Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Airthumbs on 19/09/2012 18:53:53
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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 :)
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The SpaceShipOne (http://en.wikipedia.org/wiki/SpaceShipOne) and the X-15 (http://en.wikipedia.org/wiki/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.
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fupload.wikimedia.org%2Fwikipedia%2Fcommons%2F9%2F95%2FSpaceship_One_and_White_Knight_in_flight_1.jpg&hash=48cbba43e2faba5330a7e6de9453034e)
It would seem to me that one could build a large supersonic launch vehicle like the Concorde (http://en.wikipedia.org/wiki/Concorde), the Tu-144 (http://en.wikipedia.org/wiki/Tupolev_Tu-144), the XB-70 (http://en.wikipedia.org/wiki/North_American_XB-70_Valkyrie), or the Sukhoi T-4 (http://en.wikipedia.org/wiki/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 (http://en.wikipedia.org/wiki/Non-rocket_spacelaunch) 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.
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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.
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Here is the comparison of the Dodge Ram 3500 to the Delta IV rocket. (http://news.pickuptrucks.com/2011/01/delta-iv-heavy-rocket-vs-2011-ram-3500-heavy-duty-diesel.html)
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.
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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.
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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.
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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...
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:)
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?
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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.
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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 (http://en.wikipedia.org/wiki/Delta_IV).
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 (http://en.wikipedia.org/wiki/Air_launch_to_orbit)
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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
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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.
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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 (http://en.wikipedia.org/wiki/Delta_IV).
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.
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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 (http://en.wikipedia.org/wiki/SpaceShipTwo), and SpaceShipThree (http://en.wikipedia.org/wiki/SpaceShipThree) are also supposed to be suborbital.
Perhaps they will be the next point to point business class jet, replacing the Concorde.
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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).
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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!!
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Railguns are very subject to rail erosion with each use, and are unlikely to be much use for space launch.
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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"?
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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).
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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. (http://en.wikipedia.org/wiki/Flight_altitude_record#Jet_aircraft). 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.
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Of course every little helps but there is no complete solution. You need to achieve around 17,000 mph and, even if this could be achieved at a low altitude there would be a need for some impressive (and probably weighty) heat shields and sufficient (i.e. a lot more) extra speed to allow for the considerable drag from air resistance. It would generally be best to launch from as near the equator as politically acceptable to the nation involved and to launch in an easterly direction (which is what most do). This gives over 1,000mph free because of the earth's rotation. There is some significant gain from an altitude launch; this has not much to do with the tiny gain in height (remembering that you have to get to about 400 miles if you want to stay in orbit - even a low one), but would gain from the forward speed of the launch vehicle (say another 600 mph) and probably much more from the thinner atmosphere providing much less drag. Despite all this complication there is still a lot of thrust required from the craft itself to attain an orbit.
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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"?
Supermagnets and magnetically soft iron can achieve an acceleration of 1000g
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you have to get to about 400 miles if you want to stay in orbit - even a low one),
The Hubble is at about 559 km (347 mi) speed 7,500 m/s
The ISS is at about 402 km (250 mi), speed: 7,706.6 m/s (27,743.8 km/h, 17,239.2 mph) but notes indicate that the orbit is currently decaying at about 2km / month.
speed: 7,706.6 m/s (27,743.8 km/h, 17,239.2 mph)
Geostationary orbit is at 35,786 kilometres (22,236 mi)
Anyway, one could likely save fuel and resources by building a short range, reusable heavy lift mach 4 supersonic jet for the first stage. But, the engineering cost might be extreme, and it still could be limited in capacity.
I am still a bit puzzled on why Pegasus is considered more expensive than other launch methods, but it must have to do with the custom work for a one-time use rocket with a small payload.
Since volume increases by the cube of the length, but surface area by the square, potentially larger rockets are also more efficient than smaller ones.
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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"?
Supermagnets and magnetically soft iron can achieve an acceleration of 1000g
People become puddles of goo at 1000g.
Or, at least looking more like bugs on a windshield.
Wind friction and heat generation would be high from an extreme velocity, low altitude launch, but it might get one up a few miles of vertical displacment.
At 10,000 m/s2, in one second, one would get about 5km, and 10,000 m/s, or about 36,000 kph.
Earth's escape velocity (without wind resistance?) is listed as 11,190 km/s.
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As I thought then, it can be done quite easily. We have the technology already. In fact it's fair to say I think that the potential speeds an object could reach would well exceed orbital levels. At the very least you could use a normal rocket fired from a ground launch system to maintain velocity. Is it coincidence that there is current research underway to produce circuitry that can withstand 1000g impacts?
