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m1omg
2007-Aug-08, 09:04 AM
Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?It would be capable of arriving to the Moon in 16.5 minutes and it would be a good interplanetary space engine for a start of the manned missions and colonisation of the Solar system.

Bob B.
2007-Aug-08, 01:09 PM
Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?

Certainly not using chemical propulsion. The current record velocity for the launch of a spacecraft is 16.2 km/s for New Horizons, launched in January 2006. That is probably about the limit under chemical rocket power, though man-manned objects have reached higher velocities through gravity assist, or simply by flying inward toward the Sun.

Very high efficiency ion engines have been used but they are of exceedingly low thrust and no good for accelerating large payloads to high velocities. Nuclear engines have been tested but nothing has ever been made operational. The highest specific impulse I've heard for any of these technologies is about 3,000 seconds, which I doubt could theoretically achieve anything more than about 100 km/s.

Laguna
2007-Aug-08, 01:16 PM
Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?It would be capable of arriving to the Moon in 16.5 minutes and it would be a good interplanetary space engine for a start of the manned missions and colonisation of the Solar system.
Hmm, how did you calculate that?

Distance Earth-Moon d=380000km
Speed v=300km/s

d/v=1266s = 21.1 minutes
Adding the time to speed up to 300km/s and decelerating would add even more time on those 21 minutes.

To get to the moon in a time of t2=16.5 minutes it takes an average speed of v/t2=383.8km/s = 23030km/h

As far as I know, the phoenix probe is traveling roughly at that speed on its way to mars.

m1omg
2007-Aug-08, 01:36 PM
Hmm, how did you calculate that?

Distance Earth-Moon d=380000km
Speed v=300km/s

d/v=1266s = 21.1 minutes
Adding the time to speed up to 300km/s and decelerating would add even more time on those 21 minutes.

To get to the moon in a time of t2=16.5 minutes it takes an average speed of v/t2=383.8km/s = 23030km/h

As far as I know, the phoenix probe is traveling roughly at that speed on its way to mars.

1.I used the simple figure of 300000 km as the Moon's distance.
It doesn't matter.Do not waste time with things that are absolutely not important.

2.Your calculation is wrong, because;
383800 m/s = 1381680 km/h .

Laguna
2007-Aug-08, 01:45 PM
1.I used the simple figure of 300000 km as the Moon's distance.
It doesn't matter.Do not waste time with things that are absolutely not important.

2.Your calculation is wrong, because;
383800 m/s = 1381680 km/h .

1. Ok, so roughly rounded.

2.You are right, its 1381680km/h. And I am wrong a second time, the 20000km/h for phoenix are wrong (this will teach me to trust on a major newspaper again :lol:). Its >7000km/h, and thus far away from the 300km/s engine.

NEOWatcher
2007-Aug-08, 02:17 PM
1.I used the simple figure of 300000 km as the Moon's distance.
I have absolutely no issue with using such a non-exact figure, but mixing apparent resolutions confuses the point of view.
The answer including the resolution it did, indicated that you started with a higher resolution. So, while I understand what you did, I hope you don't take issue when somebody questions your numbers.

Laguna
2007-Aug-08, 02:20 PM
Now take this a step further.

The intention is to get to the moon in not more that 16.5 minutes.
We need an average speed of 384km/s to do it.

Assuming an uniform acceleration and deceleration, and about two minutes to turn the vehicle around (assuming just one engine), brings us to a top speed of 1140 km/s and a steady acceleration of 2714m/s2.
Thats about 270G...
At least if I did not make a mistake again.

m1omg
2007-Aug-08, 03:36 PM
Now take this a step further.

The intention is to get to the moon in not more that 16.5 minutes.
We need an average speed of 384km/s to do it.

Assuming an uniform acceleration and deceleration, and about two minutes to turn the vehicle around (assuming just one engine), brings us to a top speed of 1140 km/s and a steady acceleration of 2714m/s2.
Thats about 270G...
At least if I did not make a mistake again.

No.
Why are you all missing the point?!
Ok, so no 16 min. to moon.
The point is, how can we achieve 300 km/s, because it would make interplanetary travel more practical.

Laguna
2007-Aug-08, 03:41 PM
No.
Why are you all missing the point?!
Ok, so no 16 min. to moon.
The point is, how can we achieve 300 km/s, because it would make interplanetary travel more practical.
Ok get aside with the moon.
You can achieve them by continous and steady acceleration over time.
As an example a continuos aceleration at 10m/s2 would get you to 300km/s in 8.3 hours.

Kelfazin
2007-Aug-08, 04:52 PM
No.
Why are you all missing the point?!
Ok, so no 16 min. to moon.
The point is, how can we achieve 300 km/s, because it would make interplanetary travel more practical.

Why are you getting so annoyed already? People have been answering your question as well.

danscope
2007-Aug-08, 05:10 PM
No.
Why are you all missing the point?!
Ok, so no 16 min. to moon.
The point is, how can we achieve 300 km/s, because it would make interplanetary travel more practical.

Hi, And remember: You need to put the brakes on when you arrive....IE
decelerate. You are asking alot.
Bottom line: Robots don't care how long it takes to get to the destination.
And people can only stand so much acceleration.
Robotic missions are the way to go....foe many many reasons.
Dan

Laguna
2007-Aug-08, 05:17 PM
Hi, And remember: You need to put the brakes on when you arrive....IE
Yep, thats what many forget, you have only half the time to speed up.
The other half is needed to come to stop at your destination.

Can someone give us a ballpark estimation about how much fuel would be needed to accelerate a ship large enough to give place to lets say 20 persons, their food, supplies and not to forget the fuel to get home, for 8.5 hours at 1G? Oh and to decelerate it too...

Bob B.
2007-Aug-08, 08:47 PM
The point is, how can we achieve 300 km/s, because it would make interplanetary travel more practical.

High mass ratio and high specific impulse.

To reach 300 km/s you'd probably need something with a specific impulse (http://en.wikipedia.org/wiki/Specific_impulse) in the 10,000 second range.

Ilya
2007-Aug-08, 08:58 PM
High mass ratio and high specific impulse.

To reach 300 km/s you'd probably need something with a specific impulse (http://en.wikipedia.org/wiki/Specific_impulse) in the 10,000 second range.

AT LEAST.

Even then you could only impart 300 km/sec to a tiny probe on top of a gigantic fuel tank.

For reasonable fuel/payload ratios, specific impulse must be close to (desired speed) * 100.

Larry Jacks
2007-Aug-08, 09:07 PM
Back to the OP:

"Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?"

The answer to that is, sadly, no. Chemical engines can't do it. Some form of high impulse engine such as ion might eventually be able to reach 300 km/s but the acceleration is so weak that it'd probably take months if not years to reach that velocity (if it could at all). That wouldn't help much with interplanetary exploration. A solar sail might be able to reach that velocity (again, eventually) if you have a large enough sail and a low enough mass being accelerated. However, solar sails are presently an untested technology so we can't say that it could do the job (yet). To the best of my knowledge, none of the direct nuclear propulsion techniques (e.g. NERVA, particle bed engines, Timberwind, etc) could come close to that velocity. NERVA was cancelled in the early 1970s. I don't think Timberwind ever got very far in R&D nor have particle bed reactors as rocket engines.

