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Methods of Decelerating a Spacecraft Through Atmospheric Re-entry Using a Shuttlecock-like Design

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Abstract

Pre-Summary This sub-page to www.rocketslinger.com describes how payload fairings for an upper stage could be modified to remain attached to the satellite(s) deployment mechanism(s), and to one another, and also (optionally but highly desirable) to the entire interim upper stage (fuselage, fuel and oxidizer tanks, and rocket engines, etc.) as well. Whereas a commonly used design today involves the use of 2 (two) clamshell fairings, which are jettisoned before satellite deployment, the base design here envisions "N" fairing-segments, or "flower petals", or simply "petals". The petals can also be thought of as "feathers" in a feathered badminton shuttlecock. Each of 2 clamshell fairings are now subdivided (sliced) into smaller segments, with each shell-slice being vaguely reminiscent, not only of a flower petal, but also of the skin-slices of a sliced orange. For this document, "N" will be set to "4", with one (marked) exception. Each petal remains attached to the base of the assembly (ideally but not always, this assembly is the entire upper stage), at the base of the petal, by hydraulic actuators. During re-entry, the petals are sometimes more-retracted (less deployed) and sometimes more-deployed (less retracted), as one travels radially around the periphery of the bulk (center of mass) of the "shuttlecock". "N" = 4 petals is enough to control the descent path (vector), as controlled by the hydraulic (or otherwise-powered) actuators. Unlike the grid fins used by Space X on Falcon 9, these petals will not rotate on an axis that skewers the centerline of the fuselage, but rather, will be retracted to be almost vertically parallel with the fuselage when fully retracted, and nearly perpendicular to the fuselage when fully deployed. This is the "degree of freedom" which is needed already anyway, to protect the payload on ascent ("flower" is in the "bud" stage; payload = pollen not yet deployed, so to speak). The "bud" must turn into a "flower" to deliver the payload. "Petal control" is a bit complex, but highly important! Not only are the petals adjusted to control the descent path, but also, from one side of the center of mass (of the fuselage or capsule) to the other, the deployed petals are more-deployed on one side than on the other. This lop-sided deployment slowly spins around the center of mass. Thus, the (usually cylindrical) center of mass tilts, and does a slow "rotisserie roll" to spread the heat of re-entry across all of its surfaces. Each petal also gets to spend some time partially protected from the highest re-entry heat as well. A given fuselage-surface (or petal) element will slowly alternate time in the heat v/s time in the relatively sheltered slipstream. The probably-ideal flight path might best be described as a corkscrew. This will prolong the travel distance and time, providing more time to shed heat. Solid petals would gather too much force from the hot air or plasma during re-entry, requiring excessive mass (for both petals and actuators) for strength, to avoid being sheared off. This is why Space X uses "grid fins" rather than planar solids. But we need solids to fully protect the payload during ascent. "Having your cake and eating it too" is obtained here as follows: The petals are manufactured as grids, but are filled in (grid-holes plugged) by optimized plastics or ceramics (or other lower-melting-or-burning-point materials) formulated to melt, burn, and-or fall away during the heat of re-entry. This means more work for refurbing the petals before re-using them (if they are re-used at all), but this is a small price to pay for recycling an entire upper stage.
From (by) RocketSlinger@SBCGlobal.net (email me there please)… This is a
sub-site to main site at www.rocketslinger.com
This web page last updated 15 Sept 2021
Methods of Decelerating a Spacecraft Through
Atmospheric Re-entry Using a Shuttlecock-like Design
Abstract / Pre-Summary
This sub-page to www.rocketslinger.com describes how payload fairings
for an upper stage could be modified to remain attached to the satellite(s)
deployment mechanism(s), and to one another, and also (optionally but highly
desirable) to the entire interim upper stage (fuselage, fuel and oxidizer tanks, and
rocket engines, etc.) as well. Whereas a commonly used design today involves
the use of 2 (two) clamshell fairings, which are jettisoned before satellite
deployment, the base design here envisions “Nfairing-segments, or “flower
petals”, or simply “petals”. The petals can also be thought of as “feathers” in a
feathered badminton shuttlecock. Each of 2 clamshell fairings are now
subdivided (sliced) into smaller segments, with each shell-slice being vaguely
reminiscent, not only of a flower petal, but also of the skin-slices of a sliced
orange. For this document, “N” will be set to “4”, with one (marked) exception.
Each petal remains attached to the base of the assembly (ideally but not
always, this assembly is the entire upper stage), at the base of the petal, by
hydraulic actuators. During re-entry, the petals are sometimes more-retracted
(less deployed) and sometimes more-deployed (less retracted), as one travels
radially around the periphery of the bulk (center of mass) of the “shuttlecock”.
“N” = 4 petals is enough to control the descent path (vector), as controlled by the
hydraulic (or otherwise-powered) actuators. Unlike the grid fins used by Space X
on Falcon 9, these petals will not rotate on an axis that skewers the centerline of
the fuselage, but rather, will be retracted to be almost vertically parallel with the
fuselage when fully retracted, and nearly perpendicular to the fuselage when fully
deployed. This is the “degree of freedom” which is needed already anyway, to
protect the payload on ascent (“flower” is in the “bud” stage; payload = pollen not
yet deployed, so to speak). The “bud” must turn into a “flower” to deliver the
payload.
