Conference 7.286::space

    	See SPACE Topic 216.
    
    	Larry
    

    re .0
    
    Most large missiles and launch vehicles are not aerodynamically
    stable, a real nuisance when trying to build flying models of them.
    (you'd think NASA would show some consideration here :-) )
    
    They rely upon active guidance and control for the entire flight.
    
    gary

    re .1 
    
    I don't mean a railgun that acelarates the payload to orbital velocity.
    I mean a railgun that just gives an initial helping hand. A little
    like the take off catepults in aircraft carriers. 
    
    re .2
    
    Rockets do have some areodynamic stability, after that have aquired
    some air speed. Unless my history fails me, didn't lots of rockets
    with adequate thrust etc fail simply because they couldn't go straight
    up in the first few seconds after launch.
    
    Even in the shuttle extra stuff had to be included, like engine
    gimbaling, etc... that they probaly could have gotten by without,
    if it weren't for the balancing act they go through right after
    launch.
    
    I guess, maybe its too much trouble to go to, for too little gain.
    Just like this note... :-) !!!
    			Whatever the little gain is...
    Whatever the little gain is ?

    re: .4
    
    Take a look at the Titan series, the Atlas series and even the Saturn
    V series of rockets.  *IF* they even had fins (as is the case with
    the Saturn V) they were grossly undersized.  As for the finless
    rockets, they were not stable at any speed without the engines running
    and the computers working!  There are other examples, but I can't
    think of them now (Gary?)  (Note, also, that the Saturn V second
    and third stages had no fins...)
    
    jim
    

    Some rockets HAVE aerodynamic stability but the larger ones that
    have some form of thrust vector control (e.g. gimballed engines)
    do not NEED it.
    
    Look at the Thor, Atlas, Titan, Delta, etc. They all have approximately
    neutral static stability if not negative stability. They rely
    exclusively upon their TVC to maintain the correct attitude. There
    is no way something shaped like the shuttle would be stable without
    TVC at any speed.
    
    You are right in that many early flights failed in the first few
    seconds, usually as a result of guidance or gimballing failure (or
    whatever form of TVC is in use).
    
    Some early missiles had fins simply because noone in the USAF would
    fund one without fins!! (If you read about the history of the MX-774
    you find a lot of this stuff)
    
    In case anyone asks why the Saturns had fins... they are present
    to provide DYNAMIC stability in the event of a guidance failure.
    The vehicle would begin to pitch over and the fins were intended
    to dampen that motion so that the launch escape system could function.
    The early Saturn 1 flights did not have fins.
    
    To get back to the original topic, it would be possible to build a
    vehicle for rail launch that relied upon static stability (i.e. fins)
    and upon having sufficient velocity at release for that stability to be
    useful. If you could arrange things so that you exited the launch rail
    at the right attitude you could use a 'big, dumb booster', e.g. a big
    solid with no guidance or TVC. Although you tend to lose some
    efficiency in a rail launch, the economic gains may be worth it.
    
    gary

I don't think it matters anyway, whether it rains at lunch time or not.
If launch is early in the morning, lunch time will occur high in Earth
orbit, where weather effects are virtually nonexistent :-)

/Eric

    re .6
    
    What is TVC?
    

    TVC = Thrust Vector Control
    
    jim
    

    Isn't it "When Worlds Collide" where they have the launch rail sitting
    on the side of a mountain and shaped like a J?  They started off
    going *down* and then did a quick flip around the loop of the j
    at the bottom of the mountain and off they went.  I always wondered
    if there was any logic to this scheme.
    
    Burns

    Thats the one. Not much logic, but it does look pretty.
    
    gary

    As per 305.13
    I will now continue!! You may have put man in space but the links
    to down under are as reliable as the SRB's.
    Anyway has anyone up there heard of the British Areospace's HOTOL
    launch proposal?
    Fred 

    re .14
    
    The HOTOL gets a fair amount of publicity here. Why do you ask?
    
    gary

    re .15
    
    Thanks .15, I have not heard much about it down here but since it
    has horizontal takeoff capability there must be a reduction in cost
    copmpared to the shuttle?. Can you point me to anymore info on the
    beast?.

    re .16
    
    Why do you think horizontal takeoff must result in a reduction of
    cost? Certainly using atmospheric oxygen for as long as possible
    should help.
    
