Is 10% of the speed of light technologically achievable?

[Jokodo]

A projectike designed to make a splash at impact? Sure.

A probe designed to take a few photos during flyby? Probably, though there's always a chance a random dust particle will blast your camera to pieces en route (or the entire probe).

A lander, manned or unmanned? Not very likely. The hard part isn't speeding up, it's allowing down at a rate crew and equipment can survive.

 

[Loren Pechtel]

A lander, manned or unmanned? Not very likely. The hard part isn't speeding up, it's allowing down at a rate crew and equipment can survive.

If you're not using a laser pump a lightsail can stop the same way it started. Otherwise, though, I do agree that stopping is probably harder than starting. You get some impressive numbers looking at using the target star for an aerobrake--and that might not be good for the planets even if you could pull it off.

 

[steve_bank]

A solar sail.

The solar radiation pressure value is taken the link.

By my reckoning it would take about 1.5 years to get an SUV to Mars with 10,000 m^2. Final velocity .0025%C.

With 1kg and 10,000m^2 final velocity about 0.1%C, ,.001C

It has to be reworked a little for a laser.

//solar sail
clear

au = 149597870700  // meter
C = 300000000
ptab = zeros(6,1)
r = zeros(6,1)
//micro newrons
ptab(1) = 227e-6
ptab(2) = 59.7e-6
ptab(3) = 17.6e-6
ptab(4) = 9.08e-6
ptab(5) = 3.93e-6
ptab(6) = .34e-6
r(1) = .2 * au
r(2) = .39 * au
r(3) = .72 * au
r(4) = 1 *au  // Earth
r(5) = 1.52 * au  // Mars
r(6) = 5.2 * au  //Jupiter


function [pressure] = solar_power(distance,pressure_ref, distance_ref)
    //inverse square law
    pressure = pressure_ref*(distance_ref^2)/(distance^2)
endfunction




time_step = 60*60*24  // 1 day seconds
velocity = 0
distance = r(1) //first data point
//Orion capsule 33446kg Jeep Cherokee SUV  2300kg
ship_mass = 2300 //kg
sail_area = 10000 //m^2
n= 300  // days

for i = 1:n
 
    pressure = solar_power(distance,ptab(1), r(1))
    force = pressure * sail_area
    acceleration = force/ship_mass
    //Euler's method
    delta_v = acceleration * time_step
    velocity = velocity + delta_v
    distance = distance + (velocity * time_step)
    f(i) = force  //newtons
    p(i) = pressure  // pascals
    v(i) = velocity  //m/s
    t(i) =i/360. // years
    d(i) = distance/au // AUs
    pcc(i) = 100*velocity/C //percent C
    a(i) = acceleration/9.8
end

w1 = scf(1)
clf(w1)
subplot(2,3,1)
plot2d(t,p)
xgrid
title"PRESSUR PASCALS"
subplot(2,3,2)
plot2d(t,f)
xgrid
title"FORCE NEWTONS"
subplot(2,3,3)
plot2d(t,v)
xgrid
title"VELOCITY"
subplot(2,3,4)
plot2d(t,pcc)
xgrid
title"%C"
subplot(2,3,5)
plot2d(t,d)
xgrid
title"DISTANCE AU"
subplot(2,3,6)
plot2d(t,a)
xgrid
title"ACCELERATION G"

 

[Jokodo]

A solar sail.

The solar radiation pressure value is taken the link.

By my reckoning it would take about 1.5 years to get an SUV to Mars with 10,000 m^2. Final velocity .0025%C.

With 1kg and 10,000m^2 final velocity about 0.1%C, ,.001C

It has to be reworked a little for a laser.

//solar sail
clear

au = 149597870700  // meter
C = 300000000
ptab = zeros(6,1)
r = zeros(6,1)
//micro newrons
ptab(1) = 227e-6
ptab(2) = 59.7e-6
ptab(3) = 17.6e-6
ptab(4) = 9.08e-6
ptab(5) = 3.93e-6
ptab(6) = .34e-6
r(1) = .2 * au
r(2) = .39 * au
r(3) = .72 * au
r(4) = 1 *au  // Earth
r(5) = 1.52 * au  // Mars
r(6) = 5.2 * au  //Jupiter


function [pressure] = solar_power(distance,pressure_ref, distance_ref)
    //inverse square law
    pressure = pressure_ref*(distance_ref^2)/(distance^2)
endfunction




