(originally written in 2001)
The Kimbo series of rockets trace their lineage directly back to the DC-X/XA (also known as the Delta Clipper and later, the Clipper Graham) prototype reusable launch vehicle. Milestones include the flights of five increasingly complex LOX/ethanol rockets and four static fire tests [as of February 2001]. Particularly noteworthy were the Kimbo IV vehicle, which accomplished the first-ever flight of a composite LOX propellant tank, and the Kimbo V, which achieved 100% recovery.
The initial motivation for developing these vehicles arose in 1996 when an effort was made by some of the DC-XA flight team personnel to get McDonnell Douglas' DC-XA project management to sponsor a flight demonstration of such a composite LOX tank. The intent was to build upon the DC-XA's pioneering flights with the first-ever LH2 composite tank and to prepare for future vehicles like the upcoming X-33. Management's advice was that "...if you think it is such a good idea, then go do it yourself ..."
Early efforts involved hunting through scrap yards in Alamogordo and Las Cruces, New Mexico (imagine Junkyard Wars without the competition) and getting parts machined at local shops during down times when the White Sands Missile Range was closed for THAADs testing. Fellow DC-XA engineers and technicians provided immensely valuable advice and help, which they continue to do even now, five years later.
When the DC-XA suffered its untimely end on 31 July 1996, the Kimbo team regrouped back in Huntington Beach, CA. The actual Kimbo name came into being at this time, when the project leader named the vehicle after his wife Kim (Kimbo being her nickname when playing volleyball) in part to make up for filling the family garage with a wide assortment of surplus rocket hardware. A key step was the link-up with the non-profit Reaction Research Society (RRS), which owns and operates the unique Mojave Test Area for amateur rocket testing. The RRS probably has more experience in launching liquid rockets than any other non-governmental/non-corporate organization in the world.
These Kimbo projects have been amateur in the sense that there was no customer or external source of funding. The motivating factors were/are comparable to those found in home-built aircraft and boating initiatives. However, the skill level frequently compared with that found on commercial launch vehicles (not really a surprise given that most of the team works on such vehicles in their day jobs). One key appreciation was/is that the rocket is just one element of the launch architecture, even for amateur projects. Ground support equipment, both mechanical and electrical, has received at least the same amount of attention and resources as the flight hardware.
The first visible achievement of the Kimbo team's efforts came in February, 1998, when the Kimbo I was successfully static fired on the MTA Vertical Test Stand-1 (VTS-1) for slightly more than ten seconds. It was then outfitted with the rest of the recovery system and launched in May 1998 on the second day of the RRS' Live Fire weekend. The single main parachute deployed, but due to "weather-vaning," there was excessive horizontal velocity and the lines hung up on one of the fins.
The subsequent "hard landing" damaged the vehicle, but enough survived that the growing Kimbo team was able to refurbish it and actually improve performance by adding a regulated Helium propellant tank pressurization system. The Kimbo II flew slightly less than three months later. This time, the recovery system failed entirely and the 18 ft long K-II buried itself in the ground. Amazingly, the 500 lbf thrust engine survived and was retrieved yet again for future use.
Despite the not-so-secret desire of several spouses that their husbands would
call it quits after the K-II, the team regrouped with plans for bigger and better
vehicles. For the brand-new Kimbo III, the team decided to use a skin
& stringer airframe design. This configuration greatly facilitated
development and
field logistics. Whereas the K-I/II had a maximum diameter of six inches,
the Kimbo III increased that to twelve inches. In parallel, the simple
toggle-switch ground command box was replaced by a PC-based system that enabled
both analog and discrete data acquisition during ground operations and an
automated countdown sequence.
Two static fire tests in late
1999 validated the Kimbo III vehicle. One of these included gimbal testing
of an advanced composite engine chamber donated by Compositex. The Kimbo III took flight in
February 2000, following a January attempt that had to be scrubbed because of
weather. As with the K-I, the recovery system functioned only partially,
but enough to land the vehicle in one piece, thereby enabling refurbishment and
later re-flight as the Kimbo IV. Among the highlights from the K-III were the
first use of a new portable launch rail, in-flight imaging with a 35 mm camera
and logging of GPS-based trajectory data.
The Kimbo IV vehicle represents the most complex vehicle attempted by the team to date. Its most notable feature was a composite LOX tank contributed by Microcosm, Inc. of El Segundo, CA. Because of potential mass savings relative to aluminum tanks, composite cryogenic propellant tanks are considered a key structural technology for future launch systems. As noted above, previously, only the DC-XA had flown such a composite cryogenic tank, for the LH2 fuel. With its flight in June 2000, the Kimbo IV became the first, and to date only, rocket to manifest a composite tank for LOX. It serves as a demonstration of the maturity of this technology and provides solid evidence that the compatibility issues between LOX and composite tanks are indeed manageable.
Unfortunately, the recovery again failed, largely because of the relatively low thrust-to-weight ratio of the vehicle. Consequently, the K-IV buried itself eight feet beneath the Koehn "dry" lake bed. However, once again, the team was able to dig up the airframe and the engine was salvaged one more time.
Having achieved the initial goal behind the early Kimbo vehicles, the team regrouped and pushed forward with a more streamlined vehicle, the Kimbo V. Through a series of weight reduction measures, such as cutting the vehicle's diameter to ten inches, switching to three instead of four fins and eliminating the regulated Helium pressurization subsystem, a lift-off weight of 136 lb was achieved. This put the thrust-to-weight ratio back into a more comfortable range (about 3.5 to 4), as verified by the vehicle's perfect flight in January 2001. Not only did it take off and fly a true trajectory, but for the first time, all of the recovery elements functioned as intended. Additionally, a simple flight telemetry system provided real-time confirmation of both nosecone/drogue chute and then main parachute deployment.
While the K-V could be flown again with very minimal effort, the team has instead elected to use it as a reference model for future vehicles.
With these recent successes, there exists great momentum to continue building rockets. The Kimbo V now serves as the baseline configuration for several initiatives. Presently, in a cooperative program with CSULB, the students in the school's AIAA chapter are integrating the Prospector 1 vehicle (also known as Kimbo VI*) for flight later this year [note - this activity has since evolved into the CALVEIN** program noted elsewhere on this site].
With these successes, more resources are becoming available from a variety of sources. These in turn should enable more ambitious Kimbo projects in the future.
FINAL NOTE: In response to numerous questions regarding the Kimbo team's perspective on the CATS and FINDS prizes, we have never considered participating in either of these activities. As demonstrated by both the Delta Clipper and Kimbo IV, a great deal of progress can be achieved with respect to adapting and flight-testing new launch vehicle technologies without exceeding the local altitude limitations at the MTA.
* "Prospector" is the name used by CSULB for its set of test vehicles, whereas GSC employs the "Kimbo" title for all the vehicles it is involved with, which includes the Prospectors developed in partnership with CSULB, as well as those implemented on other projects.
** CALVEIN – California Launch Vehicle Education Initiative