Conference 7.286::space

    According to a report in Aviation Week, the National Commission
    on Space (the Paine Commission) will reccomend development of a
    nuclear-powered space tug when it reports to President Reagan in
    June.  This would be a 50K lbs. thrust booster for use in earth
    orbit and for interplanetary missions.  It's similar to the Nuclear
    Upper Stage proposed for the Saturn V back in the sixties.  I believe
    the projected initial operational capability will be sometime after
    the turn of the century.

    Can anyone provide a short description of how the engine mentioned
    in .1 works? (e.g., how does the nuclear part fit in?)
    
    - dave

        Re: .0
        
        Do mass drivers count?
        
        Re: .2
        
        I'm not sure about all of this, but the basic idea is to use the
        energy from a nuclear reactor to propel protons (hydrogen atoms
        with electrons stripped off) out the back of the vehicle at near C
        velocities. The reaction from this will propel the rocket thru
        space. Thrust levels are very low, but the engine can continue
        operation for the entire trip, reaching very high speeds. Halfway
        there, the vehicle would turn around, breaking till reaching its
        destination. It is also theorized that the rocket can collect
        interplanetary gasses and use them as a hydrogen source, extending
        the range. I'm sure someone will correct me if I am wrong about
        any of this. 

    re: .3 last part of second paragraph.
    
    The idea of obtaining hydrogen to fuel the engine has been considered
    for many years (quite often in SciFi novels).  The concept is called
    the Hydrogen Ramjet.  The priciple involved scooping up hydrogen
    from a given area around the ship.  As the speed increases you pass
    through larger volumns of space in a given ammount of time and,
    thus, can gather more fuel and go faster...
    

A number of prgrams were conducted on various new forms of propulsion, mostly
during the 60s.

Nuclear Propulsion

The basic operation is to use  the heat generated by a fission reaction
to heat and therefore accelerate hydrogen, providing thrust. Most effor
has been concentrated on homogeneous thermal reactors, where the core has
the fissionable material mixed in with the moderator (usually graphite in
this case). The hydrogen flows through holes in the core. Although other
schemes appear simpler in design they generally require the containment
vessel be made out of some moderator material and materials science has
not produced anything with the right combination of properties yet (i.e.
moderator capability, stable at high temperatures and physical strength).

The homogeneous core reactor has the capability to acheive specific impules
of around 3,000 (LOX/LH2 delivers around 400) but engines that have been
built have been restricted to temperatures below about 3,300 C which
corresponds to specific impulses around 1,000. These projects had names
like Kiwi (a flightless bird of New Zealand), Phoebus and NRX.

The NERVA program was started as part of the 'moon race' and was cancelled
in the late 60s. The original objective was to build a flight stage with
a 55,000lb thrust. NERVA 2 was to be around 200,000lb thrust and was envisaged
for a manned Mars mission, using a cluster of three to boost each spacecraft
out of Earth orbit. I don't think any NERVA hardware ever flew.

Electric propulsion

There are a couple of schemes involved here. The electrothermal motor uses
elctricity to heat the propellant. These engines can acheive efficiencies of
around 40%. The electromagnetic or plamsa motor ionises the propellant gas and
uses magnetic and electric fields to accelerate the plasma. In the
electrostatic or ion motor, the propellant is again ionised but the liberated
electrons are removed from the ioniser before the propellant is accelerated.
These engines could acheive efficiencies in excess of 80%. The first flight
trials of ion motors were the SERT flights. 

Other schemes have been proposed including fusion reactions and a series
of small fission bombs exploded in sequence. A non-nuclear flight test of
the latter was conducted as Project Put-Put.

A lot of these schemes use hydrogen as the propellant and the idea behind
the hydrogen ramjet or ramscoop is to gather up hydrogen in a large magnetic
field in front of the vehicle and funnel it into the propulsion system.
Mining propellant from the upper atmosphere has also been proposed.

gary

    I rather thought that there had been a couple of NERVA flights,
    although I could be wrong.  And what about SNAP?  (System for Nuclear
    A-something Propulsion?)
    
    Finally, don't forget that great Larry Niven favorite, the Bussard
    Ramrocket.  The idea is to scoop up interstellar hydrogen as has
    been mentioned before, but then you compress it so hard it fuses.
    The result goes out the end and voila! propulsion.
    
