What does the shuttle roll program do?

[steve_slitheen]

Hi all, have been enjoying the fantastic coverage of STS-121 recently. I think I know a lot about the shuttle, but a friend asked me a question today that I couldn't answer, so I promised to find out for him. So here it is:<br /><br />Why does the shuttle roll after clearing the tower? Is it to set the orbital inclination or are there other reasons? <br /><br />Thanks in advance!

 

[CalliArcale]

Slitheen? Give Steve his skin back right now! <img src="/images/icons/tongue.gif" /><br /><br />The purpose of the roll program is twofold. Firstly, it orients the vehicle in the right direction to get into the right orbit (inclination, just as you guessed). Secondly, it rolls the vehicle such that it is climbing head-down. This is more stable during the first part of the ascent, through the dense lower atmosphere. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[steve_slitheen]

ok, so I guess if you looked closely enough on different missions you could observe different amounts of roll, dependent on the inclination they are aiming at. <br /><br />Supplementary question - do all launches include a roll, or are there any practical orbital inclinations where the stack (not necessarily a shuttle) could simply lift off before lying on its side? I guess local geography around the Cape pads has a lot of influence on the starting position, but I could imagine that if 39A/B were positioned differently then less roll would be needed.

 

[henryhallam]

Repositioning the pads would probably allow for a reducted/eliminated roll for a given orbit tracjectory, but it would be a big hassle and I don't think the roll has much penalty on payload capability, after all the stack is still thrusting upwards.

 

[vogon13]

I think the Vandenberg shuttle pad was oriented for a no-roll to polar orbit launch.<br /><br />But I am going back 25+ years on my recollection and would appreciate a firm answer either way.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[kurtwagner]

Isn't one other factor regarding the roll program to unmask certain orbiter telemetry antennae that the ET blocks unless the stack is rolled accordingly? I believe I read that somewhere, but can't recall the source.