Breakthrough Starshot

[AmrlKJaneway]

http://www.space.com/32546-interstellar-...rshot.html

Kinda surprised this isn't being discussed here already.

So, our first starship may be a beamriding microchip. If we can work out a way to shield it against space dust as it hurtles through the cosmos at 0.2c.

Lots of big names are interested, like Hawking, and I personally can seriously see this as humanities first voyage into the interstellar medium.

Anyone else excited? Anyone foresee any major problems with the idea?

[Rynn]

Correct me if I'm wrong but this is just a rehash of the Starwisp concept. There's no work being done to actually build this, it's just a presentation piece with some recognisable names attached.

Don't get me wrong a light/mag sail swarm of ultra-light proves would be great to see in my life time. But there are soooo many practical engineering and economic considerations. Keeping multi-gigawatt lasers running for years, cramming everything you need onto the probe (including messaging laser), convincing someone to actually pay for it etc.

[AmrlKJaneway]

Yeah, the estimate is something like $5 billion for the project.

One thing I never understood about any one way beamrider is; how does the ship slow down? Can it? I imagine there'd have to be a beam of equal energy at the other end to apply the same amount of thrust in deceleration. Unless we contact some alien race at Proxima Centauri and kindly ask them to build this for us, I can only imagine the probe will reach the destination, and then just keep going until it crashes into something. And I see the probability of my alien theory as infinitesimally small.

[Drashner1]

Actually this idea has been posted to the forum earlier this year:

Link

IIRC the general consensus was that it was interesting, but needed a huge amount of development work to take it much of anywhere past the 'fun idea' zone. Also, that the political issues of getting anyone to approve giant laser cannon being built on or near Earth might be a bigger challenge than all of the technical challenges combined.

The idea of it being built within our lifetimes was deemed pretty improbable.

Regarding your question:

A minimalist one-way star probe design such as Starshot is not designed to slow down. The individual probes just fly through their target system, transmitting as much data as they can and then zip off into interstellar space, never to be seen again. Space is very big and the odds of the probes hitting anything significant or ever being recovered are considered to be infinitesimal. Or, they will eventually just be ground away or outright destroyed via collisions with interstellar gas and dust.

Todd

[stevebowers]

The Starshot concept doesn't include a deceleration phase; it just involves sending a probe through the target system at a small but significant fraction of light. As a data-collection strategy this doesn't compete very well with building larger telescopes with wide interferometer baselines.

In OA there were a few starwisp-type beamrider probes
http://www.orionsarm.com/eg-article/47f42ab73ce60
but in general much better info could be achieved by telescopes like the Eyes of Neptune
http://www.orionsarm.com/eg-article/564e2f6599744
at least, until the first decelerating probes were constructed.


A probe could reconfigure in flight to deploy a magbrake, which requires no fuel (but does require some energy), or it could use Robert Forward's idea of a reflecting sail, which would need very tightly focused beams from the launch system. Forward's idea also included a lens for focusing purposes, as seen here.

[AmrlKJaneway]

Sorry, I didn't spot the earlier thread. I looked, but must have missed it. Can the threads be merged?

Okay, that clears that up. Yeah, I figured it wouldn't be too long before dust just ate away at the thing.

[AmrlKJaneway]

The Starshot concept doesn't include a deceleration phase; it just involves sending a probe through the target system at a small but significant fraction of light. As a data-collection strategy this doesn't compete very well with building larger telescopes with wide interferometer baselines.

In OA there were a few starwisp-type beamrider probes
http://www.orionsarm.com/eg-article/47f42ab73ce60
but in general much better info could be achieved by telescopes like the Eyes of Neptune
http://www.orionsarm.com/eg-article/564e2f6599744
at least, until the first decelerating probes were constructed.


A probe could reconfigure in flight to deploy a magbrake, which requires no fuel (but does require some energy), or it could use Robert Forward's idea of a reflecting sail, which would need very tightly focused beams from the launch system.

Okay, I've read about magbrakes before, but how is the probe in that diagram returning to Earth?

[stevebowers]

This is purely a beamsail concept. The outermost 1000km ring of the sail acts as a mirror to reflect the beam onto the 320km rendezvous stage; this stage slows down to examine the system in detail and at leisure.
The rendezvous stage splits further to reflect the beam onto the return stage, which eventually comes home (and is decelerated finally by the lasers directly).

[Drashner1]

The problem with beamsails is that (much like photon drives) they are quite inefficient since only a tiny fraction of the photon energy is imparted to moving the ship (since photons must always move at the speed of light). In contrast, a beam-rider can arrange things so that the incoming mass-beam imparts nearly all of its kinetic energy to the ship (leaving the remnants of the beam almost dead in space relative to their origin).

By way of comparison:

Robert Forward's beamsail starship would use 43,000 Terawatts of laser power to accelerate an 80,000 ton ship with 3000 tons of payload (the rest of sail and supporting structures) at 1/3g up to half the speed of light after 1.6 years.

Gerald Nordley's beamrider starship would start out using mass beams operating in the tens of Terawatts to accelerate a 1000 ton ship at 5 gravities (the crew would be in protective acceleration/biostasis tanks for this part) to 86.6% of the speed of light. As the ship went faster and got further away, the energy going into accelerating the mass beam would increase until it peaked at 44,000 TW after 47.4 days of operation. The beam generator then shuts down, although the mass beam itself continues on into space to keep accelerating the ship.

The ship itself takes a full 126 days (from the frame of reference of the mass beam generator, for the ship it's only 96 days) to accelerate, after which it coasts on to its destination. Deceleration could be handled in a variety of ways

Todd

[AmrlKJaneway]

That's amazing. Never heard of it. Sounds like there's still a few issues to iron out first, but I'm glad we're making theoretical progress by designing such things.

Given all the other alternatives, like fusion and antimatter rockets, it still seems most likely to me that the future of interstellar travel is laser driven. I'm no expert in the field, it just sounds right.