Bear Cub to tether

I've been playing with Len Cormier's Bear Cub. As a tether
enthusiast, I'm interested in the impact of using a tether with the
Bear Cub.

A hanging tether can give as much as 800 m/s sub orbital grapple or
trapeze target. The payload of the Bear Cub grows from 455 kg to
about 1200 kg for such a tether.

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 $/kg
455 9.472 549
620 9.233 403
900 8.865 278
1000 8.744 250
1200 8.516 208

Len estimated a per flight cost of about $250,000. I couldn't resist
adding the cost per kilogram to this table.

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?

Henry

For sanity; these are the figures I used in my spreadsheet.

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