Reaching for Interstellar Flight

space.com ^ | 12/17/03 | Leonard David

[PatrickHenry]

... see how truly awful those 'engineering problems' become.

I know. At the moment it's out of the question. Nevertheless, it's a worthy goal. Ten percent of c is, at least in principle, not impossible. But I readily admit I'm fresh out of practical suggestions.

[exmarine]

Don't count on such space travel. Do you know what a speck of space dust will do to a spacecraft at extreme speeds, or thousands of specks (or larger pieces) over years? Star Trek is fiction. Such a spacecraft would be battered to pieces. Space is a dangerous place.

[RightWhale]

Such a spacecraft would be battered to pieces.

Space is kind of empty. But there are dust particles and very tenuous gases out there. Suppose a spaceship the size of the Space Shuttle were moving between the sun and Alpha Cent at, say 1/2 c so the trip would take 10 years. What are the odds it would make it all the way without hitting something that would turn it to instant debris? 1 in 10? 99 in 100?

[sandydipper]

"Dave - will I dream?"

[Junior]

I've seen conjecture on using an electromagnetic "screen" to deflect such particles from the path of vessels travelling at far slower speeds within the Solar System (~40 km per second). Such a system would probably work at near relativistic speeds...

[Brett66]

The Fermi Paradox is just a rational means for organizing speculation about something that we have no clue. If they aren't here (and that can't be proven) then there's a reason for that that's beyond our limited understanding. The Drake equation is simply a rational way of categorizing what we don't know, but I believe the true answer to Fermi's paradox is simply that it's beyond our capability to understand why, the rest is speculation over Fermi's assumptions.Just remember Benny Hill's philosophy about assumptions..........

[PatrickHenry]

Such a system would probably work at near relativistic speeds...

The cow-catcher has already been invented and proven in actual usage:

[KevinDavis]

There are some dangers here on Earth also...

[Physicist]

A sail, either unaugmented or augmented, might well reach 0.05 c via repeated planetary boosts in the host system. I don't know enough orbital mechanics to be sure.

If by "planetary boosts" you mean gravitational slingshot maneuvers, the biggest (absolute) delta-v you can get out of a slingshot is, I believe, twice the orbital velocity of the planet. (And that's only under certain conditions: you have to hit the planet head-on, and be travelling slowly enough to do the full 180-degree turn, given that your impact parameter can't be smaller than the radius of the planet.) Just one of those will probably send you out of the solar system. If you're lucky with planetary alignments, you might get two or three assists before absquatulating off into the vast abrupt, but not all of them can be head-on. Planetary orbital velocities range from a few km/sec to a few tens of km/sec, but .05c is 15,000 km/sec.

If you want to get a solar sail up to mildly relativistic velocities, you'll need a monstrous laser driver in the system of origin.

[boris]

"absquatulating"

I learned a new word. My OED says:

absquatulate, v.

(&b"skwQtju;leIt)  Also absquotilate.  [A factitious word, simulating a L. form (cf. abscond, gratulate) of American origin, and jocular use.] 

   To make off, decamp.

   1837–40 Haliburton Clockmaker (1862) 363 Absquotilate it in style, you old skunk,+and show the gentlemen what you can do.  1858 Dow Serm. I. 309 in Bartlett Dict. Amer., Hope's brightest visions absquatulate.  1861 J. Lamont Seahorses xi. 179 He [an old bull-walrus] heard us, and lazily awaking, raised his head and prepared to absquatulate.  


======================

Absquatulating is not given but I suppose since it's a verb nobody can stop you from adding "-ing" to it.

--Boris

[boris]

I mentioned the use of magnetic fields for the charged particles. The other idea is like a "cow catcher": you have a BIG and THICK hunk of lead flying in front of you to absorb anything physical or uncharged. The problem is that the "cow-catcher" causes a drag; as the momentum of the incoming bad stuff is absorbed, the ship (hiding to the rear) must continually replenish the cow-catcher's momentum. Most unfortunately it adds to the mass that has to be accelerated initially and that is a very bad deal.

But it may be the only way...

--Boris

[RadioAstronomer]

Like I said, I did nto run the numbers. I was not sure of the long term acceleration vs drag on the sail from the parent star.

Thanks for the clarification.

[PatrickHenry]

The other idea is like a "cow catcher": you have a BIG and THICK hunk of lead flying in front of you to absorb anything physical or uncharged. The problem is that the "cow-catcher" causes a drag; as the momentum of the incoming bad stuff is absorbed, the ship (hiding to the rear) must continually replenish the cow-catcher's momentum. Most unfortunately it adds to the mass that has to be accelerated initially and that is a very bad deal.

Everything's a problem, which is why we're not launching starships yet, and why it's going to be quite some time until we get around to it.

I had in mind that the "cow-catcher" shield would (somehow) have a dual function, and it would also be the scoop for a Bussard ramjet. I know that Bussard ramjets aren't highly regarded these days, because they won't do all that much in providing thrust, but they will do something, and if they also provide a shielding function at the same time, they may well be worth their mass.

If I'm way off base here, I trust that those more knowledgable than I am will be reasonably gentle in their criticism.

[boris]

"I know that Bussard ramjets aren't highly regarded these days, because they won't do all that much in providing thrust"

Long ago I read Bussard's initial paper in Astronautica Acta and a long trail of subsequent papers (some by a fellow named Fish[?]) detailing the limits. But I was not aware than more recent work deprecates the idea.

It is true we don't know how to do p-p fusion, nor how to decelerate the incoming stream (it has to stay in the ship long enough to be fused!)...but what other problems have been pointed out?

--Boris

[RadioAstronomer]

One of them is the drag created by the scoop. However, I have read conflicting papers on that. Some saying can be overcome and others saying it cannot.

Note: None of those in a peer reviewed journal of astrophysics.

[PatrickHenry]

what other problems have been pointed out?

This is far from a peer reviewed surce, but NASA's website says: "There are a variety of limitations to this concept, such as how many protons can be scooped up, the drag created from scooping them, and, not to mention, the feat of getting these protons to engage in nuclear fusion for a rocket."
Source: HERE.

Further discussion of a different set of negatives of Bussard ramjets at another website: HERE. The author is an aerospace engineer at JPL.

[boris]

"I had in mind that the "cow-catcher" shield would (somehow) have a dual function, and it would also be the scoop for a Bussard ramjet."

A physical scoop would weigh too much. Doubtful it could be fashioned out of any known solid material. Bussard scoops are generally thought to be big magnetic fields. These can do nothing to stop neutral particles or dust grains. Hence the big lead cowcatcher in addition to the Bussard scoop.

--Boris

[PatrickHenry]

Hence the big lead cowcatcher in addition to the Bussard scoop.

Ungainly, isn't it? But if a ship needs a shield, as it probably does, then it may as well have the scoop too. Hey, I didn't promise you a warp drive, or even a pretty ship.