Question for any Missile Propulsion Experts out There!

[bobbymike]

There has been a long standing rocket propulsion improvement research program that I'm sure most members here are aware of called the Integrated High Payoff Rocket Propulsion Technology Program or IHPRPT. Here are some numbers from a chart from a report as to the programs goals, which are apparently being met with advances in propulsion technology/component technology.

Goal Phase I Phase II Phase III
Mass Fraction 15% 25% 35%
Payload Increase 28% 52% 93%

My question is what is the difference between mass fraction increase and payload increase? I'm guessing mass fraction refers to pounds of rocket to pounds of payload?

And if payload goals are for a 92% increase than (possibly an obvious question to follow) would a "phase III" Peacekeeper clone under this program have a payload of approx. 16,700 lbs (8700 X 1.93)?


Please advise and thank you

 

[Orionblamblam]

My question is what is the difference between mass fraction increase and payload increase? I'm guessing mass fraction refers to pounds of rocket to pounds of payload?

Mass fraction is simply the mass of the vehicle before the rocket burns, and the mass of the vehicle after it stops. In simplest terms...

Mass before = structure + payload +propellant

Mass after = structure + payload

Of course, propellant mass might not entirely vanish (especially for liquids, which can start and stop numerous times), and structure mass can change (bits falling off and the like).

You can also increase mass fraction by changing payload mass. If you simply dump ten times as much mass into the payload, your mass fraction can change a lot. But if your rocket performance doesn't change, then jacking up the mass fraction this way reduced your delta-V (change in velocity). The preferred way to increase mass fraction is to reduce structural mass... thinner tanks, lighter, stronger materials, etc.

 

[mz]

EDIT:ah nevermind I probably misunderstood.