Re: Can't We call the early Atlas a SSTO?



Henry Spencer wrote:

Yep. Fifty years ago, airbreathers had much more future potential than
chemical rockets. Today, airbreathers have much more future potential
than chemical rockets. And fifty years from now, probably, airbreathers
will *still* have much more future potential than chemical rockets. :-)

Trouble is, turning that future potential into proven, useful technology
seems to require several miracles. A whole lot of money has been spent on
this in the last half-century, with a marked shortage of results.

I think one of the problems is that they keep associating airbreathers with a _reusable_ spacecraft, not as a part of a expendable system like Gnom.
There's no reason you can't make a fairly low priced ramjet, (or possibly even a scramjet) and use it as a way to add velocity to a ascending booster before it reaches an altitude where it won't operate anymore.
Considering that you have to pitch over the ascent trajectory as you head toward orbit anyway, you might as well use the ramjet to add horizontal velocity to the vehicle during its climb out of the atmosphere by getting the pitch-over maneuver to occur fairly quickly after liftoff, and trading off the increased aerodynamic drag for the added velocity that the ramjet can give the vehicle prior to first stage jettison.
It's going to save a lot of LOX, and given the weight of LOX and its mixture ratio to the fuel, this would be well worth it.
You can get a conventional ramjet up to at least Mach 6, and it could use the first stage's rockets to get it up to operating speed, and then be jettisoned after the atmosphere was too thin to promote efficient combustion.

Pat
"Air breathing is a privilege that should be reserved for the crew... the
ideal Mach number to transition at is zero."
- Mitch Burnside Clapp, Space Access 95.

It really has to do with finding the right approach.

Yes, and so far, all the evidence indicates that rockets are the right
approach. Most every time somebody buckles down and actually designs an
airbreathing launcher -- doing real engineering, not just waving hands and
doing a calculation or two on the back of an envelope -- it comes out to
be inferior to an all-rocket approach.

Even if you assume multiple miracles, as the NASP project basically did in
their quest for an airplane that could fly to orbit, you get something
that isn't really competitive. NASA Langley studied rocket SSTO with the
same assumptions on materials etc., and came out with something half the
size, with half the dry mass, less than half the propellant cost, maximum
dynamic pressure 2-4 times lower, and max heat load orders of magnitude
lower, concluding that it was absolutely clear that "rocket vehicles could
be operated in a more aircraft-like manner". (This wasn't welcome news,
they added: "We had to sit on this for about two years.")

With all-rocket designs the potential improvement looks mighty bleak to me.

However good or bad one thinks it is, adding airbreathing makes it worse.

Actually having apples and oranges compared to apples.

Comparing rockets to the hypothetical future glories of miraculous
airbreathers is comparing applies to a painting of a fruit basket. The
painting may be very pretty, and you actually can eat it (assuming that
the paints are non-toxic), but the apples make a much better meal.
.

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