RTLS

My understanding of the RTLS abort is that it has been regarded with varying
degrees of [dis]taste throughout the program. Generally, a TAL is preferable
over RTLS (anything is preferable over RTLS) where at all possible. To my
understanding, this is due to several things, two of which a

1) Additional engine failues during the downrange velocity cancelling phase
can be lethal.
2) Base heating on the orbiter with the engines firing into the velocity
vector has been regarded with some degree of concern.

Is anyone aware of the current thinking on RTLS aborts?

Jon

"Jon Berndt" wrote:

My understanding of the RTLS abort is that it has been regarded with varying
degrees of [dis]taste throughout the program. Generally, a TAL is preferable
over RTLS (anything is preferable over RTLS) where at all possible. To my
understanding, this is due to several things, two of which a

1) Additional engine failues during the downrange velocity cancelling phase
can be lethal.
2) Base heating on the orbiter with the engines firing into the velocity
vector has been regarded with some degree of concern.

Is anyone aware of the current thinking on RTLS aborts?

This is from 1996 --

RTLS: An option NASA doesn't want to exercise
http://www.floridatoday.com/space/ex...96/032596e.htm

These from NASA --

Space Shuttle Transoceanic Abort Landing (TAL) Sites
http://www-pao.ksc.nasa.gov/kscpao/nasafact/tal.htm


SMK: The RTLS abort mode sounds pretty hair-raising to me...

Return to Launch Site Abort Mode
http://spaceflight.nasa.gov/shuttle/...orts/rtls.html

The RTLS abort mode is designed to allow the return of the orbiter,
crew, and payload to the launch site, Kennedy Space Center,
approximately 25 minutes after lift-off. The RTLS profile is designed
to accommodate the loss of thrust from one space shuttle main engine
between liftoff and approximately four minutes 20 seconds, at which time
not enough main propulsion system propellant remains to return to the
launch site.

An RTLS can be considered to consist of three stages -- a powered stage,
during which the main engines are still thrusting; an ET separation
phase; and the glide phase, during which the orbiter glides to a landing
at the KSC. The powered RTLS phase begins with the crew selection of
the RTLS abort, which is done after SRB separation. The crew selects
the abort mode by positioning the abort rotary switch to RTLS and
depressing the abort push button. The time at which the RTLS is
selected depends on the reason for the abort. For example, a
three-engine RTLS is selected at the last moment, approximately 3
minutes, 34 seconds into the mission; whereas an RTLS chosen due to an
engine out at liftoff is selected at the earliest time, approximately
two minutes 20 seconds into the mission (after SOR separation).

After RTLS is selected, the vehicle continues downrange to dissipate
excess main propulsion system propellant. The goal is to leave only
enough main propulsion system propellant to be able to turn the vehicle
around, fly back towards KSC and achieve the proper main engine cutoff
conditions so the vehicle can glide to the KSC after external tank
separation. During the downrange phase, a pitch-around maneuver is
initiated (the time depends in part on the time of a main engine
failure) to orient the orbiter/ external tank configuration to a heads
up attitude, pointing toward the launch site. At this time, the vehicle
is still moving away from the launch site, but the main engines are now
thrusting to null the downrange velocity. In addition, excess orbital
maneuvering system and reaction control system propellants are dumped by
continuous orbital maneuvering system and reaction control system engine
thrustings to improve the orbiter weight and center of gravity for the
glide phase and landing.

The vehicle will reach the desired main engine cutoff point with less
than 2 percent excess propellant remaining in the external tank. At
main engine cutoff minus 20 seconds, a pitch-down maneuver (called
powered pitch-down) takes the mated vehicle to the required external
tank separation attitude and pitch rate. After main engine cutoff has
been commanded, the external tank separation sequence begins, including
a reaction control system translation that ensures that the orbiter does
not recontact the external tank and that the orbiter has achieved the
necessary pitch attitude to begin the glide phase of the RTLS.

After the reaction control system translation maneuver has been
completed, the glide phase of the RTLS begins. From then on, the RTLS is
handled similarly to a normal entry.

