[Airthumbs (OP)]

Given all the different forms of technology that we now have for accelerating objects to high speeds I found myself wondering what reason there would be not to combine several of them together to obtain escape velocity and reach a stable orbit.

As an example, lets say you start off with an object at one metric ton.  The energy required to get that object moving is quite considerable.  It seems a bit silly to use an enormous amount of rocket fuel in just getting off the ground.  Instead you might use a huge spring of some sort for the first ten meters, then some kind of magnetic accelerator, then something like a scram jet, finally using the small amount rocket fuel for the final approach into space.

By combing different technologies a large part of the work can be done horizontally or at least up a very long slope.  CERN is quite long and manages to accelerate particles nearly to the speed of light!  You don't need anywhere need the speed of light to get into orbit.

This kind of device would have to be very, very long for someone to withstand the G force's to obtain escape velocity but for firing small objects such as moon supplies it might work very well.

I think it would work but what about you?

It's all down to privateers to get to the moon so come on lets get on with it

[CliffordK]

The SpaceShipOne and the X-15 were both launched in the air from an airplane, and thus use conventional fuel, and the lift generated with wings to get up off the ground.



It would seem to me that one could build a large supersonic launch vehicle like the Concorde, the Tu-144, the XB-70, or the Sukhoi T-4.

However, it may be problematic to launch a large underbelly, or even internally carried cargo at Mach 3.

One could, of course, use a subsonic launch vehicle to get some altitude, and the rocket up to thinner air.  Perhaps part of the problem is the cost of developing an enormous launch vehicle.

Ahh, I found this Wiki Page of Proposed non-rocket space launch vehicles  Some may be more practical than others.  I think there had been some work on heavy lift balloon launch vehicles, but perhaps there are some drawbacks.

[wolfekeeper]

Yup, rockets love it if you give them a push at the beginning.

The problem is, it takes quite a lot of pushing to make much difference.

Orbital speed is extremely fast; it's about 25 times the speed of sound, and allowing for the losses, you'd better figure on it being more like 30 times the speed of sound.

Balloons don't help very much, you mainly need sideways speed to get to orbit, going up to high altitude isn't a lot of help. Even subsonic aircraft aren't such a massive help, although they are used.

Very fast supersonic aircraft like the SR-71 would be a help, but there's difficulties with the separation, all supersonic aircraft are surrounded by powerful shockwaves, and the separation at these high speeds is challenging.

[CliffordK]

Here is the comparison of the Dodge Ram 3500 to the Delta IV rocket.

The Dodge RAM has better 0 to 60MPH acceleration (on the level) than the Delta IV (vertical).

It would take a massive launch tower, perhaps ascending the side of a mountain, but I wonder what the fuel savings would be to accelerate the rocket to, say 200MPH before launch.  And, while one might use conventional fuel for the acceleration, it would reduce the onboard fuel requirements, and thus the overall weight of the launch vehicle.

One could, of course, also simply launch from a launch platform a couple of miles in elevation.  Denver, the "mile high city"?  Gran Tetons?

Of course, Florida was chosen by NASA because of being quite far south (closest to the equator), and that launch failures (which there have been many) would occur over the Atlantic.

[wolfekeeper]

200 mph isn't very fast, using the rocket equation, I calculate that it would make less 3% difference to the size of the rocket you need to build to reach orbit.

[Airthumbs (OP)]

 On Jan 2008 BAE delivered a Railgun to the American navy that fired an object delivering 32 MegaJoules.  The example given was 1 mega joule is like moving a one ton truck at 100mph!  Now this little gadget is about 20 meters long maximum.
The concept seems to be blowing something up as quickly and efficiently as possible and something that they can use on current hardware such as big ships. 

If you removed the size constraint and had more distance to obtain higher velocity and included factors such as altitude and position for a suitable site then this could be done for a lot less money then it cost to build CERN I bet!

A very high place with a nice big mountain at the right angle would be perfect. 

[bizerl]

Now I know this suggestion is entirely impractical, however I'm curious as to how much lift could be acheived through a buoyant object emerging from water.

I had a friend ask me about this after he witnessed his nephews playing in the pool with a bodyboard, by holding it underwater then releasing it to make it fly up into the sky. How scalable would something like this be if we could submerge a vessel full of helium or something, deep underwater (using weights or something), then release it. Or something.

