The new Fox column is up. It's an expansion of my earlier post on why we don't need scramjets to reduce the cost of space launch.

I would strongly suggest you go back and study propulsion again. In your article you make several completely contradictory statements. And others that simply are incorrect.

"There are other issues. Airbreathing engines tend to optimize at a certain cruise speed, and perform very poorly in what engineers call "off-design conditions." That's exactly the propulsion system that you don't want in a launch system, which is under continuous acceleration--not cruising along at a single speed. In addition, rocket engines are indifferent to vehicle speed (they're sensitive only to atmospheric pressure)."

This is but one example of what I hope is simply a misstatement. I'm sure you are aware that a rocket engine would spend just as much time in "off design" performance over the same mission.

"It costs less than a few cents per pound."

In speaking of Oxidizer you also play with the facts to mold them to your argument. The high cost of Oxidizer is not due to acquisition expenses, you are correct there, rather it is storage and transportation of the oxygen.

A little bit of knowledge can be a dangerous thing.

Brendan L. Corrigan
Aeronautical Engineer
Advanced Aircraft Design

What "off-design condition" does a rocket engine operate at, other than a change in exit pressure? That's much less of a problem than a change in inlet velocity, in terms of performance implications.

And I don't know what you mean by the cost of "storage and transportation of oxygen." Even including those factors, it remains pennies per pound. At least, last time I checked, Airco would deliver it for that. Even if it were a dollar a pound, it would still be an insignificant portion of the total launch cost, at current costs.

I've studied this stuff for a living, Mr. Corrigan, for both NASA and the Air Force. I've a little more than a "little" knowledge.

Mr Corrigan-

I work with oxidizers routinely, and even when buying LOX retail from Praxair, it costs me only $0.29/lb. My boss has quotes in hand for delivery of 40,000 lb tanker truckloads at about $.05/lb.

Even when renting dewars from the supply company, the storage cost is only about $.04/lb/week. With purchased or long-term leased storage, this would be under $.01/week- and with additional supplies only a phone call away, I won't need more than a week's worth of local storage.

The direct cost of LOX handling, on the EZ-Rocket, comes to about $50 per flight for technician labor. Larger vehicles will need little more labor thanks to economies of scale; I anticipate the same labor cost for loading the Xerus with 5,000 lb of LOX. This would add about $.01/lb, and with all storage, handling, and labor costs, LOX will still be well under $.10/lb.

LOX really *is* cheap.

Thrust of a typical rocket engine might be reduced by 20% when operating at sea level, vs its vacuum performance. The thrust is not sensitive to vehicle speed at all (although the vehicle drag might change some due to base bleed/pumpdown effects). On the other hand, scramjets don't work at *all* subsonically, nor do they work at over mach 8. Rand is correct; ram- and scramjets are not suited to accelerator missions.

As for my credentials, I have had a major hand in the design of eight or nine rocket engines of up to 7000 lb thrust, which have been run in excess of 1500 times and over 11,000 seconds, including 15 manned rocket aircraft flights. If you want to argue from authority, bring it on...

Doug Jones, Rocket Engineer
XCOR EZ-Rocket Crew Chief

Seems like using an aerospike engine could provide better overall performance than a scramjet.

Yes, but it's still not necessary. If people who are in so in love with fancy technologies would instead focus on developing markets and raising money, there'd be lots of ways to skin the cat.

>> lots of ways to skin the cat.

We have far more ways than skin. Considering that skin pays for the ways....

>>when buying LOX retail from Praxair, it costs me only $0.29/lb. My boss has quotes in hand for delivery of 40,000 lb tanker truckloads at about $.05/lb.

Yay! My dad is a truck driver for Praxair, he hauls LOX, Argon, and Nitrogen all over the place.

In spite of what the Aussies might say, the Russians at the Central Institute of Aviation Motors (CIAM) were the first to fly scramjets beginning in 1992. True, the first couple, including one joint one with the French, operated in the ramjet mode at a max Mach of 5.0 to 5.5, but they were genuine scramjet designs flown at less than hypersonic speed. On the other hand, NASA had a joint project with the same Russians and successfully flew an improved scramjet configuration at Mach 6.5 (fully hypersonic) in Feb. 1998 ? some four years before the Australians. And, based on actual flight data and post-flight CFD analysis, CIAM claims they indeed achieved supersonic combustor flow (Mach 1.5) during the almost 70-sec. test phase at about 26 km. I know about this because I was the NASA Dryden project manager for that joint effort and recently retired. I know the Australian team well and they often set in on our AIAA presentations on the CIAM result, so I don?t know why they or anyone else would make such a claim for the HyShot flight given a lack of thorough data analysis and the highly dynamic ?downhill? trajectory they flew. The Russian test was at least semi-steady state at the top of the ballistic arch of the SA-5 booster.

By the way, I spent nine frustrating years on the X-30 NASP, worked the CIAM activity and created/started the X-43 Hyper-X project at NASA. So you can imagine I don?t agree with you on the ?stinkin? technology? view of scramjets. Part of that comes from my experience with the Shuttle which was suppose THE RLV solution back in the 60s/70s and has never panned out. So much for rockets. The 50 flight-per-year frequency, less that $5K/payload lb. transport cost, etc. never was realized on the Shuttle/rocket approach as you well know. On top of the high maintenance, low launch rate, high manpower for flight turnaround (thousands at KSC and four months time on average), etc., NASA still acknowledges it costs about $500M per launch ? the infrastructure being huge! That works out on average to around $20K/payload lb. which almost doubles the cost of the ISS itself just to haul components up on some 45 Shuttle flights (for the full, original ISS). You?re right in that airbreathing technology has a long way to go and the U.S. (DOD/NASA) have done a dreadfully wasteful job of pushing it over some 30+ years, but I still believe it?s achievable and provides cheaper space access in the future - which is why I tried so hard to get things like scramjets in flight after the demise of NASP. I still think $2K-4K/lb. payloads are possible if you not only carry less internal propellant load (admittantly just keying on oxidant is naive and overly simplistic) but fly much more often and with quicker turnaround times ? which rockets cannot and have not demonstrated! The Russians, Germans, Japanese and French reached that conclusion in their own SSTO or TSTO analysis studies based not only on much higher Isp, less propellant and other performance issues, but because of more airline-like simpler, lesser infrastructure required and much, much higher flight rates. You know ?one-shot? ELVs can?t do that (high cost per item, non-reusability, etc.) and rocket-powered RLV concepts like Shuttle haven?t shown it either. It?s got to be a much more routine operation with tens of ground crews instead of thousands.

- John Hicks
- Retired NASA Dryden