NASA 

National Aeronautics and 

Facts

Space Administration 

Dryden Flight Research Center 

P.O. Box 273

Edwards, California 93523 

Voice 661-276-3449 

FAX 661-276-3566 

pao@dfrc.nasa.gov FS-2002-09-049-DFRC 

Eclipse Tow Launch Demonstration

Project

Eclipse project’s EXD-01 lifts off under tow by a USAF C-141A 

aircraft. NASA photo EC97 44357-10

 NASA Dryden Flight Research Center supported a 

Kelly Space and Technology, Inc. (KST)/U.S. Air Force 

project, known as Eclipse, which demonstrated a reusable tow launch vehicle concept.

 The purpose of the project was to demonstrate a 

reusable tow launch vehicle concept conceived and 

patented by KST. Kelly Space obtained a contract with 

the USAF Research Laboratory for the tow launch 

demonstration project under the Small Business Innovation Research (SBIR) program. The USAF SBIR contract included the modifications to turn the QF-106 into 

the Experimental Demonstrator #1 (EXD-01), and C141A aircraft to incorporate the tow provisions to link the 

two aircraft, as well as conducting flight tests. The 

demonstration consisted of ground and flight tests.

 These included a Combined Systems Test of both 

airplanes joined by a tow rope, a towed taxi test, and six 

towed flights. The project’s primary goal of demonstrating the tow phase of the Eclipse concept using a scaleddown tow aircraft (C-141A) and a representative aerodynamically-shaped aircraft (QF-106A) as a launch vehicle 

was successfully accomplished.

 On Feb. 6, 1998, the Eclipse project made its sixth and 

final towed flight, bringing the project to a successful 

completion. Preliminary flight results determined that the 

handling qualities of the QF-106 on tow were very 

stable; actual flight measured values of tow rope tension 

were well within predictions by the simulation, aerodynamic characteristics and elastic properties of the tow 

rope were a signficant component of the towing system; 

and Dryden’s high-fidelity simulation provided a representative model of the performance of the QF-106 and 

C-141A airplanes in tow configuration. Total time on 

tow for the entire project was five hours, 34 minutes, and 

29 seconds. All six flights were highly productive, and 

all project objectives were achieved. 

Project Goals

 All three of the project’s objectives were successfully 

accomplished. The objectives were: demonstration of towed 

take-off, climb-out, and separation of the EXD-01 from the 

towing aircraft; validation of simulation models of the towed 

aircraft systems; and development of ground and flight 

procedures for towing and launching a delta-winged airplane 

configuration safely behind a transport-type aircraft. 

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Participant’s Roles

 NASA Dryden served as the responsible test 

organization and had flight safety responsibility for 

the Eclipse project. Dryden also supplied engineering, 

simulation, instrumentation, range support, research 

pilots, and chase aircraft for the test series. Dryden 

personnel performed the modifications to convert the 

QF-106 into the piloted EXD-01 aircraft. During the 

early flight phase of the project, Tracor, Inc., provided 

maintenance and ground support for the two QF-106 

airplanes.

Eclipse project’s EXD-01 and a USAF C-141 takeoff for the 

first flight on Dec. 20, 1997. NASA photo EC97 44357-8 

The Air Force Flight Test Center (AFFTC) 

provided the C-141A transport aircraft for the 

project, its flight and engineering support, and the 

aircrew.

 Kelly Space and Technology provided the modification design and fabrication of the hardware that 

was installed on the EXD-01 aircraft.

 Kelly Space and Technology hopes to use the 

data gleaned from the tow tests to develop a series 

of low-cost reusable launch vehicles, in particular to 

gain experience towing delta-wing aircraft having 

high wing loading, and to demonstrate various 

operational procedures such as ground processing 

and abort scenarios. 

Kelly Space and Technology 

Eclipse Astroliner Tow-Launch Concept 

Background

 The first successful towed flight occurred on Dec. 

