The HabForum

I found a fantastic article which tells in the astronauts' own words what it's like to before and during launch. They describe their emotions, physical sensations, everything. Very cool!
http://www.space.com/missionlaunches/fl ... 21006.html

I'll have to check the article out later after i get home from school. also dont forget the shuttle is scheduled to launch today at 3:46 pm est. For those of you like me who dont get NASA TV , Cnn ussualy has coverage but be patient because it probably wont start till about a minute before launch. Or if you have real player on your computer NASA TV is available on the web at the United Space Alliance sight among others. So lets keep our fingers crossed that it wone be delayed again.

Well i hope i wasn't the only one who got to see the shuttle launch today. The new view from the externally mounted camera was great. Unfortunately it was only a clear picture till SRB seperation. It appeared to be blocked up by debris following that or it may have just been glare from the sun its not really clear what happened. But anyway it was a great shot you could see tue right SRB and the orbiter as well as some of the external tank from the camera view. And ofcorse you could see some engine exhaust and the east coast of florida below. And CNN actually gave coverage till the shuttle reached space with commentary from a past shuttle commander. Actually it was some of the best shuttle coverage ive seen in a long time.

I missed it, sadly. I couldn't break away from work or I would have watched it...

Thats what VCR's are for. I didnt get to see it live either but i taped it and watched when i got home.

But what an AMAZING article... I gotta save that one for the future. Great stuff!!!

Oh i knew i was forgetting to do something i guess i should read it shouldnt i.

Well your right that was a good article and brought up a couple things that even i didnt know. Like the part about using the bathroom on the pad before boarding the shuttle. And that the trusters on the nose fire during the ascent to orbit for course corrections i thought the main engines gimbling handeled it all.

wow... i too thought the tvc gimbals on the ssme's controlled ascent trajectory... learn something new every day

Well i may have read it wrong but that was the impression i got.

i'm sure your right because thinking about it now i dont see the tvc controlling it by itself... and i dont believe the control surfaces are functioning during ascent ( or are they? not sure.... are the hydraulics on during ascent? i guess i should know this lol), so i guess using the rcs thrusters is a good idea

The hydraulics are on during ascent but not for the control surfaces. During ascent they are used to control the engine gimbals. I remember at camp as pilot having to power up the apu's for controlling the engine gimbals during ascent.

The NASA Shuttle reference describes the roles of the TVC and control surfaces during first stage ascent:

During the first 90 seconds of flight, the flight control system provides load relief by making adjustments to reduce vehicle loads at the expense of maintaining a precise trajectory profile. A special schedule of elevon position with respect to velocity is followed to protect the wings from excessive loads and to hold the body flap and rudder/speed brake in place. The surface position indicator displays the position of the aerosurfaces. To keep the dynamic pressure on the vehicle below a specified level, on the order of 580 pounds per square foot (max q), the main engines are throttled down at approximately 26 seconds and throttled back up at approximately 60 seconds. This also reduces heating on the vehicle. Because of the throttling at this time, the term ''thrust bucket'' evolved. Maximum dynamic pressure occurs shortly after throttle up.

Thrust vector control is the hub of flight control. In the ascent phase, the four ascent thrust vector control drivers respond to commands from the guidance system. Thus the TVC commands from guidance are transmitted to the ATVC drivers, which transmit electrical signals proportional to the commands to the servoactuators on each main engine and solid rocket booster.

Thrust vector control closes the acceleration and rate loops within the outer attitude loops to generate body axis attitude error rates, which eventually are nulled out by the main engines and SRBs. The main propulsion system processor of the digital autopilot converts body axis and attitude error signals generated in TVC into pitch and yaw nozzle deflection commands for the main engines. The SRB processor of the DAP accomplishes the same functions as the MPS, except that it is referred to as rock and tilt instead of pitch and yaw.

The SRB pitch and yaw rate gyros are used exclusively during first-stage ascent, and control is switched to the orbiter rate gyros when the SRBs are commanded to null in preparation for separation. Pitch and yaw axes and a combination of rate, attitude and acceleration signals are blended to effect a common signal to the main engines and the TVC for both SRBs. In the roll axis, rate and attitude are summed to provide a common signal to both the main engines' and SRBs' TVC.

It says nothing about the RCS until SRB seperation:
At SRB separation command, a three-axis attitude hold is commanded by the reaction control system for four seconds. When the SRB separation command is received, the SRB nozzles are positioned to null, and the flight control system is switched to the orbiter rate gyro assemblies. Four seconds after SRB separation, second-stage main engine guidance takes over.


Second stage guidance is, of course, to reach proper conditions for MECO, after which the RCS (DAP) takes over once again.

Anyway, I don't see any mention of the RCS being used to control trajectory during first stage ascent. If the MPS uses RCS thrusters along with TVC and control surfaces to control attitude, it isnt mentioned.

Well that was verry intresting thanks for the info.