Physics Help Forum Launching satellites from high flying aircraft.
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 May 13th 2018, 09:58 PM #1 Senior Member   Join Date: Apr 2017 Posts: 427 Launching satellites from high flying aircraft. This idea came up in a recent thread , and it's stuck in my mind .... An old commercial jet is fitted out with long 'gun'/launcher the length of the craft... about 70 meters . The plane flies to it's maximum altitude , about 13Km , where atmospheric pressure is 10% that at sea level. The launcher uses compressed air for initial stage , then coil gun or rail gun principles to get a rocket up to perhaps mach 5 or higher ... The rocket and launcher need be no more than about 10 cm diameter , once clear of the aircraft the rocket ignites , taking the 'soda can' sized satellite into orbit ... there is a big market for putting small satellites into earth orbit ... 15,000 dollars per Kg .... Perhaps the mass of each rocket is about 50kg (500 dollars to make) ...payload perhaps 2 kg ... plane could launch 200 of these on one flight. Is it feasible??? Last edited by oz93666; May 13th 2018 at 10:16 PM.
 May 14th 2018, 01:51 AM #2 Senior Member     Join Date: Jun 2016 Location: England Posts: 688 The main issue I can see would be recoil. Firing even a 2kg payload to orbital velocity would generate a sizable recoil absorbing that recoil into the structure of the aircraft could prove problematical. __________________ ~\o/~
May 14th 2018, 03:59 AM   #3
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 Originally Posted by Woody The main issue I can see would be recoil. Firing even a 2kg payload to orbital velocity would generate a sizable recoil absorbing that recoil into the structure of the aircraft could prove problematical.
Hmmmm.... that's one thing I hadn't thought about ...

the length over which acceleration will take place is 70 meters.

lets say final velocity Mach 5 , 1715 m/sec

v = ft ..... 1715 = ft

s = 1/2 ftt .... 140 = ftt ..... so then t = 140/1715 = 0.0816secs

f = 21 Km/sec squared !!! .... 2 thousand g !! is that right???

mass rocket and payload 50Kg .... 50 x 21,000 = 1 million newtons push back on the plane over 0.0816 seconds .

Mass of plane 200 tonnes .... 1 million N will decelerate the whole plane at 5m sec squared ...half a g for 0.0816 secs , reduce the planes speed from 300m/sec to 299.5 m/sec .

The recoil will be down the length of the plane , if the launcher was held by springs secured at many points along the length of the plane , to spread the load , I think it could probably survive ..

But it's an important factor to consider , the launcher would have to be central along the axis of the plane , exit point below the pilot.

Consider a plane in normal flight ... the engines push at about 500,000N , and this is balanced buy a back push , perhaps half from the wings and about half from the fuselage (all from wind resistance )

So in normal flight the plane has 250,000 N pushing in the same manner as our recoil ... an extra million Newtons does sound a lot .

If springs suspending the launcher could cause the recoil to act over 1 sec this would reduce the recoil force to 100,000N

 May 14th 2018, 06:02 AM #4 Senior Member     Join Date: Jun 2016 Location: England Posts: 688 Aircraft based satellite launch is used by the Pegasus launch system. A gun based launch system was tried (HARP), but never quite got to fruition. Putting the two together is an intriguing idea, just not sure how practical... oz93666 likes this. __________________ ~\o/~
 May 14th 2018, 12:38 PM #5 Senior Member   Join Date: Jun 2010 Location: NC Posts: 405 P-51 Blasts Guns and Slows Hey oz93666... Here's a calculation in the vein of your case. http://http://www.thermospokenhere.com/wp/05_tsh/E5520___P_51/P_51.html Good luck... JP oz93666 likes this.
May 14th 2018, 07:38 PM   #6
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 Originally Posted by THERMO Spoken Here Hey oz93666... Here's a calculation in the vein of your case. http://http://www.thermospokenhere.com/wp/05_tsh/E5520___P_51/P_51.html Good luck... JP
Interesting work THERMO ... ( it deals with how much a burst of gunfire will slow a mustang )...conclusion ,the speed would drop from 440 to 385 ft/sec over 10 secs thats 134 m/sec to 117 m/sec

v = u + ft ...............134 - 117 = 10f that's a deceleration of 1.7m/sec squared over 10 sec .... the pilot should feel about 1/5th of a g pushing him forward ....

Searching more I see gas guns have projectile speeds of over mach 20 .... 7km/sec !! ... orbital speed is only 7.6km/sec ...

The advent of micro satellites makes this idea feasible ... Big companies may have overlooked it , they tend to think big .

May 14th 2018, 07:58 PM   #7
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 Originally Posted by Woody Aircraft based satellite launch is used by the Pegasus launch system. A gun based launch system was tried (HARP), but never quite got to fruition. Putting the two together is an intriguing idea, just not sure how practical...
That pegasas link is interesting , designed in 1990 when a small payload was half a tonne !!!

Dropped from a plane @ 12Km altitude , rocket mass 20 tonnes , payload 1/2 tonne , first stage had small wings for lift.

May 15th 2018, 05:22 AM   #8
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 Originally Posted by Woody The main issue I can see would be recoil. Firing even a 2kg payload to orbital velocity would generate a sizable recoil absorbing that recoil into the structure of the aircraft could prove problematical.
The rocket doesn't have to fire until after it has been released from the airplane. This was, in fact, the way the x-10 rocket plane was released. Although the x-10 never achieved orbit, it did get outside the atmosphere.

 Tags aircraft, flying, high, launching, satellites

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