Repost and Additional Info on the DART Aerospike.
For Background a Repost:
For those who had not seen this previously, here is some information on the NASA-Dryden DART aerospike solid rocket flown at the Pecos County Spaceport in Texas. I was a co-principal investigator on this project.Photos of the aerospike and the rocket can be found at: You can also go to the medium or large jpeg photo sections and zoom in and check out the aerospike in detail.
The DART aerospike rocket is documented in a tech article authored by Scott Bartel and myself published in the August 2004 issue of High Power Rocketry Magazine (Vol. 35, No. 5). The tech article has lots of photos and complete documentation on the aerospike rocket. It's available as a back issue from High Power Rocketry.
The aerospike was built by Cesaroni Technology Incorporated (CTI). The aerospike retrofits onto a CTI O5100 motor case in place of the conventional conical nozzle.
Additional (New) Info:
Aerospike uninstalled performance is measured by taking the thrust coefficient of the aerospike and dividing it by the ideal thrust coefficient with ideal expansion (thus no divergence losses, throat losses, or under- or over- expansion losses). CF/CFideal is plotted versus the chamber pressure divided by the atmospheric pressure (Pc/Pa). Below is an example plot from a post some time ago on sci.space.policy by Kevin Ryan.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
Where Nozzle Efficiency is CF/CFideal. Note that if the lines don't line-up in the plot above, check here for a possibly better version of the plot:Sea Level Pc/Pa values for chamber pressures of 400 psia to 1,500 psia vary from 27 to 102. Near vacuum Pc/Pa values are in the 1,000 to 10,000 range. Note that the plot above has a log scale for Pc/Pa going out to Pc/Pa = 10,000.
Historical Rocketdyne annular (toroidal) aerospike performance data, and other aerospike performance data similar to the plot above typically show a delivered CF/CF ideal = 0.90 - 0.92 at operating conditions of Pc/Pa = 20 - 80.
How well did the centered Prandtl-Meyer all-external expansion DART aerospike perform? The DART aerospike delivered the following uninstalled performance in static test:
CF/CFideal = 0.97 at Pc/Pa = 25.5
Remember, all of the above is uninstalled performance, i.e., a uniform pressure field around the aerospike (Pa), with zero velocity (static conditions). Flow around the rocket in flight creates an initial flowfield in front of the aerospike which makes the installed performance different from the uninstalled performance; measurement of which was one of the key technical objectives of the DART aerospike rocket flights.
More on the inflight-measured installed performance in future posts, although I will mention that we did see a dip in installed performance at transonic Mach numbers, which had been predicted in many prior studies and expected from CFD predictions, but which many have wondered whether it would actually occur in flight.
Will the DART aerospike design hold the high level of CF/CFideal uninstalled performance (97% of ideal efficiency) all the way out to vacuum conditions (Pc/Pa = 1,000 - 10,000)? We had plans to do a hot fire test using a complete motor in a ground test facility at a simulated 100,000 ft altitude (Pc/Pa = 2,360), but it turned out that our "free" test was going to use up half our budget, so we had to drop the test.
Chuck Rogers email@example.com