On Sept. 12, 1985, Rockwell International's Shuttle Operations Co., Houston, Texas, was awarded the Space
Transportation System operation contract at NASA's Johnson Space Center, consolidating work previously
performed under 22 contracts by 16 different contractors.
 
On July 31, 1987, NASA awarded Rockwell's Space Transportation Systems Division, Downey, Calif., a contract
to build a replacement Space Shuttle orbiter using the structural spares. The replacement orbiter will be
assembled at Rockwell's Palmdale, Calif., assembly facility and is scheduled for completion in 1991. This
orbiter is designated OV-105.
 
Mission Profile.
 
In the launch configuration, the orbiter and two SRBs are attached to the external tank in a vertical
(nose-up) position on the launch pad. Each SRB is attached at its aft skirt to the mobile launcher platform
by four bolts.
 
Emergency exit for the flight crew on the launch pad up to 30 seconds before liftoff is by slidewire. There
are seven 1,200-foot-long slidewires, each with one basket. Each basket is designed to carry three persons.
The baskets, 5 feet in diameter and 42 inches deep, are suspended beneath the slide mechanism by four
cables. The slidewires carry the baskets to ground level. Upon departing the basket at ground level, the
flight crew progresses to a bunker that is designed to protect it from an explosion on the launch pad.
 
At launch, the three Space Shuttle main engines - fed liquid hydrogen fuel and liquid oxygen oxidizer from
the external tank - are ignited first. When it has been verified that the engines are operating at the
proper thrust level, a signal is sent to ignite the SRB. At the proper thrust-to-weight ratio, initiators
(small explosives) at eight hold-down bolts on the SRB are fired to release the Space Shuttle for liftoff.
All this takes only a few seconds.
 
Maximum dynamic pressure is reached early in the ascent, nominally approximately 60 seconds after liftoff.
Approximately 1 minute later (2 minutes into the ascent phase), the two SRB have consumed their propellant
and are jettisoned from the external tank. This is triggered by a separation signal from the orbiter.

The boosters briefly continue to ascend, while small motors fire to carry them away from the Space Shuttle.
The boosters then turn and descend, and at a predetermined altitude, parachutes are deployed to decelerate
them for a safe splashdown in the ocean. Splashdown occurs approximately 141 nautical miles (162 statute
miles) from the launch site. The boosters are recovered and reused.
 
Meanwhile, the orbiter and external tank continue to ascend, using the thrust of the three Space Shuttle
main engines. Approximately 8 minutes after launch and just short of orbital velocity, the three Space
Shuttle engines are shut down (main engine cutoff), and the external tank is jettisoned on command from
the orbiter.
 
The forward and aft reaction control system engines provide attitude (pitch, yaw and roll) and the
translation of the orbiter away from the external tank at separation and return to attitude hold prior to
the orbital maneuvering system thrusting maneuver.
 
The external tank continues on a ballistic trajectory and enters the atmosphere, where it disintegrates.
Its projected impact is in the Indian Ocean (except for 57-degree inclinations) in the case of equatorial
orbits KSC launch) and in the extreme southern Pacific Ocean in the case of a Vandenberg launch.
 
Normally, two thrusting maneuvers using the two OMS engines at the aft end of the orbiter are used in a
two-step thrusting sequence: to complete insertion into Earth orbit and to circularize the spacecraft's
orbit. The OMS engines are also used on orbit for any major velocity changes.
 
In the event of a direct-insertion mission, only one OMS thrusting sequence is used.
 
The orbital altitude of a mission is dependent upon that mission. The nominal altitude can vary between
100 to 217 nautical miles (115 to 250 statute miles). The forward and aft RCS thrusters (engines) provide
attitude control of the orbiter as well as any minor translation maneuvers along a given axis on orbit.
 
At the completion of orbital operations, the orbiter is oriented in a tail first attitude by the reaction
control system. The two OMS engines are commanded to slow the orbiter for deorbit.
 
