From: dw229@hermes.cam.ac.uk
As far as I can see, the main problem with this is how the spacecraft is
meant to climb while attached to the tow-rope. As it gets higher, the
atmospheric pressure drops, and so would the lift across its wings. This
requires either larger wings for high-flying craft (e.g. U2 spyplane) or a
higher velocity...but in this case the velocity is fixed by the tow-plane.
Given that it will be much harder to keep the tow-plane flying fast at
its much lower altitude than a plane at higher altitude I'm guessing this
isn't very efficient.
That's what I thought anyway - feel free to rip my arguments to shreds!
D
On Wed, 30 Jun 2004, Alex Terrell wrote:
> Works with water skiing.
>
> I wonder what sort of performance you could get out of it?
>
> How about electrically winching in the space craft. If the tow plane
> travels at Mach 1, and the cable is winched in at Mach 1, you have a
> Mach 2 launch speed. You'd need a long cable and a very fast reeler.
>
> nospam@nowhere.nil.retro.com wrote in message news:...
>> I saw this idea on rec.aviation.homebuilt.
>> I thought it ought to be posted here, so I copied and posted.
>> The origional idea is NOT mine.
>> It was posted by Tim Ward
>>
>>
>> I dunno, but this seems as good a time as any to bring up a stupid,
>> complicated idea of mine for access to space.
>>
>> First, you should be familiar with the Kelly Aerospace idea of towing
>> the spaceship to altitude.
>> If not, Google for "Eclipse project", NASA, and perhaps F106.
>>
>> They towed an idling F106 behind a C141 as a proof of concept project.
>> Second, you should be aware of the "payout winches" used to ground
>> launch hang gliders. These just pay the line out at a constant
>> tension, rather than reeling them in at a high rate of speed, as in
>> sailplane launches.
>>
>> So here's the scheme:
>> You build a tow plane about the size of a 747. The payout winch is
>> mounted such that it "pays out" from the CG of the airplane, on top.
>> You have somewhere around 100,000 lbs of Vectran tow rope (several
>> tens of kilometers) on the payout device. This is within the cargo
>> capability of a 747, though you may want to throw on a couple of extra
>> engines because of the additional drag.
>>
>> The spacecraft has a CG hook on the bottom.
>> You take off, and climb as high as you can, while paying out the tow
>> line. The spacecraft pilot basically controls the pay out. Pitch up,
>> and a little more line pays out. Pitch down, and it stops.
>>
>> If the spacecraft can maintain a 45 degree angle behind the towplane,
>> it will be 70% of the towrope's length higher than the towplane.
>>
>> At some point, the true airspeed of the tow plane will not provide
>> enough airspeed for the spacecraft to continue to climb. So the
>> towplane starts to turn, and the spacecraft maneuvers to the outside
>> of the turn. Now it's just like playing "crack the whip". The
>> air-breathing booster is down in the (relatively speaking) thick
>> atmosphere at 50,000 feet, while the spacecraft is above most of the
>> atmosphere at say, 100,000 feet.
>>
>> That's when the spacecraft releases and fires its rockets.
>> Because the atmosphere is so much thinner, and the spacecraft is going
>> faster than it would be at lower altitudes, the increase in peak
>> altitude achievable should be much higher than just the 50,000 ft
>> altitude difference between the tow plane and the spacecraft.
>>
>> After the spacecraft releases, the towplane also releases the towline,
>> and it descends under a parachute, separately.
>>
>> There, I feel better.
>> Tim Ward
>
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