Re: VTVL?
- From: Russell Wallace <russell.no.spam@xxxxxxxxx>
- Date: Mon, 30 Jul 2007 18:56:19 +0100
richard schumacher wrote:
Because jet engines have a small thrust to weight ratio compared to rockets. At takeoff the vehicle is full of fuel, so the 1st stage weighs roughly ten times what it does when landing. The wings and jet engines required for horizontally launching such a heavy thing are far larger than those needed to land the same 1st stage when it is empty. Much bigger wings mean much larger aerodynamic stresses during ascent.
Right, so you do want to use the rocket engines for takeoff.
Though isn't there an argument for not doing parallel staging, because then the orbiter engines don't have to be designed to work at sea level?
Note also that if an orbiter launches in one orientation and lands in another it needs internal structure to withstand stress along multiple axes. That makes it heavier than one which only moves along one axis. Heavier is not so bad because that just requires making the 1st stage larger, and fuel is cheap; but worse, it also makes the orbiter denser, meaning that its re-entry heating and terminal speed also increase.
Right, so that's an argument for doing horizontal takeoff (albeit still using the rocket engines). Plus it cuts out the operational step of moving the vehicle from horizontal to vertical orientation.
There might also be useful applications for operating either stage by itself, as a sub-orbital vehicle.
More likely the first stage, I imagine?
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