The reaction control system turns the orbiter's nose forward for entry. The reaction control system
controls the orbiter until atmospheric density is sufficient for the pitch and roll aerodynamic control
surfaces to become effective.
 
Entry interface is considered to occur at 400,000 feet altitude approximately 4,400 nautical miles (5,063
statute miles) from the landing site and at approximately 25,000 feet per second velocity.
 
At 400,000 feet altitude, the orbiter is maneuvered to zero degrees roll and yaw (wings level) and at a
predetermined angle of attack for entry. The angle of attack is 40 degrees. The flight control system
issues the commands to roll, pitch and yaw reaction control system jets for rate damping.
 
The forward RCS engines are inhibited prior to entry interface, and the aft reaction control system engines
maneuver the spacecraft until a dynamic pressure of 10 pounds per square foot is sensed, which is when the
orbiter's ailerons become effective. The aft RCS roll engines are then deactivated. At a dynamic pressure
of 20 pounds per square foot, the orbiter's elevators become active, and the aft RCS pitch engines are
deactivated. The orbiter's speed brake is used below Mach 10 to induce a more positive downward elevator
trim deflection. At approximately Mach 3.5, the rudder becomes activated, and the aft reaction control
system yaw engines are deactivated at 45,000 feet.
 
Entry guidance must dissipate the tremendous amount of energy the orbiter possesses when it enters the
Earth's atmosphere to assure that the orbiter does not either burn up (entry angle too steep) or skip out
of the atmosphere (entry angle too shallow) and that the orbiter is properly positioned to reach the desired
touchdown point.
 
During entry, energy is dissipated by the atmospheric drag on the orbiter's surface. Higher atmospheric
drag levels enable faster energy dissipation with a steeper trajectory. Normally, the angle of attack and
roll angle enable the atmospheric drag of any flight vehicle to be controlled. However, for the orbiter,
angle of attack was rejected because it creates surface temperatures above the design specification. The
angle of attack scheduled during entry is scheduled during entry is loaded into the orbiter computers as a
function of relative velocity, leaving roll angle for energy control. Increasing the roll angle decreases
the vertical component of lift, causing a higher sink rate and energy dissipation rate. Increasing the roll
rate does raise the surface temperature of the orbiter, but not nearly as drastically as an equal angle of
attack command.

If the orbiter is low on energy (current range-to-go much greater than nominal at current velocity), entry
guidance will command lower than nominal drag levels. If the orbiter has too much energy (current range to
go much less than nominal at the current velocity), entry guidance will command higher-than-nominal drag
levels to dissipate the extra energy.
 
Roll angle is used to control cross range. Azimuth error is the angle between the plane containing the
orbiter's position vector and the heading alignment cylinder tangency point and the plane containing the
orbiter's position vector and velocity vector. When the azimuth error exceeds a computer-loaded number, the
orbiter's roll angle is reversed.
 
Thus, descent rate and down ranging are controlled by bank angle. The steeper the bank angle, the greater
the descent rate and the greater the drag. Conversely, the minimum drag attitude is wings level. Cross
range is controlled by bank reversals.
 
The entry thermal control phase is designed to keep the backface temperatures within the design limits. A
constant heating rate is established until below 19,000 feet per second.
 
The equilibrium glide phase shifts the orbiter from the rapidly increasing drag levels of the temperature
control phase to the constant drag level of the constant drag phase. The equilibrium glide flight is defined
as flight in which the flight path angle, the angle between the local horizontal and the local velocity 
ector, remains constant. Equilibrium glide flight provides the maximum downrange capability. It lasts until
the drag acceleration reaches 33 feet per second squared.
 
The constant drag phase begins at that point. The angle of attack is initially 40 degrees, but it begins
to ramp down in this phase to approximately 36 degrees by the end of this phase.
 
In the transition phase, the angle of attack continues to ramp down, reaching the approximately 14-degree
angle of attack at the entry Terminal Area Energy Management (TAEM) interface, at approximately 83,000 feet
altitude, 2,500 feet per second, Mach 2.5 and 52 nautical miles (59 statute miles) from the landing runway.
Control is then transferred to TAEM guidance.
 
