Pros and Cons of Various Methods of Interstellar Travel

It’s a staple of science fiction, and something many people have fantasized about at one time or another: the idea of sending out spaceships with colonists and transplanting the seed of humanity among the stars. Between discovering new worlds, becoming an interstellar species, and maybe even finding extra-terrestrial civilizations, the dream of  spreading beyond the Solar System is one that can’t become reality soon enough!

For decades, scientists have contemplated how humanity might one-day reach achieve this lofty goal. And the range of concepts they have come up with present a whole lot of pros and cons. These pros and cons were raised in a recent study by Martin Braddock, a member of the Mansfield and Sutton Astronomical Society, a Fellow of the Royal Society of Biology, and a Fellow of the Royal Astronomical Society.

The study, titled “Concepts for Deep Space Travel: From Warp Drives and Hibernation to World Ships and Cryogenics“, recently appeared in the scientific journal Current Trends in Biomedical Engineering and Biosciences (a Juniper Journals publication). As Braddock indicates in his study, the question of how human beings could explore neighboring star systems has become more relevant in recent years thanks to exoplanet discoveries.

A list of some of the recently-discovered potentially habitable exoplanets. Credit:

As we reviewed in a previous article, “How Long Would it Take to Travel to the Nearest Star?“, there are numerous proposed and theoretical ways to travel between our Solar System and other stars in the galaxy. However, beyond the technology involved, and the time it would take, there are also the biological and psychological implications for human crews that would need to be taken into account beforehand.

And thanks to the way public interest in space exploration has become renewed in recent years, cost-benefit analyses of all the possible methods is becoming increasingly necessary. As Dr. Braddock told Universe Today via email|:

“Interstellar travel has become more relevant because of the concerted effort to find ways across all of the space agencies to maintain human health in ‘short’ (2-3 yr) space travel. With Mars missions reasonably in sight, Stephen Hawking’s death highlighting one his many beliefs that we should colonize deep space and Elon Musk’s determination to minimize waste on space travel, together with reborn visions of ‘bolt-on’ accessories to the ISS (the Bigelow expandable module) conjures some imaginative concepts.”

All told, Dr. Braddock considers five principle means for mounting crewed missions to other star systems in his study. These include super-luminal (aka/ FTL) travel, hibernation or stasis regimes, negligible senescence (aka. anti-aging) engineering, world ships capable of supporting multiple generations of travellers (aka. generation ships), and cyogenic freezing technologies.

Artist’s concept of a spacecraft using an Alcubierre Warp Drive. Credit: NASA

For FTL travel, the advantages are obvious, and while it remains entirely theoretical at this point, there are concepts being investigated today. A notable FTL concept – known as the Alcubierre Warp Drive – is currently being researched by multiple organizations, which includes the Tau Zero Foundation and the Advanced Propulsion Physics Laboratory: Eagleworks (APPL:E) at NASA’s Johnson Space Center.

To break it down succinctly, this method of space travel involves stretching the fabric of space-time in a wave which would (in theory) cause the space ahead of a ship to contract and the space behind it to expand. The ship would then ride this region, known as a “warp bubble”, through space. Since the ship is not moving within the bubble, but is being carried along as the region itself moves, conventional relativistic effects such as time dilation would not apply.

As Dr. Brannock indicates, the advantages of such a propulsion system include being able to achieve “apparent” FTL travel without violating the laws of Relativity. In addition, a ship traveling in a warp bubble would not have to worry about colliding with space debris, and there would be no upper limit to the maximum speed attainable. Unfortunately, the downsides of this method of travel are equally obvious.

These include the fact that there is currently no known methods for creating a warp bubble in a region of space that does not already contain one. In addition, extremely high energies would be required to create this effect, and there is no known way for a ship to exit a warp bubble once it has entered. In short, FTL is a purely theoretical concept for the time being and there are no indications that it will move from theory to practice in the near future.

“The first [strategy] is FTL travel, but the other strategies accept that FTL travel is very theoretical and that one option is to extend human life or to engage in multiple-generational voyages,” said Dr. Braddock. “The latter could be achieved in the future, given the willingness to design a large enough craft and the propulsion technology development to achieve 0.1 x c.”

In other words, the most plausible concepts for interstellar space travel are not likely to achieve speeds of more than ten percent the speed of light about 29,979,245.8 m / s (~107,925,285 km/h; 67,061,663 mph). This is still a very tall order considering that the fastest mission to date was the Helios 2 mission, which achieved a a maximum velocity of over 66,000 m/s (240,000 km/h; 150,000 mph). Still, this provides a more realistic framework to work within.