As an example a continuos aceleration at 10m/s2 would get you to 300km/s in 8.3 hours.

Except that no existing technology can provide a 10m/s2 acceleration for more than a few minutes. The only technology we have today that can provide that acceleration is conventional chemical rockets and they simply can't carry enough fuel to maintain a 1G acceleration for very long.

Can someone give us a ballpark estimation about how much fuel would be needed to accelerate a ship large enough to give place to lets say 20 persons, their food, supplies and not to forget the fuel to get home, for 8.5 hours at 1G? Oh and to decelerate it too...

Sadly, it can't be done because we have no technology existing or even proposed that can maintain 1G acceleration for more than a few minutes much less for hours.

mugaliens
2007-Aug-08, 09:12 PM
Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?It would be capable of arriving to the Moon in 16.5 minutes and it would be a good interplanetary space engine for a start of the manned missions and colonisation of the Solar system.

Getting off-planet efficiently requires the most oomph. Getting from LOE to wherever is a tradeoff between acceleration and time. Where humans are concerned, expendables in terms of food become a very key issue. Ion rockets have far great impulse, but take a long time. Chemical rockets provide the oomph, but they're very inefficient.

Bob B.
2007-Aug-08, 09:29 PM
NERVA was cancelled in the early 1970s.

NERVA was able to acheive a specific impulse in the 800-900 second range. About twice as good as the best chemical propulsion but still a very long way from the Isp needed to attain 300 km/s.

There has been talk about a gas-core nuclear engine that could reach a specific impulse of 3,000 seconds or more, but I don't know how much progress has been made. NERVA used a solid-core of graphite, which therefore limited operating temperatures. A gaseous nuclear fuel could theoretically reach extremely high temperatures, thus producing higher specific impulse. It's still not enough to get 300 km/s though.

Larry Jacks
2007-Aug-08, 09:45 PM
From what I've read about gas core engines, there's a huge leakage problem. It proved very difficult to keep the radioactive material in the engine. Kind of hard to keep your engine running when it keeps spewing out the fissionable material. Pretty dirty, too. At least they did static tests of NERVA. I don't think they ever got very far with gas core engines.

Laguna
2007-Aug-08, 10:05 PM
Can someone give us a ballpark estimation about how much fuel would be needed to accelerate a ship large enough to give place to lets say 20 persons, their food, supplies and not to forget the fuel to get home, for 8.5 hours at 1G? Oh and to decelerate it too...

Sadly, it can't be done because we have no technology existing or even proposed that can maintain 1G acceleration for more than a few minutes much less for hours.
Just in theory. I know we do not have that technology.
You can even assume a 85 hour burn with 0.1G or a 850 burn at 0.01G.
The required energy should roughly be the same.

Bob B.
2007-Aug-08, 10:46 PM
Just in theory. I know we do not have that technology.
You can even assume a 85 hour burn with 0.1G or a 850 burn at 0.01G.
The required energy should roughly be the same.

It can't be done with the efficiency of current engines.

Let's say your rocket is 90% propellant by mass and you're using LOX/hydrogen at a specific impulse of 450 s. To maintain steady 1g acceleration you're constantly throttling down the engine as you burn off propellant. You stop when all the propellant is gone, i.e. when you're down to 10% of your starting mass. At this rate all the propellant is consumed after 17 minutes 16 seconds. At that point your velocity is 10,161 m/s.

Let's now say you're using a NERVA-type engine with an Isp of 850 s. Since your engine is more efficient, it takes less propellant to produce the thrust needed to achieve 1g acceleration. You therefore burn less propellant per second for a longer period of time. This time you're out of propellant after 32 minutes 37 seconds and you've attained a velocity of 19,194 m/s.

Suppose now you’re using a gas core nuclear rocket with an Isp of 3,000 s. You’ll now be out of propellant in 1 hour 55 minutes 8 seconds and you’ll reach a velocity of 67,742 m/s.

Bob B.
2007-Aug-08, 11:41 PM
Here’s another way to look at the problem…

For a rocket to attain a velocity of 300 km/s with a propellant mass fraction of 90% (from the previous example), the specific impulse must be 13,286 seconds. The highest propellant mass fraction I have ever heard off for a single stage, with no payload, is about 97%. At this mass fraction the Isp must be 8,724 s to reach 300 km/s. If the Isp is 3,000 s, approximately the highest currently attainable with ion propulsion, the rocket propellant mass fraction must be 99.9963%. Of course using multiple stages can lower this some.

The Supreme Canuck
2007-Aug-08, 11:52 PM
Just in theory. I know we do not have that technology.
You can even assume a 85 hour burn with 0.1G or a 850 burn at 0.01G.
The required energy should roughly be the same.

This (http://www.projectrho.com/rocket/TransitNomogram03b.pdf) handy-dandy nomogram may be of some help. (Warning: PDF)

Laguna
2007-Aug-09, 07:37 AM
So, you say that given a certain fuel, I can add as much of it to my craft as I want, I won't be able do get faster than a certain speed?

CJSF
2007-Aug-09, 12:22 PM
I'm confused - why is 1G acceleration so important, both generally and in reference ot the original post? For human comfort and health?

CJSF

m1omg
2007-Aug-09, 12:54 PM
I'm confused - why is 1G acceleration so important, both generally and in reference ot the original post? For human comfort and health?

CJSF

I do not know.
You can make artifactal gravity with rotation.
Maybe more would be very difficult to achieve more and unpleasant for the crew.
And robotic probes need to be faster 'cos people use them.

m1omg
2007-Aug-09, 12:57 PM
http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket
:) that can do it!

"Current VASIMR designs should be capable of producing specific impulses ranging from 10,000-300,000 m/s (1,000-30,000 seconds)"

Larry Jacks
2007-Aug-09, 01:32 PM
VASIMR offers the potential for high Isp but at a low thrust. Your acceleration would be quite lot but if you could maintain it long enough (days, weeks, months), you'd end up going very fast.

Laguna
2007-Aug-09, 02:43 PM
I'm confused - why is 1G acceleration so important, both generally and in reference ot the original post? For human comfort and health?

CJSF
It was just an example, as I thought 1G would be quite comfortable for the humans on board.
You can choose 0.1G or 0.01G or even less too, if you like.

Bob B.
2007-Aug-09, 06:23 PM
So, you say that given a certain fuel, I can add as much of it to my craft as I want, I won't be able do get faster than a certain speed?

There are basically two points I’m trying to get across.

