Ask a Rocket Scientist

7ronin said:

Why does it have to be hidden somewhere other than on earth? Why did you place the number of warheads at 500? You realize of course that the number of warheads does not necessarily equal the number of delivery systems. I hope you weren't thinking about an exterrestrial launch. One of the principles of nuclear warfare is that you try to minimize the time between launch and impact. The greater that time, the more chance your enemy has to respond to your strike with one of his own. A launch from somewhere other than earth would take too long.



There is no such thing as a "covert" first or second strike. Once the missile leaves the silo or the submarine, it's out there for everyone to see. There are "covert" launch platforms, for example, strategic nuclear submarines. Parking your weapons someplace other than on Earth is impractical. You want your weapons close at hand where you can get to them when you need them. You don't have the time or luxury to wait a week while your nuclear weapons valet drives them over from the parking lot on the far side of the moon. It's my opinion that this is not necessary and in any case is not doable with exisiting technology.

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I don't know for sure, but what I'm thinking is

i) The Earth's gravity-well [and the Sun's] will accelerate returning warheads to enormous velocity

ii) Radar point "over the horizon" not directly up into space


And thus that during the return voyage, warheads would be undetected until they were close to Earth, by which time they could be travelling at a small fraction of the speed of light. Give them a stealth shielding, and the enemy might only have a few seconds to respond [ie he can't respond].

The added velocity means it will break through armoured targets [ICBM silos]. For getting it into space, some cover such as a 1,000 ton "Mars Colony" or similar will be sufficient.

I just wanted to know if there was a good place in the Solar System to hide them. Pakistan/Earth may be a good place to hide nukes, but it's not a good place to launch them.

Well you would need to get used to having your first/retaliatory strike happening many many months or years after you intended it because the solar system is huge.

Ayn Rand said:

ii) Radar point "over the horizon" not directly up into space

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There are other means of tracking space objects besides radar. There are a legion of scientists in both the military and civilian sectors who do nothing but look for and keep track of space objects in the vicinity of Earth and elsewhere in the solar system. Your warheads would quickly be detected.

And thus that during the return voyage, warheads would be undetected until they were close to Earth, by which time they could be travelling at a small fraction of the speed of light. Give them a stealth shielding, and the enemy might only have a few seconds to respond [ie he can't respond].

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You are overestimating the velocity to which these warheads could be accelerated. In any case, it's moot because they would most certainly burn upon entering the Earth's atmosphere no matter what protective measures you might employ.

Of course, if your purpose is science fiction/fantasy then you are free to choose any scenario you wish irrespective of physics or reality.

Question for the Rocket Scientist:

Not sure if you can shed light on this or not; it has to do with fluid dynamics:

Why are the yaw control surfaces of planes, rockets, and boats at the rear of the hull?

Cars' steering surfaces are at the front, using the rear contact surfaces as a pivot. Cars travel on a solid surface, unlike these other vessels. It's the reverse for any vessel that moves through a fluid medium. Any idea why?

peter grimes said:

Question for the Rocket Scientist:

Not sure if you can shed light on this or not; it has to do with fluid dynamics:

Why are the yaw control surfaces of planes, rockets, and boats at the rear of the hull?

Cars' steering surfaces are at the front, using the rear contact surfaces as a pivot. Cars travel on a solid surface, unlike these other vessels. It's the reverse for any vessel that moves through a fluid medium. Any idea why?

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Good question, and yes!

It has a lot to do with fluid dynamics and the answer varies slightly between aircraft and boats. It's essentially a matter of efficacy, as what these yaw/pitch/roll controls do is alter the flow of the fluid.

We didn't originally know why putting a motor at the back of the motorboat was best - that bit was figured out through trial and error. But now it's more-or-less understood that any propulsion system that relies on the motion of a fluid over or through it should be attached to an aerodynamic body that conflicts with that motion least. The basic idea is wherever you have a craft moving through a dense fluid medium, you want to be altering the flow of the fluid behind or around the craft in a way that gives you the most bang for your buck. A rudder at the front of the boat is fighting against the entire rest of the hull to change the overall motion of the flow (the hull wants the fluid to travel along its surface; the rudder separates that flow from the hull, generating what is called a stall condition and a ton of drag). A rudder at the back of the boat, however, isn't fighting anything (except the fluid's viscosity, but that's another matter) - it changes the direction of the flow and that's all there is to it.

