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Jun 22, 2010

How do you stop that?

A funny video about a rollerblade man. The question is how do you stop that fast if you need to?

Here seems to be an answer (at the end of the next video):

This looks also rather "hardheaded" but must be fun also.

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Jun 9, 2010

Light Re-entry Space Suit or Device

Or: How to Do a Re-entry?

The aerodynamic heating at the re-entry makes it difficult to produce a small and light weighted re-entry device. It is known that at some point if the weight compared to the structural volume of the re-entry configuration is low enough the re-entry temperatures will get lower. Also the selected path will affect to the heating.

It is possible to reject small objects from the space and rescue them. Corona was the first successful recovery of film from an orbiting satellite and the first mid-air recovery of an object returning from Earth orbit.

Fire proximity suits first appeared during the 1930s, and were originally made of asbestosfabric (hence also known as the asbestos suit). Today they are manufactured from vacuum-deposited aluminized materials that reflect the high radiant loads produced by the fire.

An old 3 part NASA study about the re-entry maximum heat is below. What is told to be important is the maximum surface temperature formula:

T^4 ~ sqrt( W / (CD*A*R))

This tells us that minimal weight (W) with maximal drag (CD), surface area (A) and surface radius (R) yield the minimium maximal surface temperature (T). The following videos have the whole story.

Part 1:

Part 2:

Part 3:

Space Shuttle Re-entry

Angle of Attack

The following description about the physics of the space shuttle re-entry tells that the shuttle really uses lift to lower the descend speed and to lower the temperatures involved. The next question would be: Why the descend speed is still so high that special materials have to be used? Can't a device just keep descending so slow that it would take several rounds around the world to descend and that no special materials at all would be needed?

What is required to achieve that? Maybe the re-entry vehicle must fly very high in the atmosphere several rounds around the world until the speed is low enough and then dive in it. The main requirement would be not to dive too early and to be able to handle the plasma which at very high level does not yet have very much energy.

Next more about the shuttle re-entry. Here is a diagram which shows different parameters related to the shuttle re-entry:

STS-5 Re-entry Data

It is really shown that the shuttle drops very fast during the first 5 minutes from 120 km to 75 km where the peak heating (and most intense deceleration) also begins. Angle of attack drops from 40 degrees and the shuttle starts to fly. The energy levels above 75 km are not very high as the speed change is also very small. At an altitude of 85 km, the flight surfaces of the orbiter become usable when the air is dense enough.

So there is an usable flight region above 75 km at least until 85 km where a flying device could fly making turns and even generate lift. And this would be the region where the light re-entry device could be kept most of the time to loose it's excess speed and energy and finally just fly down to the earth. Of course it is another story how to do it. More about skip entry is in the following link:

"Although the space shuttle is capable of skip reentry, NASA has carried it out only in computer simulations (Scott Horowitz, NASA interview, Jan. 25, 2007). It is unclear how thermal shielding would fare under the rapid heating, cooling and reheating. In theory STS-107 might have survived if a skip trajectory had been attempted - giving more time for heat dissipation - but this cannot be proven." /6/

Skip re-entry: As soon as it gets too hot you jump back to the space and cool it down.

The General Electric MOOSE and the link "Early Reentry Vehicles" give some answers to these questions.

Blunt body entry vehicles

NACA made the counterintuitive discovery in 1951 that a blunt shape (high drag) made the most effective heat shield. Here is more about that.

Balloon Re-entry

The Rockwell Saver concept

The Rockwell Saver concept promised a compact, lightweight solution and allowed the possibility to modulate drag and re-entry loads during re-entry by changing the size of the balloon. It required new materials technology at it's introduction time for the nosecap and balloon material.

In 2002 Japan achieved a new record: an ultra-thin-film balloon named BU60-1 made of polyethylene film was launched from Sanriku Balloon Center at 6:35 on May 23, 2002. The balloon kept ascending slowly at a speed of 260 m/min and successfully reached the altitude of 53.0 km (174,000 ft), establishing a new world record for the first time in 30 years.

Balloon BU 60-1

Other Ideas

Most of the re-entry ideas originate from the 1960's when the space boom was at its' hottest phase.

General Electric MOOSE

"MOOSE was perhaps the most celebrated bail-out from orbit system of the early 1960's. The suited astronaut would strap the MOOSE to his back, and jump out of the spacecraft or station into free space. Pulling a ripcord would fill an inflatable heat shield with polyurethane. The astronaut would use a small hand-held gas to orient himself for retro-fire, and then fire a solid rocket motor strapped to his chest to return to earth."

"General Electric conducted a number of technology proving tests. A heat shield was manufactured and folded. Test subjects were foamed into place with various formulae of polyurethane (it was found necessary to add a little castor oil to the formula to allow the pilot to extract himself from the foam). In a final test the test pilot jumped six meters from a bridge in Massachusetts and successfully survived water impact and floated downstream (a competitor claimed there was a little bit of a difference between 6 m and 500 km)."

There is a big list of different re-entry proposals in this link.


/2/ Heat Shields

/4/ Early Reentry Vehicles

/5/ Atmospheric Re-entry (pdf)

/6/ Skip Re-entry

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