Where hibernation and stasis regiments are concerned, the advantages (and disadvantages) are more immediate. For starters, the technology is realizable and has been extensively studies on shorter timescales for both humans and animals. In the latter case, natural hibernation cycles provide the most compelling evidence that hibernation can last for months without incident.

The downsides, however, come down to all the unknowns. For example, there are the likely risks of tissue atrophy resulting from extended periods of time spent in a microgravity environment. This could be mitigated by artificial gravity or other means (such as electrostimulation of muscles), but considerable clinical research is needed before this could be attempted. This raises a whole slew of ethical issues, since such tests would pose their own risks.

Strategies for Engineered Negligible Senescence (SENS) are another avenue, offering the potential for human beings to counter the effects of long-duration spaceflight by reversing the aging process. In addition to ensuring that the same generation that boarded the ship would be the one to make it to its destination, this technique also has the potential to drive stem cell therapy research here on Earth.

However, in the context of long-duration spaceflight, multiple treatments (or continuous ones throughout the travel process) would likely be necessary to achieve full rejuvenation. A considerable amount of research would also be needed beforehand in order to test the process and address the individual components of aging, once again leading to a number of ethical issues.

Then there’s worldships (aka. generation ships), where self-contained and self sustaining spacecraft large enough to accommodate several generations of space travelers would be used. These ships would rely on conventional propulsion and therefore take centuries (or millennia) to reach another star system. The immediate advantages of this concept is that it would fulfill two major goals of space exploration, which would be to maintain a human colony in space and to permit travel to a potentially-habitable exoplanet.

In addition, a generation ship would rely on propulsion concepts that are currently feasible, and a crew of thousands would multiply the chances of successfully colonizing another planet. Of course, the cost of constructing and maintaining such large spaceships would be prohibitive. There are also the moral and ethical challenges of sending human crews into deep space for such extended periods of time.

For instance, is there any guarantee that the crew wouldn’t all go insane and kill each other? And last, there is the fact that newer, more advanced ships would be developed on Earth in the meantime. This means that a faster ship, which would depart Earth later, would be able to overtake a generation ship before it reached another star system. Why spend so much on a ship when it’s likely to become obsolete before it even makes it to its destination?

A concept for a multi-generation ship being designed by the TU Delft Starship Team (DSTART), with support from the ESA. Credit and Copyright: Nils Faber & Angelo Vermeulen

Last, there is cryogenics, a concept that has been explored extensively in the past few decades as a possible means for life-extension and space travel. In many ways, this concept is an extension of hibernation technology, but benefits from a number of recent advancements. The immediate advantage of this method is that it accounts for all the current limitations imposed by technology and a relativistic Universe.

Basically, it doesn’t matter if FTL (or speeds beyond 0.10 c) are possible or how long a voyage will take since the crew will be asleep and perfectly preserved for the duration. On top of that, we already know the technology works, as demonstrated by recent advancements where organ tissues and even whole organisms were warmed and vitrified after being cryogenically frozen.

However, the risks also greater than with hibernation. For instance, the long-term effects of cryogenic freezing on the physiology and central nervous system of higher-order animals and humans is not yet known. This means that extensive testing and human trials would be needed before it was ever attempted, which once again raises a number of ethical challenges.

In the end, there are a lot of unknowns associated with any and all potential methods of interstellar travel. Similarly, much more research and development is necessary before we can safely say which of them is the most feasible. In the meantime, Dr. Braddock admits that it’s much more likely that any interstellar voyages will involve robotic explorers using telepresence technology to show us other worlds – though these don’t possess the same allure.

Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit:

“Almost certainly, and this revisits the early concept of von Neumann replication probes (minus the replication!),” he said. “Cube Sats or the like may well achieve this goal but will likely not engage the public imagination nearly as much as human space travel. I believe Sir Martin Rees has suggested the concept of a semi-human AI type device… also some way off.”

Currently, there is only one proposed mission for sending an interstellar space craft to a nearby star system. This would be Breakthrough Starshot, a proposal to send a laser sail-driven nanocraft to Alpha Centauri in just 20 years. After being accelerated to 4,4704,000 m/s (160,934,400 km/h; 100 million mph) 20% the speed of light, this craft would conduct a flyby of Alpha Centauri and also be able to beam home images of Proxima b.

Beyond that, all the missions that involve venturing to the outer Solar System consist of robotic orbiters and probes and all proposed crewed missions are directed at sending astronauts back to the Moon and on to Mars. Still, humanity is just getting started with space exploration and we certainly need to finish exploring our own Solar System before we can contemplate exploring beyond it.

In the end, a lot of time and patience will be needed before we can start to venture beyond the Kuiper Belt and Oort Cloud to see what’s out there.

