Ask a Rocket Scientist

[Crezth]

Why did you become one?

I wanted to use my love of physics to contribute to a cause that I believed in, specifically the exploration of space.

I also wanted to challenge myself intellectually and see what I could accomplish.

 

[zjintz]

Can you explain how moon produces waves?. May be a silly question but is not clear for me.

 

[Blue Emu]

Can you explain how moon produces waves?. May be a silly question but is not clear for me.

Do you mean tides?

Since the OP isn't on-line, I can take a stab at answering that.

Before considering the Moon's effect on the Earth, it might clarify things to first look at the other side of the coin... the Earth's effect on the Moon.

Pick two rocks on the Moon... one at the center of the near-side, and one at the center of the far-side. The nearest rock is (on average) somewhat over 384,000 km away from the Earth's center... the further rock is more than 1,700 km further away.

Left to themselves (ie: if you suddenly plucked the Moon out from between them), those two rocks would move in completely different orbits, and would quickly move apart... with the nearer rock moving faster along a shorter path and pulling ahead, while the further rock moves slower along a longer path and falls behind.

So there IS a force trying to pull the Moon apart. Gravity holds it together. This force... the Tidal force... depends on the mass of the bodies, the distance between them, and on the RATIO between the Moon's radius and the distance between them. If you were to bring the Moon close enough to the Earth... within the Roche limit... those two rocks would simply float apart: the Moon would be ripped to pieces by the tidal force.

All of these remarks apply equally to the Earth, since the Earth and Moon orbit each other. Rocks (and water) on the side of the Earth nearest the Moon are forced to move at less than orbital velocity... held back by the bulk of the Earth, to which they are bound by gravity. They sag inward toward the Moon. Rocks (and water) on the far side of the Earth are forced to move faster than orbital velocity... dragged ahead by the bulk of the Earth. They bulge outward, away from the Moon.

The result is two tidal bulges, one facing the Moon, and one facing directly away from it. As the Earth rotates, the continents pass through each of these tidal bulges, giving two high (and two low) tides each day.

My own question for the OP: What do you think of Zubrin's Mars Direct plan, with its in-situ rocket-propellant manufacturing concept?

 

[zjintz]

thanks, I get the idea.

 

[Singularity]

That's an interesting point of view. What makes you think that we're regurgitating the work of Von Braun and Kuznetsov? We've made great strides since them. Speaking overall, that is.

When talking of rockets directly, however, there is more cause for concern. There hasn't been a large national priority on the construction of large-payload rockets, so the technology hasn't advanced much beyond the adjustments necessary for your next deep space mission. Most of the development hasn't been in propulsion, it's been in the design of spacecraft and their component parts, and the application of robotics, which account for most of the technological difference between the rockets of today and that of the 1960's. Nevertheless, the field is advancing on all fronts, but in terms of new technology it's mainly held back because designing a rocket is not easy. A lot can go wrong. That's why the axioms espoused by many of the great rocket designers from back in the day are still looked to for guidance. Even most of Von Braun's designs were catastrophic failures.

In airplane design, however, America is doing fantastically. Engineers are developing new and better technologies all the time and the United States is handily leading the world when it comes to aeronautical engineering.

If I had to attribute the gully between the relative "success" of these branches to anything, I'd say it was funding that was doing it. There's a lot of government cash that goes into the air force and in all NASA jet design and supersonic flow labs, and private industry is constantly trying to develop new ways to improve their airfleets. This itself is because there are a lot of goals that are easy to identify, and there's a healthy incentive to fulfill them: there is considerable talk about trying to build private jets that can go at supersonic speeds... and don't cause a sonic boom. How it's done is pretty cool, but the status of airplanes as high-technology, high-expense items means that, as long as there exists an absurdly wealthy upper class, the industry will do quite well when it comes to innovation.

As for rockets, well, it's much more difficult to design a rocket than an airplane, and because the number of people who specialize in that field are shrinking the knowledge-base for designing a rocket from scratch is also starting to disappear. There is very, very little incentive to go into rocket design because it's twice as much work for almost a third less of the money.

Thanks for the reply. I'm talking very narrowly about LEO vehicle design and their propulsion systems. The lack of innovation to go beyond the stacked vehicles with single use elements should be a primary concern I would think. We're still stuck dreaming about exotic launch systems that hasn't gone beyond the drawing tables of concept artists.

