There are many wonderful places in the universe that we want to see, and perhaps more unspoken numbers that we have not yet seen or heard of. Unfortunately … they are all far away. With the help of current technology, one of the best scenic trips to Mars takes about six months, meanwhile, if you want to go to Alpha Centauri, it’s a full four light years away!
While covering this great distance, conventional chemical rocket technology does not simply cut mustard. As it turns out, lasers can hold the key to reducing space travel time!
Laser 45 days on Mars
Laser thermal propulsion is a relatively simple concept, and our spacecraft can travel around our sky faster than ever before. A powerful laser beam emitted from the earth aims at a large heat exchanger in the ship, through which a pilot is pumped. As the heated propellant expands, it eventually exhausts in the same way as a conventional rocket outside a nozzle. This is similar to the concept of atomic thermal conduction, but instead of using heat from a nuclear reaction, it relies on the laser power supplied externally.
A recent study suggests that such a propulsion system can run at a certain tendency for about 3000 seconds. It is basically a measure of how much thrust an engine produces per mass of fuel. At 3000 seconds, a laser thermal propulsion system can be said to be at least 12 times more fuel efficient in thrust position than solid shuttle booster (SRBs) in space shuttles.
This allows a laser thermal propulsion to achieve much greater change in speed with less fuel, enabling a space mission to send payloads faster and faster. Calculations show that with an ideal mission plan, a payload of about 1000 kg could be sent to Mars in just 45 days, much faster than the usual 6-7 months on a normal chemical-fuel mission.
The technology involved is complex, you’d expect. The mission will require a large laser array of 100 MW power. The spacecraft itself will be launched from the atmosphere in a conventional chemical rocket, allowing it to isolate and emit a large swollen parabolic reflector. The ground-based laser will then catch fire for up to an hour, using adaptive optics to counteract the effects of the Earth’s atmosphere on the rays. The spacecraft’s parabolic reflector will then focus energy in a chamber to heat the hydrogen propellant which will be expelled from the nozzle at high speed, providing thrust.
If desired, the spacecraft could be designed to release a payload capsule on its way to Mars, separate the laser thermal propulsion unit, and return to a stable Earth orbit for fuel. This has the advantage that the propulsion system itself can be used multiple times in a series of fast loft payloads across the earth.
Such a system has one major flaw that stands out. Although a laser is used on Earth to accelerate a spacecraft at high speeds, there is no laser array on Mars that can slow down the spacecraft upon arrival. Nor is it a practical way to slow down chemical conduction, as it would take up much more of the useful payload of craft. Researchers have instead determined that a very careful arrow-breaking technique could be used to slow down an incoming craft in the Martian atmosphere. However, it is a delicate operation that must be performed flawlessly to ensure success.
Overall, such a system could easily be developed in the near future. Although no one has a 100-megawatt laser array, modern fiber optic laser technology does not mean that such power images are out of the question. Similarly, much work needs to be done to create a reliable laser thermal spacecraft and ground system that is capable of sending payloads in useful directions into space, not limited to the relative position of spacecraft and ground lasers.
Ride the laser to the star
If you want to get to our nearest star Alpha Centauri, you need to travel faster. Even at the speed of light, it will take four years to get there. Thus, a search that wants to go this far will want to go as close to that speed as possible to make it within a reasonable time.
Laser sails can hold the answer to this problem. They rely on the concept of photon radiation pressure, where light hits a surface and actually creates pressure and pushes it along. These are referred to as sails because the concept is similar to that of a sailing ship dating back centuries. Instead of cloth and air, though, a laser sail replaces advanced nano-materials and powerful laser light.
Recent research suggests that a laser sail on a scale of a few meters can propel a gram-weight craft at 0.2 times the speed of light. It will be able to reach Alpha Centauri in about 20 years, not a few thousand years with conventional rocketry.
The concept would require the use of a sail made of extremely thin sheets of material such as aluminum oxide, silicon nitride and molybdenum disulfide. Measured a thousand times thinner than a sheet of paper, the flock must be strong enough not to tear and must also be able to dissipate heat so that it does not melt away from the power of the laser driven along it.
Advanced nano-patterning of sails will be the key to achieving this goal. The idea is to create a sail with high reflection to maximize acceleration due to photonic pressure, as well as to maintain high heat emission to keep the sail cool enough to not melt. With 100 GW laser array firing in the sail, this is no average feat. Much like a conventional sail on a sailing ship, the material will be let out under the pressure of incoming light. This significantly reduces the chances of crying.
At best, the sail will only be able to carry a small payload weighing a few grams. It is hoped that advanced fraudulent methods could create a microprocessor, camera and communication hardware for the probe that would be able to communicate over vast distances between Alpha Centauri and Earth.
It’s a bold plan, and one that could enable space exploration to tackle far-reaching issues. However, the challenges involved are great. The requirements for extremely powerful laser arrays are beyond our current capabilities, and the equipment problem still needs to be addressed. In addition, any message sent from a search by Alpha Centauri would take four years to return to Earth, so communication problems also appear.
However, research conducted by Breakthrough Initiatives shows that laser pelvic concepts are not only necessary for science fiction. With proper investment and development, they may one day prove to be an effective propulsion method for research craft.
Unlike other seemingly science-f technology, like ion thrusters, these laser propulsion methods are still far from being fielded in real space missions. There is a huge challenge to overcome and it is also a thought for any bird or other unfortunate wildlife that finds itself in a megawatt- or gigawatt-class laser beam.
However, if we want to open heaven, we will need more than what our existing technology can achieve. Thus, these projects, or perhaps other fancy new ideas, may one day take us out of our own solar system.