It’s All Relative
Said Albert Einstein back in 1905. According to his theory of special relativity, nothing can travel faster than the speed of light in a vacuum, as to attain 1 X light speed would require an infinite amount of energy. And that’s a problem. Especially when it comes to travelling in space which is “really, really big.“ But humans are curious. We want to know what’s out there.
So let’s take a look. Where is it is we want to go, and how are we going to get there? And let’s also look at a reasonable amount of time for a round trip, both for robotic and human missions. For a robotic mission, we might define a reasonable amount of time as being within the lifetime of the current generation, say 40 years max. This would include getting the spacecraft to its intended destination, and then sending back data (at the speed of light, of course).
For a manned mission, it’s a bit different. Astronauts have survived a year or more aboard the ISS, but the ISS is regularly resupplied with food, medicines, etc. from nearby Earth. On a long mission, resupply becomes impossible, so food and other commodities would have to be carried along on the voyage. Water and oxygen would have to be meticulously recycled with almost zero waste. The crew would also have to be prepared to deal with repairs, illnesses (both physical and psychological), and even the effects of aging on a long voyage. Thus, it might be wise to limit our trips to well under a year, perhaps even less.
Our current space faring technology is limited , primarily to chemical rockets. The strategy has always been to burn the majority of the fuel at launch, or upon leaving Earth orbit, giving the spacecraft a kick in the right direction, and then coasting the rest of the way, except for slight midcourse corrections. To achieve orbital (LEO) velocity, a speed of 28,000 km/h (17,500 mph) is required. To escape Earth’s gravity and head to another body within our solar system, a speed of 40,270 km/h (25,020 mph) is required.* However, to escape the sun’s gravity and head to another star system within our own Milky Way galaxy, a velocity of 151,278 km/h (94,000 mph) is required. And finally, if we ever hope to leave our own galaxy to visit another galaxy, we will need an escape velocity of 537,000 km/h (334,000 mph).
*These calculations do not include an initial stop in Earth orbit, gravitational assist from outer planets, nor slingshotting around the sun.
And when you get there, remember that you will need fuel (which has to be carried from earth) for a braking maneuver. We can consider the fuel needed for the barking maneuver as additional payload. This, we need additional fuel at takeoff for this additional payload.
For robotic missions, we can abandon the spacecrafts at their destinations. Human beings, not so much. They tend to be much more autophobic than robots.
Thus, we need to also plan for food, water, shelter, and other supplies while on the surface of extraterrestrial bodies, as well as the fuel to lift these items off the Earth as well. Finally, we will need the equipment for creating fuel for the return trip (assuming the raw materials are available at our destination and discounting, of course, some new-fangled antimatter drive or whatever).
Using current chemical rocket technology, here are the approximate distances and times it takes to get to various places in our solar system.
It would appear from these numbers that chemical rockets are not viable for a manned mission beyond Europa. Even 13 months in space, without even the Earth below to comfort us, would be stretching the limits of man’s psychological endurance, let alone the problem of food, medical supplies, etc. which would be needed for longer journeys.
With regard to the distances, we must say approximate, as the position of the Earth relative to the destination, gravitational assists from other planets, and many other factors are all a part of determining the elapsed travel time. But it does put things into perspective.
So what about technologies other than chemical rockets?
1) Ion Propulsion
Ion propulsion was used in NASA’s mission to asteroids Ceres and Vesta. Ion propulsion engines can attain speeds of over 200,000 mph. However, with three engines, each producing only 91 millinewtons of thrust, the Dawn spacecraft took four days to increase its speed by just 60 mph. Thus it took 979 days to reach Vesta, Dawn’s first destination. That’s OK if you’re not in a hurry, but not a good choice for a manned mission. So scratch that one.
2) Laser Propulsion Using Earth-based Lasers
In 2016, a program called Breakthrough Starshot was proposed by Yuri Milner, Stephen Hawking, and Mark Zuckerberg. The idea was to use a giant field of 1600 synchronized lasers producing 100 gigawatts of power in total. Mind you, this is nine times the electrical power that New York City uses in a day (11 gigawatts)! A phased array of these lasers would focus a light beam on 1000 wafer thin crafts towed by light sails 4 meters across. They then plan to accelerate the probes one by one to the target speed (12.5% C, (speed of light) over a 10 minute period. That’s one every 6/10 of a second, then aiming (exactly) for the next one! Doubtful.
