ASTRID Rocket Flight Test

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OR more than 5 years, theLaboratory has been developing

a new kind of liquid rocket propulsionsystem with support from theDepartment of Defenses BallisticMissile Defense Organization. Ourlightweight propulsion technology,which won an R&D 100 award in1992, features miniature pumps thatcan react to thrust changes within amillisecond to meet a range of

vehicle-control requirements. Thethrust-on-demand, pumped-propulsiontechnology for spacecraft is describedin more detail in the March 1993 issueof

EEnneerrggyy aanndd TTeecchhnnooll ooggyyRReevviieeww.This year, we flight tested the specialengine for the first time with the

required so that the fuel tanks canremain thin-walled and lightweight.Pumps would give the high pressuresthat are desired without the addedweight needed for high-pressure tanks

Small rocket systems now operateby adding a high-pressure inert gasto pressurize the propellant tankto slightly above thruster pressure.All spacecraft to dateincludingcommunication satellites and planetary

spacecraft such as Viking, Voyager,Magellan, Galileo, Clementine, andthe Mars Observeruse propellanttanks that operate at a higher pressurethan the thrust chambers. Such apressure-fed system is simple andgenerally reliable, but, once again,

ground launch of the worlds smallestpump-fed rocket.

Why a New Propulsion System?

The performance of small liquidpropulsion systems for spacecraft hasalways been limited by the absenceof pumps. Small propulsion systemsthat run their tanks and engine atabout the same pressure, using no

pumps in the process, represent acompromise. Their performance isconstrained because designers haveto settle on an intermediate valuebetween the high pressure requiredso that thrusters can be small andlightweight and the low pressure

ASTRID Rocket Flight Test

Our recent ground launch of the worlds smallest pump-fed rocketdeveloped at LLNL shows that our new technology can propel a miniaturerocket fast enough to intercept theater ballistic missiles. We now envisioncost-effective uses for the new propulsion system in commercial aerospace

vehicles, exploration of the planets, and defense applications.

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the performance is limited. Inparticular, tanks designed for standardspacecraft pressures of about 2 MPa(300 psi) can store and deliver 10 to

20 times their own mass in propellant.Thrusters designed to be fed from suchmoderately pressurized tanks typicallycan lift 10 to 20 times their own weight.

In contrast, our new approachaunique propulsion system that isdesigned around pairs of reciprocatingpumps that stroke alternately(Figure 1)allows spacecraft togo faster and farther with less totalweight than was previously possible.

Low-pressure tanks compatible withour technology can hold about 50 timestheir own mass in propellant, and ourengine (including pumps and high-

pressure thrusters) can deliver thrustequal to 50 times its own weight.Figure 2 compares ASTRID withexamples of existing rocket-propulsionsystems. In addition to the weight oftanks and engines, this graph takesinto account accessory propulsionhardware, which is found on bothASTRID and pressure-fed spacecraft.Our advance in rocketry means thatit is now possible to plan a variety of

missions in space with smaller andlighter propulsion packages thanwere feasible before.

About the ASTRID Vehicle

We just completed a year-longproject, which culminated in the firstflight test of our new rocket engine.Many of the propulsion componentswe tested in the rocket evolved overa 5-year development effort that hadits origins in the Brilliant Pebblesprogram, which focused on newminiature interceptors. Owing in

ASTRID Flight Test E&TR July 1994

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Figure 1. Our newthrust-on-demand

propulsion system

uses four

reciprocating free-

piston pumps and

monopropellant

hydrazine. The quad-

piston pumpset

(inset) delivers its

own mass (365 g)

in hydrazine each

second at a pressure

of 7 MPa (1000 psi).


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part to this history, our project wasnamed the advanced, single-stagetechnology, rapid-insertiondemonstration, or ASTRID for short.

We built the ASTRID rocket(Figure 3) to demonstrate thefeasibility of a small, high-velocityinterceptor vehicle that would alsobe equipped with a navigation systemand side-mounted thrusters for steering.Such interceptors were intended tobe carried aloft and launched fromunmanned, high-altitude aircraftcalled RAPTORs, which werebeing developed in parallel by theLaboratorys Theater Missile DefenseProgram to safeguard our military,

our allies, and their population centersfrom hostile attacks by theater ballisticmissiles. (See the article beginningon p. 1 for a description of one ofthe RAPTOR prototypes, calledPathfinder.)

The ASTRID project culminatedin a successful demonstration of theability of our new propulsion systemto function in atmospheric flight. Tominimize risks, we kept the ASTRIDvehicle quite simple for the flight test.For example, we built a monopropellantmachine using components alreadytested. Monopropellant systems aresimpler and require fewer parts thanthe pumped bipropellant (fuel plusoxidizer) system ultimately envisioned.For added simplicity and reduced cost,we opted for a fin-guided, roll-stabilizedvehicle and did not employ activeflight control.

