Space pioneers won’t settle habitable planets unless people figure out how to cross vast interstellar distances in reasonable lengths of time. Voyager 1 is currently the fastest spacecraft ever built and is travelling at about 61,200 kilometers per hour with respect to the Sun. It is the first spacecraft to cross the heliopause, a somewhat arbitrary boundary that astronomers consider separates our solar system from interstellar space. In slightly more than 42 years, it has traveled a distance of 147 astronomical units from the Sun.
The nearest star system, Alpha Centauri, is about 4.3 light years or 40.76 trillion kilometers. At Voyager’s current speed, it would take about 75,880 years to cover that distance.
Voyager 1 and all other spacecraft to date are powered by chemical rockets. Voyager picked up extra speed by getting gravitational assists from Jupiter, Saturn, Uranus, and Neptune. Now that it’s in the interstellar void, there are no additional energy sources to make it go faster. If humans are ever to settle on exoplanets, new methods of spaceflight propulsion will need to be developed.
Exploring new spaceflight technologies is the mission of Icarus Interstellar, a nonprofit foundation whose mission statement says it is “dedicated to achieving interstellar flight by the year 2100.” Founded in 2011, Icarus Interstellar has since 2013 held bi-annual Starship Congresses that incorporate a range of presentations related to how we may get from present space technology to voyages among the stars. This year’s event was held from September 13-15, 2019 at the San Diego Air and Space Museum. Here’s a summary of a few of the more interesting talks.
Richard Obousy holds a PhD in physics from Baylor University and was the first president of Icarus Interstellar. In the first part of a rambling discussion, he reviewed several theoretical reasons to believe the warping of space might be employed to enable faster-than-light travel.
By postulating the existence of a 5th dimension beyond space and time, he reasons that if it were possible to expand the extra dimension behind a spacecraft and compress it in front, the craft could achieve speeds that would cross light-years of interstellar distance in fractions of a year.
Among many unknowns surrounding this hypothesis is whether the amounts of energy required for the warping of space are achievable. A summary of his arguments can be found in a paper titled “Putting the ‘Warp’ into Warp Drive” that can be downloaded here.
The second part of his talk was given over to describing his current business venture, CitizenShipper, an online service linking shippers of everything from boats to pets with contractors who will haul these items. Dr. Obousy started this business because “the job market for FTL physicists is sparse.” He hopes to sell his company for enough money to enable him to work full time on the physics of FTL.
A roadmap to interstellar travel
Even with space warp, the path to interstellar travel begins with mastering the ability to live and work in space. Interstellar ships will need to be enormous because of the energy and life-support requirements. It might make sense to build them in space with materials mined on Earth’s moon or from asteroids. Most of the papers at the Starship Congress focused on various technologies that would enable travel throughout the solar system and dramatically reduce its cost.
Michael Laine, founder and CEO of the LiftPort Group, outlined a plan for a “Lunar Space Elevator Infrastructure” that he believes will enable construction of spaceships and stations using materials from the moon. Laine claims to have spent 20 years working on concepts for “space elevators,” a notion first proposed in 1895 by Konstantin Tsiolkovsky. According to Wikipedia, “A space elevator is conceived as a cable fixed to the equator and reaching into space. A counterweight at the upper end keeps the center of mass well above geostationary orbit level. This produces enough upward centrifugal force from Earth’s rotation to fully counter the downward gravity, keeping the cable upright and taut. Climbers carry cargo up and down the cable.”
Earth-based space elevators probably won’t ever work because no material is strong enough to withstand the stresses such a cable would have to endure. But a space elevator on the moon might because the moon’s mass is 81 times less than Earth’s.
Laine proposes building a permanent space station at the L1 Lagrange point of the Earth-Moon system. This point is about 320,000 km from Earth’s surface, but only 56,300 km from the Moon. From there a Lunar space elevator could lift construction materials mined on the moon to the station. Or if that method doesn’t prove feasible, conventional rockets could get the job done for a fraction of the cost that it takes to reach orbit from Earth.
Once one has built a spaceship at one of the Lagrange points, the additional energy required to reach Mars or the asteroid belt is relatively modest. Laine thinks economical travel throughout the Solar System begins with constructing spaceships and fueling them from materials on the Moon.
Little that Laine had to say is particularly new. In 1976, a Princeton physics professor named Gerard O’Neill wrote a book called The High Frontier: Human Colonies in Space. He proposed building a permanent space settlement at the L5 Lagrange point of the Earth-Moon system. Objects at L5 and L4 are in stable orbits on the same path as the moon. Orbits at L1, L2, and L3 are not stable, although a modest amount of thrust can keep them near the desired points.
