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July
12, 2005
Jon Goff responds
to Dave Ketchledge comments given below:
I'm always
grateful for a thoughtful reply to one of my articles. Mr Ketchledge
makes several good points, and they deserve a good response. While
some of them touch on matters that I was planning on discussing
in some follow-ons to my orginal article, some of them can be
quickly answered here.
As a comparison of background, I'm only just about to turn 25,
and have only been involved in commercial space projects and discussion
for about 9 years or so. I'm now working with my second alt.space
firm, and have only been doing real rocket hardware for the past
year or so. I've got a lot to learn, but hopefully some useful
ideas and insights to add to the conversation. My undergraduate
work was in Manufacturing Engineering, with an emphasis in Operations
Management, and that tends to flavor my opinions a bit.
Anyhow, as to some of Dave's specific technical comments, I'll
just briefly touch on a few of them (as Clark's comments section
is hardly the place for a lengthy rebuttal on my part).
First I'd like to comment on some of the things Dave implied about
capsules vs. lifting bodies. Admittedly I'm not really much of
a fan of either. I look at capsules as a neccessary evil or an
intermediate stage, but greatly prefer fully reusable vehicles
to either. That said, I have a few nits to pick.
1. Capsules have and can be designed with reusability in mind.
At least one Gemini mission succesfully reflew a previously flown
capsule. The Soviet TKS system was also designed to be a reusable
capsule system. More to the point is some of the work currently
being done by George Herbert's company Venturer Space. It is quite
possible to reuse a capsule, it's just easier if you design it
from the start with reusability as design intent instead of as
an afterthought.
2. While lifting bodies can get lower G's on reentry, capsules
flying lifting trajectories (almost no capsules intentionally
fly fully ballistic reentries except in emergencies) can also
greatly reduce the G-loadings. Also reentry from trans-lunar velocities
is much harder with a highly lifting reentry profile as I understand
it. Most high lift reentry techniques tend to trade lower peak
heating rates for higher total heating rates. Ie they spread out
the heat over a longer duration, often using some sort of radiative
system where the shield radiates away as much heat as it is sucking
up. The kinds of heat shield that do well with high total loading
generally don't do well with high peak loading. Getting a shield
that can handle both isn't impossible, but is quite difficult,
as I understand it.
3. There's no reason a capsule can't have steerable parachutes
(if you prefer to use parachutes for landing). And it is quite
possible to do landings on land instead of in the ocean with a
capsule. IIRC, either Gemini or Mercury had at one point done
some development using a steerable parafoil and landing skids
for landing on dry lakebeds and such. Don't know how far they
got though. Steerable Parachutes and crush structures are also
quite feasible. Or you could always land the way God and Robert
Heinlein intended. :-)
4. Reverse engineering a J-2, and requalifying it for flight is
not going to be a trivial matter. It might not be as expensive
as redoing it from scratch, but it may end up being worse. Many
components are obsolete, most of the contractors are long gone,
all of the tooling is gone, and most of the engineers who worked
on it have retired. It isn't impossible, it's just not going to
be as trivially cheap and easy as ATK et al try to paint it.
5. Good point about nuclear power. It will be a real asset if
it can be fielded practically. There are some differences though
between submarine based nuclear and space based. Subs have access
to a massive heat sink known as the ocean. Space based systems
have to painstakingly pump that heat out through radiators into
space or into thin planetary atmospheres. That alone makes things
vastly more difficult. The point about the importance of reliability
is dead on though. Operability and reliability trump bleeding-edge
performance in my book almost every day of the week.
6. Qualifying a new solid with a new flight profile is not trivially
easy either. Saying we're reusing existing hardware, only to say
later that....well, we're reusing stuff that's based on existing
hardware is kind of disingenuous.
Anyhow, the rest of the points are ones I want to cover back on
my blog in further posts. If anyone else is reading this and wants
to comment, feel free to do so on my blog: http://selenianboondocks.blogspot.com
July
11, 2005
Dave Ketchledge
comments on Jon Goff's Shuttle
Derived Sillyness Part I: Getting Shafted by "The Stick Selenian
Boondocks - July.7.05:
I am a HPR
and MR flier with 40 tyears in rocketery, and 20 years in nuclear
power and engineering. My works are published by both the NAR
and TRA. With intererst I read Mr. Golf's comments on the CEV
booster and where NASA is headed in its booster selection. And
I would like to compliment and comment on Mr. Golf's commentary.
