ever traveled.
The Space Launch System, a new rocket that will carry the Orion spacecraft, is scheduled to experience its first manned mission in 2021, a flyby of a captured asteroid in lunar orbit, with a month-long mission to Mars in the offing. Today, designers envision the Orion's typical top speed in the vicinity of 19,900 mph (32,000 km/h). But the Apollo 10 land speed record could be surpassed even while maintaining Orion's base configuration. "Orion is designed for many different purposes over its lifetime," says Bray. "Its speed could be much higher than we plan now."
Rapid acceleration and deceleration can be fatal to the human body
However, Orion will not represent the peak of our speed potential either. "There's no real practical limit to the speed we can travel at other than the speed of light," says Bray. Light glides at about a billion kilometers per hour. Can we hope to safely bridge the 40,000 km/h gap at these speeds?
Surprisingly, velocity, defined as the rate of movement, is not itself a physical problem for us as long as it is relatively constant and unidirectional. Therefore, humans should theoretically be able to travel at speeds just below the "speed limit of the universe" - the speed of light.
But provided we can overcome the significant technological hurdles in building faster spacecraft, our fragile bodies, made mostly of water, will have to contend with significant new dangers that come with high-speed travel. Speculative dangers could also arise if humans succeed in traveling faster than light, either by exploiting gaps in known physics or by making paradigm-breaking discoveries.
Resistance to G-forces
However we reach speeds in excess of 40,000 km/h, we must patiently walk uphill (and downhill). Rapid acceleration and deceleration can be deadly to the human organism - look at the physical trauma of car crashes when we go from just tens of miles an hour to zero in a matter of seconds. The reason? A property of the universe known as inertia, by which any object with mass resists changing its state of motion. The concept is famously expressed in Newton's first law of motion as "an object at rest remains at rest and an object in motion keeps moving at the same speed and in the same direction unless acted upon by an external force."
"Consistency is good for the human body," explains Bray. "It's the acceleration we have to worry about."
Pilots are tested in centrifuges like this one to see how many G's their bodies can withstand (Credit: Science Photo Library)
About a century ago, the invention of robust aircraft that could maneuver at high speeds led to pilots reporting strange symptoms related to changes in speed and direction. These included a temporary loss of vision and a feeling of heaviness or weightlessness. The cause are G-forces, also called gravitational forces or simply Gs. These are units of g-force on a mass, such as a B. a human body. A G equals the Earth's gravitational pull to the center of the planet at 9.8 square meters per second squared (at sea level).
It's the G-forces experienced vertically, from head to toe or vice versa, that can be really bad news for pilots and passengers. Blood pools in the head of those who are G negative from head to toe, causing a congested feeling, like when we do a handstand. The "redness" begins when the translucent, blood-swollen lower eyelids lift to cover the pupils. Conversely, when the acceleration is positive, the eyes and brain become depleted of oxygen from head to toe as blood pools in the lower extremities. Blurred vision known as "darkening" occurs first, followed by complete loss of vision, or "blackout." These high G levels can lead to a complete blackout, known as G-induced loss of consciousness (GLOC). Many aviation fatalities are due to pilots losing consciousness and crashing.
Even if it's just for a few moments, humans can endure much stronger Gs without serious injury.
The average person can withstand a sustained force of about five G's from head to toe before losing consciousness. Pilots wearing special high-G suits and trained to tense their upper body muscles to keep blood from spurting out of their heads can still steer their plane at around nine Gs. "For short periods of time, the human body can withstand much more than nine Gs," says Jeff Sventek, executive director of the Alexandria, Virginia-based Aerospace Medical Association. "But not many people can maintain that over a long period of time."
Even if it's just for a few moments, humans can endure much stronger Gs without serious injury. The record for instantaneous Gs is held by Eli Beeding Jr., a US Air Force Captain. He was driving a rocket-powered sled backwards in 1958 and registered 82.6 G's on his chest accelerometer as the sled accelerated to approximately 55 km/h in a tenth of a second. Beeding passed out but suffered little more than a contusion on his back, a remarkable display of physical endurance.
Astronauts have also experienced fairly high Gs, depending on the vehicle, ranging from three to eight during launches and atmospheric re-entry respectively. These G-forces are mostly harmless front-to-back Gs, thanks to the clever practice of tying space visitors into forward-facing seats. Once they have reached a steady cruising speed of about 26,000 km/h (16,150 mph) in orbit, astronauts feel their speed no more than passengers on an airliner.
The Orion spacecraft must have a foot-thick shield in some places because of the danger of mini-meteors (Credit: NASA)
If G-forces aren't a problem for Orion's longer-duration missions, small space rocks, "micrometeoroids," could be a problem. These grain-sized bits can reach impressively devastating speeds of almost 300,000 km/h. To protect the ship and its crew, the Orion features a protective hull that's between 18 and 30 cm thick in places, in addition to other armor plates and clever gear placement. "So that we don't lose a critical flight system, we have to look for the entire spacecraft from which angle a micrometeoroid can come," says Bray.
Certainly, micrometeoroids are not the only hurdle to future space missions where higher human travel speeds would likely come into play. A mission to Mars has other practical issues to address, including crew food supplies and an increased lifetime risk of cancer from exposure to cosmic rays. However, reducing travel times would alleviate these problems, making a faster approach highly desirable.
Space travel, the next generation
This need for speed will raise new obstacles. New NASA spacecraft that could challenge the Apollo 10 land speed record will continue to rely on proven chemical rocket propulsion systems used since the earliest space missions. But such systems have severe speed limitations due to the small amounts of energy they release per unit of fuel.
