Laser-sailing alternative: Pellet-beam riding!

[StrandedonEarth]

https://www.sciencealert.com/shooting-tiny-high-speed-bullets-at-a-spacecraft-could-speed-up-travel-to-the-stars

I wonder how far out they think they can hit the target?

What happens if they trace a pellet beam across Mars, Phobos, Deimos, or Psyche?

Edited January 28, 2023 by StrandedonEarth

[kerbiloid]

With pusher plate of clay.

***

The laser beam is still a cone, not a line. The energy per cross-section area is ~1/distance ²

[mikegarrison]

Using a stream of driven mass to push spacecraft is an idea that has been around for quite some time. The main attraction, of course, is to evade the rocket equation by having an external source of energy and propulsion mass so you don't have to accelerate all that heavy stuff.

[farmerben]

The article says they use ablative pellets accelerated by lasers.  Pretty cool.  Back of the envelope says the typical laser pointed at Jupiter makes a spot the size of Jupiter.

[mikegarrison]

1 hour ago, farmerben said:

The article says they use ablative pellets accelerated by lasers.  Pretty cool.  Back of the envelope says the typical laser pointed at Jupiter makes a spot the size of Jupiter.

I would not necessarily assume that a stream of pellets has less dispersion than a laser. They certainly are not going to magically all be perfectly aimed over such a long distance, and then there will be gravitational perturbations on their paths, etc. They may hit tiny dust particles, get pushed by photons, or whatever.

[sevenperforce]

5 hours ago, farmerben said:

The article says they use ablative pellets accelerated by lasers.  Pretty cool.  Back of the envelope says the typical laser pointed at Jupiter makes a spot the size of Jupiter.

The typical laser pointed at the moon makes a spot much larger than the moon, so you may be off by several dozen orders of magnitude.

[kerbiloid]

Spoiler

U, Pu:  17.5 kt/kg
D+D, D+T: 80 kt/kg

1 kt = 4.2*10¹² J.

c = 3*10⁸ m/s

E  = mv²/2

(17.5 .. 80) * 4.2*10¹² * m = mv²/2

v = sqrt(2 * (17.5 .. 80) * 4.2*10¹²) / (3*10⁸) ~= 0.04 .. 0.09 c

If accelerate the bullet up to 0.1 c, its kinetic energy will exceed a nuclear blast energy per mass, thus it can blow up an Orion charge from back without a fissile,

Then like always, the tungsten membrane, tungsten jet, pusher plate.

So, it would be an inert and safe version of the orionuke, a laser-driven kickback orion scheme.

[Shpaget]

One more of those ideas that would/could/should work in practice, if only all the problems with it could be engineered away.

What happens when the pellets start hitting the shield off center, and the spacecraft is pellet-weeks away?

I'm having trouble imagining a shield sturdy enough to withstand continuous relativistic impacts, big enough to be a viable target for an interplanetary shooting range, yet still light enough to fit the one-ton-spacecraft description.

[kerbiloid]

The Orion charge with a ballast instead of its nuke, is the shield to turn the bullet energy into the conical tungsten jet energy, and thus protecting the pusher plate from concentrated central hits.

[KSK]

On 1/29/2023 at 8:57 AM, Shpaget said:

One more of those ideas that would/could/should work in practice, if only all the problems with it could be engineered away.

What happens when the pellets start hitting the shield off center, and the spacecraft is pellet-weeks away?

I'm having trouble imagining a shield sturdy enough to withstand continuous relativistic impacts, big enough to be a viable target for an interplanetary shooting range, yet still light enough to fit the one-ton-spacecraft description.

No problem. We build the Medusa variant, aim the pellets past the spacecraft and allow them to impinge on a parabolic sail.

What? Why are you looking at me?

[farmerben]

It needs either a heavy duty pusher plate, or a low relative velocity

 

Frozen CO2 makes a good pellet.  It can be ablated by lasers and ablated on impact with the spacecraft.  I'm not sure what the maximum safe relative velocity would be, at some point it does damage.

[Kerbart]

9 minutes ago, farmerben said:

Frozen CO2 makes a good pellet.  It can be ablated by lasers and ablated on impact with the spacecraft.  I'm not sure what the maximum safe relative velocity would be, at some point it does damage.

But do we have enough CO₂ on Earth to just shoot it out into space?

Edited January 31, 2023 by Kerbart

[farmerben]

https://www.nasa.gov/centers/wstf/site_tour/remote_hypervelocity_test_laboratory/two_stage_light_gas_guns.html