a Q regarding a Space Shuttle launch

[Drop and Stop]

I have always been intrigued as to why, during the initial acceleration off the launch pad, the Space Shuttle rolls around 180 degrees. I’ve checked the NASA site <A HREF="http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_mes.html#mes_count" TARGET="_blank">http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_mes.html#mes_count</A> which describes a typical launch.

It says:

First-stage ascent extends from SRB (Solid Rocket Booster) ignition through SRB separation, or SRB staging. The sequence of major guidance, navigation and control events proceeds as follows: The vehicle lifts off the pad 0.3 second after SRB ignition, rising vertically in attitude hold until the SRBs' nozzles clear the lightning rod tower by approximately 41 feet. The vehicle begins a combined roll, pitch and yaw manoeuvre that positions the orbiter head down, with wings level and aligned with the launch pad. The orbiter flies upside down during the ascent phase. This orientation, together with trajectory shaping, establishes a trim angle of attack that is favourable for aerodynamic loads during the region of high dynamic pressure, resulting in a net positive load factor, as well as providing the flight crew with use of the ground as a visual reference. By about 20 seconds after lift-off, the vehicle is at 180 degrees roll and 78 degrees pitch.

My question’s are:
Why does it have to roll through 180 degrees?
Why can’t they just turn the Shuttle around on the launch pad?
Could it possibly be because of the way the Shuttle comes out of the hangar(ie.orientation)?
Does the Shuttle have to head/climb out over the Atlantic? (I believe the Solid Rocket Boosters splash down in the Atlantic to be reused).

Any takers?

[pax domina]

Can confirm that the solid rocket boosters do fall in to the Atlantic. Before the most recent launch NOAA Weather Radio was broadcasting a special marine notice advising boaters to stay out of a specified "drop zone" around the scheduled launch time.

Good luck with your other queries . . . wish I still knew some people working at the Cape who I could ask to help you!

[Mike Echo]

Just guessing but I would suspect economics came into it. The Shuttle launch pads were originally built for the Saturn 5/Apollo rockets and modified for the Shuttle launches. The ramp up to the pads was laid out for the Saturn 5 with no sharp bends. The Saturn 5 I don't think had quite the same aerodynamic limitations as the Shuttle+boosters+external tank. Having seen the structures I'd hate to think what it would cost to re-orientate the pads.

There are I believe at least three reason why they take off to the east.
1) Taking off to the west over the Orlando Theme parks is not good public relations.
2) I understand that taking off heading east as near to the equator as possible they gain some speed from the earths rotation- less fuel required.
3) Obviously it is easier to drop off the unwanted bits into the atlantic and makes recovery of the boosters easier.
Someone can probably correct me, but I think NASA have already tried rolling again later in the flight to put the Shuttle on top of the tank but I didn't understand why?
Any other thoughts?

[This message has been edited by Mike Echo (edited 05 December 2000).]

[A Very Civil Pilot]

Whenever I've seen pictures of the SS in orbit, it is with its roof facing towards the earth. I don't know if that's the cause or effect of the turn.

Just off the top of my head the Thrust: Drag couple, if similar to a conventinal a/c, would indicate a pitch up moment, so perhaps the turn is to compensate for this.

[This message has been edited by A Very Civil Pilot (edited 08 December 2000).]

[G-OOFY]

Found out that thirty seconds after take-off if anything happens (other than an explosion) the landing alternate is.....

.........Morroco!

I couldn't believe it but apparantly it would take too much time/altitude to turn it around.

[inverted flatspin]

I seem to recall reading about this many years ago and if memory serves correctly the Center of Gravity shifts quite rapidly in the early launch phase because of the massive fuel burn and the roll on its back is weight and balance related.

[Bear Cub]

I'm led to believe that the roll is also for "Comms"...where are the aerials (or antennas - as it's American).

------------------
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Support the right to arm Bears!!

[773]

The reason why the doors open is because it lets off any unnecessary heat in the cargo bay caused by surface heating produced by the sun. Pretty smart idea when you consider that they carry many million dollars worth of equipment.

If anyone has another reason as to why the doors open I would very much like to hear it, cause that's what I was told.

[Bullethead]

G’day D&S,
If you re-read the sentence in your post that begins “This orientation…….” I think you will find most of the answers you want. After the SS has performed the roll maneuver it is effectively on the upside of a loop, a very large loop, that eventually puts it into orbit. As the statement says the crew have a good visual reference and a positive ‘g’ loading. Much more comfortable than having to do an outside loop.
All orbital launchers gain considerable advantage, be it payload or increased fuel load, by launching to the east, in the direction of the earth’s rotation, and as close to the equator as possible. As an aside even jet airliners gain a small advantage if they happen to flying east at low latitudes. The speed of the airliner around 500kts plus the rotational speed of the earth at the equator 1000kts gives a velocity of 1500kts. This to a small degree counters the effect of gravity so that although the mass of the airliner is unchanged the weight is effectively reduced by about 1%. There is a measurable fuel saving associated with this. Lookout if you happen to be flying west. It is all explained in CH13 of the latest edition “Mechanics of Flight” by Kermode.
Mike Echo has a good point about the economics of rebuilding the launch site.
Regards.
:)

[Jim lovell]

I believe the 180 degree roll manouver is to place the shuttle in the correct orientation for orbit. Depending on what apogee and perigee need to be obtained during a shuttle mission is all dependant on the orientation of the shuttle as it climbs- e.g 90 degrees above horizon/ 70 degrees above horizon etc etc etc- it differs. Most shuttles only orbit at relatively low altitudes- 300 km or so and although the altitude of the orbit can be changed/modified while in orbit i think it all comes down to the orientation at liftoff/climbout. And yes the SRB'S do splashdown in the Atlantic to be reused again for a future mission- the fuel tank however does not and burns up on re-entry.

[Drop and Stop]

Cheers everybody. It all makes a lot of sense. Would anybody know how many missions your average astronaut (pilot) would complete in his/her career?

Nasa would not be short of candidates, but their training must cost a fortune.

[Jim lovell]

Bit of a guess here but i'd say about 3-4 missions in a shuttle pilot's career is about the max. You have to fly at least 2 missions as pilot and then you get promoted to Commander- which you'd probably command about 2 missions. If memeory serves me right i think Nasa's most experienced pilot of all time was John Young??- He flew the shuttle twice, went to the moon twice and went up on a Gemini mission( 5 flights in total)

[Ford Fairlane]

The shuttle orbits facing earth so as to minimise possible damage caused by collisions with space junk.

I guess it also gives the crew a nice view of home.

Would it be feasible to put some long range tanks in the cargo hold and go for a trip around the moon? Maybe even take a moon lander?

[This message has been edited by Ford Fairlane (edited 07 December 2000).]