High Altitude Launch

A friend points out that a launch rocket uses an extra 1250 m/s of delta V to penetrate the atmosphere, and this doubles the amount of total rocket needed. Possible. I vaguely recall that a huge lumbering beast like the Saturn V used only about 120 m/s, but it was pointy and very very tall, a lot of rocket moved through the hole it punched in the sky.

This led to a discussion about launching from balloons - popular with the Sacramento L5 Society due to JP Aerospace. Numbers like 15 kilometers altitude were bandied about. The gravitational altitude makes little difference, the benefits acrue from punching through a thinner air column. The air pressure (a proxy for the density overhead) at 15 km is 12% of sea level, so presumably the delta V loss from that altitude is 150 meters per second, and the "extra rocket" needed is 8.7% more instead of 100% more.

Which raises the question, why not launch from a mountaintop? Mountains are challenging environments, but they are not weight-limited, they are fireproof, and they don't leak (well, OK, volcanoes do, let's avoid those). China launches from three launch centers, and is building a new one, closer to the equator, where the rotating earth provides extra useful delta V, 465 cos(lat):

Launch Center



465 cos(lat)






1000 m







1500 m







1500 m





Wenchang (new)


0 m





and one hypothetical launch center on a very tall mountain, vs. a hypothetical balloon:

Buka Daban Feng


6850 m





15 km Balloon


15000 m





See Wikipedia and http://www.chinadaily.com.cn/en/doc/2003-10/15/content_272334.htm

So balloon launch is pretty good, and launching from a tall mountain is almost as good, right?

Wrong. China is closing Xichang, supposedly its best by delta V, and opening Wenchang, the worst for delta V. They don't build launchers on any of their tallest mountains (which includes the north face of Everest), for the same reason they are opening Wenchang:

!!!!!!!!!!!!!!!!!!!!!!! Logistics !!!!!!!!!!!!!!!!!!!!!

Wenchang has a seaport, and the Chinese can bring much larger rockets in there than to the earlier inland, mountainous sites connected by narrow railroads, under bridges and through tunnels. A rocket is just the tip of the iceberg - there's also the fuel, supplies, building materials, test stands, and a big ocean to drop the empty tanks on the way up. Wenchang is a lot like Cape Canaveral (Kennedy Space Center) - facing east over a big ocean.

Insurance is a proxy for risk, and the Chinese may not bother with insurance but they can calculate risk. A launch out of KSC spends a lot more on launch insurance than it does on fuel. China's other launch centers drop the empties onto land to the east, perhaps onto a farmer from time to time.

Weather may be even more important - can't launch in a typhoon. Mountains are stormy, oceans are mostly calm but sometimes stormy, and the weather is more broadly predictable. The "weather" at stratospheric balloon altitudes is ragingly high winds - a balloon launch center is either pulling on some heavy tethers, or sailing through airspace around the world. That makes going to work at a balloon spaceport very difficult - not as difficult as space, perhaps, ... or perhaps even more difficult.

The most important factor is people. The people working at space launch centers need to live nearby, which means they prefer a nice place to live. The space coasts used by NSA, ESA, ISRO, and soon CNSA are beachfront - and with some development and air conditioning and mosquito abatement, good places to raise families, and relax after work. Mountains not so much, balloons, fuggetaboudit.

There is a possibility that the engineers who plan launch sites know what they are doing. This possibility is probably larger than the possibility that high mountains or balloons are better.

AltitudeLaunch (last edited 2015-08-15 02:30:42 by KeithLofstrom)