Wednesday, May 11, 2011

Designing Plausible Spacecraft for RPGs: More work on IPVs

The USS Example II
         In order to help everyone get a feel of what I'm trying to accomplish with my Interplanetary Vehicle (IPV) design, and not just the long time followers of this blog, I made this list of vital statistics. I'm including the technical stuff as well; this being one of the places where such data is both expected and welcome.

Length: 240 meters on the longest axis.
Primary Mission: Space denial; to interdict the space around an asteroid base with Kessler-type Missiles in order to deny said base resupply.
Secondary Mission: Resource acquisition; force the surrender of asteroid bases though space denial and then occupy said bases.
Crew: 40 core crew, 10 Espatiers, 30 mission specialists, 75 maintenance robots, 80 combat robots.
Powerplant: Two 50 Gw He³-He³ fusion reactors
Primary Propulsion: Two Mini-Magnetospheric Plasma Propulsion (M2P2) arrays.
Secondary Propulsion: Two Laser propulsion thrusters fed with Hydrogen or Oxygen from water electrolysis. Used only for emergency vector changes.
M2P2 Field on: as seen from the front
Radiators: 32 lithium droplet radiators
Propellant: Liquid Hydrogen and Liquid Oxygen stored primarily as water.
Habitats: Two 25x25 meter cylindrical habitats on opposite sides of the IPV. Docking ports for up to 16 optional attachable Habitat Modules (mass removed from cargo capacity).
Dry Mass: 31,000 tons
Structure: 14,000 tons
Cargo Capacity (including habitats and all consumables): 16,000 tons
IPV under sail; spacecraft is traveling to the right.
Propellant Mass: 120,000 tons (stored as water)
Total Mass: 150,000 tons
Mass Ratio: 5
Specific Impulse: 400 s
Acceleration: 1 millegee (0.00981 m/s²)
Mass Flow*: 7.6 kg/s
Exhaust Velocity*: 4000 m/s
Thrust: 882,900 N
v: 116,171 m/s
Brachiostrome Duration Terra/Mars: ≈ 10 wks
*Data is for the M2P2 system

Fell free to comment!


  1. What are the 7.6kg/s and 4000m/s exhaust velocity?
    I thought it used M2P2, in that case, exhaust velocity would be that of the solar wind (400-800km/s) with pitiful thrust.
    On the other hand, a 5GW laser thermal rocket can easily achieve 10km/s exhaust velocity. You just need to use smaller lumps of propellant for more even and deeper heating.
    The low impulse of laser thermal rockets is mostly because of laser pulses blasting bits off the propellant lump, leaving cold bits with low velocity mess up the total exhaust velocity.

  2. The mass flow is the amount of ionized gas needed to inflate the magnetic bubble. The exhaust velocity is 1% of the speed of the solar wind. Both figures were assumptions. I still have no hard data on the actual exhaust velocity for an M2P2 sail; However, current research shows that the mass flow is much, much lower. The computer models predict a mass flow of only one kg/day per 1kW of power fed into the system. I believe this only yields 6-10N of thrust, but even so, that's still a seven-fold reduction in mass flow per second from the above data. Revisions will be posted when I have time.


Questions, comments, criticisms? All non-Trolls welcome!