SSTO propulsion overview

Indeed, the single biggest problem of early spaceflight -- reentry -- was
solved only when Harvey Allen realized that a reentering spacecraft was
*NOT* an aircraft and should not be designed like an aircraft.
Bless Harvey Allen but some would say that the reentry problem has yet to
be solved. We invented better thermal insulation and called it a reentry
solution but it's an unsatisfactory way of descending from orbit, as we
witnessed with Columbia.
It's premature to say airplanes can't reenter. More designs and
techniques must be explored.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~

Attempting a separation at hypersonic
velocities, with every leading-edge surface experiencing absurdly
high dynamic pressures while glowing red to white hot, is an
exercise only for insane lunatics.
Another myth-maker emerges. [As if it's so hard to believe that hypersonic
craft will be safe and controllable.]
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~

In article ,
Allen Meece wrote:
Indeed, the single biggest problem of early spaceflight -- reentry -- was
solved only when Harvey Allen realized that a reentering spacecraft was
*NOT* an aircraft and should not be designed like an aircraft.

Bless Harvey Allen but some would say that the reentry problem has yet to
be solved. We invented better thermal insulation and called it a reentry
solution but it's an unsatisfactory way of descending from orbit, as we
witnessed with Columbia.

Some would say that the reentry problem was solved quite satisfactorily,
until the aircraft nuts got their foot in the door and started insisting
that spaceships had to look and act like aircraft. The Apollo heatshield
had tremendous safety margins, and a little bash from falling debris
wouldn't have bothered it in the slightest (not least because the really
crucial part of it wasn't exposed during launch).

But ablative heatshields don't work very well if you start insisting that
the vehicle has to have *wings*. That's what killed Columbia: the long,
slow, reentry of a winged vehicle gives it a prolonged roasting rather
than a quick blowtorching, requiring thermal protection that radiates heat
away rather than soaking it up... and thus needs exotic high-temperature
materials, which typically involve compromises in areas like physical
durability.

It's premature to say airplanes can't reenter.

Nearly half a century ago, we already understood that an airplane shape
was not the best choice for reentry.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

"Henry Spencer" wrote in message
...

[snip]

But ablative heatshields don't work very well if you start insisting that
the vehicle has to have *wings*. That's what killed Columbia: the long,
slow, reentry of a winged vehicle gives it a prolonged roasting rather
than a quick blowtorching, requiring thermal protection that radiates heat
away rather than soaking it up... and thus needs exotic high-temperature
materials, which typically involve compromises in areas like physical
durability.

Henry, having said that.. what are your thoughts on something along the
lines of Rutans' SpaceShipOne "shuttlecock" design? That has wings but
would reenter quicker than a conventional airframe shape.

Would something like that (but with an Apollo-style ablative shield on the
belly) offer any advantages?

Thanks,
Cameron:-)

It's premature to say airplanes can't reenter.

Nearly half a century ago, we already understood that an airplane shape
was not the best choice for reentry.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Henry Spencer) wrote:
[...]
Aircraft were not built by making cars or locomotives faster and lighter.

Nit: the development of a decent internal combustion engine that made
cars lighter and faster was pretty important to powered flight. I'm
not sure what the analogue for space flight is; maybe lighter guidance
components, but gyro weight probably wasn't much of an issue for a
plane.

/dps

Henry Spencer wrote:

Some would say that the reentry problem was solved quite satisfactorily,
until the aircraft nuts got their foot in the door and started insisting
that spaceships had to look and act like aircraft. The Apollo heatshield
had tremendous safety margins, and a little bash from falling debris
wouldn't have bothered it in the slightest (not least because the really
crucial part of it wasn't exposed during launch).

Indeed. It was buried in the middle of the spacecraft during launch and
in-flight. Anything that could damage the TPS on Apollo would be doing
critically bad things to the rest of the spacecraft.

And even when it did take a hit, as it (probably) did with the LOX tank
explosion during Apollo 13, it still performed like a champ.

Design Margins. Why is that so hard for some people to understand?

The Space Shuttle has 5 flight computers, any one of which could fly the
spacecraft alone. But it only has _one_ very fragile TPS! There were
people saying it was a bad design 30 years ago, and they're still not
being listened to.

But ablative heatshields don't work very well if you start insisting that
the vehicle has to have *wings*. That's what killed Columbia: the long,
slow, reentry of a winged vehicle gives it a prolonged roasting rather
than a quick blowtorching, requiring thermal protection that radiates heat
away rather than soaking it up... and thus needs exotic high-temperature
materials, which typically involve compromises in areas like physical
durability.

And if the fragility of the tiles themselves weren't bad enough...

Everyone should have already read about the tremendous amount of time
and effort needed to maintain the Shuttle's TPS. We're talking tens of
thousands of man-hours, for every flight. I'm sorry, but that's just
insane.

Now compare that to the time and effort needed to attach oak blocks to
the bottom of a capsule.

Sure, maybe you'd need to hire Norm Abrams to work on your TPS, instead
of relying upon your uncle Bob who has a table saw in his garage. But
we're talking several orders of magnitude easier to design and
impelement.