We built two complete vehicles.Vehicle assembly and most of theparts fabrication was done at LLNL;

other parts were purchased. We usedthe first vehicle for 10- and 30-secondstatic fire tests on the ground inNovember and December 1993. Thesecond ASTRID rocketwith itsinnovative pumped-propulsiontechnologywas launched fromVandenberg Air Force Base on themorning of February 4, 1994.

As shown inFigure 4, the testrocket was 1.9 m long and had adiameter of 0.16 m. The empty massof the ASTRID flight vehicle was

8.25 kg. Of this mass, the lightweightpropulsion components weighed less

than 3 kg. The airframe was basicallybuilt around the lightweight, 15.3-literfuel tank made from a titanium alloy.We designed the tank with a large

safety margin for pressure (about afactor of 4) and avoided 90% of the

E&TR July 1994 ASTRID Flight Test

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Propellant weight/propulsion-hardware weight

S-II, stage 2 Saturn V

Delta stage 1

0.11001010.1

Thrust/propulsion-hardwarewe

ight

Clementine maneuveringsystem

Propulsion with reciprocating pumps

Launch vehicle propulsion with turbopump engines

Spacecraft propulsion with pressurized tanks

1

10

100

ASTRID with full tankand full vacuum thrust

S-IC (first stage of Apollo's Saturn V)

Clementine attitude-control system

Near-Earth asteroid rendezvous

Miniature Seeker Technology Integration(MSTI) 3 and 4

Space shuttle, full externaltank and 3 engines in vacuum

ASTRID as flown (sea level thrust)

Figure 2. ASTRID compared with examples of existing rocket propulsion systems. Bothpropellant weight and thrust are normalized to total propulsion hardware weight (including

tanks and engines) because rocket systems must provide both propellant storage and thrust

with as little hardware as possible. Note that pressure-fed spacecraft systems are generally

found in the lower portion of the graph, whereas high-performance, launch-vehicle

propulsion systems (fed by turbopumps) fall toward the upper right. ASTRID lies near the

upper right of the graph, which indicates that the LLNL piston pumps can support launch-

vehicle performance capability on a small scale. ASTRIDs 2.6 kg of propulsion hardware

stored 12.7 kg of propellant before the flight, and delivered 440 N of thrust.
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pressure safety documentationnormally required for spacecrafttanks. Prior to flight, we loaded thefuel tank with 12.7 kg of industry-

standard monopropellant fuel, high-purity hydrazine (N2H4).

The ASTRID avionics werehoused in the fiberglass nose of therocket. These components consistedof sensors for vibration, acceleration,airspeed, and system pressures; acontroller to demonstrate the thrust-on-demand capability of the propulsionsystem; and an encoder and transmitterto relay the in-flight data.

The Launch and Flight

At first, we proposed to makeASTRID an inertially guided vehicle.

However, to reduce the cost andcomplexity associated with flightelectronics, we decided to eliminateactive control altogether. This decision

enabled us to focus on our primarytest objective: to demonstrate thepropulsion technology in theconditions of free flight. In a parallelactivity at the Nevada Test Site, theengineering issues related to activelyguiding an agile, small interceptorwere being addressed.

We launched the vehicle, as showninFigure 5, under essentially windlessconditions from an 18.3-m-long (60-ft)rail that was set at an angle of 80 degfrom horizontal. After the rocket left

the rail (Figure 6), fixed fins on theaft section provided aerodynamicstability and guided the rocket in a

gravity-turn trajectory. The four finswere canted to induce rollthat is, torotate the vehicle just after it left therail. Through roll-rate stabilization,

any slight asymmetries associatedwith aerodynamics, thrust, structure,or mass distribution are averaged out.

During the 1-minute flight, ourengine enabled the ASTRID vehicleto soar 2 km up and to reach nearlythe speed of sound (Mach 1, whichis 300 meters per second) beforesplashing down in the Pacific Oceanabout 8 km downrange. The testclearly demonstrated the ability ofour new propulsion system tofunction in atmospheric flight.

The speed attained was limitedbecause ASTRID was launched fromsea level for this experiment. Avehicle flying in this densest part ofthe atmosphere is subjected to severeaerodynamic drag. Had the launchtaken place in the upper atmospherefrom an aircraft such as RAPTOR,ASTRID would have gone about sixtimes as fast (in excess of 2 kilometersper second).

ResultsFrom the ASTRID flight, we

obtained a large quantity of data,including measurements of axialacceleration, thrust level, vibration,trajectory, velocity, airspeed, and rollrate. However, the primary objectiveof ASTRID was to demonstrate howreciprocating rocket pumps wouldperform in flight and to make twokey pressure measurements. Thesemeasurements indicated that the

pumps boosted the pressure of thefuel delivered to the thrusters, asexpected, to more than 10 timestank pressure throughout thepowered flight.

An obvious concern related tousing pumps is vibration. Amongother things, vibration could adversely


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Figure 3.The pump-fed

ASTRID rocket.

Standing next to

the rocket prior to

sunrise before launch

at Vandenberg Air

Force Base is the

inventor of the

propulsion system,

J ohn C. Whitehead.


