(Len) wrote in message . com...
(Henry Cate, Jr) wrote in message
I use the rocket equation to get a table of the net velocity available
to this configuration with increased payloads. This gave me the
following table.

Payload Ideal DV
455 9.472
620 9.233
900 8.865
1000 8.744
1200 8.516

Henry

Len gave an expected ideal DV for each of the pieces; the Tupelov
carrier, the booster stage, and the orbiter. He quoted the ISP for
the RL-10. The booster stage uses Kerosene, Len does not provide an
ISP for the booster stage. I infer an exhaust of about 3200 m/s from
the mass and DV.

Payload Ideal DV ISP m/s Empty Fuel GLOW
455 5.553 4422 Orbiter 1945 6025 8425
3.249 3200 Booster 2340 19000 29765
0.670 Tupelov95 94400
Total 9.472


This last table is essentially correct. The Isp
assumed for the booster is 3195 m/s. However, I
calculate that reduction of the orbiter delta v
requirement by 800 m/s to 4753 m/s would reduce
the required mass ratio to 2.93, which would give
a payload of about 930 kg, rather than 1200 kg--
which is still a very nice improvement.

I assumed the Tupelov could carry and extra mass and not notice the
difference. I assumed the fuel load stayed constant, and only the
final payload changed, though that changes the effective mass ratio of
the booster stage. That's how the 1200 worked out. Is the Bear Cub
payload mass limited, or volume limited? How hard would it be to
stuff an extra 1000 kg into the orbiter?

Of course,
the tether isn't free, so this would also add to
total costs. The $250,000 per flight recurring cost
is a goal, not an estimate--although I think it is
a reasonable goal.

I agree that this is a reasonable goal. It seems high if we could get
a high flight rate (I.e. if we fly often, the cost per flight should
be lower.)

The tether isn't free, but the operating costs are low, so the major
cost would be paying for the R&D. (I'm interested in tourists, where
there is round trip traffic, so there is little or no net energy cost
to the tether.) I believe the investment dominates the Bear Cub
flight costs also.

The gross orbiter mass should remain the same,
in order to maintain initial thrust-to-weight
ratio. Higher payload means higher burnout and
reentry mass; so this would have an impact on
TPS, reducing the payload somewhat.

I don't follow this. The initial mass has changed by 465 (or 750) kg,
out of 29.7 tons. That doesn't seem to impact the thrust to weight
very much?

Higher payload means lower burnout velocity for the booster. I don't
see what impact on reentry mass. Why would the reentry mass change by
adding 465 kg to the payload (the booster delivers 8880 instead of
8425)?

My spread sheet assumed both the booster and the orbiter deliver less
DV due to the increase in payload. I assumed I could carry the same
fuel load, since more payload doesn't impact the fuel tank?

The Tu-95 would launch the same mass. The booster
would also remain about the same (although I might
opt for a different recovery concept).

I'd assumed we could add 465 or 750 kg to payload in the Bear Cub
orbiter without changing either the Tu-95 or the booster. As I said
above, the Tu-95 wouldn't notice the difference between 29.7 tons and
30.1, would it?

I'm a bit tentative about the conversion from "Ideal DV" to orbital
altitude. If I use the Buzz Aldrin 15% loss to gravity, air
resistance, etc. Then 9.474 km/s should produce an effective 8.23
km/s. If I spend 8.07 to get into a transfer orbit, and 0.16 to
circularize the orbit, that looks like 550 km altitude. Does that
work?

And the
total delta v requirement would be the same for
the same basic ISS orbit.

So the Bear Cub is aimed at the ISS orbit, of 400 km altitude at 57
degree inclination?

BTW most of the delta v
losses are early in the game; this--along with the
near-elimination of the altitude compensation
requirement--are the main benfits of subsonic launch
at altitude.

I thought the Aldrin 15% would be generous. It appeared to my logic
that just getting to 15 km altitude could easily cost 350-400 m/s in
gravity loss, for example (with vertical launch rockets). I don't
know how to calculate gravity and other Delta V losses with
confidence.