During the entry phases described, the orbiter's roll commands keep the orbiter on the drag profile and
control cross range. 

TAEM guidance steers the orbiter to the nearest of two heading alignment cylinders, whose radii are
approximately 18,000 feet and which are located tangent to and on either side of the runway centerline on
the approach end. In TAEM guidance, excess energy is dissipated with an S-turn; and the speed brake can be
used to modify drag, lift-to-drag ratio and flight path angle in high-energy conditions. This increases the
ground track range as the orbiter turns away from the nearest Heading Alignment Circle (HAC) until sufficient
energy is dissipated to allow a normal approach and landing guidance phase capture, which begins at 10,000
feet altitude. The orbiter also can be flown near the velocity for maximum lift over drag or wings level for
the range stretch case. The spacecraft slows to subsonic velocity at approximately 49,000 feet altitude,
about 22 nautical miles (25.3 statute miles) from the landing site.
 
At TAEM acquisition, the orbiter is turned until it is aimed at a point tangent to the nearest HAC and
continues until it reaches way point 1. At WP-1, the TAEM heading alignment phase begins. The HAC is
followed until landing runway alignment, plus or minus 20 degrees, has been achieved. In the TAEM pre-final
phase, the orbiter leaves the HAC; pitches down to acquire the steep glide slope, increases airspeed; banks
to acquire the runway centerline and continues until on the runway centerline, on the outer glide slope and
on airspeed. The approach and landing guidance phase begins with the completion of the TAEM pre-final phase
and ends when the spacecraft comes to a complete stop on the runway.
 
The approach and landing trajectory capture phase begins at the TAEM interface and continues to guidance
lock-on to the steep outer glide slope. The approach and landing phase begins at about 10,000 feet altitude
at an equivalent airspeed of 290, plus or minus 12, knots 6.9 nautical miles (7.9 statute miles) from
touchdown. Autoland guidance is initiated at this point to guide the orbiter to the minus 19- to 17-degree
glide slope (which is over seven times that of a commercial airliner's approach) aimed at a target 0.86
nautical mile (1 statute mile) in front of the runway. The spacecraft's speed brake is positioned to hold
the proper velocity. The descent rate in the later portion of TAEM and approach and landing is greater than
10,000 feet per minute (a rate of descent approximately 20 times higher than a commercial airliner's
standard 3-degree instrument approach angle).
 
At 1,750 feet above ground level, a pre-flare maneuver is started to position the spacecraft for a
1.5-degree glide slope in preparation for landing with the speed brake positioned as required. The flight
crew deploys the landing gear at this point.
 
The final phase reduces the sink rate of the spacecraft to less than 9 feet per second. Touchdown occurs
approximately 2,500 feet past the runway threshold at a speed of 184 to 196 knots (213 to 226 mph).

Aborts.
 
Selection of an ascent abort mode may become necessary if there is a failure that affects vehicle
performance, such as the failure of a Space Shuttle main engine or an orbital maneuvering system. Other
failures requiring early termination of a flight, such as a cabin leak, might require the selection of an
abort mode.
 
There are two basic types of ascent abort modes for Space Shuttle missions: intact aborts and contingency
aborts. Intact aborts are designed to provide a safe return of the orbiter to a planned landing site.

Contingency aborts are designed to permit flight crew survival following more severe failures when an intact
abort is not possible. A contingency abort would generally result in a ditch operation.
 
Intact Aborts.
 
There are four types of intact aborts:

Abort To Orbit.
 
The ATO mode is designed to allow the vehicle to achieve a temporary orbit that is lower than the nominal
orbit. This mode requires less performance and allows time to evaluate problems and then choose either an
early deorbit maneuver or an orbital maneuvering system thrusting maneuver to raise the orbit and continue
the mission.
 
Abort Once Around.
 