“Petal control” is a bit complex, but highly important! Not only are the
petals adjusted to control the descent path, but also, from one side of the center
of mass (of the fuselage or capsule) to the other, the deployed petals are more-
deployed on one side than on the other. This lop-sided deployment slowly spins
around the center of mass. Thus, the (usually cylindrical) center of mass tilts,
and does a slow “rotisserie roll” to spread the heat of re-entry across all of its
surfaces. Each petal also gets to spend some time partially protected from the
highest re-entry heat as well. A given fuselage-surface (or petal) element will
slowly alternate time in the heat v/s time in the relatively sheltered slipstream.
The probably-ideal flight path might best be described as a corkscrew. This will
prolong the travel distance and time, providing more time to shed heat.
Solid petals would gather too much force from the hot air or plasma during
re-entry, requiring excessive mass (for both petals and actuators) for strength, to
avoid being sheared off. This is why Space X uses “grid fins” rather than planar
solids. But we need solids to fully protect the payload during ascent. “Having
your cake and eating it too” is obtained here as follows: The petals are
manufactured as grids, but are filled in (grid-holes plugged) by optimized plastics
or ceramics (or other lower-melting-or-burning-point materials) formulated to
melt, burn, and-or fall away during the heat of re-entry. This means more work
for refurbing the petals before re-using them (if they are re-used at all), but this is
a small price to pay for recycling an entire upper stage.
The body of this document contain far more details, and sometimes-
implausible variations. However, the above covers the most important basics.
As with other sub-pages of www.rocketslinger.com, the intent here is to
“defensively publish” propulsion-related (and “misc.”) ideas, to make them
available to everyone “for free” (sometimes called “throwing it into the public
domain”), and to prevent “patent trolling” of (mostly) simple, basic ideas.
Accordingly, currently-highly-implausible design ideas (usually marked as such)
are included, just in case they ever become plausible, through radical new
technology developments (often in materials sciences).
Introduction / Basics
Please read the abstract above… Some of those basics may not be
thoroughly (completely) repeated here below. Here is a random gathering of a
few web sites which one can use to familiarize oneself with some of the basics,
or, of the current state of the art, in common practice today: Start here, perhaps,
with https://finance.yahoo.com/news/stoke-space-stakes-claim-launch-
202145047.html Stoke Space stakes its claim in the launch industry’s rush to
fully reusable rockets”. This is a sample of a potential user (or target audience)
for the design ideas here listed. Another one (skimpy root page here) is
https://www.rocketlabusa.com/rockets/neutron/ (another potential user).
See the following also: Ruag Space is a leading manufacturer of fairings.
See https://www.ruag.com/en/products-services/space/launchers/launcher-
fairings-structures . Then the below are simply listed, without any comments
from the author. https://en.wikipedia.org/wiki/Payload_fairing . Also
http://sicsa.egr.uh.edu/sites/sicsa/files/files/projects/ices-2019-113-leonardo-
guzman.pdf Payload Fairing Geometries as Space Stations with Flexible “Plug
and Play” Rack System”. Also
https://apmonitor.com/do/uploads/Main/Report_rocket_landing2019.pdf and
https://en.wikipedia.org/wiki/Grid_fin. Also
https://www.spaceandscience.fr/en/blog/grid-
fins#:~:text=Falcon%209's%20first%20stage%20is,ascent%20and%20deployed
%20during%20reentry.&text=Grids%20Fins%20acts%20like%20classic,can%20f
ind%20on%20an%20airplane.
Now Dear Reader, please excuse me as I often slip away from the stilted
use of third-person writing. I will much more-so use a more informal style from
here on in, using “I”, “we”, “you”, etc. “We” is you and me. “You” are an
engineer, manager, or other interested party in what is described here. Let’s get
ON with it!
As here envisioned here, the relative orientation of the upper stage /
payload deployment (payload delivery) device will stay fairly constant (ignoring a
bit of tilt in varying directions), through launch, ascent, and descent. The top will
stay the top, and the bottom will stay the bottom. “Bottom” = aft end on ascent
(directional-of-travel-wise), but = the “fore” end on descent, and vice versa. So,
to reduce confusion, from here on in, “top” = “top” (or tip(s)), and “bottom” =
“bottom” (or base). Clear enough?
Applying to all of the below, if I haven’t provided enough drawings to
clarify what I have written about, please email me at
RocketSlinger@SBCGlobal.net. I can always provide more drawings for
clarification. Generally, more-plausible design variations will be listed first, and
less-plausible variations will be listed last.
OK then, let’s REALLY get ON with it, now!
It is possible for the four “petals” (AKA orange-slice skins-segments) to be
sharp-pointed, and meet each other at the very top-most tips. I judge this to be
HIGHLY impractical! On ascent, these tips would be highly stressed (buffeted)
by prevailing winds, and hard to keep secured to one another. On descent, the
petals (to include sharp petal-tips) would be far longer than is needed. Examine
(for example) the relatively stubby (short) grid-fins on Space X’s Falcon 9, Falcon
Heavy elements, and now, also the “Starship’s” booster. As we turn the “petals”
into “feathers” for a feathered shuttlecock (AKA into grid fins), so to speak, these
petals need to be (usually fairly largely) shortened anyway.
So the first drawing (below) shows a top-down view of the tips of the
petals, with a large carve-out for what will here be called a “discard tip” of the
fairings (AKA “flower bud”). The “discard tip” most likely will be cast away
(discarded entirely, and not recycled in any way), in this design.
Tip-Down View of Tip, Pre-
Payload-Deployment
Petal-to-Petal Joints, Qty 4
Petals, 4
Discard
Tip
Figure #1
If Figure #1 (above) can be called the flower “bud” before the flower
opens, then the next drawing shows the flower after it has opened, and the
payload has been deployed. For simplicity, no satellite(s) deployment
mechanism(s) is/are shown. Note, however, that per one design option, the
“discard tip” is shown as being attached (via a tether) to the tip of one of the
petals. The discard tip could be equipped with a cold-gas (or other) thruster(s) to
ensure that it is pulled out of the way during payload deployment.
