> On Thursday 24 February 2005 09:32 pm, DwayneDay wrote:
>
>> Boeing is currently pushing a version of the Delta IV-Heavy that would use
>> six core vehicles clustered together.
>>
>> There are some reasons to be wary of this, however. Delta IV-Heavy climbs
>> very slowly, and it is actually scorched by its own exhaust. In fact,
>> portions of the vehicle even catch fire. This makes for some dramatic
>> photographs that make it look like the rocket is blowing up. Can you
>> really imagine that happening with six core vehicles--or a crew aboard?
>
> Yeah, I'm not really thrilled with the whole Delta IV design, though it looks
> cool. I believe it is the only launch vehicle to use LH2 exclusively as a
> liftoff fuel (all other launchers which burn LH2 at liftoff have strapons
> fuelled by something else, either solids, RP1 (kerosene) or some hydrazine
> mixture). Despite the high ISPs you get with LH2, its low density leads to
> a large volume which results in large pumps and a relatively slow liftoff
> speed, with the consequences you see on Delta IV.
>

As I posted some weeks ago, a man-rated version would have to face the risk
of a pad-abort after main engine start (it happened several times with the
Shuttle).

Could you imagine a large launcher, filled with hundreds of tons of cryo
propellant, sitting quietly inside a fireball? I don't feel ready to sit
just upon that one.

At the Paris Airshow, ATK promoted various shuttle derived vehicles,
including a manned version derived from a single SRB with a cryo upper
stage. Lockheed Martin also presented concepts for a widebody Atlas 5 (Atlas
6?) with 5.4-m diameter stages powered by twin RD-180s. This concept seems
much more evolutive (and powerful) than Boeing's stuff.

A version with two widebody strap-ons is quoted at 68 tons to LEO and 28
tons to escape trajectory.

A version with two or thre more strap-ons is claimed to be a Saturn 5
equivalent (> 135 tons to LEO, 44 tons to escape).

Transition from the current Atlas 5 would be progressive.

--

Stefan Barensky
Senior Space Editor
http://www.space-launcher.com