The AOA is designed to allow the vehicle to fly once around the Earth and make a normal entry and landing.
This mode generally involves two orbital maneuvering system thrusting sequences, with the second sequence
being a deorbit maneuver. The entry sequence would be similar to a normal entry.
 
Transatlantic Landing.
 
The TAL mode is designed to permit an intact landing on the other side of the Atlantic Ocean. This mode
results in a ballistic trajectory, which does not require an orbital maneuvering system maneuver.
 
Return to Launch Site.
 
The RTLS mode involves flying downrange to dissipate propellant and then turning around under power to
return directly to a landing at or near the launch site.
 
There is a definite order of preference for the various abort modes. The type of failure and the time of
the failure determine which type of abort is selected. In cases where performance loss is the only factor,
the preferred modes would be ATO, AOA, TAL and RTLS, in that order. The mode chosen is the highest one that
can be completed with the remaining vehicle performance. In the case of some support system failures, such
as cabin leaks or vehicle cooling problems, the preferred mode might be the one that will end the mission
most quickly. In these cases, TAL or RTLS might be preferable to AOA or ATO. A contingency abort is never
chosen if another abort option exists.
 
The Mission Control Center-Houston is prime for calling these aborts because it has a more precise knowledge
of the orbiter's position than the crew can obtain from onboard systems. Before main engine cutoff, Mission
Control makes periodic calls to the crew to tell them which abort mode is (or is not) available. If ground
communications are lost, the flight crew has onboard methods, such as cue cards, dedicated displays and
display information, to determine the current abort region.
 
Which abort mode is selected depends on the cause and timing of the failure causing the abort and which
mode is safest or improves mission success. If the problem is a Space Shuttle main engine failure, the
flight crew and Mission Control Center select the best option available at the time a space shuttle main
engine fails.
 
If the problem is a system failure that jeopardizes the vehicle, the fastest abort mode that results in the
earliest vehicle landing is chosen. RTLS and TAL are the quickest options (35 minutes), whereas an AOA
requires approximately 90 minutes. Which of these is elected depends on the time of the failure with three
good Space Shuttle main engines.
 
The flight crew selects the abort mode by positioning an abort mode switch and depressing an abort push
button.
 
Contingency Abort.
 
Contingency aborts are caused by loss of more than one main engine or failures in other systems. Loss of
one main engine while another is stuck at a low thrust setting may also necessitate a contingency abort.
Such an abort would maintain orbiter integrity for in-flight crew escape if a landing cannot be achieved
at a suitable landing field.
 
Contingency aborts due to system failures other than those involving the main engines would normally result
in an intact recovery of vehicle and crew. Loss of more than one main engine may, depending on engine
failure times, result in a safe runway landing. However, in most three-engine-out cases during ascent,
the orbiter would have to be ditched. The in-flight crew escape system would be used before ditching the
orbiter.
 
Orbiter Ground Turnaround.
 
Spacecraft recovery operations at the nominal end-of-mission landing site are supported by approximately
160 Space Shuttle launch operations team members. Ground team members wearing self-contained atmospheric
protective ensemble suits that protect them from toxic chemicals approach the spacecraft as soon as it
stops rolling. The ground team members take sensor measurements to ensure the atmosphere in the vicinity
of the spacecraft is not explosive. In the event of propellant leaks, a wind machine truck carrying a large
fan will be moved into the area to create a turbulent airflow that will break up gas concentrations and
reduce the potential for an explosion.

A ground support equipment air-conditioning purge unit is attached to the right-hand orbiter T-0 umbilical
so cool air can be directed through the orbiter's aft fuselage, payload bay, forward fuselage, wings,
vertical stabilizer, and orbital maneuvering system/reaction control system pods to dissipate the heat of
entry.
 
A second ground support equipment ground cooling unit is connected to the left-hand orbiter T-0 umbilical
spacecraft Freon Coolant loops to provide cooling for the flight crew and avionics during the postlanding
and system checks. The spacecraft fuel cells remain powered up at this time. The flight crew will then exit
the spacecraft, and a ground crew will power down the spacecraft.
 
