The shuttle reentry is upside down? Is this the only angle of attack at which the shuttle can re-enter? I guess the answer is self-evident, or else they’d do something else, of course! Still, any Dopers have more info to share about this? Like, wouldn’t a nose dive at a steep angle work, too? - Jinx
Upside-down? What are you talking about? The shuttle comes in nose-first, with the nose raised somewhat so that the heat is taken by the special tiles that coat its underside.
CurtC, the news (and NASA) described that the shuttle comes into the upper reaches of the atmosphere upside down and then, at some point, fires some repositioning thrusters (for lack of the proper term) to rotate the craft right-side up. At that point, it is placed in the proper attitude for the remainder of the return flight home.
Also, one Shuttle astronaut interviewed said that the shuttle makes a series of “S” curves to lose speed before landing. This surprised me, too. The media keeps showing it simply as a straight-line*(*2-D projection of the actual trajectory over a US map) trajectory
Perhaps some other SDopers can share what they know about the rotation of the craft and/or “S” curves? -Jinx
The goal of re-entry is to slow down. The high angle of attack, the nose up attitude, increases lift and drag. If the nose were pointed down the low drag would let speed build up and friction would burn up the ship. Also note that only the bottom and some of the front surfaces are covered with heat resistant tiles.
Hmm…could this explain it? Perhaps the media’s description of this rolling procedure MEANT while breaking out of the sustained orbit? (i.e.: the firing of “braking rockets” the media keeps saying - or retro rockets, I assume is equivalent?) And then, what I heard NASA officials say later, perhaps in lesser detail, may have been misinterpreted by me in light of what I heard said previously? - Jinx
The black tiles are not the only heat resistant tiles, as white ones, or a material replacing the white tiles, covers the rest (top of shuttle)
It starts upside down, but before re-entry, rockets get it positioned…I believe the ‘upside down’ posture allow the rockets to spin it to the precise attitude by just turning it around.
The braking engines are at the back so they have to start the process backwards. The small thrusters on the nose are just for fine maneuvering.
In space, the shuttle usually travels upside down and backwards. This is for two main reasons. First, flying “upside down”, or having the belly facing space, exposes the thickest and most durable parts of the shuttle (ie the thermal tiles) to the “elements” of space such as micrometeorites, heat, radiation, etc… This not only protects the more delicate parts of the shuttle, but shields the astronauts working in the payload bay from dangerous radiation and debris. The advantage to flying backwards is mainly that the shuttle is always in a ready position to quickly deorbit.
To come down, the shuttle has to lower its orbit enough to allow air friction to take hold and “pull it back” to earth. This is accomplished using a retrograde OMS (Orbital Maneuvering System) burn, which slows the shuttle down, thus lowering its orbit. Once this is completely, the shuttle does a 180, so that its heat-resistant belly is now facing the earth again. From there they initiate 2 (?) giant S turns to slow down before coming in for a final approach, during which two sonic booms are generated as the shuttle drops below Mach 1 (one from the nose, one from the tail). At this point the shuttle begins flying like a glider, and lands just a few minutes later.
I can see that they make S-turns just before landing, to give themselves some slack in the approach. If they planned the approach to be straight in, and there was a larger headwind or something, they might otherwise come up short, which would be a major problem on a dead-stick bird like the shuttle.
About the two sonic booms - I can see how there could be dual shock waves, from the nose and the tail, but wouldn’t those then be separated in time by about a tenth of a second? I would think the source of the two booms would instead be from two different points on the S-turn trajectory that it’s taking.
I’m not quite sure I understand your question, Curt. The whole shuttle slows through Mach 1 at the same time, so both shockwaves are generated simoultaneously. Even though they’re 37 metres apart (between nose and tail), at the speed it’s going they both reach the observer at practically the same time, plus or minus a few microseconds.
Shock waves are generated any time a body is traveling above local Mach 1. It isn’t passing through Mach 1 that generates a sonic boom.
