Re: Dumb SS1 questions

From: Mike Miller (cray74_at_hotmail.com)
Date: 06/26/04 

To: sci-space-tech@moderators.isc.org
Date:  25 Jun 2004 18:10:04 -0700

Scott Moore <samiam@moorecad.com> wrote in message news:<OJQBc.157831$Ly.127326@attbi_s01>...
> If you can forgive a dumb space question or two:
>
> 1. assuming the next "big prize" would be an orbital vehicle, what is the lowest
> altitude an object can be orbited at, if only for a circuit or so ?

At 90-100 miles, drag should be low enough to complete one orbit.
 
> 2. If SS1 wanted to go somewhere instead of straight up, would it be able to,
> say, cross the United States at several mach, above the atmosphere ?

If you go straight up...well, you go straight up, with no sideways
velocity to cover any distance over the ground. You need some
horizontal speed, too.

> 3. How much bigger (more thrust) would SS1 have to have to achieve orbit ?

SS1 had plenty of thrust - after all, it went up at first, not down.

The issue is more a matter of "how much fuel is needed to get to
orbit?"

Orbital velocity is a matter of moving far enough sideways to avoid
the horizon when gravity pulls you down. What SS1 did is not approach
orbit. Rather, it approached space - it got above the atmosphere.
That's a nice step toward orbit (because atmospheric drag will slow
you down and thus hit the horizon), but it's just a small step.

The big step is moving fast enough to miss the horizon.

That involves moving tangent to the ground at about 17500mph for a low
orbit. Another 2000-3000mph is wasted going up and getting above the
atmosphere.

To get to orbit, a rocket with highly efficient engines (unlike SS1)
would need about 90% of its mass to be fuel and oxidizer. SS1 would
need about 95-97% of its mass to be fuel and oxidizer. This would
probably demand more thrust (at first), but the more important issue
is the amount of fuel.

Mike Miller

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