    Burns
    

    SNAP was a power supply system, if I remember correctly. Similar
    to the radioisotope thermal generators (RTGs) used on probes to
    the outer planets.
    
    gary

    Yes, SNAP was/is a power supply.
    
    The ramjet is the  Bussard Interstellar Ramjet.
    
    	A serious proposal published by an American chemist by the
    	name of Robert Bussard.  Want a copy of his paper ?  NASA
    	has a rather extensive library which includes a great deal
    	of work around the Bussard interstellar ramjet...
    
    Dwight

    Not being too familar with what NERVA is, I recently read that some
    kind of an ION engine has been sucessfully tested.
    
    Is it shades of Star TREK or is it real?
    
    Mark

As an aside, the recent novel "Footfall" makes use of the atomic bomb drive.

re .9
    The ion engine refers to an impulse derived from ejecting accelerated
    particles (ions) out as a jet; standard Newtonian reaction.  The
    method was mentioned in an earllier reply.

    Ion engines are nothing new.  We have been using them on our satalites
    for years a manuvering rockets.  Believe it or not Teflon is the
    fuel.  
    
    steve

	re .12:  Huh!?!  Teflon-fueled ion engines?  Can you tell us
    some specific satellites?  My impression was that many (most?) comsats
    used hydrazine and/or compressed cold gas thrusters.
    
    Burns

    I am sorry. I do not have any of the  data availble, but when Teflon
    has a charge inducted on it Ions are released and you have a low
    thrust when directed.  These is used only for small changes in
    attitudes.
    Steve

Article: 38148
From: [email protected] (Ron Baalke)
Newsgroups: sci.space
Subject: NASA to Research New Rocket Propellant
Date: 4 Dec 91 23:06:19 GMT
Sender: [email protected] (Usenet)
Organization: Jet Propulsion Laboratory
 
Drucella Andersen
Headquarters, Washington, D.C.                  December 4, 1991
(Phone:  202/453-8613)
 
Jim Doyle
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)
 
RELEASE:  91-197
 
NASA TO RESEARCH NEW ROCKET PROPELLANT
 
	A soccerball-shaped carbon molecule may be the perfect propellant
for a type of spacecraft engine that produces thrust by expelling charged
atoms or molecules.
 
	Stephanie D. Leifer, an engineer at NASA's Jet Propulsion Laboratory
(JPL), Pasadena, Calif., and Winston A. Saunders of the California Institute of
Technology (Caltech), Pasadena, propose to use the molecule Carbon 60 as
a fuel in ion engines.  These engines, which generate thrust by ionizing and
accelerating propellants, use less fuel than conventional chemical thrusters.
 
	 Leifer believes Carbon 60 has properties that will reduce the energy
required to ionize the propellant.  "For applications where it is desirable to
operate at a relatively low to moderate exhaust velocity, ion engines using
low ion mass propellants become less efficient," Leifer said. "A large
molecule such as Carbon 60 would allow for more efficient operation at low
exhaust velocities," she said.
 
	Because the structure of Carbon 60 resembles a geodesic dome, it is
also called "buckminsterfullerene" in honor of the dome's inventor R.
Buckminster Fuller.  Scientists informally refer to the molecules as
buckyballs."
 
	JPL and Caltech have started a joint effort to examine the use of
Carbon 60 in ion thrusters.  The program will study the basic properties of
the molecule important to ion propulsion and will evaluate it as a fuel in a
small ion engine testbed.
 
	The first practical application of ion engines most likely will 
be in orbital transfer missions and station-keeping for satellites in
geosynchronous orbit 22,300 miles above Earth.  Later, Carbon 60 could
give advanced ion engines much higher thrust and power levels than are
possible today.
 
	 "This project is an excellent example of looking beyond one's sub-
specialty to find new and potentially useful technologies," said Saunders.
"Stephanie and I got together over lunch one day to talk about using
clusters in ion thrusters.  I knew something about Carbon 60, but nothing
at all about ion engines.  She knew about their current limitations and
requirements of ion engines.  On the spot, we cooked up this idea to use
C60 and within 2 weeks we had filed a patent disclosure.  "It's the kind of
synergetics Buckminster Fuller advocated," added Saunders.
 
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [email protected]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3602 Telos | There's no limit to what
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | can be done if it doesn't
|_____|/  |_|/       |_____|/                     | matter who gets the credit.