[X] My Assistant

[ngunn]

Thu, that's an interesting approach. The only thing I wonder about is whether your web still might be excessively vulnerable to debris damage to the degree that the structural integrity of the entire vehicle could be compromised, regardless of payload redundancy.

No, Thu has it absolutely right. The craft is thin so the impactors go straight through with only a minimal transfer of kinetic energy to cause damage.

[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...

[deglr6328]

I think we are neglecting a VERY important issue here. The cosmic microwave background radiation! If I calculated right (which is questionable!) at just 10% of C the CMBR would be blueshifted into the deep ultraviolet range. CMBR photons outnumber photons from all other sources in the universe by an enourmous ratio, I suspect you would be absolutely ROASTED alive by the UV flux.

[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.

[J.J.]

Lots of good ideas in this thread.

I also favor a free-flying shield, as well as a simple precursor IEE mission (think Pioneer 10 and 11) that could give us important data on what the ISM is like at 5-15% c. I'm guessing that as little as a decade or two of data would be enough for us to extrapolate the risks of more ambitious missions.

For the record, my dream target for a first mission would probably be the Sirius system; even though it's twice as far as AC, assuming we find no planets at the latter, the former will give us in situ data on two objects very different from the Sun.

[Mongo]

I think we are neglecting a VERY important issue here. The cosmic microwave background radiation! If I calculated right (which is questionable!) at just 10% of C the CMBR would be blueshifted into the deep ultraviolet range. CMBR photons outnumber photons from all other sources in the universe by an enourmous ratio, I suspect you would be absolutely ROASTED alive by the UV flux.

Huh? At 10% of C, relativistic effects are still quite small, since y = 1 / (1 - v^2), where v is measured in C (half light speed = 0.5) is still only about 1.01 (Time dilation = T/y, Lorentz contraction = L/y), so the biggest effect by far would be the CMB directly ahead blue-shifted by 10% due to the vehicles velocity relative to the CMB. The radiation would remain in the microwave domain, undetactable except by special antennae.

Bill

[deglr6328]

Oops! I guess I did that wrong! Hey I was only 5 orders of magnitude off. Hmmm so I suppose we can neglect that issue until we get to the 99.999% C area (~16nm wavelength)...... Did I do THAT one right?

[nprev]

Don't feel bad, Deglr; I was too lazy to do the math at all! Thanks to you & Mongo for fleshing it out.

Thu, I understand you now. Been thinking that it would decelerate & remain in the target system, but a fast flyby mission would at first glance be much easier to execute from an engineering standpoint. Two problems, though:

1. Given the large relative speed, would a fast flyby yield enough scientifically worthwhile data to justify the trip?

2. Re the debris collision problem: There's a LOT more of it within a solar system; do you think the probe can survive the encounter phase?

[Thu]

Nprev, I'm sorry for not mentioning it's a flyby trip earlier.

1. Given the large relative speed, would a fast flyby yield enough scientifically worthwhile data to justify the trip?

Actually I'm thinking of this mission is somehow kind of Pioneer 10/Pioneer 11 mission when we were not sure whether a s/c can safely pass the asteroid belt or not. Technically speaking it is also feasible within the next some decades, I think. However for a mission to yield enough data to satisfy UMSF fans here I think a much better s/c design is obvious

2. Re the debris collision problem: There's a LOT more of it within a solar system; do you think the probe can survive the encounter phase?

You have a reason but let's think of sending multiple spacecrafts for redundant.

[nprev]

Gotcha. But 0.1c translates into around 30,000 km/sec in-system relative velocity. I'm concerned that it would be difficult to target close planetary flybys (to say nothing of acquiring a useful data set).

You could certainly get some good particle & field data for the target system (note: this was the primary focus of the Pioneers) as well as detailed observations of the star itself, but I have my doubts that such a mission could acquire planetary imagery comparable to some of the more ambitious Terrestrial Planet Finder (TPF) proposals, and literally any of those would be less risky & more cost-effective. So, apparently the type of mission is fundamentally dependent upon its goals!

EDIT: Here's a thought: What if the Web's payload packages are equipped with retros? Specifically, if there are, say, 100 payload packages with onboard guidance, control & propulsion (notionally each of them an MRO-equivalent in terms of payload capability) & they each have a smaller version of our magic drive, why can't the probe drop them off just before it passes through the system? Each surviving probe would be targeted to a specific planet within range of the "root" trajectory (that of the Web), and capable of achieving at least a highly elliptical orbit around its target planet. (Yes, we're gonna need some good AI here...)

One concern would be returning data to Earth from these critters. Some of the payload elements would have to be relay comsats with laser tranceivers capable of reaching Earth, and multiplex RF links for the exploratory elements.

EDIT2: Heck, you could even equip the payload packages with solar sails to augment deceleration if you release them early enough...solar drogue chutes?

[Bob Shaw]

Have a look at this:

http://en.wikipedia.org/wiki/Project_Daedalus

Project Daedalus was a BIS study carried out in the 1970s to look at a 'reasonable' interstellar mission, and most of the points in this thread were addressed by it (bar the light-sails, which hadn't been thought of at that point).

And:

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1989007533.pdf

The US Naval Academy/NASA Centuari probe study - unlike the BIS flyby study, it would go into orbit around the new star after it's 100-year journey.


Bob Shaw

[nprev]

Thanks, Bob. I had just barely heard of the Centauri study; looks like some good reading!

Well, we're certainly not re-inventing the wheel here; that would assume that the wheel already exists! Re enabling technologies for an interstellar mission, the only one that seems to be advancing at the desired rate is electronics; there seems to be little if any magic engine research in the offing...