    Aviation Week & Space Technology (aka Aviation Leak & Spy Technology)
    has occasional articles on Hotol. A Better source is the British mag
    Space Flight News. You can get that on larger newsstands in the Boston
    area or by subscription. It has a more international outlook than AW&ST
    and is especially interested in Hotol. The BIS mag Spaceflight also
    covers it from time to time but I think you have to subscribe to it in
    the US. I have never seen it on sale here.
    
    gary 

   re .17
    
    Thanks again. I would assume that the cost could be reduced mainly
    due to the reduction in the fuel amount and if the launch were done
    by an assisted groundrail launcher. I will check for the British
    Mag Space Flight News down here.
    
    Fred

Newsgroups: sci.space
Subject: New type of railgun
Posted: 24 Jun 88 20:24:37 GMT
 
    Interested parties might want to read this article:
 
  "Electromagnetic Launch: Highway to the Stars", IEEE Trans. on
  Magnetics, Vol. 24, No. 2, March 1988, pages 703-710.
 
    It is highly readable, if somewhat hyperbolic, and makes some
interesting claims.  To summarize... 
 
    Use of space has been blocked by the stagnation of launch cost
using chemical rockets.  Historically, further progress depends on the
introduction of new technology.  Electromagnetic launchers promise much
higher payload ratios.  Recent progress in e.m. launcher and
associated technology has been rapid. 
 
    The article describes one particularly attractive concept, called
the solenoid quench gun.  The launcher is a superconducting solenoid
with a field of 20-30 Tesla.  The projectile coil, also
superconducting, is accelerated up the solenoid, quenching solenoid
segments as its goes (so the coil remains at the "end" of the
solenoid).  If the quenched coils are shunted through a s.c. circuit
the efficiency can approach 100%. 
 
    The most interesting things about the launcher are its inherent
simplicity and small size.  The article claims that a 3 ton projectile
(1 ton of which is payload destined for geosynchronous orbit) could be
launched by a gun with a mass in the *tens* of tons. 
 
    E.m. launchers would seem to be well suited to materials
processing, since only a modest kick motor is needed to raise the
projectile into a long elliptical orbit (and, similarly, to deorbit it). 
 
	Paul F. Dietz
	dietz@gvax.cs.cornell.edu

    "Anyone who is not shocked by quantum theory has not understood it."

From:	DECWRL::"dietz@cs.rochester.edu"  "2-Sep-88 1617 EDT"  2-SEP-1988 21:07
To:	space-tech@cs.cmu.edu
Subj:	Electromagnetic Launchers
 
    I haven't received anything from this list yet, so I thought I'd
submit a summary of some ideas on earth-based electromagnetic
launchers (hereafter EMLs).  Comments welcome. 
 
    Motivation and Payloads
    -----------------------
 
    First, why from Earth, and not the Moon?  Isn't a lot more energy
required? Yes, but unless there's a sophisticated infrastructure in
place, the cost of power on the Moon will be far higher (the same for
labor & capital). 
 
    Earth is also a better source of refined materials (rather than
just raw rock).  Volatiles are much more abundant here. 
 
    What payloads could be launched?  They would have to be
acceleration resistant, so no people or fragile equipment could be
launched.  However, bulk materials are acceptable, including water,
metal ingots, storable liquid propellants, some foods, bulk plastic,
and so on.  Most any material that might be obtained from extraterrestrial 
sources can be launched by EML in a more refined form. 
 
    The launch vehicles themselves will be made mostly of useful
materials, probably steel, which can be reused in space. 
 
