-
#180 by nathan.moeller on 26 Feb, 2007 22:12
-
Great info on the ejection seats. Thanks guys. Now here's another question; this time a bit more relevant
Does anyone have the launch window charts for STS-118? I've been wondering what time of day it might go. I have summer classes again this year. Discovery managed to launch between terms for STS-121 and I had the ability to watch NTV via wireless internet during class and I'm wondering what's going to happen this time. If they delay a few days it won't be an issue as far as watching the launch. Landing is the only potential problem. If it's a night launch, it's a moot point.
-
#181 by kanathan on 26 Feb, 2007 22:26
-
I'm not sure how accurate it is, but spaceflightnow.com lists STS-118's launch time at 11:40 am ET on June 28th.
-
#182 by Mark Dave on 04 Mar, 2007 18:11
-
I was curious on why the hatches look difernt on each mission. For example if you compare the Orbiter Access hatch of Columbia on STS-107 to Discovery's on STS-114 there is some extra dark tiles around the porthole. Why is that? Some missions have it pure white around the porthole, and sometimes not.
-
#183 by Jim on 04 Mar, 2007 18:40
-
Quote
MarkD - 4/3/2007 2:11 PM
I was curious on why the hatches look difernt on each mission. For example if you compare the Orbiter Access hatch of Columbia on STS-107 to Discovery's on STS-114 there is some extra dark tiles around the porthole. Why is that? Some missions have it pure white around the porthole, and sometimes not.
different orbiters have different TPS patterns based the lessons learned from OV-102, OV-099, etc as the other orbiters were built later -
#184 by Mark Dave on 04 Mar, 2007 21:55
-
I see. Yeah a good example is on the Real Space Model decal sets on Challenger's hatch design next to the other hatch.
Thanks for clearing that up.
-
#185 by mkirk on 05 Mar, 2007 23:27
-
The following disussion has been moved from L2 since the subject has deviated from the original topic and fits in the Shuttle Q&A.Quote
kneecaps - 5/3/2007 5:27 AM
Quotemkirk - 5/3/2007 1:08 AM
This is a hefty set of questions, all of which have complex answers made up of lots of ifs, ands, ors and buts.
I can't wait, as much as I absorb myself, nothing beats hearing from a professional on the subject!
Pete
Here is what I can tell you about Command Path Failures, I will try and answer at least one of the other questions each day...time permitting.
Command Path Failures:
The main engine controller operates by comparing the commands within its 3 command channels, if at least 2 of those incoming commands are identical then the command is executed (refer to the diagram I attached below). If all 3 commands are different, a Command Path Failure is declared and the controller informs the GPCs (general purpose computers) which annunciate the failure for that engine.
The training philosophy is to pound into crew members heads two important points concerning Command Path Failures; 1) the affected engine MUST be shutdown manually and 2) the engine MUST be shutdown using what is called the AC/PB method.
When an engine is experiencing a Command Path Failure it will not accept any incoming commands, including the command to shutdown - the engine should remain at its last valid commanded setting.
The crew can not use the Main Engine Shutdown Pushbuttons (PBs), located on the center console, to initiate a shutdown because the buttons only send out a GPC shutdown command. That shutdown command will be rejected by the engine controller because of the Command Path Failure.
The crew has to shutdown the engine by taking the respective engine power switches known as the “ACs” to off. These switches which are located to the right of the Pilot (on panel R2) will remove all electrical power from that engine’s main engine controller – with a complete loss of the controller the engine will perform a pneumatic shutdown using the helium supply as a safety feature to ensure an uncontrolled engine is not allowed to keep running.
A pneumatic shutdown uses helium to close the 5 main SSME valves, these are normally closed hydraulically.
Since the engines were shutdown using the power switches (rather than the pushbuttons) the GPCs do not know what has happened. From the perspective of the GPCs, data is no longer coming in from the engine and they therefore assume a Data Path Failure (I will cover those in my next post) has occurred. In order to let the GPCs know that the engine has been shutdown the pushbutton for that engine is pressed.
Pressing the PB is referred to as “moding guidance”. This is important because you want the guidance system to know it doesn’t have the engine running any more, otherwise it will assume the engine is running and fly accordingly.
The timing of the manual shutdown is dictated by the type of ascent being flown (i.e. Nominal, ATO, RTLS, or TAL) and the number of engines operating. For a nominal uphill ascent with all 3 engines running, the one with a Command Path Failure will be shutdown at Mach 23. This allows the engine to run as long as possible but shuts it down with enough time for guidance to compensate for the lost engine prior to MECO. The engine needs to be shutdown in this manner to protect it from possible fuel starvation and to protect against LO2 NPSP (net positive suction pressure) violations caused by a rapid loss of acceleration at MECO.
Mark Kirkman
-
#186 by hmh33 on 06 Mar, 2007 01:08
-
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
-
#187 by Jim on 06 Mar, 2007 01:19
-
Quote
hmh33 - 5/3/2007 9:08 PM
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
The engine exploding is what could take out the stack -
#188 by rfoshaug on 06 Mar, 2007 14:36
-
A quick question that comes from a discussion on another forum:
As the shuttle lifts off the pad, it translates a bit in the direction of the tank (north). I'm not talking abot the "twang" but the first few seconds after liftoff.
It can be seen here: http://youtube.com/watch?v=2Ok3-_K3XUU (28-31 seconds into the video).