[end of NASA cite]

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Scott M. Kozel Highway and Transportation History Websites
Virginia/Maryland/Washington, D.C. http://www.roadstothefuture.com
Philadelphia and Delaware Valley http://www.pennways.com

Seems easier just to ditch the excess baggage of the ET and SRBs. Ditch the
orbitor at sea after bailing out. (chicken little syndrome applies
here--this is the heads up phase) Could try to save the ship using
inflatable air bags (or silicon ablative drag chute that doubles for rapid
re entry deceleration)

(be kind my team lost yesterday)--and don't say I'm not surprised



..





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Jon Berndt wrote:

My understanding of the RTLS abort is that it has been regarded with
varying degrees of [dis]taste throughout the program. Generally, a TAL is
preferable
over RTLS (anything is preferable over RTLS) where at all possible. To my
understanding, this is due to several things, two of which a

1) Additional engine failues during the downrange velocity cancelling
phase can be lethal.
2) Base heating on the orbiter with the engines firing into the velocity
vector has been regarded with some degree of concern.

Is anyone aware of the current thinking on RTLS aborts?


Maybe they are looking at ECALs?

Craig

From Craig Fink:
Jon Berndt wrote:

My understanding of the RTLS abort is that it has been regarded with
varying degrees of [dis]taste throughout the program. Generally, a TAL is
preferable
over RTLS (anything is preferable over RTLS) where at all possible. To my
understanding, this is due to several things, two of which a

1) Additional engine failues during the downrange velocity cancelling
phase can be lethal.
2) Base heating on the orbiter with the engines firing into the velocity
vector has been regarded with some degree of concern.

Is anyone aware of the current thinking on RTLS aborts?


Maybe they are looking at ECALs?

My guess is that you hit the nail on the head, Craig. ECAL strikes me
as a smart compromise between the thermal issues of TAL and the
maneuver issues of RTLS. But I expect that the cost of verifying ECAL
to the intact level is not insignificant. We will see where NASA
decides to put their priorities.


~ CT

"Stuf4" wrote in message

My guess is that you hit the nail on the head, Craig. ECAL strikes me
as a smart compromise between the thermal issues of TAL and the
maneuver issues of RTLS. But I expect that the cost of verifying ECAL
to the intact level is not insignificant. We will see where NASA
decides to put their priorities.

~ CT

Another thing is, for -107, I don't know what their ECAL opportunities were,
but they may have been non-existent.

Jon

Lynndel Humphreys wrote:
Seems easier just to ditch the excess baggage of the ET and SRBs. Ditch the
orbitor at sea after bailing out. (chicken little syndrome applies
here--this is the heads up phase) Could try to save the ship using
inflatable air bags (or silicon ablative drag chute that doubles for rapid
re entry deceleration)

You can't ditch the SRBs when they are lit.
You have to wait until burnout.


--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
My inner child can beat up your inner child. - Alex Greenbank

From Jon Berndt:
My guess is that you hit the nail on the head, Craig. ECAL strikes me
as a smart compromise between the thermal issues of TAL and the
maneuver issues of RTLS. But I expect that the cost of verifying ECAL
to the intact level is not insignificant. We will see where NASA
decides to put their priorities.

~ CT

Another thing is, for -107, I don't know what their ECAL opportunities were,
but they may have been non-existent.

I would agree that the inclination was too low for ECAL. Bermuda was
probably an option.

But either way, moot.


~ CT

You can't ditch the SRBs when they are lit.
You have to wait until burnout.



IF the ship could detach from the stack (which continues on its way) , what
are the chances the shuttle could survive the SRB plume(s) falling away?





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Lynndel Humphreys wrote:


You can't ditch the SRBs when they are lit.
You have to wait until burnout.



IF the ship could detach from the stack (which continues on its way) , what
are the chances the shuttle could survive the SRB plume(s) falling away?

I don't think that the shuttle can seperate from the stack when the
SRBs are lit, as the thrust holds them on.

This was discussed a lot after the challenger problem.
If you jettison the SRBs lit, then bad things happen as the plumes impinge
on the stack.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
If it can't be expressed in figures, it is not science, it is opinion.
-- Robert A Heinlein.