Further Reading: ResearchGate

Is Human Hibernation Possible? Going to Sleep for Long Duration Spaceflight

Sleeping for Centuries?

We’ve spent a few articles on Universe Today talking about just how difficult it’s going to be to travel to other stars. Sending tiny unmanned probes across the vast gulfs between stars is still mostly science fiction. But to send humans on that journey? That’s just a level of technology beyond comprehension.

For example, the nearest star is Proxima Centauri, located a mere 4.25 light years away. Just for comparison, the Voyager spacecraft, the most distant human objects ever built by humans, would need about 50,000 years to make that journey.

I don’t know about you, but I don’t anticipate living 50,000 years. No, we’re going to want to make the journey more quickly. But the problem, of course, is that going more quickly requires more energy, new forms of propulsion we’ve only starting to dream up. And if you go too quickly, mere grains of dust floating through space become incredibly dangerous.

Based on our current technology, it’s more likely that we’re going to have to take our time getting to another star.

And if you’re going to go the slower route, you’ve got a couple of options. Create a generational ship, so that successive generations of humans are born, live out their lives, and then die during the hundreds or even thousands of year long journey to another star.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO

Imagine you’re one of the people destined to live and die, never reaching your destination. Especially when you look out your window and watch a warp ship zip past with all those happy tourists headed to Proxima Centauri, who were start enough to wait for warp drives to be invented.

No, you want to sleep for the journey to the nearest star, so that when you get there, it’s like no time passed. And even if warp drive did get invented while you were asleep, you didn’t have to see their smug tourist faces as they zipped past.

Is human hibernation possible? Can we do it long enough to survive a long-duration spaceflight journey and wake up again on the other side?

Before I get into this, we’re just going to have to assume that we never merge with our robot overlords, upload ourselves into the singularity, and effortlessly travel through space with our cybernetic bodies.

For some reason, that whole singularity thing never worked out, or the robots went on strike and refused to do our space exploration for us any more. And so, the job of space travel fell to us, the fragile, 80-year lifespanned mammals. Exploring the worlds within the Solar System and out to other stars, spreading humanity into the cosmos.

Artist’s impression of astronauts exploring the surface of Mars. Credit: NASA/JSC/Pat Rawlings, SAIC

Come on, we know it’ll totally be the robots. But that’s not what the science fiction tells us, so let’s dig into it.

We see animals, and especially mammals hibernating all the time in nature. In order to be able survive over a harsh winter, animals are capable of slowing their heart rate down to just a few beats a minute. They don’t need to eat or drink, surviving on their fat stores for months at a time until food returns.

It’s not just bears and rodents that can do it, by the way, there are actually a couple of primates, including the fat-tailed dwarf lemur from Madagascar. That’s not too far away on the old family tree, so there might be hope for human hibernation after all.

In fact, medicine is already playing around with human hibernation to improve people’s chances to survive heart attacks and strokes. The current state of this technology is really promising.

They use a technique called therapeutic hypothermia, which lowers the temperature of a person by a few degrees. They can use ice packs or coolers, and doctors have even tried pumping a cooled saline solution through the circulatory system. With the lowered temperature, a human’s metabolism decreases and they fall unconscious into a torpor.

But the trick is to not make them so unconscious that they die. It’s a fine line.

The results have been pretty amazing. People have been kept in this torpor state for up to 14 days, going through multiple cycles.

The therapeutic use of this torpor is still under research, and doctors are learning if it’s helpful for people with heart attacks, strokes or even the progression of diseases like cancer. They’re also trying to figure out if there are any downsides, but so far, there don’t seem to be any long-term problems with putting someone in this torpor state.

A few years ago, SpaceWorks Enterprises delivered a report to NASA on how they could use this therapeutic hypothermia for long duration spaceflight within the Solar System.

Currently, a trip to Mars takes about 6-9 months. And during that time, the human passengers are going to be using up precious air, water and food. But in this torpor state, SpaceWorks estimates that the crew will a reduction in their metabolic rate of 50 to 70%. Less metabolism, less resources needed. Less cargo that needs to be sent to Mars.

Credit: SpaceWork Enterprises, Inc

The astronauts wouldn’t need to move around, so you could keep them nice and snug in little pods for the journey. And they wouldn’t get into fights with each other, after 6-9 months of nothing but day after day of spaceflight.

We know that weightlessness has a negative effect on the body, like loss of bone mass and atrophy of muscles. Normally astronauts exercise for hours every day to counteract the negative effects of the reduced gravity. But SpaceWorks thinks it would be more effective to just put the astronauts into a rotating module and let artificial gravity do the work of maintaining their conditioning.

