Although the airship starts off flaccid , the helium and the ethane expand as it gains altitude .
尽管飞船松弛着就起飞了，氮气和乙烷随着海拔的增长逐渐膨胀变大。
And it has rejuvenated several industries , including petrochemicals , where ethane produced from natural gas is a feedstock .
这其中就包括石化产业，其原料之一就是从天然气中提取出的乙烷。
And since ethane has roughly the same density as air , the fuel in effect weighs nothing , further reducing the amount of helium needed to create buoyancy .
由于乙烷和空气的密度大体相当，燃料的重量没有什么多大的影响，进一步减少氮气的重量需要去产生浮力。
This is because air is pumped back into the tail envelopes as the ethane fuel is burned by the craft 's thrusters , and is also pumped into the tail and head during descent as the inner envelopes contract .
In fact , many scientists believe that warming of the earth occurred at much higher levels than those seen today due to the presence of gases like carbon dioxide ( co 2 ) , methane , ethane or ammonia .
