Re: How big would an SSTO be?
- From: BradGuth <bradguth@xxxxxxxxx>
- Date: Thu, 05 Jul 2007 21:14:12 -0000
On Jul 5, 1:08 pm, eina...@xxxxxxxxx wrote:
BradGuth wrote:
On Jul 2, 3:22 pm, Len <l...@xxxxxxxxxxxxxx> wrote:
On Jul 1, 6:23 pm, Sylvia Else <syl...@xxxxxxxxxxxxxxxxxxx> wrote:
Len wrote:
On Jun 30, 6:03 am, Alex Terrell <alexterr...@xxxxxxxxx> wrote:
On 30 Jun, 04:38, Sylvia Else <syl...@xxxxxxxxxxxxxxxxxxx> wrote:
Len wrote:I believe Len is an expert and would take his word for it.
On Jun 29, 6:55 pm, Sylvia Else <syl...@xxxxxxxxxxxxxxxxxxx> wrote:Would you care to expand on your concerns. At the moment, you've
David Cornell wrote:I have probably looked at as many launch vehicle concepts
If someone were to build an SSTO using realistic assumptions about massYou didn't say so, but I'm assuming you mean a reusable craft.
ratios and available power systems, how big a vehicle would be needed to
send (say) three people and a modest amount of cargo into LEO? I have
seen Apollo capsules in museums, so I am using them as my baseline.
Would such a thing be the size of a regular jetliner? Or the new Airbus
super jumbo jet? Or are we talking about a Zeppelin on steroids?
Also, how would these things scale? If we wanted to increase the crew
from three to four, would the vehicle size go up by a third? Or more?
Thanks
David Cornell
Disposable SSTO's seem a waste of effort.
The most developed design I've seen for a reusable SSTO is
http://www.reactionengines.co.uk/skylon_vehicle.html
It has a payload of 12 tonnes, and a maximum takeoff weight around 280
tonnes, similar to that of a 777-300. It uses a new engine design with
some technological challenges, but they seem to have made some progress
with it. They're obviously financially constrained, so if you have a
spare $billion, I'm sure they be interested in talking.
Skylon is an automated system, and as such is not designed to have a
crew, but could carry people as payload. This document
http://www.reactionengines.co.uk/downloads/JBIS_v56_118-126.pdf
discusses that application using a module carrying 40 people, though
that's obviously in a transport application (to a space hotel, perhaps).
If you have space tourism in mind, with passengers not leaving the craft
and floating around the cabin, then presumably they'd need more space
per passenger.
It's hard to say how this scales for a smaller payload, but at a guess,
I'd say you could get a craft to carry four people that was the size of
a small airliner in the 50 seat range.
Sylvia.
--rocket powered and airbreathers--as anybody in the world.
The devil is in the details. I would not consider Skylon
anywhere close to realistic. As for purely rocket-powered
approaches, I have never been able to convince myself
that any SSTO having a gross mass of
less than about 800 tonnes was very realistic. And for
HTOL, some type of ground cart to support the vehicle
at gross mass is probably necessary--thus making it
really an assisted SSTO, rather than a pure SSTO.
Staging--even subsonically at altitude or at low supersonic
speeds greatly relieves the challenge. IMO, staging
can sometimes be beneficial from the operations point
of view--as wsll as the performance point of view. SSTOs
are undoubtedly appealing from the psychological point
of view. However, they may not be a good way to run
an airline.
At some combination of size and yet-to-be-discovered
technology, SSTOs will make technical, economic and
marketing sense; but I don't see this happening soon.
Len
basically said that you're an expert and that we should believe your
claim that Skylon is not realistic.
Sylvia.
Nevertheless, an expansion on the concerns would be of interest.
However, I don't see the benefit in SSTO when concepts like Quickreach
2 (http://www.astronautix.com/lvs/quieach2.htm) could reach orbit for
relatively low cost.
Len - how does Quickreach 2 compare to the latest space van proposals?
I have been out of town. I'll respond in more detail
tomorrow.
As a quick answer, Quickreach should be able
to launch a nearly twice as large payload a
couple of years earlier than the Space Van 2011.
We expect to carry 2000-kg--or eight passengers
--to an ISS-type orbit (not our main mission) for
a price (including ROI) of $2,000,000 per flight
in 2007 dollars. This compares to a Quickreach
cost (price?) of $20,000,000 in 2005 dollars.
The Space Van should be able to achieve much
more frequent flights, since there are no expendable
parts or reusable parts that require extensive
refurbishment between flights.
The Space Van should have good abort options
throughtout its flight regime--starting with
engine-out abort capablility just after liftoff
with derated engines. The engines are
derated for much improved time between
overhaul.
