# Tag Info

20

It's theoretically possible to collect fuel from near empty space, the bussard ramjet is an example of an engine designed to do just that. The principle is that you use magnetic fields to collect and concentrate hydrogen atoms from the near vacuum of space, and then a fusion rocket would turn some of this into propulsion for speed and a fusion reactor would ...

11

The density of the interstellar medium varies hugely, so the specific problem of Sol-to-Proxima-Centauri travel is different from the general problem of interstellar travel. According to WP: In cool, dense regions of the ISM, matter is primarily in molecular form, and reaches number densities of $10^6$ molecules per $cm^3$ (1 million molecules per $cm^3$). ...

11

Not a chance. Those "clouds" are a vacuum, but just a vacuum that has a few more particles than outside those "clouds". The density of those "clouds" around 1–100 particles per cm³. You can't breathe it at all. You may want to look at this Scaling in Density page at Princeton University: Earth: 5.5 gram/cm³, $1.8 \cdot 10^{23}$ molecules per cm³, Earth ...

9

Even at the high atmosphere level, far below 'space' it is barely possible. Look at Skylon, whose core focus is to inject enough oxygen from the very thin air, cool it and compress it very fast down to LOX to then use it as oxidizer, since normally oxygen at high atmosphere is not usable for this. I.e. Extend ability to run 'air-breathing'. And Skylon is ...

8

Based on this answer: $$E \approx \frac{1}{2} m v^2 = \frac{1}{2} m c^2 \left(\frac{v}{c}\right)^2$$ The mass of a proton $m_P c^2$ is about 938 MeV, so if an innocent atom of hydrogen or bare proton in space were hit by a spacecraft at 0.1 c, in the spacecraft's frame it would look like a speedy proton. Of what energy? E = \frac{938}{2} 0.1^2 = 4.7 \text{ ...

8

I don't see how it could possibly be the cause--it would make interstellar travel harder, it wouldn't make it impossible and it wouldn't destroy the species--once they found out about it they could beef up the defenses of their starships.

8

The heliopause is not expected to be a sharp cutoff, but instead a turbulent and fluctuating area, outside of which there is one norm, and inside another. The transition could be much wider than we expect, hence the IBEX mission has been sent to understand this further, but no one is doubting that the data shows something is happening at the heliopause. ...

7

Yes. On the 25th of August, 2012, Voyager 1 measured very abrupt changes in two out of three of the criteria listed in the question. This was in fact Voyager 1 crossing the heliopause. In a single day. The kicker was that the magnetic field direction only changed by 2°. This was a puzzlement. By sheer luck, a large coronal mass ejection from the Sun ...

7

Theoretically yes. But it would take hell of a lot of time. In all phases, the interstellar medium is extremely dilute by terrestrial standards. In cool, dense regions of the ISM, matter is primarily in molecular form, and reaches number densities of 106 molecules per cm3. In hot, diffuse regions of the ISM, matter is primarily ionized, and the density ...

6

Others have already clarified that the chance of encountering another massive body in interstellar space is astronomically small. However, there is still something to consider for course corrections, which is that a very small error in velocity early in your transfer orbit to Alpha Centauri can result in a huge error in your intercept with the system. ...

6

Interstellar comets are icy bodies traveling in the areas between stars. They're just like the comets in the Oort Cloud, with the exception that they've been ejected from whatever stellar system they formed in. Wikipedia cites a good paper that analyzes the distribution of these comets, The Demographics of Long-Period Comets by Paul J. Francis. Francis gives ...

5

The issue is that the collection mechanism tends to produce more drag than thrust. Robert Zubrin and Dana Andrews showed that this makes most Bussard Ramjet-type starship propulsion impractical. In fact, this sort of mechanism is so good at producing drag, it actually does function well for decelerating a starship once it reaches its destination, meaning ...

4

The effects of gravity falls off very quickly (following the inverse square law) at large distances, so the pull of other stars would be negligible on the probe. This is even more so for planets in other systems, or comets/asteroids. As they are so far away, stars and planets would not be an issue. Encountering an ejected planet, asteroid, comet, etc. ...

4

Let's start with a few unspoken assumptions Radiation refers to emissions from any body in space. To name a few possible sources Star Nebula Gas giant Danger means danger to humans Sun refers to our very own Sol The answer may appear to contradict itself at times. This may be because my attempt here is to provide a ... holistic (for want of a better ...

4

Yes as you move away from our solar system the radiation from the sun decreases because it follows inverse square law.. But other source of radiation is Galactic cosmic radiation : Galactic Cosmic Radiation (GCR) Galactic cosmic radiation originates outside the solar system. It consists of ionized atoms ranging from a single proton up to an uranium nucleus. ...

4

No. The interstellar medium is almost a vacuum, just like the heliosphere. In fact, this is a lower pressure than we've ever created on Earth, at 1-1000 atoms/cm3, so 1020 times lower than atmosperic pressure on Earth.

3

Overview Having an interstellar probe brings up several major design issues. Two of the biggest are power and communication systems. Additional problems such as thermals, propulsion/trajectory are relatively trivial compared to the systems above. Major Problematic Subsystems Power: As solar intensity drops off at 1/r^2 anything beyond about 8 AU isn’t ...

3

This 2012 blog post reports progress from one study into this question. In summary, using a 1MW transmitter with a 40m dish on the interstellar probe, and an array of telescopes spread over a 10km or so circle on Earth, they estimated a data rate of a few hundred kilobits per second from a nearby star. They also suggest some more exotic solutions, such as ...

3

From the Nasa missions page: "We literally jumped out of our seats when we saw these oscillations in our data -- they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble," Gurnett said. "Clearly we had passed through the heliopause, which is the long-...

3

Interstellar travel isn't the issue — stars are close together and even at 10%c the Milky Way could be traversed safely in 10M years. 10M years isn't a factor. Even if it's 100x slower at 0.1%c, 1bn years to colonize an 11 or 12bn year old galaxy with 6-10bn year old metallic stars (thought to be required for life) isn't a strong filter. If a filter ...

2

The problem you have with this concept is that there simply isn't enough mass out there to accelerate to make this worthwhile. The average density of hydrogen in space is 1 atom per cubic centimeter, which is essentially nothing. Say you had an engine which could impel the hydrogen atoms in 10 cubic meters of space per second, that would be 10,000,000 ...

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