The S-turns aare the shuttle’s way of adjusting glide range. When the shuttle rolls to one side it increases its sink rate. It could also increase its sink rate by an increase in angle of attack. It turns that an increase in AOA produces a big increase in skin tenperature. NASA found out that you can get a decent increase in decent rate without the big increase in skin temperature by a roll maneuver. FWIW
MonkeyMensch already pointed out that the sonic boom occurs anytime it’s flying supersonic - think of the shock wave as the same thing as the bow wave from a boat.
But if it’s flying just over the speed of sound, which would be near the time of landing and I assume at the time when someone might hear two sonic booms, the shock from the nose and the one from the tail would be separated by over 100 milliseconds, or less than a tenth of a second. Of course, my point was that this is too close together to be the twin booms that I’ve heard about.
Actually, from the moment the last engine shuts down the shuttle is flying as a glider. No reason you can’t glide at Mach whatever. After the de-orbit burn you have some manuvering thruster fire, but that’s to change attitude and orientation, not to hold the thing up.
“S-turns” can beused by aircraft of all size to adjust an approach. They aren’t unique to the shuttle
THe shuttle has 2 sets of engines, the main OMS (Orbital menuvering system) and the RCS (reaction control system). The OMS is used to change orbit & slow down to reenter and are in the back of the shuttle. The RCS is throughout the craft and is used mainly for stearing (angling the shuttle).
During orbital flight the shuttle used to fly ‘upside down’ with nose pointed forward and cargo bay doors open and the bay pointed at the earth. Due to some impacts with space junk the SS now orbits ‘upside down’ with the nose at right angle to the orbital direction (a wing in in the direction of travel). The trailing cargobay door is opened fully while the leading cargobay door is 1/2 open to protect the cooling coils from impacts.
For the deorbiting burn the shuttle must swing around so the tail is facing in the direction of the orbital path. THe OMS fires to slow the shuttle. THe shuttle turns around using the RCS and gets in position for reentry (something like nose up 20-36 degrees IIRC, the actual tollerance is much smaller but I can’t remember the actual number).
When in the atmosphere the RCS is still active and totally under computer control. It is fired to correct any any problems with the angle it is comming in. (There is talk about how the Columbia was firing RCS engines before it broke apart). S-turns are made to further blead off speed. Most of this is automated but the landing is still done manually.
True, but it’s not ‘flying like a glider’ during most of re-rentry. It’s falling like a rock. (Sounds like fun, doesn’t it? :eek: )
This cannot be correct, can it? Are you saying, for example, the Concorde SST plane made one continuous sonic boom for almost the entire duration of a trip from NY to Paris, let’s say? I’ve never heard or read anything to indicate this is true.
To the best of my knowledge, the sonic boom is strictly the result of crossing the sound barrier. Once the sound barrier is crossed
from sub-sonic to super-sonic, a vehicle does not continue to make a sonic boom when flying above the speed of sound.
Maybe some others have additional information to add? - Jinx
Here is a link.
No, Jinx, that’s right. Nice link carnivorousplant. From that link: *
The strongest sonic boom ever recorded was 144 pounds per square foot and it did not cause injury to the researchers who were exposed to it. The boom was produced by a F-4 flying just above the speed of sound at an altitude of 100 feet. *
Why don’t they ever invite me to any of these sort of things!
Even rocks can glide if you throw them fast enough. And CurtC I’ve heard the shuttle’s sonic boom and it is audibly double. Think ba-boom rather than boom…boom. FWIW.
I’ve also heard the shuttle’s sonic boom more than once and can back this up. I usually hear it as boomBOOM but then it often startles me out of sleep. (You’d think I’d learn to check when they’re gonna be landing at Edwards …) In any case, I always know what it is because it’s definitely two distinct booms.
:smack:
Sorry, I wasn’t thinking when I wrote that about sonic booms being generated as it passes Mach 1. 11PM is not a good time to be thinking about aeronautical engineering. 
You’re absolutely right, whenever it is traveling faster than Mach 1 it generates a continuous shockwave, aka sonic boom. It only sounds like a “boom” because the wavefront passes across the observer in just a few seconds.
Same goes for the whole microseconds thing. For whatever reason I was thinking of light, not sound :smack:
You beat me to it
By flying like a glider, I meant using its aerosurfaces to steer rather than its RCS.