A 150 mg. atomic battery, powered by plutonium-238 or americium-241, is planned as the power source. The best theoretical power obtainable from a nuclear battery is only 50 mw/g or 7.5 mw for a 150 mg. battery if 100% of the battery could be converted into RF energy. Since the probes are not expected to reach Alpha Centauri for over 100 years or so, the battery will have long since been depleted. And even if it were still at full power, the signal received at Earth would be 1.42e-16 mw due to the inverse square law. Then considering that the probe antennas are omnidirectional, the signal would be scattered even more. There is absolutely no way that this weak of a signal could be separated out from background noise at this low level, even with the best super-cooled detectors placed in space with a sunshade similar to the Webb telescope.
Alpha Centauri is constantly moving relative to Earth. There would be almost no possibility of a midcourse correction. The Starshot probes are to have four sub-gram scale “photon” thrusters, each minimally capable of performing at a 1W diode laser level. However, since the battery is only 150 mw, this means that power would have to be stored in a super-capacitor and then released in pulses in order to have any meaningful effect. The weight of the capacitor alone would likely negate the entire mission. Unable to steer toward a planet, even if it found one, the Starshot mission, again, is doomed to failure. If the probes are off just 1/1000 of a degree, they will miss the Alpha Centauri system entirely by over 17 million miles.
Consider that Pluto was not even discovered until 1930. Even the mighty Hubble could only give us a picture just a few pixels wide. What then can we expect of Starshot, with its “gram scale” 2 megapixel cameras? Most cellphone today, by comparison, have at least 12 mpx cameras, with one Samsung Galaxy model boasting 108 mpx! Assuming the probes even get to Alpha Centauri, the chances of one of them glimpsing a planet are zero (imagine trying to first locate Mars and then take a decent picture of it, our closest planetary neighbor, with your cell phone.)
Starshot has no more chance of reaching Alpha Centauri than Icarus of Greek mythology had trying to reach the sun on wings made of wax.
The Starshot project is estimated to cost $5-10 billion. Why, you ask yourself, would intelligent, wealthy people invest in such a fool-hearty endeavor? We have only to look at recent examples such as the Theranos scam by Elizabeth Holmes. Holmes was able to sweet-talk such well known people such as Henry Kissinger, George Shultz, Jim Mattis, Betsy DeVos, Rupert Murdoch, the Walton family, the Cox family of Cox Enterprises and Carlos Slim, out of almost $1billion in total for a bogus product. She was convicted on four counts of fraud and is currently awaiting sentencing. It seems that almost anyone can be mesmerized, especially when they don’t do their own math or research. Remember the old adage: if it sounds too good to be true, it probably isn’t.
3) Vasimir Plasma Rocket
The Vasimir plasma rocket proposed by Ad Astra would have a theoretical top speed of 197,950 kph (123,000 mph). This could get us on our way to Alpha Centauri, 4.4 ly away (4.2X1013 km) in 38,813 years. According to Wikipedia: “In order to conduct an imagined crewed trip to Mars in 39 days, the VASIMR would require an electrical power level far beyond anything currently possible. On top of that, any power generation technology will produce waste heat. The necessary 200 megawatt reactor “with a power-to-mass density of 1,000 watts per kilogram” [(Franklin Chang) Díaz quote] would require extremely efficient radiators to avoid the need for “football-field sized radiators” [(Robert) Zubrin quote]. Conclusion: Vasimir is not viable for manned or unmanned interstellar travel.
4) Nuclear propulsion
“Engineers from NASA estimate that a mission to Mars powered by nuclear thermal propulsion would be 20%-25% shorter than a trip on a chemical-powered rocket. Another nuclear-based rocket system is called nuclear electric propulsion. No nuclear electric systems have been built yet, but the idea is to use a high-power fission reactor to generate electricity that would then power an electrical propulsion system like a Hall thruster. This would be very efficient, about three times better than a nuclear thermal propulsion system. But while nuclear electric rockets are extremely promising, there are still a lot of technical problems to solve before they are put into use.”*
*The Conversation, May 2020
Adding to this is the fact that nuclear rockets have the inherent problem of a very wimpy thrust.
