# Tag Info

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 ...

62

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-...

56

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 ...

53

“Bouncing off the atmosphere” is a misleading turn of phrase. When returning to the Earth from the Moon, a spacecraft is on an elliptical orbit with the high end somewhere around the moon’s altitude and the low end just grazing the top of Earth’s atmosphere. The concern around a too-shallow reentry angle is that it won’t slow the spacecraft enough for a ...

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 ...

42

There were no nominal activities for the middeck crew related to flying the vehicle. There were no switches or controls on the middeck accessible to seated crewmembers in the ascent/entry seats. The rectangular objects in the photo are middeck lockers which are located external to the avionics bays. Mission Specialist 3 (MS-3) did have responsibility over ...

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....

40

That is the remnant of one of the attachments between the Command and Service modules (there were three). Here is a cutaway drawing showing the bolt penetrating the heat shield (labeled "tension tie"). From Apollo Experience Report Spacecraft Structure Subsystem Here's a closer picture showing that the circular areas are not penetrations. Photo source ...

39

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.

39

Not much research has been done on this question in recent years, but some researchers are worried enough to research into wooden satellites. The question on the environmental impact of deorbiting satellites burning up in the upper atmosphere was partly addressed in a 1994 report (warning: not peer reviewed) by the Environmental Management of the Space & ...

36

Would you even be able to open the door? It would depend on the capsule, but since the Apollo 1 fire, one expects crewed American capsules to have explosively-jettisoned hatches that can be activated by the crew. If you had a regular skydiving parachute with you, is there any way you could skydive and survive? Yes. Terminal velocity for falling ...

34

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 ...

34

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 ...

33

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 ...

33

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 ...

33

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)...

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'...

32

The mass of Earth's atmosphere is 5E+18 kg and the Troposphere alone has 3/4's of that. With an average height of 13 km that makes its volume $4 \pi r^2 h$ or about 6.6E+18 m^3. If we break up one thousand 100 kg satellites into semi-porous PM2.5 particles that works out to be 1.5E-08 micrograms per cubic meter, and we generally worry about tens of ...

31

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 ...

31

Can't speak to the trajectory aspects but the Orbiter crew compartment was very intolerant of crush pressure loading. The two negative pressure relief valves protect the crew compartment from being crushed if ambient pressure rises above the pressure in the cabin. These negative pressure relief valves will crack when ambient pressure is 0.2 psid greater ...

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", ...

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 ...

30

Service module attachment point The service module (SM) was attached to the command module (CM) using tension members which pulled the two modules towards each other. The SM used cups that rest on the compression pads on the CM heatshield (also visible in your photo). This cross section shows the CM on the left, heat shield in the middle and the cups of ...

28

Ground testing of heatshield components and materials can and has been done in arcjet facilities. (image source) An arcjet typically combines a super- or hyper- sonic wind tunnel with a large electrical heating device. "The gases (typically air) pass through a nozzle aimed at a test sample in vacuum, and flow over it, producing a reasonable ...

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 ...

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