time_step = 60*60*24  // 1 day seconds
velocity = 0
distance = r(1) //first data point
//Orion capsule 33446kg Jeep Cherokee SUV  2300kg
ship_mass = 2300 //kg
sail_area = 10000 //m^2
n= 300  // days

for i = 1:n
 
    pressure = solar_power(distance,ptab(1), r(1))
    force = pressure * sail_area
    acceleration = force/ship_mass
    //Euler's method
    delta_v = acceleration * time_step
    velocity = velocity + delta_v
    distance = distance + (velocity * time_step)
    f(i) = force  //newtons
    p(i) = pressure  // pascals
    v(i) = velocity  //m/s
    t(i) =i/360. // years
    d(i) = distance/au // AUs
    pcc(i) = 100*velocity/C //percent C
    a(i) = acceleration/9.8
end

w1 = scf(1)
clf(w1)
subplot(2,3,1)
plot2d(t,p)
xgrid
title"PRESSUR PASCALS"
subplot(2,3,2)
plot2d(t,f)
xgrid
title"FORCE NEWTONS"
subplot(2,3,3)
plot2d(t,v)
xgrid
title"VELOCITY"
subplot(2,3,4)
plot2d(t,pcc)
xgrid
title"%C"
subplot(2,3,5)
plot2d(t,d)
xgrid
title"DISTANCE AU"
subplot(2,3,6)
plot2d(t,a)
xgrid
title"ACCELERATION G"

10,000 square meters is for noobs.
Try 100 square kilometers.

You may not be able to make a 100 square km solar sail that's both strong enough not to immediately tear, and light enough so you stay within your mass limits, with any material found on Earth.

That's not such a biggie though. All you need to do is mine the ultrathinfilmium we know must be there just below the surface of the moon.

BTW, are you interested in buying stocks of my ultrathinfilmium mining operation? It's going to be *the* big thing in the next decade.

 

[Jokodo]

A lander, manned or unmanned? Not very likely. The hard part isn't speeding up, it's allowing down at a rate crew and equipment can survive.

If you're not using a laser pump a lightsail can stop the same way it started. Otherwise, though, I do agree that stopping is probably harder than starting. You get some impressive numbers looking at using the target star for an aerobrake--and that might not be good for the planets even if you could pull it off.

Using a star for aerobraking sounds like you will need several tons of extra mass just for thermal insulation - and that won't save you either of you're the tiniest fraction of an arcsecond off course.

 

[Tigers!]

BTW, are you interested in buying stocks of my ultrathinfilmium mining operation? It's going to be *the* big thing in the next decade.

Will you accept bitcoin?

 

[lpetrich]

G. Marx in Communication with Extraterrestrial Intelligence (CETI) (Carl Sagan, ed. 1973), pp. 215 - 226 worked out equations for rockets, Bussard ramjets, and laser-reflection propulsion. I remembered that from long ago, and I am now checking those equations with Mathematica.

 Tsiolkovsky rocket equation - Newtonian limit - independently derived by William Moore (1810, 1813), Konstantin Tsiolkovsky (1903), Robert Goddard (1912), Hermann Oberth (1920). The relativistic version was derived by Jakob Ackeret in 1946.

 Bussard ramjet

 Laser propulsion a form of  Beam-powered propulsion

I checked all the math, and I found one typo that doesn't affect any of the main results, a typo in a series expansion of one of the integrals.

It was an elliptic integral, and I used Mathematica to find an exact expression in terms of a basic set of such integrals, the Jacobi elliptic integrals.

 

[lpetrich]

 Breakthrough Starshot

Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail interstellar probes named Starchip,[1] to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.[2][3]

A flyby mission has been proposed to Proxima Centauri b, an Earth-sized exoplanet in the habitable zone of its host star, Proxima Centauri, in the Alpha Centauri system.[4] At a speed between 15% and 20% of the speed of light,[5][6][7][8] it would take between twenty and thirty years to complete the journey, and approximately four years for a return message from the starship to Earth.

The conceptual principles to enable this interstellar travel project were described in "A Roadmap to Interstellar Flight", by Philip Lubin of UC Santa Barbara.[9][10] Sending the lightweight spacecraft involves a multi-kilometer phased array of beam-steerable lasers with a combined coherent power output of up to 100 GW.[11]

I am totally skeptical. There are a lot of engineering challenges that must be overcome, challenges like keeping the beams aimed at the spacecraft and keeping high-power lasers in phase and the spacecraft being able to communicate back to home what they find.

