SpaceX, launching thinsats

This is a summary of data at http://www.spacex.com, plus some estimates for M288 and M480 thinsat launches

vehicle

Falcon 1

Falcon 1e

Falcon 9

F. Heavy

Saturn5

Pad Weight kg

27670

35180

333400

1400000

2800000

1st Stg Dry kg

1360

2580

288000

1st Propellant

Kero/LOX

Kero/LOX

Kero/LOX

Kero/LOX

RP-1/LOX

1st Proplnt kg

21490

39460

2012000

1st ISP sec

300

304

304

263

2nd Stg Dry kg

544

544

36000

2nd Propellant

Kero/LOX

Kero/LOX

Kero/LOX

LH2/LOX

2nd Proplnt kg

4040

4040

444000

2nd ISP sec

317

317

421

LEO payload kg

410

1010

10450

53000

GTO payload kg

4680

cost M$

10.9

54

MoreLater - Server sky estimated launch

How Cheap Can It Get?

To an outside observer, the main added value for SpaceX appears to be high automation, mass production, and relentless logistic improvement. If SpaceX can run a rocket program the way PayPal runs an online bank, they will launch a lot of payload while improving performance and reliability with a small staff. For the physical aspects of production, I hope they copy best practices from the electronics industry. A rocket is like a very large cell phone, and can be put together with larger robots. Massive amounts of flight telemetry from many flights can be assembled into reliability models, improving launch yield while reducing expensive defects.

Assume 6 grams per thinsat (including a fraction of the stack dispenser). Assume 6000kg to M288 for a Falcon 9, or 1 million 6 gram thinsats. The spaceX web page does not give stage dry weight for the Falcon 9, so we will guess. Assume a Falcon 9 with a 10 to 1 propellant to weight ratio. That means 300,000 kg of propellants, 27,000 kg of tanks and engines and avonics, and 6000 kg of payload. Assuming $2/kg for RP4 and $0.20/kg for LOX, and a 25%/75% weight ratio (slightly fuel-rich), the propellant cost is $0.65 per kilogram. The propellant weight will cost about $200,000.

The energy cost of the propellant is about 15MJ/kg for the RP4 (equivalent electrical generation potential) and 3.6MJ/kg for the LOX, so the energy cost for 300,000 kg of propellants is about 2E12J. 30,000 kg of aluminum at 54MJ/kg is 1.6E12J. The total is 3.6E12J, or 1 million kilowatt hours, about a kilowatt hour per thinsat. If each thinsat produces 4 watts with 60% duty cycle, 2.5 watts average, they pay back their launch energy cost in 16 days.

The dry weight is expensive; while SpaceX assumes return and re-use, that will require extra hardware for recovery, the weight of which comes right out of the payload fraction. Further, mechanisms wear out. Designing them for many flights will mean stronger construction, more weight, and more rework of damaged systems between flights. Metal is cheap; aluminum is $2/kg, carbon fiber is $11/kg, glass fiber is $2/kg, etc. With enough automation, the dry weight might cost an additional $300,000 , materials and labor. If SpaceX gets good at this, they might be able to sell a flight for $6M and still make an 80% profit. If they get really good at this, payloads will show up, get tested and mated and launched by robots, with just a salesperson and a range safety operator (who sweeps floors between launches). We can dream, anyway ...

That works out to $1000/kg to M288, and $6 per thinsat launch cost.

If thinsats can be made much thinner, with space debris or lunar ballast added by already deployed dispensers in orbit, the launch weight can drop below a gram and the launch cost below a dollar per thinsat.

An additional two orders of magnitude cost reduction may someday be provided by the launch loop, along with lunar glass substrates, and in-orbit automated assembly and repair. In the long run, only the semiconductor die and the thin film InP solar cells need be launched from earth, with aluminum and glass from the moon. Earth launch might drop below 100mg per 3 watt thinsat.