Interstellar Probes

[Airbrush]

Does anyone know about how long it will take for the human race to build unmanned interstellar probes to be sent at the highest speeds possible to nearby stars? These would be sent to stars we find with nice Earth-like planets. Easier to build a craft for a one-way trip and there are no humans to support.

 

There is no mention in this wiki article about interstellar probes using multiple methods of propulsion. Such a craft could be built in Earth orbit. It should be as small as possible so less mass needs to be accelerated. How about start it off using conventional rockets to get away from Earth. Ion thrusters can help. Then kick in the nuclear pulse propulsion to get it up to a high initial speed. Use gravity kicks from the outer planets. Outside the solar system spread a giant solar sail or some kind of Medusa propulsion. It will also have to slow down using the same means. Then it gets into orbit around an Earth-like planet of interest and studies it for a few years, then transmit its findings back to Earth. How about launching it a hundred years from now? Could it reach an interesting planet in a hundred years travel time? Could we know up-close details about another Earth within 250 years from now?

 

https://en.wikipedia.org/wiki/Interstellar_probe

Edited March 23, 2016 by Airbrush

[EdEarl]

Some large telescopes are planned, with primary mirrors larger than 20 meters, one day there may be one that's 100 meters. In addition, fairly large space telescopes are planned. Eventually, one will be able to see well enough to perform spectroscopic analysis of some exoplanet atmospheres. Oxygen in an atmosphere is, as far as we know, a sign of life. Thus, we may be able to send a few robotic probes to planets that are likely to have life, or at least some whose atmosphere may be modified for life. Nonetheless, such trips will probably take centuries. So far our fastest space probes would take more than 50,000 years to travel to the nearest star, but faster travel is possible. However, we cannot achieve the speed of light, and probably not even 10% the speed of light. A trip to a star that is 1000 light years distant at 10%c would take more than 10,000 years, and there seems to be no way around that.

 

BTW, the Milky Way is about 100,000 light years across; at 10%c traveling across would take 1M years.

 

See: Interstellar Travel

Edited March 23, 2016 by EdEarl

[Airbrush]

The next generation of space telescopes will certainly find plenty of interesting stars within 100 light years that have habitable zone planets. What are the current probability estimates of how far away is the nearest Earth-like planet or Superearth? I vaguely recall info based on Kepler's findings of a high probability of such a planet within about 13 light years. I suggested launching in 100 years or more to use better propulsion methods we don't even know about yet. Also you want such a probe to carry lots of bells and whistles, such as a number of landing craft and surveying devices we haven't even thought about, but also keep it light-weight so you can reach higher speeds for a shorter travel time. Is it unreasonable to speculate that in 100 years from now we should be able to send a probe at about 10%C? If the planet is 15 light years away it could get there in about 150 years travel time.

 

Who cares about habitable planets over 1000 light years distant?

Edited March 24, 2016 by Airbrush

[swansont]

Does anyone know about how long it will take for the human race to build unmanned interstellar probes to be sent at the highest speeds possible to nearby stars? These would be sent to stars we find with nice Earth-like planets. Easier to build a craft for a one-way trip and there are no humans to support.

 

There is no mention in this wiki article about interstellar probes using multiple methods of propulsion. Such a craft could be built in Earth orbit. It should be as small as possible so less mass needs to be accelerated. How about start it off using conventional rockets to get away from Earth. Ion thrusters can help. Then kick in the nuclear pulse propulsion to get it up to a high initial speed. Use gravity kicks from the outer planets. Outside the solar system spread a giant solar sail or some kind of Medusa propulsion. It will also have to slow down using the same means. Then it gets into orbit around an Earth-like planet of interest and studies it for a few years, then transmit its findings back to Earth. How about launching it a hundred years from now? Could it reach an interesting planet in a hundred years travel time? Could we know up-close details about another Earth within 250 years from now?

 

 

 

This isn't going to happen any time soon. We don't have any of the manufacturing technology up and running. Nuclear propulsion is politically iffy even if anyone knew how to get it to actually work. But the main problem is that we can't get them going fast enough to be viable.

 

http://io9.gizmodo.com/5786083/what-are-the-fastest-spacecrafts-ever-built

the heliocentric speed of Voyager 1, some 17.05 kilometers per second, which is faster than any of our outward bound spacecraft but would take well over 70,000 years to reach Alpha Centauri, assuming Voyager 1 were pointed in that direction.

 

 

Even if we boosted that by an order of magnitude, it's still 7,000 years to a nearby star. Do we know how to build anything that would last 7,000 years, and work after that time?

 

So if there's basically no point, then there probably isn't any serious work going on in this arena.

[EdEarl]

There are about 16 exoplanets currently known within 100 ly that are similar to Earth. Now, we cannot image any of them well enough to know anything about their atmosphere, if any. There may be more found within that radius. It seems likely that as we learn more about these 16 planets, some will not be suitable. About 50 exoplanets are currently known within 3500 ly that are similar to Earth.

 

I think 10%c is very ambitious for anything we make, and the larger it is the less likely we can make it go that fast. Our best chance of making a drone that can travel that fast is to keep its mass small, such as a ping pong ball, but afaik no one is working toward it atm. That 10%c is 18,600 miles per second; whereas, our fastest spacecraft has gone 38,600 miles per hour = 11.7 miles per second. It's Voyager going that fast, which was launched in 1977. It seems unlikely we will push anything 10%c within 250 years since we have made virtually no progress toward that goal in 40 years.

