[X] My Assistant

[nprev]

If this thread's in the wrong place, please relocate...thanks!

Assuming for the sake of argument here that someday we'll have propulsion systems capable of propelling vehicles at a significant fraction of the speed of light, what kinds of technical challenges will be presented by the interstellar medium?

Right out of the gate, I can't see how anything we might build could survive hitting so much as a dust grain at even 0.01C. Heavy forward shields have been proposed, but the jolts from such collisions even if the spacecraft isn't vaporized would seem a bit unsettling to the payload.

Assuming that issue can be overcome and that we can actually go even faster (<0.5C), at what point would interstellar hydrogen become aerodynamically (or even hydrodynamically!) significant as far as drag? Would true starships actually have to look something like hypersonic aircraft, or even subs depending on relative hydrogen density?

[nprev]

You know, I was thinking that too, but I also kept thinking that the entire vehicle would have to be pretty mechanically robust just to survive continuous acceleration up to cruise speed via the magic high-energy drive, so this would imply some very firm (and therefore kinetic-energy-transmissive) connections between the various sections of the Web.

However, what if the payload elements were very light & small themselves and therefore did not require a robust physical support structure? For example, we're really not far from nanoprocessors based on quantum principles...the only catch seems to be that optical & RF sensors have to have comparatively large surface areas, unless there are a lot of them working in a coordinated fashion al a TPF or the VLA. Catch # 2 then is that the whole Web would have to be functional upon arrival for nominal performance...

[mchan]

the entire vehicle would have to be pretty mechanically robust just to survive continuous acceleration up to cruise speed ...

If it can withstand 1G, continuous acceleration for about 35 days will get it to 0.1c. The mechanical robustness would come from a structure that can store the volume and accelerate the mass of fuel required to run the engine for 35 days.

[nprev]

If it can withstand 1G, continuous acceleration for about 35 days will get it to 0.1c. The mechanical robustness would come from a structure that can store the volume and accelerate the mass of fuel required to run the engine for 35 days.

...and 35 days of deceleration plus terminal manuevering as well. Thanks, Mchan.

Deglr, could you please post your source equations? That sure sounds like a scary possibility...this whole mission isn't gonna be easy for somebody, someday...

EDIT: The CMBR is non-directional, right? Therefore, the only "enrichment" of the radiation would be directly along the flightpath of the spacecraft with some sort of probabilistic distribution (normal, Gaussian, etc.); is the relative "density" of it along an interstellar trajectory significant enough to induce undesirable effects?

AFAIK, the same argument would also apply to cosmic rays, though those that the ship would encounter with flight paths directly opposite to the ship's vector would be fearsome in terms of energy; maybe these deserve some thought!

[Thu]

EDIT: The CMBR is non-directional, right? Therefore, the only "enrichment" of the radiation would be directly along the flightpath of the spacecraft with some sort of probabilistic distribution (normal, Gaussian, etc.); is the relative "density" of it along an interstellar trajectory significant enough to induce undesirable effects?

Agree with you on this, I don't think CMBR will be a danger for the ship.

I'd like to summarize the idea for the first interstellar spacecraft as below.

S/C design:
- Giant spider web-like space craft with payload distributed at the nodes (maybe a kilometer in diameter)
- Very light weight with miniatured instrument (less than 100kg for the whole s/c?)
- It carries no engine nor fuel but propelled by light pressure from a powerful laser beam from Earth orbit
- The material will be strong enough to withstand acceleration of 1g without affecting the web structure (is carbon nanotube suitable for that job?)

Pros:
- Because it is so light that the amount of energy is required to accelerate it to 0.1c is not unimaginable. A quick calculation with a s/c mass of 100kg showed an energy of 45*10e9 megajoules. I think we can achieve this amount of energy at the middle of this century.
- Low surface area -> reduced chance of dust hitting the s/c (but this is also bad for light propulsion from Earth)
- Large "virtual aperture" is good for radar communication with Earth (but I'm not sure whether it is good for optical remote sensing or not)
- Required technologies: nanotech, quantum computer, solar sail... is technologically feasible within this century.

Cons
- Chance of hitting by dust particle, although low but still can happen
- There's no way to decelerate the s/c once it gets to its destination (don't tell me that ET has prepared another laser beam station at their site to slow the craft down )

With this design, I believe we can see the first close-up images of the nearest star system by the end of this century

[marsbug]

Cons
- Chance of hitting by dust particle, although low but still can happen
- There's no way to decelerate the s/c once it gets to its destination (don't tell me that ET has prepared another laser beam station at their site to slow the craft down )

With this design, I believe we can see the first close-up images of the nearest star system by the end of this century

Thu; Very nice summary, although if we had ET at the other end with a deceleration laser at least we'd be gauranteed someone for the probe to take pictures of at the other end! The problem of decellerating without a co-operative space alien at the destination has been looked at in a couple of papers: T. Taylor, R.C. Anding et al., “Space Based Energy Beaming Requirements for Interstellar Laser Sailing,” CP664, Beamed Energy Propulsion: First International Symposium on Beamed Energy Propulsion, ed. By A.V. Pakhomov (2003), American Institute of Physics 0-7354-0126-8. The original Forward paper — now considered a classic — is “Roundtrip Interstellar Travel Using Laser-Pushed Lightsails,” Journal of Spacecraft and Rockets 21 (1984), pp. 187-195. I'm still working out how to post links, sorry im a bit of a technophobe to be honest, but if you put 'interstellar laser sail' into google you should get a good sweep of material on the subject. Hope this is of some use.