NASA is faced with twin issues in crating the CEV design. First
to support the remaining life of the ISS effort and by 2020 time
frame landing again on the moon.
The CEV to support the ISS flights could be flown by Big Gemini
as sugggested. But no one has ever flown a capsule with reusability
in mind. Going with a lifting body design gets you reuability
and this is where Lockheed is headed. A lifting body gets us lower
G loads, lower reentry heating rates, and cross ranging north
and south of the orbital track. If we look at usiing X-38 style
para foils you can land at any point +/- 3 feet thanks to GPS
controls. No more of this landing at sea method of the capsule
era. And your volume efficiency is very good in a lifting body
as well. So from an engineering stand point capsules are not all
that good.
My second concern is no one is talking about a lunar lander ....yet.
WE had better do that because to support a crew of 6 on the moon
for 90 days will require a vehicle about 4 times the mass of the
old LEM. Far better to make this in a manned and a cargo style
to lessen the problem. the old LEM could support a duration of
6 man-days, We now want a vehicle to do
450 man-days. So the real problem of going back to the moon will
be the lander. Likely powered with 2 to 4 RL-10's. Why ? because
the Isp using hydrozine is only 270-280. Whereas a H2/O2 based
LEM would have an Isp of 360-450. As to reliability you can not
get much better than the RL-10. Suggest weight for this craft
would be 70-95 L pounds, double that of the old LEM The one benefit
we have today vs the 1960's is composite materials and we could
shave about 15% of the mass of the structure down. And the power
requirements with today's technology is far better. You could
fly using off the self avionics. But would NASA do that ?
So going with a SDV stack makes absolute perfect sense for NASA.
You have to haul the mail and the Delta IV and Atlas V wont do
the job. You need a H2/O2 upperstage with around 150-200K pounds
to LEO to do the moon mission in a pair of flights. Flying 12-14
Delta IV to do the same job will take months and what if one of
those missions fails? The SDV stack will do the job. And with
only slight further modifications can handle a manned Mars mission
For Mr Griffin not to look at the infrastructure he has and the
equipment available would cost time, money and I believe be very
expensive. So we should take the Shuttle ET and add 3 or 4 RS-68,
I do not support continued use of the highly stressed SSME's In
fact, if one does one's homework you will note how marginal the
engine was until Pratt and Whitney redesigned the turbopumps.
the RS-86 is a better H2/O2 power plant with start of the art
features and controls.
As to the upper stage needs in terms of an engine the J-2 or a
pair of J-2's would be a perfect choice, as mentioned there is
no need for a 3K psi combustion chamber in an upper stage. The
flight history and testing of the J-2 were impressive. One even
ran on a test stand for 90 minutes and showed no wear even with
multiple restarts. You can not get a SSME to run
more than 2 times. So any mention of the SSME is pure junk for
an upper stage. NASA has several J-2 in storage, so we can use
those as models to create a replacement with CNC technology, powder
metallurgy and methods that Pratt and Whitney excel at.
As to the ATK Stick vehicle. the comments as to the 5 segment
version are correct , it has never flown a manned mission. And
changing the thrust profile of a SSRM is not some grossly difficult
thing either. Its all the mandrills you use. Now doing the qualification
will take 2-3 flights. But the 5 segment motor is not under any
higher stress levels in fact its lower since
the SRM has a really impressive flex every shuttle mission. A
5 segment stick wont have that. The upper stage the size of a
S-1C with the J-2 will do well. And you can flight that also on
a lunar mission.
I offer this
to MSFC, DO NOT take this program as a chance to experiment with
new engine designs. You did that with the SSME. LEARN the world
reliable operation. do you think I would put a pump in my nuclear
power plant if it had a one time operation life ?
I suggest the NASA MSFC engineering staff spend a week on a nuclear
submarine, they will learn something about reliability. I certainly
did on the 6 years I spent at sea. And I am a better engineer
for it. Admiral Rickover demanded it of every contractor and his
staff.
We should return to the moon and get established there again.
Its better to cut our teeth there then to immediately jump to
Mars. And we will need different equipment on Mars than on the
Moon to some degree.
