# Are there enough stray gasses in space to justify streamlining a probe?

Space isn't empty - there are tons of things floating around in it. Seem of these things are pockets/molecule of gas - and a space probe is very likely to encounter some of these at some point in its lifespan.

Are there high enough concentrations of gasses to justify "streamlining" spacecraft? Are there any examples?

• Commented Sep 10, 2013 at 22:29

Let's just assume the interstellar density of about 10^6 particles/m^3. Let's also assume they are hydrogen. Plugging those numbers in to the drag formula $F_D\, =\, \tfrac12\, \rho\, v^2\, C_D\, A$, and let's assume that 1mN is the first force that is significant enough to merit correcting for. Putting all of that together, assuming a hideous coefficient of drag of 2, and an area of 100 m^2 (For solar panels), the appropriate velocity becomes 2,496,000, or almost 1% of light speed.

Bottom line, Aerodynamics only makes a difference if you are going really fast, much faster than anything we've sent so far.

• When colliding with gas at that speed I don't know if the drag formula applies... Commented Mar 3, 2014 at 17:09
• 1 mN (millinewton) would be significant for a probe that spends years...maybe over 10 years...journeying through space. Probes usually weight around 1 ton, and assuming a constant 1 mN acted over 10 years makes a dv of 315.6 m/s. It might not sound like much but it's plenty to change the trajectory; the probe would miss its target. Did you mean micronewton instead? However, I agree that 2,496 km/s is pretty far outside the envelope of flight and has no chance of every seeing a probe come near it. Commented Jul 14, 2015 at 22:25
• My numbers assume 1% light speed, which is so far above anything we have now, it's negligible. And it's a v^2 problem, so... Commented Jul 15, 2015 at 2:14

Within interstellar space or within our local solar system, aerodynamics isn't going to make much of a difference. And from @PearsonArtPhoto's calculations, at the speed at which they DO make a difference, the particles are going to ram into the probe with enough energy to erode the outer-surface. Gases and particles in interstellar space are often ionized (i.e. charged) and some atoms are very hot. It is akin to driving a car at 100mph through a dust-cloud - your windshield is going to be poc-marked and if one drove long enough, it might crack and fail.

With that in mind, you'd want to make the cross-section of a ship small to deal with erosion more than aerodynamics. Probably made of thick and durable material, and ideally shielded somehow - possibly with a magnetic field to help push particles away from the ship.

Have a look at: http://en.wikipedia.org/wiki/Interstellar_medium for a bit more detail.

For a real-world example, Voyager 1 - traveling at a brisk 17 Kilometers per SECOND away from the sun isn't very aerodynamic at all. Big clunky right angles, a giant radio dish on the back, etc.