# Would a relativistic ship really need much shielding?

• Albertgauss
In summary, a relativistic ship traveling in deep space would need much less shielding than if it were at rest in space. The energy of a proton hitting a spacecraft would be much less than the energy of a dental X-ray.
Albertgauss
Gold Member
Hi all,

It doesn't seem that a relativistic ship traveling in deep space would need much shielding due to particles at rest in the space frame, appearing relativisitc now in the ship's frame. Here's the calculation I did:

Let's imagine a ship the size of a space shuttle traveling with γ of 7 (β = 0.99 ). I assume that when a society can build such a ship, it will be a decent size, comparable to our space shutttle, and use such values therein. I'll approximate the cockpit as a flat circle(normal vector parrallel to direction of travel) with a diameter of 8.7m, for an area of 59 m^2. Now, let's allow 1 proton per m^3 (over estimate) in deep space and sort them in an area of 59 m^2 so that, at a particular time, 30 protons or so will impact the cockpit of our ship. I know that 1 proton per m^3 is a volume density, so making such a number an area density is, again, an overestimate.

In the ship's frame, the ship will be at rest, and 30 protons will impact the cockpit. THe rest mass of a proton is 900 MeV, we have 30, and they each have γ=7, so the ship will encounter an energy of 1.89(10^11) eV worth of energy.

Compare this to the energy of a dental X-ray. E=hf, f = 10^17, so the energy of a photon here is 65eV. In a typical dental X-ray, there would be 10^26 particles or so, so we have about 10^27 eV in a dental X-ray, and ~10^11 eV from outerspace protons.

Thus, a ship traveling with a γ = 7 will encounter much less energy from protons in deep space than it would by bombarding it with a dental X-ray. It is true that the deep space protons themselves are far more energetic than a dental X-ray photon, but there are so few, would it even be worth much worry? I would guess there are more relativistic protons from our own atmosphere via solar wind that pass through a human body per second than a ship traveling at light speed would have to worry about in deep space.

Does this calculation make sense? Why is shielding from outer-space protons appearing relatvistic in the ship's frame so much of a problem for near light speed travel? Or maybe its not so big a deal for β=0.99 but is more of a concern for higher β's.

Several major problems:

1) You don't compute dose over the whole journey. You compute a dose (even given all your figures) corresponding to the time it takes the ship to go one ship length. You need to mulitply this by, e.g. 100 light years / ship's length.

2) Your figures for the energy of an x-ray dose are way too high. See: http://en.wikipedia.org/wiki/X-ray

3) You ignore interstellar dust. You need to ask how much dust there is in ship's cross section X 100 light years. One speck could be devastating.

4) Your figures for overall density of interstellar medium are way off. See: http://en.wikipedia.org/wiki/Interstellar_medium. Note, you may encounter regions with 10^6 molecules per cubic centimeter.

5) You forget very rare events (that are not so rare over 100 light years). For example, a pinhead size piece of debris kicked into an interstellar region.

## 1. Would a relativistic ship experience significant radiation exposure without shielding?

Yes, a relativistic ship traveling at high speeds would encounter a high concentration of radiation from cosmic rays and other sources. Without proper shielding, this radiation could be harmful to the crew on board.

## 2. What kind of shielding would be needed for a relativistic ship?

The type of shielding needed would depend on the speed and direction of the ship's travel. For example, a ship traveling at near-light speeds would require thick layers of lead or other heavy materials to block radiation, while a ship traveling at slower speeds may only need lighter materials such as aluminum or plastic.

## 3. Is it possible to completely shield a relativistic ship from radiation?

No, it is not possible to completely shield a relativistic ship from all forms of radiation. However, with proper shielding and design, the amount of radiation exposure can be greatly reduced to safe levels for the crew.

## 4. How does the size of the ship affect the need for shielding?

The size of the ship does not necessarily affect the need for shielding, but it can impact the type and amount of shielding needed. A larger ship would require more shielding to protect the entire vessel, while a smaller ship may be able to get away with less shielding due to its size.

## 5. Can the crew of a relativistic ship be protected from radiation without the use of shielding?

No, shielding is currently the most effective way to protect the crew of a relativistic ship from radiation exposure. However, advancements in technology and research may lead to alternative methods of protection in the future.

• Special and General Relativity
Replies
17
Views
1K
• Sci-Fi Writing and World Building
Replies
4
Views
2K
• Special and General Relativity
Replies
8
Views
1K
• Sci-Fi Writing and World Building
Replies
52
Views
4K
• Sci-Fi Writing and World Building
Replies
6
Views
1K
• Special and General Relativity
Replies
5
Views
2K
• Special and General Relativity
Replies
30
Views
2K
• Sci-Fi Writing and World Building
Replies
96
Views
6K
• Sci-Fi Writing and World Building
Replies
90
Views
7K
• Special and General Relativity
Replies
2
Views
2K