Discard
Tip
(Not to Scale)
Center
of Mass
Fuselage or Re-
Entry Capsule
Gaps!
(See Text)
Petals
Powered,
Hinged
Actuators Tether
Option
Side View, “Flower” Opened
Figure #2
Figure #2 (above) shows the discard tip as being attached (via a tether) to
the tip of one of the petals. Some various options are available here:
‘A) Put a cold gas (or other) thruster on the discard tip, skipping the tether
option, and maneuver the tip away, add a de-orbit burn, and trash it. A variation
here is to add a 'Terminator Tape'… See https://www.space.com/space-junk-
removal-terminator-tape-satellite-test.html 'Terminator Tape' did its job in
space-junk test and it will be back. Presumably, the tether, if properly
designed (with the bulk of it left attached to the discard tip), could double up as a
“terminator tape”.
‘B) To save mass on the above-mentioned thruster, skip the thruster, and
add the tether. Count on the heat of re-entry to burn away the tether during re-
entry. This may be dangerous, in that the discard tip might “bang around”
uncontrollably during the de-orbit burn, or early re-entry, damaging the petals or
even the spacecraft. So a sub-option is to add a pyrotechnic (or other) cutting
device to cut the tether after the de-orbit burn has at least started, to pull the
discard tip out of orbit.
‘C) Do “B” above, but spool the tether out WAY long during the de-orbit
burn, to vastly reduce the “banging around” hazard.
‘D) Don’t discard it at all… Bring it out of orbit separately, perhaps with a
parachute descent at the tail end of the ride. I have no special ideas or
comments to add to this item.
E) Be irresponsible, and leave the discard tip in a stable orbit! This isn’t
at all recommended!
The above drawing shows a warning label about “Gaps!” left between the
bases of the petals, and the center of mass (fuselage or re-entry capsule). The
reason why, here, is that there’s no plausible way to make a strong hinge which
is flexible. A hinge must have a straight-line actuation (rotation) axis. A single-
point hinge (as where a straight line hits the outer rim of the circumference of the
cylindrical fuselage at a tangent or point) is clearly an absurdity.
So this leaves us a few options, none of which are totally ideal.
‘A) At 4 points, for 4 powered hinges where petal-bases meet the
fuselage, change the profile of both fuselage and petals to assume those straight
lines, with these straight-line hinges entirely outside of the circular periphery of
the cylindrical rocket body (fuselage). This adds manufacturing complexity. It
also means that our fairings design has now partially changed to a
“hammerhead” design (meaning that the girth of the fairing exceeds the girth of
the rocket body). This means more aerodynamic drag (and aerodynamic
instability) during ascent. This is probably still the best option.
‘B) At these same 4 points, add a complex powered mechanism to, first,
shove the hinges up and-or away from the mating circle, and THEN splay the
petals outward (with details left unspecified here). This is beyond my expertise! I
will not begrudge you for your well-earned patent(s) for fleshing this out!
‘C) As a version of the above, have relatively simple powered hinges
mate petals to the fuselage, with these hinges buried (or partially buried) inside
the fuselage circumference. Comes open-up-the-flower-bud-time, these hinges
are thrust straight outwards from the vertical centerline of the fuselage, on sliding
rails (say, 2 per petal) or a sliding plate (1 per petal), well away from the
fuselage, before the hinges are activated.
Note that options B and C above will allow (presumably superheated) air
to flow between the petals and the fuselage (no sheltered “slipstreams” to be had
there). The hinges or other actuators will need to be designed to withstand high-
speed winds. For option “C”, the sliding plate should thus (most likely) be a grid
rather than solid-planar.
‘D) Keep the cylindrical profile for the petals and fuselage (do not go to
the partial “hammerhead” design). Keep the hinge-lines buried inside the
fuselage. Before the hinges are activated, however, the bottoms of the petals
(the parts that would otherwise bang into the fuselage when opening up the
petals) are blasted away (discarded) by pyrotechnic device, or otherwise cut
away. Complexity and-or debris left in orbit, are difficult problems here.
As usual, email me at RocketSlinger@SBCGlobal.net for more details or
drawings if needed.
The “joints” where one petal meets another, or the fuselage (or capsule or
base of the deployment stage), or the “discard tip”, can be made secure (airtight),
and then broken free from one another, according to what I understand is
standard industry practice today. That is, presumably use some sort of gasket
material with some flexible “give” (compliance), for the air-sealing function.
Mechanical rails and mechanical or electro-mechanical latches provide the
retention-release functions. Pyrotechnic separation devices may also be used at
selected locations (such as, at the base of the fairings).
It might be possible to add pressurized (inflatable) tubing in there as well,
but that’s an implausible idea. Such tubes might be able to help suppress shock,
vibration, and sound. When pressurized (inflated), the tubes would tend to push
parts apart from each other, though, and so, retention latches would still be
needed anyway. I will add no more details about this implausible idea at this
time.
The below drawing shows (via cross-section) that, during re-entry,
imbalance from one side to another, in degree of deployment (v/s retraction) of
the petals will cause a “falling bias” or vector in the vehicle’s path. If we slowly
roll this imbalance around the petals, the imbalance vector will travel in a circle,
controlling both the direction of travel and which side of the vehicle (and petals)
are most subjected to heat, alternating with being allowed to cool down a bit, on
the lee side (in the sheltered slipstream). Thus, we do a slow “rotisserie roll” to
distribute the heat-pain! We also have a method of flight-path control. Both can
be done at the same time, if the planned flight path describes a cork-screw route.