Finally, anyone out there thinking you can mount Mars missions
effectively without a few 100Kw of nuclear power, I suggest you
read scientific American. Look at the article on VISMIR. We could
drop the flight time to Mars to as short as 4 months! All it takes
is a plasma drive. And about 20 MW of electric capability. Modern
subs run around 120 MW, so you are talking a small power plant,
and that have around 2500 years of operational history. I see
no reason we could not be on Mars by 2030 with 6 people at a cost
no more than Apollo.
Commercial space flight both suborbital and orbital will be make
rapid progress thanks to SpaceX, Scaled Composites, and Bigelow
Aerospace. But NASA is focus towards ISS support and the Moon.
So those saying we are going to something bad to the early commercial
space industry returning to the Moon, I fail to see how. Your
venture capital has not been from the government. In fact we very
much need a public that starts to wake up to the fact we are on
a 3 rock in a vast solar system and there is a whole lot of space
out there.
So I fully support a SDV stack. And an upper stage that can put
the CEV to the ISS and haul some 70-120K pounds to the Moon. And
all this effort can be done with a great deal of what we have.
But drop the SSME, its a museum piece. Lets build good reliably
systems and get back out there.
Dave Kechledge
Senior Member of the NAtional Association of Rocketry
Member Tripoli Rocketry Association
March
26, 2005
Dave Ketchledge
comments on the thesis The
Decision Maker’s Guide To Robust, Reliable And Inexpensive Access
To Space by Gary N. Henry, Lt Col, USAF - Air War College - Feb.2003
- pdf mentioned on March
23rd:
Sad to say
this fellow missed the mark to reducing cost to LEO access. He
is correct its a two stage to orbit sytem. Based ont he fact its
so difficult to get a mass fraction in a SSTO ( single stage to
orbit ) configuration. As an example the failure of the H2 tank
on the X-33 resulting in a 10-15% weight growth to go back to
aluminum tanks. and thus killed the program. And the Isp on the
plug nozzle at ground level was below expectations. So a TSTO
(two stage to orbit ) pres3ents more margin in the mass fraction
and from a propulsion point of view is a whole lot easier.
One of the things that bothers me is the SSME, look at the stress,
pressures and rpm's those turbopumps art at. And to go from dead
stop to around 34,000 rpm in 3 seconds presents you with bearing
issues that are impressive. Had Rocketdyne stayed with the Staturn
J-2 we would have a Chevy engine. The J-2 was famious for running
over an hour with no shown wear. And match that to todays materials
and CNC technology youy may really have a low cost engine. Space
X is follow down that road with the Merlin on the Falcon 1.
So rule number one its the pumping system of the orbiter and first
stage that contribute significantly to the cost of your vehicle
and its reliablity. If you have to overhaule after every two flights
(SSME) and replace the ceramic metal bearings your labor and manpower
cost are going to put you in the high operational cost area.
As to the assumption of waverider hypersonic first stage and an
orbiter on top of that in a horizontal takeoff. The study is flawed
in two key points. And I reffer as a referance to Andrews Space
and Technology, ACES concept.
The ideal design based on the work on the Gyphon from Andrews
is this:
(1) A first stage, turboject aircraft with one or several liquid
fuel rocket engines at the base.
(2) The first stage powered by turbojects that run over of liquid
gasified H2. The first stage also carries no LOX ( at a density
of 64 pounds per cubic foot) and you gcan get to a GLOW of 750,000
(a bit latrger than a 747 ) in order to loft 55000 pounds of pauyload
to LEO or an orbiter with a crew of 4-6 and a few thousand pounds
of payload. The piggy back orbiter has only its liquid hydrogen
on board, again no LOX
Your first stage is ideally a canard configuration long body.
On takeoff its a turbo jet running on H2. After you get airborne
you start to duct some of the jet compressor air into a pair of
heat exchangers. The air is liquified and the N2 content is centerfuged
out to get you 95% pure LOX. You spend the next 3 hours filling
your LOX tanks in the orbiter and the first stage. And you are
flying only at around 500 mph. No need on the first stage for
expensive metals you could do it in aluminum and titaminum. You
size the wings to act like a big heat sink and lots of surface
area.