20, 1997. Prior to the first tow test flight, the C-141A 

and EXD-01 were used to conduct a series of tethered 

taxi tests to validate the tow procedures. Previously, a 

successful joint flight test was conducted in late 

October 1996, by Dryden, AFFTC, and KST, in which 

one of Dryden’s F-18 chase aircraft flew at various 

ranges and locations behind the C-141A to define the 

wake turbulence and wingtip vortex environment. This 

flight test was replicated in July 1997, with an unmodified QF-106 flight proficiency aircraft. 

Simulation

 To enhance flight safety and reduce the number of 

unknowns during flight tests, the Eclipse project relied 

on a high-fidelity flight simulator. Full nonlinear 

mathematical models of the EXD-01 aircraft, C-141A 

aircraft, and the tow rope were modeled in the Eclipse 

simulator, which had a piloted and an off-line, batch 

version. The former was used to train pilots for normal 

and emergency operations, while the latter was used 

for dynamic analyses and for validation of major 

design decisions. As the flight project progressed the 

simulation validated the flight data. An additional 

benefit of the fully validated simulation is the ability 

to extrapolate the Eclipse tow dynamics to larger, 

future tow launch concepts. 

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Aircraft Modifications

 Modifications to the QF-106 included shortening 

the nose pitot boom, and the addition of a tow cable 

attachment and release mechanism. In addition, 

cockpit modifications such as the addition of a tow 

rope tension display were made.

 Modifications to the C-141A were minimal, with 

all of its towing and tow rope jettison equipment 

placed on a standard cargo pallet secured in the rear of 

the aircraft. During earlier tests, smoke-generating 

devices were placed on the C-141’s wingtips to enhance the visualization of the aircraft’s wake vortices 

as the EXD-01 flew behind it.

 The QF-106 was selected by KST because the 

aircraft has a delta wing planform representative of the 

Astroliner spacecraft that the company plans to build. 

The QF-106 is a rugged, reliable aircraft, which was 

available from the Air Force’s drone target aircraft 

inventory. The C-141A was chosen because it can be 

configured as a tow aircraft with no modification to 

the airframe.

 The 1000 foot-long 

tow “train” used to tow 

the EXD-01 aircraft 

consisted of the tow rope, made of a 

synthetic fiber normally 

used in marine 

applications; a 

breakable link designed for safety and 

to break if too much 

stress was placed on 

the tow train. Nylon 

straps were used on the 

first three flights in the 

middle of the tow train for 

damping to help any 

spring tendencies in the 

tow train. The straps 

were not needed for the 

last three flights. 

Funding

 Kelly Space and Technology obtained a contract 

with the USAF Research Lab for the tow launch 

demonstration project under the Small Business 

Innovation Research (SBIR) program. The USAF 

SBIR contract includes the modifications to the 

QF-106 and C-141A aircraft to incorporate the tow 

provisions to link the two aircraft. 

Technology 

Commercialization

 Kelly Space and Technology’s Eclipse Astroliner 

concept, which the current Eclipse project is demonstrating, will use a Boeing 747 to tow the planned 

Astroliner vehicle from a conventional runway to a 

launch alti- tude of about 45,000 feet. At that 

altitude the tow line would be released, 

and the Eclipse Astroliner’s rocket 

engine would be ignited. Releasing a vehicle at that altitude 

results in greater fuel 

economy for the launch 

vehicle than would a 

typical ground-launching. 

The Eclipse Astroliner would then 

climb to its designated payload 

separation altitude of about 400,000 

feet. Following ejection from the 

Eclipse Astroliner, the payload’s 

upper stages would be ignited to 

deliver the payload to its specified 

orbital destination. The Eclipse 

Astroliner vehicle then would descend 

as a glider, much like 

the Space Shuttle, to 

land using either 

remote piloting 

capability or an 

automatic landing 

system. 

Three view of QF-106 aircraft. 

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