"Space Launch System" seem to be all applied science and not theroretical/visionary science. I guess my question is, does your school have courses on exotic/next generation systems or are you all thought to construct&maintain old rocket designs?

 

[Kozmos]

All I know for rockets is the software side in that programming control software for the Space Shuttle took 400 programmers and 4 years. Admittedly it was back in the day when computers weren't so developed as they are now.

 

[Crezth]

Can you explain how moon produces waves?. May be a silly question but is not clear for me.

You probably noticed but for everyone else: Blue Emu answered this beautifully.

Thanks for the reply. I'm talking very narrowly about LEO vehicle design and their propulsion systems. The lack of innovation to go beyond the stacked vehicles with single use elements should be a primary concern I would think. We're still stuck dreaming about exotic launch systems that hasn't gone beyond the drawing tables of concept artists.

"Space Launch System" seem to be all applied science and not theroretical/visionary science. I guess my question is, does your school have courses on exotic/next generation systems or are you all thought to construct&maintain old rocket designs?

Good question. I think I touched on, but did not elaborate, why the prevailing knowledge is prioritized so heavily when it comes to rocket design in the propulsions department.

To reiterate: propulsion systems are the most complicated part of a rocket (or an aeroplane, for that matter), and principally why rocket science is considered "difficult" by people inside and out of the field (although fluid dynamics makes mechanical engineers very nervous). Controls and dynamics are ubiquitous in many fields, aerodynamics is a matter of modeling and for practical applications is something we have mostly pinned down, and engine design (while sophisticated) has been around, as a concept, for over two centuries. Propulsion systems are less than a century old as a matter of hard science and are hard to apply due to the goals: propel much mass using not as much mass in three or four different environments (all atmospheric layers, space, and deep space, etc).

The University of Cincinnati has one of the oldest institutions for aerospace systems and absorbed a lot of German scientists after the war (including a few that worked directly with von Braun). The department head is also a propulsions expert. So, they understand the value of the old knowledge and tend not to go outside that field for the undergraduate purposes. The School of Aerospace Systems also focuses on training engineers to work in the private sector (like most engineering schools), which means - mostly - working for the Air Force, GE, Boeing, Lockheed-Martin, etc. Most aerospace engineers, in general, end up working for the private sector, where experimental designs and new rocket types are not a priority. Even SpaceX is still using the old propulsion systems.

That being said, graduate research and much higher-level research has aspirations for new rocket designs, but remember that most of the old rockets that we've been using for decades were originally designed when the government was pouring a lot of money into NASA and the national labs. That same cash flow doesn't exist anymore, and R&D is actually more expensive than it was in the past, so it isn't considered very viable to develop new systems.

That doesn't stop us from trying, but there's only so much we can do to make viable multiple-use deep-space shuttles with nuclear engines (to give one insane example) on a limited R&D budget.

All I know for rockets is the software side in that programming control software for the Space Shuttle took 400 programmers and 4 years. Admittedly it was back in the day when computers weren't so developed as they are now.

That's true, but more developed computers also gives us the opportunity to develop more complex software, so those programmers can remain quite busy.

To give an example, in jet design a big priority for the control systems guys is modeling software so that they can know how the jet behaves. They want to design autopilot systems that can take over in the case of user error (it happens more often than you might think and it's hard to fly a jet or helicopter - personally I'm amazed that air force pilots can do anything with how much they need to know).

I once got in an argument with someone who said that people like me were making the air force obsolete because of our designs for unmanned flyers. I couldn't convince him that UAVs are there because they're small and can take off from anywhere, which makes them ideal for recon. I also couldn't convince him that the air force will always have a use for pilots because we can't model for every possible condition in flight, given the complex nature of airflow, and the experience of a pilot is somehow more valuable in weird situations than a one-million dollar computer. Pick your poison, I guess.


Keep the hard questions coming, guys. Your indictments about the uncreativity of rocket scientists is providing valuable introspection on my end. I appreciate it and we can maybe all walk away a little more knowledgeable about all this.

 

[uppi]

I once got in an argument with someone who said that people like me were making the air force obsolete because of our designs for unmanned flyers. I couldn't convince him that UAVs are there because they're small and can take off from anywhere, which makes them ideal for recon. I also couldn't convince him that the air force will always have a use for pilots because we can't model for every possible condition in flight, given the complex nature of airflow, and the experience of a pilot is somehow more valuable in weird situations than a one-million dollar computer. Pick your poison, I guess.