Here's another way of thinking about it: the fluid motion of matter "behind" a boat, aircraft, or rocket is what moves those objects "forward." Conservation of momentum and all that. This flow is where you're getting your acceleration, so it's what you want to be manipulating. Flow coming off the trailing edge of a wing is what's really pushing the wing up, so that's where you want to be manipulating the flow in order to get your roll, pitch, and yaw. For a rocket, this is intuitive.

You can see that a car wouldn't have this problem as it does not rely on propelling fluid behind it in order to move. It relies on static friction and a rotor to get going. The propulsion isn't based on the motion of fluids so it doesn't really matter where you put the controls. We put them at the front because it makes more intuitive sense to we who operate those vehicles.

I hope that makes sense. Thanks for your question!

In our days there seems to be a lack of willingness to risk lives in space programs. Do you think this statement to be true and if so what might be the reasons for it?

Some people asked earlier why there has been "so little progress" in rocket sciences during the last years. I think in the beginning there was a lot of trial an error and today we try to understand why things work how they do.
E.G. during my bachelor thesis I worked on a project with EADS/Arianespace who build the Vulcain 2 engines for the Ariane rockets
For the combustion chamber a Cu-Ag-Zr alloy is used which has been in use since the 60's (NASA used nearly the same). The working condition for this combustion chamber are about 60 K on the outside due to the liquid hydrogen fuel which is used as coolant. On the inside there are about 3600 K during the combustion. In addition there is mechanical and chemical corrosion (due to the O² and H² gas stream environment) while the whole engine is driven in a pulsed mode. As you can see it's a system with plenty of variables. The knowledge of the properties of the Cu-Ag-Zr system was close to zero before the project started in 2003 (after the failed Ariane 5 start in 2002) as even many basic mechanical properties were only vaguely known. Now 8 years later we still don't know exactly what happens in this system during a launch but we can at least have clue now

Samez said:

In our days there seems to be a lack of willingness to risk lives in space programs. Do you think this statement to be true and if so what might be the reasons for it?

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No, I don't agree with that. The problem from our end seems to be a lack of willingness to spend money on space programs. Lives is irrelevant (as misanthropic as that sounds) as there will be no shortage of people willing to take the risk and go boldly where no man has gone before etc.

Some people asked earlier why there has been "so little progress" in rocket sciences during the last years. I think in the beginning there was a lot of trial an error and today we try to understand why things work how they do.
E.G. during my bachelor thesis I worked on a project with EADS/Arianespace who build the Vulcain 2 engines for the Ariane rockets
For the combustion chamber a Cu-Ag-Zr alloy is used which has been in use since the 60's (NASA used nearly the same). The working condition for this combustion chamber are about 60 K on the outside due to the liquid hydrogen fuel which is used as coolant. On the inside there are about 3600 K during the combustion. In addition there is mechanical and chemical corrosion (due to the O² and H² gas stream environment) while the whole engine is driven in a pulsed mode. As you can see it's a system with plenty of variables. The knowledge of the properties of the Cu-Ag-Zr system was close to zero before the project started in 2003 (after the failed Ariane 5 start in 2002) as even many basic mechanical properties were only vaguely known. Now 8 years later we still don't know exactly what happens in this system during a launch but we can at least have clue now

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Yes, rocket design is a very sensitive science and has a lot of variables. It's not easy: the entire reason the US space program got anywhere was because we had brilliant German and Hungarian rocket scientists who had been working in the field for some time and had a knack for it.

There are still some advances being made in rocket design, as I touched upon earlier, but many of them are done as part of military research, which is generally moving away from rockets and towards fixed-wing aircraft and rotorcraft. There's no big rush to produce ICBMs or anything like that, but faster airplanes is always nice.

A big recent advance has been made in the development of a Mach 5 aircraft that mainly uses jets, not rockets, to accelerate. Again, though, much of aerospace engineering is tied to the relevant interests of the military.

