Space Shuttle Folly of Our AgeThe space shuttle.

Derek Lyons wrote:
"Jeff Findley" wrote:
5 tons may be a bit tight to develop a pressurized people carrier for a
dozen people, but I'd think 6 to 8 people ought to be doable.


So what do you think Derek? Sound reasonable to you?

5 tons as a weight seems like a reasonable starting point - but the
sticky part is (as I point out to George), 5 tons of what? (I.E. when
you get beyond Power Point, volume matters.) A cargo bay 1 meter by 2
is a different matter than one that is 2 meters by 10, even if both
are limited to five tons gross capacity.

This matters in the 5 tons and orbital assembly scenario greatly.

There are some reasonable bounds we can put on the problem,
at least.

Minimum acceptable volume would start somewhere around
the density of water. I don't know of any spacecraft
parts or propellants significantly denser than that (peroxide
and nitrogen tetroxide and nitric acid are, but not by a
large factor). So at least that much volume.

Maximum credible volume would be something like the density
of a tank full of liquid hydrogen, which is roughly 13.5 cubic
meters per ton (assume 12 cu m/ton including a tank).

Real tanks are going to have endcaps and the like,
but let's for now simplify to those numbers.

See, easy, we already almost got it to within an order of
magnitude range, in two easy paragraphs ;-)

5 tons at 12 cu m/ton would be 60 cu m. In rough terms,
3 m diameter by 9 or 10 m cargo bay, or 4 m diameter by 5 m
long.

5 tons at 1 cu m/ton is 5 cubic meters, which is only
going to be something like 1.5 m diameter by 3 m long.

If you're putting people in, a seated person plus access
space is no less than 1 cu m, more like 2 cu m. You could
credibly put at least 1 person per 500 kilograms, perhaps
as good as 1 person per 250 kilograms. 5 tons therefore
is 10 to 20 people. 10 people at 1 cubic meter per is
10 cubic meters; 20 people at 2 cubic meter per is 40
cubic meters. I think that range is a more reasonable
lower bound range. Reasonable realistic minimum is
probably somewhere around 20 cubic meters, or say a
2 m diameter 6 m long volume.

2 m is also likely the minimum credible diameter to
get berthing module / hatch assemblies which are
big enough for people and racks to get through.

Where you go from here depends a lot on the RLV
design issues.

Keep in mind that the Fluffy Capsule arguments work
as well on most RLV designs: low density is good,
and larger cargo volume may not be a weight or
design problem as much as you might think on first
analysis of the problem.


-george william herbert

Derek Lyons wrote:
(George William Herbert) wrote:
Derek Lyons wrote:
Looking at the Phase A designs in Jenkins, few (if any) appear to have
any significant capability for incremental testing. In theory the
Shuttle was have is capable of at least some incremental testing, even
though that was never done. Probably for the same reasons it wouldn't
have been done for the Phase A designs either. (Money, the need to
get Something Flying, Now.) Choosing a Phase A design doesn't change
the fiscal and political restraints that NASA was starting to face.
Nor does a Phase A design simplify the SSME or TPS design - both were
at the time huge unknowns.

Without Jenkins in front of me...

As I recall, most of the early phase proposals were TSTO of some
sort, and there would have been the opportunity to incrementally
test with the Booster and inert upper stages. The booster stages
were larger but lower risk and stress compared to the upper stages.

But that wouldn't have taught you much - because as you point out the
booster is the lowest risk portion and in need of the least testing.
(Of course lowest risk is a relative term.)

OTOH even today something like one of those Phase A designs is going
to be a daunting task to get right - and incremental testing doesn't
help much there. Incremental testing is all about bug ranching and
envelope expansion, it works in aviation because there is (by and
large) a massive experience base to draw from, an experience base
noticeably absent for spaceplanes.

I actually disagree whether this approach is suitable for incremental
testing or not.

Launch and particularly main rocket engines, and reentry,
are the two flight regimes where the most risk is likely to
be found in the vehicle development.

