Solar pumped laser sustained propulsion

Laser sustained detonation rockets have been proposed as launchers.

http://www.islandone.org/Propulsion/...areBiblio.html


At 30% efficiency throughout - and 2,200 second specific impulse - we
can compute the following;

Exhaust velocity;

Veff = 9.82 m/s/s * 2,200 s = 21,604 m/s

To achieve orbit a final velocity of;

Vf = 9,300 m/s

This implies a mass fraction of;

u = 1 - 1/EXP(Vf/Veff) = 0.35


Allowing 0.15 as the structural fraction, implies half the lift off
mass is payload.

With a lift-off gee force of 1.5 gee this implies 3 kg of force for
each kg of payload. Knowing Veff we can compute the power required
for each kg of force produced by the rocket;

F = m*a = mdot * Veff

Where mdot is the mass flow rate.

E = 1/2 * m * Veff^2

and differentiating;

Power = 1/2 * mdot * Veff^2

So, we can combine these equations to obtain;

F = 2 * Power / Veff

and

Power = F * Veff / 2
= 3 * 9.82 * payload mass * 21,604 / 2
= 0.318 MW per kg payload

So, a space shuttle payload mass of 60,000 kg requires;

Power = 0.318 * 60,000 = 19.1 GW

At 30% efficiency throughout - this implies the collection of 63.6 GW
of solar energy. This requires a little less than 29 sq miles of
solar collectors to operate. At a cost of $0.05 per watt - this
entire system would cost $3.18 billion.

Assuming linear scaling of the collector area we can see the
following;

PAYLOAD COST OF PANELS AREA OF PANELS
60,000 kg $3.18 billion 30 sq miles
20,000 kg $1.06 billion 10 sq miles
6,000 kg $318 million 3 sq miles
2,000 kg $106 million 1 sq miles
600 kg $32 million 0.3 sq miles
200 kg $11 million 0.1 sq miles

Basically, you can have an array of collectors feeding sunlight into a
solar pumped laser. That laser illuminates an optical fiber that
combines with other optical fibers to illuminate a single stationary
laser. That laser passes through a beam steering apparatus to direct
the beam onto a laser sustained detonation rocket which projects
payloads to orbit. The system cycles through a launch every 20
minutes - launching 3 payloads an hour when the sun is shining. If
operated in White Sands there is an average of 5 hours of sunlight per
day - so an average of 15 payloads could be launched per day. That's
5,478 payloads per year. So the annual launch rate would be;


328,725 tonnes per year 30 sq miles
109,575 tonnes per year 10 sq miles
32,872 tonnes per year 3 sq miles
10,957 tonnes per year 1 sq miles
3,287 tonnes per year 0.3 sq miles
1,095 tonnes per year 0.1 sq miles

The space shuttle could fly 6x per year and so could put up 360
tonnes.

Since beam steering, propulsion system, guidance, control, space
vehicle, and payload processing have a combined development cost on
the order of 1 billion - it seems reasonable to develop a 6,000 kg to
20,000 kg vehicle.

Charging $15 million to $50 million per flight ($2,500 per kg) would
match today's flight vehicles in cost. If safety could be
demonstrably higher - with lower insurance premiums - then, this
would be the preferred method of launch. At a cost of say 50% current
prices, higher launch rates could be explored.

There are around 20 commercial launches per year. At $25 million per
launch that's $500 million in revenue. Assuming a $2 billion capital
invested to develop this system - we would have a 25% ROI - and a
surplus capacity of hundreds of times the current launch rate. This
surplus capacity could be exploited to loft new systems into orbit -
including solar power sat components, nuclear pulse rocket components,
and more.