Introduction
 Overview
 Development
 Propulsion
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Author:
Steve Baughman

Web Updated Aug 15
© 1999
All Rights Reserved.

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ROCKET DEVELOPMENT

	The program has come a long way since this, the XRV Mk I.  Photo by Dave Towers

The XRV program started with a commercial design which used straightforward construction techniques and materials familiar to anyone who has built a model rocket of any size. Early in construction, potential improvements were identified in the design, and the assembly sequence was modified to allow these initial structural upgrades. When assembly was complete, the rocket was transported to a north Texas flight range and tested over the course of three flights on July 25-26 1998. After each flight, a critical analysis was performed to validate performance goals and results. From this analysis, valuable data about the performance of the design arose pointing the way to new opportunities for improvement. These new upgrades, when implemented, would further increase the vehicle's reliability, durability and flight performance.

The original rocket used in these first three test flights was designated the XRV Mk. I. The upgrades which followed were completed over a period of five weeks, and included many structural improvements and a preliminary telemetry device. With these new upgrades complete, the rocket was redesignated the XRV Mk. II. And so began a repeating cycle of testing, evaluation and improvement, with future design revisions being continually incorporated into the existing vehicle to boost its capability. Through the continuation of this evolutionary design process, the Mk. II was eventually succeeded by the Mk. III and again by the Mk. IV, each of which incorporated significant design revisions. To expand the program further, a more powerful booster section was designed and constructed, and this configuration was designated the Mk V.

In this section we present a closer look at the XRV Mk IV as well as the upgraded Mk V. For historical purposes we include a development matrix presenting an overview of each revision of the XRV.

INTRODUCING THE MK IV

 "Can you hit anything with this?" - Mark Wyatt, interested neighbor, during examination of the XRV.

The XRV Mk. IV is a fiberglass laminated, three-finned rocket designed to be flown using restricted-access commercial solid rocket motors to altitudes in the 1+ mile range. With a stage weight of 12.75 pounds, it can attain velocities of 415 mph in 1.6 seconds (Telemetry: Flight 20) and altitudes over 6000 ft. (Telemetry: Flight 15). It uses on-board digital avionics to record air pressure and acceleration data, and to deploy parachutes for a safe return to earth, where it is recovered for future flights.

The airframe is 76 inches long and 4 inches in diameter, and consists of three sections: a forward section including a nosecone and main parachute bay, a central avionics payload section, and a lower booster section which includes the drogue parachute bay. Two slip-fit friction couplers join the three sections together and allow each of the two parachute bays to be opened independently using separate pyrotechnic charges.

Figure 2-1 The XRV Mk IV can reach 415 miles per hour in 1.6 seconds and an altitude of 6000 ft.  Animated graphic by the author

 

The forward section combines the nosecone with the main parachute bay, with a forward bulkhead of 1/4" thick G10 fiberglass separating the two. An eyebolt in this forward bulkhead provides attachment for one end of the main parachute harness. The harness itself is 12 ft. in length with stainless steel carabiners at either end. The 52" main parachute is a skirted triform design and is attached to the harness with a 1000 lb. rated swivel link.

The payload bay holds two avionics modules: TMU & PIM  Photo by the author

A central payload section contains two avionics modules: a telemetry microcontroller unit (TMU) and a pyro ignition module (PIM). The TMU and PIM are both mounted in a removable rack which slides into the top of the payload section and is retained by four nuts at the bottom. In addition to recording a log of air pressure and acceleration during flight, the TMU software detects flight apogee and ground proximity, and activates ouput circuits in the PIM to fire explosive charges which open each parachute bay as required. To cool these ejection gases, small screw-on thermal absorbing baffles are integrated into each end of the avionics payload section, with eyebolts for attaching the ends of each parachute harness. To verify the deployment of the drogue and main parachutes, two fail-safe sensors are present which indicate the status of each parachute bay. These are monitored by the TMU, which records all deployment events to the flight log. At the conclusion of each flight, the log is dumped from the TMU to a laptop computer over a RS-422 serial connection for storage and analysis.