Perhaps this is slight hyperbole, but the TPS inspection could be done
with a hammer in 15 minutes. Anything which falls off after being given
a good whack needs to be fixed.

Simple. Robust. Reliable. I like it.

Sure, you can call the Chinese space program primitive. I'd rather be
primitive and alive, than sophisticated and dead.

- - - - - - - - - - - - - - - - - -

BTW, 'reliable' isn't the same thing as 'robust'. Lots of people forget
that too.

- - - - - - - - - - - - - - - - - -

Fuel is Cheap. Simplicty is a Virtue. Design Margins are Good.

How many billions have been wasted ignoring these sentiments?

- - - - - - - - - - - - - - - - - -

What the heck are the wings on the shuttle good for anyway? It isn't as
if the SS has any kind of cross-range ability. You can't, at the last
minute, abort or even pick a different runway.

James Graves

Henry Spencer wrote:

In article ,
Allen Meece wrote:

Indeed, the single biggest problem of early spaceflight -- reentry -- was
solved only when Harvey Allen realized that a reentering spacecraft was
*NOT* an aircraft and should not be designed like an aircraft.

Bless Harvey Allen but some would say that the reentry problem has yet to
be solved. We invented better thermal insulation and called it a reentry
solution but it's an unsatisfactory way of descending from orbit, as we
witnessed with Columbia.


Some would say that the reentry problem was solved quite satisfactorily,
until the aircraft nuts got their foot in the door and started insisting
that spaceships had to look and act like aircraft. The Apollo heatshield
had tremendous safety margins, and a little bash from falling debris
wouldn't have bothered it in the slightest (not least because the really
crucial part of it wasn't exposed during launch).

But ablative heatshields don't work very well if you start insisting that
the vehicle has to have *wings*. That's what killed Columbia: the long,
slow, reentry of a winged vehicle gives it a prolonged roasting rather
than a quick blowtorching, requiring thermal protection that radiates heat
away rather than soaking it up... and thus needs exotic high-temperature
materials, which typically involve compromises in areas like physical
durability.


It's premature to say airplanes can't reenter.


Nearly half a century ago, we already understood that an airplane shape
was not the best choice for reentry.


Faget had an interesting compromise to that by making the
re-entry at high attitude which essentially made the winged
vehicle a capsule for the re-entry. The wings helped reduce the
thermal loading, IIRC.

In article ,
Cameron Dorrough wrote:
But ablative heatshields don't work very well if you start insisting that
the vehicle has to have *wings*...

Henry, having said that.. what are your thoughts on something along the
lines of Rutans' SpaceShipOne "shuttlecock" design? That has wings but
would reenter quicker than a conventional airframe shape.

I don't know quite enough about its reentry profile to confidently compare
it. The impression I have is that it's a pure drag device, non-lifting,
until it swings its tail back down. That's actually *too* drastic for an
orbital reentry, or even a higher suborbital, where you want a little bit
of lift to reduce the G-loads. Unless you get quite a bit of lift,
though, its reentry is still in the "sharp and short" category where
ablators etc. do well.

Would something like that (but with an Apollo-style ablative shield on the
belly) offer any advantages?

I would worry about ablators on aerodynamic surfaces, because of concern
that uneven ablation would change the shape or leave a rough surface.
There are also a lot of surfaces needing protection -- the belly is worst
but it's not the only concern -- which is going to run up the ablator mass.

That aside, there is a lot of advantage in variable geometry, or more
generally, in being able to change vehicle modes to deal with the changing
environment. The more you can separate the problems of reentry from those
of landing -- for example, by using different vehicle configurations --
the easier the problems are to solve, because you don't have to satisfy
several sets of constraints simultaneously.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Allen Meece) writes:

Attempting a separation at hypersonic velocities, with every leading-
edge surface experiencing absurdly high dynamic pressures while glowing
red to white hot, is an exercise only for insane lunatics.

Another myth-maker emerges. [As if it's so hard to believe that
hypersonic craft will be safe and controllable.]

There is a very distinct difference between attempting to control _one_
hypersonic vehicle controllable under relatively smooth external conditions,
versus attempting to control _two_ of them in extremely close proximity,
with their shock-waves and plasma-sheaths mutally interacting and
impinging on each other, under conditions of very rapidly changing
and almost certainly turbulent airflow. The latter case makes attempting
to do something as stupid as practicing "touch and goes" on the back of a
flying 747 look positively safe and easy by comparison.


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article ,
James Graves wrote:
What the heck are the wings on the shuttle good for anyway? It isn't as
if the SS has any kind of cross-range ability. You can't, at the last
minute, abort or even pick a different runway.

The shuttle does have considerable cross-range capability earlier in
reentry, which is useful because you can reach a landing site that is
significantly to one side of your orbit track. This is helpful in normal
operations, reducing the need for either in-orbit waits or retrieval from
contingency landing sites. Moreover, it's essential if you want to be
able to do a once-around mission from Vandenberg, either deliberately or
because a problem causes an Abort Once Around, since there's nothing much
but water west of Vandenberg.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |