# starship-design: Drag

```Kelly you wrote:

>I'm not sure, but I think we gave up on using interstellar media for drag?
> Probably their just isn't enough of it to be worth using.  Anyone remember?

You may determine it yourself:

A     = effective scoop surface (m^2)
v     = ship's velocity (m/s)
rho   = density of space (kg/m^3)
Mship = Ship's mass including scooping system (kg)
Mdot  = Total scooped mass per second (kg/s)

Mdot = A*v*rho

Resulting deceleration = 2*Mdot*v/Mship            (F*t=p=m*v and F=M*a)

Note that the deceleration is only valid for the velocity that you use. The
deceleration will likely decrease when you loose speed, unless your scoop
starts working better at lower speeds.
This may actually happen, since for lower ship speeds the to-be-scooped
particles have more time to reach the scoop mouth and thus may be scooped
from further away.

If you find a small deceleration for the initially high velocities, then
that most likely means that you won't slow down in time. The only thing you
may then try is increasing the effective scoop area. You might you should
remember that it will take a long time to slow down to velocities that might
have a better deceleration.

Timothy

P.S. Would you mind mailing me the density of the interstellar medium once
again?

```