[swansont]

There are about 16 exoplanets currently known within 100 ly that are similar to Earth. Now, we cannot image any of them well enough to know anything about their atmosphere, if any. There may be more found within that radius. It seems likely that as we learn more about these 16 planets, some will not be suitable. About 50 exoplanets are currently known within 3500 ly that are similar to Earth.

 

I think 10%c is very ambitious for anything we make, and the larger it is the less likely we can make it go that fast. Our best chance of making a drone that can travel that fast is to keep its mass small, such as a ping pong ball, but afaik no one is working toward it atm. That 10%c is 18,600 miles per second; whereas, our fastest spacecraft has gone 38,600 miles per hour = 11.7 miles per second. It's Voyager going that fast, which was launched in 1977. It seems unlikely we will push anything 10%c within 250 years since we have made virtually no progress toward that goal in 40 years.

Fast requires fuel, which is a conflicting requirement to making it small.

[EdEarl]

Laser beam and light sail. I agree, if a spacecraft carries fuel it cannot be really small.

[swansont]

Photon propulsion is quite wimpy for anything macroscopic. F=2P/c under ideal conditions, where P is the power of the light. So 1 Megawatt gets you 6.7 millinewtons.

 

Whoa. Fasten your seatbelt.

 

A 10 kg payload gets up to 21 km/s after a year*. In reality, your thrust will decrease as the target gets further away and the laser expands. Plus you have to track the probe.

 

EDIT: *if there's no gravity

[Airbrush]

"...A Medusa spacecraft would deploy a large “spinnaker” sail ahead of it, attached by separate independent cables, and then launch nuclear explosives forward to detonate between itself and its sail. The sail would be accelerated by the plasma and photonic impulse, running out the tethers as when a fish flees the fisherman, and generating electricity at the “reel”. The spacecraft would then use some of the generated electricity to reel itself up towards the sail, constantly smoothly accelerating as it goes.^[10]

 

In the original design, multiple tethers connected to multiple motor generators. The advantage over the single tether is to increase the distance between the explosion and the tethers, thus reducing damage to the tethers.

 

Medusa performs better than the classical Orion design because its sail intercepts more of the explosive impulse, its shock-absorber stroke is much longer, and all its major structures are in tension and hence can be quite lightweight. Medusa-type ships would be capable of a specific impulse between 50,000 and 100,000 seconds (500 to 1000 kN·s/kg)."

 

https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion#MEDUSA

 

Can such a spacecraft be built within the next 200 years? Assuming we don't return to a pre-industrial age due to human stupidity through nuclear war or extreme climate change, or supervolcano eruption. Could such a spacecraft reach 10%c? If so then could a habitable planet (for us) be studied up close and the results of the study beamed back to Earth within the next 500 years?

[EdEarl]

Medusa seems complex compared to a laser and light sail. In addition, Medusa parts that might "wear out" are traveling on the ship, where repairs cannot be made, or additional mass is required for replacement parts and robots to perform repairs. The laser would be near Earth and accessible for repair. The light sail has nothing to wear out. The simple solution is usually preferable. Why add the complexity of Medusa?

[Airbrush]

... The light sail has nothing to wear out. The simple solution is usually preferable. Why add the complexity of Medusa?

 

Yes indeed.

 

Let's meet here again in about 50 years and discuss this issue.

 

Because of the problems of such high speeds it now seems the way to interstellar travel is by generational ships. Get used to the idea of traveling at modest speeds, but be able to live comfortably in space in artificial one g gravity and able to make repairs, grow food, stopping at asteroids or rogue planets to pick up water and metals. Sending probes to the nearest stars through the interstellar medium at such high speeds may not be practicable. We may send out 100 of them and never hear from any of them again due to unknown mishaps. So we need to walk there at a leisure pace and have fun along the way. The ultimate destination, the habitable planet, is tens of thousands of years travel time.

Edited March 25, 2016 by Airbrush

[EdEarl]

Photon propulsion is quite wimpy for anything macroscopic. F=2P/c under ideal conditions, where P is the power of the light. So 1 Megawatt gets you 6.7 millinewtons.

 

Whoa. Fasten your seatbelt.

 

A 10 kg payload gets up to 21 km/s after a year*. In reality, your thrust will decrease as the target gets further away and the laser expands. Plus you have to track the probe.

 

EDIT: *if there's no gravity

Further developments:

 

Stephen Hawking joins futuristic bid to explore outer space

 

With famed physicist Stephen Hawking at his side, an Internet investor announced Tuesday that he's spending $100 million on a futuristic plan to explore far outside our solar system.

 

Yuri Milner said the eventual goal is sending hundreds or thousands of tiny spacecraft, each weighing far less than an ounce, to the Alpha Centauri star system.

IDK if they intend these hundreds or thousands of tiny craft will be individual or a swarm, but a swarm seems like a good architecture. They could rob a bit of energy from the laser to keep formation and to communicate. They could cooperate to beam a signal to Earth, and probe the Alpha Centauri system with microwaves.

Edited April 18, 2016 by EdEarl

[swansont]

There's a reason why I said macroscopic. Also, I wasn't considering something 5 orders of magnitude larger in power. That's...aggressive.

[Enthalpy]

Medusa performs better than the classical Orion design because its sail intercepts more of the explosive impulse, its shock-absorber stroke is much longer, and all its major structures are in tension and hence can be quite lightweight. Medusa-type ships would be capable of a specific impulse between 50,000 and 100,000 seconds (500 to 1000 kN·s/kg)."

 

Even if a Medusa were feasible, its specific impulse isn't up to the task. At 100,000s=1Mm/s you can accelerate and then brake the vessel to 2Mm/s or very little more. 5Ly to the next star still take 1500 years. Same worry with nuclear fusion.