# What is currently used to protect spaceships from meteoroids?

What is used to protect a Mars or possibly interstellar spacecraft against meteoroids and asteroids?

How risky it it to travel through space and does higher speeds equal more risk?

Would a long wedge shaped ship like a long needle with enough of a shallow angle that the object would just be moved to the side with no damage?

• There are no interstellar spacecraft (from Earth, anyway). Therefore, there is no need to protect them from meteors (or other debris). Apr 1 '18 at 19:01

Interstellar travel typically involves much higher velocities than current probes achieve. Depending on how long you are willing to allow the mission to take, you need velocities of a decent fraction of the speed of light. At that speed, anything you collide with, even the smallest speck of dust is quite dangerous. For instance at $0.1c$ (40 years to the nearest star) a $1 mg$ spec of dust carries about $500 MJ$ of relative kinetic energy, equivalent to the explosion of about 120 kg of TNT. Shape of the spaceship doesn't matter. Even a glancing collision will do huge damage. Even a single hydrogen atom behaves like incoming radiation, with a kinetic energy of $7 MeV/c^2$ similar to the neutrons released by a fusion reaction.

We're in the realm of speculation, or even science fiction, as we consider how to shield against this, but most likely you need a shield that can go in front of the spaceship and take the damage. This could be a thick layer of armour, maybe made from ice, or a cloud of electrically charged dust or gas held in place by magnetic fields. If you can make sure anything you might hit is electrically charged (perhaps using electron beams or UV lasers), you could use magnetic fields to divert it.

• Can you help me with my question? You have a good answer. I keep getting down votes?
– Muze
Apr 1 '18 at 17:38
• Is that better?
– Muze
Apr 1 '18 at 18:20

One should consider vectors of the items in question and allow that shape of the ship will have little impact on an impact.

A good comparison is a vehicle traveling on a roadway. As it approaches an intersection with a green light, traveling at high speed, another vehicle disregards its red light and collides with the first vehicle.

The shape of the first vehicle is inconsequential, as the impact is at 90° to the direction of travel of the first vehicle.

Avoidance is the primary method for today's spacecraft to avoid collisions, at least until energy shields are created. This is more a sci-fi response, however.

• Yes some kind of long range sensor would be needed.
– Muze
Mar 31 '18 at 23:37
• "Avoidance is the primary method for today's spacecraft to avoid collision" Do you have any references to back up your assertion that today's spacecraft use "avoidance" to prevent colliding with meteors? How do they detect these meteors? Mar 31 '18 at 23:39
• That portion is clearly off the mark, as avoidance is used on orbit for debris and not meteors. Thanks for catching that error. Apr 1 '18 at 0:09

Current spacecraft outside Earth orbit have little or no protection.

• they have no sensors that can detect small objects, and we can't detect small objects (say, less than 100 m in diameter) from Earth either
• they don't carry enough fuel to make course corrections quickly enough to avoid an object
• their structure is not built to withstand impacts from anything larger than a speck of dust at 10 km/s.

There are a few exceptions. Comet missions like Giotto and Stardust have a Whipple shield, because the environment around a comet is dense enough to guarantee hits.

For risky operations (flying through an area where debris is known to exist) spacecraft are sometimes commanded to fly in the 'antenna to ram' direction. This means the dish antenna faces forward, and the dish can act as a Whipple shield. Cassini used this on occasion, for example.

This was one of the contingency plans for New Horizons' encounter with Pluto (there was a suspicion Pluto might have rings).

See also this question on the preparations for New Horizons' flyby of Pluto. There were concerns that there might be a lot of debris in Pluto's orbit.

How risky it it to travel through space and does higher speeds equal more risk?

Generally, space is empty. Very empty. Empty enough that we can travel to Pluto without hitting anything. There are a few exceptions:

• man-made debris in Earth orbit
• planets with moons can have lots of debris (meteoroid impact on the moon, debris of the impact reaches escape velocity and orbits for a while). The ultimate case of this is a ring system.

And higher speeds equal more risk. The amount of kinetic energy Ek in a collision depends on the square of the speed:

$$E_\text{k} =\tfrac{1}{2} mv^2$$

This means that at the usual speeds reached by interplanetary probes (10-100 km/s) a grain of sand will go right through a plate of aluminium. You can protect against small debris (up to a few mm in diameter) using a Whipple shield, but you can forget about protecting against larger debris.

A wedge shape provides more protection. This principle is used in armored vehicles. The problem is that the energies involved are so high, you'd need a very shallow angle, which creates a very long, heavy cone. Interplanetary probes don't have the weight budget to accommodate that.

From what I understand and correct me if I am wrong. Radar today cannot detect small particles/meteors in space out far enough to make adjustments at speeds needed for interstellar travel currently.

To conclude the least time spent in space after a certain speed decreases the risk of collision. The faster the ship travels the narrower the collision window. Avoidance would still currently be the best option. Although we cannot scan the flight path ahead to make coarse adjustments, probes could travel ahead of ship and laser relay back to the mother ship coarse corrections do to debris that may trigger the net between them.