Re: Multiple Engines???

> >  Alas, SSTO fuel fraction is prohibitive.
> 
> Not necessarily.  When people have been pushed hard to try to build
> expendable stages with that sort of fuel fraction, they have generally
> succeeded.  And with 1960s technology, too, in some cases. 

  Yup, true. I meant (thinking context evident) "RLV" SSTO. Apologies.
  Wings, heatshield, deorbit propellant - all dip hard into payload.

> > 2STO typically uses 1/3 the
> >  propellant for a given payload, although vehicle empty weights are higher.
> 
> However, since propellant costs are negligible, and empty mass and
> complexity are the expensive parts... 

  Hmmm. I misspoke. Try these numbers....

  Assume the VentureStar was built and worked as advertised.
  257 klb inert, 50 klb payload, 2313 klb LHOx, 8 Aerospikes, fuel fraction .883

  2 smaller editions, 3 Aerospikes on Booster, and 1 on Orbiter, have *together*
  198 klb inert, 50 klb payload, 927 klb LHOx, 4 Aerospikes, fuel fraction .824
  The only added complexity is crossfeed, already proven on the STS.

> The SRB separation may look simple but it isn't; NASA spent a lot of time
> and money making sure it would work.

  But work it does, yes?