First, the velocity a spacecraft can reach is a function of the mass ratio and the specific impulse of the propulsion system. Mass ratio is the fully fueled mass of the rocket divided by the empty mass of the rocket. For instance, in my example of a rocket containing 90% propellant the mass ratio is 10. A rocket with a mass ratio of 20 contains 95% propellant, a mass ratio of 30 is 96.67% propellant, and so on. Specific impulse, Isp, is a measure of the efficiency of the propulsion system. There are many factors that influence Isp, such as type of propellant, mixture ratio, combustion chamber pressure, and nozzle expansion ratio. In general, a liquid bipropellant engine designed to operate in the vacuum of space will have a specific impulse in the range of about 300-450 seconds, with LOX/hydrogen providing the best performance.

Knowing the mass ratio and specific impulse, the attainable velocity change (delta-v) is determined by Tsiolkovsky’s rocket equation ( http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation). For example, a rocket with a mass ratio of 10 and an Isp of 450 s will attain a delta-v of,

dV = 9.80665*450*LN(10) = 10,161 m/s.

To go faster you must increase the mass ratio, the specific impulse, or both. Specific impulse is limited by the available technology. To my knowledge the best thing we have going right now is ion propulsion with an Isp of around 3,000 s. The OP asked about what we “currently” have, thus discussing anything higher than 3,000 s is purely speculative and shouldn’t be considered.

If 3,000 s is our Isp limit, then the only way we have to go faster is by increasing the mass ratio, which brings us to the second point I was trying to make. You just can’t add more and more propellant to obtain absurdly high mass ratios. Adding propellant means you have to add tankage to hold it. The extra tankage drives up the dry mass of the rocket and places a practical limitation on the mass ratio that can be achieved. The highest mass ratio I’ve ever heard of for a single rocket stage is about 30, and that doesn’t include a payload. A rocket without a payload is pretty useless. In practice I doubt you can get a mass ratio higher than about 20 or so. With a mass ratio of 20 and an Isp of 3,000 s our delta-v is,

dV = 9.80665*3000*LN(20) = 88,134 m/s.

I previously calculated that to obtain 300 km/s with an Isp of 3,000 s would require a rocket containing 99.9963% propellant by mass. That’s a mass ratio of about 27,000! I suppose then the answer to your question is that for every one kilogram of spacecraft mass you require 27,000 kg of propellant. Of course this is absurd and entirely impossible to achieve.

danscope
2007-Aug-09, 08:58 PM
"........and now, my young Jedi,only at the end......do you understand..." :)

cjl
2007-Aug-10, 06:53 AM
There are basically two points I’m trying to get across.

First, the velocity a spacecraft can reach is a function of the mass ratio and the specific impulse of the propulsion system. Mass ratio is the fully fueled mass of the rocket divided by the empty mass of the rocket. For instance, in my example of a rocket containing 90% propellant the mass ratio is 10. A rocket with a mass ratio of 20 contains 95% propellant, a mass ratio of 30 is 96.67% propellant, and so on. Specific impulse, Isp, is a measure of the efficiency of the propulsion system. There are many factors that influence Isp, such as type of propellant, mixture ratio, combustion chamber pressure, and nozzle expansion ratio. In general, a liquid bipropellant engine designed to operate in the vacuum of space will have a specific impulse in the range of about 300-450 seconds, with LOX/hydrogen providing the best performance.

Knowing the mass ratio and specific impulse, the attainable velocity change (delta-v) is determined by Tsiolkovsky’s rocket equation (http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation). For example, a rocket with a mass ratio of 10 and an Isp of 450 s will attain a delta-v of,

dV = 9.80665*450*LN(10) = 10,161 m/s.

To go faster you must increase the mass ratio, the specific impulse, or both. Specific impulse is limited by the available technology. To my knowledge the best thing we have going right now is ion propulsion with an Isp of around 3,000 s. The OP asked about what we “currently” have, thus discussing anything higher than 3,000 s is purely speculative and shouldn’t be considered.

If 3,000 s is our Isp limit, then the only way we have to go faster is by increasing the mass ratio, which brings us to the second point I was trying to make. You just can’t add more and more propellant to obtain absurdly high mass ratios. Adding propellant means you have to add tankage to hold it. The extra tankage drives up the dry mass of the rocket and places a practical limitation on the mass ratio that can be achieved. The highest mass ratio I’ve ever heard of for a single rocket stage is about 30, and that doesn’t include a payload. A rocket without a payload is pretty useless. In practice I doubt you can get a mass ratio higher than about 20 or so. With a mass ratio of 20 and an Isp of 3,000 s our delta-v is,

dV = 9.80665*3000*LN(20) = 88,134 m/s.

I previously calculated that to obtain 300 km/s with an Isp of 3,000 s would require a rocket containing 99.9963% propellant by mass. That’s a mass ratio of about 27,000! I suppose then the answer to your question is that for every one kilogram of spacecraft mass you require 27,000 kg of propellant. Of course this is absurd and entirely impossible to achieve.
Of course, this could be staged to further boost it, but even that has limits. For example, if you have a mass ratio of 3 for the first stage, and then the top stage is the same 20 as mentioned before, the delta v would be:

1st stage:
dV = 9.80665*3000*ln(3) = 32,321 m/s

Second stage is the same as above:
dV = 9.80665*3000*ln(20) = 88,134 m/s

So, the total delta v in this case would be 120,455 m/s. However, the initial vehicle would be impractically large for the payload size - at a minimum it would be around 62 times the mass of the payload to achieve this velocity, and the "payload" includes the structure in the upper stage. The actual, useful payload would only be about 1/3 of this amount, or about 1/186 of the initial mass. A rocket that started the mass of the Saturn V in this configuration would only have about 16 metric tons of usable payload. Not the most efficient way to boost objects to high speed (not to mention the difficulty of getting something the size of a saturn V into space to start with, as these rockets could not leave the ground with the levels of thrust that they create). Also, if you decided to keep adding more stages to get it up to 300 km/s (I'm assuming a 20:1 mass ratio for fuel to structure in each additional stage), with a total mass ratio of 3 for the stack with each additional stage, you would need another 6 stages, creating a total of an 8 staged vehicle. If this one started out with comparable mass to the saturn V, the final useful payload would be on the order of a few tens of kilograms. Yes, it would be doing 300 km/s, but that kind of payload mass just isn't at all useful. Without more efficient engines, there isn't any point in attempting this kind of thing.

m1omg
2007-Aug-10, 12:07 PM
There are basically two points I’m trying to get across.

First, the velocity a spacecraft can reach is a function of the mass ratio and the specific impulse of the propulsion system. Mass ratio is the fully fueled mass of the rocket divided by the empty mass of the rocket. For instance, in my example of a rocket containing 90% propellant the mass ratio is 10. A rocket with a mass ratio of 20 contains 95% propellant, a mass ratio of 30 is 96.67% propellant, and so on. Specific impulse, Isp, is a measure of the efficiency of the propulsion system. There are many factors that influence Isp, such as type of propellant, mixture ratio, combustion chamber pressure, and nozzle expansion ratio. In general, a liquid bipropellant engine designed to operate in the vacuum of space will have a specific impulse in the range of about 300-450 seconds, with LOX/hydrogen providing the best performance.