Once you test out and qualify the booster, that then gives you some
leverage to start incrementally testing the upper stage.

Fly a trajectory northeast out of the Cape, along the Eastern
Seaboard, for example. Booster probably lands in northern
Florida or Kings Bay or something. Start off with having
the upper stage just detach and do the same reentry as the
booster does. Then add some more propellants, run its
engines for a little while, kick it a little further downrange
and a little faster reentry. You have airports long enough
to land at pretty much up the coast, if you have a reasonably
aerodynamically configured vehicle. It's what, roughly 2000 km
to Boston from the cape? That's your whole ascent phase.
If you immediately reenter at that point, from orbital velocity,
you're probably going to come down in Newfoundland, but there are
airports there too.

Or launch West from the Cape, and recover in Texas or New Mexico.

giving a half-reusable system.

Of course, this approach is not without significant potential problems
and delays of it's own - to wit, designing/redesigning an expendable
to ride piggyback on the reusable Booster.

Or picking one off the shelf. S-IVB might well fit on top of your
booster, for the specified Shuttle Phase A boosters...

As Robert points out, once
you've done this, the rationale for completing the work on the
reuseable upper stage peters out.

If the economics for continuing to develop the reusable
upper stage once you have an expendable upper stage ready
don't work out, they didn't work out when you started to
design the vehicle, and you should have just gone with
a semi-reusable vehicle from day one.

In fact, in our time line it's just about exactly that which has
happened - except the Booster turned out to be the expensive and (they
thought) Very Hard part. Therefore, a simpler, 'cheaper', expendable
Booster was created to support the Orbiter - and development dead
ended for a variety of well known fiscal and political reasons.

I think that the Orbiter was felt to be the expensive and
hard part all along, but that the Booster was the easy place
to save money, whereas the Orbiter was not, as long as your
design constraint is "mostly reusable system".

I think that many of the Phase-A boosters plus an expendable
upper stage would clearly have been a more optimized, cheaper
solution, but that wasn't as "sexy" in R&D terms.


-george william herbert

"Pete Lynn" wrote:

"Derek Lyons" wrote in message

Five tons of what? Feathers or lead?

Remember the basic specification here is for a
reuseable vehicle - the size of that five tons matters.

A direct answer to that question might be five ton of people and there
stuff.

Fluffier cargos would be atypical, and could fly on other launch
vehicles if need be.

The tricky question is 'how atypical?'. When you limit solution space
to 'people and their stuff', you are right back at the position we
started from - 'k311, we can launch people, who needs cargo?'. That
position leads to grief because it splits your flights across multiple
types and decreases the launch rate of each.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

"Derek Lyons" wrote in message
...
"Pete Lynn" wrote:

"Derek Lyons" wrote in message

Five tons of what? Feathers or lead?

Remember the basic specification here is for a
reuseable vehicle - the size of that five tons
matters.

A direct answer to that question might be five ton of
people and there stuff.

Fluffier cargos would be atypical, and could fly on
other launch vehicles if need be.

The tricky question is 'how atypical?'. When you limit
solution space to 'people and their stuff', you are right
back at the position we started from - 'k311, we can
launch people, who needs cargo?'. That position
leads to grief because it splits your flights across
multiple types and decreases the launch rate of each.

I think with aircraft, cargo is typically more dense than people
carrying, is this correct?

For a space transport the cargo will on average be more dense again due
to the requirement for bulk high density goods like water, LN2,
propellants, steel, etcetera. A space transport designed to carry
people should have sufficient payload volume to carry most cargo. With
cargo density juggling, (already done for aircraft), only oversized
cargo would seem to be problematic.

A few quick calculations infer that even a large pressurised cabin could
weigh little extra. Payload volume seems to be primarily constrained by
aerodynamic drag, (frontal area), while within the atmosphere. Unlike
aircraft, there are many ways of mitigating this.