When your LOX tanks are now filled. You ignite the liquid fueled
first atage and acelerate to about Mach 4 to 5 and climb above
300,000 feet. You then stage to the orbiter that flies the remain
flight. The first stage.pancales into the lower air and requires
no reenetry coatings. A brief inspection and she is ready to fly
again
While Andrews prefers a delta wing orbiter, I prefer a lifting
body configuration. The lifting body is more robust during reentry
heating, and better suited for hypersonic flight. there is a internal
volue efficency as well So you get a large base area that reduces
the reentry heating flux, and room for propellant and the crew.
The key aspects to this design are no significant engineering
design challenges that add both cost or reduce reliability (ie
we want a chevy) And you get a vehicle that can liftoff from nearly
any commercial or military airport as long as you can feed it
liquid H2.
Now NASA is not going to buy into this design becuse they are
very much in the camp of keeping KSC in operation and see space
flight only in a vertical launch mode. But Andrews Space and Technolgy
did theor homework right. It is elegant and pratical in its design.
So while I agree with the TSTO comment. Their cost structure is
deeply flawed because they are making the first stage the expensive
and untested waverider to get to a mach 10 or so staging velocity.
When Andrews has shown its not cost effective to do this. Making
two hypersonic craft is costly, [instead] have only one and a
design we can build today using designs like the J-2 or the RS-68.
I would love to see us wake up to the day we have hotels in orbit,
and industry. We are headed that way. But we need folks like Scale
Composites, Space X, Andrews Space and Technology and Bigalow
Aerospace. We can do it if we use good engineering economics in
our designs.
March
1, 2005
Andrew Case,
head of the Suborbital
Institute, responds to the comments
of Jim Albaugh, president and CEO of Boeing Integrated Defense Systems
(IDS):
The bottom
line, Albaugh said, was that this industrial transformation wasn't
happening. "Any honest assessment of aerospace will conclude that
ours is a static industry. It took us 66 years to go to the moon.
With huge
amounts of federal funding. That level of funding is never coming
back barring an alien invasion. The Apollo Project established
a completely unrealistic baseline for "the way things are done."
By 2035,
yet another 66 years will have passed. And where will we be then?
Two options:
stuck in the Apollo paradigm, praying for the return of huge federal
grants like some sort of cargo cult, or in a completely new paradigm
where more government money is spent on ensuring passenger safety
than on launch vehicle R&D.
What is
the next 'giant leap for mankind?'
The next
giant leap is giving up on demands for giant leaps. In the long
term evolution beats revolution.
Where
is the innovation? What was the last real breakthrough technology
that transformed aerospace?
The last
breakthrough was orbital rendezvous. Every technology we need
to go to Mars, mine the Moon and Near Earth Asteroids, build space
stations and colonies is already in the bag, or within relatively
easy reach. We have all the building blocks, we just need to assemble
them in the right order.
Where
is the next one?"
Markets.
Business plans that don't include the words "and then a miracle
occurs," either explicitly or implicitly. Business models that
don't depend on federal money.
Albaugh
had the courage to state publicly what many have been thinking.
The aerospace industry has become so risk-averse that it has lost
the power to innovate - a far cry from the trail-blazing days
of the first half of the 20th century, when risk-taking mavericks
and innovation were synonymous with the business.
Albaugh is
still stuck in the techno-centric paradigm for spaceflight. We
need a market-centric paradigm. As long as the price in executive
career damage from program failure due to excessive caution is
lower than the price of embarrassing video of a test failure,
federal money will always flow to powerpoint projects. This will
always be the case as long as the government is funding the development
of vehicles. The solution is for the government to buy services,
not vehicles. There should be a standard spec for government payloads
(obviously different specs for different payloads), and the launch
service should go to the lowest bidder. This will encourage innovation
where it counts (launch costs), and will help drive innovative
business models to take advantage of the lower launch costs. It's
not about technology. It's about making a buck. Lots and lots
and lots of bucks. We need more airmail and less Langley Aerodrome.
January
28, 2005
Luke
Colby, a graduate student at Georgia Tech and a rocket
developer, urges people to keep an open mind about the
possibility someday of gravity
control propulsion (in reference to this RLV
News item):
... I saw
that article on gravity that you posted about in the RLV news
section and I just thought I might offer some comments on it because
looking into breakthrough propulsion is one of my side hobbies
while my main focus is of course as a conventional "rocket scientist".