Knowing the mass ratio and specific impulse, the attainable velocity change (delta-v) is determined by Tsiolkovsky’s rocket equation ( http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation). For example, a rocket with a mass ratio of 10 and an Isp of 450 s will attain a delta-v of,

dV = 9.80665*450*LN(10) = 10,161 m/s.

To go faster you must increase the mass ratio, the specific impulse, or both. Specific impulse is limited by the available technology. To my knowledge the best thing we have going right now is ion propulsion with an Isp of around 3,000 s. The OP asked about what we “currently” have, thus discussing anything higher than 3,000 s is purely speculative and shouldn’t be considered.

If 3,000 s is our Isp limit, then the only way we have to go faster is by increasing the mass ratio, which brings us to the second point I was trying to make. You just can’t add more and more propellant to obtain absurdly high mass ratios. Adding propellant means you have to add tankage to hold it. The extra tankage drives up the dry mass of the rocket and places a practical limitation on the mass ratio that can be achieved. The highest mass ratio I’ve ever heard of for a single rocket stage is about 30, and that doesn’t include a payload. A rocket without a payload is pretty useless. In practice I doubt you can get a mass ratio higher than about 20 or so. With a mass ratio of 20 and an Isp of 3,000 s our delta-v is,

dV = 9.80665*3000*LN(20) = 88,134 m/s.

I previously calculated that to obtain 300 km/s with an Isp of 3,000 s would require a rocket containing 99.9963% propellant by mass. That’s a mass ratio of about 27,000! I suppose then the answer to your question is that for every one kilogram of spacecraft mass you require 27,000 kg of propellant. Of course this is absurd and entirely impossible to achieve.

Did you not read my post?VSIMR ; http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket ; is much better and it can be done with current technology and it provides specific impulse 1000-30000, the high end of this range can get to 300 km/s, trough I do not know how many fuel and how long you must accelerate to achieve this, but it is much better than the puny plain ion or hall thruster in both thrust and Isp and also it can operate in high thrust , low Isp mode which is useful in leaving the orbit.
Also, side effect of it's magnetical technology is that it protects astronaut from charged particle radiation with it's magnetic field.
The only bad thing is that it requires nuclear fission reactor on board of the spaceship that it propells because it requires much more energy than solar panels or RTG is able to achieve

cjl
2007-Aug-10, 02:20 PM
The thing about that is that you need a nuclear fission reactor onboard. That's heavy. You would still need a huge rocket, because even with the much better mass ratios, your payload that you need to carry has just massively increased in size.

m1omg
2007-Aug-10, 02:46 PM
The thing about that is that you need a nuclear fission reactor onboard. That's heavy. You would still need a huge rocket, because even with the much better mass ratios, your payload that you need to carry has just massively increased in size.

Yeah, but it could be done.

Bob B.
2007-Aug-10, 03:21 PM
Did you not read my post?

I did not; I was responding to a post by Laguna2.


VSIMR ; http://en.wikipedia.org/wiki/Variable_specific_impulse_magnetoplasma_rocket ; is much better and it can be done with current technology<emphasis mine>

In other words, we don’t have it yet. Being able to derive something from current technology is not the same as currently having the derived technology. The first sentence of your link calls VSIMR “a hypothetical form of spacecraft propulsion”. The highest Isp technology we currently have in operation is ion propulsion. Everything else is still speclative.


The only bad thing is that it requires nuclear fission reactor on board of the spaceship

Nuclear reactors in space are banned by international treaty. Even if VSIMR can be developed, it may still not ever fly because it is presently illegal.

djellison
2007-Aug-10, 03:39 PM
Yeah, but it could be done.

In the same way that a nuclear fusion reactor can be done i.e. it can be done in powerpoint - but not sustainable, or flight ready, or legally

The best estiamtes I've seen for the 10 MW required are about 48,000 kg (http://www.adastrarocket.com ) giving a thrust of about 15N, using fuel at about 2g/sec

http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation then tells us, given an M1 of 48,000 - we would require an M0 of 135,000 kg (i.e. fuel loading of approx 87,000kg.

That fuel would take 82 years to consume to give you a delta V of 300km/sec - and the initial thrust would be about 0.0001 m/s^2

I may have the maths wrong - but it would appear that whilst technically possible - it's also fairly impractical - the crew would be dead before you reached the target velocity.

Doug

Bob B.
2007-Aug-10, 03:56 PM
Of course, this could be staged to further boost it, but even that has limits.

Yes, staging is certainly important in achieving high velocity. You provided a very good example, cjl. Going back to my 20 mass ratio example, more delta-v can be achieved by simply redistributing the mass into multiple stages without adding any more propellant. For instance, let’s say we have the following configured into a single stage and payload:

Payload mass: 1,000 kg
Stage dry mass: 4,000 kg
Stage propellant mass: 95,000 kg
Total dry mass: 5,000 kg
Total initial mass: 100,000 kg

The mass ratio is, 100,000/5,000 = 20.

Assuming Isp=3,000 s, the delta-v is (as previously calculated):

dV = 9.80665*3000*LN(20) = 88,134 m/s

Suppose now we redistribute the mass of the single stage into two stages, with 80% going to the first stage and 20% to the second:

Payload mass: 1,000 kg
Stage 2 dry mass: 800 kg
Stage 2 propellant mass: 19,000 kg
Stage 1 dry mass: 3,200 kg
Stage 1 propellant mass: 76,000 kg
Total dry mass: 5,000 kg
Total initial mass: 100,000 kg

Overall the mass ratio is still 20 but we have to calculate the delta-v of the two stages separately and then add the results together. The mass ratio for stage 1 is the initial mass divided by the initial mass less the stage 1 propellant:

Stage 1 mass ratio = 100,000/(100,000-76,000) = 4.1667

For the second stage, the initial mass is the total of the payload plus the gross mass of stage 2 (stage 1 has been jettisoned). The mass ratio is therefore:

Stage 2 mass ratio = 20,800/(20,800-19,000) = 11.5556

The delta-v is therefore:

dV1 = 9.80665*3000*LN(4.1667) = 41,986 m/s

dV2 = 9.80665*3000*LN(11.5556) = 71,996 m/s

Total dV = 41,986 + 71,996 = 113,982 m/s

So we increased the delta-v by about 29% without adding any propellant at all; simply by reconfiguring the rocket into two stages.

Larry Jacks
2007-Aug-10, 08:19 PM
Nuclear reactors in space are banned by international treaty.

