Saturday, January 02, 2010

More on the rockets that launched the microcomputer revolution

In this month's edition of the Citizen Scientist, Forrest Mims III provides more details about his early rocket experiments in Vietnam in 1967.  His experiments sound impressive and the stories about his encounters with MPs and helicopter gun ships are fascinating. Here's an excerpt:
Thereafter the military took more interest in my experiments with rockets and infrared travel aids for the blind. The night launch program was placed on hold, and on 16-17 June I resumed flights from a large field by the main gate at Tan Son Nhut and the race track, this time with a rocket equipped with a sun-tracking guidance system and a rocket that emitted pulses of ram air in response to radio signals controlled by holes punched in the tape of a modified, compact reel-to-reel recorder.

Photo courtesy of the USAF (and Forrest).

Cool stuff!  Looks like an Estes Big Bertha was his testbed.

Oh, yeah, then there's the whole deal about his rocket flashers leading to MITS and the legendary Altair 8800 microcomputer.  Yeah, cool stuff!

Here are other links about the author:


  1. I don't think either of those payloads would fit inside a Bertha... especially not the guidance system!

  2. Dick,

    It was a Big Bertha or homemade copy. I went to Vietnam with a footlocker loaded with rocket and electronic supplies and hardly any clothes. Since I worked at night (aerial photo interpretation officer), the rocket launches could be done during the day. The night launches were before I went to work (midnight).

    The gunship episode was pretty serious. It really looked as if they were going to shoot us with the 0.50 cal. This is why so few of the boys showed up after I got permission to continue launches from the old race track.

    A photo of my MITS-era workbench with the original light flasher and some rockets is on both my main web sites (see below).


    Forrest M. Mims III

  3. EGE: see Forrest's comments ;)

    Forrest: And we worry about park rangers, locals, and even the BATFE...none of whom pack 0.50 cals. Thanks for reminding me about those links.

  4. EGE: The rocket in the photo (see my editorial in the January THE CITIZEN SCIENTIST at was not fully guided. It was fitted with a rotating shutter that controlled whether or not air entering the forward facing port was jetted out the side of the nose cone. A sequence of radio pulses (controlled by the tape recorder in the photo) produced sideways thrusting at the nose, which altered the flight path. The trajectory changes were recorded by photographing the smoke trail.

    The sun seeking rockets that I built were much smaller. They used a turbine that was spun by ram air and which diverted the air stream out a series of ports around the nose cone. When a photodiode received less than full sunlight through the ram air port, the turbine was braked. This caused a corrective jet of air to push the rocket back toward the sun. When the photodiode was again illuminated, the brake was switched off and the turbine continued to spin.

    This system was launched multiple times, and obvious course changes were photographed. The problem was that the braking of the turbine caused the rocket to spin, which negated the ram air control force. I was working on a dual system with motor driven (no turbine), oppositely rotating air deflectors to cancel this effect when MITS began taking all my time.


  5. Okay, that makes a bit more sense. Thanks.