If an orbiting spacecraft slowed to match the Earths rotation, could it reenter our atmosphere w/o burning up?

Question

It has no heat shields. It will just be free falling, assuming it slowed itself very quickly with retro-rockets to match the Earths rotation. It would be entering the atmosphere with theoretically 0mph forward motion.

Answer 1

You could do that, but the fuel needed would be as much as was required to launch the vehicle in the first place. If you did have enough fuel and did that, you would fall straight down, like SpaceShip One did. There would be some heating, but not nearly as much as with a traditional reentry directly from orbital speed. But a vertical fall from 300 miles up (SpaceShip One only went 67 miles up) would gain more speed during the part of the fall in vacuum and encounter the denser lower atmosphere more quickly than a more oblique entry, resulting in a much higher G load. Starting at 0 speed at 450 km up, you reach 2.6 km/s (over 5,000 MPH) in the fall before the atmosphere starts slowing you down, and peak deceleration is over 18 Gees by my calculation, compared to about 5 for SpaceShip One and 3 for the Shuttle with its high heat, very long and shallow entry. But if you first put yourself in an elliptical orbit with a perigee just high enough to avoid reentry (about as high as SpaceShip One went, 100 km), and then at that point fired your rockets to slow to zero ground speed, it would work with minimal heating. But the real problem is you could never carry enough rocket fuel to do that.

Answer 2

I guess you are talking about a total reversal of velocity to make the craft go from 12,000 mph to 0 mph. Without the speed to maintain orbit, the craft would fall to the earth.

It would probably fall just like you said but would be out of control. Also, the change in inertia would be pretty rough on the people inside the craft. The word "splat" comes to mind. Also, it seems like an incredible waste of fuel. Using the fuel to fire engines long enough and hard enough to instantly stop the craft is more wasteful than using the atmosphere and friction to slow the craft down.

On the plus side, it should reduce the amount of burn that the craft experiences when it re-enters. However, I do not think that this is a good or even doable trade-off.

Answer 3

Highly unlikely - the main problem is heating when re-entering the atmosphere. An astronaut in low Earth orbit is moving at 8 km/s (relative to the Earth), he needs to shed most of this speed in order to land safely. Also, if your astronaut is in a stable orbit you first need to reduce his speed enough so that the periapsis of his orbit is far enough inside the atmosphere to slow him down further - this will require rocket engines of some sort strapped to your astronaut. Once you've done that, the astronaut will re-enter the atmosphere at the above 8 km/s. Think of what happens to the Space Shuttle when it re-enters the atmosphere, it glows white-hot from the friction of re-entry - that kind of heat will reduce your astronaut to cinders in a few seconds. So you need to encase him in some kind of heat shielding, which will probably end up looking more like a miniature spacecraft than a space suit. Assuming you can survive the brutal heating, a multi-stage parachute (à la Project Excelsior, which you linked to) should get your astronaut down the rest of the way, assuming he hasn't spun out of control during re-entry. Bottom line: theoretically possible, very hard to do in practice.

Answer 4

You have the problem that orbital velocity is a lot faster than the earth's rotation. You have a lot of slowing down to do. Also, you start to fall and you have to counter this with fuel too. This implies that you need an huge amount of fuel. Unfortunately, space missions can't afford to take an extra fuel burden which is why heat shields are used instead.

Answer 5

It is still encountering air molecules in free-fall. The net vector due to the effect of gravity would appear to be a straight line perpendicular to the surface of the earth. The craft would encounter friction from the atmosphere and would heat up.

The earth's rotation is practically irrelevant here.

Answer 6

We have dozens of satellites orbition above the equator in what are termed Geostationary orbits (eg communications, weather and television broadcast satellites).
They are at about 22,500 miles from Earth's center (geostationary altitude) and travelling about 140,000 mph above the equator with an orbital period of 24hours (1 day). Thereby they remain over the same point of the Earth's surface (actually a small figure eight).

If you retrofired rockets to arrest this motion the satellite would be drawn directly torwards the Earth's mass (straight down) with zero forward motion. From that distance it would attain a fairly high speed when entering the atmosphere.

Answer 7

Many satelites, like the ones that bring you staleite TV shows, do orbit at a rate that matches the Earth's rotation. That does not make them fall.

Answer 8

Yes.

Essentially, this is what Space Ship One did a few years ago - it boosted itself up 62 miles, and, rotating with the Earth, fell back. It didn't have to worry about orbital speed, it simply had to deal with the speed of falling from so high.

Answer 9

At the point of entry it will have 0 forward motion. But then it will start plummeting like a rock so unless it has enough fuel to counter that acceleration, it will crash.

Answer 10

Yes, but it would still be plummeting towards the earth. To stop THAT slowly enough to just a regular descent would need an ENORMOUS amount of fuel.