I don't think this is an accurate statement. Nuclear weapons have been banned in space for decades (Nuclear Test Ban Treaty of 1963 and the Outer Space Treaty of 1967, to name a couple). I know of no treaty that bans reactors. The former Soviet Union launched a bunch of them back in the Cold War days to power their RORSAT (http://en.wikipedia.org/wiki/RORSAT) (Radar Ocean Reconnaissance Satellite) program. They did have their problems with the technology such as when one of the reactors came down over Canada. Note that these were full blown reactors and not RTGs.

The US also had an active space reactor research program (SP-100) that was part of the Strategic Defense Initiative (http://www.fas.org/nuke/space/c06sdi_1.htm). There was also the SNAP-50 (http://www.time.com/time/magazine/article/0,9171,829657,00.html) project. The US actually launched a SNAP-10 reactor (http://www.knoxnews.com/kns/opinion_columnists/article/0,1406,KNS_364_4936066,00.html) back in 1965. Nuclear propulsion such as the old NERVA engine used a nuclear reactor to heat the working fluid.

publiusr
2007-Aug-10, 08:29 PM
NTR for thrust, NEP for speed/duration. Have one as an upper stage and the other as a payload and you have a good interstellar precursor like TAU.

m1omg
2007-Aug-10, 09:26 PM
Nuclear reactors in space are banned by international treaty.

I don't think this is an accurate statement. Nuclear weapons have been banned in space for decades (Nuclear Test Ban Treaty of 1963 and the Outer Space Treaty of 1967, to name a couple). I know of no treaty that bans reactors. The former Soviet Union launched a bunch of them back in the Cold War days to power their RORSAT (http://en.wikipedia.org/wiki/RORSAT) (Radar Ocean Reconnaissance Satellite) program. They did have their problems with the technology such as when one of the reactors came down over Canada. Note that these were full blown reactors and not RTGs.

The US also had an active space reactor research program (SP-100) that was part of the Strategic Defense Initiative (http://www.fas.org/nuke/space/c06sdi_1.htm). There was also the SNAP-50 (http://www.time.com/time/magazine/article/0,9171,829657,00.html) project. The US actually launched a SNAP-10 reactor (http://www.knoxnews.com/kns/opinion_columnists/article/0,1406,KNS_364_4936066,00.html) back in 1965. Nuclear propulsion such as the old NERVA engine used a nuclear reactor to heat the working fluid.

Yeah.Only the weapons, but that was reason for banning Orion!
I do not see any logical reason, Orion drive has nothing common with weapon testing or war.They banned them just because there were nukes in it.

Van Rijn
2007-Aug-10, 11:09 PM
Nuclear reactors in space are banned by international treaty.

I don't think this is an accurate statement. Nuclear weapons have been banned in space for decades (Nuclear Test Ban Treaty of 1963 and the Outer Space Treaty of 1967, to name a couple). I know of no treaty that bans reactors.


Yes and Prometheus would have been a nuclear reactor program. It didn't go through, but I don't recall any discussion of treaty limitations. Even so, there would be severe limitations on practical delta-v of any system we could hope to build with current or near current technology.

Van Rijn
2007-Aug-10, 11:17 PM
Yeah.Only the weapons, but that was reason for banning Orion!
I do not see any logical reason, Orion drive has nothing common with weapon testing or war.They banned them just because there were nukes in it.

"Nothing in common with weapon testing" . . . "just because there were nukes in it"? :lol:

I'm picturing the protests when somebody decides to fly hundreds of nukes up to orbit in the Shuttle (or whatever), then starts lighting them off for tests. And I'm not convinced a real Orion would necessarily work that well, even if it was allowed, or that anyone would be seriously interested in trying.

Larry Jacks
2007-Aug-11, 02:23 PM
The fact that Orion depended on detonating nuclear explosions (using what are essentially nuclear weapons) for propulsion is what prohibited it under international treaties.

m1omg
2007-Aug-11, 07:16 PM
The fact that Orion depended on detonating nuclear explosions (using what are essentially nuclear weapons) for propulsion is what prohibited it under international treaties.

Why?It is not bad until these explosives are used as weapons, and,also, it is a very "wise" treaty, you cannot detonate nukes even ly's from Earth but you could do it underground right here on Earth or level the civilan population with it as an "act of war"...I guess that more wise treaty would be banning their use in killing people altogether and banning atmospheric,underground and tests in space conducted IN MAGNETOSPHERE OF OUR PLANET, testing or using them for propulsion them, for example, on the Moon, does no harm.
You can ban knives for the same "reason", because they could be used to kill people.

m1omg
2007-Aug-11, 07:19 PM
"Nothing in common with weapon testing" . . . "just because there were nukes in it"? :lol:

I'm picturing the protests when somebody decides to fly hundreds of nukes up to orbit in the Shuttle (or whatever), then starts lighting them off for tests. And I'm not convinced a real Orion would necessarily work that well, even if it was allowed, or that anyone would be seriously interested in trying.

These Greenpeace madman are not allowed to destroy the spaceflight developement.
Throw some cans of good ol' CS tear gas on them! ;)
Then is the cutting salami with a knife the same thing as stabbing the knife into someone's heart or preparingto mudred of someone with it?
And Orion drive is unfortunatelly the best thing for space propulsion that we are currently able to create.
Protesters?I would simply ignore them,somewhat more politely tell them that they sucks and if they will try to sabotage the Orion nuclear pulse propulsion spacecraft launch, I will throw a few cans of tear gas ,spray them with a pepper spray and sue them.
I am strongly against nuclear weapons but this is a radically different thing.

danscope
2007-Aug-11, 08:27 PM
Hi, You need to do a little reading of modern history. Rockets that boost things into space are about as good as they can make them; and yet the
historical record of this activity is marked by more than occasional failure.
You need to understand that having a nuclear reactor fall out of the sky when
a second stage fails is an extraordinary event we shall must needs make damned
sure does not happen. This is perhaps why cooler heads are in charge of NASA
and you do something else. You will find very few proponents of "THAT" kind of technology for many good reasons.
When it comes to boosting nuclear materials, there are no acceptable risks.
No question.
*********
"Quoth the Raven...' Nevermore ' " .

Laguna
2007-Aug-11, 09:38 PM
"........and now, my young Jedi,only at the end......do you understand..." :)
Yes master, and I am very pleased that I had the possibility to actually learn a little rocket science.
Thank You, Bob B!

I am off. I need to earn some money to pay for the 189.000.000.000t
of fuel to propel my 7000t interstellar spaceship.
:whistle:

Larry Jacks
2007-Aug-11, 10:16 PM
Originally Posted by Larry Jacks
The fact that Orion depended on detonating nuclear explosions (using what are essentially nuclear weapons) for propulsion is what prohibited it under international treaties.

Why?It is not bad until these explosives are used as weapons, and,also, it is a very "wise" treaty, you cannot detonate nukes even ly's from Earth but you could do it underground right here on Earth or level the civilan population with it as an "act of war"...I guess that more wise treaty would be banning their use in killing people altogether and banning atmospheric,underground and tests in space conducted IN MAGNETOSPHERE OF OUR PLANET, testing or using them for propulsion them, for example, on the Moon, does no harm.

