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Author Topic:   Space shuttle launch roll program
thump
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posted 05-18-2007 12:38 PM     Click Here to See the Profile for thump   Click Here to Email thump     Edit/Delete Message   Reply w/Quote
Somebody had asked me why the shuttle has the roll program. Reading through the internet, I've found notes that it is to set orbital inclination. I thought that I had read somewhere, though, that it was so that the communications antennas would be facing earth and Houston. So my question is, which is correct?

Ben
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posted 05-18-2007 01:10 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
It's done for several reasons. The inclination/azimuth is really not one of them, because it could head that way no matter the orientation of the shuttle.

The main three reasons are:

  • So, as you said, the antennas, located mainly in an area above the cabin, have better line of sight.

  • Aerodynamic loading is less with the shuttle on the bottom.

  • So the astronauts have a view of the horizon out their window.

Ben
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posted 05-18-2007 01:16 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
Also, it is not so the antennas face Houston, but face the communication/tacking stations on the ground located on Merrit Island and New Smyrna beach.

kr4mula
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posted 05-21-2007 11:29 AM     Click Here to See the Profile for kr4mula   Click Here to Email kr4mula     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Ben:
Aerodynamic loading is less with the shuttle on the bottom.
If I remember (and can translate!) correctly what one of the NASA engineers told me, the difference this makes has to do with the position of the orbiter and the rest of the stack. With the shuttle (and its SSMEs) on top, it would essentially be "pulling" on the ET, putting a lot of stress (tension) on the mounts. With the shuttle on the bottom, it is "pushing" on the other components, with the resulting compressive forces being easier to design for, with regards to the interface.

sts205cdr
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posted 05-21-2007 11:58 AM     Click Here to See the Profile for sts205cdr   Click Here to Email sts205cdr     Edit/Delete Message   Reply w/Quote
More about the roll program from Ask The Expert:
The shuttle rolls to an inverted position just after launch so that it can point antennas on the top surface of the vehicle at ground tracking stations. While there are antennas on the lower side of the vehicle, they are blocked by the external tank and the solid rocket boosters.

As for the second part of your question, why not start out in this position in the first place? The answer stems from the fact that we are reusing facilities built for the Apollo program. We mate the shuttle with its tank and boosters in the Vehicle Assembly Building, and then it is transported to the launch pads along the crawlerway by the crawler/transporters, some of the largest tracked vehicles ever made. The crawlerways are specially constructed to handle the immense weight of the crawler, mobile launch pad, and the shuttle stack; but they have no place to turn around. So, whatever leaves the VAB for the pads ends up facing the same direction as when it left. The costs to add such a feature to the crawlerway are so high that it was much cheaper to turn the shuttle in the air than it was to turn it on the ground.

star61
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posted 05-21-2007 01:37 PM     Click Here to See the Profile for star61   Click Here to Email star61     Edit/Delete Message   Reply w/Quote
Begs the question, why did Apollo also have a roll program? It was after all a symmetrical tube.

star51L
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posted 05-21-2007 03:14 PM     Click Here to See the Profile for star51L   Click Here to Email star51L     Edit/Delete Message   Reply w/Quote
I believe it was to orientate the crew cabin to view the horizon during launch.

Ben
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posted 05-21-2007 03:42 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
I believe antennas are involved in all of the rolls to some degree. Even unmanned rockets have roll and pitch programs; including today.

MiliputMan
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posted 05-24-2007 07:02 AM     Click Here to See the Profile for MiliputMan   Click Here to Email MiliputMan     Edit/Delete Message   Reply w/Quote
This is what I understand about the roll manoeuvre.

The cheapest way to put something in space (satellite or shuttle) is at the equator while launching due East with an orbital inclination of zero degree (relative to the plane that cuts the earth at the equator). Why is that? Well, at the equator the rotation speed (relative to a fix point in space) is at its maximum and that is free speed that your ship will not have to generate. That would obviously put your ship in an orbit that fly strait above the equator. Logically we want to fly above more than a single strip of land and that's where the roll is used. If you need to fly over land that is half way toward the North Pole you would then have an orbital inclination of 45 degrees. By doing so you lose some of the earth initial speed and your launch would cost more money or you would have to compromise on weight to accelerate faster. The maximum orbital inclination (unless you have money to throw out the window) is then 90 degree and that would put your ship in a polar orbit, which is the most expensive one. So, unless there's a good reason, you always want to launch with as little orbital inclination as you can.

Where is the roll in all that? Normally, your ship on the launch pad is always pointing in the same direction, unless you have a fancy launch pad that can pre-orient the ship before takeoff. This means that the ship will have to rotate (roll) early in the flight to orient itself in the plane of the orbit.

Why is the shuttle rolling if the cheapest way to launch is at an orbital inclination of zero? It all depends on the location of your launch pad. Let's start by saying that the further you are launching from the equator the bigger your minimum orbital inclination will be. Like I mentioned before, at the equator the minimum orbital inclination you can achieve is 0 degree but at the poles the minimum is 90 degrees. This is because you can only achieve an orbit where the orbit plane is cutting the planet through it center of mass. In the case of the earth, since it's fairly round and the density is not uneven, orbit planes would cut the planet in half. The location and orientation of the shuttle launch pad and the target orbital inclination for each mission will, most certainly, force the shuttle to roll to set his orbital plane. The distance from the equator is also why the ISS orbital inclination is 51.6 degrees (far from zero). This is because of the Russian launch pad location is very far from the equator and the minimum orbital inclination that can be achieved from there is 51.6 degrees.