These 2 goals are complementary.
We COULD alternate between modes of path-control v/s “rotisserie roll”,
and have the planned path be less-so a corkscrew, and more-so a straight line.
This is far less desirable! One reason why is, what if one or more actuators
(powered hinge or other) fails, or becomes crippled? The more-natural
“corkscrew” path-method involves less stress on the actuators (is more resilient),
and so, is more likely to attain mission success, than a more-straight-line-descent
method, if one or more petals and-or actuators becomes compromised.
OK, so, then, finally the drawing:
Figure #3
The rotisserie roll will most likely cause the entire vehicle to spin a small
amount. However, excessive spin is not likely to be a problem. Why? Because
of the inertia of the ever-thicker air which the vehicle will descend through. This
inertia will damp excessive spin. Another way to think about this would be,
WHEN would be the only case where the preceding statement would NOT be
true? Answer: When the vehicle is descending down the middle of the funnel of
a tornado or other wind-storm! If I’m wrong, and spin IS a problem, then add
more air-flow control (at the added costs of additional mass and complexity)…
Such as the ability to rotate one or more petals, out at the tip perhaps, or, add a
separate airflow-control fin.
As previously mentioned in the abstract, solid planar “petals” here would
collect too much force from the flow of air or super-heated plasma. The is why
Space X uses grid fins, not planar solids. “Beefing up” the petals and actuators
to withstand such high forces would add probably-prohibitive mass penalties. So
on our way down, we will want to convert our planar petals to short grid-fins. We
could do this by one or both of two methods (or perhaps more, that I can’t think
of, that may be possible or even plausible):
‘A) The core structure of the petal can be made of strong, durable
material, with a metal being the only candidate that sounds plausible to me. The
metal is arranged in a grid. The metallic grid is surrounded by fastened-in
blocks, or surrounded by cast “sacrificial” material, which will burn, ablate, or fall
away, early in the process of re-entry. Candidate “sacrificial” materials are
plastics, fiber-and-epoxy material similar to “FR4” circuit-board materials, inflated
small airbags, ceramics, or even wood (see
https://arstechnica.com/science/2020/12/wooden-satellites-an-intriguing-idea-but-
wont-solve-space-junk-problems/ ). As far as ceramics are concerned, see more
details about ceramics formulated to absorb “heat work”, in a different propulsion
context, at www.rocketslinger.com, where “ceramic turbine blades” are
discussed. The ceramics-firing industry already has a handle on fairly precisely
formulating “ceramic cones” to deform with varying amounts of “heat work”
absorbed. See http://en.wikipedia.org/wiki/Pyrometric_cone. Other “sacrificial”
materials may be plausible… And using a mix of different sacrificial materials
may be possible as well.
‘B) It seems to me that this following idea is quite plausible: The metallic
core-grid of the petals could be staggered materials. The innermost part could
be made of (highly heat resistant) titanium. This portion is fastened (welded,
bolted, etc.) to one or more less-heavy, less-heat-resistant metals travelling
towards the tip. Stainless steel, less expensive plain steel, and even aluminum
could be used. The further away from the fuselage (closer to the tip) that we go,
the less durable the metal might become. The tip-most metal grids, then, can be
regarded as being “sacrificial” as well. Aluminum tips could even catch fire
during descent, without adding excessively great dangers, in some contexts.
Note that the petal actuators being very flexibly controllable, with respect
to tilt, can compensate for large imbalances from one petal (or grid fin) to
another, in the magnitude of airflow-force gathered. That is, where the degree of
degradation in “sacrificial materials” (at a given instance in time) varies greatly,
from one petal to another, we have plenty of control available, to compensate for
that.
Putting all of that together, then, we could, for example, make grid fins out
of titanium (innermost) bolted to aluminum (towards the tips). Then we could
place the grid fins in large molds, and inject a suitably formulated plastic material
all around the grid fins. Cure the plastic, pop them out of the molds, add the
trimmings, and now we’re done!
A slight variation on the above would be to very deliberately plan on
having the aluminum (or other less-robust metal) part of the grid fin separate
away from the inner titanium (or other more-robust metal) part of the grid fin, at a
reasonably-well-controlled time in the flight profile. This could be done with
pyrotechnic devices, of course, but they might add unneeded extra cost,
complexity, and danger. Perhaps “heat worked ceramics” fasteners could be
devised… See the above mention of “ceramic cones”. Such a ceramic or
partially ceramic fastener (perhaps made of both metals and ceramics) could
replace pyrotechnic devices. The degree of control of “break timing” would not
be as precise, but, as remarked above, precise control isn’t really needed in this
case (petals actuators control makes precision break timing superfluous). The
brittleness of ceramics does, however, present obstacles here.
The inner surfaces (upper or downwind surfaces during descent) of the
petals could be lined with “terminator tapes” (see https://www.space.com/space-
junk-removal-terminator-tape-satellite-test.html). As an alternate to such tape,
artificial feathers (or any other plausible lightweight drag-adding devices) could
be used. These would “grab” at passing air, to add drag. That would be at
cross-purposes to having the petals turn into grid fins to reduce drag. However,
in the very earliest phases of re-entry, adding these would PERHAPS make
sense, in terms of reducing the amount of reaction mass expended during the
de-orbit burn, and spreading more of the re-entry heat into the earliest part of re-
entry. In any more-plausible scenario, the feathers or tape would tear or burn
away later during re-entry.