Let's see, where to start. First, the original Orion concept called for a vehicle to use nuclear detonations to propel it from the Earth's surface into space. Detonating nuclear devices inside the atmosphere was outlawed by the Comprehensive Test Ban Treaty of 1963. Such a launch would release a lot of radiation into the atmosphere. Given the massive misunderstanding and fear of radioactivity by the population at large, people would freak on a scale almost unimaginable.

As the vehicle climbed high above the atmosphere, the nuclear detonations would cause massive damage to electrical and electronic systems due to electro-magnetic pulses. This isn't theory - the US actually did one or two nuclear tests in space before they were banned. It caused a lot of damage. Under the Outer Space Treaty of 1967, the launching country would be liable for the damages that would probably total in the billions if not trillions of dollars.

Once the vehicle is in orbit, it'd still be carrying a lot of nuclear devices. The sad fact is that those devices potentially could be used as weapons even if that isn't their stated purpose. Sure, they couldn't withstand reentry without heat shields but you could still do a lot of damage with them. In diplomatic speak, nuclear, chemical, and biological weapons are classified as "weapons of mass destruction" and WMDs are prohibited by treaty.

danscope
2007-Aug-12, 02:22 AM
Yes master, and I am very pleased that I had the possibility to actually learn a little rocket science.
Thank You, Bob B!

I am off. I need to earn some money to pay for the 189.000.000.000t
of fuel to propel my 7000t interstellar spaceship.
:whistle:

Hi, Good one, Bob. :)
Best regards, Dan

m1omg
2007-Aug-12, 02:50 PM
Yes master, and I am very pleased that I had the possibility to actually learn a little rocket science.
Thank You, Bob B!

I am off. I need to earn some money to pay for the 189.000.000.000t
of fuel to propel my 7000t interstellar spaceship.
:whistle:

Not if you can use amat or fusion rocket, amat could practically achieve around 0.2 c and max 0.5 c or even more and fusion 0.1 c max..
VASIMR or Orion or any chemical, electrical or nuclear fission powered rocket are not for interstellar.

djellison
2007-Aug-12, 03:51 PM
m1omg - you've not commented on post 36 in this thread relating to the plausibility of what you're talking about w.r.t an 80 year acceleration period so that you can make it to the moon in in a short period of time.

Doug

mugaliens
2007-Aug-12, 06:24 PM
Is my brain on fire, or are some of the posts in this thread lacking in proper grammer?

It's very difficult and annoying to read posts which are poorly written. Let us all please make an effort to write clearly.

cjl
2007-Aug-12, 09:00 PM
Not if you can use amat or fusion rocket, amat could practically achieve around 0.2 c and max 0.5 c or even more and fusion 0.1 c max..
VASIMR or Orion or any chemical, electrical or nuclear fission powered rocket are not for interstellar.
Any propellant can achieve any sublight speed. Admittedly, the mass ratios become ludicrous when the desired velocity is more than about a few times the exhaust velocity of the propellant.

danscope
2007-Aug-12, 11:45 PM
Yes,......and there is a limit to how much mass you can initially accelerate so as to have something to expell as an accelerant or propulsive exhaust.
You can't just make heat and accelerate.
Something has to give, and there is no free lunch.
Dan

danscope
2007-Aug-13, 04:08 AM
Hi, There "are" ways to cheat. Boost enough fuel into orbit...ie 18,000 MPH
and "Build" your completed rocket in orbit, and, to a lesser degree, boost additional fuel or srb packages to advanced staging areas....ie orbit mars or saturn, after which assembly/integration you "Press on " from there, and enjoy some spactacular velocity , at a some what dear price. Still....no free lunch.
But if you are back-packing, and some one has staged lunch ahead for you, it's lunch you didn't have to carry. In this scenario, it's lunch that was already accelerated ahead of time, tweaking the pure capability of rockets as we know them. Advanced robotic staging is an esoteric and exotic method of obtaining extreme velocities , apart from gravity slingshot effects, which are the other
wild card in the deck. After that, you are digging fuel on other planets, which means you have to slow down to stop in the neighborhod for your next lunch.
Still, there is no free lunch, apart from gravity. Voyager is a piece of mathematical genius. A brilliant gem to be respected and appreciated.
We stand on the shoulders of giants. The view is spactacular.
That's about it for rockets. Where is Catain Kirk when you need him...
and his little friends? :) That's fiction. It would be nice.....but....
there is no replicator...and no free lunch. That's a law. Murphy's ultimate law.
Best regards, Dan

Laguna
2007-Aug-13, 09:16 AM
Not if you can use amat or fusion rocket,
I thought we were talking about existing technology?
Not science fiction!

ASEI
2007-Aug-13, 12:29 PM
If you want to relate delta-V, Isp, and mass fraction, you can use the rocket equaton.

inert-mass/total-mass = exp(-DV/(Isp*9.8m/sec^2))

or 1-(propellant-mass/total-mass) = ....

Isp for:
hypergolic propellants and solids - 280-300 sec or so
kerosene/lox 280-340 sec
hydrogen/oxygen 400-420 sec
NERVA nuclear thermal 800-1000 sec
ion drives 3000 sec

m1omg
2007-Aug-13, 08:03 PM
m1omg - you've not commented on post 36 in this thread relating to the plausibility of what you're talking about w.r.t an 80 year acceleration period so that you can make it to the moon in in a short period of time.

Doug

I said that so no moon 15 min. trips with VASIMR.
You are scaring me.You are all playing "sciencist" and behaving like computers.
I clearly said the answer
Or look at ATM when one do not ansewr your question after 5 minutes, you are going to ban him even if he was in hospital with a terminal disease.
But you never had to prove your mainstream opinions.
Sorta inqusition.

m1omg
2007-Aug-13, 08:04 PM
I thought we were talking about existing technology?
Not science fiction!

But you cannot build interstellar ships and definitely not 7000 t now.

danscope
2007-Aug-13, 08:12 PM
Young Sir: No one is going interstellar.....and it isn't likely that that man will be
taking any really long trips to that big gravel pit in the sky any time soon.
Our best efforts will be in robotic exploration . No question.
Dan

Bob B.
2007-Aug-13, 08:43 PM
You are scaring me.You are all playing "sciencist" and behaving like computers.

You scare me when you don’t behave like a scientist.

Five Easy Pieces
2007-Aug-13, 08:54 PM
What kind of budget do you have in mind for this engine?

korjik
2007-Aug-13, 09:18 PM
Hi, You need to do a little reading of modern history. Rockets that boost things into space are about as good as they can make them; and yet the
historical record of this activity is marked by more than occasional failure.
You need to understand that having a nuclear reactor fall out of the sky when
a second stage fails is an extraordinary event we shall must needs make damned
sure does not happen. This is perhaps why cooler heads are in charge of NASA
and you do something else. You will find very few proponents of "THAT" kind of technology for many good reasons.
When it comes to boosting nuclear materials, there are no acceptable risks.
No question.
*********
"Quoth the Raven...' Nevermore ' " .