Scott
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posted 05-24-2007 08:54 AM     Click Here to See the Profile for Scott   Click Here to Email Scott     Edit/Delete Message   Reply w/Quote
Thank you everyone for this fascinating information.

I was wondering: Is there any advantage to putting humans in polar orbit? I know Mike Mullane wrote in his book that this was planned for one of his Shuttle missions (but was cancelled for safety reasons, because populated areas existed under the proposed launch path).

OV-105
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posted 05-24-2007 11:57 AM     Click Here to See the Profile for OV-105   Click Here to Email OV-105     Edit/Delete Message   Reply w/Quote
There is no advantage to having humans in a polar orbit. The advantage is that the shuttle's payload would cover more of the land mass than from a launch from KSC. The flight STS 62-A would not launch over populated areas. I would have went over the Pacific. If you were to do the same incline from KSC SRB sep and ET sep would happen over populated areas.

kr4mula
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posted 05-24-2007 12:59 PM     Click Here to See the Profile for kr4mula   Click Here to Email kr4mula     Edit/Delete Message   Reply w/Quote
Polar orbit is only useful for humans if they're looking at the Earth. The higher the inclination, the more ground goes underneath you, eventually. The original planned shuttle polar orbital missions, launched from Vandenberg, were necessary for the DoD payloads that could benefit from such a position (e.g. spy satellites).

Ben
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posted 05-24-2007 01:06 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
The shuttle or any vehicle does not have to roll to reach a certain inclination; that's what I was trying to convey in my initial post. It could get into any inclination in any orientation as long as you steer properly.

Thus, I think the roll should be seen as independent of inclination.

Just as an example, if the shuttle were launching due south, then no, it would not have to roll to put the shuttle on the bottom. But if they wanted to launch south with the shuttle on top, it would roll 180 degrees.

Danno
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posted 05-24-2007 03:21 PM     Click Here to See the Profile for Danno   Click Here to Email Danno     Edit/Delete Message   Reply w/Quote
Did the Delta Heavy launch vehicle roll after it was launched?

Ben
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posted 05-24-2007 04:17 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
I would say D4H rolled very slowly, very gradually over a whole minute. It stayed in the same orientation for quite a while, pitching over without changing orientation at first. But by the time it was 'way up' it had changed.

I think the question is not so much "why does the shuttle roll?" - it rolls to put the shuttle on the bottom - but "why does the shuttle have to go on the bottom?"

Lunar rock nut
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posted 05-24-2007 07:10 PM     Click Here to See the Profile for Lunar rock nut   Click Here to Email Lunar rock nut     Edit/Delete Message   Reply w/Quote
Here is the answer to this same question asked elsewhere in 2003. The answer was provided via courtesy of Aaron Brown, a NASA aerospace engineer.

Flying Dutchman
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From: Nieuw Vennep
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posted 02-17-2010 04:55 PM     Click Here to See the Profile for Flying Dutchman   Click Here to Email Flying Dutchman     Edit/Delete Message   Reply w/Quote
I know that the reason that the shuttle rolls on its back is because of the fact that the vehicle is accelerating through the area of maximum dynamic pressure. Throttling back to 64% of rated thrust.

But does anyone know why the commander has to announce "Roll Program" to mission control and that Mission Control confirms "Roger Roll [Endeavour]"? What is the reason for this?

Editor's note: Threads merged

Jay Chladek
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posted 02-17-2010 06:05 PM     Click Here to See the Profile for Jay Chladek   Click Here to Email Jay Chladek     Edit/Delete Message   Reply w/Quote
All the reasons are valid ones. The comm antennas are on top, so the heads down position is to allow for better data transfer to the MILA antenna at KSC. About 6 minutes into the flight, the orbiter rolls to a heads up position to acquire with the TDRS satellites for communications. Apparently stresses on the orbiter to ET struts aren't really that bad (nor are the stresses on payloads or the crew in the cabin), so a shuttle could roll heads up for a little wing borne lift. Indeed I believe that was a consideration for Vandenberg launches to give them a little more lifting capacity, but of course it was never done as SLC-6 was never used.

Apollo had similar communication concerns as I believe the antennas were on one side of the rocket. The horizon view typically wasn't that big a concern there as only the center seat had a view until the BPC was blown off, giving the CDR a view out the left side window.

Flying Dutchman
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posted 02-18-2010 02:11 PM     Click Here to See the Profile for Flying Dutchman   Click Here to Email Flying Dutchman     Edit/Delete Message   Reply w/Quote
Yeah right. I know why the roll program is done.

But does anyone know why the commander has to announce "Roll Program" to mission control and that Mission Control confirms "Roger Roll [Endeavour]"? What is the reason for this?

teopze
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posted 02-18-2010 04:25 PM     Click Here to See the Profile for teopze   Click Here to Email teopze     Edit/Delete Message   Reply w/Quote
Maybe to give the crew an impression that they are needed at this stage.

Ben
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posted 02-18-2010 11:04 PM     Click Here to See the Profile for Ben   Click Here to Email Ben     Edit/Delete Message   Reply w/Quote
I think it is simply to acknowledge all is well on both ends, just like the throttle up call.

moorouge
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posted 02-24-2010 02:20 PM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
This acknowledgment of an event caused huge problems in the UK at the time of the Challenger disaster. Many of the 'experts' in the media interpreted the response from Challenger, "Roger, go at throttle up", as being when the engines were throttled up and that this was the cause of the explosion. Of course, the engines had been throttled up some seconds before and the calls were simply to acknowledge that, as far as this aspect of the flight was concerned, all was well.

All times are CT (US)

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