Space Forum / Space Flight / December 2005

I'm trying to guesstimate the mass budget for a
Falcon 1.  Public information seems to be limited
at the moment, especially since SpaceX has
removed its Falcon 1 payload users guide from its
web site.  I'm wondering if anyone has the information
on-hand.

But I did download a copy of the guide last year.

site, and from old news clippings, I have found the
following information.

Vehicle total mass:  27.2 tonnes
Stage 1 Sea Level Thrust:  34.92 tonnes
Stage 1 Vacuum Thrust:  41.72 tonnes
Stage 2 Vacuum Thrust:  3.175 tonnes
Acceleration at Stage 1 Burnout:  6.5 g
Acceleration at Stage 2 Ignition:  0.65 g
Acceleration at Stage 2 Burnout:  4.5 g
Payload to 200 km x 28.5 deg LEO:  0.57 tonnes
Claimed Stage 1 Mass Fraction Goal:  94%
Claimed Stage 2 Mass Fraction Goal:  91%

Payoad fairing separation occurs after Stage 2
ignition.  The acceleration data was provided
without specifying the assumed payload mass,
and the payload fairing mass is unknown.

So I have a problem with too many unknowns
to provide absolute answers.  If I guess
0.35 tonnes for both the payload fairing and the
modeled payload used to provide the acceleration
numbers, I get the following results.

Stage 1 Mass at Liftoff:  22.315 tonnes
Stage 1 Mass at Burnout:  1.533 tonnes
Stage 2 Mass at Ignition:  3.965 tonnes
Stage 2 Mass at Burnout:  0.357 tonnes
Payload Fairing Mass:  0.35 tonnes

This provides a 93% Stage 1 mass fraction and
a 91% Stage 2 mass fraction.  The Stage 1
fraction seems believable because SpaceX
ended up with a heavier Merlin than originally
planned, according to updates on the SpaceX
web site.

But there is a great deal of uncertainty in these
numbers.  A different payload mass assumption
would drive second stage mass above 4 tonnes,
for example.  Does anyone have better numbers?

- Ed Kyle