I told my friend I thought that the closer to the surface the object got, the less the drive would be to move upwards and therefore the energy would be fairly dissapated by the time it breached. But I was only speculating because I don't really know...

[yor_on]

Jules Verne smiles benevolently upon us now. Didn't he write a book where the rocket was shot out as a bullet from inside a mountain? Maybe you could use electro magnetic accelerators inside a deep hole? Or anchor them in the sky somehow? The further up you start the launch, the energy cheaper it has to be as a thought?

[CliffordK]

Now I know this suggestion is entirely impractical, however I'm curious as to how much lift could be acheived through a buoyant object emerging from water.

something similar was discussed here on TNS:
http://www.thenakedscientists.com/forum/index.php?topic=39998.0

If you had the spaceship open to the water, then I would imagine even the most aerodynamic submarine would reach terminal velocity rather quickly, and would be lower than one might hope.

Hull stresses from positive underwater pressure and negative space pressure may be quite different, and may require significantly different designs, although, perhaps one could encapsulate the spaceship with a capsule that would be ejected as part of the launch.

[CliffordK]

200 mph isn't very fast, using the rocket equation, I calculate that it would make less 3% difference to the size of the rocket you need to build to reach orbit.

A 3% savings would be HUGE.
Consider the Delta IV rocket.
Mass: 249,500-733,400 kg (550,000-1,616,800 lb)
Payload to LEO    8,600-22,560 kg (18,900-49,740 lb)
Payload to GTO 3,900-12,980 kg (8,500-28,620 lb)

A 3% savings would be essentially equivalent to about 100% of its payload.

There would be both velocity and altitude components of the launch. 

If the goal is to reach an altitude of say, 200 miles.  Then, launching from Denver (1 mile altitude) might be equivalent to saving about 0.5% of the launch energy.  Launching from about 11,000 feet might be equivalent to about 1%, which might be HUGE.

Launching from 80,000 feet (about 15 miles), at Mach 3,
Ok, so one still has quite a bit to go, but it might save 10% to 20% of the launch weight which would be HUGE when comparing to the payload.

Has the military done testing of bomb drops from supersonic jets?

I found another Wikipedia page that is related.
Air Launch to Orbit

[evan_au]

The difficulty with building up a high speed near ground level is that there are considerable losses due to air friction and shock waves. Rockets tend to get accelerate more when they get above most of the atmosphere, partly because that is most efficient.

Most efficient of all is if you don't have to carry the fuel/energy source with you, otherwise most of the fuel goes into lifting other fuel...

The old Space Elevator would be a good idea if you could supply electrical current up the tether (but I fear that lightning would also make use of these electrical conductors!). http://en.wikipedia.org/wiki/Space_elevator

[CliffordK]

Most efficient of all is if you don't have to carry the fuel/energy source with you, otherwise most of the fuel goes into lifting other fuel...

2H₂ (MW 4)+O₂ (MW 32) ----> 2H₂O (MW 36)

The majority of the weight in the fuel is in the Oxygen.

For the first 15 miles or so of altitude, if one only had to carry hydrogen, and not oxygen, it could potentially be a big savings.  Also, adding 80% nitrogen to the fuel mix may not be bad, as it would add more to the thrust being expelled out the back of the rocket.

It is just not as simple as one might hope to combine the two technologies.

[wolfekeeper]

200 mph isn't very fast, using the rocket equation, I calculate that it would make less 3% difference to the size of the rocket you need to build to reach orbit.

A 3% savings would be HUGE.
Consider the Delta IV rocket.
Mass: 249,500-733,400 kg (550,000-1,616,800 lb)
Payload to LEO    8,600-22,560 kg (18,900-49,740 lb)
Payload to GTO 3,900-12,980 kg (8,500-28,620 lb)

A 3% savings would be essentially equivalent to about 100% of its payload.

Nope.

That's 3% off the lift off weight (GLOW). The second stage is the one that carries the payload, and everything there is about 10% of the first stage's mass. So you've knocked ~0.3% off; you can get 2.3% payload relative to the GLOW instead of 2% payload relative to the GLOW.

That's a useful amount, but then you need a really huge, expensive, aircraft to carry everything.

It's just about worth it for suborbital because you don't have the multiplier.

The only orbital vehicle that does this Pegasus is significantly more expensive than other launch vehicles.

[CliffordK]

I was surprised to see the speed rating on SpaceShipOne as:  Mach 3.09 (2,170 mph, 3,518 km/h).