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affect sensitive inertial guidanceinstruments that might be used infuture applications. We found thatvibration both along and transverse

to the axis of the ASTRID vehiclewas not unusually high duringlaunch, and the magnitude of

vibration peaks decreased duringfree flight.

Following ignition, the rocket wasreleased after a short holding time of

8.3 seconds. The rail ascent itselftook 1.7 seconds, and the poweredflight time from the rail top was

27.7 seconds. Data fromaccelerometers clearly indicatethat the thrusters operated for37.6 seconds.

Operation and shutdown of thepropulsion system performed asexpected, with no major problems or


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Figure 4.The 1.9-m-long,

pump-fed ASTRID

rocket. The fiberglass

nose houses avionics

for sensing, control,

and transmitting data

back to the ground.

The forward section o

the vehicle, betweennose cone and tank,

is an aluminum shell

containing pressure

transducers and

hardware for filling

the fuel tank. The

titanium fuel tank

occupies just about

half of the vehicles

length and serves

as the center body.

The components

associated with

propulsion occupy

only about half of the

aft skirt. The four fins

made of lightweight

Kevlar, provide

aerodynamic

stability.

Fiberglassnose cone

Avionics deckand computer

Filler port

Fuel tank

Propulsioncomponents

0.16 m

Gas generator(1 of 2)

4-portvalve

Aft skinpanel(1 of 4)

Fin withfoil (1 of 4)

Drainline andvalve

Thrusters (2 of 4)

1.9 m


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surprises occurring during the flighttest. Our preliminary analysis of thedata shows that the thrust level wasinitially just over 440 N and was

about 420 N during ascent on the railand flight. This thrust is within thepredicted range. The maximum rollrate of 4.1 revolutions per second(rps) also compares well with thedesign rate of 4.5 rps.

Collaborations and Future Plans

The ASTRID flight test was a trulycollaborative effort involving more

than 40 LLNL technicians, engineers,and scientists and a well-coordinatedteam of outside collaborators. Thisgroup built the rocket, developed the

data-acquisition systems, performedall fielding operations, and analyzedthe data. Organizations that madecritical contributions to developingand testing the pump-fed rocketinclude: Olin Aerospace Company(formerly Rocket ResearchCompany). Moog, Inc. Ball Aerospace Company.

Johns Hopkins Applied PhysicsLaboratory (APL). Vandenberg Air Force Base. Catto Aircraft Inc.

We envision a variety of potentialuses for the miniature propulsionsystem we have developed andsuccessfully flight tested. Forexample, we have worked for morethan six years with Olin AerospaceCompany, whose engineersdeveloped the thrusters for ASTRID.We will explore the possibility ofcommercializing our technology withthis company and others for possibleuse on spacecraft and launch vehicleupper stages.

Our propulsion system can beused in an upper stage to boost asatellite from low Earth orbit (at analtitude of a few hundred kilometers,where the Space Shuttle circles Earth)to geosynchronous orbit (at an altitudeof about 35,000 km above Earth, wherea satellite remains stationary overone geographic location). Once inorbit, the system can be used to makehard maneuvers and adjust the orbit.

Our new technology providesmore propulsive capability per unitmass of propulsion system hardwarethan any other means available todayfor small liquid systems. In particular,our pumped propulsion can makemissions to the moon and planets muchmore economical than in the past.

A mission to make a soft Marslanding and retrieve rock and soilsamples would benefit greatly fromthe high performance, low mass, andthrust-on-demand features of thissystem. The precision-throttling

capability conferred by the responsivepumps would facilitate control of thedescent vehicles landing. Then, afterlanding and sample collection, avehicle would need to be launchedfor the return flight to Earth. Ournew technology provides the requiredlaunch-vehicle performance on asmall scale.


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Figure 5. ASTRIDascends the launch

rail on February 4,

1994. The glow of the

four thrust chambers

can be seen, but the

plume is invisible

because hydrazine

fuel decomposes

cleanly and at a lower

temperature than

other rocket

propellants.


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On another front, several ongoingdefense programs can benefit fromour technology, particularly those thatrequire small defensive missiles thatare highly maneuverable. We plan toexplore these and other potentialapplications for the new pumped-propulsion technology in the future.

Work funded by the Pentagons Ballistic Missile

Defense Organization. BMDO is the successor to

the Strategic Defense Initiative Organization.

Key words: advanced single-stage technology rapid

insertion demonstration (ASTRID);RAPTOR;

rocket propulsion.


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Figure 6. Sequence of three photos taken of the ASTRID flight test. At t=1.7 seconds after launch, ASTRID leaves the launch rail atVandenberg Air Force Base on its way to spashdown about a minute later in the Pacific Ocean.

For informationcontact John C.Whitehead(510) 423-4847,

Lee C. Pittenger(510) 422-9909, or

Nicholas J. Colella(510) 423-8452/(412) 268-6537.

Documents

ASTRID Rocket Flight Test