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Hot answers tagged

65

Skipping reentries aren't unheard of. The Apollo command module performed a single skip when returning from lunar missions. However, there are several reasons why a skipping reentry (especially one involving multiple skips) would be disadvantageous for the shuttle: As uhoh points out, a skipping reentry results in losing lateral speed at a very high ...


64

Although the temperature at altitude can be several thousands of degrees, the atmosphere is so thin it does not transfer heat efficiently. Wikipedia explains it very well - The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is ...


61

I've done a lot of work on this subject with researchers and engineers at JPL, NASA Langley, and NASA Ames. There are some interesting things that come out of high-fidelity CFM (Computational Fluid Mechanics) modeling of entries or re-entries, and also from flight experience. This FAA tutorial segment is a good general reference for the principles involved. ...


58

I think bounce back causes intermittent heating so heat shield tiles get a lot of time of radiate heat out. Your thinking is reasonable as far as it goes... But once you lose too much velocity and become deeply sub-orbital, you will sink like a rock into thicker atmosphere. Within five minutes you'll either be toast from heating or jelly from pulling 15-...


53

The heat of re-entry is highly dependent on speed. The second stage of the rocket is responsible for providing most of the speed needed for orbit, after the first stage lifts it out of dense atmosphere. Falcon 9 separates its first and second stages at relatively low speed, so its reentry starts off drastically slower than a reentry from orbit -- about ...


49

Hobbes has already showed you a diagram of the Falcon 9 launch profile, so I won't repeat that. Note: This answer is not intended to be a complete, scientific treatment of the subject. I knowingly and deliberately simplify, gloss over and ignore things in several places, in order to explain this in a way that hopefully makes sense to the OP while still ...


46

Trajectory of the Falcon 9 first stage: Graphic courtesy ZLSA Design (zlsa.github.io) As you can see, before the boostback burn, the stage flips so the engines point in the direction of travel. When the engines fire, this slows down the stage. This trajectory is used when the stage returns to the launch site (and for some early experiments where the ASDS ...


46

Nearly all the velocity is cancelled by atmospheric deceleration of the descent module, before its parachutes are deployed. ISS orbital velocity is around 7700 m/s. An initial retro-burn of the Soyuz engines, of something like 115 m/s magnitude, is sufficient to lower the perigee of orbit into the uppermost part of the atmosphere. The orbital module and ...


43

The capsules designed to reenter the atmosphere have to slow down from about 8 km/s to zero by the time they get to the ground. They actually don't use the part that looks like a cone to do that. They all have flat bottoms that they face into the wind to do that. If you compare the Dragon capsule from your link to a Soyuz capsule, the Orion capsule, or the ...


41

Throwing it down at 5 m/s will do basically nothing. That will simply cause it to advance in its orbit a bit. To deorbit, you need to throw it backwards, not down. However in this case, since the feather has a such a low ballistic coefficient, it will promptly deorbit from ISS altitude on its own, without you having to do anything at all. Just wait a bit....


39

The answers to all your questions are described at length in section 6.4 (page 173) "Possibility of Rescue or Repair" of the CAIB Report. Appendix D-13 "STS-107 In-flight Options Assessment" is a very detailed description of the process that was utilized to come up with the self-repair and rescue options. Major elements of the process: Assumptions were ...


35

It's just the aerodynamics. There is high pressure where the air spills out the side that tends to push them apart more than the forces that you mention that pulls them together. Good thing too. A giant parachute with the same drag would take too long to open. Clustering is very commonly used for cargo.


32

Page 331 in the Shuttle Crew Operations Manual, an official NASA astronaut training document, confirms that The deorbit burn usually decreases the vehicle's orbital velocity anywhere from 200 to 550 fps, depending on orbital altitude. The deorbit burn was not intended to reduce the Orbiter's velocity to a small value, but rather to change its orbital ...


32

Here's an image of the bottom of the stage before launch. As you can see, the entire bottom is covered in white panels. I suspect those panels are a heat shield. This SpaceX press release on the introduction of the Falcon 9 v1.1 refers to a heat shield. The reference is a bit oblique, but I think this refers to the first stage. Here's the same area ...


32

The advantages of the blunt end first design were known well before either vehicle was launched (1958, a few years earlier for spy satellite designers). However, pointy end first is the simplest design that works. Falling objects generally want to go heavy end first, draggy end last. With a heavy heat shield on the front and a light but bulky parachute in ...


32

It's not the temperature that matters, it's the heat transfer. The density of the atmosphere up in the thermosphere is very very thin. There simply isn't nearly enough mass to transfer any significant amount of heat from the thermosphere to a spacecraft travelling through it. Spacecraft do need heat protection to survive re-entry, but that is because they'...