 

[steve_bank]

From what I see on the net there is a raction force with a laser. Maybe yiu need two lasers, one n the opposite direction to make the platform recoiless.

Keeping the laser o a sail could be accomplished with a simple radio feedback system. Radio feedback to adjust a mirror at the laser.

The laser beam diameter will expand with distance.

Having nothing better to do, a macro done in Open Office Basic. For those interested in designing their own space ship.

REM  SOLAR SAIL

Sub Main
au = 149597870700  ' meters
time_step = 60*60*24 'm 1 day seconds
velocity = 0
distance_ref =  .3 * au
distance =   distance_ref
pressure_ref = 227e-6 ' first data point pressure
C = 300000000
ship_mass = 100.  ' kg 
sail_area = 1000 ' m^2
 n= 150 ' days
 
 dim     f(n) as double   'force
dim     p(n) as double    'pressure
 dim    v(n) as double    'velocity
dim     t(n)  as double    'days
dim     d(n) as double    'distance
dim     pcc(n) as double  '%C
 dim    a(n) as double     'acceleratio
 
 dim i as integer
 
for i = 1  to n

   ' inverse square law
   pressure = pressure_ref*(distance_ref^2)/(distance^2)
    force = pressure * sail_area
    acceleration = force/ship_mass
    rem Euler's method
    delta_v = acceleration * time_step
    velocity = velocity + delta_v
    distance = distance + (velocity * time_step)
    
    f(i) = force  'newtons
    p(i) = pressure  ' pascals
    v(i) = velocity ' m/s
    t(i)  =  i/360.  'years
    d(i) = distance/au  ' AUs
    pcc(i) = 100*velocity/C  ' percent C
    a(i) = acceleration/9.8  ' gs
    
 next i
 
'write to spreadseet
Dim Doc As Object
Dim Sheet As Object
Doc = ThisComponent
Sheet = Doc.Sheets (0)

' zero cells
for i = 0 to n

    Cell = Sheet.getCellByPosition(0,i)
    Cell.Value = 0
    
    Cell = Sheet.getCellByPosition(1,i)
    Cell.Value = 0
    
    Cell = Sheet.getCellByPosition(2,i)
    Cell.Value = 0

next i

for i = 1 to n-1

    Cell = Sheet.getCellByPosition(0,i)
    Cell.Value = t(i)
    
    Cell = Sheet.getCellByPosition(1,i)
    Cell.Value = d(i)
    
    Cell = Sheet.getCellByPosition(2,i)
    Cell.Value = pcc(i)
    
    
next i



End Sub

 

[lpetrich]

It's not about using lasers as rocket engines. It's about a stay-at-home laser that is aimed at a spacecraft to propel it by radiation pressure.

Lasers as rocket engines?

Though a laser has an "exhaust" velocity of c, inefficiencies in the laser's powerplant and in the laser itself reduce the effective value to well below c. A 35% efficient steam engine and a 20% efficient laser combine to give 7% total efficiency.

A simpler approach would be to use a radiator panel that is insulated on one side. With sufficiently good insulation, most of the heat energy will be radiated on the non-insulated side. That radiation is approximately isotropic, giving an efficiency factor of 50%.

One may get better collimation by radiating the heat from a ball onto a much larger parabolic mirror. The infrared light then bounces off that mirror and becomes approximately collimated, getting an effective exhaust velocity close to c.

 

[Jokodo]

It's not about using lasers as rocket engines. It's about a stay-at-home laser that is aimed at a spacecraft to propel it by radiation pressure.

Lasers as rocket engines?

Though a laser has an "exhaust" velocity of c, inefficiencies in the laser's powerplant and in the laser itself reduce the effective value to well below c. A 35% efficient steam engine and a 20% efficient laser combine to give 7% total efficiency.

A simpler approach would be to use a radiator panel that is insulated on one side. With sufficiently good insulation, most of the heat energy will be radiated on the non-insulated side. That radiation is approximately isotropic, giving an efficiency factor of 50%.

One may get better collimation by radiating the heat from a ball onto a much larger parabolic mirror. The infrared light then bounces off that mirror and becomes approximately collimated, getting an effective exhaust velocity close to c.

An exhaust velocity of c doesn't give you high momentum of the exhaust consists mostly of low energy (infrared) photons. Effectively, if I don't have a knot in my head, the acceleration would be, best case scenario, equal to the tiny mass difference between the plutonium and its fission products ejected at effectively c. You can look that difference up, it's quite small. Am I missing something?