In the not-very-plausible-at-all category, blocks of sacrificial material in the
holes in the grid fins could be replaced by one-way air-flow gates (in the grid-
gaps). See http://rocketslinger.com/Var_Cfg_Rck_Nzl/ Figure #2 and Figure #3
to envision such air-flow gates. In your mind, the “Direction of Exhaust Flow”
arrows should be replaced by “Direction of Air Flow” arrows (when viewing those
drawings). These one-way air-flow gates could be buried inside the sacrificial
materials (which, of course, are burned away early, during re-entry heating). The
“grid fins” approach is preserved during the time that the one-way flow gates are
exposed after sacrificial material burn-off, by designing the one-way flow gates to
pass air upwards, but not downwards, from one side of the petal to the other.
Now after entering the lower atmosphere, with way-excessive speed and
heat having passed away already, the bases of the petals could be rotated 180
degrees (the ability to provide any of this rotation is otherwise pretty much totally
unneeded). Now, the gates no longer permit upward airflow. By blocking
upward airflow, they form a parachute function better than grid fins alone would
provide. Such one-way airflow gates could replace SOME (not all) grid-fin holes,
and still be useful. I consider this idea to be impractical but possible.
Solid Planar Petals Option
The below is fairly highly implausible, but is included in the interests of
completeness. It is enough different from the above far-more-plausible scenario,
that it deserves a fairly complete, separate description.
The above scenario envisions higher-pressure air being retained inside
the fairings (“petals”, flower-bud-stage here) during ascent. This allows clean-
room-quality air to be retained with the satellite(s), inside the fairings. Many
satellites can be contaminated or damaged by dirty air. Clean air on the
pressurized inside helps prevent dirty air from leaking in. On the other hand,
higher-pressure air conducts noise (and shock and vibration, which, in air, are
noise as well) more intensely. Rockets make a tremendous amount of noise,
early on during launch, and this noise is, to a surprisingly large degree, a major
hazard to delicate satellites. Ideally, to reduce this noise, we’d fill the air-filled
voids inside the fairings with a vacuum… The better the vacuum, the less noise-
energy that we conduct to our delicate payload!
A VERY serious, major downside (above and beyond the hazards of
inward-leaking dirty air) for having an encapsulated vacuum here is that “nature
abhors a vacuum”, and will squeeze our fairings, just as water pressure
squeezes a deep-sea bathyscaphe. Like a bathyscaphe, our pressure-resisting
fairings-walls will now have to become heavier in order to be stronger. The mass
penalty on a rocket vessel will be a steep price to pay. The actuators will need to
be “beefed up” as well, here, if the petals stay planar or partially planar.
However, for completeness, let’s consider some of the added
ramifications. We could then have the stronger petals stay planar (solid) or
partially planar for more of the descent. Regardless of whether we go completely
planar, or partially planar and partially “grid fin” here, the planar petals or planar
petal portions will add far more “shade from the heat” (compared to grid fins,
which block very little of the airflow) for the other petals, which could at least
spend some of their time in the heat-shielded leeward or slipstream-protected
wake of the heat-shielding petals.
Whereas the first (more plausible design above) has 4 clamshell fairings
or petals, this design variation here envisions “Set A” and “Set B” (each
consisting of a low number “N”; from here on in set to “3” and “3” for simplicity,
while also retaining re-entry-steering functions) of “flower petals”, or simply
“petals”. The petals can also be thought of as “feathers” in a feathered
badminton shuttlecock. Each of 2 clamshell fairings (in a currently-common
design not involving actuated, attached “petals”) are now subdivided (sliced) into
3 segments, with each shell-slice being vaguely reminiscent, not only of a flower
petal, but also of the skin-slices of a sliced orange.
Each petal remains attached to the base of the assembly by actuators,
just as in the first-described design. We are moving from a nominal 4 to a
nominal 6 total petals, so that “Set A” and “Set B” sets of 3 petals each, can
spend time in the heat, v/s time in the shade (to shed heat), while alternating
deployed v/s retracted, while 3-each deployed petals will still provide robust
steering capabilities. During re-entry, the petals are interleaved, alternating
deployed-retracted-deployed-retracted-deployed-retracted, as one travels radially
around the periphery of the bulk (center of mass) of the “shuttlecock”.
The above “short and sweet” description should be enough. In case it is
not, here below I repeat myself, in slightly different words. A deployed set of
petals (3 of them) is enough to control the descent path (vector), as controlled by
the actuators. Call that “Set A”, while “Set B” petals remains relatively retracted,
out of the reach of at least some of the superheating air or plasma as “Set A” is
currently exposed to. That is, “Set B” is currently cooling down, in the sheltered
slipstream above the descending center of mass of the “shuttlecock”, plus
deployed petals. After “Set A” petals become heated, they are retracted for a
“cooling break”, while “Set B” is deployed, and takes its place in the heat. Sets A
and B take turns, being heated and shedding heat, eliminating or much reducing
the need for heat-shielding materials. With “N” set to 3 or higher, thorough
steering control is preserved at all times.
“Petal control” is even more complex now, but highly important! Not only
are sets A and B alternately deployed v/s retracted for heating v/s cooling breaks,
but also, from one side of the center of mass to the other, the deployed petals
are more-deployed on one side than on the other. This lop-sided deployment
slowly spins around the center of mass. Thus, the (usually cylindrical) center of
mass tilts, and does a “rotisserie roll” to spread the heat of re-entry across its
surfaces. A given surface element will slowly alternate time in the heat v/s time
in the sheltered slipstream. The probably-ideal flight path might best be
described as a corkscrew. This will prolong the travel distance and time,
providing more time to shed heat. The preceding is a bit of a repeat from before,
but is retained to emphasize that all of these functions are still kept from the
earlier design, so that our new design is yet more complex in terms of avionics
(actuators) controls, but is still plausible.