Anyways I thought I could offer some comments on the whole issue
that your readers might find interesting.
First of all, I was very disappointed to see two top ESA scientists
say that gravity control would be useless for propulsion...??
Are they kidding do they not have even an elementary understanding
of basic propulsion and launch vehicle principles? ALL of the
fuel used by a conventional rocket is used to escape earth's gravity
well and if that gravitational field could be negated then it
would make travel to LEO as easy as walking down the street, well
almost. Further what they seem to forget is that control of gravity
doesn't loose it's usefulness once you reach orbit or escape the
Earth's sphere of influence, because you have to remember in the
solar system you then have the gravitational field from the sun
to contend with, so the ability to control gravity would be truly
revolutionary for space travel, NOT as they put it; "not as useful
as conventional propulsion ideas"...
At any rate,
I don't want to go into too much detail for the sake of brevity
and since this is not my most qualified area to comment in, but
if anyone is interested in an excellent engineering analysis of
gravity control craft and the potential for its use, then they
should read a book by the late Dr. Paul Hill of NASA Langley research
center called "Unconventional Flying Objects". Dr. Hill is an
amazing engineer who worked on aerospace systems for over 40 years
and was instrumental in the development of many of the aerospace
systems we take for granted today. In his book (which he requested
be printed posthumously,) he unabashedly discusses UFO sightings
(I know I don't usually like to even mention them around other
aerospace engineers either), but he does a wonderful job of taking
the sightings at face value and applying our conventional laws
of physics to their motion. He proves quite deftly in my opinion,
that they in fact follow the laws of physics and are perfectly
explainable phenomena if we are willing to look at the data objectively.
For example, my favorite part is when he elegantly points out
that the reason these vehicles are able to travel through the
atmosphere at 9,000 mph is that if you can control gravity and
create a field of anti-gravitons around your craft then you can
modify the airflow over the vehicle by use of the body force term
in the Navier-Stokes equations that we so commonly neglect in
our work. Basically, by using a sufficiently strong field that
acts on all the air molecules equally you can decelerate the flow
so that it just stops at the craft skin and thus results in no
adverse pressure distributions which are responsible for shockwaves
and heating at supersonic speeds. The result then is that the
vehicle can fly at any desired speed with the surrounding air
being nothing more than a minor inconvenience. In fact, the aerodynamics
analysis simplifies down to simple subsonic invicid flow analysis
with potential flow equations making all that difficult hypersonics
work we have done obsolete... So going back the two ESA scientists
this is yet another aspect of gravitational control that they
completely ignore, as it also completely solves the aerodynamics
issues involved with hypersonic flight. As a result sonic booms
and reentry heating become mute points that are no longer a concern.
Of course,
all this is predicated on the ability to effect gravity (which
Dr. Hill does not attempt to credibly explain how to do, but does
offer the tentative idea that possibly anti-proton/Neutron annihilation
reactions will generate an anti-graviton and soft x-ray. Of course
this is not my area of expertise nor was it his especially, so
I wouldn't presume to comment on the validity of this idea scientifically.)
The point though is that the ability to control gravity would
be the single most important event in human engineering history.
Hopefully someday we will be able to figure it out and in fact,
we may not be as far off as some think. As I understand it there
is a team of Russian physicists (led by Dr. Podkletnov I believe)
that by using large superconducting rotating disks and spark generators
have managed to generate gravity waves. These waves supposedly
generate 10,000 g's of acceleration for about a millisecond and
as a result have the ability to punch through solid steel and
concrete walls up to 10 km away! Obviously such technology is
going to be held very close to the Russians chest if they get
a repeatable working system put together, so we may not see too
much about it here in the US, but we'll see... Who knows in a
few years the Russians may be selling rides into space on more
than just their Soyuz rockets... In the mean time, we will just
have to keep pushing forward with conventional rocket propulsion
systems.
So, my motivation
for writing this was to point out that gravity control is not
without its uses and may even be something within our grasp some
time in the future. As a result folks in the aerospace field should
at least tentatively be willing to consider the idea rather than
simply scoffing at it off hand and ignoring it entirely as is
often the case today. Certainly, I am not suggesting that we should
all start running around talking to UFO cult folks and start looking
for little grey men and their flying machines, but we should at
least accept that the idea of gravity control propulsion as something
worth keeping in mind and not a totally quack fringe idea that
should be scorned.