 

[Jokodo]

In other words, you still need plenty of fuel unless you have access to a way of transforming mass to energy that's way more efficient than fissioning uranium and plutonium, right?

 

[bilby]

From what I see on the net there is a raction force with a laser. Maybe yiu need two lasers, one n the opposite direction to make the platform recoiless.

it's probably easier to just attach the laser to something heavy (like the Moon); There's a reactive force, of course, per Newton's third law (did you really need to look that up on the net?). But as long as your space probe has a mass very considerably smaller than that of the Moon, this is utterly negligible.

 

[steve_bank]

A theoretical isotropic radiator is infinitely small and massless radiating equally in all directions. A distant star to us approzimates an isotropic radiator. Antenna gain is relative to isotropic. A flat radiator is not isotropic.

For a flat plate rate of radiation depends on temperature above absolute zero, and total radiated power is proportional to area.

You can't isolate thermal radiation. If you thermally insulate the plate from the ground it means the plate will get hotter.

The plate is not focused. Thermal radiation is EMR so it can be optically focused.

Ipetrich is thinking like an engineer, sometimes somebody comes up with an entirely new idea that works. You never know until yiu run the numbers.

 

[Loren Pechtel]

A lander, manned or unmanned? Not very likely. The hard part isn't speeding up, it's allowing down at a rate crew and equipment can survive.

If you're not using a laser pump a lightsail can stop the same way it started. Otherwise, though, I do agree that stopping is probably harder than starting. You get some impressive numbers looking at using the target star for an aerobrake--and that might not be good for the planets even if you could pull it off.

Using a star for aerobraking sounds like you will need several tons of extra mass just for thermal insulation - and that won't save you either of you're the tiniest fraction of an arcsecond off course.

I meant "impressive" as in no way it could happen. It makes gun-rated look like easy street.

 

[Loren Pechtel]

It's not about using lasers as rocket engines. It's about a stay-at-home laser that is aimed at a spacecraft to propel it by radiation pressure.

Lasers as rocket engines?

Though a laser has an "exhaust" velocity of c, inefficiencies in the laser's powerplant and in the laser itself reduce the effective value to well below c. A 35% efficient steam engine and a 20% efficient laser combine to give 7% total efficiency.

Yeah, photon engines only make sense if you have some freebie energy source. Otherwise, lasers are power-beaming, not propulsion.

A simpler approach would be to use a radiator panel that is insulated on one side. With sufficiently good insulation, most of the heat energy will be radiated on the non-insulated side. That radiation is approximately isotropic, giving an efficiency factor of 50%.

One may get better collimation by radiating the heat from a ball onto a much larger parabolic mirror. The infrared light then bounces off that mirror and becomes approximately collimated, getting an effective exhaust velocity close to c.

Both of these would be more efficient but lower maximum thrust.

 

[Bomb#20]

Keeping the laser o a sail could be accomplished with a simple radio feedback system. Radio feedback to adjust a mirror at the laser.

How could that possibly work, when the probe is a lightyear away and any signal it sends requesting a direction adjustment has no effect on the beam at its sail until two-plus years after the signal is sent? Keeping the laser on the sail has to mean only keeping the laser perfectly steady relative to galactic coordinates, and relying on the probe to notice it's starting to drift out of the center of the beam and take corrective action locally.

 

[lpetrich]

An exhaust velocity of c doesn't give you high momentum of the exhaust consists mostly of low energy (infrared) photons. ...

Except if one makes a LOT of infrared photons.

The real problem is low momentum for one's energy.

(momentum) / (kinetic energy) = 2/(exhaust velocity) in the Newtonian limit, 1/c in the relativistic limit.

So photonic propulsion is grossly inefficient until one's speed gets close to c.

In fact, that Wikipedia article on laser propulsion lists a possible application with an exhaust velocity much less than c: aiming the laser at a rocket to heat its propellant.

 

[steve_bank]

Keeping the laser o a sail could be accomplished with a simple radio feedback system. Radio feedback to adjust a mirror at the laser.

How could that possibly work, when the probe is a lightyear away and any signal it sends requesting a direction adjustment has no effect on the beam at its sail until two-plus years after the signal is sent? Keeping the laser on the sail has to mean only keeping the laser perfectly steady relative to galactic coordinates, and relying on the probe to notice it's starting to drift out of the center of the beam and take corrective action locally.

There would be a practical limit to how much energy could be transmitted and the divergence of the laser beam.

You can look at the beam as a cone. The farther you get away from the laser watts/m^2 goes down.

It might work in the solar system to some degree.