Human-Rated Options
There are no major differences here (for these design ideas) that differ
from what has so far been described, for human-rated vehicles. If I have missed
some, please feel free to email me at RocketSlinger@SBCGlobal.net.
One obvious difference is that the petal-to-petal joints (and any other
joints, such as to the base, or to the discard tip, if it exists) will no longer need to
be airtight. The petals could be grid-fin-like from the git-go (from the beginning,
at launch), without added sacrificial filler materials or blocks. Our passengers
obviously can’t be exposed to vacuum when the “flower bud” opens up to
become a flower! So they will have their own, permanent, separate air-pressure
structural walls.
So then our “discard tip” isn’t needed any more, and we’re left with very
little other than the grid fins as used by Space X, except that we tilt (instead of
roll) our grid fins.
Where the petals join one another (at “joints”) in the satellite-ferrying
version previously described, we can leave gaps. These gaps leave space for
maneuvering thrusters, which will be needed for many or most human-rated
vehicles.
That’s all that I have (here) for now…
Converting Petals to Landing Legs
I consider this below idea to be fairly implausible as well, but I include it,
once more, in the name of completeness.
Suppose the petals actuators are designed to not only swing through
almost 90 degrees of actuation (as described above), but through almost 180
degrees of actuation, instead. Now, they can double up as landing legs! If the
center of mass (of the “shuttlecock”) is inside a sharp-rimmed re-entry capsule,
the locations of the actuators may remain fixed, at the outer capsule rim, during
the entire journey.
If the center of mass is inside a cylindrical rocket body, the actuators will
need to travel from the upper tips (rim) of the rocket’s cylindrical body, down to
the lower rim, close to the rocket engines. These actuators could be forced
through a powered journey down the outside of the fuselage, down some
(cogged?) tracks. The tracks could double up as structural stiffeners (Space X
apparently calls them “stringers”) for the rocket’s fuselage. The actuators will be
able to complete the last half of their approximate 180 degree rotations, only after
having been forced down the tracks. I trust that no drawings will be needed, but
please advise me to the contrary if this is the case.
Such a transformation (latter half of the 180 degree swing, and track-travel
if applicable) will need to happen right before landing. The time spent dangling
under a parachute, late in the journey, would be a good time to do it.
Whether the excess complexity and mass needed to do all of this is worth
it, or not, is an open question, but my best guess is “no”. Sensible landing legs
include shock absorbers. Adding shock absorbers here (perhaps above and
beyond the “crushability” of the petals) sounds prohibitive to me.
Power-Supplies Concerns and Options
Near-constantly adjusting and readjusting the petals is going to require
plenty of power. Its even possible that the total amount of power required here
makes this entire set of design ideas implausible. Power density per mass and
volume carried to orbit is the gating item here, quite clearly. However, sensible
options for powering the actuators would include batteries and fuel cells.
Probably less sensible would be flywheels, turbines, or internal combustion
engines. (Nuclear or solar? Forget it!). Fuel-burning turbines or internal
combustion engines would require not only fuel, but also, compressed air or
oxygen to be carried to orbit (in COPVs, or Composite Overwrapped Pressure
Vessels, for example), to carry them through start-up and the first parts of the
descent, at the very least (far more likely, for all of the trip). Power density here
might be better than with batteries, though. After the vehicle enters thicker
atmosphere, it might even be possible to “live off of the land” (AKA, use in-situ
resources) by compressing ambient air for the turbines or engines. This
(compression) wouldn’t be needed in the lower-lower atmosphere at all, where
the air is really thick, but that’s not where the bulk of our power needs are likely
to reside.
We need lots of power during high-speed descent through thin air. There,
we can scoop up super-heated air on the bottom of the vehicle, but, using it to
burn fuel in a turbine or engine won’t work well at all… We need a temperature
and-or pressure differential, high on the intake side, low on the outlet side, to
extract useful power (work energy). And if we capture lower-pressure, lower-
temperature air on the lee side (top side) of the descending vehicle, we’d have to
compress it before using it! And compressing any gas heats the gas, and to
where will we shed that extra heat? All of this goes nowhere fast, but is added
here in the interests of completeness.
Let the spit-balling (brainstorming) continue! Perhaps thermoelectric
materials could extract power for the heat differential between the heated
(windward) sides and the cooler (lee) sides of the petals. See
https://www.science.org/news/2021/08/cheap-material-converts-heat-electricity
for example. Or perhaps such materials could also be used elsewhere in the
vehicle. Of course, they won’t work without a heat differential.
Perhaps the voids (holes) in the grid fins could be filled with small “inverse
propellers” that spin in the wind, and power electric generators in so doing. This
is implausible to the point of absurdity, but let’s spell it out anyway. They could
be embedded in the sacrificial filler materials, which is absurd, but then they’d
also have to withstand tremendous heat and pressure after the sacrificial material
is cast off, which is also absurd. Or they could be sheltered inside the fairings
(petals), and then rotated out later, after payload delivery, individually, or in long
strips that look like the wings on these VTOL aircraft here: https://lilium.com/jet
... (Take the ducted propellers that use electricity on the Lilium design, and invert
them to become mini-turbines (that burn no fuel), powered by airflow, basically,
to generate electricity instead). Or these mini-turbines could be NOT encased in
the sacrificial materials in the grid-holes, but rather, air-flow-plugged during
ascent, using some other method (while still residing in the grid-gaps). But all of
this is absurd, using technology that we have today, in transonic and supersonic
flight regimes. Such turbines can’t be built small, lightweight, and strong enough,
today, for our particular needs, clearly. Still, we’re brainstorming here!