As for Sylvia's request, I am not sure
exactly what cycle Skylon plans to use,
but I suspect that it is some type of
combined-cycle engine. The poor-man's
approach to analyzing combined cycle
performance (except for potential benefits
from saving installation space through
integration) is to imagine separate rocket
and airbreathing engines. The resulting
thrust and specific impulse usually equals
the goals for the combined cycle engine.
This anaylis trick allows a quick
assessment of how much airbtreathing
and how much rocket the designer would
like to have. If one then goes through some
tradeoffs of different ratios and allows for
real-trajectory estimates of drag losses and
real-structure mass estimates allowing for
realistic inlets and the impact of flying the
whole vehicle at relatively high dynamic
pressures and velocities, I have always
found that the best ratio is 100 percent
rocket. Many others--including highly
knowledgeable people like Henry Spencer
--have noted that the airbreathing appeal
is rather superficial and vanishes under
realistic analyses.
Len
Yet Reaction Engines have gone through the same process, and reached the
conclusion that for their craft and engine the numbers do add up. The
people involved in the project are not amateurs. If you want to claim
that Skylon won't work, you need to point specifically to where Reaction
Engines have gone wrong, not make vague claims about analyses of other
craft.
Sylvia.
Actually, I do not feel any need to justify not
wasting any more of my life on airbreathers
for acceleration. The 1960's aerospace plane,
the more recent NASP and many other fiascoes
spent far more money failing to meet their
promises than has been spent on
rocket-powered space planes--before finally
admitting failure. And then another group
come along with the same claims. They are
welcome to try; I--and many others--prefer
to put our resources into more productve efforts.
The summary reasons that I gave earlier for
doubting that airbreathing designed to operate
over a significant mach-number range can
outperform pure-rocket approaches for acceleration
missions are not vague. These are very real,
specific and damning.
Reaction Motors may have "reached the
conclusion that for their craft and engine the
numbers do add up." This claim has been made
many times before--only to have such claims
quietly fade away when the admittedly complex.
somewhat counter-intuitive analyses are made
in sufficient detail and honesty.
Normally I am a "live and let live" type of guy.
However, NASP type claims have several times
derailed much more promising, rocket-powered
approaches. Of course, that is in a government-
sponsored world. In a commercial world, I am
only concerned about being able to attract
investment for the approach that I think is most
workable in the near future. If investors choose
to fund something like Skylon as well, I wish them
luck. However, I shall not be particularly
concerned about real competition.
Len- Hide quoted text -
- Show quoted text -
Your honest input is well taken by way of how I've thought about this
SSTO Skylon, as simply being too much fly-by-rocket pie in the sky,
especially at their impressive ratio of 23.3:1 for accommodating 12
tonnes worth of most anything LEO, is just way more than a little
outside of the regular laws of physics.
Unless Skylon is assisted with a pair of reusable LRBs, there's no way
such a SSTO monocraft is ever going to deliver those 12 tonnes into
LEO, especially if limited to LOx/LH2. Possibly 6 tonnes.
Therefore, I still like your 800 tonne SSTO alternative, seems capable
of perhaps getting as much as 24 tonnes into LEO.
-
Brad Guth
An interesting and informative threat you people have here. One way to
square the equation might be for the thing to take off only partially
fuelled, then once airborne and at a reasonable altitude it could tank
up in the air.
How ...
read more »- Hide quoted text -
- Show quoted text -
This topic is way over your head, and as such you can't hardly
contribute much of anything but the obvious that has already been
taken into considerations as of years if not decades ago.
Not that a spendy, terribly energy consuming and NOx polluting Skylon
couldn't be refueled on the go, as in duh, no kidding folks.
How many extra tonnes of CO2 and NOx per kg of payload getting to LEO
is worth the all inclusive environmental birth to grave consequences?
Do you ever think of taking everything into consideration, and thus
thinking anything out to the final end-result?
It's called seeing the big picture.
-
Brad Guth
.
- Follow-Ups:
- Re: How big would an SSTO be?
- From: einarbb
- Re: How big would an SSTO be?
- References:
- Re: How big would an SSTO be?
- From: Len
- Re: How big would an SSTO be?
- From: Sylvia Else
- Re: How big would an SSTO be?
- From: Len
- Re: How big would an SSTO be?
- From: BradGuth
- Re: How big would an SSTO be?
- From: einarbb
- Re: How big would an SSTO be?
- Prev by Date: Re: How big would an SSTO be?
- Next by Date: Re: How big would an SSTO be?
- Previous by thread: Re: How big would an SSTO be?
- Next by thread: Re: How big would an SSTO be?
- Index(es):
Relevant Pages
|
Loading
