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4. Questions - Got a question about Mass Ratio then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

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6. Returns - still worried that even after all of the above your Mass Ratio wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Mass Ratio then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Mass Ratio site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Mass Ratio, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Mass Ratio, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, it is the ratio of the rocket's wet mass (vehicle plus contents plus propellant) to its dry mass (vehicle plus contents). A more efficient rocket design requires less propellant to achieve a given goal, and would therefore have a lower mass ratio.

The mass ratio is a useful quantity for back-of-the-envelope rocketry calculations: it is an easy number to derive from either delta-v numbers or from rocket and propellant mass numbers, and therefore serves as a handy bridge between the two. It is also a useful number to give an impression of the size of a rocket: while two rockets with mass fractions of, say, 92% and 95% may appear similar, the corresponding mass ratios of 12.5 and 20 clearly indicate that the latter system requires much more propellant.

Typical multistage rockets have mass ratios in the range from 8 to 20. The Space Shuttle, for example, has a mass ratio around 16.

Derivation The definition arises naturally from the Tsiolkovsky rocket equation:

\Delta v = v_e \ln \frac {m_0} {m_1}

where *delta-v is the desired change in the rocket's velocity *ve is the effective exhaust velocity (see specific impulse) *m0 is the initial mass (rocket plus contents plus propellant) *m1 is the final mass (rocket plus contents)

This equation can be rewritten in the following equivalent form:

\frac {m_0} {m_1} = e ^ { \Delta v / v_e }

The fraction on the left-hand side of this equation is the rocket's mass ratio by definition.

This equation indicates that a Δv of n times the exhaust velocity requires a mass ratio of e^n. For instance, for a vehicle to achieve a \Delta v of 2.5 times its exhaust velocity would require a mass ratio of e^{2.5} (approximately 12.2). One could say that a "velocity ratio" of n requires a mass ratio of e^n.

References See also

• Rocket fuel
• Mass fraction
• Payload fraction

In aerospace engineering, mass ratio is a measure of the efficiency of a rocket. It describes how much more massive the vehicle is with propellant than without; that is, it is the ratio of the rocket's wet mass (vehicle plus contents plus propellant) to its dry mass (vehicle plus contents). A more efficient rocket design requires less propellant to achieve a given goal, and would therefore have a lower mass ratio.

The mass ratio is a useful quantity for back-of-the-envelope rocketry calculations: it is an easy number to derive from either delta-v numbers or from rocket and propellant mass numbers, and therefore serves as a handy bridge between the two. It is also a useful number to give an impression of the size of a rocket: while two rockets with mass fractions of, say, 92% and 95% may appear similar, the corresponding mass ratios of 12.5 and 20 clearly indicate that the latter system requires much more propellant.

Typical multistage rockets have mass ratios in the range from 8 to 20. The Space Shuttle, for example, has a mass ratio around 16.

Derivation The definition arises naturally from the Tsiolkovsky rocket equation:

\Delta v = v_e \ln \frac {m_0} {m_1}

where *delta-v is the desired change in the rocket's velocity *ve is the effective exhaust velocity (see specific impulse) *m0 is the initial mass (rocket plus contents plus propellant) *m1 is the final mass (rocket plus contents)

This equation can be rewritten in the following equivalent form:

\frac {m_0} {m_1} = e ^ { \Delta v / v_e }

The fraction on the left-hand side of this equation is the rocket's mass ratio by definition.

This equation indicates that a Δv of n times the exhaust velocity requires a mass ratio of e^n. For instance, for a vehicle to achieve a \Delta v of 2.5 times its exhaust velocity would require a mass ratio of e^{2.5} (approximately 12.2). One could say that a "velocity ratio" of n requires a mass ratio of e^n.

References See also

• Rocket fuel
• Mass fraction
• Payload fraction

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