Should we send interstellar probe to Alpha Centauri?

[Urvabara]

I wonder how we would react to a probe coming in
that was useing H-bombs to slow down

My reaction would be: "So, there is a civilization that found a good use for their H-bomb stockpiles!"

 

[Oberst Villa]

I saw operational railguns 20+ years ago (with muzzle velocities of 3 km/s), and the Navy is now testing one for naval artillery.

Here's a Popular Mechanics article on the BAE system delievered to the US Navy.
http://www.popularmechanics.com/technology/military_law/4231461.html

First thing, thanks a lot for the link, I was not aware of this latest development, I have to admit that it makes my ranting a bit pointless.

As for the railguns that were operational 20+ years ago, probably I have communicated my thoughts quite badly. English is not my native language and I sometimes use words sloppily even in german. The heart of the problem seems to be my (possibly wrong) usage of the word "operational". What I had in my mind when saying that I have not seen an operational railgun yet was something like "a weapon system that is ready to be used in the field right now", (as opposed to a prototype in the lab). The best I could find in this context was a definition of "Initial Operational Capability", don't know whether it's an offical definition of this term, but anyway this is quite precisely what I meant:

"The first attainment of the capability to employ effectively a weapon, item of equipment, or system of approved specific characteristics, and which is manned or operated by an adequately trained, equipped, and supported military unit or force."

Now I have the impression that when YOU say "operational" you mean "something that works" (as opposed to something that is not working yet) and OK, this might just be the normal meaning of the word.

Anyway, maybe I should have said "I have not seen an operationally deployed railgun yet", then I could have avoided this misunderstanding, sorry for this.

 

[Oberst Villa]

Whether you are impressed or not, you have to realize that being technically able to do something means nothing in reality. There is a lot of other things that have to happen. This is where 99% of failed ventures get tripped up. We went to the moon not only because we had a lot of talented technical people, but mostly because Kennedy set the government on the path that it would be done and gave NASA the support they needed.

Hmm, I don't disagree with you on this. But I think it's not very probable that such a foccussing of the nations scientific and industrial ressources on a single goal will be repeated in the near future. There is nobody in sight against whom the US would have to compete like they did against the Soviets.

 

[Oberst Villa]

I don't know how long a time the accelerating takes exactly. If a = 10g = 98,1 m/s², then accelerating to 0.1c takes about 85 hours.

10g is muuuuuuuuch to high.

First thing, for the probe to tolerate such an acceleration without breaking apart, you would need a massive support structure, which would add a lot of mass to your probe => Kiss your 99,78% goodbye.

Second thing, there is no need for such a high acceleration. You need 40 years as a minimum, so would it hurt much to add e.g. 850 days for the acceleration phase ?

 

[D H]

Ok. I just calculated that about 99.78% of the mass of the probe will be fuel, if assuming \Delta v = 29979245.8 + 29979245.8 = 59958491.6 m/s and maximum exhaust velocity of hydrogen nuke Orion of v_{e} = 9800000 m/s. That's a big fraction of fuel, I know...

An Orion-type rocket will need a *lot* of mass to protect the payload from the explosions.

I just used the Tsiolkovsky's rocket equation and put the numbers (\Delta v and v_{e}) in.

You are hypothesizing relativistic velocities, so you need to use the relativistic rocket equation:

\frac{\Delta v}{c} = \tanh\left(\frac {v_e}{c}\,\ln\frac {m_0}{m_1}\right)

You chose an extremely unrealistic rocket. A more realistic choice of rocket technology will yield a very different mass ratio. For example, a VASIMR engine has an effective exhaust velocity of up to 300,000 m/s. The fuel mass ratio for a VASIMR engine is 99.999...%: 87 nines! There is no room for vehicle structure here. We need something a bit more exotic than VASIMR engine but something that has a ghost of a chance. How about injecting small amounts of antimatter into a plasma, forcing some plasma to escape at a high velocity, and just making a fly-by? Ths gets us down to 99.999...% fuel mass (13 nines). There's still no room for structure, but an improvement.

