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  Space Shuttles - Space Station
  Manual reentry

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Author Topic:   Manual reentry
ASCAN1984
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Posts: 1004
From: County Down, Nothern Ireland
Registered: Feb 2002

posted 02-25-2007 09:27 AM     Click Here to See the Profile for ASCAN1984   Click Here to Email ASCAN1984     Edit/Delete Message   Reply w/Quote
Is it possible if an event ever occurred for example if both computers failed the for the commander and the pilot of an orbiter to fly a manual reentry (controlling the orbiter from de orbit burn to touchdown). As unlikely as that is I was just wondering?

disglobes
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Posts: 552
From: Fort McCoy, WI USA
Registered: May 2000

posted 02-25-2007 11:27 AM     Click Here to See the Profile for disglobes   Click Here to Email disglobes     Edit/Delete Message   Reply w/Quote
I believe that Joe Engle on STS-2 had to due a manual re-entry. At least that is what was announced at the Edwards AFB airshow a couple of years ago.

Charles

Naraht
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Posts: 232
From: Oxford, UK
Registered: Mar 2006

posted 02-25-2007 01:51 PM     Click Here to See the Profile for Naraht   Click Here to Email Naraht     Edit/Delete Message   Reply w/Quote
There is manual and then there is manual. The Shuttle uses a digital fly-by-wire system, which means that there are no direct links between the controls and the RCS thrusters, rudder, flaps, etc... everything goes through the computers. So while the pilot could control the Shuttle without the aid of computer calculations (for re-entry and the like), it's my understanding that controlling its flight without computer assistance would be either impossible or only marginally possible. The Shuttle isn't very aerodynamically stable so it flies at the very outside of human capabilities to control.

Still, I'd like to hear from someone who knows more about engineering than me.

katabatic
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From: Oak Hill, VA, USA
Registered: Jun 2005

posted 02-25-2007 05:14 PM     Click Here to See the Profile for katabatic   Click Here to Email katabatic     Edit/Delete Message   Reply w/Quote
This is from way, way back in my memory, so forgive me if I don't have it exactly right, but I remember an article in Aviation Week around the time of STS-1 which said that the most critical part of the fly-by-wire system were the rate gyros, of which the Shuttle had three. It said that it was thought impossible to land with all three out, because the vehicle became especially unstable at two points in reentry, one at (I think) Mach 33 and one at Mach 3. The article said that, in the simulator, John Young had come the closest to bringing it in with all three rate gyros out, making it through the Mach 33 part only to lose it at Mach 3. If anyone has one of the two "special editions" AvWeek put out around the time of STS-1 (compilations of Shuttle articles they previously published), I'm sure the article was in one of them.

spacecraft films
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Posts: 802
From: Columbus, OH USA
Registered: Jun 2002

posted 02-25-2007 05:26 PM     Click Here to See the Profile for spacecraft films   Click Here to Email spacecraft films     Edit/Delete Message   Reply w/Quote
Because of the fly-by-wire you can't really fly the vehicle without some computer control. "Fly-by-wire" by its very nature, requires electrical signals in order to move the control surfaces.

That having been said, there are 4 redundant computers that are synchronized (and must agree or be voted out) providing primary control, then a fifth computer that contains a completely different software system. The fifth runs what is termed the "backup flight software" and was a minimal program developed completely independently of the primary software to eliminate the possibility that a software bug could cause a malfunction. So the possibility of a complete computer failure is extremely remote.

Mark

divemaster
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Posts: 1341
From: ridgefield, ct
Registered: May 2002

posted 02-25-2007 05:44 PM     Click Here to See the Profile for divemaster   Click Here to Email divemaster     Edit/Delete Message   Reply w/Quote
Yeah, but Clint Eastwood was able to pull it off in Space Cowboys!

Greggy_D
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From: Michigan
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posted 02-25-2007 07:05 PM     Click Here to See the Profile for Greggy_D   Click Here to Email Greggy_D     Edit/Delete Message   Reply w/Quote
I thought I read one time (way back when) Bob Overmyer was the first pilot to manually bring the shuttle in from reentry to landing, because he wanted the challenge of it.

spacecraft films
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Posts: 802
From: Columbus, OH USA
Registered: Jun 2002

posted 02-25-2007 07:26 PM     Click Here to See the Profile for spacecraft films   Click Here to Email spacecraft films     Edit/Delete Message   Reply w/Quote
For the purposes of this discussion, you really need to define what is meant by "manual."

Mark

taneal1
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Posts: 196
From: Orlando, FL
Registered: Feb 2004

posted 02-25-2007 10:54 PM     Click Here to See the Profile for taneal1   Click Here to Email taneal1     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by spacecraft films:
Because of the fly-by-wire you can't really fly the vehicle without some computer control. "Fly-by-wire" by its very nature, requires electrical signals in order to move the control surfaces.
Mark

Mark is EXACTLY correct. The Shuttle, like any fly-by-wire airplane has no "mechanical" connections as a backup for computer failure. In the event of a total failure of ALL onboard computers, moving the "stick" would no longer move the flight controls, because the stick only sends signals to the computers. The computers determine which control surface to move and how much to move them predicated upon air density, velocity, mach number, and other factors. Also, for stability purposes the computer will command flight control movements without input from the pilot. The computers also control the position of the body flap for Center-of-Gravity control.

According to several shuttle CDRs that I've spoken to, control-stick-steering rather than automatic mode, isn't at all challenging as they are simply following Flight Director commands generated by the computers until the last few minutes prior to landing. During entry they prefer to remain in auto to allow them to focus on the orbiter's flight path and systems.

John Youskauskas
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posted 02-28-2007 11:47 AM     Click Here to See the Profile for John Youskauskas     Edit/Delete Message   Reply w/Quote
Joe Engle explained at his talk a few years back at the Air & Space Museum. The reason his reentry was manually flown was that in these early test flights, they had some maneuvers to fly that the software engineers were not able to to have ready for STS-2.

STS-1 was an auto reentry because on the first flight, they wanted no surprises...get it into orbit and get it back safely. STS-2 was tasked with exploring the envelope of the vehicle at different angles of attack to evaluate L/D at hypersonic speeds. Engle also input several "pulses" to look at the vehicle's aerodynamic stability.

There was no bravado or "let's see what this does" involved...it was all carefully planned and executed. The needs of moving the program forward just outpaced the ability of the software guys to program those antique GPC's they had.

ASCAN1984
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Posts: 1004
From: County Down, Nothern Ireland
Registered: Feb 2002

posted 03-01-2007 05:07 AM     Click Here to See the Profile for ASCAN1984   Click Here to Email ASCAN1984     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by spacecraft films:
For the purposes of this discussion, you really need to define what is meant by "manual."

Mark


Definition of manual reentry- No assistance to the pilots from computers or any other piece of equipment or hardware. Pure flying from the pilots as a pilot would fly an aeroplane

spacecraft films
Member

Posts: 802
From: Columbus, OH USA
Registered: Jun 2002

posted 03-01-2007 05:57 AM     Click Here to See the Profile for spacecraft films   Click Here to Email spacecraft films     Edit/Delete Message   Reply w/Quote
Given the above definition, this isn't possible with space shuttle for the reasons (surrounding fly-by-wire) mentioned above.

Mark

nasamad
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Posts: 1890
From: Essex, UK
Registered: Jul 2001

posted 03-01-2007 09:40 AM     Click Here to See the Profile for nasamad   Click Here to Email nasamad     Edit/Delete Message   Reply w/Quote

Regarding John Young flying the SIM, I read that he was able to fly the otbiter through an aileron roll !?

Adam

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