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I never said that ALL operations had to be confined to a crater or two.

It would be stupid to send people to do a task that robotics can handle wouldn't it?

This is trivial and easily solved. If burial of the lines and/or cooling of the lines doesn't work, then replace them ever so often. Hardly a deal breaker.

False. The ultimate fate of all comets we can see is to one day join the Sun. This is also true of many asteroids as well as they slowly spiral down into the Sun over the eons. Since the Sun is the final destination of so many celestial objects, doesn't it make sense that Mercury has intercepted more debris than the Moon which only occasionally gets in the way?

LMAO, come on guys, it's only 800 degrees! If I can touch the sides of my household oven when it is in cleaning mode (900 degrees) then sure we can build a rover capable of withstanding those temps indefinately. You people make it sound like this is some kind of impossible enginering task, it's not. People work everyday in nuclear power plants around the world without fatalities in an environment that is every bit as dangerous. But they do it so successfully because it is so well planned out.

Fine. I'm willing to accept that judgement.
But it isn't as bad as you make it sound either.

The challenges facing Mercury are technical ones. History has proven that when profit is to be made from abundant energy and/or resources, technical problems get solved and rather quickly I might add.

Different propellants have different reaction velocities, that's what I meant. Taken out of context I can see how you might reach that conclusion. However, the overall topic is about rocket efficency.

As for the nuclear option, what about this...

Why not use a reactor to produce electricity which could then genrate a magnetic feild that forces air out of the back of our rocket at much higher speeds and without the dangerous heat you mentioned?

Obviously you didn't understand my question, but that's ok. Thanks for the 'in-depth' explanation of basic physics...

Granted GCNR, but doesn't this assume that the efficency of a slow and fast burn rocket are the same?

You seem to have a good grasp of nuclear physics, so help me understand why we can't acheive much higher thrust from a nuclear powered rocket? I understand that the force of a rocket's engines are directly related to the speed of a rocket's exhaust.

So my question is this: can a small reactor be used to super-heat air, perhaps even incoming air from the surrounding atmosphere, or stored air to produce a thrust greater than that of conventional rockets?

Think about it...

If they do confirm ice on the Moon, then logic would demand that Mercury have several times the reserves. We already know it is rich in metals so uranium and plutonium should be abundant as well. It is THE prime real estate for a solar powered industry. When nuclear powered spacecraft become the means of getting around the solar system, Mercury will be a fantastic source of fuel. With an excess of energy, Mercury will have everything one needs to power commerce within the solar system. I'm sure it has rich deposits of helium-3, greater than the Moon in fact. Hydrogen can be collected from the surface or the solar wind and combined with oxygen in the rocks to create water. There is no atmosphere to interfere with rail-gun launched resources and spacecraft. And don't forget that it is cheaper to ship goods to Mercury than to Mars or the asteroids. If what is shipped back is energy in the form of microwaves, then you defeat the disadvantages of going deeper into the Sun's gravity well!

No one gives a hoot about Mercury, but this will all change when Messenger shows what Mercury really has to offer. You heard it here first!

I just read another great article by Jeffery Bell.

http://www.spacedaily.com/news/oped-05zy.html

In this article he correctly points out the difficulties of reaching orbit in a single stage reusable vehicle. Basically the meat of the article is that to reach orbit in a SSTO you need a dry mass weight of only about 8%, meaning that your vehicle must me 92% fuel by weight.

Obviously, contractors and NASA have been feeding us pipe dreams with the DC-X and the like that don't even come close to meeting this weight requirement. Projects such as these have just been an exercise in pork for the aerospace giants apparently.

So my question is this...

Why isn't NASA seriously considering alternatives to the 'take the fuel with you' approach?

What happened to dreams of building a rail gun like launch facility to accelerate small spacecraft up to say Mach 1 before turning on the engines?

Yes, I know this would be a huge engineering task that would require miles of track to be built, but if we can build super-colliders on the same scale, then why is this out of our reach?

Also, why isn't NASA, Boeing or Lockheed looking into a two stage transport the likes of which was used by Burt Rutan to capture the X-prize? Granted, NASA could get 1-3 people to orbit like this and not much else, but it isn't unmanned transport that is terribly expensive. Cargo and supplies could be launched seperately on traditional rockets that are much cheaper and not as safe.

Here's what I am envisioning...

Stage One: A supersonic vehicle capable of carrying the stage 2 vehicle reaches an altitude of about 20,000 feet traveling at Mach 2-3. It then drops the stage two vehicle and returns to the landing strip.