A space transport payload volume sized to carry people seems the obvious
design optimum to go for, but this is way down the list of things to
worry about.

Pete.

Derek Lyons wrote:

That
position leads to grief because it splits your flights across multiple
types and decreases the launch rate of each.

If you want to have a healthy industry, there must be several types,
from different vendors. And they will have different characteristics.
And only after we have seen them some time in action, we will see which
type of vehicle is really suited best for which type of customer.

If there is only one vendor, no matter how well the vehicle is designed:
Once it flies long enough, it will get harder to build a competing
vehicle because the payloads will be optimised for just the one vehicle
available, and not enough customers will trust a newcomer, and the banks
will not fund the effort because of this.

Best Regards

Robert Kitzmueller

"Derek Lyons" wrote in message
...
"Jeff Findley" wrote:

5 tons may be a bit tight to develop a pressurized people carrier for a
dozen people, but I'd think 6 to 8 people ought to be doable.


So what do you think Derek? Sound reasonable to you?

5 tons as a weight seems like a reasonable starting point - but the
sticky part is (as I point out to George), 5 tons of what? (I.E. when
you get beyond Power Point, volume matters.) A cargo bay 1 meter by 2
is a different matter than one that is 2 meters by 10, even if both
are limited to five tons gross capacity.

This matters in the 5 tons and orbital assembly scenario greatly.

Agreed. My guess would be 10 feet (about 2 meters) in diameter by 15 to 20
feet (4.5 to 6 meters) in length. In other words, big enough to hold a
pressurized module with 6 to 8 people seated in pairs, or three across
(across the diameter), with a bit of extra length at the end(s) to hold
consumables, the toilet, and etc.

It's also worth pointing out that the 'general purpose (insert auto
type here)' used as an example is, here on Earth, but one component of
a much larger system. Nobody rational would make it the universal
standard - but it's equally true that the overall system on Earth
suffers less from the number-of-trips issues that bear on the orbital
system.

In the US, a bigger "standard size" would be the volume and weight capacity
of a standard semi-truck trailer that's not an "oversized load". Once your
load is "oversized" by law, you're subject to much greater scrutiny,
including being regularly pulled over by the police to check your paperwork
and inspect your rig. Regular sized loads are scrutinized far less.

You could also use the internal dimensions and load capacity of largest
"standard size" shipping container, which can travel by truck, rail, and
ship.

Anything bigger than those and you're out of the range of "typical", and it
costs you quite a bit more to go after that very small segment of the
market.

You might want to consider a bay big enough to launch (unfueled) satellites
roughly the size and weight of a GEO comsat, which would be fueled (station
keeping fuel), and attached to another stage to take it to GEO. This "space
tug would likely be reusable, and would originally have been launched dry on
an ELV (perhaps multiple flights to attach tankage). To reuse, it would be
filled by RLV tanker flights which would transfer only fuel and oxidizer
into its tanks.

Now I'm not sure if you can fit today's unfueled comsats in that size of
payload bay. Some repackaging of the comsat hardware may need to be done in
order to get them to fit. Perhaps splitting off its station keeping
propulsion package and launching it separately would help.

To me, that's a development path that leads you to ultimately replace ELV's.
It requires very little "orbital assembly", other than docking bits together
and then fueling the resulting vehicle(s) with tanker flights. Such an
approach necessarily requires a high flight rate, but that's a good thing
for an RLV. It spreads out fixed costs over many flights, making your per
flight cost dominated by reoccurring costs, not your fixed costs.

Jeff
--
Remove icky phrase from email address to get a valid address.

Pat Flannery a écrit :


If you were going to design something that is reusable, something like
this with a recoverable upper stage would probably be a pretty good
point to start: http://www.buran.ru/htm/strbaik.htm
That's one of the cleverest rocket booster designs I've seen in some time.

On the paper, it seems like a particularly smart design. A Baikal
booster of that type was shown two years ago at the Paris Air Show. I
haven't heard of it since...
Cyrille