From: MUNIZB%RWTMS2.decnet@consrt.rockwell.com ("RWTMS2::MUNIZB")
Subject: Terminal Velocity of DCX? (was Re: Shuttle . . .)
X-Added: Forwarded by Space Digest
Organization: [via International Space University]
Original-Sender: isu@VACATION.VENARI.CS.CMU.EDU
Distribution: sci
Date: Fri, 18 Dec 1992 00:59:19 GMT

My apologies to the net if this has been discussed before, but I've been 
pretty far behind in my reading.  Anyway, . . .

In article <1992Dec3.143759.2535@ke4zv.uucp> gary@ke4zv.UUCP (Gary 
Coffman) writes:
>tested. Later it intends to use aerospike engine designs that have
>*never* been tested, even on the ground. It will be difficult for 

This is definitely not true!

On Date: Thu, 19 Nov 1992 15:04:00 GMT, "Allen W. Sherzer" <aws@iti.org>
writes:
>conventional bell nozzles. The GD design could enter base first but had
>to have an aerospike nozzle to do it. Since aerospike nozzles have never
>flown, that would add another risk to the propulsion system.

This is more correct, but not the total story either.

In the Spring 1992 (No. 8) issue of Rocketdyne's *Threshold* magazine 
there is an article "Nozzle Design" by R. A. O'Leary and James E. Bech 
which states "During the 1960's, Rocketdyne tested numerous aerospike 
engines, ranging in size from subscale, cold-flow models to this 
250,000-pound-thrust oxygen/hydrogen shown at a test stand in Nevada 
(picture of engine firing).  The low altitude performance advantage of 
the aerospike over conventional bell nozzle is clearly seen".  The curve 
presented looked like this:

             1.0 .----.----.----.----.----.----.----.----.----.----. 
                 |            + T  +T T   +   +/   +/   +/   +/ T +/
                 |    T +                   /
                 :  +                    /                  
                 |                    /           
             0.9 |                  / 
                 :                 /      Area Ratio = 75:1
  Nozzle         |                /       nozzle length = 25% equivalent 
  Efficiency     |              /                         conical
                 :              /
             0.8 |            /            /  Bell Nozzle
                 |           /             +  Aerospike (predicted)
                 :          /              T  Aerospike (test data)
                 |         /
                 |
             0.7 :----.--/-.----.----.----.----.----.----.----.----.
                 |      |     |     |     |       |     |       |
                 10    100   200   400   800    2000  4000    10000
 
                             Pressure Ratio:  Pc/Pa

Various propellants and both conical (1-D) and axial (2-D) models were 
been tested.  I have heard from several sources that Rocketdyne's 
original proposal for the Space Shuttle Main Engines used an aerospike 
design.  At the California Space Development Conference held in San Diego 
in February 1991, Vern Larson from Rocketdyne gave a presentation on the 
aerospike test program.

At that same conference, I asked Max Hunter ("father" of the Delta rocket 
and a major player in the SSTO field) why it seemed that an aerospike was 
not baselined for the DC-X or the proposed DC-Y and DC-1.  He replied 
that there was concern regarding the lack of *flight-test data* (he 
acknowledged that there was plenty of ground test data), in particular 
for the transonic regime.  However, the Rocketdyne article states ". . . 
from Mach 1 to about Mach 3, *wind tunnel tests* (emphasis mine) indicate 
a drop in nozzle efficiency due to the slipstream turning into the nozzle 
region . . . Nevertheless, the interval of time that is spent in this 
adverse flight regime is short for typical flight trajectories, and 
overall performance of the aerospike nozzle remains well above that of a 
conventional bell-type nozzle".

Wind tunnel test results and CFD simulations are usually sufficient for 
design of experimental flight vehicles.  Therefore the question remains: 
If lack of *flight-test* data is seen as the long pole in the tent 
(holding things up), why isn't it being flown on the admittedly 
experimental DC-X (and DC-Y)? 

A reference on aerospike engines that I've seen noted but haven't had a 
chance to get is: Ballard, R. O., "The Aerospike/Aeroplug Engine: A 
Technology Development Summary", Sverdrup Technology Inc., MSFC Group, 
Contract NAS8-37814, 1991.

In regards to technology for SSTO, I came across an article by C. E. 
Tharratt of Chrysler Corporation Space Division in JBIS Vol. 28, pp.3-25, 
1975, entitled "SERV - A Reusable Single Stage to Orbit Space Shuttle 
Concept".  It says that a reusable SSTO could be built to NASA 
requirements with the technology level of the day, except for an added 
"requirement for large cross range (1500 nautical miles with crew and 
cargo) and through it, the ability the ability to launch and land in one 
earth orbit."

I seem to recall this as an Air Force driven requirement, and that the 
original NASA requirement was less stringent.  The paper states the 
original requirement as a return to a preselected [launch?] site every 24 
hours (approximately 15 orbits), rather than one orbit.  Any idea what 
the requirement will be for DC-Y (and DC-1)?

In order to meet the cross range requirement, the article mentions the 
weight benefit of using a reusable reradiative heat shield (todays 
Shuttle tiles) rather than the baselined ablative material, and a major 
advance in specific impulse from using an activated oxygen/hydrogen 
engine with a 650 second vacuum specific impulse.  It ruled out weight 
reduction based on materials technology (which today is a most  viable
technology!).

Ben Muniz: President, Rocketdyne Employees Space Society/a chapter of NSS
Internet:munizb@rocket.rdyne.rockwell.com  w(818)700-5549  h(818)346-6647

Newsgroups: sci.space