Perhaps more plausibly, build turbines and generators that aren’t ducted
at all. Imagine a long, perhaps tapered, screw-like (or narwhal-tusk-like) rotating
device that points upwards, up out of the base of the fairing-cavity. This “screw-
propeller” now resides exactly where our satellite(s) payload wants to live, which
is a big penalty! But perhaps we can elongate the fairings and cavity, or perhaps
we can store the “screw-propeller” elsewhere, and electro-mechanically,
robotically, or otherwise move it to where it belongs, after payload deployment.
(Far better, see further below).
The “screw-propeller” would be made of strong, durable metal (perhaps
titanium or stainless steel) and point upwards, out of the center of the base of the
fairings cavity, partially protected from the worst of the heat of re-entry, but still
being free to rotate in the wind, and imparting rotational energy to a generator at
its base. But now we add “spin” to the descending vehicle, in so doing. The fix?
Use (not just one) but TWO counter-rotating “screw-propellers”, egg-beater-style,
to cancel this imparted “spin”. In general, use an even number of such screw-
propellers, and balance their numbers of spin directions. It might also be
necessary to do electrical load balancing (from one generator to another), to help
with spin-balancing the vehicle’s descent path. More electrical load added to a
given screw-propeller (screw turbine) should add more airflow-resistance for that
given turbine, that is. If we have (as postulated in most of all of these above
notes) four (4) “petals”, then perhaps we can place 4 of these “screw-propellers”
(screw turbines), in a balanced fashion, close to where the 4 petals meet in
“joints” (and away from the center-line). Now, the “screw-propellers” won’t need
to be moved, and they’ll not get in the way of the payload, so much. Perhaps this
scheme is actually plausible! It would generate power, while also helping to
decelerate the falling vehicle.
This deserves a drawing for clarity. The below is a top-down view of the
flower petals partially opened, with the payload already deployed. The drawing
shows what I consider to be the most plausible design, which is the “partial
hammerhead” design, where the powered hinges reside outside of the rocket
fuselage’s circular profile. The 4 “screw turbines” spin counter-clockwise v/s
clockwise, in sets of 2 and 2. These turbines are located close to the joint-lines
between the petals, but still inside the fairings (petals) during ascent. Here, the
turbines can catch upward-flowing air that forced to flow nearby, by the hinges,
petals, and fuselage. The turbines also don’t (much) obstruct the payload space,
when located here.
Top-Down View of Screw-Turbines
Placements in a Partial-Hammerhead
Design
Petals, 4
Opened
Hinges, 4
Powered
Profile of
Rocket
Fuselage
= 4
Screw
Turbines
Figure #4
The above describes what I think to be the best design options here. The
screw-turbines are simply and directly coupled to generators, which can be
sheltered within the base of the deployment stage, or the upper part of the rocket
body. There, the turbines are partially sheltered from the wind, yes, but that
helps protect them, while they should STILL be exposed to plenty of wind that
“whips around the corners” of the upper rim of the rocket body.
The below, I consider to be far-less-plausible options. After payload
deployment, the turbines could be thrust out, away from centerline, to catch more
wind. This adds complexity and mass, however it is done. And now, we will
have to expose the generators to the wind (an absurdity), or somehow (belts,
chains, gears?) transfer mechanical spin energy to sheltered generators, which is
only slightly less absurd.
Screw-turbines could be replaced by something else, resembling,
perhaps, the old paddle-wheels on old steamboats, or short vertical-shaft
windmills (with the vertical windmill spin axis rotated 90 degrees for our
application), such as are shown here: See https://blog.arcadia.com/vertical-axis-
wind-turbines-advantages-disadvantages/ and
https://en.wikipedia.org/wiki/Vertical-axis_wind_turbine. In my opinion, such
devices wouldn’t be rugged and durable enough here, in our harsh environment..
I have no special expertise or any more plausible ideas concerning any
associated matters here, so I will sign off at this time. This concludes my ideas
as of this time. Comments or questions (or idea contributions) are welcomed at
RocketSlinger@SBCGlobal.net
Stay tuned… Talk to me! RocketSlinger@SBCGlobal.net
Back to main site at www.rocketslinger.com
Article
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Abstract This sub-page to www.rocketslinger.com is meant to describe methods for converting a vacuum rocket engine nozzle (with a large bell shape) into one that can operate efficiently and safely at sea level (with a much smaller bell shape, with today's typical design). Three primary alternatives are described… '1) One could put an array of hinged gates (NOT permitting one-way flow of hot rocket exhaust gasses into the lower-pressure ambient environment, for vacuum or low-ambient-pressure applications) into the extended areas of the bell shape (those exceeding what is needed for sea-level operation). However, the one-way-gas-gates WOULD allow ambient air to flow (at sea level or in other higher-pressure environments) inwards into the rocket nozzle, thereby reducing "back flow" of air (along the insides of the outermost rim of the nozzle, when the nozzle is "over-expanded"), which is associated with inefficiency, chaotic oscillations, and danger. '2) One could design the outermost (lower) extensions of the nozzle to be used in a vacuum environment (as in, for example, the Space-X Falcon 9 interim upper stage, formerly being design-tweaked to begin emulating the upper stage of the "BFR" system, AKA, the BF Spaceship), but to fall away (be discarded) immediately after the final de-orbit burn. This converts the bell shape from a vacuum nozzle into a sea-level nozzle, by drastically reducing the nozzle in size. '3) One could formulate the materials and construction of the outermost extensions of the nozzle to be burned away by the heat of atmospheric re-entry. This might be an especially attractive option if one uses a shuttlecock-style re-entry method with the rocket engine(s) at the "fore" end during re-entry. Options for precisely this method (rocket engines at the fore end in shuttlecock-style re-entry) have already been described (citations provided here). Designing these outermost nozzle portions to be sacrificially burned or ablated away will help protect the engines, and facilitate their re-use.