Stage Two: Already traveling near Mach 3 fires its rockets clear of the atmosphere and begins to build the needed velocity to reach orbital speed. This stage will include a capsule for the crew to re-enter the atmosphere safely while the spent stage two re-enters under auto pilot to be reused if it survives intact AND is cheaper than replacing.

Surely this is much safer than the shuttle we now use for several reasons. Capsules have never let us down when it comes to re-entry. They are tried and true tech while being relatively inexpensive as well. The stage two vehicle/glider wouldn't suffer from the same re-entry pains as the shuttle being much smaller and lighter without a crew compartment.

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Finally I have a physics question for someone like GNCRevenger. Would the fuel needed to reach orbit be reduced by using an elliptical plan of attack rather than a circular one?

Let me explain, we current reach orbit by using Hydrogen/Oxygen burns for an extremely high exhaust thrust so that we can reach 25,000 mph in what, two minutes?

Why not gain more altitude with a slower, continuous burn going straight up at say 80 degrees to the plane of Earth till we are say 10,000 miles above the Earth where the orbital velocity needed is much less. Then we could use the pull of The Earth to our advantage couldn't we? Once we start to fall back towards Earth, we could accelerate toawrds the edge of the atmosphere in a second burn, just barely miss it, and sling shot to the other side. Then once we have the needed speed, we could use a few well timed burns to round out our orbit could we not?

Thanks for the reply. I understand that even at those altitudes there is a LOT of drag, especially on something this large. So to counter that drag, why wouldn't it be possible to flatten out your 'balloon' into a solar sail? Couldn't it be possible?

In fact, couldn't small ion engines help pull it into a sail shape, greating increasing the surface area of our balloonsail?

Robs, as it stands now the FAA is supposed to keep their hands off until a disaster happens. If one or two rich people die, so what? This is by no means a safe adventure. People should agree to waive their rights to sue in the effect of a serious problem. That takes care of that little problem without regulation.

Companies investing this kind of money in a risky manner would be stupid. Virgin Enterprises didn't get to be one of the largest corporations in the world by being stupid. To answer your question, the EPA usually defines what is toxic and already has a set of rules regarding chemical usuage, so we don't need more.

We have rules for what you can and can't do in the privacy of your own home. We have rules requiring us all to waer seat belts so that insurance companies don't have to pay too much. We have rules requiring us to buy this same insurance from companies that make incredible profit margins.

Sometimes rules are put in place by lobbied politicians, not for ur greater good.

Ok.....I'll leave the hard physics to you to work out, but how wouldn't raising a spacecrafts launch platform to 60 miles or more help? You are talking about a tremendous difference in air pressure / resistance. Also, the higher your orbit the slower the required orbital velocity right?

Again, we are assuming that buisness is stupid and it is far from stupid. Would Virgin Galactic fly a sub-orbital ship releasing toxic fumes over a populated area? No. That begs to be shut down and you dont invest $200M just to tempt fate.

As for crossing international boundries, this isnt even an option for sub-orbital craft. So lets worry about that bridge when we cross it.

My point is, you and I dont need the government looking over us while we sleep. These are smart buisness endeavours that arn't going to be anymore risky than they need to be. Give them time to actually design a spacecraft before you tell them what not to is all im saying.

Spacenut, actually I was thinking of hauling an asteroid into orbit (if Mars' moons are off limits) with a solar sail over the coarse of a decade and then using railguns to launch decent sized rocks at our target until a respectable depth is reached. We probably wouldnt have to go the full 45K either. That was for a full bar of air pressure. Plants get by with a third or less of air pressure. Plus the scientist didn't take into consideration the creation of a heatsink.

Actually, I agree. You either need something that 'changes the game', as you put it, or an incredibly complex scramjet that is beyond the scope of the private industry.

What I see most likely happening is something similar to Scaled's SS1 effort in the sense that TWO RLVs are employed in unison. Afterall, WhiteKnight did most of the hard work for SS1 or it never would have reached that altitude.

Space travel difficulties stem from many things, but perhaps the most challenging is dealing with two different environments. A single stage RLV is so daunting because you must reach incredible speeds in a high friction / high drag environment. Rocket efficency is seriously slashed by not only fighting gravity, but also by shearing forces and resistance in general. Ask yourself, would you use a rocket to travel from ocean floor to surface, or would you just float?

The Canadian Arrow team is on the right track with their balloon assisted concept. Unfortunately, they are seriously underfunded. On the upside, high altitude ballons and true lifting bodies show incredible promise and are experiencing a revolution. In theory, it is even possible to reach orbit with a lifting body, as Air Force research has shown.

In summary, leave rockets to space, its their natural environment. Take advantage of the atmosphere with scramjets and high altitude balloons, its their natural environment.