On Apr 6, 10:38*am, Robert Clark wrote:
On Apr 5, 3:29*pm, Robert Clark wrote:
...
*Now if we only require an altitude considered space of 100 km and the
carrier craft already gives us 20 km altitude this could just barely
give us sufficient delta-V for orbit. This delta-V would also be
helped by using a "lifting ascent trajectory" mentioned in Day's
articles:

Fire in the sky: the Air Launched Sortie Vehicle of the early 1980s
(part 1)
by Dwayne Day
Monday, February 22, 2010
http://www.thespacereview.com/article/1569/1

*However, there is a question of the max take-off weight of the B-1,
and how much of that could be fuel compared to payload. For this
application used only for a short dash to high altitude at high speed
were long range would not be needed, so therefore much less fuel load,
could we strengthen the airframe as done for the 747 carrier craft for
the shuttle so that B-1A could carry the ca. 270,000 lbs loaded weight
of the X-33?

* As I mentioned in the section on lifting trajectories in the first
post of this thread, you need a good lift/drag ratio at hypersonic
speeds to get significant propellant savings using a lifting
trajectory. See section IV he

Newsgroups: sci.space.policy, sci.astro, sci.physics
From: Robert Clark
Date: Sun, 1 Nov 2009 05:20:13 -0800 (PST)
Subject: A kerosene-fueled X-33 as a single stage to orbit vehicle.http://groups.google.com/group/sci.s...b04a58b08278e?...

*The "Air Launched Sortie" vehicles discussed in Day's articles had
such good ratios. However, for the X-33 it's as poor as for the space
shuttle, only around 1 at hypersonic velocities. Then it's doubtful
the lifting trajectory could make up for the delta-V shortfall for
this air-launched X-33.
*But perhaps we could increase the propellant load. By reducing their
respective temperatures down to near their freezing points, it's known
you can increase the density of the LH2/LOX combination by about 10%.
So let's say the propellant load is now 231,000 lbs. Using still the
45,800 lbs dry weight, and 453 s vacuum Isp, we get a delta-V of
453*9.8*ln(1+231,000/45800) = 7,987 m/s. Adding on the 600 m/s we get
from the Mach 2 carrier craft and the 462 m/s we get from the Earth's
rotation at the equator we have a total of 9,049 m/s delta-V.
*This is about right when you consider that for either the single SSME
or dual J-2 engine option, the initial launch thrust/weight ratio will
be high at nearly 2 to 1, which will result in lower gravity losses.
*However, in any case you would be able to carry only minimal payload.
You might be able to carry 2 crew members with environmental systems.

*However, a problem still is the weight the B-1A would have to carry
compared to its max takeoff weight. See the specifications he

B-1 Lancer.http://en.wikipedia.org/wiki/B-1_Lan...ns_.28B-1B..29

*The max takeoff weight of the B-1B is given as 477,000 lbs. If you
subtract off the 231,000 lbs X-33 propellant load and 45,800 lbs X-33
dry weight that leaves 200,200 lbs. But the empty weight of the B-1B
is 192,000 lbs, so only 8,000 lbs is left over for the B-1B fuel, and
that does not even include the extra weight that would need to be
added to add strength to the airframe to support the much higher
payload.
*One possible way you could reduce the strengthening mass is an idea
used with rockets: the propellant tank being pressurized can help to
support both compressive and bending loads that normally would require
extra strengthening mass. Then by placing the fuel tank for the B-1A
in the fuselage rather than the wings, which is possible because you
no longer need bomb bays, you might be able to solve the problem of
extra strengthening mass.
*However, another problem is that the B-1A actually had a lower max
takeoff weight than the B-1B, while also a lower empty weight. You
would need to find a way to give the B-1A the same max takeoff weight
as the B-1B while maintaining its Mach 2+ top speed.
*Another solution would not be as palatable to the Air Force. The
Russians currently have in actual operation a Mach 2 bomber that is
larger than the B-1:

Tupolev Tu-160.http://en.wikipedia.org/wiki/Tupolev_Tu-160

*It has a max takeoff weight of 606,000 lbs and an empty weight of
242,000 lbs. That leaves 364,000 lbs left over. That would be well in
excess of what's needed to carry the X-33 and even give it a
significant payload, and for the Tupolev to still have a significant
fuel load.

*The design of the X-33 lifting body airframe was not particularly
advanced once you get by the problem of lightweighting the tanks,
which I have given some methods to solve. The most advanced
characteristic of the vehicles design were the aerospike engines, and
these would not even be needed for this air launched application. Note
also the other competing proposals for the X-33 suborbital
demonstrator by Rockwell and McDonnell-Douglas were about the same in
size and capabilities as the selected Lockheed version, but these
would offer no complications at all in getting the tanks to have the
needed lightweight character since they were of circular cross-
section.
*Then it would not be difficult at all for the Russians to make such a
X-33 class spaceplane. And they already have the carrier craft to
serve as its launch platform to orbit.

* *Bob Clark


The maximum takeoff weight is effected by two factors: the wing area,
for the amount of lift they can generate for the heavier weight, and
the thrust, for generating sufficient speed for takeoff at the heavier
weight.
Use of the X-33 as the orbital craft could resolve both of these
issues. Most versions of such air launched systems have the orbital
craft quite small with respect to the carrier craft. However, an X-33
class spaceplane with an B-1 class carrier craft would have a
significant proportion of the carrier crafts wing area. Then why not
use this additional wing area to provide additional lift at takeoff?
The problem is for biplanes, as this in effect would be, the lift is
reduced when the wings are close together. However, the lift can be a
large proportion of that due to the total wing area when the gap
between the wings is about a chord length:

BIPLANE AND TRIPLANE WING LIFT AND EFFICIENCY.
http://tpbweb.com/media/catalog/781.pdf

By this data the lift can be upwards of 80% of that expected from the
separate wing areas, for a gap of wing chord distance. For delta-
wings, it would be the mean chord length. But would it be that of the
upper wing or lower wing? If the B-1's mean chord is used it might be
40 feet. But if the X-33 means chord is used if might be 30 feet.
The X-33 suspended this distance away from the carrier craft would
make for a quite ungainly looking vehicle but it would work, at least
for takeoff and low speed, where this biplane data is available. A
question that would need to be answered is how effective is the
biplane lift at supersonic speeds.
A disadvantage of biplanes is that they have higher drag compared to
a single wing of the same wing area. This is where the high thrust of
the X-33 would come in. Using a SSME or 2 J-2 engines would give about
400,000 lbs thrust at sea level. This is multiple times greater thrust
than the B-1 and would be sufficient for takeoff of the combined
vehicle using aerodynamic lift. So both the B-1's jets and X-33's
rocket engines would be used.
In fact using both the lift and the thrust of the X-33 gives you more
leeway in your carrier craft. You could use the Concorde for example.
Note also that use of the rocket thrust from the X-33 would also allow
you to reach higher speeds say Mach 3+ before release. This would
allow greater payload, since less delta-V would need to be supplied by
the X-33 after release. The extra rocket propellant for the X-33
required for firing during the linked portion of the trip would be
carried in the carrier craft fuselage.



Bob Clark