They envision a module that’s 4 metres high and 8 metres wide. If you spin the habitat at 20 revolutions per minute, you give the crew the equivalent of Earth gravity. Go at only 11.8 RPM and it’ll feel like Mars gravity. Down to 7.8 and it’s lunar gravity.

Normally spinning that fast in a habitat that small would be extremely uncomfortable as the crew would experience different forces at different parts of their body. But remember, they’ll be in a state of torpor, so they really won’t care.

Credit: SpaceWork Enterprises, Inc
Credit: SpaceWork Enterprises, Inc

Current plans for sending colonists to Mars would require 40 ton habitats to support 6 people on the trip. But according to SpaceWorks, you could reduce the weight down to 15 tons if you just let them sleep their way through the journey. And the savings get even better with more astronauts.

The crew probably wouldn’t all sleep for the entire journey. Instead, they’d sleep in shifts for a few weeks. Taking turns to wake up, check on the status of the spacecraft and crew before returning to their cryosleep caskets.

What’s the status of this now? NASA funded stage 1 of the SpaceWorks proposal, and in July, 2016 NASA moved forward with Phase 2 of the project, which will further investigate this technique for Mars missions, and how it could be used even farther out in the Solar System.

Elon Musk should be interested in seeing their designs for a 100-person module for sending colonists to Mars.

Credit: SpaceWork Enterprises, Inc
Credit: SpaceWork Enterprises, Inc

In addition, the European Space Agency has also been investigating human hibernation, and a possible way to enable long-duration spaceflight. They have plans to test out the technology on various non-hibernating mammals, like pigs. If their results are positive, we might see the Europeans pushing this technology forward.

Can we go further, putting people to sleep for decades and maybe even the centuries it would take to travel between the stars?

Right now, the answer is no. We don’t have any technology at our disposal that could do this. We know that microbial life can be frozen for hundreds of years. Right now there are parts of Siberia unfreezing after centuries of permafrost, awakening ancient microbes, viruses, plants and even animals. But nothing on the scale of human beings.

When humans freeze, ice crystals form in our cells, rupturing them permanently. There is one line of research that offers some hope: cryogenics. This process replaces the fluids of the human body with an antifreeze agent which doesn’t form the same destructive crystals.

Scientists have successfully frozen and then unfrozen 50-milliliters (almost a quarter cup) of tissue without any damage.

In the next few years, we’ll probably see this technology expanded to preserving organs for transplant, and eventually entire bodies, and maybe even humans. Then this science fiction idea might actually turn into reality. We’ll finally be able to sleep our way between the stars.

Who Discovered Helium?

Scientists have understood for some time that the most abundant elements in the Universe are simple gases like hydrogen and helium. These make up the vast majority of its observable mass, dwarfing all the heavier elements combined (and by a wide margin). And between the two, helium is the second lightest and second most abundant element, being present in about 24% of observable Universe’s elemental mass.

Whereas we tend to think of Helium as the hilarious gas that does strange things to your voice and allows balloons to float, it is actually a crucial part of our existence. In addition to being a key component of stars, helium is also a major constituent in gas giants. This is due in part to its very high nuclear binding energy, plus the fact that is produced by both nuclear fusion and radioactive decay. And yet, scientists have only been aware of its existence since the late 19th century.

Continue reading “Who Discovered Helium?”

NASA Investigating Deep-Space Hibernation Technology

Manned missions to deep space present numerous challenges. In addition to the sheer amount of food, water and air necessary to keep a crew alive for months (or years) at a time, there’s also the question of keeping them busy for the entirety of a long-duration flight. Exercise is certainly an option, but the necessary equipment will take up space and be a drain on power.

In addition, they’ll need room to move around, places to sleep, eat, work, and relax during their down time. Otherwise, they will be at risk of succumbing to feelings of claustrophobia, anxiety, insomnia, and depression – among other things.

NASA has been looking at a few options and one proposed solution is to put these crews into an induced state of hypothermia resulting in torpor – a kind of hibernation. Rather than being awake for months or years on end, astronauts could enter a state of deep sleep at the beginning of their mission and then wake up near the end. This way, they would arrive refreshed and ready to work, rather than haggard and maybe even insane.

If this is starting to sound familiar, it’s probably because the concept has been explored extensively by science fiction. Though it goes by different names – cryosleep, reefersleep, cryostasis, etc. – the notion of space explorers preserving their bodies through cryogenic suspension has been touched upon by numerous sci-fi authors, movies and franchises.