AT KSC, the orbiter and ground support equipment convoy move from the runway to the Orbiter Processing
Facility.
 
If the spacecraft lands at Edwards, the same procedures and ground support equipment are used as at the KSC
after the orbiter has stopped on the runway. The orbiter and ground support equipment convoy move from the
runway to the orbiter mate and demate facility at Edwards. After detailed inspection, the spacecraft is
prepared to be ferried atop the Shuttle carrier aircraft from Edwards to KSC. For ferrying, a tail cone is
installed over the aft section of the orbiter.
 
In the event of a landing at an alternate site, a crew of about eight team members will move to the landing
site to assist the astronaut crew in preparing the orbiter for loading aboard the Shuttle carrier aircraft
for transport back to the KSC. For landings outside the United States, personnel at the contingency landing
sites will be provided minimum training on safe handling of the orbiter with emphasis on crash rescue
training, how to tow the orbiter to a safe area, and prevention of propellant conflagration.
 
Upon its return to the Orbiter Processing Facility (OPF) at KSC, the orbiter is safed (ordnance devices
safed), the payload (if any) is removed, and the orbiter payload bay is reconfigured from the previous
mission for the next mission. Any required maintenance and inspections are also performed while the orbiter
is in the OPF. A payload for the orbiter's next mission may be installed in the orbiter's payload bay in the
OPF or may be installed in the payload bay when the orbiter is at the launch pad.
 
The spacecraft is then towed to the Vehicle Assembly Building and mated to the external tank. The external
tank and solid rocket boosters are stacked and mated on the mobile launcher platform while the orbiter is
being refurbished. Space Shuttle orbiter connections are made and the integrated vehicle is checked and
ordnance is installed.
 
The mobile launcher platform moves the entire space shuttle system on four crawlers to the launch pad,
where connections are made and servicing and checkout activities begin. If the payload was not installed
in the OPF, it will be installed at the launch pad followed by prelaunch activities.

 
Space Shuttle launches from Vandenberg will use the Vandenberg Launch Facility (SL6), which was built but
never used for the manned orbital laboratory program. This facility was modified for Space Transportation
System use.
 
The runway at Vandenberg was strengthened and lengthened from 8,000 feet to 12,000 feet to accommodate the
orbiter returning from space.
 
When the orbiter lands at Vandenberg, the same procedures and ground support equipment and convoy are used
as at KSC after the orbiter stops on the runway. The orbiter and ground support equipment are moved from
the runway to the Orbiter Maintenance and Checkout Facility at Vandenberg. The orbiter processing procedures
used at this facility are similar to those used at the OPF at the KSC.

Space Shuttle buildup at Vandenberg differs from that of the KSC in that the vehicle is integrated on the
launch pad. The orbiter is towed overland from the Orbiter Maintenance and Checkout Facility at Vandenberg
to launch facility SL6.
 
SL6 includes the launch mount, access tower, mobile service tower, launch control tower, payload preparation
room, payload changeout room, solid rocket booster refurbishment facility, solid rocket booster disassembly
facility, and liquid hydrogen and liquid oxygen storage tank facilities.
 
The SRB start the on-the-launch-pad buildup followed by the external tank. The orbiter is then mated to the
external tank on the launch pad.
 
The launch processing system at the launch pad is similar to the one used at KSC.
 
Kennedy Space Center Launch Operations has responsibility for all mating, prelaunch testing and launch
control ground activities until the Space Shuttle vehicle clears the launch pad tower. Responsibility is
then turned over to Mission Control Center-Houston. The Mission Control Center's responsibility includes
ascent, on-orbit operations, entry, approach and landing until landing runout completion, at which time the
orbiter is handed over to the postlanding operations at the landing site for turnaround and re-launch. At
the launch site the SRBs and external tank are processed for launch and the SRBs are recycled for reuse.

 
 


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