The lower booster section uses a 54 millimeter diameter motor mount, allowing the use of solid rocket motors up to a maximum power rating of 1706 Newton-seconds. Motors are retained in the mount using clips attached to three 3/16" studs surrounding the nozzle area. A dual-chamber thermal absorbing baffle unit is installed to cool ejection gases from an optional motor-delay ejection charge which can be used as a backup to the primary recovery services provided by the avionics. The booster baffle unit includes an eyebolt which is used for attachment of one end of the drogue parachute harness. The drogue harness is 30 ft. long with stainless carabiners at each end, with the fully reefed 20" skirted triform drogue positioned at its middle with a stainless swivel. The motor is started using a pyrogen-dipped electric igniter wrapped with Thermalite detonation cord, with launch guidance provided by two 1/2" diameter launch lugs.

THE UPGRADED XRV MK V

 "Beep... beep... beep... BEEP..." - The simple yet comforting sound of a radio tracking transmitter in action.

The most significant of the Mk V upgrades involves a new fiberglass laminated, three-finned booster section designed to replace the booster of the Mk IV. This booster section extends the flight capabilities of the XRV by enabling the use of larger restricted-access commercial solid rocket motors. With a maximum capacity of 5120 Ns of installed impulse, it can acheive altitudes in the 2+ mile range and velocities approaching (and hopefully breaking) the speed of sound. (Telemetry: Flight 35). The Mk V shares the same on-board digital avionics as those used in the Mk IV, however the avionics software has been upgraded to allow for the longer ascents experienced by the Mk V.

Figure 2-2 The XRV Mk V has reached 688 miles per hour in 2.9 seconds and an altitude of 10,066 ft.  Animated graphic by the author

 

The airframe of the Mk V is 93 inches long and 4 inches in diameter, and shares most of the characteristics of the Mk IV. Notable changes in the Mk V include the removal of the motor-ejection baffle unit in the airframe, and in its place a double walled G10 bulkhead which holds the eyebolt used for recovery system attachment. Other changes include the use of four 1/2" thick centering rings, and the use of G10 fiberglass fin cores instead of the plywood fin cores of the Mk IV. Instead of the internal foam reinforcement used in the Mk IV, the Mk V has internal fin fillets reinforced with 6 oz carbon fabric laminate.

To address the increased weight of the Mk V, the main parachute was upgraded to a 60" skirted triform design. Also, in order to aid in recovery during high altitude attempts, a long-range, long-duration XLF-3 radio tracking transmitter was enclosed in the nosecone. This transmitter enables the use of a directional antenna and properly tuned radio receiver for radio direction finding (RDF) during flights out of visual range.

DEVELOPMENT HISTORY

 "What I really need is a motor with the thrust of a K1100 and the burn time of a K185." - the author.

These tables present a detailed historical comparison of each of the prior XRV rocket development revisions. With each revision, relevant upgrades are noted in blue. We suggest you view this technical reference with your browser font set to the default 12 point size. 16-bit color helps too.