Note well that both of these rockets are way out there in terms of specific impulse. Nonetheless, neither a 200 fold or 600 fold increase in Isp will enable us to send a payload to Alpha Centauri.

 

[DaveC426913]

10g is muuuuuuuuch to high.

First thing, for the probe to tolerate such an acceleration without breaking apart, you would need a massive support structure, which would add a lot of mass to your probe => Kiss your 99,78% goodbye.

Second thing, there is no need for such a high acceleration. You need 40 years as a minimum, so would it hurt much to add e.g. 850 days for the acceleration phase ?

1] I am fairly certain a probe could be built to withstand much 10g's or more.
2] You don't need to add mass, you just need a good shock absorbing system.

 

[Urvabara]

10g is muuuuuuuuch to high.

First thing, for the probe to tolerate such an acceleration without breaking apart, you would need a massive support structure, which would add a lot of mass to your probe => Kiss your 99,78% goodbye.

Second thing, there is no need for such a high acceleration. You need 40 years as a minimum, so would it hurt much to add e.g. 850 days for the acceleration phase ?

I just chose a number (10 g) I could imagine a machine could withstand. Ok, < 10 g will do...

 

[blimkie.k]

It bothers me how some can be so quick to shoot down optimistic ideas about space exploration. And not even just space exploration all kinds of sceintific ideas and engineering. Without optimistic and thinking "outside the box" we woulndt be where we are today. Throughout human history there was been many profound discoverys that have comepletly changed the way we see our universe. Many people believed Copernicus was crazy but he right to some extent. Back to the main idea...

I don't know much about using H-bombs as propulsion device but these things release a great deal of energy that could probably be used as something bette then just a way to destroy life as they did in the past. As somone said early in the post using H-bombs to propel a craft is still science fiction but nukes haven't been tested in like 30 years or something like that I believe China was the last country to stop testing.

What if we were to try a test a safe distance from out planet, Is there a safe but not too far distance from Earth where a nuke could actually be detonated without casuing harm to the planet. If this was going to be tested I would suggest the probe and nuke be strapped to a rocket and fired a safe distance from Earth before the nuke is detonated. Even if the probe doesn't make it there the first time it could still end up being a milestone as Urvabara said.

As for using an H-bomb as a way to slow down...I don't think ET would be to happy if we came flying into his solar system and detonated a nuke haha, they might not want much to do with us after that.

 

[DaveC426913]

It bothers me how some can be so quick to shoot down optimistic ideas about space exploration.

We have no power to stop anyone from doing anything. We're all just talking here; I don't imagine anyone's attempts to build their own rocket are hinging on the postive feedback of PFers.

 

[DaveC426913]

I would suggest the probe and nuke be strapped to a rocket and fired a safe distance from Earth before the nuke is detonated. Even if the probe doesn't make it there the first time it could still end up being a milestone as Urvabara said.

Probes that don't make it to places have a way of coming back to where they started.

Can you see why we are reluctant to strap bombs to ... well, other bombs ... and lob them around our neighborhood?

 

[Oberst Villa]

As for using an H-bomb as a way to slow down...I don't think ET would be to happy if we came flying into his solar system and detonated a nuke haha, they might not want much to do with us after that.

Why does everybody assume that the extraterrestrials would be like ET ? Think of the evil creatures in "Aliens". Blowing up some fat nukes in front of their doorstep might be a nice way of saying "Don't you mess with us !" (let alone thinking of eating us...)

 

[D H]

It bothers me how some can be so quick to shoot down optimistic ideas about space exploration.

This is a scientific forum, not a complete fantasy and bad science fiction forum. The ideas proposed in this thread are pure science fiction. If we ever do send a probe to another star system, it will not be with any of the propulsion systems discussed in this thread.

