# How high *could* a glider reach, to catch a skyhook reaching down from orbit? [closed]

At the beginning of the third part of Seveneves Neal Stephenson describes how the protagonist Kath Two travels from the Earth's surface into the orbit with the aid of a Skyhook-named system. The route between the earth's surface and the skyhook is laid back using a glider, which can reach without any drive only by clever exploitation of thermals up to about 100 to 200 km altitude. My question now would be, is it possible to ascend to such a height using a sail glider?

• are you sure it's that high? It's been a while since I read the book, but I don't recall the glider going up that far. – Hobbes Apr 8 '17 at 19:29
• I started to read Seveneves, because clueless people recommended me it. Apart from the Moon inexplicably breaking up like that, in the first couple of pages an amateur astronomer is said to be looking into his telescope. It is not disclosed why. Is it broken? Has he opened it? So I leave all of that Moon debris stuff glider sailing stuff to Dart Vader to figure out. And of course there's very serious attempts for an airship to orbit You never know what'll work, some of the stupidest things do. – LocalFluff Apr 8 '17 at 19:40
• All the book says about the altitude is that the hanger reaches down to "the uppermost reaches of the atmosphere". – Austin Apr 9 '17 at 7:27
• I'm voting to close this question as off-topic because the core question has nothing to do with space exploration. Aviation.SE may be able to answer. – Rory Alsop Apr 9 '17 at 10:44
• There is a problem, the glider needs the atmosphere to fly but the skyhook should be out of the atmosphere to avoid drag and heat up. – Uwe Apr 12 '17 at 8:13

From my memory of the book there's no actual altitude listed, but the suggestion was that the glider had to reach very high. The current glider altitude record is just over 50,000ft:

The highest altitude obtained in an unpowered aircraft is 15,460 m (50,720 ft) on 30 August 2006 by Steve Fossett (pilot) and Einar Enevoldson (co-pilot) in their high performance research glider

So I would say that currently it is not possible for a glider to reach the kind of altitudes the book alluded to. Seveneyes described a society with much more advanced technology than we have now, the glider itself had the ability to morph its shape considerably, it's hard to say how high a glider like that could get. This is science fiction after all.

• They do believe they can get to 100000 feet with their project, but that's still only 1/3rd to 1/6th of the height in the OP's question. – Jörg W Mittag Apr 10 '17 at 16:32
• One of the advantages of that type of skycrane though is that it can dip pretty deep into the atmosphere with little loss - the airspeed of the sinking end is quite low. So while Seveneves might have implied 'edges of the atmosphere', 30km might suffice if the arm is long enough so that the airspeed at which it moves through the air is low. – SF. Apr 12 '17 at 14:16

Project Perlan 2 aims to fly a glider up to 90 000 feet. 100 000 feet (30km) also appears possible, but more expensive — presumably due to complex composite construction to reduce weight.

Soaring that high requires specific atmospheric conditions, a standing mountain wave and the right wind conditions to prevent that wave being blocked in the troposphere. As the book is set in the future with advanced materials, presumably the glider could be a lot lighter so you could go a bit higher and maybe have a wider range of conditions in which you could get to altitude.

However the required conditions are somewhat rare, so it might not be practical for skyhook(s) as they wouldn't often align with the right weather.