Thanks,
Luke
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Luke S. Colby
Graduate Student
Space Systems Design Lab
Georgia Institute of Technology
School of Aerospace Engineering
January
26, 2005
Matthew
Morris
responds to the comments
from Dave Ketchledge about what type of crew module design is best
to launch on a Falcon V:
I'd like to
comment on the letter by Dave Ketchledge posted on January 24.
I'm not a technical writer for anyone, nor am I an engineer. However,
I am fairly good at researching the figures I use, crunching numbers,
and viewing the 'overall picture'. I'm also the creator of the
Gemini-3X thread on Space.com which RLV News referenced on January
18th, and which Mr. Ketchledge's letter comments on.
In his letter, he states definitively that the rapid deceleration
of a capsule would generate G forces of 12-15 Gs'. To date, I
have not been able to locate any example of a capsule that generated
15 G's on re-entry. The closest I have been able to find is that
of Gus Grissom's Liberty Bell flight, which hit 11.7 G's. Even
that was high, as the average max load for the Mercury capsules
was reported to be about 7.7 G's. By contrast -- documentation
on the Gemini capsules generally shows a max load of about 4G's.
The Gemini IV max was 7.5 G's -- although this was unusually high
because an error on the re-entry burn forced the crew to significantly
increase drag to reduce the landing error. Using a more contemporary
example -- documentation on the Soyuz re-entry capsules generally
indicates they pull about 4 G's on re-entry. In another example
of an unusual circumstance, on the flight returning Dennis Tito,
they had a targeting error similar to Gemini IV which required
them to pull 7 G's.
From this -- it would seem that a modern capsule-based spacecraft
would average around 4 G's on re-entry, with the potential of
pulling 7-8 G's in the event of a significant targeting error.
This would seem acceptable given Mr. Ketchledge's own statement
that we have a flying public that can handle about 4 G's. I don't
doubt that there are steep reentry flight paths that capsules
*could* take that would generate loads in the realm of 12-15 Gs.
However, those are not the flight paths used in real life. If
Mr. Ketchledge has documentation to back up his statements, I'd
be very interested to see it. Here's mine.
Liberty Bell:
www.mitchell.k12.in.us/Junior%20High/social%20studies/missions.html
Gemini IV: www.hq.nasa.gov/office/pao/History/SP-4203/ch11-4.htm
Gemini V: www.hq.nasa.gov/office/pao/History/SP-4203/ch12-8.htm
Gemini VII: www.wilhelm-aerospace.org/Space/Gemini/chap4.html
Soyuz: www.floridatoday.com/columbia/columbiastory2A51384A.htm
As to his suggestion of a lifting body being the shape of choice,
and in particular his example of using a design like the X-38
-- there are some significant problems. One of the X-38 models
was 28.5 feet long, 14.5 feet wide, and weighed approximately
16,000 pounds, yet was a 1/6 scale model of the actual CRV spacecraft
(ref. www.ed.arizona.edu/ward/X-38/X38-index.html).
This places it several thousand pounds outside of the lift capacity
of the Falcon V even before you start scaling up to full size,
adding a launch escape system, ECLSS, crew, de-orbit module, etc.
At that scale (too small for 4-5 people by far), it's about twice
as long as the Gemini capsule and ~50% wider. Generously assuming
that a production version double the size would carry a crew of
five (this would still be 1/3 the planned size for the CRV), it
would be 57 feet long and 29 feet wide. Given that the Falcon
V itself is only specced at 100 feet long and 12 feet wide --
there would seem to be a serious issue with using it for the launch
vehicle. I am unaware of any lifting-body design that will meet
the weight and size restrictions of the Falcon V.
In response to his assertion: "When you get down to 25,000 feet
out goes the parawing. And that will weight in the range of only
300 or so pounds." The X-38's parafoil alone weighed 9.8% of the
landing weight as compared to the Apollo parachute's 2.8% of capsule
weight. (ref: mae.ucdavis.edu/faculty/sarigul/AIAA_2003_0909_revised_Sep03.pdf).
That puts the weight of the parafoil at about 1500 pounds. It
also doesn't include the weight of the landing gear, drogue chutes,
and compartments.