Hardly. The reactor would be assembled in space, and if a piece did have a boost failure, the fact that the impact was a fuel rod container would be much less important than the fact that it weighed several tons.

danscope
2007-Aug-14, 01:21 AM
Hi, I'm sure that the people down range will find your words and philosophy most reassuring.
So....what's the scheme in utilizing an nuclear reactor in space to provide
thrust? By what specific impulse will you do the job with this?
Just curious.
Best regards, Dan

Laguna
2007-Aug-14, 09:01 AM
But you cannot build interstellar ships and definitely not 7000 t now.
That was a joke...
I know we are unable to build interstellar ships.

Laguna
2007-Aug-14, 09:05 AM
But you never had to prove your mainstream opinions.
Many others have shown evidence for what is considers mainstream.

BTW. You cannot prove a positive...

djellison
2007-Aug-14, 10:00 AM
I clearly said the answer

You did?

You asked "Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?"

Some ideas were suggested - some light analysis of those idea was done - showing that the answer is essentially, no. You did not respond in any sensible or proactively responsive way to that analysis. You also acted very strangely and almost rudely toward people early in this thread "It doesn't matter.Do not waste time with things that are absolutely not important." and "Why are you all missing the point?!"- were you being intentionally confrontational and obscure or is this a language barrier thing?

"Or look at ATM when one do not ansewr your question after 5 minutes, you are going to ban him even if he was in hospital with a terminal disease.
But you never had to prove your mainstream opinions.
Sorta inqusition."

You're really lost me here. This is a place for discussion, debate, understanding, figuring things out. That's what we've done. You hadn't commented on the limitations of VASIMR as I had calculated them (i.e. I DID take the time to prove the mainstream opinion) - but you have now gone off on an anti-forum rant that has nothing to do with this thread or the posts within it. If anyone was acting like the inquisition - it was your posts on the first page of this thread.

What was your point in starting this thread? Something tells me that 300km/s is only part of something larger you're trying to talk about.

Doug

Bob B.
2007-Aug-14, 12:41 PM
Nuclear reactors in space are banned by international treaty.

I don't think this is an accurate statement. Nuclear weapons have been banned in space for decades (Nuclear Test Ban Treaty of 1963 and the Outer Space Treaty of 1967, to name a couple). I know of no treaty that bans reactors. The former Soviet Union launched a bunch of them back in the Cold War days to power their RORSAT (http://en.wikipedia.org/wiki/RORSAT) (Radar Ocean Reconnaissance Satellite) program. They did have their problems with the technology such as when one of the reactors came down over Canada. Note that these were full blown reactors and not RTGs.

The US also had an active space reactor research program (SP-100) that was part of the Strategic Defense Initiative (http://www.fas.org/nuke/space/c06sdi_1.htm). There was also the SNAP-50 (http://www.time.com/time/magazine/article/0,9171,829657,00.html) project. The US actually launched a SNAP-10 reactor (http://www.knoxnews.com/kns/opinion_columnists/article/0,1406,KNS_364_4936066,00.html) back in 1965. Nuclear propulsion such as the old NERVA engine used a nuclear reactor to heat the working fluid.

You are probably correct about that. I know nuclear fission reactors have been launched in the past by both the USA and USSR, but for some reason I was thinking they are now illegal. I probably just got confused with the outlawing of nuclear pulse propulsion, which uses small nuclear explosions, by the 1963 Atomic Test Ban Treaty. NERVA wasn't canceled until, I think, early 1973 and I'm pretty sure the Soviets were still launching reactors until the late 1980s.

danscope
2007-Aug-14, 05:33 PM
Hi Bob, If I recall correctly, the nuclear devices that were launched were
intended to provide extended electrical power for deep space probes which
must needs required this , owing to the distant proximity to solar radiation,
solar panels being beyond effective use. Not for propulsion...correct?
Best regards, Dan

Bob B.
2007-Aug-14, 05:59 PM
Hi Bob, If I recall correctly, the nuclear devices that were launched were
intended to provide extended electrical power for deep space probes which
must needs required this , owing to the distant proximity to solar radiation,
solar panels being beyond effective use. Not for propulsion...correct?
Best regards, Dan


The devices used on deep space probes have been Radioisotope Thermoelectric Generators (RTG). An RTG uses the heat generated by the decay of a radioactive material, usually plutonium-238, to generate electricity. RTGs are not nuclear reactors. A reactor uses sustained controlled nuclear fission to to produce heat. Both the USA and USSR have launched full fledged nuclear reactors but not for deep space missions. The USA launched one reactor, SNAP-10A, while the USSR launched about 30 or so RORSATs (Radar Ocean Reconnaissance Satellites). The USA worked on nuclear propulsion in the 1960s and 70s, Kiwi and NERVA projects, and tested several systems but none made it into space.
_

Five Easy Pieces
2007-Aug-14, 07:30 PM
Nuclear reactors in space are banned by international treaty.

Uh oh. (http://library.thinkquest.org/C001124/gather/ssun.html)

m1omg
2007-Aug-14, 11:04 PM
You did?

You asked "Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?"

Some ideas were suggested - some light analysis of those idea was done - showing that the answer is essentially, no. You did not respond in any sensible or proactively responsive way to that analysis. You also acted very strangely and almost rudely toward people early in this thread "It doesn't matter.Do not waste time with things that are absolutely not important." and "Why are you all missing the point?!"- were you being intentionally confrontational and obscure or is this a language barrier thing?

"Or look at ATM when one do not ansewr your question after 5 minutes, you are going to ban him even if he was in hospital with a terminal disease.
But you never had to prove your mainstream opinions.
Sorta inqusition."

You're really lost me here. This is a place for discussion, debate, understanding, figuring things out. That's what we've done. You hadn't commented on the limitations of VASIMR as I had calculated them (i.e. I DID take the time to prove the mainstream opinion) - but you have now gone off on an anti-forum rant that has nothing to do with this thread or the posts within it. If anyone was acting like the inquisition - it was your posts on the first page of this thread.

What was your point in starting this thread? Something tells me that 300km/s is only part of something larger you're trying to talk about.

Doug

Sorry, but I am just annoyed by the thing that everyone is asking things that should be obvious to as smart people as most of people on this site are.

danscope
2007-Aug-15, 02:42 AM
Hi, You should realize that all of our posts should reflect on our entire thought,
such that anyone who reads them can get "Up to speed" on the topic at hand,
and be as coherent as possible .
If some of the discourse appears obvious, it is to remain inclusive to all,
and not just "the few in the realm" .

Dan

publiusr
2007-Aug-18, 07:44 PM
I have often wondered just how fast the command service module would be if a Fully fueled Saturn V were somehow placed in orbit, and went through its staging sequence--each stage burning to depletion, as well as the service module.