Conclusion: Another “promising” technology BUSTED!
Even an exotic theoretical propulsion system proposed by AsteronX which they call “Muon Catalyzed Aneutronic Fusion” and which they claim would have a speed of 8% the speed of light, a mission to Alpha Centauri would take 55 years in each direction. Assuming it ever becomes a reality, this system is still only viable for unmanned probes. Plus the facts that the original researchers would likely be dead before any meaningful data were ever received.
Also, remember that, with conventional means, we are bound by Einstein’s theory of relativity, which tells us that as we approach the speed of light, our mass would become almost infinite, and we would be crushed to death by our own mass. And then there are the g forces to get us up to the speed of light.
Finally, consider this. At light speed, a grain of sand has the energy of two sticks of dynamite. And according to William Edelstein of the Johns Hopkins University School of Medicine in Baltimore, Maryland, “Although only present at a density of around one atom in a cubic centimeter, the cosmos’s ambient hydrogen would translate into a bombardment of intense radiation. The hydrogen would shatter into subatomic particles that would pass into the ship, irradiating both crew and equipment. At speeds around 95% of light, the exposure would be near-instantly deadly. The star ship would heat up, too, to melting temperatures for essentially any conceivable material, while water in the crew’s bodies would promptly boil. These are all nasty problems.” So any attempt to travel near the speed of light in a conventional subliminal craft will end in both the destruction of the spacecraft and the annihilation of the occupants.
So where does that leave us? As a species, we are batting zero for four on the most “promising” technologies for reaching the stars, never mind wasting hundreds of millions, or even billions, of dollars in doing so.
But there is hope.
Faster Than Light (FTL) Travel, AKA Warp Drive
In 1994, Mexican physicist, Miguel Alcubierre, showed mathematically that it is possible to travel faster than the speed of light without violating any of Einstein’s principles. Alcubierre’s design is to create a “warp bubble” around a spacecraft. This bubble would warp the space around the craft in such a manner that the space behind the craft is compressed while the space in front of the craft is expanded.
The craft them moves through space much like a surfer being propelled by a wave. Interestingly, the occupants of such a craft would not experience any movement because it is space that is moving, and not the craft itself. The FTL craft, however, would require the use of negative matter, and not just a small amount, but negative matter with the mass of the planet Jupiter.
However, in 2011, a paper published by NASA scientist Harold G. “Sonny” White further improved upon Alcubierre’s designs, dramatically reducing the amount of exotic (negative) matter needed to fuel the hypothetical drive from a Jupiter sized amount to something akin to the size of the NASA Voyager 1 probe. According to White, this is accomplished by adjusting the warp field into more of a rounded doughnut, as opposed to a flat ring, while oscillating the warp field intensity.
The scientific community has begun to take warp drive seriously, as evidenced by a recently filed patent application. In April of 2020, two engineers from Chicago, Jessica Gallanis and Eytan Halm Suchard published a patent application for a warp drive using the updated Harold White designs. The patent also notes the work of scientist H. David Froning, whom they say observed how, “if sufficient warping is achieved, (the space)ship speed is slower than light speed within the region that surrounds it, even if it is moving faster-than-light with respect to Earth.”
Following Whites discoveries, astrophysicist Erik Lentz realized there were specific configurations of space-time bubbles that had been overlooked. These bubbles take the form of solitons, compact waves that travel at a constant velocity, without losing their shape. Lentz found that certain soliton configurations could be formed using conventional (positive) energy sources, without violating any of Einstein’s equations, and without requiring any negative energy densities.
One other problem still to be overcome is the tremendous amount of energy which has been calculated to create the warp field necessary for FTL travel. While a warp drive that uses conventional energy sources could be a major breakthrough, the new soliton method has its own hurdles. It would still require an absolutely enormous amount of energy which isn’t feasible at this time, but there may be hope yet. Lentz tells us, “The energy savings would need to be drastic, of approximately 30 orders of magnitude to be in range of modern nuclear fission reactors. Fortunately, several energy-saving mechanisms have been proposed in earlier research that can potentially lower the energy required by nearly 60 orders of magnitude.”
