Following
an Orbiter vehicle landing or demate from the mate/demate device (MDD),
the vehicle is moved to the Orbiter
Processing Facility (OPF). Previously Orbiter towing, aligning, and spotting
into the OPF high bays have been an inaccurate process. Moving a large
vehicle into the OPF bays combined with a high-precision alignment requirement
makes the task extremely challenging. The task is made more difficult
because the tug design and task requirements limit the tug driver’s
field of vision. The tug driver depends on verbal directional instructions
from
the Orbiter Move Director (OMD). When the tug driver cannot see the towlines
and misses the towpath, the driver must back up and start again. High
variability in alignment and spotting made the process unreliable and
dependent on
the skills and luck of the tug driver and OMD. This time-consuming process
can waste many valuable man-hours while OPF personnel wait for the OPF
high bay to open for work. Accurate alignment of the Orbiter is also
essential for the functional use of workstands on all levels throughout
the entire
OPF process flow, particularly those with flip-down plates and extensions.
An Orbiter misalignment may require use of pic-boards in place of existing
platforms later in the vehicle process flow to complete other tasks.
The solution was to provide an inexpensive and highly effective laser
alignment and spotting system visible to the tug driver and OMD. United
Space Alliance
(USA) Optics, Corrective Action Engineering, Orbiter Handling Engineering,
and Industrial Engineering/Human Factors formed a team to develop a
process that uses two off-the-shelf laser theodolite digital
transit units for
alignment spotting. One laser is used for guiding the tug driver and
the second is used for cross-checking the Orbiter Main Landing Gear
(MLG) during
roll-in. A translucent laser “target” was constructed and
is used on the tug during this process. The first laser projects a dot
on
the target providing a directional reference for the tug operator towing
the Orbiter. Simultaneously, a second laser projects a beam onto the
MLG for the OMD to verify the Orbiter vehicle alignment accuracy.
Roll-in process time from Spacecraft Operator (SCO) change-out to
final spot was previously as long as 4 hours. Improved roll-in
process time
and final spot is now 15 to 30 minutes. During the testing phase
of the system
in August 2001, Discovery was aligned and spotted in the OPF highbay
2 within 13 minutes. The new process has saved man-hours, and costly
wear
and tear on the tug, Orbiter nose wheel, and struts. In addition,
this new process cuts back on Orbiter fuel cell usage and allows
the Orbiter
to be jacked and leveled sooner, which provides quicker access to
time-critical ground support equipment. This also allows for
interfacing to Power
Reaction, Storage, and Distribution and securing facility cooling
and ground power
quicker, thus relieving the SCO in less time. Additional benefits
include functional improvements throughout the entire OPF flow
for workstand
flip-down and extention platform access. The possibility of unecessary
pic-board
installation for access, in place of an existing platform, has been
reduced because of improved alignment accuracy of the Orbiter.
Key accomplishments:
- 2001: Researched
laser systems and types for application. Met with stakeholders for
customer interviews. Tested laser alignment prototype process
in the Vehicle Assembly Building highbay 4. Formed continuous improvement
project
team. Tested laser alignment system in OPF. Purchased system
components for OPF-owned laser package. Began tug driver process familiarization
and
training.
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Orbiter Tow Tug
First Laser Spot on Translucent Tug Target
Second Laser Spot on Main Landing Gear
Key milestones:
- 2001: Began OPF
technician hands-on training during roll-in. Completed laser operating
system turned over to OPF ownership.
- 2002: Completed
OPF technician laser training package.
Contacts: M.M. Groh-Hammond (Marcia.Groh-Hammond-1@ksc.nasa.gov),
PH-M3-A, (321) 861-0572; and R.J. Carrillo, PH-H1, (321) 861-3623
Participating Organization: United Space Alliance (C.R. Floyd, D.G. Sheriff,
P.S. Dickey, M.W. McClure, and K.D. VanDyke
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