RLVs and strap-ons

It seems intuitive that, if the technology for SSTO is not quite here yet, it
should be possible to do the job by building an RLV which is almost capable of
SSTO by itself and then add strap-on boosters, solid or liquid. Yet I've read
that, in RLV design studies, this does not work out. Why? Is it the heavier
frame on the RLV needed for the stress imparted by the strap-ons, or is there
another factor?

Thanks,


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

In article ,
MattWriter wrote:
It seems intuitive that, if the technology for SSTO is not quite here yet, it
should be possible to do the job by building an RLV which is almost capable of
SSTO by itself and then add strap-on boosters, solid or liquid.

Yes, it's plausible. The original Kistler design was an almost-SSTO with
a "launch assist platform" that would carry it up to modest altitude, a
low-performance recoverable booster. And the Roton design apparently had
provisions for strap-ons, as a hedge against poor engine performance.

Yet I've read that, in RLV design studies, this does not work out. Why?

As above, sometimes it does. When it doesn't, the likeliest reason is
structural: an SSTO needs very light structure, and strap-ons impose
concentrated loads that are awkward to handle. Other considerations
include controllability -- most strap-on options do not have thrust
vectoring, so the core vehicle has to have enough control authority to
maintain control despite the rather higher thrust -- and the tricky
process of jettisoning strap-ons.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
MattWriter wrote:
It seems intuitive that, if the technology for SSTO is not quite here yet, it
should be possible to do the job by building an RLV which is almost capable
of
SSTO by itself and then add strap-on boosters, solid or liquid.

Yes, it's plausible. The original Kistler design was an almost-SSTO with
a "launch assist platform" that would carry it up to modest altitude, a
low-performance recoverable booster. And the Roton design apparently had
provisions for strap-ons, as a hedge against poor engine performance.

Yet I've read that, in RLV design studies, this does not work out. Why?

As above, sometimes it does. When it doesn't, the likeliest reason is
structural: an SSTO needs very light structure, and strap-ons impose
concentrated loads that are awkward to handle. Other considerations
include controllability -- most strap-on options do not have thrust
vectoring, so the core vehicle has to have enough control authority to
maintain control despite the rather higher thrust -- and the tricky
process of jettisoning strap-ons.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

It was certainly my intention to add the scar weight on the first orbital
Roton; odds are it would have been needed. I made a point of briefing that to
Mike Dornhiem of AW&ST when they did an article on us and as I recall, it got
into the story, but I am not certain.

The hardpoints would have be located right at the base of the lox tank and that
would have minimized the weight penalty by driving the loads into the perfect
spot which was already reinforced and pressure stiffened. The open issues are
type of strap-on, and the other points Henry makes.

Gary C Hudson