Multiple private and government laboratories are currently working on miniaturizing nuclear reactors for use on the moon, Mars, and remote locations on Earth. Rather than putting our efforts into a nuclear rocket to power an ion type rocket, perhaps a better use of new nuclear technology would be to power an FTL spacecraft.
Going back to the problem of interstellar particles ripping holes in our spaceship and ions cooking us like a microwave oven on steroids, an unnamed source (attributed to the company AsteronX), claims to have solved that problem with a “photon” shield. According to the source, unlike Star Trek’s energy force fields, which weakens and eventually collapses under bombardment, a photon shield would not. It would act much like the surface tension on a pond of water, which deflects flat rocks thrown at it, and sends them skipping merrily on their way.
So let’s assume for a moment that the day has arrived when we finally have a working FTL spacecraft. Hooray! So how fast would we have to be going to visit some likely destinations in space? Remember, at the beginning of this article, we defined a reasonable amount of time for an unmanned mission as 40 years (including the return of data at light speed) and one year roundtrip for a manned mission. Note that sending back data will be near impossible due to both lag time and signal to noise ratio unless we also invent instantaneous quantum-entangled communication. Therefore, our exploration vehicle must return to Earth with its data, manned or unmanned. The chart below gives us some idea of the speeds which will be needed for a round trip.*
It should be noted that Alcubierre’s mathematics do not indicate any top speed. Just fill ‘er up with premium and step on it! So with Alcubierre at the helm, we should fare much better than past science fiction space travelers. According to many of the TV shows and movies, traveling to another galaxy is next to impossible, and even traveling within our own galaxy is extremely limited. According to the Star Trek Encyclopedia:
Warp Factor 1 – 1x light speed
Warp Factor 2 – 10x light speed
Warp Factor 3 – 39x light speed
Warp Factor 4 – 102x light speed
Warp Factor 5 – 214x light speed
Warp Factor 6 – 392x light speed
Warp Factor 7 – 656x light speed
Warp Factor 8 – 1,024x light speed
Warp Factor 9 – 1,516x light speed
Warp Factor 9.99 – 7,912x light speed
Warp Factor 10 – Infinity (Impossible, even according to Star Trek)
At Warp 9.9, the Enterprise would take 13 years or 4,613 days to cross the Milky Way galaxy. The TV program discussed going from “quadrant to “quadrant” of the galaxy in a matter of hours or days, a feat not possible according to the program’s own science. And for the Enterprise to travel to the Andromeda galaxy, some 2,500,000 ly. away, it would take 316 years at Warp 9.9.
The Millennium Falcon of Star Wars fame fares even worse. In the first Star Wars movie (Episode IV),
the 10,000 ly. trip from Tatooine to Alderaan took 16 hours, putting its speed at only roughly equivalent to Star Trek’s warp 7 (656X light speed).
So where does that leave us? Clearly, the less-than-FTL proposals on the drawing board are exercises in futility, but we can’t give up on FTL. We went from the first powered manned flight at Kitty Hawk in 1903 to landing a man on the moon in 1965, just 62 years later! We were once bound to earth by gravity. Currently, we are similarly bound to the solar system. But history is full of examples of persistence eventually paying off. Edison failed somewhere around 3,000 times before he perfected the light bulb. In his best seller, “Think And Grow Rich,” the late author and philosopher, Napoleon Hill states, “Whatever the mind can conceive and believe, the mind can achieve.”
At some time in the future, perhaps another form of space travel which uses wormholes or a technology not even yet envisioned, will be discovered. But for now, FTL is our best bet. Aliens depicted in science fiction often say, “People of Earth: Throw down your weapons; they are useless against us!” I would paraphrase that and say, “People of Earth: Throw away your sub-luminal spacecraft efforts; they are useless for getting to the stars.”
Author Ken Lunde is the President and CEO of
Space Mission Architects, Inc.; Coconut Creek, Florida.
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