Energy to Launch Server Sky

Assume that 3 million 3.8 gram thinsats are launched with an Ariane 5ECA, and that each thinsat produces an average of 4 watts of usable power. The total power is 15 MW .

The 5ECA, with comsat apogee insertion motors, are a 3 stage vehicle:

Stage

Fuel weight

MJ/kg

Energy J

0

Solid (both)

554,000 kg

6 ?

3.3E12

1

LOX/LH2

148,000 kg

16

2.4E12

2

LOX/LH2

14,000 kg

16

0.2E12

3

Hydrazine

4,600 kg

10 ?

- - - -

Total

5.9E12J

Stack Weight at Pad

777,000 kg

GEO Satellite Dry Weight

4,030 kg

The mass ratio - launch weight over satellite dry weight - is 193 . This is approximately proportional to the exponential of the delta V divided by the effective exhaust velocity (including tanks and engines and the rest of the expended booster dry weight).

Total Delta V, m/s

M288

M360

M480

M720

GEO

Kourou to Transfer

8669

8848

9051

9289

9956

Transfer to Injection

1102

1196

1295

1393

1505

Stationkeeping 15y

0

0

0

0

750

Total

9771

10044

10346

10682

12211

Assumed exhaust velocity

2320

Mass ratio

68

76

86

100

193

Dry weight (kg)

11400

10200

9030

7700

4030

( more information at EarthOrbits )

The energies given are the chemical energies of the fuels. If we assume 20% fuel manufacturing energy efficiency, relative to generated electricity, then the total "electrical" energy needed to fuel an Ariane is 30E12 Joules. Thinsats can pay back that energy in 2 million seconds, or about 3 weeks. Not bad.

Possibilities

The theoretical energy cost of moving 3 grams to the 12789km m288 server sky orbit is derived from the 8669m/s launch delta V and the 1102 m/s insertion delta V, or 38MJ/kg . That works out to 1.14E5 Joules per thinsat, which a thinsat makes in 8 hours. While no existing technology can get there, systems such as the launch loop can get within an order of magnitude of that.

Most of the mass of a server sky satellite is a 70 micron aluminum substrate. Later, if much of the aluminum and interconnect metal are made from lunar materials, the complex technical materials manufactured and launched from Earth can be reduced to a small fraction of that.

So, although Server Sky makes energy sense now, it can make vastly more energy sense in the future as technological improvement is driven by volume manufacturing. Getting on a Moore's Law development curve, and moving towards electromagnetic and lunar launch powered by space energy, will continue making the system cheaper. We must get on such a development curve if we expect to bring the developing world up to first-world energy abundance while eliminating carbon fuels and remediating their effects.

LaunchEnergy (last edited 2014-09-13 03:28:54 by KeithLofstrom)