Jul 25, 2016 10:52 michael.million@sky.com Posted on: Centauri Dreams

Hi Zac

'Apr 23, 2016 23:11michael.million@sky.comPosted on: Breakthrough Initiatives
"Might be better to have a radioactive source emitting alpha particles onto a steerable deflecting sheet which can then be used to move the sail around. Or have radioactive material sprayed onto the sail and then use electrical impulses to twist the sheet so the radioactive particles give directional thrust."'

Answer:
Yes, there may be alternatives to photon pressure. The problem I see with a radioisotope source is in deflecting the particles in the direction you want, which could require very dense materials and mechanical actuators. Both would add significant weight to the spacecraft.

A dense very thin material such as tungsten (nm) could be used with the alpha emitter sprayed on and MEM actuators used to change the direction of emission, these MEMS would be very small and weigh very little. The problem I see with photon thrusters is their very poor momentum response, and they still need power which can only be applied from the laser or stars (on close approach), the battery power would be to small I would think. As for MEM ion thrusters the material fuel can be a solid as well like Iodine, these thrusters can then be switched on close to the star using solar cells for power for direction changes.

Aug 25, 2016 15:29 Monroe Pattillo Posted on: Breakthrough Initiatives

Evaluate the gained momentum based upon photon incidence angle of reflection. An engineered oblique angle should gain more momentum than a reflective surface with a random or near perpendicular incidence angle.
Consider using ion beam etching to create a photon sieve with millions of microscope frustums in an alumina surface. Face the wider open end of the frustums towards the photon source. Additional momentum is gained from single photons over multiple relfections as the individua photons traverse the frustum. Photons reflected at near perpendicular angles would be exhausted out the narrow end of the frustum as reflections at their near perpendicular angles would reduce the gained momentum.
Use a chemical rocket to boost the craft beyond the dominance of the gravitational field of the Earth.
Power the photonic thrusters using a nano version of an RTG per photon source. Through the maximization of momentum gained and the minimization of counter momentum loss a nano RTG per photon emitter should provide sufficient power and longevity. Using a nano RTG for electrical power works well beyond the limits of solar radiation for photovoltaic power and doesn't require ground based lasers for propulsion.

Aug 25, 2016 15:44 Monroe Pattillo Posted on: Breakthrough Initiatives

The photon sieve reflector would be a microscopic hard surface per photon source and not a flexible sail. The sieve would be within close proximity to the photon source.
The concept of force on a billowing sail works great on Earth to push vessels through water. The push is not the problem. Changing the direction of propulsion to slow down or turning at oblique angles (tacking) is the problem. In order to tack a vessel in water relies upon the presence of far higher than air density water combined with the existence of a keel. Once a photon powered vessel is up to high velocities even atmospheric breaking might not be sufficient for orbital entry. The thrust source must be capable of being pointed in any direction.

Sep 18, 2016 21:35 michael.million@sky.com Posted on: Centauri Dreams

If we had a slower sail which was coated in a very, very thin layer of tungsten and then an alpha emitter we could potentially use it to stop at the solar gravity focal line and use the powerful magnification property of the Sun to observe other stars in great detail, this includes communicating with spacecraft on the way to a target star. The alpha emitter could also be used as an energy supply for communications and moving in an arc to observe other objects.

Sep 25, 2016 10:35 michael.million@sky.com Posted on: Centauri Dreams

If we had a few of these slower stoppable sails we could allow each to catchup to each other to form a much larger telescope, if we arrange them to equally spaced to follow the edge of the light cone all the way to the solar focus line we could get high quality images back sooner than having to wait until the arrangement gets there.

Sep 28, 2016 05:21 michael.million@sky.com Posted on: Centauri Dreams

If we go for a slower telescope sail ~600 km/s to the solar focus line the power/energy requirements are a lot less, on the order of 1/10000 ! so we could use a modular laser unit or two to deliver the 10 - 50 MW's needed to develop the mission communication and target acquisition infrastructure before the main probe launch.

Nov 02, 2016 03:13 Breakthrough Initiatives Posted on: Breakthrough Initiatives

"Sep 18, 2016 21:35michael.million@sky.comPosted on: Centauri Dreams
If we had a slower sail which was coated in a very, very thin layer of tungsten and then an alpha emitter we could potentially use it to stop at the solar gravity focal line and use the powerful magnification property of the Sun to observe other stars in great detail, this includes communicating with spacecraft on the way to a target star. The alpha emitter could also be used as an energy supply for communications and moving in an arc to observe other objects."

Answer:
The laser launch system envisioned for Starshot could, of course, be used for a variety of other missions. Using gravitational lensing for both astronomical observations and communication has been studied extensively, but it would be impractical for a spacecraft to travel the 542 AU distance to our Sun’s focal point with current propulsion technology. Fortunately, the lensing effect can be used far beyond the initial 542 AU focal point, so stopping the spacecraft would not be necessary.

– Zac Manchester, Breakthrough Starshot

Nov 18, 2016 10:39 michael.million@sky.com Posted on: Centauri Dreams

"The laser launch system envisioned for Starshot could, of course, be used for a variety of other missions. Using gravitational lensing for both astronomical observations and communication has been studied extensively, but it would be impractical for a spacecraft to travel the 542 AU distance to our Sun’s focal point with current propulsion technology. Fortunately, the lensing effect can be used far beyond the initial 542 AU focal point, so stopping the spacecraft would not be necessary.

– Zac Manchester, Breakthrough Starshot"

If we use radioactive materials to slow and power the sail we will have a lot longer to observe a target without a smear effect and we can also move around to see more, I can imagine lots of these sails observing the galactic plane (CBH as well) where the most targets will be.

Dec 06, 2016 18:09 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Nov 18, 2016 10:39 michael.million@sky.com Posted on: Centauri Dreams
If we use radioactive materials to slow and power the sail we will have a lot longer to observe a target without a smear effect and we can also move around to see more, I can imagine lots of these sails observing the galactic plane (CBH as well) where the most targets will be."

Answer:
This is a good idea. At this time we do not know how to supply enough radioactive materials to be meaningful to meet our mass budget. We cannot get heavier because that would require we develop even a larger beamer.

– Avi Loeb, Breakthrough Starshot

Dec 07, 2016 08:10 michael.million@sky.com Posted on: Centauri Dreams

Since we only need to get the sail to around 600km/s for a decent trip time we will need a much smaller beam power, it would just be one of the module beamers that will eventually make up the much larger laser system. As for the weight of radioactive material it would be around 5 to 10 grams with a suitable half-life. The way I see it is that the RM (decay fragment) will cover some paddles that are controlled by MEM actuators, to slow down the paddles can sit where they are or could be moved out to the sides to prevent interference of the sail components. Since the RM is on paddles which can be rotated it will allow pointing and direction changes to the sail. There is also the possibility of making the RM more efficient by covering the materials with a graphene layer to prevent evaporation of the unused RM and perhaps having a honeycomb surface material that can be positivity charged to get better exhaust direction.