I'm doing Aerospace Engineering. 1st year
My lecturer said that Aerodynamics is harder then rocket science its just that rocket science sounds sexier do you agree?
Do you think rockets in the traditional sense will be phased out in favour of jet engines? (assuming rockets are single use is this assumption correct?)
On a slightly related note is space a complete vaccuum? Ie i assume its has some gasses albeit at very -very low concentrations.

Wernher von Braun: best of bestest Rocket Scientist?

kristopherb said:

I'm doing Aerospace Engineering. 1st year
My lecturer said that Aerodynamics is harder then rocket science its just that rocket science sounds sexier do you agree?
Do you think rockets in the traditional sense will be phased out in favour of jet engines? (assuming rockets are single use is this assumption correct?)
On a slightly related note is space a complete vaccuum? Ie i assume its has some gasses albeit at very -very low concentrations.

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One at a time:

1. Welcome to the discipline! Good luck!

2. Well that's a very black-and-white way of looking at things, but let me put it this way. You don't need a complete understanding of fluid dynamics to build an airplane. A rocket, however, demands total awareness of everything you're doing. It's a much more expensive endeavor and the details are much more important.

When it comes to fluid dynamics, though (the modeling/theory of and calculations behind), it might be the most complicated physical science. We still don't know how to solve a lot of the equations behind fluid dynamics and computational fluid dynamics is one of the most difficult and challenging fields in aerospace.

3. Jets can't function in space, so no, not entirely. Jets will probably be spearheading all endeavors for getting into space as we go into the future, however.

4. Space is a practical vacuum. Particles - of any type - in space are an astronomically low concentration. This includes planets, stars, and nebulae in this consideration.

Power_of_Beer said:

Wernher von Braun: best of bestest Rocket Scientist?

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Yes.

Jokes aside, he was an incredibly brilliant man and one of the most important and influential figures in all of aerospace engineering.

Why do the wings of most aircraft types taper towards their outer ends? What is gained by this?

Cutlass said:

Why do the wings of most aircraft types taper towards their outer ends? What is gained by this?

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Having smaller wingtips decreases the size of the wingtip vortices, the strength of which are partially influenced by the chord length (the distance from the leading edge to the trailing edge). Smaller wingtip vortices means less induced drag, which is ideal if you're trying to construct a fast aircraft; most fighter-jets have a "delta", or triangular-shaped, wing for this reason.

The cost is decreased stability since ailerons are normally situated near the wing-tips which, in this case, host a much smaller share of the lift distribution than that part of the wing closest to the fuselage. This is why passenger liners and cargo airplanes do not have as dramatic a taper as the aforementioned fighter-jets: the risk of going into a dangerous tailspin is too great.

Do you secretly want to be an astronaut?

Perfection said:

Do you secretly want to be an astronaut?

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Not so secretly.

Can an airplane stan still in middle of air if there is stong enough wind? (I am not reffering planes like harrier but commercial airlines) Is it scientifically possible?

Yes, if you got a headwind with the speed required to keep the plane airborne. Though it might be hard to control the plane.

I'll repeat my question, in case it got overlooked:

Blue Emu said:

What do you think of Zubrin's Mars Direct plan, with its in-situ rocket-propellant manufacturing concept?

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muhtesem insan said:

Can an airplane stan still in middle of air if there is stong enough wind? (I am not reffering planes like harrier but commercial airlines) Is it scientifically possible?

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Yeah, theoretically*. The velocity that is accounted for in the generation of lift is the velocity of the air relative to the wing. Wind contributes to this velocity just as much as thrust would.

Many instances have been recounted of aircraft that have been lifted into the air by a strong gust of wind, so securing and sheltering aircraft during windy weather is an important concern.

*Practically, the exact scenario you describe is impossible.

Blue Emu said:

I'll repeat my question, in case it got overlooked:

What do you think of Zubrin's Mars Direct plan, with its in-situ rocket-propellant manufacturing concept?

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It's an ambitious plan with some workable, if practically expensive, concepts. I am a personal fan of Mars to Stay, however, for non-technical reasons.