If the highest landmass on Earth was used to site a launch system then I would expect the air resistance would be considerably less and given much higher velocity such as 100,000kph, or even 500,000kph, maybe heat shields could be incorporated into an outer protective shell, during initial launch.
If breaking the sound barrier is a problem then maybe it could be done inside a vacuum environment although I would expect the shock wave to be massive when it hits even the thinner air at high altitude? Maybe the shock wave could be reduced by shooting up supersonic jets of air into the area the capsule will come into contact with the air when it exists then vacuum sealed accelerator.
I think the "U" tube launch idea for a magnetic system is fantastic, as done inside a vacuum, Gravity can do a very large part of the work.
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Note the change of units for the calculated mag gun above at 36,000 kph, and the escape velocity of 11,190 kps. [xx(]
With the U above, using gravity alone, one would get high speed at the bottom of the U, but not at the top, so it would be ineffective of aiding the launch.
However, the level, then curve up might be effective as it would be easier to create a long path allowing slow acceleration, and the elevation change from start to release might be less than a a vertical acceleration pathway.
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A pure gravity U shaped track would essentially give no significant benefit over a static launch.
That's actually wrong. There's a (somewhat) significant advantage.
When you turn a rocket engine on, pointing downwards, you gain speed from the gravity and the rocket.
And then when you're moving, the rocket engine acts over the distance; generating work, so the faster you're moving the more energy you make.
The net upshot is that the rocket gains speed from turning on at the top of the U, going downwards and back up again.
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Ok,
So, if you drilled a hole 5 miles deep for the launch, then you would have 5 miles of extra gravity to contend with, reducing the velocity by 9.8 m/s2 for every second until one gets back up to ground level.
If you launched horizontally, then turned up, you would not have to contend with the extra gravity during the initial acceleration phase.
Interesting thinking about the U-shaped launch.
So, if the time is greater for the downward path, and shorter for the upward path.
Then the effect of gravity may not in fact be symmetrical, and one may get and extra boost from the gravity.
The same would be true if you bored a hole through the center of the moon for some kind of a magnetic accelerator. One would spend more time travelling towards the center of moon than away from the center of the moon. And, thus would get an extra boost from the moon's gravity, albeit weak.
This time effect of gravity may also explain why there is a benefit of a nearly vertical launch of a wingless rocket vs launching at an angle, say 45 degrees. One wants a launch that gets to as high of an altitude as possible, as quickly as possible.
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The same would be true if you bored a hole through the center of the moon for some kind of a magnetic accelerator. One would spend more time travelling towards the center of moon than away from the center of the moon. And, thus would get an extra boost from the moon's gravity, albeit weak.
Oh, no, not weak at all, that would be a MASSIVE win!
You would wait till you reached very nearly the middle before turning on the rocket engine. You should always use rockets when you're going as fast as possible.
edit: Mmm come to think of it, you should light the rocket at the bottom of the U for the same reason.
This time effect of gravity may also explain why there is a benefit of a nearly vertical launch of a wingless rocket vs launching at an angle, say 45 degrees. One wants a launch that gets to as high of an altitude as possible, as quickly as possible.
I think that that's just the Earth's atmosphere. In the absence of atmosphere you would launch very nearly horizontally, with the rocket angled to support its own weight, and to give as much sideways thrust as possible, although that would vary somewhat if you are trying to achieve a particular orbit, then you would launch more steeply upwards and then lean over.
The "time effect of gravity" is more normally called 'gravity losses' and are a thing though.
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Did anyone see the successful test of the British inventors space rocket recently? I did refer to him earlier on in the discussion and am very excited about it's development. It uses air drawn into the rocket externally to power combustion. I may have heard that it makes a 50% weight loss for the same performance as a normal rocket. Interesting prospect for a combo Airthumbs solution :P
Read what I wrote previously about a British Inventor and carefully read this article if you dare!!
http://www.bbc.co.uk/news/science-environment-20510112
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I'm glad to see work on Jet/rocket hybrids.
Do they count the extra weight for carrying liquid helium coolant? Or, would the liquid hydrogen used for fuel be enough for the precooling?
Of course, helium has a much lower density than hydrogen.
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Hi Clifford K, I think the information you might be interested in can be found here... http://www.reactionengines.co.uk/sabre.html
The engine is called Sabre.
If this was used in conjunction with a ground launch system as discussed then I do not see how it would not work. I have not seen any of the people at NASA, ESA or any of the private space companies give this a good look over yet but I hope they do as it would be great to get some feedback from the people who have all the experience.
I have e-mailed the company and asked them for some input into my idea so watch this space........ exciting times.