Low mass ratio SSTO

Zoltan Szakaly wrote:
I spent the last few days reading past messages in this group on the
subject of SSTO vehicles. It seems to me that building an SSTO vehicle
is not even a great challenge.
snip
1. Composite fuel tanks and structure
How much can we gain here?

A bit, it varies depending on what sort of stuff you'r talking about,
from epoxy/fiberglass to kevlar.


2. Aluminum - magnesium - lithium alloys
How much better or lighter are they?

They can be a fair bit lighter, it depends.

3. Air breathing propulsion

This can be a plus, or a minus.

Do a search on "the airbreathers burden" in this group on google-groups.

In short, adding stuff to handle massivequantities of air at varying
speeds for a very short time can be a net loss.
Added to that the extra weight demands if you want to extend the time it
spends in air (thermal protection) and it starts to look very doubtfull.


4. Higher Isp, high density fuel/oxidizer

I will not get into other more exotic high tech concepts like nuclear
reactions or plasma thrusters.
snip
4. If we insist on using rocket engines, we have many ways of
improving rocket performance. We can get 450 Isp with hydrogen and I
read in here that 550 Isp was achieved with Fluorine-Hydrogen-Lithium.
At a 550 Isp we need a mass ratio of 5.3 to get to 9 km/s which is
clearly achievable and results in a good payload fraction. We could
also try mixing solid lithium chips into propane (I read that here)

Exotic fuels while they seem to have higher ISP look nasty at a deeper look.
The exhausts are generally very,very toxic for example.

Am I wrong somewhere or SSTO is really easy to build?

I'd certainly not go as far as really easy.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
"I am the Emperor, and I want dumplings." - Austrian Emperor, Ferdinand I.

(Zoltan Szakaly) wrote in message . com...
I spent the last few days reading past messages in this group on the
subject of SSTO vehicles. It seems to me that building an SSTO vehicle
is not even a great challenge.

...

It makes a lot more sense to simply use the air breathing
propulsion in the first stage phase up to mach 8.

"not even a great challenge" and "air breathing propulsion up to mach 8"???

John Carmack
www.armadilloaerospace.com

(John Carmack) wrote in message . com...
(Zoltan Szakaly) wrote in message . com...
I spent the last few days reading past messages in this group on the
subject of SSTO vehicles. It seems to me that building an SSTO vehicle
is not even a great challenge.

..

It makes a lot more sense to simply use the air breathing
propulsion in the first stage phase up to mach 8.

"not even a great challenge" and "air breathing propulsion up to mach 8"???

John Carmack
www.armadilloaerospace.com

My take based on the literature is that ramjets have been flown to
mach 6 at least and they have an Isp of over 3000 at 2km/s.

The ramjet I built is little more than hollow ducting and some heat
exchanger tubes. There is a nice ramjet on display nearby here at the
March air force base museum next to the 215 freeway. This was used for
the BOMARC missile ( a SAM). The engines being hollow ducting there is
no reason they would have to have high mass. If the same engine is
used during all phases of flight there is no weight penalty for air
breathing. With a simple variable intake scoop arrangement one can
minimize the drag penalty.

Zoltan

I spent the last few days reading past messages in this group on the
subject of SSTO vehicles. It seems to me that building an SSTO vehicle
is not even a great challenge.

No wonder. The people who are trying to actually do this have invested
lifetimes.

In order to allocate some dV for the
atmospheric drag and also to allow for a reduced nozzle performance in
the air we might need 9 to 9.5 km/s delta V to get into orbit.

There's yer problem. You're rounding things off. You need more detailed
accounting, especially of drag, to see how difficult it is.

Based on data on existing rocket stages we can achieve 0.88 mass
fraction (fuel and oxidizer are 88 percent of the mass) using
conventional aluminum fuel tanks and structures and using turbopump
fed engines feeding hydrocarbon fuel and LOX.

If you say so. But then, these stages are not accounted the payload fraction.
Yes, I understand the entire second stage and more is the payload for the
first, but in the bookeeping for the first, structure is only posted to the
first stage if it separates with that stage.

1. Composite fuel tanks and structure
How much can we gain here?

Oh, a lot. But an ECO in a developmental vehicle made with composites costs
some 100s that for the equivalent change NC machined into, see below:

2. Aluminum - magnesium - lithium alloys
How much better or lighter are they?

Mg is stiff, light, and flammable. Lithium is light, soft, and flammable. The
STS main tanks are made of an aluminum lithium alloy, which is friction stir
welded.

