Space Forum / Space Flight / September 2006

The rocket launchers are not economical because they
are not reusable. When they reenter the atmosphere,
their slender bodies soak up so much heat from the
ambient atmosphere that they burn up. The Space
Shuttle is somewhat reusable, but its slender body
has to be protected with a thermal protection system
that is expensive (because it covers large surface)
and unreliable (because it has to be lightweight despite
its large size). A rocket launcher shaped like a big
conical reentry capsule would be more reusable than the
Space Shuttle because its thermal protection system
would be smaller (because it would cover only the bottom
surface of the cone) and cheaper.

The conventional rocket launchers are shaped like a
pencil to minimize aerodynamic drag during the first
minute of the flight. A cone-shaped rocket launcher
would generate too much drag unless it was slowly lifted
above the dense part of the atmosphere (to the altitude
of about 30 kilometers) with a balloon or a helicopter.
Hydrogen balloons are cheap, but not reusable. Helicopters
are reusable, but they need special engines that can
operate at the altitude of 30 kilometers. There are
three such engines:
1. Hydrogen peroxide monopropellant turbine has simple
  design, but the monopropellant is rather expensive
  and its catalyst bed can be contaminated with commercial
  grade monopropellant.
2. Steamjet engine is described in U.S. patent 6,202,404.
  Its most practicable implementation, called mass injection
  precompressor cooling (MIPCC) is a turbojet cooled with
  copious amounts of water and liquid oxygen. The cooling
  enables the turbojet to generate thrust up to the altitude
  of about 30 km. More info: http://tinyurl.com/msqra
3. Electric motors are cheap and can operate at the altitude
  of 30 km. Their energy source can be either a battery or a
  generator standing on the ground. The motors and the
  batteries need a cooling system when they operate at high
  altitude.
3a.Magnesium hydride battery with Ni catalyst has the highest
  energy density (http://www.energyadvocate.com/batts.htm)
  but it is not yet mature technology. Li-ion batteries have
  energy density of only 534 kJ/kg, but they are very reliable
  and reusable. (They provide auxiliary power for my laptop
  computer.) The Li-ion batteries can be used as the power
  source if used up batteries are discarded during the flight.
  It takes about 300 watts of helicopter power to lift 1 kg
  of weight. At the beginning of the flight the total weight
  of the batteries is about one half of the launcher weight.
  During 15 minutes of vertical flight the helicopter reaches
  its maximum altitude of 30 km, drops off nearly all its
  batteries on parachutes, and finally drops off the launcher.
  When the helicopter descends, most of its propellers (rotors)
  are used as wind turbines which provide power for the
  remaining propellers. The last batteries are used up during
  landing.
  My laptop batteries cost $418/kg. Assuming payload fraction
  of 6 percent and total battery weight of one half the
  launcher weight, the batteries cost 418/0.06/2 = $3483 per
  kilogram of payload. The capital cost of the batteries may
  seem rather high, but the batteries are reusable and very
  easy to use.
3b.Aluminum wires linking the motors with a high voltage generator
  standing on the ground are expensive and difficult to use.
  High voltage generators are available from many sources, for
  example: http://www.kato-eng.com/hacgen.html They cost about
  $0.1/W. At the payload fraction of 6 percent, the generator
  cost is about 0.1*300/0.06 = $5556 per kilogram of payload.
  In the absence of the generator, the power is provided by
  the grid. The cost of connecting to the grid depends on the
  distance; electrical utilities charge between $10,000 and
  $50,000 per kilometer of transmission line.
  The wires must be reinforced with strong (Zylon) rope and
  suspended on balloons so that they do not touch the ground. The
  design of such helicopter is similar to the design of airborne
  wind turbine generator: http://www.skywindpower.com
  The helicopter is vulnerable to lightenings and strong winds,
  so it must fly near the equator (away from the jet streams):
  http://www.skywindpower.com/ww/page010.htm.

Electric motors powered by batteries are the best choice because
they are cheap, reliable, safe, and easy to use. If the helicopter
lifts the rocket launcher above the dense part of the atmosphere,
the launcher can transport payloads that have low density and large
size, for example large space telescope or large greenhouse. THE
LAUNCHER SCALES DOWN VERY WELL BECAUSE IT IS REUSABLE AND BECAUSE
ITS ATMOSPHERIC DRAG IS NEGLIGABLE. ITS TRUNCATED CONICAL SHAPE
LEAVES PLENTY OF ROOM FOR A VERY LARGE EXHAUST NOZZLE WHICH IMPROVES
THE EXPANSION RATIO AND SPECIFIC IMPULSE. LAST, BUT NOT LEAST, THE
SHAPE OF THE EXHAUST NOZZLE IS OPTIMIZED FOR FLIGHT IN THE VACUUM,
BECAUSE IT IS NOT USED IN THE DENSE ATMOSPHERE. This means that a
little guy can cobble together a little rocket launcher that has high
specific impulse despite its primitive, low-pressure design, and
that he can compete on launch cost with the giants of the industry
(if he can afford the legal expenses). If the launcher has three
stages, only the last stage has to be protected with the expensive
composite called reinforced carbon-carbon. The second stage can be
protected with a thick coating of silicone rubber. The first stage
does not need any thermal protection.