Scientists recognize that new approaches will be required to achieve significantly faster travel speeds for humans to Mars and beyond. "The systems we have today will be good enough to get us there," says Bray, "but he'd like to see a revolution in propulsion."
With antimatter-powered motors, spacecraft could accelerate for months or years.
Eric Davis, senior research physicist at the Institute for Advanced Study in Austin and a contributor to NASA's Innovative Propulsion Physics Program, a six-year research project that ended in 2002, describes three of the most promising means (assuming conventional physics). to bring humanity to reasonable interplanetary cruising speeds. In short, they are the energy release phenomena of fission, fusion, and annihilation of antimatter.
The first method is the fission of atoms, as practiced in commercial nuclear reactors. The second, fusion, joins atoms into heavier atoms: the reaction that powers the sun, and a technology that remains temptingly unattainable; “Forever 50 years” is an old industry motto.
"These technologies are advanced," says Davis, "but they are conventional physics and have been well established since the dawn of the atomic age." Hopefully, various propulsion systems based on nuclear fission and fusion concepts could theoretically accelerate a ship to up to 10% the speed of light - a staggering 62,000,000 mph (100,000,000 km/h).
Flying at Mach 5 is no problem, but 60 million per hour brings other problems (Credit: US Air Force)
By far the best case for powering fast spacecraft is antimatter, twice the amount of normal matter. When the two materials touch, they cancel each other out as pure energy. Technologies currently exist to create and store (admittedly tiny) amounts of antimatter. However, producing antimatter in usable amounts would require dedicated next-generation facilities, and many engineering challenges would lie ahead of the proposed spacecraft. But Davis says there are many good ideas on the drawing board.
With antimatter-powered thrusters, spacecraft could accelerate to very high percentages of the speed of light for months or years, maintaining Gs at levels tolerable for the occupants. However, these fantastic new speeds would bring new dangers to the human body.
a vigorous greeting
Traveling at hundreds of millions of kilometers per hour, every speck in space, from stray hydrogen gas atoms to micrometeoroids, becomes a high-powered bullet slamming into a ship's hull. "If you're traveling at high speed, that's equivalent to a particle moving towards you at high speed," says Arthur Juwel. He collaborated with his late father, William Gem, a professor of radiology at Johns Hopkins University School of Medicine, on a 2012 paper examining the effects of cosmic hydrogen atoms on ultrafast spaceflight.
Although only present at a density of about one atom per cubic centimeter, the cosmos's surrounding hydrogen would result in a bombardment of intense radiation. The hydrogen would break down into subatomic particles that would penetrate the ship and irradiate both crew and equipment. At light speeds of about 95%, exposure would be fatal almost instantly. The spacecraft would also heat up to melting temperatures for virtually every material imaginable, while the water in the crew's bodies rapidly boiled. "These are all nasty problems," quips Juwel.
To use an analogy, we don't have to worry about drowning if we can't even reach the water - Marc Miilis, Nasa
He and his father roughly estimated that without some sort of magnetic shield to deflect the deadly rain of hydrogen, spacecraft could not travel more than half the speed of light without killing their human occupants.
Marc Millis, a propulsion physicist and former head of NASA's Innovative Propulsion Physics Program, warns that this potential speed limit for human travel remains a distant problem. "Based on the physics already gathered, speeds greater than 10% the speed of light will be very difficult to achieve," says Millis. "We're not in danger yet. To use an analogy, we don't have to worry about drowning if we can't even reach the water."
Faster than light?
Assuming we learn to swim, so to speak, to extend the analogy, could we someday learn to surf space-time and travel at speeds faster than light (superluminal)?
The Apollo 10 astronauts may be the fastest humans in history, but for how much longer? (Pot)
The inherent survivability of the superluminal realm, while speculative, isn't without some well-informed shots in the dark. An intriguing faster-than-light setting works like Star Trek's "warp drive." The so-called Alcubierre momentum involves the normal space-time described by Einstein's physics compressing in front of a spacecraft while it expands behind it. Essentially, the ship is in a piece of space-time, a "warp bubble" that's moving faster than the speed of light. However, the ship remains at rest within its normal spacetime, avoiding any violation of the universal speed limit of light. "Rather than swimming across the water" of normal spacetime, Davis says, the Alcubierre unit will "take you along like a surfer riding a surfboard on the crest of a wave."
The problem: The concept requires an exotic form of matter that has negative mass to contract and expand in spacetime. "Physics doesn't forbid negative mass," says Davis, "but there are no examples of it and we've never seen it in nature." The other catch: A 2012 study by researchers at the University of Sydney suggested that the warp bubble would house high-energy cosmic particles as they inevitably interact with the contents of the universe. Some particles would enter the bubble itself and blow up the ship with radiation.
Trapped in the underlight?
Are we stuck at sublight speeds forever because of our fragile biology? The answer is important not only to setting a new speed record in the human (galactic?) world, but also to the possibility of our species ever becoming an interstellar society. At half the speed limit of light that Juwel's research imposes on our bodies, a trip to the nearest star is more than a 16-year round trip. (Time dilation effects, where the crew of the crashing spaceship would spend less time in their frame of reference than humans on Earth in a different frame of reference would not have dramatic effects at half the speed of light).
Millis remains hopeful. Given that humanity has invented high-g suits and micrometeor shields to allow safe travel at incredible speeds in the big blue yonder and the star-studded blackness of space, we think we'll find ways to survive , no matter what speed limits you throw at us next.
"The types of technologies that could enable unanticipated new transit speeds, if future physics discovers such technology is possible," says Millis, "would also give us unanticipated new ways of protecting crews."