But I wonder whether the pilot will need to be in the plane in the future air force. There are a lot of systems that are just there to keep the pilot alive. If you can drop this and let the pilot steer the plane remotely you might be able to build a much better plane.

If you have a secure broadband data-link to your plane, you could just feed the information to a pilot somewhere who then reacts on the information. Like a video game, but with a real plane. And then playing video games will become a patriotic duty for the youth to train for the air force.

 

[Kozmos]

That's true, but more developed computers also gives us the opportunity to develop more complex software, so those programmers can remain quite busy.

To give an example, in jet design a big priority for the control systems guys is modeling software so that they can know how the jet behaves. They want to design autopilot systems that can take over in the case of user error (it happens more often than you might think and it's hard to fly a jet or helicopter - personally I'm amazed that air force pilots can do anything with how much they need to know).

I once got in an argument with someone who said that people like me were making the air force obsolete because of our designs for unmanned flyers. I couldn't convince him that UAVs are there because they're small and can take off from anywhere, which makes them ideal for recon. I also couldn't convince him that the air force will always have a use for pilots because we can't model for every possible condition in flight, given the complex nature of airflow, and the experience of a pilot is somehow more valuable in weird situations than a one-million dollar computer. Pick your poison, I guess.


Keep the hard questions coming, guys. Your indictments about the uncreativity of rocket scientists is providing valuable introspection on my end. I appreciate it and we can maybe all walk away a little more knowledgeable about all this.

Oh yes, programming is the devils work no doubt, it never ends. Always just the tip of the spear. Flying indeed is amazing, especially those who fly Harriers and other VTOL aircraft because they have to know and be good at flying both helos and jets to properly control them.

Unmanned flyers are the way of the future; the transition step being fly-by-wire at least until those neurosynaptic chips that DARPA is hogging right now combined with some interesting developments in cultured neuronal networks come into play. Then we could very well have intelligent and autonomous unmanned flyers. The wisdom of that is however discussable.

 

[Cutlass]

But I wonder whether the pilot will need to be in the plane in the future air force. There are a lot of systems that are just there to keep the pilot alive. If you can drop this and let the pilot steer the plane remotely you might be able to build a much better plane.

If you have a secure broadband data-link to your plane, you could just feed the information to a pilot somewhere who then reacts on the information. Like a video game, but with a real plane. And then playing video games will become a patriotic duty for the youth to train for the air force.

That assumes you can be absolutely certain of your communications. Your enemy is trying as hard to disrupt those as you are to maintaining them.

 

[Crezth]

But I wonder whether the pilot will need to be in the plane in the future air force. There are a lot of systems that are just there to keep the pilot alive. If you can drop this and let the pilot steer the plane remotely you might be able to build a much better plane.

If you have a secure broadband data-link to your plane, you could just feed the information to a pilot somewhere who then reacts on the information. Like a video game, but with a real plane. And then playing video games will become a patriotic duty for the youth to train for the air force.

Cutlass responded to this pretty well. In my own (feeble) knowledge of the workings of the US military, a large part of our overall doctrine is disruption and logistical impairment. It's why we had utterly neutralized the efficacy of Iraqi command in something like an hour after the war had started.

That being said, the fact remains that radio signals are relatively easy to jam from a defensive standpoint, and no amount of technological advancement will ever not make this the case (waves will be waves). Unmanned aircraft will have their place, but those that need attendant operators will need them on-board if they're expected to go deep (all jet fighters).

You can mitigate this need if you made the UAV truly independent of human operation (something we are working on), but we're a fair way off from that. Plus there's sort of an ethics thing with sending robots out there to mercilessly annihilate the puny flesh-humans. Or is that just me?

In all seriousness, unmanned aircraft that don't rely on human operators to function are probably the way of the future, especially when it comes to space exploration. A computer that could regulate the operations of a spacecraft during a long flight to Mars is almost a necessity in terms of making that sort of trip regular and functional.

Oh yes, programming is the devils work no doubt, it never ends. Always just the tip of the spear. Flying indeed is amazing, especially those who fly Harriers and other VTOL aircraft because they have to know and be good at flying both helos and jets to properly control them.

Unmanned flyers are the way of the future; the transition step being fly-by-wire at least until those neurosynaptic chips that DARPA is hogging right now combined with some interesting developments in cultured neuronal networks come into play. Then we could very well have intelligent and autonomous unmanned flyers. The wisdom of that is however discussable.