In response to his concerns about the reusability of the heat
shield: I disagree with his basic premise. I spent a great deal
of time researching LI-2200, AETB, and the various advanced metallics.
In the end -- I decided that the best option for the capsule design
was simply to use a COTS ablative coating (DOW Corning 93-104
Ablative Material is the leading contender) on a one-shot framework
that can be attached to the rear of the capsule and replaced after
each flight. My calculations on the volume of ablative required
at a cost of $750/gallon put it at about $9,000. This is nothing
compared to the other costs of a launch, and given the amount
of man-hours required to maintain re-usable heat shields, it's
extremely economical and will contribute to very fast turnaround
times for the capsule. Reusability in manned spacecraft is a great
thing -- so long as it's not taken to extremes that defeat the
intent. The intent of making a reusable spacecraft is to reduce
the cost of manned spaceflight.
The way to minimize the cost of placing people into space is to
minimize the amount of mass being launched. The spacecraft design
that allows for the abolute minimization of launch mass is a capsule.
Lifting bodies and winged craft WILL be considerably heavier.
They have several benefits over a capsule design, but they also
have several drawbacks. My vote -- at least at the cost per pound
of current launchers, and even for that expected of the V, is
to use a capsule.
Matthew Morris
January
24, 2005
Dave
Ketchledge offers some comments on the suggestion
of launching an upgraded Gemini on top of a Falcon V:
As
a technical writer for the NAR and TRA I have been involved in
rocketry for several decades. My soon to be released book "The
Next Shuttle" drives to the very concept of what kinds of hardware
do we fly to carry people into orbit and why. The book is not
just historical, but considers the Engineering issues of propulsion,
aerothermodynamics and aerodynamics.
My 1988 work "Mirco Shuttle" was a Lear jet sized shuttle flown
on a pair of Titan II sized boosters. Rockwell had a strong interest
in my reentry tile design of pyrolized graphite and foaminated
glass. Compared to the current shuttle LI-1500 and LI-3000 tiles
my concept took a lot more abuse and stayed on. My only drawback
was weight or density, my tiles were heavier but my lower surface
area made allowed the craft to stay within weight margins. My
current book also uses R/C model airplanes as a a design tool.
A trait Edwards and Dale Reed applied quite often.
Briefly if comes down to 3 choices, capsule, winged or lifting
body. Using a Falcon V every pound in structural weight of the
payload is going against your crew size. So lets drop a wing craft.
That saves likely 500-2000 lb.
Why not capsules as one writer has suggested. There are several
reasons. Gemini, Mercury and Apollo would in as little as 5 minutes
shed all their velocity. That large delta V would decelerate the
crew in the range of 12-15 Gee's. All I can tell you is that at
even 6 gee's life gets pretty ugly. Did it once is a plane and
nearly passed out. Do you want the crew knocked out or have heart
issues ? I don't think so. And the heat shield will only be good
enough for one flight because you have such a low surface area
and a high BTU heating rate. A metal heat shield of Inconnel like
ARMOUR is going to be over stressed. So I do not recommend a capsule.
Any of you Max Faget (MSFC) supporters need to consider this.
You guys design a great capsule but we have a flying public that
can handle about 4 gee's . And if we can build a design with a
large surface area you get a host of good things.....
This leaves us with lifting bodies, similar to the X-38. If you
do the research you can use a GPS and parawing to land at speeds
as low as 40 mph.That's a Piper cub ! And the GPS puts you within
3 feet of your runway. No water landing is needed. And thanks
to the body shape alone you can cross rage about 500 miles north
or south of the orbital track, have a 4 G reentry loading and
a reusable heat shielding. When you get down to 25,000 feet out
goes the parawing. And that will weight in the range of only 300
or so pounds.
So my vote goes to a 4-5 man lifting body close to the X-24 /
38 shape in top of a Falcon V with a high energy second stage
( Centaur ). And in the end you will get around 12-15 flights
a year per vehicle. At a cost well below what Boeing or Lockhmart
is going to be able to achieve.
Both Space X and Scaled Composites stand to win the lion share
of the manned space market in 20 years. By using inovative designs
that sit and collect dust at NASA technical servers you can save
a great deal of time and energy using modern materials and manufacturing.
Look at the Merlin engine as an example of this.
Dave Ketchledge
Instrumentation Engineer
fmr: US Naval Reactor Operator
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