    Orbits
    ------
 
    Any EML launching from Earth's surface will require that the
vehicle traverse the atmosphere.  The trajectory cannot be horizontal,
since atmospheric heating would be excessive.  It need not be exactly
vertical; an angle of 60 degrees increases the amount of atmosphere
encountered by only 15 percent (= 1 - (1/sin 60)).  I am not
considering schemes where the EML is levitated above the atmosphere
(Launch Loops or whatever); these seem too complicated and fragile. 
Clearly, it is preferable to put the EML on a mountain, this can
reduce the amount of atmosphere to be traversed by perhaps half. 
 
    An EML cannot fire directly into a stable Earth orbit, since the
vehicle will be placed in an orbit with perigee beneath Earth's
surface.  So, the vehicle must undergo some change in velocity to
place it into a stable orbit.  One can imagine active systems (the
projectile has a kick motor) or passive systems (the vehicle hits a
mass catcher).  For a number of reasons I don't consider the second
scheme to be viable, at least for Earth-based EMLs.  I'll concentrate
on active systems. 
 
    Direct launch into LEO does not appear to be feasible.  Either the
EML launches onto a trajectory with apogee a few hundred km up, in
which case the kick motor must do most of the work, or the orbit is higher, 
in which case the kick motor must kill the vertical velocity component. 
 
    EMLs do much better launching to high orbits.  This is because
velocity changes can be made far from Earth, where they provide much
more angular momentum (the moment arm is much longer). 
 
    Launching to high circular orbit is more feasible than launching
to LEO, since orbital velocity drops off as r^-1/2.  Even for large
orbits a delta-V of 2 km/sec or so is needed. 
 
    Easier targets are highly eccentric Earth orbits (HEEOs).  These
orbits don't have a lot of angular momentum (at most twice that of
LEO), yet they allow the vehicle to change its velocity at great
distances from Earth (at apogee). 
 
    Consider launching to an orbit with apogee at 20 earth radii (from
Earth's center) and perigee at low altitude.  The angular momentum of
such an orbit will be just about 1.4 (in canonical units where radius
of Earth = 1 and the period of an orbit of radius 1 is 2 pi).  So, a
launcher at an angle of 60 degrees provides 1/2 the angular momentum. 
The kick motor at the top must supply the rest:  A velocity change of
1 / (2 x 20), or about 200 meters per second.  Launching to an orbit
with apogee at 40 radii means the delta V is only 100 m/sec. 
 
    Will such a large orbit be stable?  I don't know.  Tides from the
Sun and Moon will exert torque, and if the angular momentum decreases
the payload will reenter.  If the angular momentum increases the
perigee will be raised, which might be nice.  The mean radius of the
Moon's orbit is about 60 Earth radii.  A little simulation might help
resolve this. 
 
    Getting into orbit is only half the problem.  The vehicle must
also rendezvous with a space station.  If the space station is in LEO,
one can use the following scheme.  Launch into HEEO with the same
inclination as the space station's.  Wait for regression of nodes to
make the orbital planes coincident (this might take up to two months
for typical space station orbits).  Aerobrake down to LEO and enter a
phase-matching orbit, then rendezvous.  One has to arrange the HEEO so
that the vehicle will be near perigee when the orbital planes coincide.  
Aerobraking might be done over many orbits to reduce heating. 
 
    To reach a space station in HEEO, put the space station in polar
orbit and launch the payloads into polar HEEO, doing a plane change at
apogee. Ideally, one would put the launcher at the pole, but high
latitude would also work. 
 
    Payloads in HEEO can also be redirected onto orbits intersecting
the Moon. Directing plastic-carrying vehicles to impact near a colony
may be a good way to supply the colony with volatiles. 
  
    The Launch Vehicle
    ------------------
 
    Anything shot out of an EML will experience thousands of gees of
acceleration.  The vehicles had better be rugged.  They should also be
cheap; ideally, we should not have to reuse them. 
 
    Since the vehicle will have to use on-board rockets for course
corrections and raising the perigee, we will have to know its position
and orientation in space.  It is likely a good idea to move guidance
functions off of the vehicle - gyros and accelerometers are expensive
and sensitive. 
 