But NASA’s plan is a little different than what you might remember from 2001: A Space Odyssey or Aliens. Instead of astronauts stepping into a tube and having their temperature lowered, torpor would be induced via the RhinoChill – a device that uses invasive tubes to shoot cooling liquid up the nose and into the base of the brain.

Artist's concept of "sleeping to Mars". Photo Credit: SpaceWorks Enterprising
Artist’s concept of “sleeping to Mars”. Photo Credit: SpaceWorks Enterprising

To research the technology, NASA has teamed up with SpaceWorks, an Atlanta-based aerospace company that is investigating procedures for putting space crews into hibernation. During this year’s International Astronomical Congress – which took place from Sept. 29th to Oct. 3rd  in Toronto – representatives from SpaceWorks shared their vision.

According to the company, inducing torpor in a crew of astronauts would eliminate the need for accommodations like galleys, exercise equipment, and large living quarters. Instead, robots could electrically stimulate key muscle groups and intravenously deliver sustenance to ensure the health and well being of the astronauts while in transit.

As Dr. Bradford, President of SpaceWorks Enterprises Inc., told Universe Today via email:

“We have completed the initial evaluation of our concept which demonstrated significant benefits against non-torpor Mars mission approaches and established the medical plausibility of torpor. We have expanded our team and put together a development plan that we are in the process of executing. While the longer term goal of enabling access to Mars is our ultimate objective, we have a number of near-term, commercial applications for this technology that we will develop along the way.”

In addition to cutting down on the need for room and supplies, keeping crews in hibernation would also save on another all-important factor: costs. With a crew in stasis, ships could be built smaller or have more room to accommodate safety features like radiation shields. At the same time, smaller, lighter ships would mean that material, construction, and fuel costs would be lower.

According to SpaceWorks’ mockups, the size of a crew living quarters for a Mars mission could be reduced from the currently-proposed dimensions of 8.2×9 meters to just 4.3×7.5. Also, current projections indicate that a Mars ready-habitat for a 4-person crew would weight roughly 31 tons. But the company claims that a torpor-stasis habitat could weigh as little as 15.

Image Credit: SpaceWorks
Artist’s concept for Mars-ready habitat. Image Credit: SpaceWorks

Of course, SpaceWorks also emphasized the psychological benefits. Rather than being awake for the entire 180 day journey, the crew would be able to go to sleep and wake up upon arrival. This would ensure that no one succumbs to “space madness” during the months-long journey and does something terrible – like take their own life or those of the crew!

Naturally, there is still plenty of research and development that needs to be done before a torpor hibernation system can be considered a feasible option for space travel. RhinoChill has so far only been used in therapeutic scenarios here on Earth. The next step will be to test it in orbit.

Luckily, the potential savings during a trip to Mars or somewhere in the outer Solar System could be just the incentive to make it happen. And no matter what, it seems that some form of induced-hibernation will be necessary if ever humanity is ever to explore the depths of space.

“We are at the dawn of a new era in space and my company is excited to be working at the forefront,” Bradford said. “I believe our technology will be required to support human missions to Mars. It offers an affordable solution by leveraging ongoing medical research to address challenges spanning engineering, human health, and psychology for which we do not have alternate solutions. This can be ready for the first Mars mission and we are talking with partners to make this happen.”

Further reading: SpaceWorks Enterprises

NASA Tanks: Not Just Heavy Metal Any More

NASA’s future in fuels will see less heavy metal. Literally.

The agency just finished testing on a composite propellant tank that holds cryogenics, or super-chilled gases that are commonly used as rocket fuel (such as for the space shuttle). The agency brought the test tank down to -423 degrees Fahrenheit, put it through a few cycles and ramped up the internal pressure.

Composites are lighter material than the traditional metals that are used to hold these gases. NASA is excitedly throwing out descriptors such as “game-changing” when it talks about this, and has some reason to do so: composites are lighter than metals.

The light weight of composite tanks makes them lighter to lift off the ground. This reduces the costs of launch, which in turn reduces the overall cost of a mission. That will make penny-counters at the agency happier as the agency battles for funding dollars in fiscal 2014 and beyond.

The first of these tanks is likely to be used in the upper stage of NASA’s Space Launch System rocket, which is under development right now. That’s the rocket that’s supposed to send the Orion spacecraft (aiming for a 2014 test flight) into space in the latter years of this decade.

“The tank manufacturing process represents a number of industry breakthroughs, including automated fiber placement of oven-cured materials, fiber placement of an all-composite tank wall design that is leak-tight, and a tooling approach that eliminates heavy joints,” stated Dan Rivera, the Boeing cryogenic tank program manager at Marshall.

Boeing and NASA are now working on another composite tank that should be tested at Marshall later in 2013.

Source: NASA