Talk:Propellant mass fraction

From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics (Rated Start-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
 
WikiProject Spaceflight (Rated Start-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Spaceflight, a collaborative effort to improve the coverage of spaceflight on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
Checklist icon
 Low  This article has been rated as Low-importance on the project's importance scale.
 

Powered re-entry[edit]

Ok, I yield on the powered re-entry thing. It really was pretty pointless to begin with. --Doradus 01:39, May 7, 2005 (UTC)

When is lower mass fraction better?[edit]

The article used to have this statement:

When applied to a rocket as a whole, a low mass fraction is desirable, since it indicates a greater capability for the rocket to deliver payload to orbit for a given amount of fuel.

It is true that given two vehicles of equal mass, the one with the lower mass fraction gets more vehicle+payload into orbit. This statement has been reversed:

When applied to a rocket as a whole, a higher mass fraction is desirable (everything else being equal), since it gives a higher delta-v.

It is true that given two vehicles of equal specific impulse, the one with the higher mass fraction will achieve higher delta-v.

Neither of these statements is false. I think we just need to be more specific about what we mean by "everything else being equal". --Doradus 19:16, 19 June 2006 (UTC)

The first statement is not true (not necessarily false, but not true in general). You can trivially get a lower mass fraction by adding lead ballast to the vehicle.

No you can't. If you add ballast to a rocket, you must also add more fuel, or else it won't reach its destination. --Doradus 17:26, 22 August 2007 (UTC)

Whilst a vehicle that can achieve orbit with a lower mass fraction is desirable, that's a statement more about engines or other aspects of vehicles, than about mass fraction, so probably shouldn't be in this article anyway.WolfKeeper 00:12, 20 June 2006 (UTC)

On the contrary, a high mass fraction is desirable since you can usually add more payload or reduce the fuel you add to the vehicle, and save costs.WolfKeeper 00:14, 20 June 2006 (UTC)

I don't understand this claim. If you have a rocket with a given mass ratio, and remove fuel, you must remove a corresponding quantity of payload or else the rocket will not reach its destination.
NASA web sites make it clear that lower mass fractions are desirable: [1], [2]. If you can cite a source for your claim that high mass fractions are better, please do so. Otherwise, let's put this article back in a state that agrees with NASA. --Doradus 17:26, 22 August 2007 (UTC)
I have made the change. I hope you find this acceptable. --Doradus 17:01, 29 October 2007 (UTC)


Inconsistent, unclear wording[edit]

The article title is "propellant mass fraction". For an overall vehicle, that's the fraction of propellant mass vs everything else (structure, payload, engines, etc). However the article wording seems rambling and inconsistent. E.g, "...(SSTO) vehicle the mass fraction is simply the fuel mass divided by the mass of the full spaceship, but with a rocket employing staging, which are the only designs to have reached orbit, the mass fraction is higher because parts of the rocket itself are dropped off en route". Shouldn't that be lower? Relative to an SSTO of equal payload, a staged vehicle will have lower propellant mass fraction. Article may be confusing payload mass fraction with propellant mass fraction.

Another example: the table shows the Saturn V mass fraction is 0.957. However Saturn V total vehicle wet mass is about 3,038,500 kg. The total three-stage propellant mass is about 2,708,090 kg, or a propellant mass ratio of 2,708,090 / 3,038,500 = 0.891.

Similarly, the table lists the Space Shuttle mass fraction at 0.935. However the Space Shuttle wet mass is about 2,040,000 kg. The total propellant mass is about 735,601 kg for the ET, and 998,000 kg for the SRBs. That gives a propellant mass fraction of (735,601 + 998,000) / 2,040,000 = 0.850.

You can't use the formula for mass ratio of single stage vehicle (mf / mo), convert it to propellant fraction (prop mass fract = 1 / (1 - mass ratio)) and apply it to a multi-staged launcher. It doesn't yield the overall vehicle propellant mass fraction, which is the article title. Joema (talk) 15:22, 25 March 2008 (UTC)

I think the article should probably cover:
  • mass fraction
  • propellant fraction
  • payload fraction

They're all different. I agree that the article is currently inconsistent. The table currently covers mass fraction, rather than payload fraction, which is what the article name is.- (User) Wolfkeeper (Talk) 22:18, 26 December 2008 (UTC)

  • I concur. The rule of thumb I learned is that propellant mass fraction is typically 0.8 ± 0.1. In the table, the V-2 measure is correct because it is a single-stage vehicle, but the other rockets' Lp are far too high (>>0.9) for a realistic Vp / Vi (propellant to inert mass ratio). Here is another table with Lp estimates, and the entire slideshow is a good intro to the topic. --IanOsgood (talk) 14:40, 9 September 2009 (UTC)

External links modified[edit]

Hello fellow Wikipedians,

I have just modified one external link on Propellant mass fraction. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.

As of February 2018, "External links modified" talk page sections are no longer generated or monitored by InternetArchiveBot. No special action is required on behalf of editors regarding these talk page notices, other than regular verification, as with any edit, using the archive tools per instructions below. This message updated dynamically through the template {{sourcecheck}} (last update: 1 May 2018).

  • If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
  • If you found an error with any archives or the URLs themselves, you can fix them with this tool.


Cheers.—InternetArchiveBot (Report bug) 08:01, 11 November 2017 (UTC)