MadSci Network: Engineering
Query:

Re: How much fuel would be saved if the shuttle ignited from 4km altitude?

Date: Tue May 8 17:42:35 2001
Posted By: Jason Goodman, Postdoctoral Fellow, Department of Geosciences
Area of science: Engineering
ID: 988658108.Eg
Message:

The fuel savings is important, but not huge. As I've said elsewhere in the MadSci Network, a rocket must go fast to enter orbit: going high is less important and less difficult. The main benefits of launching from high altitude (in rough order of importance) are:

I've done some very rough calculations based on information cited below which suggest that the fuel savings from launching at 4 kilometers altitude will amount to very roughly 10%. I've assumed a single-stage to orbit rocket with an exhaust velocity of about 3.5 km/s. The savings will vary a great deal depending on the type of rocket, the altitude it's launched from, and how well it's been designed to take advantage of a high-altitude launch.

Note that the fuel savings doesn't translate directly into increased payload. A typical large rocket might weigh 1000 tonnes at launch and carry 15 tonnes of payload. Launching from high altitude might save 100 tonnes of fuel, but that does not mean you can carry 115 tonnes of payload. The best you could do is about 16.5 tonnes of payload.

Sources:


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