I love that process. Ever hear of it? They actually stir the weld nugget with
mechanical "fingers" and the weld comes out beautiful. A whole machine was
built to do it. With an NC stir welder, a lot of small stuff could be done up
quickly.





Yours,

Doug Goncz, Replikon Research, Seven Corners, VA
Unequal distribution of apoptotic factors regulates
embryonic neuronal stem cell proliferation

Zoltan Szakaly wrote:

[snip]

The ramjet I built is little more than hollow ducting and some heat
exchanger tubes. There is a nice ramjet on display nearby here at the
March air force base museum next to the 215 freeway. This was used for
the BOMARC missile ( a SAM). The engines being hollow ducting there is
no reason they would have to have high mass. If the same engine is
used during all phases of flight there is no weight penalty for air
breathing. With a simple variable intake scoop arrangement one can
minimize the drag penalty.

Zoltan


The 'simple variable intake scoop' doesn't exist for high Mach
numbers. (Even at SR-71 speeds, things can get tricky) The shape of the
airframe in general must become part of the air inlet and compresion.
And there are thermal issues as well.....

(Zoltan Szakaly) :

The engines I have gets 4,000 Isp at standstill, I have not had the
luck of testing them at high mach numbers. Their significance is that
they bridge the gap from zero to mach 3 where ramjets are not used. I
can have the same engine with unchanged exhaust system configuration
from standstill to mach 6 or maybe more. I have no moving parts and I
don't use any oxidizer from standstill up.

If I lean it out I can get higher Isp values, perhaps up to 8,000. I
use propane for fuel.

Zoltan

Charts are charts, and hardware is hardware - and rarely do the two meet.
Try just flying your ramjet as a simple lifter - I believe that even if you
get it to work you are in for a big surprise when you near mach 1 and the
nature of the air stream changes.

All I need to make my peroxide processor work is a high volume ratio pump
that can handle a phase change. So far the only pumps I can find that will
do that are molecular drag pumps and molecular turbo pumps at $5000 each.
The design idea is easy, building something that works and works well is very
hard.

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time? http://webhome.idirect.com/~earlcp

(Zoltan Szakaly) wrote in message . com...
Based on data on existing rocket stages we can achieve 0.88 mass
fraction (fuel and oxidizer are 88 percent of the mass) using
conventional aluminum fuel tanks and structures and using turbopump
fed engines feeding hydrocarbon fuel and LOX.

88%? That's distinctly average. Atlas I managed around 94.5% for its
first stage (*including* the 'stage 0' rockets that normally fall off
at altitude).

Am I wrong somewhere or SSTO is really easy to build?

No, it's not easy.

Zoltan

"Zoltan Szakaly" wrote:
I spent the last few days reading past messages in this group on the
subject of SSTO vehicles. It seems to me that building an SSTO vehicle
is not even a great challenge.

Expendable SSTO? No, not a great challenge. Except perhaps a
challenge to the inertia of the aerospace industry (and that's
as large a challenge as any technical difficulty). We could
even do a fair job performance and cost wise with basically
off the shelf component technology (the technology of
integrating off the shelf stuff into a single design and an
operational and business design is still nevertheless important,
but not, I think, a showstopper). But only just barely.
Although some, myself included, would argue that the way
forward to improved designs and systems is pretty clear and
obvious (such as composite LOX tanks or composite non-cryogenic
fuel tanks, which have already been essentially proven).

However, because of the added mass overhead needed for RLVs,
and RLV SSTO is still not within our technological grasp, not
quite yet. The logical thing to do would be to begin from a
starting point that can be developped toward an RLV SSTO,
such as evolving an ELV SSTO, or an RLV sub-orbital vehicle,
for examples.


[snip]
1. Composite fuel tanks and structure
How much can we gain here?

A fair amount. Especially if you choose wisely. LOX and
Kerosene work just fine in composite tanks. One of the big
problems for this though is that composite technology and
industry, though quite substantial and advanced, are still
fairly limited in a lot of aspects. Especially in terms of
the *size* of structures. For an SSTO, even more so for an
RLV SSTO, you're going to want really, really big tanks,
both because you need a lot of propellant (due to lack of
staging) and because bigger tanks give you better dry mass
fractions. And that means you'll probably need composite
tanks the size of or larger than the tanks on the Saturn V
first stage (S-IB). I'm not well versed in the details of
the current state of composite manufacturing but I'm pretty
sure that structures of that size are very difficult (and
expensive) to manufacture, if they can be at all. My guess,
and it's just a guess, is that if you wanted to build
composite structures of that size today you'd probably have
to build your own facilities for making them.


