Space launch

Previous outstanding posts:

• The failed F-35 - The $380 billion mistake, II, III
• Costs of electric highways - Electric car: wires beat gas
• The safest nuclear reactor

  I will now further illustrate why the idiots at DARPA should not do engineering.
  The illustration shows haw a recoverable experimental launch vehicle should have been built.  DARPA and the air force got together and decided to build a reusable launch vehicle with clam-shell doors over a cargo bay.  Unfortunately, no one involved understood engineering.
   They built the thing with landing gear instead of, as illustrated, an air capture vehicle.  Slowing for landing means substantially larger wings to generate lift at low speeds; lift is proportional to the square of the speed with an additional bonus for compressibilty, landing at 200mph, 300 feet per second (fps) versus flight at 800 fps, 540 mph, is 9:64 for square of velocities, but there is a bonus of 1.5 for compressibility, Praqndtl-Glauert, so the total is 9:96.  If lift is considered at 40 000 feet air density is 1/4 so the total effect is 9:24.  The effective lifting surfaces can be under 1/2 as large, although one must make adjustments for smaller wings being less efficient.

example of boom from f-35 post

   The smaller wings mean less weight ad less surface for drag and heating on re-entry.  In addition, the higher speed may allow the elimination of the vertical stabilizer, tail, which further reduces weight and stresses; it is harder to maintain stability at lower speeds so the vertical stabilizer adds additional control forces, at higher speeds the wing devices, ailerons, can provide sufficient control.
   The vehicle should have had an attachment point ahead of the clam-shell doors for an aircraft to connect a boom to the vehicle and then lift it with a cable ( see The $380 billion mistake).   Attaching at the front means
 that the center-of-mass, c-m, is in back of the connection guaranteeing stability in flight.  Once the vehicle is placed beneath the recovery aircraft, additional supports and stabilizers can be attached at the rear sides of the vehicle to firmly secure it for landing.
   The recovery aircraft would be manned.  If the vehicle is traveling at 800 fps and has a glide ratio of 1:10, it will be descending at a rate of 80 fps.  From 40 000 feet it will have 500 seconds, 8 minutes before crashing into the ocean.  That should be enough time for recovery as long as the vehicle is fully tracked and its flight path is co-ordinated with the recovery aircraft.
   An even better result can be obtained with a reusable engine package.  The next illustration shows a package of three space shuttle main engines, SSMEs, in a winged recovery vehicle.
   For  launch, the nose cap of the vehicle would be swung away to the lower side of the vehicle with the fuel line attached to the top.  By swinging the cap out of the way, the frame of the vehicle can transmit engine thrust directly to the structure of the fuel tank.  The cap would be placed to offer minimal aerodynamic forces.  Struts from the fuel tank would attach to the lower end of the vehicle to stabilize it and allow for the engines to rotate their thrust.  For separation the struts would be bent backwards an out of the way by internal explosive charges, allowing the vehicle to separate backwards away from the fuel tank.
   For re-entry, the cap would swing closed to provide a smooth aerodynamic envelope and the vehicle would again be air-captured by a boom connected to the fuel connection on its top.  The vehicle would be landed and the engines and vehicle serviced and re-used.
   By removing landing gear and placing the fuel attachment to the upper surface, the underside would have no openings and would be easier to cover with thermal tiles.

   A further possibility  is to air launch the engines, fuel tank and payload.   In a^, is depicted a vertical ground-launched stack.  In c, d, e are depicted the assemblage attached to the top of a launch aircraft.  To launch 3 SSMEs, the rocket would way 1 500 000 lbs.  The aircraft would way a similar amount, at least, for a total of 3 000 000 lbs.  Flying at 800 fps, 540 mph, 1200 lb/  square foot of wing lift would be generated at a coefficient of lift of 1 at sea-level.  At a release altitude 0f 60 000 feet, the air density is 1/8 and the lift is 150 psf, pounds per square foot.  For an efficient coefficient of lift of .6-.7, the effective lift would be 100 psf.  For a 3 000 000 lb aircraft that would be 30 000 square feet  of wing area.  An efficient high-altitude wing of aspect ratio 10 would be 550 feet span and 55 feet mean cord.
   Their is a problem with wing weight.  If a wing is scaled up by doubling all dimensions, the wing is 2X as long, 2X cord and the center of lift is 2X from the body for a total moment of 8X.  The wing root is only 2X as deep and 2X the perimeter for 4X resisting moment unless the wing skin is thickened.  Scaling allows 2X lift and 2X area for 2X weight if skin thickness is constant.  For the higher moment, either the wing root must be greatly expanded or the skin made twice as thick.  The weight might prevent the flight of the aircraft.   I have shown it with 6 engines, with current engines it would need 10
   After take-off the aircraft would climb to perhaps 10 000 feet and the roll upside down.  The pilots, b, would be in a cockpit which would look like an old Gemini capsule.  The pilots would be seated side-by-side with the windshield opening on hinges to allow entry.  The entire cockpit capsule would be mounted on a ring mount which would allow it to rotate.   In front of the capsule would be a rocket assembly allowing the pilots to separate from the aircraft  before ascending to escape catastrophes.  After the pilots roll the aircraft 180 degrees they would rotate the capsule 180 degrees, they would be upright but the aircraft would be inverted.  They could now refuel if necessary and climb to the release altitude.   Since modern aircraft are fly-by-wire and only electronic signals are used for control inputs, rotating the cockpit only requires continuous transmission of the  control signals to maintain control of the aircraft whether upright or inverted.
   This design allows for short, heavy landing gear and easy access to the rocket before take-off, although it might require additional supports under the payload and engine modules to reduce stresses.  The release at 60 000 feet allows less drag, 7/8 of the atmosphere would have been cleared.  At release, the rocket is conveniently supported below the aircraft for easy release.
  One other possibility would be to liquify oxygen in flight, taking off with excess hydrogen to chill the oxygen. At 1 500 000 lb, oxygen is 8/9 of the fuel weight or 1 300 000 lb.  At sea level air weighs 1/14 lb/cubic foot , pcf, 20% is oxygen or oxygen is 1/70 pcf.  At 60 000 feet, oxygen is 1/560 pcf;  it would be best to climb to altitude and then liquify as this lightens the weight while climbing.  So, for 3 600 seconds per hour 800 fps, 560X1 300 000/ 800X3 600= 250..  That is 250 square feet X hours.  For a 3 hour flight = 80 square feet which is about the frontal area of the current largest jet engines.  There would also be inefficiencies, so maybe twice that area would be required.  That would still be acceptable.
   The SSMEs are designed for 60 000 feet, that is their most efficient operating point.  Releasing them at 60 000 feet allows for them to be reset for vacuum design point, and slightly better efficiency.
   The aircraft-rocket combination would take-off  from Cape Kennedy and fly south-east over the Atlantic placing itself closer to the equator for east-west launches and far enough over open water for north-south launches.  Vandenburg could then be closed.
   For high speed flight the most efficient wing profile has a flat top, called a super-critical wing.  It was developed by a guy named Whitcomb.  For take-offs, the most efficient wing shape has a flat bottom .  By rolling the aircraft while  in air, the wing at take-off would have a flat bottom and then when rolled over it would become an efficient flat top.  It would be advantageous at both ends.
   The fuel lines could be fed through the open front end of the engine vehicle with an attachment point for recovery built into the upper surface.
   Obviously, a smaller rocket and a smaller launching aircraft could be more easily built.
   I sent the idea for a launch aircraft that rolls to drop the rocket to DARPA.  They do not read their mail, but considering how bad they are at engineering, maybe they are illiterate, too.

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