    Position can be determined using position determination
satellites.  In space, one does not have errors introduced by
refraction in the ionosphere, so high accuracy should be possible
using a Geostar-like system.  Measurements with an accuracy of 1 meter
over 1,000 seconds should enable one to compute velocities to within a
few millimeters per second. 
 
    To determine the orientation of the vehicle, we can illuminate the
vehicle with microwave beams from a number of satellites.  The vehicle
measures phase differences between antennas on its periphery.  We
don't need very accurate measurements; errors of perhaps a few degrees
or so around each axis are ok.  Inaccuracies lead to errors in
delta-V, but these errors can be measured and corrected. 
 
    The vehicle doesn't need much maneuvering capability - total
delta-V of only a few hundred meters per second.  For simplicity, one
should probably use a pressure-fed liquid monopropellant, like
hydrazine, or even just compressed gas.  The engines need not have
high thrust; the perigee-raising maneuver can take hours.  For a vehicle 
with a mass of a few tons this requires a thrust of O(100) newtons. 
 
    The launch vehicle must have a high ballistic coefficient (ratio
of mass to cross-sectional area) in order to keep aerodynamic
deceleration tolerable. Just what the limit is depends on the drag
coefficient of the vehicle at extreme hypersonic velocities.  I don't
know what C_d is at 11+ km/sec.  I guess one should make the vehicle
have at least one kilogram of mass per square centimeter of cross
section (the column density of air at sea level).  For a 10 cm radius
vehicle, this gives a mass of 300 kilograms. If the vehicle has an
average density of 5 grams/cm^3 it would be at least two meters in
length - an aspect ratio of 10-1.  Probably the vehicle should be
larger, perhaps 1000 kilograms, and have a lower average density. 
 
    The Launcher
    ------------
 
    The major expense of the launch system is probably the EML itself.
 The kinetic energy of a 1000 kilogram vehicle at escape velocity is
63 gigajoules, or about the energy of 15 tons of high explosive. 
Quite a bit to deliver quickly. 
 
    If the launcher is arranged nearly vertically, it must be at most
a few km long (running up a mountain side).  Perhaps you could bury or
submerge the lower end, but that seems complicated and expensive.  To
reach 11 km/sec in 1 km requires an average acceleration of over 6,000
gravities. 
 
    Perhaps a way to reduce the acceleration the EML has to supply is
a "ski-jump" launcher.  A long, low acceleration EML is placed
horizontally. At the end, a ramp diverts the vehicle from horizontal
to a 60 degree angle.  The vehicle is suspended above the ramp by
repulsive magnetic levitation.  The centripetal acceleration supplied
by the ramp is high, but no high power storage or switching circuitry
is needed: power is supplied by the vehicle's motion.  Also, the force
is applied laterally, so it can be spread over a larger area (remember, 
the vehicle is long and narrow).  I chose 60 degrees as the angle because 
this cuts the vertical size of the ski jump in half compared to one 
diverting the vehicle 90 degrees (with the same radius of curvature). 
 
    Repulsive maglev normally required the vehicle to have a magnet
that induces currents in the track.  It probably is uneconomical to
put super- conducting magnets in the vehicle, especially if it isn't
reusable, so some scheme using currents induced in normal conductor
coils in the vehicle is probably required.  I hope this doesn't
require excessive currents in the vehicle coils.  If it is necessary
for the vehicle to use SC coils in the horizontal part, perhaps they
can be placed in a sabot that is detached and decelerated before the
ramp (as in a mass driver). 
 
    Military Applications
    ---------------------
 
    The EML + guidance system described here would have military
applications. Aside from being able to launch payloads into space, it
can be used for nonnuclear intercontinental bombardment.  The kinetic
energy of a vehicle would greatly exceed its own mass in high
explosive, so by simply guiding vehicles to impact on enemy targets
one could do a great deal of damage, with no risk of pilots being shot
down and captured.  If projectiles are long-lived they could be stored
in HEEO.  Equiped with terminal guidance systems they would make
potent weapons against industrial targets, surface ships, airfields
and perhaps against missile silos.  However, vehicles that had been
deorbited at apogee would be obvious hours or days before impact. 
 