What is the reason for this translation, and does it happen on every shuttle launch? -
#189 by kneecaps on 06 Mar, 2007 15:48
-
Quote
Jim - 6/3/2007 2:19 AM
Quotehmh33 - 5/3/2007 9:08 PM
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
The engine exploding is what could take out the stack
My understanding is this situation causes the tubopumps to overspeed and fly apart (which is obviously very bad). -
#190 by Jorge on 06 Mar, 2007 16:12
-
Quote
rfoshaug - 6/3/2007 9:36 AM
A quick question that comes from a discussion on another forum:
As the shuttle lifts off the pad, it translates a bit in the direction of the tank (north). I'm not talking abot the "twang" but the first few seconds after liftoff.
It can be seen here: http://youtube.com/watch?v=2Ok3-_K3XUU (28-31 seconds into the video).
What is the reason for this translation,
The SSMEs are on the orbiter, which is on the side of the stack, and are gimballed to point through the stack c.g. This results in a component of thrust toward the ET.Quoteand does it happen on every shuttle launch?
Yes.
--
JRF -
#191 by rfoshaug on 06 Mar, 2007 16:26
-
Thank you. That was what I thought.
-
#192 by edkyle99 on 06 Mar, 2007 16:45
-
Quote
Jorge - 6/3/2007 11:12 AM
Quoterfoshaug - 6/3/2007 9:36 AM
A quick question that comes from a discussion on another forum:
As the shuttle lifts off the pad, it translates a bit in the direction of the tank (north). I'm not talking abot the "twang" but the first few seconds after liftoff.
It can be seen here: http://youtube.com/watch?v=2Ok3-_K3XUU (28-31 seconds into the video).
What is the reason for this translation,
The SSMEs are on the orbiter, which is on the side of the stack, and are gimballed to point through the stack c.g. This results in a component of thrust toward the ET.Quoteand does it happen on every shuttle launch?
Yes.
--
JRF
Isn't this a momentary effect, in that the SSMEs and SRBs gimbal to offset each other's non-X-axis (vertical at liftoff) force components shortly after liftoff?
- Ed Kyle -
#193 by nathan.moeller on 06 Mar, 2007 17:07
-
A good reference point to watch the horizontal translation of the vehicle is the lightning protection tower. You see the tower pass through the gap between the orbiter and ET about 5 seconds into the flight.
-
#194 by Jim on 06 Mar, 2007 17:39
-
Quote
edkyle99 - 6/3/2007 12:45 PM
QuoteJorge - 6/3/2007 11:12 AM
Quoterfoshaug - 6/3/2007 9:36 AM
A quick question that comes from a discussion on another forum:
As the shuttle lifts off the pad, it translates a bit in the direction of the tank (north). I'm not talking abot the "twang" but the first few seconds after liftoff.
It can be seen here: http://youtube.com/watch?v=2Ok3-_K3XUU (28-31 seconds into the video).
What is the reason for this translation,
The SSMEs are on the orbiter, which is on the side of the stack, and are gimballed to point through the stack c.g. This results in a component of thrust toward the ET.Quoteand does it happen on every shuttle launch?
Yes.
--
JRF
Isn't this a momentary effect, in that the SSMEs and SRBs gimbal to offset each other's non-X-axis (vertical at liftoff) force components shortly after liftoff?
- Ed Kyle
Correct. Also the stack flies at an angle of attack, so it isn't completely zeroed out.
the translation is sometimes referred to a "walk". -
#195 by astrobrian on 06 Mar, 2007 21:45
-
The SSME thrust goes through the CG of the orbiter I thought, not the entire stack.
-
#196 by Jim on 06 Mar, 2007 21:51
-
Quote
astrobrian - 6/3/2007 5:45 PM
The SSME thrust goes through the CG of the orbiter I thought, not the entire stack.
It goes through the stack. The CG of the orbiter would cause a rotation of the whole stack -
#197 by aftercolumbia on 06 Mar, 2007 21:54
-
Quote
hmh33 - 5/3/2007 7:08 PM
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
The HPFT spins at about 35,000RPM, and the chamber pressure is 2900psia...trust me, it can take out the whole stack! -
#198 by joema on 06 Mar, 2007 22:37
-
Quote
aftercolumbia - 6/3/2007 4:54 PM
Quotehmh33 - 5/3/2007 7:08 PM
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
The HPFT spins at about 35,000RPM, and the chamber pressure is 2900psia...trust me, it can take out the whole stack!
A little more on this, the HPFT produces about 85,000 shaft horsepower, in the space of a large trash can. The pump discharge pressure is 8,000 psi (!!!), about 4x a SCUBA tank: http://www.nasa.gov/offices/oce/llis/0750.html
http://history.nasa.gov/SP-4221/ch6.htm
-
#199 by Antares on 07 Mar, 2007 00:34
-
Quote
kneecaps - 6/3/2007 11:48 AM
I don't have the amount here at home, but the LOX pump can ingest a rather large amount of vapor and still survive. Watch this space for an edit if you're curious.QuoteJim - 6/3/2007 2:19 AM
Quotehmh33 - 5/3/2007 9:08 PM
I have heard in a couple of places that if an SSME ingests vapours the turbopumps will fail catastrophically and cause loss of vehicle. Is this really true? Can see it damaging/destroying the engine but is it really violent enough to take out the whole stack?
The engine exploding is what could take out the stack
My understanding is this situation causes the tubopumps to overspeed and fly apart (which is obviously very bad).
Does anyone have the launch window charts for STS-118? I've been wondering what time of day it might go. I have summer classes again this year. Discovery managed to launch between terms for STS-121 and I had the ability to watch NTV via wireless internet during class and I'm wondering what's going to happen this time. If they delay a few days it won't be an issue as far as watching the launch. Landing is the only potential problem. If it's a night launch, it's a moot point.