I'll starting with what we know now (i.e., chemical rockets). Using chemical rockets to send even a small payload on a fly-by mission to another star in any reasonable time would require a mass of propellant that vastly exceeds the mass of the universe. Chemical rockets are obviously a non-starter. How about more advanced propulsion techniques?

The best propulsive technique developed to date is the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). In one mode it has a very high specific impulse but a very low thrust. Suppose we develop something that maintains this high specific impulse but also generates a reasonable amount of thrust. We want to get up to 1/10 of the speed of light so a fly-by mission to a nearby star will occur in a reasonable amount of time. The relativistic rocket equation dictates that the vehicle be 99.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999% fuel. In other words, the mass of the fuel must be 10⁸⁷ times the tare mass of the vehicle, including the fuel tank, vehicle structure, propulsion system, and payload. Getting a one gram payload with an otherwise massless vehicle would require a fuel mass equal to that of 10³⁰ universes. Still a no-starter.

Claims for the specific impulse for an Project Orion-based vehicle (nobody has built one) are up to 30 times that of the VASIMR engine. This drops the fuel requirements considerably. For a fly-by mission at 0.1 c, the fuel mass need be a mere 19 times that of the tare mass of the vehicle. One big problem with a Project Orion-type vehicle: The fuel is nuclear bombs. Using hydrogen bombs is ludicrous. A Tsar Bomba would destroy even a city-sized spacecraft . A much, much smaller explosion is needed.

The obvious thing is to use fusionable material in the form of very, very small bombs. A huge spacecraft will still be needed to shield the payload from the explosions and to maintain structural integrity of the vehicle itself. The vehicle itself will need to mass several tons. Now another problem arises: We need twenty times that much mass in fuel. We don't know how to make deuterium fuse with deuterium. Deuterium and tritium? We don't have tons of tritium. Fusion bombs use a very small amount of tritium. Project Daedelus proposed deuterium/helium 3. They would get the helium 3 by mining Jupiter's atmosphere.

 

[russ_watters]

It bothers me how some can be so quick to shoot down optimistic ideas about space exploration. And not even just space exploration all kinds of sceintific ideas and engineering. Without optimistic and thinking "outside the box" we woulndt be where we are today.

My standard response to that is that in order to properly think outside the box, you first have to understand where the box is and what is in it.

Throughout human history there was been many profound discoverys that have comepletly changed the way we see our universe. Many people believed Copernicus was crazy but he right to some extent.

Things like that are commonly cited, but they are incorrect analogies. Copernicus lived before science, so the reason people thought he was wrong was that no one had a way to properly analyze his ideas. That isn't the case today. We can properly analyze these ideas.

Also, please note that while the quality of people varies on any site, we're not just armchair scientists and engineers here - virtually every PF regular involved in this conversation is a professional at a related science or engineering discipline. So we really know what is and isn't likely, technologically, for the near future.

 

[Urvabara]

Why does everybody assume that the extraterrestrials would be like ET ? Think of the evil creatures in "Aliens". Blowing up some fat nukes in front of their doorstep might be a nice way of saying "Don't you mess with us !" (let alone thinking of eating us...)

ET = Extraterrestrial life form.
ET = The Extra Terrestrial film.

Many people may use the letters "ET" without referencing to the famous ET film.

 

[DaveC426913]

ET = Extraterrestrial life form.
ET = The Extra Terrestrial film.

Many people may use the letters "ET" without referencing to the famous ET film.

At first I thought that's what he meant too, but it isn't.

He doesn't mean 'why is everyone talking about E.T.'?

He's reading our posts and we keep talking about the alien race we'll encounter and he's hearing us assume it will be friendly and non-belligerent. He's wondering why we don't think it'll be a race that wants to eat us.

 

[Oberst Villa]

At first I thought that's what he meant too, but it isn't.

He doesn't mean 'why is everyone talking about E.T.'?

He's reading our posts and we keep talking about the alien race we'll encounter and he's hearing us assume it will be friendly and non-belligerent. He's wondering why we don't think it'll be a race that wants to eat us.

