Could someone explain to my why the shuttle re-entry - - or maybe I should ask any re-entry from orbitl has to be such a violent undertaking. Is it possible to have a craft that could slowly re-enter (with fuel propulsion to slow the descent)? If aliens were going to land on Earth, would they come screaming through the sky at 13,000 MPH, or would they slowly descend in a controlled fashion?
I understand that energy is required to break through the atmosphere… but after that couldn’t we have a craft that slowed itself down and came into a landing in a more leisurely manner?
It would probably require more fuel than we have the capability to send into space considering the weight of tanks and fuel. If we ever develop an alternative light-weight propulsion system, I’m sure we’ll figure out a less hazardous way to reenter Earth’s atmosphere.
Energy isn’t required to “break” the atmosphere. The Shuttle, in orbit moves damn fast, and it’d take a whole lot of fuel to slow it down, which the atmosphere will do for free if you can stand up to it. Heat is created from the speed (in a nutshell).
I don’t know, but I have wondered the same thing. I suspect that the issue is carrying the extra fuel (and weight) for slowing more before deorbit.
I wonder if it might be possible to launch separately supplemental fuel tanks which the shuttle could somehow dock with to provide the fuel to slow the shuttle’s speed while still in orbit so that the reentry would be accomplished at a much slower speed.
bernse has the right answer. When the shuttle is in orbit, it’s traveling at about 17,000 miles per hour relative to the surface of the earth. In order for the shuttle to come out of orbit, it needs to slow down. It does this by firing its engines in the opposite direction. Problem is, as soon as you slow down enough, you start falling into the atmosphere. To slow down more, you would need to keep burning more and more fuel to reduce your orbital velocity. This is rather pointless, since, as bernse said, the friction of the air will do this for free.
You do need some energy to “break” through the atmosphere, right? I’m thinking of Apollo 13 and how they had to hit it at just the right angle or they would bounce off and head into space.
“This is rather pointless, since, as bernse said, the friction of the air will do this for free”
This was kind of the point of my first post - - if it is less risky to go screaming into the atmosphere at 12k MPH in a glider, aren’t there other ways that are less risky? Such as firing rockets to slow you down…
Have you seen those giant rockets they have to accelerate the shuttle from zero to 17,000 mph? You’d need ones just as big to decelerate from 17,000 mph down to zero. And of course, it would take a whole bunch of even bigger rockets to get those decelerating rockets into orbit in the first place. On the other hand, you can shield the craft from the heat and let the atmosphere do it for free. And although it’s somewhat risky, this is the first mishap we’ve ever had in the re-entry phase.
No, you don’t need energy. They just had to hit the atmosphere at the right angle. If the angle were too shallow, they would basically have “refracted” right back out into space. They could have shielded the hell out of the Apollo command module, and hit it at any old angle steeper than that. But that would have required lots more shielding, which weighs a lot, and extra weight costs a whole lot to launch. So they designed the heat shields with just enough capacity to do the job. The downside is that there is a narrow angle that they had to hit to neither burn up or refract into space.