From: johnhare@tampabay.rr.com
"Peter Fairbrother" wrote in message
news:BC4AF29A.42A8D%zenadsl6186@zen.co.uk...
> johnhare wrote
>
> > My personal opinion is that the most profitable launch system in the
near
> > term
> > would be based on a HTHL launch assist platform capable of Mach 3-6 with
> > staging at very high altitude and low dynamic pressure. Upper stage,
dunno.
>
> Let's consider the upper stage first, and work backwards. Say we want 10
> tons in LEO. A mass ratio of around 4 is good, because we can get dry mass
> to around 10% without expensive scrimping, leaving 15% of the gross mass
for
> payload. So the gross mass is 65 tons for our 10 tons of payload.
> Nice'n'easy.
>
This is one of the reasons I suggested on SSP that a healthy suborbital
industry*
is more than halfway to a healthy orbital industry. It was fairly easy for
you to
figure the numbers on an upper stage. It will be easy for others to do the
same.
> If a LOX/LH2 stage is used, with an isp of 440 and a mass ratio of 4,
that's
> 6,000 m/s delta V. To get somewhere interesting you need to start at about
> 1600 m/s horizontal velocity and 100 km of height (second stage start at
100
> km is good, no Q to worry about so you can leave the aerodynamic structure
> mass in the booster, you get vacuum isp's, plenty of coast time for
> separation, and so on).
>
> So that's the target. 65 tons to 100 km altitude and 1600 m/s horizontal.
> You can mess with that a bit, but somewhere in there is what's needed.
>
I'm more in favor of flexible performance targeting early on. This involves
finding the break points of various systems and staying well under
them. If, for instance, the prefered TPS becomes a problem after Mach
5.5 on reentry, then it might be more profitable to stage at a velocity
and altitude that gives less than that.
> I don't think a pure airbreather will do that, at least not easily. But I
do
> think a HTHL airbreather with LOX/kero rocket boost could do it.
Preferably
> piloted, though the second stage needn't be man-rated.
>
I'm quite sure that airbreathing will not do the whole booster job. It will
take rockets to get the Mach numbers/altitude I suggested. OTOH, if
it turns out that airbreathers can economically provide mach 2.5 at 40
km, then it might be more profitable to use the single system on boost.
Understanding that no current airbreather will do this.
> Something like:
> jet fuel 70 tons
> rocket fuel/oxidiser 190 tons
> 2nd stage gross mass 65 tons
> 1st stage dry weight 110 tons
> flyback fuel 15 tons
>
> for a 450 ton GLOW, suitable for standard aviation-type runways. No pads,
> just an extra hanger with LOX/LH2 supplies at an airport.
>
And smaller. There is some market for smallsats if you get the price down.
> You can maybe even use the jet turbines as pumps for the rocket fuel. Or
> part-burn fuel to run the jet engines when there is no air. Use the rocket
> engines as RATO's. And so on.
>
Rocket pumps are a severe mismatch to jet turbines. Your point on looking
at all possibilities is right though, as long as you keep using numbers and
letting them do their job.
> --
> Peter Fairbrother
>
> BTW - I was looking at teeny jets recently, around the 100N size. They
have
> a T/W around 11, and exhaust velocities around 1150 m/s. Cost a couple of
> kilobucks. But, they have radial compressors :(.
>
What is wrong with radial compressors? Any idea on the turbine inlet
temperatures?
I should mention that teeny compressors can get into trouble at altitude due
to
the drop in Renolds numbers.
>
>
*A healthy suborbital industry being 2 or more vehicle types being flown
daily
by 3 or more companies. If the operating companies have to look through
their records to figure out how many flights since the last abort, we are on
the way.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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