O’Neil proposed that the L5 space colonies would be used to make things needed in space. This includes not only spaceships and stations, but also solar power collectors that could be placed in geosynchronous orbits. These orbiting power stations could, O’Neil opined, beam electric power though earth’s atmosphere using microwaves.
The problem O’Neill was trying to solve in the 1970s was a perceived shortage of petroleum. Today, we are awash in oil and gas. Our problem now is that rising CO2 levels in the atmosphere threaten our quality of life on earth.
Laine also suggests that an L1 space station could be used to fabricate solar-electric generators. He estimates that orbiting space generators could supply all the energy needs of Earth’s 300 largest cities where 35% of its human population lives. More than 40 years after O’Neill’s book, the time for a space-manufacturing station at an appropriate Lagrange point may be nearing.
Beyond chemical rockets
The first step to getting anywhere in space is to reach earth orbit. That feat requires reaching speeds in excess of 27,400 km/hr (17,000 mph). The SpaceX website claims that its Falcon Heavy rocket is able to launch payloads to low-earth orbit (LEO) for $1,400 per kilogram.
Several Starship Congress presentations suggested novel ways of getting to LEO cheaper or reducing the cost of deploying payloads to other orbits once a big rocket has gotten them there.
A hydrogen cannon
John Hunter, founder and CEO of Green Launch, talked about how his company plans to get payloads to orbit for as little as $220 per kg. His idea is called a “hydrogen impulse launcher.” It works a lot like a cannon, but with important differences.
A cannon fires a projectile from a rifled tube that’s closed at one end and open at the other. High pressure gases created by burning gunpowder drive a projectile out the barrel of the gun, after which it coasts to its target. Green Launch’s proposed devices use hydrogen heated by the sun instead of explosives that are burned. Plans for the device include a system for recovering and re-using the hydrogen.
The impulse launcher would be built on the Earth’s surface. An ideal location would be on the top of a large mountain where atmospheric drag would be reduced. The launcher would also need a clear area down range so that parts of the launch projectile that drop away after firing would not hit anybody.
Like any artillery piece, the launch vehicle accelerates only while in the barrel. Consequently, to reach orbital velocity at the muzzle of the launcher, acceleration rates must be extremely high, between 15,000g and 30,000g. So the impulse launcher would not be suitable for transporting people. Hunter says it would be suitable for transporting supplies to orbit including food, fuel, structural components of spacecraft, and even properly hardened electronics. He believes that 95 percent of the material for a Mars mission could be launched to low earth orbit with Green Launch’s system. He also says small satellites with deployable solar panels can be designed to withstand 15,000g and could also be launched.
Green Launch has plans for three phases of prototypes of its launch system. The first would launch a projectile to an altitude of 100 km. The second will reach 200 km. The third will put a cubesat (a small satellite) in orbit. This system will have a muzzle velocity of 6 km/second (13,420 mph) and employ a booster rocket to achieve orbital velocity.
For commercial operations, Green Launch envisions a tube capable of launching up to 180 kg (400 pound) vehicles mass-produced for as little as $45 per kg. It’s an ambitious project, but the company’s engineers have built actual hardware including a hydrogen cannon capable of shooting a 4.5 kg (10 lb) projectile at nine times the speed of sound (about 6,900 mph). More information can be found on the company’s website: https://greenlaunch.space/.
Solar sails have been the stuff of science fiction for decades, but on July 23, 2019, Lightsail 2 became the first spacecraft ever to be powered by solar pressure. Matt Kaplan of the Planetary Society gave a polished presentation of the spacecraft, its mission, and the crowd funding that put it into orbit.
The spacecraft is small, measuring 10 by 10 by 30 centimeters and weighs 5 kg. Its sail, constructed from four triangular pieces of Mylar, measures 32 square meters (340 square feet). It was launched atop a SpaceX Falcon Heavy rocket along with 23 other satellites as part of the Air Force’s University Nanosat Program.
The primary objective of the project was to demonstrate that light pressure could be used to raise the orbit of a spacecraft once it had reached low earth orbit. To achieve this, the vehicle uses an inertia wheel to turn the sail at right angles to the sun during each orbit. Even though its rate of acceleration is a miniscule 0.058 mm per second2 the spacecraft was able to raise its orbit about 2 km in seven days starting from an initial apogee of 725 km.
The engineering behind this project is amazing, but so is the fact that it was funded by voluntary contributions. According to the Planetary Society website, “The LightSail project cost is $7 million from 2009 through March 2019. Funding of about $5.5 million was provided by some of the 50,000 Planetary Society members, other private citizens, foundations, and corporate partners. A Kickstarter campaign raised $1.24 million in 2015, while two Omaze fundraisers in 2017 and 2018 generated more than $220,000.” One member of the Planetary Society from Texas contributed a million dollars to the project. Launch costs were covered by the Air Force. More about this mission can be found on the Lightsail 2 pages of the Planetary Society website.
