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Possible Craft

Posted by: Sev - Sun Oct 10, 2004 4:10 pm
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Possible Craft 
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Post    Posted on: Thu Nov 04, 2004 8:35 pm
Is it me or does the skycat look like an inflated boiler suit? :)

I dont know whether I could bring myself to trust the lifting power of a mechanics outfit to get me to space. Although if the mechanic had curry the night before I might chance it. :lol:


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Post    Posted on: Thu Nov 04, 2004 9:36 pm
I think it lookes pretty cool.. :)
And it's main advantage over other airships/ballons is that it can land without personal on the ground because of it's hovercraft landing-gear.
Image

Here are some small videos of maiden flight of a prototype:
http://www.atg-airships.com/news/video_maiden.htm
I'm pretty sure I have seen a better quality version, but can't find it..


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Post    Posted on: Thu Nov 04, 2004 10:14 pm
OK, it does look kind of fun even if the designer has been stealing the designs of the Dalek mother ship from Invasion Earth 2150 A.D. :)

I cant see it being used to lift spacecraft to high altitute, it seems a little unstable when it takes off and lands, I wasn't sure the men on the ground were running to it or trying to get out of the way.

I think I've seen this before on the discovery channel about 3 months ago. A series with Chris Barrie called Massive Engines or something.


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Post    Posted on: Fri Nov 05, 2004 9:04 pm
Hmm, a couple of points about Airships to warn you all about.

A design like the Skycat would never work realistically, because the pressure gradient inside and outside would be too great for it's structure to withstand.

For example, the Da Vinci's project's balloon is almost deflated when it is only at a couple, and the spare room is there to allow further inflation for when it gets to higher altitudes. It is possible to build a balloon with strong enough walls to withstand the huge pressure differences, except that they are generally too heavy to take off at all. In fact, this is only one of many problems I have with JP Aerospace's plans, but that's quite another topic.

Expanding the White Knight to 747 would indeed be possible, although it wouldn't be quite as simple as that.

The basic thing you have to remember is that to double the wing-span of the White Knight, you would be quadrupling it's wing area, while octupling it's weight. This all means that you wouldn't get anything like the weight-lift ratio of the current White Knight, and so it's carry capacity (not to mention operating altitude) would note scale linearly. It would probably need to travel a good deal faster in order to be able to generate sufficient lift to combat the losses due to it's increase in size. The other down side is the construction of such a plane would be extremely expensive - a 747 costs $200M after all, so you would need a large, pre-existing launch market to make it worthwhile for launches as opposed to just using say, a Falcon V. It might be more efficient fuel and payload wise, but those are not the only issues.

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Post    Posted on: Fri Nov 05, 2004 9:31 pm
Sev wrote:
Hmm, a couple of points about Airships to warn you all about.


There's a significant problem with air-launches in general -- at least in regards to orbital as opposed to sub-orbital use. A WK-style air launch makes lots of sense *only* for a purpose like the X-Prize, suborbital tourism, or short-duration micro-G experiments. This is because of several factors:

- *Only* height is required -- there is no velocity that must be achieved.
- The ~45,000 foot launch height is almost 14% of the required 328,000 feet required for the X-Prize (it's only ~3.4% the altitude of the ISS).
- Suborbital craft are significantly lighter than an orbital craft for the same number of people carried for a half-dozen reasons. An orbital SS1 would likely be three times the weight of the original

For an orbital craft -- launching from 45K -- or even 80K feet makes little difference to the energy required to achieve orbit. It's not altitude that is important, but velocity. Making a launch from an airplane or a balloon significantly adds to the complexity -- thereby increasing the chances of failure, and provides only modest reductions in required propellant loads.

For an orbital craft -- the best bet is to design the lightest vehicle that will serve the mission goals and launch from the ground using the most efficient launch vehicle available.


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Post    Posted on: Sat Nov 06, 2004 2:30 am
http://www.abo.fi/~mlindroo/SpaceLVs/Slides/sld001.htm

plenty of studies was done about VTL/Air launch etc etc. Was curious. I read an article in Janes Defence Weekly (8 Sept 2004) abt how the USAF was still conducting some new studies for a reusable micro payload launcher. Studies studies and more studies.


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Post    Posted on: Sat Nov 06, 2004 10:37 pm
mrmorris wrote:
- The ~45,000 foot launch height is almost 14% of the required 328,000 feet required for the X-Prize (it's only ~3.4% the altitude of the ISS).

I don't have any facts, but I would imagine that in those 3-4% a rocket uses more that 3-4% of it's fuel, because of the added air resistance.. Maybe you right, maybe still not enough to pay for the added complexity of an airplane/airship as first stage..
I just like the idéa.. :D


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Post    Posted on: Sun Nov 07, 2004 12:29 am
Voyager4D wrote:
I don't have any facts, but I would imagine that in those 3-4% a rocket uses more that 3-4% of it's fuel, because of the added air resistance.. Maybe you right, maybe still not enough to pay for the added complexity of an airplane/airship as first stage..
I just like the idéa..


Facts are really useful when designing spacecraft for the real world. Imagination and cool ideas are really useful when designing spacecraft for TV shows.

