Ion-drive for fuel-depoting (was Selling power-service at non-compet

> For SPS we'd want to use something a little more exotic
> than LOX/LH. The NSTAR engine from Deep Space One
> approached an Isp of 3000s (Wiki says) & LEO to GSO is
> 3.8kmps. MR=0.129 So an extra 13% added to mass and payload.

Dr. Bruce P. Dunn has published a paper concluding that an ion-drive
space-truck might sometimes more-effectively be put to use as a pre-
positioner of chemical fuel, rather than as a tugboat (EOTV is an
electric vehicle; COTV is chemical):
http://www.dunnspace.com
http://www.dunnspace.com/jsr1987.pdf

"Refueling takes place by lifting the refueling propellant into a
high-energy circular refueling orbit (RO) using an EOTV. The COTV
with the payload then leaves LEO and ascends by Hohmann transfer to a
rendevous with the refueling vehicle. After refueling, the ascent to
GEO is completed by a second Hohmann transfer, leaving sufficient
propellant unburned to return the COTV to LEO. ...

Summary and Conclusions
Chemical OTV's offer the rapid transfer of payloads to GEO, but
suffer from both low payloads and high propellant consumption. High-
specific-impulse EOTV's offer the possibility of low propellant
consumption, but suffer from long transfer times and possible
radiation damage to sensitive payloads. Using EOTV's to refuel
payload-carrying COTV's during ascent from LEO to GEO offers the
potential of a mixed fleet that can rapidly deliver large payloads to
GEO while consuming less propellant per unit payload than an all-
chemical fleet."