2. Aluminum - magnesium - lithium alloys
How much better or lighter are they?

Quite a bit. They were able to shave about 11% of the mass
off the Shuttle ET using advanced aluminum/lithium alloys.


3. Air breathing propulsion

Probably not worthwhile at all for quite some time, except
in niche roles (sub-orbital), and maybe not even then.


4. Higher Isp, high density fuel/oxidizer

I will not get into other more exotic high tech concepts like nuclear
reactions or plasma thrusters.

In my opinion, LOX / Kero is the sweet spot for today's
technology. Plasma thrusters are space propulsion, they
won't help you during launch. Nuclear Thermal Rockets
and more advanced stuff like NSWR, Orion, VASIMR, and a
few others hold a hell of a lot of potential for use in
launch vehicles, as upper stages or (if you dare!) as
first stages. With an advanced NSWR or NTR propulsion
system it would be possible to create an RLV that could
launch and land (even on planets lacking an atmosphere)
multiple times without refueling. And, of course, using
even a first generation NTR in a launch vehicle (even an
RLV "SSTO" (think integrated stages which are not
disposed of)) would greatly increase payload capabilities.


This entire issue of SSTO came up for me because I have been obsessed
with building a flying car and spent the last few years developing an
air breathing engine for it. I have an engine that has a fuel Isp of
over 4000. I dont think there is a point in trying to develop a
SCRAMJET engine because at high supersonic speeds the airdrag is
prohibitive. It makes a lot more sense to simply use the air breathing
propulsion in the first stage phase up to mach 8.

3. At 15:1 air fuel ratio the fuel Isp is about 4400, this can improve
to 10,000 as the engine leans out at higher airspeeds. A mass ratio of
1.2 is needed to go from the ground to 2.8 km/s after that assuming a
350 Isp a mass ratio of 5 is needed to go from 2.8 to 8.4 km/s
resulting in an overall mass ratio of 6. At a mass ratio of 6 an SSTO
is clearly possible with an air breathing engine.

4. If we insist on using rocket engines, we have many ways of
improving rocket performance. We can get 450 Isp with hydrogen and I
read in here that 550 Isp was achieved with Fluorine-Hydrogen-Lithium.
At a 550 Isp we need a mass ratio of 5.3 to get to 9 km/s which is
clearly achievable and results in a good payload fraction. We could
also try mixing solid lithium chips into propane (I read that here)

Am I wrong somewhere or SSTO is really easy to build?

Not easy, but achievable. Your speculation about air
breathing engines and high-Isp propellants ignores many
of the quite important downsides of each (such as
terrible thrust to weight ratios, optimization for
cruising rather than acceleration, propellant density,
and propellant storability). Nevertheless, with very
mundane technology (decades old technology really)
SSTO is achievable.

1. Composite fuel tanks and structure
How much can we gain here?

2. Aluminum - magnesium - lithium alloys
How much better or lighter are they?

3. Air breathing propulsion

4. Higher Isp, high density fuel/oxidizer


5. ACES

Zoltan Szakaly wrote:
Charts are charts, and hardware is hardware - and rarely do the two meet.
Try just flying your ramjet as a simple lifter - I believe that even if you
get it to work you are in for a big surprise when you near mach 1 and the
nature of the air stream changes.

Earl Colby Pottinger

The ramjets and the cone shaped intake system have been well
understood for 20 or 30 years. See the BOMARC missile ramjet or the
SR71. They work like a charm. My engine works like a charm at
standstill, I have no reason to assume it will not work
supersonically. I am getting over 4,000 Isp at standstill and for my

Things don't tend to work just because you don't know a reason
why they shouldn't work.

They tend to work because you have put in the engineering and design effort
to make sure they do.

Have you done any CFD, or even wind-tunnel tests at subsonic speeds?
Have you many years in super/hypersonic design?

SSTO concept to work I am only assuming a 1,000 Isp which is much less
than actual data.

It's not reasonable to extrapolate data from static testing out to near mach 1,
let alone higher mach numbers.

Just because you'd like to believe that the ISP will stay at 1000, doesn't
mean it will, it may hit 100, 10, or even 0 at any speed above where you've
tested it.

--
http://inquisitor.i.am/ | | Ian Stirling.
---------------------------+-------------------------+--------------------------
"When I use a word," Humpty Dumpty said in a rather scornfull tone, "It means
Just what I choose it to mean - neither more nor less." -- Lewis Carrol