Re: Orbiter can save itself!


Jorge R. Frank wrote:
John Doe <jdoe@xxxxxxx> wrote in news:43EE5417.458DCAC0@xxxxxxx:

"Jorge R. Frank" wrote:
Once RCO is installed, I don't think a human crew *can* take over.
The photos I've seen show the switch panels *removed* in order to
install the RCO cable, so the switches would no longer be there for
the crew to operate.

OK. That explains well why NASA wouldn't try this kit with a crew on
board.

For this to work, the RCO kit would have to be field installable,
right ?

That's the idea. It would be installed by the crew after safe haven is
declared and before the crew egresses the orbiter for the station. For
the SAIL tests, the RCO cable was installed by STS-121 commander Steve
Lindsey.

Will they leave one on the station for a crew to install in a
shuttle if necessary, or will every shuttle have its own RCO kit with
it at all times ?

I think there's only going to be one RCO cable, and it will either rotate
among the orbiters or be left on ISS.

Don't be silly. NASA chose timetagged commands because that's how the
existing SPC capability works, not because they thought timetagged
commands were better.

I was asking about the original design of the shuttle computers, not
the current patch. Were timed commands the only technologically
possible solution back when the shuttle was designed due to computer
limitations ?

I don't know.

I'm sure there will be, from people who don't understand the relative
risks involved.

What happens if during re-entry, the shuttle looses communications,
but otherwise remains intact ? Would the shuttle still automatically
switch to "glider" mode at some timed event, and try to manage without
the air data probes ? Or would it continue to be in "re-entry
interface" mode and essentially become a controlled ballistic re-entry
falling in some random location ?

The former. The guidance software will transition from entry to TAEM to
approach/landing on its own.

From the program point of view, would the "glider" mode be able to
cope without the air data probes, using inertial systems to estimate
airspeed ?

The nav software tries to cope with the lack of air data by deriving it
from the onboard state. How well that works depends on how good the nav
state is, and what the winds are like. It may work, but introduces enough
risk that the ability to deploy the probes was deemed essential for RCO.

--
JRF

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(I am not assimilated yet either so I have to think one step ahead of
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Today, inertial guidance is a little chip that can do miracles. Ring
lasers act as gryos accurately calculating speed and direction changes
regardless of cause. In fact, air data input is just about out of
date. So, inertial guidance will do well for the 'black out' period of
reentry.

GPS, however, is a little better overall since it combines current
location with speed over ground as well as location of the runway to be
used. So, switch back to GPS as soon as possible after 'black out'.

Computers can be programmed to do everything necessary including
applying the brakes on landing. Today, the brakes are anti-lock so
steady pressure is all that is needed. The parachute is deployed by a
pullout knob, but this could be accomplished by a simple piston as
well.

To what extent the Shuttle is fly-by-wire I don't know, but believe
that computers and avionics have been recently upgraded. So, with
fly-by-wire it is just necessary to insure proper inputs with a
separate computer, or multi-tasking program, handling position inputs
from I.G. or G.P.S., calculating the outputs to fly-by-wire based on
the current position vs. the final runway landing.

If the Shuttle's computers aren't capable of handling this then a
little stripped down PC can handle it just fine, feeding the outputs
into the Shuttle computers -- 3 pounds of extra weight, tops.

Countdown timers are almost as old fashioned as the paper tape computer
used during the Apollo Missions. Today, a sophisticated algorithim can
be used in that stripped down PC I mentioned. That should be a little
better than the old paper tape timer.

Boeing (McDonnel Douglas) used some glideslope programs in experimental
aircraft, so check them out. Why reinvent the wheel?


tomcat

.

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