Space Forum / Space Flight / November 2005

The problem is referred to as a vertical pendulum. Basically like
balancing a
broom in the palm of your hand. You move your hand back and forth to
keep
the broom vertical. The weight being at the top actually reduces the
difficulty.

As to what was before digital, the control was analog and in fact for
simple
systems controlled with a very low parts count and is most often has a
faster response than digital systems. The negatives that have moved
such
systems into disfavor: That your mathematical constants must be know
and
hard-wired into the design, components have to be precision with very
little
drift, and late design changes means tearing open the box to modify the
circuit. To some degree analog components are always in the loop but
mostly to provide the muscle for the digital controls.

Even the German V2 rocket of the 1940s used a gyroscope. The thrust was
redirected by graphite vanes in the engine exhaust. I'm not sure, but
the control system might have been completely mechanical in that era.

Dave

Rocket stability does not depend on where the nozzle is placed. If you look
at Robert Goddards worlds-first liquid fueled rocket:
http://www.epower-propulsion.com/epower/gallery/Hist-Goddard%20Rocket.jpg

you'll see that he placed the nozzle on top, because he believed this to be
crucial for stability. As it turned out, it is irrelevant, where the exhaust
nozzle is placed. Which is why it's always placed on the bottom.

Sounds good to me :-) Something along those lines, at least.

Now, basic rocket stability is provided by the airflow over the rocket body
and fins. That's actually the only reason to put fins on a rocket.
Basically, if a rocket's center of gravity is located at least one body
diameter (rule of thumb) in front of the rocket's center of pressure, the
rocket is positively stable, and will direct itself back to its original
path, if diverted. See

Stability of a Model Rocket
http://www.grc.nasa.gov/WWW/K-12/airplane/rktstab.html

Model Rocket Stability
http://www.apogeerockets.com/education/rocket_stability.asp

Fins for Rocket Stability
http://members.aol.com/ricnakk/fins.html

/steen

   The development of the V-2 guidance system evolved as follows:

   * The A3 system

   * The Sg 52 platform and control system developed for the A5 in
     1938-39 This was a stable control system based on rate gyros,
     but was found not to be an ideal solution

   * The Sg 64 improved system developed for the A5 and tested in
     launches

   * The Sg 66 developed by Kreiselgeraete in 1940-42 for the
     A4. This electromechanical control system used unbalanced gyro
     accelerometers and a 'Mischgeraet' (mixing device) to combine
     inputs, thereby eliminating the need for rate gyros. However
     Kreiselgeraete was only experienced in naval equipment, and
     applying the principle to rocket guidance was completely foreign
     to them. Neverthelss, since Kreiselgeraete was a small company,
     they could respond with flexibility and speed to the rocket
     team's requests.

     Siemens developed an alternate system based on two gyros to
     determine attitude and follow a fixed-plane pitch program. The
     Siemens system was favored up to mid-1942 due to its production
     simplicity. Siemens also had a greater manufacturing and
     technical capacity. But its large size made it unresponsive to
     the rapid pace of development. A surplus Siemens guidance
     system, or an American copy, was used for the Explorer I launch
     in 1958.

   A third system by Askania-Moeller was briefly put into
   development, but quickly abandoned.

   * The Kreiselgeraete Sg 70 platform was designed as a replacement
     for the Sg 66 to eliminate aluminum gimbals in
     1944-1945. Kreiselgeraete's development labs were evacuated to
     Sudetenland in 1943 after air raids in Berlin, impacting
     development after that date.