Sailing to Alpha Centauri

There is an interesting (and quite detailed) paper on near term feasibility of laser sail systems for interplanetary and interstellar travel.
www.deepspace.ucsb.edu...

According to their calculations a small ~1g probe could reach Alpha Centauri in 15 years, at 0.26c speed, driven by a 70GW laser system. The same system could get a 100kg probe to 0.11c. So it scales pretty decently with increasing mass.

There one minor handicap though. Those would be pure flyby missions. You simply can not afford to carry the massive amounts of fuel required to slow down from those velocities. So how do we deal with that?

One idea has been to use a magnetic sail. Unfortunately magnetic sail force drops asymptotically with the velocity. The slower you go the lower the deceleration. Slowing down to orbital velocities would take way too long.

More recently an electric sail has been proposed, which works better at low velocities. Although it requires an energy source to keep the sail charged.

There is a paper looking into combining both ideas and using a magnetic sail as the first stage followed by the electric sail to get down to orbital velocities.
arxiv.org...

With a magnetic sail limited to 50km ring radius (material constraints) their example spacecraft (8250kg total) would take 300 years to decelerate from 0.05c and would buzz past Alpha Centauri. The combined system reduces this time to 28.8 years, or 0.6 light years deceleration distance. They didn't look at low mass probes. But I assume those should perform as well if not better as the magnetic sail radius constraint is less of an issue.


Imho combined laser/magnetic/electric sail systems could well be the future of interstellar exploration and travel, especially combined with mini/micro/nanobot probes.

My preferred idea for large masses (humans) would be to install a laser driver in the target system to take care of the deceleration issue. It could maybe even be constructed in situ by bots sent in advance. But that might be a not so near term solution.

How would it beam back whatever it saw there?

a reply to: moebius

Good call. The first mission should be to setup a laser braking system in-situ somewhere in the Centauri system. That would make followup trips much more feasible and bring long term costs way down. Might allow for return trips too. It would have to be done with robots, and be Solar powered for long-term feasibility. I imagine some self repair capability would be required as well.

Annual peak demand for electricity for entire US grid is currently 786GW so 70GW for a single flyby probe to capture images won't be cheap by any means. With my rusty maths I estimate the electricity bill will cost over a trillion dollars at 10c a kilowatt (1,000,000 KW in a GW) over 15 years. So lets hope the camera works.

a reply to: glend

It would be an expensive bill for sure.

But I'm thinking that we could use a completely automated nuclear reactor on board the probe to provide power to the laser.

Of course you would need to find materials that wouldn't wear out for the laser before reaching its destination.

Question...

Why do stars appear to rotate counterclockwise at the north pole, and clockwise at the south pole?

a reply to: InachMarbank

because people on south pole are upside down.

originally posted by: projectvxn
But I'm thinking that we could use a completely automated nuclear reactor on board the probe to provide power to the laser.

Wouldn't that be like blowing on your own sail on your own sailboat when there's no wind? Would that even work?

Anyway that's not the idea being discussed in the first link in the OP, which is to leave the power supply/laser source behind to reduce mass of the probe.

I can see it working for interplanetary missions, but I'm not so sure it will work for interstellar missions. Maybe it would as a hybrid technology, where they have something on-board the probe for steering since steering isn't feasible with the laser propulsion. Without some kind of on-board steering, the accuracy required to hit a target 10 light years away I suspect would be beyond the capability of the laser-sail technology alone.

originally posted by: InachMarbank
Question...

Why do stars appear to rotate counterclockwise at the north pole, and clockwise at the south pole?

Question: Why would someone attempt to hijack an existing thread with an off-topic question, instead of starting a new thread?