Yes, exactly, thanks for explaining it more clearly. And it is not only in this thread, take for example a look at the Pioneer plaque. The decision to include a drawing of a man and a woman... "Hmm, look how yummy we are !"

On a more serious note, no I don't really think there is someone out there who wants to eat us. However, if we look at our own civilization and its history, the assumption that all extraterrestrials (should they exist) are friendly and non-belligerent is certainly not justified.

 

[Urvabara]

On a more serious note, no I don't really think there is someone out there who wants to eat us. However, if we look at our own civilization and its history, the assumption that all extraterrestrials (should they exist) are friendly and non-belligerent is certainly not justified.

I do not think so either. If an ET civilization is to able to do interstellar travel, then they should also have enough food and be able to produce artificial meat. No need to eat Earth meat which in fact could be very poisonous for them.

Almost all _intelligent_ people are friendly. I can hardly imagine a scientist who would like to do any harm to ET civilization. Of course, there are people who would like to do harm to them, but this minor group of our civilization is not intelligent. They belong to a group called "brutal animals".

 

[blimkie.k]

Probes that don't make it to places have a way of coming back to where they started.

Can you see why we are reluctant to strap bombs to ... well, other bombs ... and lob them around our neighborhood?

Very good point that could be deadly, sounds like risky buisiness.

Why does everybody assume that the extraterrestrials would be like ET ? Think of the evil creatures in "Aliens". Blowing up some fat nukes in front of their doorstep might be a nice way of saying "Don't you mess with us !" (let alone thinking of eating us...)

Haha and even if they did retaliate it would be a long time before we have to worry about something gettin back to us.

Also, please note that while the quality of people varies on any site, we're not just armchair scientists and engineers here - virtually every PF regular involved in this conversation is a professional at a related science or engineering discipline. So we really know what is and isn't likely, technologically, for the near future.

Russ, I don't doubt your or any other PF's qualifications, I am just young and the idea of something like this happening in my lifetime would be amazing, especially if we did encounter intelligent life. And all this talk about exoplanets these days is really quite exciting

I do not think so either. If an ET civilization is to able to do interstellar travel, then they should also have enough food and be able to produce artificial meat. No need to eat Earth meat which in fact could be very poisonous for them.

Almost all _intelligent_ people are friendly. I can hardly imagine a scientist who would like to do any harm to ET civilization. Of course, there are people who would like to do harm to them, but this minor group of our civilization is not intelligent. They belong to a group called "brutal animals".

You mean like george bush and other political leaders, let's see if they have any oil we can take from them!

 

[Mech_Engineer]

You mean like george bush and other political leaders, let's see if they have any oil we can take from them!

Oh joy, what a wonderful turn you're taking this thread on. Let's get back to powering probes with hydrogen bombs, at least its related to the topic at hand and not mindless political commentary.

 

[blimkie.k]

Oh joy, what a wonderful turn you're taking this thread on. Let's get back to powering probes with hydrogen bombs, at least its related to the topic at hand and not mindless political commentary.

I don't even see a point for you to post on this thread. Every post you have made has been negative contains a excessive amount of sarcasm, takes a stab at belittling someone or all of the above.

 

[DaveC426913]

I don't even see a point for you to post on this thread. Every post you have made has been negative contains a excessive amount of sarcasm, takes a stab at belittling someone or all of the above.

The occasional cold, hard reality check is his point. This thread is the better for it.

 

[FredGarvin]

I don't even see a point for you to post on this thread. Every post you have made has been negative contains a excessive amount of sarcasm, takes a stab at belittling someone or all of the above.

I certainly see a point. ME's point being that this thread was marginal, at best, when talking about hydrogen bombs as propulsion. At least that topic was a technical topic for discussion and led to others. The second you introduce pointless political commentary is the moment the thread gets considered for being locked as going off topic.

 

[russ_watters]

That's as good a note as any to end it on...

Sorry, but these guys are right - there really isn't much engineering content here.