An air launch that achieved both a high altitude *and* a high velocity (multiple mach) would provide a spacecraft with a significant fraction of the energy required to achieve orbit. Unfortunately -- the dynamics of an air launch at several times the speed of sound are not pretty. In addition, the engineering difficulties for an aircraft capable of reaching high mach values while carrying a few tons of dead weight are even worse.

If the air launch is adding complexity and not providing a significant benefit, then it's not worth it. At its simplest -- space flight is one of the most complex and dangerous tasks around. Anything which adds further complexity just adds to the fisk of failure. Failure in manned spaceflight is very likely to include people dying.


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Post    Posted on: Sun Nov 07, 2004 1:04 pm
What about using a rocket sled to accelerate the craft along rails curving upwards, I think I've seen this done by Nasa on small craft during tests in the 50s and 60s why was it stopped?

Presumably the craft could be accelerated to at least a couple of 100 miles an hour before the sled dropped away. I assume this did not give a sufficient advantage to make it worth while to continue. Perhaps it would be work with a small space plane mounted on a solid rocket booster, effectively becoming a kick start to the launch.


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Post    Posted on: Sun Nov 07, 2004 2:36 pm
Andy Hill wrote:
What about using a rocket sled to accelerate the craft along rails curving upwards, I think I've seen this done by Nasa on small craft during tests in the 50s and 60s why was it stopped?


The Hopper is planed to use a Maglev launch track..
But Its nothing more that a concept for the time being..
The only thing we have seen from that plan is the test craft Phoenix..
And some faq for how the Hopper is planned to take off..
It would take of from a 2 km long Maglev track and fly up to a height of 130Km height, where it would deploy it's cargo, witch would be a 2. stage rocket, that would place the real cargo in its destination altitude.. Hopper would the fly back, and land as a normal airplane.


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Post    Posted on: Sun Nov 07, 2004 5:30 pm
Sev wrote:
Expanding the White Knight to 747 would indeed be possible, although it wouldn't be quite as simple as that.

The basic thing you have to remember is that to double the wing-span of the White Knight, you would be quadrupling it's wing area, while octupling it's weight.


I think you're meaning about doubling all the dimensions, by doubling the wingspan you'd get twice the wing area and twice the weight of the wing.


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Post    Posted on: Mon Nov 08, 2004 12:13 pm
The air-launch is subject to new discussions in this thread. No doubt, that the arguments are valid that are saying that the altitude doesn't provide advantages and that velocity is the main problem for reaching the orbit.

But according to the most recent article under www.xprizenews.org Burt Rutan in an interview has explained the reason why Scaled choosed air-launch:

"An air-launch system for piloted spaceflight, which Rutan said was far safer than conventional ground-launched rockets. 'We don’t think that ground-launched rockets are going to be safe enough unless there’s some paradigm shift that makes them significantly more robust than they always have been'".

So it will be interesting to see wether Scaled will go to orbit by modifying their Wight Knight/SpaceShipOne-air-launch-design, by SSTO, by another quite new air-launch-design or by doing the paradigm shift they consider to be required for ground-launch.



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Post    Posted on: Mon Nov 08, 2004 12:41 pm
Heared an other valid point for choosing air-launch instead for ground-launch in a broad-cast about DART and it's launch vehicle Pegaus.. Pegasus is launched in a similar way as SpaceShipOne

You only need a normal runway, you don't need a special and expensive rocket launch-site.. So launch is cheaper and you have more options, as to where you want to launch from.


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Post    Posted on: Mon Nov 08, 2004 12:43 pm
Height vs Velocity.

I just had a thought. WHilst I can see that velocity is most important for orbital flight, the higher that you get, the less speed that is needed to maintain an orbit.

So, if you go a very long way up, you need less speed to maintain an orbit.

Therefor, *maybe* getting a leg up from a air launch may help, since you could use fuel normally used for getting to launch height to get to a much higher height (and it would be more efficient due to less drag in the thinner atmosphere, and your engine would also be more efficient). Once you are at a much higher height, you need less fuel to get up to orbital speed, since that speed is lower. In effect you use most fuel to get to a height where you require less fuel to get to orbital velocity.

So, you dont need a craft to be capable of very high in atmosphere speeds, since you can just keep going up and up until you get to a height where it is easier to get to orbital velocity.

Armadillos craft comes to mind.

I have a feeling all the above is nonsense, as I dont have figures for fuel loads etc and havent worked anything else out. I suppose just thinking about it from a kinetic energy pov means that the same amount of energy is requried to get in to a stable orbit at a particular height, whatever the method. However, that still doesnt preclude a air launch. Hmm.

James

ps. SOrry in advance for any spelling issues.


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Post    Posted on: Mon Nov 08, 2004 1:55 pm
JamesHughes wrote:
I just had a thought. WHilst I can see that velocity is most important for orbital flight, the higher that you get, the less speed that is needed to maintain an orbit.
...
I have a feeling all the above is nonsense...


Yes -- it is.

The reason that higher orbits have a slower 'straight-line' velocity is due to the conservation of angular momentum (i.e. this is the same thing that causes an ice skater to spin slowly with extended arms and faster when the arms are pulled in). The amount of energy required to reach the orbit is unaffected by this.

Higher orbits have lower kinetic energy, but higher potential energy. When the kinetic and potential energy amounts are summed -- the total energy of a high orbit is larger than the total of a lower orbit.


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