Would that be enough for 75-100km/sec?

Bob B.
2007-Aug-18, 10:23 PM
I have often wondered just how fast the command service module would be if a Fully fueled Saturn V were somehow placed in orbit, and went through its staging sequence--each stage burning to depletion, as well as the service module.

Would that be enough for 75-100km/sec?

Not even close. Only about 16.5 km/s, and that's without the LM and LES.

galacsi
2007-Aug-19, 10:47 AM
May be the M2P2 technology can reach the 300 Km/s speed.
Cause it use the interplanetary medium as reactive mass.

The trick is to use a magnetic field on the the solar wind and get a push from it.
From what i have read ; it is still in infancy a little like VASIMIR and it is more adapted for small charges than a big spaceship.

But I kind of like the concept because it is a little like sailing between the planets.

Independently Contracted
2007-Aug-22, 04:45 PM
A satellite image of the contiguous US showed an irregular contrail stretching from coast to coast (in the 90's I believe).

Other unusual contrails near Groom Lake have been described as looking like "donuts on a rope" indicating a type of pulse jet. Such aircraft have been rumored to possess nuclear engines capable of achieving mach 35 in the atmosphere and mach 50 in space.

Who knows what's out there.

NEOWatcher
2007-Aug-22, 05:05 PM
A satellite image of the contiguous US showed an irregular contrail stretching from coast to coast (in the 90's I believe).
Hearsay... got any references?

Other unusual contrails near Groom Lake have been described as looking like "donuts on a rope" indicating a type of pulse jet.
I have seen those contrails from normal jets around here. If the wind conditions are just right, the dissipation of the trail looks just like the "donuts on a rope" that I've seen in CT type sites.

Such aircraft have been rumored to possess nuclear engines capable of achieving mach 35 in the atmosphere and mach 50 in space.
Oh; we can find some amazing capabilities of anything in rumors. Just browse snopes.

Bob B.
2007-Aug-22, 05:58 PM
Such aircraft have been rumored to possess nuclear engines capable of achieving mach 35 in the atmosphere and mach 50 in space.

I seriously doubt it. Although Mach 50 in space doesn’t sound particularly astounding, I can’t believe Mach 35 in an atmosphere. Acoustic velocity varies with temperature, hence altitude, but in the stratosphere it is generally around 300 m/s. That would make Mach 35 about 10,500 m/s, which is far greater than orbital velocity. In an atmosphere?... I don’t think so.

Furthermore, attaching the word “nuclear” to something doesn’t automatically endow it with fantastical performance capabilities. Mach 35 doesn’t sound like a credible number to me, and simply telling me it must be nuclear doesn’t make it sound any more credible. Nuclear propulsion is still a reaction drive and any aircraft equipped with it must deal with the same aerodynamics. I personally don’t believe an order of magnitude improvement over existing systems is possible.

Independently Contracted
2007-Aug-22, 06:24 PM
I simply posted my reply so that people can google "donuts on a rope" and "mach 35" and the like.

I'm not claiming they are true, but I know that others people have made these claims and I find them interesting.

Anyway, why would I just make up something like going mach 35 in the atmosphere?

NEOWatcher
2007-Aug-22, 06:36 PM
I'm not claiming they are true, but I know that others people have made these claims and I find them interesting.
Without any explaination why you posted these claims, and in the context of the thread, the reasonable assumption is that you are supporting the claims.

I find the claims interesting too... but more from an entertainment point of view, and as a test of rational thinking.

Bob B.
2007-Aug-22, 07:43 PM
Anyway, why would I just make up something like going mach 35 in the atmosphere?

I don't think you did make it up and I don't doubt there are sources that claim this. However my gut feeling is that the sources are probably not credible, though admittedly I have not researched them. Maybe I'm wrong, but I tend to associate claims of these super-duped high-speed aircraft with the type of people who also believe we are reverse engineering flying saucers at Area 51. Let's just say I'm skeptical.

filrabat
2009-Sep-24, 05:36 AM
I know the OP said engines rather than engine-less travel.......but...

(This assumes the VERY unlikely case that a space pier can be built on earth, although I think a Lunar space pier isn't all that far-fetched due to its much lower gravity)

Essentially, the pier would be the magnetic catapult/magnetic accelerator most of you probably know of: place a probe in magnetic levitation, then accelerate it using magnets.

Assuming the magnets themselves are suspended, what is there to prevent (relatively) small magnets from moving 300 km/s? Even if we can't use many (if any) complex mechanical parts due to the obviously high friction, could we simply have a series of high-powered electromagnets lined up, turning on and off like a theater marque - essentially using the electromagnets to push or pull the probe up to 300 km/s?

RGClark
2009-Sep-24, 07:28 PM
Back to the OP:

"Do we currently have the technology to construct a space engine capable of accelerating to a velocity of at least 300 km/s?"

The answer to that is, sadly, no. Chemical engines can't do it. Some form of high impulse engine such as ion might eventually be able to reach 300 km/s but the acceleration is so weak that it'd probably take months if not years to reach that velocity (if it could at all). That wouldn't help much with interplanetary exploration. A solar sail might be able to reach that velocity (again, eventually) if you have a large enough sail and a low enough mass being accelerated. However, solar sails are presently an untested technology so we can't say that it could do the job (yet). To the best of my knowledge, none of the direct nuclear propulsion techniques (e.g. NERVA, particle bed engines, Timberwind, etc) could come close to that velocity. NERVA was cancelled in the early 1970s. I don't think Timberwind ever got very far in R&D nor have particle bed reactors as rocket engines.

As an example a continuos aceleration at 10m/s2 would get you to 300km/s in 8.3 hours.

Except that no existing technology can provide a 10m/s2 acceleration for more than a few minutes. The only technology we have today that can provide that acceleration is conventional chemical rockets and they simply can't carry enough fuel to maintain a 1G acceleration for very long.

Can someone give us a ballpark estimation about how much fuel would be needed to accelerate a ship large enough to give place to lets say 20 persons, their food, supplies and not to forget the fuel to get home, for 8.5 hours at 1G? Oh and to decelerate it too...

Sadly, it can't be done because we have no technology existing or even proposed that can maintain 1G acceleration for more than a few minutes much less for hours.

See some of the types of propulsion here:

Space Propulsion.
http://en.wikipedia.org/wiki/Space_propulsion

A nuclear powered VASIMR system could probably do it, with an exhaust velocity of up to 300 km/s. The VASIMR system appears to be technically feasible, IF you have the space nuclear powerplant available.
Another possibility that might be possible near term that could do it might be the fission-fragment rocket:

Fission-fragment rocket.
http://en.wikipedia.org/wiki/Fission-fragment_rocket

This is a very dirty nuclear propulsion method however that spews out radioactive matter as the reaction mass.


Bob Clark

publiusr
2009-Sep-25, 09:17 PM
Let's hope for more breakthroughs.