General					retired
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Debut	July 25, 1998	Sept 5, 1998	Dec 6, 1998	Jan 30, 1999	Jun 26, 1999
Flights	3 total	4 total	3 total	22 total	7 total
Milestones	L1 certified	avionics	L2 certified	dual deployment	hi altitude
Highest	1500 ft	1849 ft	3429 ft	6060 ft	10,066 ft
Fastest	137 mph	174 mph	314 mph	415 mph	688 mph
Max Accel	10 g	10.4 g	10.6 g	17.1 g	13.5 g
Table 2-1 Incremental improvements pave the way towards the goal of supersonic flight.
Propulsion		upgrades shown in blue
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Size	38 mm	38 mm	54 mm	54 mm	75 mm
Fuel	Aerotech	Aerotech	Aerotech	Aerotech	Aerotech
Rating	H123W I242T I161W	I357T I154J I211W I284W	J275W J180T J460T	J460T J275W J415W J800T K550W K1100T	K560W L850W L1120W
Retention	Al setscrews	3/16" studclips	3/16" studclips	3/16" studclips	API 75 mm
Ignition	Turner FIH	Turner FIH	Turner FIH thermalite	Turner FIH thermalite	Turner FIH thermalite
Table 2-2 Incremental power increases have been the key to fully exploiting new designs.
Airframe		upgrades shown in blue
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Diameter	4 in.	4 in.	4 in.	4 in.	4 in.
Length	57.5 in.	57.5 in.	59.0 in.	76.0 in.	93.0 in.
Weight	48 oz.	96 oz.	109 oz.	151 oz.	190 oz.
Mount	54 mm	54 mm	54 mm	54 mm	75 mm
Nose Cone	polypropylene	polypropylene	polypropylene	polypropylene	polypropylene
Body Tube	3.90" epoxied	3.90" epoxied 3x 2oz e-glass	3.90" epoxied 3x 2oz e-glass	3.90" epoxied 3x 2oz e-glass fwd chute bay	3.90" epoxied 3x 2oz e-glass fwd chute bay
Fins	3/16" 4-plywood	3/16" 4-plywood 3x 2oz e-glass	3/16" 4-plywood 3x 2oz e-glass	3/16" 4-plywood 3x 2oz e-glass	3/16" G10 sheet 3x 2oz e-glass
Fin Root	motor mount	motor mount 6x 2oz e-glass	motor mount 6x 2oz e-glass	motor mount 6x 2oz e-glass	motor mount 6x 2oz e-glass
Structural	internal fillets ring interlock coupled interior	internal fillets ring interlock coupled interior internal foam	internal fillets ring interlock coupled interior internal foam	internal fillets ring interlock coupled interior internal foam	internal fillets ring interlock coupled interior 6oz carbon
Finish	flat paint	flat paint	gloss paint hi-vis checker	gloss paint hi-vis checker	gloss paint hi-vis checker
Table 2-3 Extensive airframe upgrades have increased durability at the cost of added weight.
Avionics		upgrades shown in blue
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Mounting	none	split rack	split rack	split rack	split rack
Sensors	none	acceleration pressure	acceleration pressure	acceleration pressure	acceleration pressure
Recording	none	20Hz/2Hz 20sec Hi Res	20Hz/2Hz 20sec Hi Res	20Hz/2Hz 20sec Hi Res	20Hz/2Hz 30sec Hi Res
Failsafes	none	none	main drogue	main drogue	main drogue
Detection	none	none	apogee proximity	apogee proximity	apogee proximity mach inhibit
Ejection	none	none	none	pyro module	pyro module
Arming	none	terminal	terminal	one-touch	one-touch
Table 2-4 Avionics development has been crucial to successful high altitude flight.
Ejection		upgrades shown in blue
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Type	single	single	single	dual	dual
Method	delay	delay	delay	barometric	barometric
Ignition	motor	motor	motor	Daveyfire (2)	Daveyfire (2)
Pyro	1gm 4FG	1gm 4FG	1.5gm 4FG	1.5gm 4FG (2)	1.5gm 4FG (2)
Heatshield	wadding	AF baffle	AF baffle	DD baffle (2) Nomex (2)	DD baffle (2) Nomex (2)
Backup	none	none	none	delay	none
Ignition	none	none	none	motor	none
Pyro	none	none	none	1.5gm 4FG	none
Heatshield	none	none	none	AF baffle	none
Table 2-5 Mk. IV ejection upgrades were implemented to support barometric dual deployment.
Recovery		upgrades shown in blue
	Mk. I	Mk. II	Mk. III	Mk. IV	Mk. V
Mounting	epoxied nylon	5/16" eyebolts	5/16" eyebolts	5/16" eyebolts	5/16" eyebolts
Drogue	none	none	none	20" skirted reefed	20" skirted reefed
Harness	none	none	none	30ft 1/2" nylon carabiners	30ft 1/2" nylon carabiners
Main	36" LOC	44" skirted	44" skirted	52" skirted	60" skirted
Harness	10ft 1/2" elastic	12ft 1/2" nylon quicklinks	12ft 1/2" nylon quicklinks	12ft 1/2" nylon carabiners	12ft 1/2" nylon carabiners
Tracking	none	none	none	none	XLF-3 radio xmitter
Table 2-6 Increasing weight has caused parachute size requirements to grow.

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