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SpaceShipOne and reentry heat
I'm just an average person with an English degree, so I'm unfamiliar
with the science and physics and space craft reentry, so this is likely a very stupid question. But it's my uneducated understanding that returning space craft, like all objects entering our atmosphere, super-heat from the friction of falling through our atmosphere. Which is why all crafts from Apollo to the space shuttles must have carefully crafted heat shields and enter at a VERY narrow angle to prevent either burn-up or "skipping" off the atmosphere. Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Thanks! Liam |
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SpaceShipOne and reentry heat
Doesn't it also need the
observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Not going nearly as ast, mach 3 instead of mach 25, and from lower/deeper in the atmosphere. And when it activates it's novel "shuttlecock" drag system, it slows the craft down in a place where the air is very very thin, by the time it hits thicker air, it has already slowed considerably. There IS reentry heating, but orders of magnitude below what a capsule or shuttle sees. The goofs who talk about the same craft becomeing orbital don't "get it" about the SS-1: it was designed for a very narrow mission, which it obviously performs well. To make the leap to orbit, will require a redesign that takes into account the much much more difficult factors involved. The system may look similar, in the way a forumula one race car has four wheels like your family commuter. But really it's a different breed of cat altogether. |
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SpaceShipOne and reentry heat
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SpaceShipOne and reentry heat
LRW wrote:
I'm just an average person with an English degree, so I'm unfamiliar with the science and physics and space craft reentry, so this is likely a very stupid question. But it's my uneducated understanding that returning space craft, like all objects entering our atmosphere, super-heat from the friction of falling through our atmosphere. Which is why all crafts from Apollo to the space shuttles must have carefully crafted heat shields and enter at a VERY narrow angle to prevent either burn-up or "skipping" off the atmosphere. Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) SpaceShipOne dropped down from a height of 100km, while a shuttle drops down from a height of some 400km AND has additionally a horizontal velocity of some 8km/s. And an Apollo spacecraft dropped down from some 400000km. That's in both cases a *LOT* of kinetic energy more to kill than SSO had to. |
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SpaceShipOne and reentry heat
In article you wrote:
snip Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Basically, as it's going much, much slower. Craft reentering from low-earth orbit come in at around mach 30. The SS1 reenters at mach 3 (?). Heating is more or less proportional to the cube of speed, so the heating will be around a thousandth of that coming in from orbit. The RS-71 flew at mach 3, and was fine with just a titanium skin. If you tried to put a titanium skin on a craft coming in at orbital velocities, you get little more than a bright shower of sparks as it atomises. |
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SpaceShipOne and reentry heat
In article , LRW wrote:
I'm just an average person with an English degree, so I'm unfamiliar with the science and physics and space craft reentry, so this is likely a very stupid question. But it's my uneducated understanding that returning space craft, like all objects entering our atmosphere, super-heat from the friction of falling through our atmosphere. Which is why all crafts from Apollo to the space shuttles must have carefully crafted heat shields and enter at a VERY narrow angle to prevent either burn-up or "skipping" off the atmosphere. Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Thanks! Liam It's all a matter of speed. Vehicles returning from the moon (Apollo) are doing about Mach 35; Orbital vehicles are doing about Mach 25; SpaceShip 1 did about Mach 3.5 today. Reentering vehicles are using the atmosphere to absorb their kinetic energy (velocity) and slow them down to touchdown speed at ground level - and that's what generates the re-entry heat. The faster you're going, the more energy there is to dissapate, the more heat is produced. So SS1 has to deal with some heating, true - but it's not the same level of heating as a shuttle or Apollo spacecraft. And since it's on a ballistic (suborbital) trajectory, it can't "skip" off the atmosphere - it's not going fast enough or heading in the right direction to do that. SS1 does have to pay attention to it's re-enty profile and make sure it can handle the heat and ends up back at the runway - but the constraints are milder than shuttle or Apollo dealt with. |
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SpaceShipOne and reentry heat
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SpaceShipOne and reentry heat
"LRW" wrote in message
om... Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Basically, SpaceShipOne was not moving all that fast when it left the atmosphere. If something is in orbit, it is moving around Mach 25 (compared with SSO's top speed of less than Mach 3). |
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SpaceShipOne and reentry heat
In article ,
LRW wrote: Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? If not, why? In simple "Physics for English Majors" language. =) Mostly, because it didn't go very high and wasn't in orbit, so it reentered at quite low speed. To reach an altitude of 100km, which SS1 (just barely) did, it needed a speed of 1.5-2km/s (depending on how steep the ascent was), and it would have come back down at around the same speed. Orbital velocity, on the other hand, is 8km/s, and return from the Moon brings you in at 11km/s. Moreover, a lot of the reentry issues scale with kinetic energy, which is proportional to the *square* of velocity, so 8km/s is not four times as bad as 2km/s, it's more like sixteen times as bad. Between the low speed and the clever design of SS1, the reentry was quite a mild one. The designers couldn't quite ignore the heating issue, but they didn't have to do anything very elaborate about it. If SS1 had gone two or three times as high, reentry heating would have needed more attention. If SS1 had been moving fast enough horizontally to be in orbit, reentry heating would have needed a *lot* more attention. -- "Think outside the box -- the box isn't our friend." | Henry Spencer -- George Herbert | |
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SpaceShipOne and reentry heat
On 21 Jun 2004, LRW wrote: [snip] But it's my uneducated understanding that returning space craft, like all objects entering our atmosphere, super-heat from the friction of falling through our atmosphere. [snip] Now, correct me if I'm wrong, but didn't the commercial SpaceShipOne reach the very edge of the atmosphere? Doesn't it also need the observe the same careful considerations for reentry? Airplanes don't superheat. Baseballs and Skydivers don't either. It's all about air friction. If you are moving through the air, you have to push it aside to get through. The faster and more energetically you do this the more you will heat it (and it will heat you). Spacecraft in orbit superheat on return because they are moving VERY fast as they enter the upper atmosphere. Spaceship one is using a trajactory that just barely rises above the atmosphere... and has no "ground speed" at all. So instead of smashing into the upper atmosphere at 5 or 6 miles per second (22,000 miles per hour) like a space-shuttle, Spaceship One hits the upper atmosphere at around 1,200 miles per hour. The energy that it's hull must absorb/shed is therefore only about 5% as much. This is easy to handle with normal aircraft materials. The numbers I've just given are really rough. But they're not completely wrong. I hope this helps. Gene Pharr New Orleans, LA -- Alcore Nilth - The Mad Alchemist of Gevbeck |
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