So, it hits about 70 miles altitude, but can't maintain it.

SpaceShipTwo, and SpaceShipThree are also supposed to be suborbital. 

Perhaps they will be the next point to point business class jet, replacing the Concorde.

[wolfekeeper]

People always talk about rockets for point to point, but they would be extremely expensive.

Rockets, Concorde and normal subsonic jet aircraft work by jet propulsion.

There's a rule of jet propulsion that says that for efficiency you want the exhaust jet to be similar speed to the vehicle.

Unfortunately rocket exhaust goes at about 10-15 times the speed of sound in air @stp.

So unless you're doing at least half that (5 times the speed of sound), the rocket is horribly inefficient.

The thing is to go a hundred miles, you don't need that much speed; rocket exhaust is much too fast.

Concorde had an exhaust jet of maybe 2.5-3 times the speed of sound, so it was a much better match, and even then it could only just make it across the Atlantic.

Rockets are optimally efficient, point to point going antipodally, but even then they use several times more fuel than normal jets (and to go that far you would have to use a two stage rocket which multiplies cost).

[Airthumbs (OP)]

Did everyone miss my comment about the railgun? I am trying to look at a practical solution to a very expensive problem.  Launching underwater only seems to add to current costs and technical issues. 

Yes rockets are great, however they can't be that good otherwise you, me, Tom, Dick and Harry, would all be having this conversation from the Moon!



So the idea I propose is quite simple really, not that technically difficult given what other achievements we have accomplished.  Yes building up speed at ground level might be a problem so put it in a vacuum!!  I mean it's that obvious isn't it!! 

[wolfekeeper]

Railguns are very subject to rail erosion with each use, and are unlikely to be much use for space launch.

[Airthumbs (OP)]

Railguns are very subject to rail erosion with each use, and are unlikely to be much use for space launch.

I'm not saying you use an actual railgun, that's an example I give for what can be currently achieved using newer technology.  And I know you want to lighten the load so to speak but rail erosion!

Forget rails altogether that's just going backwards. Think mag lev, think superconductors and that sort of malarky.....  big electro magnets. 

Given no friction and say 2 miles of tube, does anyone know how fast it is possible to theoretically accelerate a one ton object? Lets say your using magnets as the "accelerant"?

[CliffordK]

Your acceleration could be in several different methods, and does not need to be a vertical launch.

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The most unique launch might involve a horizontal acceleration followed by turning vertical.  The advantage is that one could easily extend the acceleration track for several miles, as long as the transition to vertical (or a steep angle) was done such that the G-forces would not be too great (not exceeding 9 or 10Gs?).  One could do it with a horizontal track, and use wings (detachable?) to turn the rocket vertical, and thus not even need a vertical track. 

I put in the C: U-shaped acceleration as food for thought.  A pure gravity U shaped track would essentially give no significant benefit over a static launch.

I think your equations are (assuming initial velocity and distance are zero, and constant acceleration).
Velocity = Acceleration * T
Distance = (½) * Acceleration * T²

Considering the vertical acceleration, for short distance, high acceleration, 10 seconds at 100 m/s² (just over 10G) would get one to a velocity of about 1000 m/s (3600 kph) and a distance of about 5 km.

6 seconds gives one about 600 m/s (2160 kph) and 1.8 km.

The speed of sound at ground level is about 343 m/s, or 1236 kph.  It may not be desirable to exceed the speed of sound on a rail launch vehicle.

At a 100 m/s² acceleration, then in 3 seconds one would reach a velocity of 300 m/s, and a distance of only 450 m.

Ignoring wind resistance, if one launched vertically at just below the speed of sound, 333 m/s, then one could coast for 34 seconds before one would stop at 5.6 km altitude.

Mach 4 is about 1360 m/s.  Again, ignoring wind resistance, turning vertically, one should be able to coast for about 139 seconds for an altitude of 94 km...  just about kissing the edge of space (with zero velocity).

[CliffordK]

Ok, how about this...

Design an internal cargo supersonic launch vehicle.

At high altitude, Mach 4, you turn your launch vehicle to a steep climb, where the engines begin to starve for air.  The airspeed then starts dropping to below the speed of sound, and with thin air, it should be safe to deploy the rocket cargo. 

I see the record altitude for parabolic jet flight is 37 km..  Not as high as I was hoping, but that is a lot higher than 0 km, and your rocket would not have to fight with nearly as much wind resistance as a low altitude launch.