Article
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Pre-Summary This sub-page to www.rocketslinger.com is a companion or supplementary document to other documents found at Research Gate. As previously documented, conventional (existing) satellite-deployment fairings could be modified and subdivided into (an ideal number being postulated to be 4) powered-hinge-attached fairings segments renamed to be "petals", as they open (like a flower) for satellite deployment, and thereafter serve as the "feathers" in a badminton-style shuttlecock, for descent (re-entry). As these "feathers" degrade in re-entry-generated heat and pressure, they evolve into embedded grid fins. The powered hinges and hydraulic energy management used to accomplish this have already (albeit incompletely) been described. Here, we add additional design elements, notes, and drawings to emphasize that the highest-velocity phases of re-entry could be substantially prolonged (therefore prolonging the exchange of kinetic and momentum energy in exchange for heat energy, AKA reducing "heat flux", and reducing overall thermal stresses to vehicle structures) by using lifting-body principles for the highest-thermal-stresses phases of the re-entry process. The shuttlecock elements (and flight modes) earlier described aren't entirely negated here; they are more-so (much!) improved upon. Also important is this: What is described here is a "punctuated equilibrium" of flight of a lifting body, where the vehicle periodically rolls by 180 degrees. "Belly" and "back" of the vehicle are periodically reversed, to absorb and shed heat more equally, across all surfaces.
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Abstract / Pre-Summary This sub-page to www.rocketslinger.com is a companion or supplementary document to another document found at https://www.researchgate.net/publication/354612024_Methods_of_Decelerating_a_Spacecraft_Through_Atmospheric_Re-entry_Using_a_Shuttlecock-like_Design and at http://www.rocketslinger.com/BadMinton/ (same document, 2 locations). In BOMs (Bills Of Materials) lingo, the “parent” BOM calls a “child” BOM, where the child is a sub-assembly of the parent. This document deals with sub-assemblies of the designs described in the “parent document”, and so, it will henceforward be referred to as the parent document for brevity. Temperatures endured during re-entry (both on the windward and lee sides) are briefly examined here, as are temperature tolerances of materials and subassemblies. Then a “heat wall” design is described, which can be used to protect subassemblies from heat damage. Much of this is focused on hydraulic machinery, which will need to be used to control the “petals” (or grid fins) as were described in the parent document. Many variations of a powered hinge are described here. One of the best versions consists of a curved (arc-shaped) friction plate attached to each petal-becoming-a-grid-fin (AKA, fairing segment). The friction plate is gripped between two powered, slowly rolling funnel shapes, to create a torque-limiting device, to absorb sharp peak loads without damage. This hinge system is called a “Bifrost Hinge”, and the name given to it, is explained. To harvest energy (or power used to perform work) in a spacecraft entering an atmosphere, we could use roller chains similar to (but larger and stronger than) the chains used in bicycles and chain saws. In a chain saw, some of the plates (in the chains) are extended outwards with teeth, for cutting wood or other materials. Here, instead, some of the plates are extended outwards to “catch the breeze” during re-entry, the same as windmill vanes catch energy from the wind. The overall device, then, here, will be called a chain windmill. The vanes in such a device could possibly take many forms, but two are described here. One is a single plate per each set of chain-plates that is so equipped, which is stopped (by a hard-stop) from folding past 90 degrees, with the right angle formed to “catch wind”, and not fold further towards the lee side. However, this vane is allowed (during the chain segment’s return journey towards the windward side) to fold out of the way of the prevailing wind. The alternate (here-described) vane is a “butterfly vane set”, with twin segments that “flap” to catch wind in one direction, and fold out of the way in another direction. They can each perform a partial rotation around pins protruding outwards from each pair of roller-chain plates that is so equipped. Each of the two twin vanes (“butterfly wings”) provides the hard-stop for the other, in this design. In either form, a chain windmill is not at all an optimal solution here, for us. An energy-harvesting device could also resemble a paddle wheel on a riverboat. This approach will be far less disadvantaged by lack of lubrication than a chain windmill would be. And as will be shown, lubrication WILL be a major problem for the chain windmill (unlike the paddle wheel). Also described here is an airflow spoiler that could be placed to the windward side of the energy-harvesting device, possibly sized and located in a compromise between partially protecting the energy-harvesting device (best choice being a paddle wheel) from too much heat and strong airflow, and not getting enough airflow to harvest enough power. The spoiler is composed of a hinged heatshield-covered plate that can be thrust out into (or retracted from) the airstream. It could be activated by a (heat-walled) “Bifrost hinge”, which could also double up as a “hydraulic battery” used to store extra power. These are sometimes called “hydropneumatic accumulators”. In the design context here, the variably pressurized nitrogen in such a device could be partially or entirely replaced by the variable pressure of passing air in the airflow spoiler (which pushes on the plate). Such a design choice may have to be balanced with the other possible purpose of the spoiler, which is to partially protect the paddle wheel. The body of this document contain far more details, and sometimes-implausible variations. However, the above covers the most important basics.
ResearchGate has not been able to resolve any references for this publication.