Steam powered space tug
Mikhail Kokorich thinks he has something better than light sails to move small satellites from low earth orbits to higher ones. Some venture capitalists apparently agree with him.
His company, Momentus, has raised $25.5 million to develop a series of space vehicles that can haul individual satellites into custom orbits much more cheaply than chemical rockets. Momentus currently employs 45 people and plans to begin commercial satellite positioning services in 2020.
What sets Momentus apart from most space vehicles is that its propulsion system uses no chemical reactions. Instead it employs solar photovoltaic panels to generate microwaves that heat water well beyond superheated steam to an ionized state called plasma that reaches temperatures of 10,000 degrees K. The plasma is expelled through a tiny nozzle to provide thrust.
The advantages of this system are two-fold, according to Kokorich. First, it requires one-third the mass of propellant to boost a satellite to a given orbit when compared with chemical rockets. Ejecting less mass means less fuel needs to be carried by a conventional rocket to low-earth orbit. With every kilogram currently costing at least $1,400 to reach orbit, the savings in reaction mass reduces costs.
The second advantage is safety. The system requires no combustible fuels and no pressure vessels. It can’t blow up.
The drawback to Momentus’s water-plasma propulsion system is that thrusts are relatively low: a fraction of a Newton or less than 1/10 of a pound. Because there is no air drag in orbit, low thrust is acceptable. But it can take four to seven months to reach a desired orbit according to company datasheets.
Momentus plans to begin shuttle services with the Vigoride vehicle in 2020. Its maximum payload is 250 kg. Higher capacity vehicles are planned for 2021 and 2022. To learn more about them, visit: https://momentus.space/.
Travelers on long-distance space flights must cope with a range of biological challenges including growing food, scrubbing carbon dioxide from the air, and possibly coping with the effects of low or zero gravity on their bodies. Although the scientists presenting on these topics at the Starship Congress are primarily interested in terrestrial applications of their work, they gamely spun their presentations for the starship audience.
Spirulina shipboard garden
Spirulina is a type of algae called alkaliphilic phototrophs. As the name implies, they convert light into plant material and love alkaline lakes such as Soap Lake in Washington state.
Pierre Wentzel is growing spirulina primarily to extract a blue food coloring to replace the more synthetic Artificial Blue #1 employed in packaged foodstuffs. For the Starship Congress, he devised a system for growing his algae on a spaceship that would remove CO2 from the air and provide a source of food for the astronauts. An advantage of spirulina, he told the audience, is that it settles naturally to the bottom of the growing tank instead of floating to the surface like pond scum.
Spirulina doesn’t sound appealing to eat. Wentzel says it is tasteless when “wet from the reactor” but “tastes terrible when dried.” He described the flavor as fishy or “like mud.” As Mary Roach points out in her entertaining book, Packing for Mars, NASA has a long history of creating unappetizing food for astronauts. Perhaps future space pioneers who carry a spirulina tank on their voyage won’t mind the taste. Or perhaps a variant that tastes like chocolate could be genetically engineered.
Wentzel’s company is called Spira, Inc. There is little to see on his website, but you can send the company a message for more information. Wentzel grows his algae at an algae test bed at Arizona State University.
Growing human brain organoids in space
Alysson Muotri, a professor at the School of Medicine at the University of California, San Diego, wants to better understand how brains develop in children. Since, as he pointed out in his talk, most parents won’t let scientists experiment on their kids, he is growing what he calls “brain organoids” from stem cells in his lab. These lumps of tissue look and in some ways behave like brain tissue but lack the sophisticated structure of fully developed children’s brains.
Muotri was perhaps the only presenter at the Starship Congress to have gotten a scientific experiment run on the International Space Station. The experiment, which fit into a container a little larger than a shoe box, grew brain organoids in zero gravity. Much of his talk revolved around that experience.
One of the not so surprising results he shared was that organoids in zero gravity develop a spherical shape whereas in his earthbound lab they flatten out like a hamburger patty. He hopes to repeat the experiment in the future in order to determine if the organoids age faster in zero gravity than they do at 1g. He said it has been demonstrated that shortening of telomeres in zero gravity makes the aging process run faster, but the mechanism is not well understood.
The natural acceleration of aging in space recalls the Star Trek episode “The Deadly Years” (Season 2, Episode 12) in which Captain Kirk and his officers age rapidly after a blast of radiation. Perhaps zero gravity is all it would take to make astronauts older sooner. More about Prof. Muotri and his work can be found on his laboratory’s website.
In the past, the Icarus Interstellar has posted videos of some presentations on YouTube. The 2019 presentations are not there yet, but should eventually appear. “It takes a while,” said Tiffany-Marie Austin, one of the conference organizers.