31

This appears to be a garbled recounting of a problem that occurred during STS-1 entry due to a mis-match between predicted and actual hypersonic pitch trim. Image Source All that happened was that the body flap (see aft of Orbiter on diagram) extended 5 degrees more than predicted (which did cause the body flap to see higher heating than predicted as well)...


30

From this question on Physics.SE: But other than that, there is no reason why a man couldn't be lobbed from behind Jupiter, make a slow-down loop around the Moon, then spiral down to Earth... given some marvelous suit that will withstand the atmospheric entry. From this question on Felix Baumgartner: Note that even if he jumped from "infinity", he ...


30

Spiraling down in the sense you mean is not possible, the reason is that when a spaceship is orbiting Earth, it is travelling extremely fast relative to the surface, it is not that space is so high up, but that a spaceship needs to travel very fast in order to orbit. So in order to reenter, it is not the velocity of falling that needs to be shed, but the ...


30

F9 can enter engine first because it isn't returning from orbital speeds. While fast, it's a fraction of the speeds something returning from orbit (or further) comes in at. So the engines are out as an entry surface, you need more protection. One way to achieve this is Dragon-style: put a heat shield on the bottom, and engines in the sidewalls. Great for ...


29

If you're just looking for an intuitive handle on it, try this: In circular LEO, your orbital period is about 90 minutes. If you apply a velocity change of 90 m/s, then wait half an orbit -- 45 minutes -- you should expect to be out of position by 90 m/s * 45 min * 60 s/min = 243,000m, or 243km. The distorting effect of Earth's gravity means that the ...


27

The Chelyabinsk meteor was travelling at over 65,000 km/h when it hit the brunt of the atmosphere 23 km high in the air. This is 60 times the speed on sound! NASA estimates that the meteor's mass at this point was 10,000 tonnes, and it had a diameter of 20 meters. At these incredible speeds, the body is placed under immense stress. Colossal pressure is ...


27

Mercury Atlas 7, Aurora 7, splashed down an estimated 250 miles (402 km) off course, slightly more than Voskhod 2. The error was due to a problem with the automatic attitude controls and a late firing of the retro rockets by astronaut Scott Carpenter. Passing over Hawaii at the final orbit, Kraft told Carpenter to begin his retrofire countdown and to ...


27

Dumping it into orbit, even retrograde, will still leave objects in orbit, slowly falling down until they burn up. But for that entire period of time, they become possible hazards to anything in that orbit or lower. A launcher with some minor amount of velocity would speed up the deorbiting, but it would still be there. You would probably want it somehow ...


25

In order for a combustion process to happen, you do not only need fuel, you also need an oxidizer. On Earth, that is usually the oxygen in the air. In Titan's atmosphere, there is no oxygen. This applies to other atmospheres too, like the hydrogen dominated atmospheres of Jupiter and Saturn. Hydrogen, just like the methane in Titan's atmosphere, is flammable ...


25

The process is described here, which answers nearly all of your question. The reentry burn removes about 120 m/s of velocity from the capsule (that's your 1) and the final impact is 15 miles per hour (about 6 m/s). That's your 3. That leaves about 7.5 km/s for part 2. The only remaining question is the split between 2a and 2b, ie the velocity when the ...


24

First off, a stone does not skip off the surface of the water. It skips off the water. The stone has to bite into the water to use its lift to come back out. A skipping stone can, and sometimes does, go completely under the surface in the process of skipping. The air is a fluid as well, and a lifting body can in fact skip in the same way as a stone does ...


24

Although it seems opinion-based, this is actually answerable if you interpret "harder" to mean "riskier". After the Columbia accident a Probablistic Risk Assessment was done of shuttle missions. The results show that ascent was riskier.* (LOCV means Loss Of Crew and Vehicle.) *The two columns refer to when the LOCV-causing incident actually occurs (on the ...


24

I would like to make my own compilation that includes several missions not mentioned in any other answer so far. (The record is actually 483 km of Soyuz TMA-1, not the 475 km of Soyuz TMA-11.) Gemini 5: splashed down 130 km off course due to programming error. Someone put in the rotation rate of Earth for the solar day instead of the sidereal day. Voskhod ...


23

Yes, a capsule cannot literally bounce off the atmosphere and its kinetic energy must be reduced by an encounter with the atmosphere, rather it would just pass through the atmosphere and back into space, having failed to lose enough velocity to stay in the atmosphere. After going partially around the planet it will reenter the atmosphere, that is actually ...


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