Pretty much! But as I said before, we'll have need for pilots for quite some time. Even if not in the military (also a dubious claim), it'll be awhile before people get comfortable flying without a pilot (as such) given the universal distrust of robots that is preeminent in western culture (parentheses).

That assumes you can be absolutely certain of your communications. Your enemy is trying as hard to disrupt those as you are to maintaining them.

Yup!

 

[uppi]

That being said, the fact remains that radio signals are relatively easy to jam from a defensive standpoint, and no amount of technological advancement will ever not make this the case (waves will be waves). Unmanned aircraft will have their place, but those that need attendant operators will need them on-board if they're expected to go deep (all jet fighters).

If you just try to communicate on a single frequency, then yes, it will be easy to jam with a narrowband source. But there are a lot of tricks you can do with current electronics that make jamming significantly harder. For example, you can implement fast frequency hopping to frequencies that are only known to the sender and receiver. If the enemy does not know the frequency sequence, he would have to jam all possible frequencies which would require a lot of power (and the jamming station would have a big "hit here" sign on it).

So the success of such a strategy would rely on being ahead in electronics. I admit that one might not want to rely on that.

 

[Crezth]

If you just try to communicate on a single frequency, then yes, it will be easy to jam with a narrowband source. But there are a lot of tricks you can do with current electronics that make jamming significantly harder. For example, you can implement fast frequency hopping to frequencies that are only known to the sender and receiver. If the enemy does not know the frequency sequence, he would have to jam all possible frequencies which would require a lot of power (and the jamming station would have a big "hit here" sign on it).

So the success of such a strategy would rely on being ahead in electronics. I admit that one might not want to rely on that.

It's a gamble and not one that can be practically made at our current juncture, anyway. My overall point is that we still have a need for pilots and will have that need for some time to come. By the time it is considered more practical to have the planes controlled remotely (absolutely impractical for long-range flyers and would require new airfields that are much more complicated and expensive than those currently used), it will also be more practical to have the planes completely automated anyway.

 

[Michkov]

On what do rockets stand when they are on the launchpad?

 

[GamezRule]

Has anybody ever used the expression "it's not rocket science" when trying to explain something simple to you?

 

[Crezth]

On what do rockets stand when they are on the launchpad?

I don't understand what you mean. The scaffold?

Has anybody ever used the expression "it's not rocket science" when trying to explain something simple to you?

Yes: people use it to describe economics all the time. It's not always easy to convince people that rocket science, at least, is a hard science of definite facts whereas the Austrian school is substantiated entirely by speculation.

Sometimes I respond with something like "at least if it was then I'd be able to follow your insane reasoning."

 

[Michkov]

I don't understand what you mean. The scaffold?

No no the scaffold. On which part does the rocket rest when standing on the pad. I cant imagine it stands on the nozzle

 

[Ayn Rand]

Where in the solar system is the best place to position and hide a nuclear arsenal? Assume size is 500 warheads and it is designed for two scenarios

1) A covert second-strike capability, returning in retaliation to an attack on NATO

2) A covert first-strike capability, where it will be brought back to Earth as rapidly and stealthily as possible in a surprise first-attack on hardened facilities.

Can you estimate the expense/possibility of deploying such a system?

 

[Crezth]

No no the scaffold. On which part does the rocket rest when standing on the pad. I cant imagine it stands on the nozzle

Ahhhh, well they're actually suspended on multiple large spokes (or one very large spoke) - I think. They definitely do not stand on the nozzle.

Most of the weight of the rocket is distributed down the scaffolds, however, which are also what keep the rocket upright.

Where in the solar system is the best place to position and hide a nuclear arsenal? Assume size is 500 warheads and it is designed for two scenarios

1) A covert second-strike capability, returning in retaliation to an attack on NATO

2) A covert first-strike capability, where it will be brought back to Earth as rapidly and stealthily as possible in a surprise first-attack on hardened facilities.

Can you estimate the expense/possibility of deploying such a system?

Pakistan. Nobody ever checks Pakistan. Added bonus of being very nearby China and within the same hemisphere as Russia.

 

[7ronin]

Where in the solar system is the best place to position and hide a nuclear arsenal? Assume size is 500 warheads and it is designed for two scenarios

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.

1) A covert second-strike capability, returning in retaliation to an attack on NATO

2) A covert first-strike capability, where it will be brought back to Earth as rapidly and stealthily as possible in a surprise first-attack on hardened facilities.

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.