    Paul F. Dietz
    dietz@cs.rochester.edu
 

From: lindsay@MATHOM.GANDALF.CS.CMU.EDU (Donald Lindsay)
Newsgroups: sci.space
Subject: Sandia Railgun
Date: 15 Mar 90 19:40:16 GMT
Organization: Carnegie-Mellon University, CS/RI
 
Seen in a recent magazine:
------------
Sandia National Laboratories is testing a prototype of an
electromagnetic gun, a full sized version of which could be used to
launch vehicles into orbit for a fraction the cost of current rockets.
The device, a staple of SF for years, has been proven feasible using a
new computer program, ironically called Warp-10, which has proven the
validity of the design principles, and the arrival of a new generation
of electrical capacitors. 
 
Current prototypes hurl 10 pound projectiles half a mile at the speed
of an artillery shell. Sandia has applied for funding for a 10-stage
launcher to accelerate an 850 pound projectile behond the atmosphere,
at which point a rocket engine would fire to push it into orbit. 
 
The Sandia prototype solves the problem of wear on the launcher by
eliminating contact between the system and the projectile. Set to
spinning at 100 rotations per second, the projectile floats through
the system's rings using a girdle of metal. For a full-size launcher
a heat shield will be needed because of the intense heat generated
when the vehicle is accelerated to a speed of 2.8 miles per second.
 
Finally, although the projectile will experience an initial force of
1,000 to 2,000 G's, this is mild compared to the 30,000 G's an
artillery shell is subjected to when fired from a cannon.
------------
 
If anyone out there knows more, please post. What is this "girdle"
trick? How do you build a multistage gun? - And like that.
-- 
Don		D.C.Lindsay 	Carnegie Mellon Computer Science

Newsgroups: sci.space
Subject: Re: Sandia Railgun
Summary: Not a Railgun!
Date: 15 Mar 90 20:26:25 GMT
Reply-To: dietz@cs.rochester.edu (Paul Dietz)
Organization: University of Rochester Computer Science Department
 
    In article <8436@pt.cs.cmu.edu> lindsay@MATHOM.GANDALF.CS.CMU.EDU
(Donald Lindsay) writes: 
....
>Seen in a recent magazine:
....
>The Sandia prototype solves the problem of wear on the launcher by
>eliminating contact between the system and the projectile. Set to
>spinning at 100 rotations per second, the projectile floats through
>the system's rings using a girdle of metal.
....
>If anyone out there knows more, please post. What is this "girdle"
>trick? How do you build a multistage gun? - And like that.
 
    This is NOT a railgun!  Railgun is not a generic term for
electromagnetic launcher.  This misconception is surprisingly common. 
 
Railguns send a current through two rails and through a metal or
plasma armature behind the projectile.  Because there is direct
contact between the armature and rails, rail erosion is a serious
problem.  Rail guns are essentially one-turn linear DC motors, and use
very high currents. 
 
The Sandia system is a coilgun, aka mass driver, where pulsed coils
along the barrel pull a current carrying ring.  In a coil gun there
need be no direct contact between the armature and the gun barrel.
The drive coils have many turns, and so can be energized by higher
voltages and lower currents.  In the Sandia launcher the coils are
triggered by a system using fiber optic sensors.
 
The girdle is a solid aluminum armature.  In a properly designed coil
gun the joule heating of the armature can be kept low enough so that
the aluminum does not melt.  The proposed Sandia gun's low muzzle
velocity (about 1/2 orbital velocity) helps here, although I think
going to > orbital velocity should be possible if the aluminum is
precooled with LN2, is cooled by transpiration, and/or is replaced
with beryllium.
 
For more on coil guns, see IEEE Trans. on Magnetics.  They
periodically print the proceedings of the electromagnetic launcher
conference, which covers both coilguns and railguns.
 
I note that the proposed location for the coilgun, in Hawaii, would
launch northeast into high inclination orbits.  Brilliant pebbles,
anyone?
 
	Paul F. Dietz
	dietz@cs.rochester.edu