[ExI] darpa's notion of using a retrofitted fighter jet to launch payloads

spike spike66 at att.net
Mon Feb 9 21:12:32 UTC 2015



From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of justin corwin
Sent: Monday, February 09, 2015 11:13 AM
To: ExI chat list
Subject: Re: [ExI] darpa's notion of using a retrofitted fighter jet to launch payloads


>…I don't think I've ever seen a setup with engines mounted so high on the fuselage, is there an engine/reference design that could be used for that? The artist seemed to have some very specific details one wouldn't just assume…


The nozzles-forward design has some advantages that are compelling in the case where the craft doesn’t go supersonic until you get way up into the thin air.  The usual nozzles-aft arrangement is better at high speeds low in the atmosphere, but in this case, nozzles-forward makes sense.  Reasoning: you have air-breathing relatively low speed launch, then get up to perhaps 0.2 atmospheres or less before you go supersonic and have all the shock wave headaches to spoil your day.  With the air-breathing stage you get out of most of the aerodynamic drag penalty of nozzles-forward.


You might even get away with control by throttling as opposed to gimbal nozzles, which is compelling if you are trying for minimal cost.  They don’t react as quickly as thrust vector control, but that might be OK for this application.  Furthermore, with the nozzles forward design, you have the oscillating instability problem (that design puts two poles in the right half plane) but if you get tricky with your lead/lag control system, I can envision something like that working.  If so, that is perhaps your best bet for a low cost high production run throwaway first stage.  Terminology: an aircraft launch often refers to the airplane as a half stage, so the first stage is your first non-air breathing stage.


>…I like the idea of establishing some numbers. I know that BAE in Mojave makes(or made) drones out of F-4 Phantoms to be used as targets for missile tests. Any chance somebody knows what they pay for those? You'd want it unmanned anyway…


Ja!  My first engineering job in 1983 was documenting the F-4 to drone conversion process, making a parts list, all the stuff they were doing back then.  Good chance you could get the USNavy to give you one of those.  An F-4 might be a really good choice for this application, since they didn’t really know all the forces they were dealing with back in the 1950s, so they built it strong, at the expense of weight (those are heavy bastards, but sturdy, and those engines are marvelous beasts.)  


What I don’t know is if the F-4 could handle the center-of-pressure offset with those negative dihedral tail design, however… I know for a fact the early prototypes of the F-4 had a positive dihedral tail and a few of those still exist down in the Mojave boneyard.  Retrofit an F-4 with one of those A-version tails, take off the tailhook, retrofit those crazy-big landing gear with much smaller, lighter gear that can only handle a long flat runway landing on a calm day with tanks empty, then launch the thing with a railcar, getting up to near 300 knots on the deck.  That would be a fun project to design.


Anyone here have buddies at DARPA?  


>...If there were a dedicated small payload rocket, I think more cubesats might get made, but assuming there aren't, you have a market of about two successful launches a year of an 18U carrier. If you could kick your prices down, more might occur. Also, currently small payloads often have to wait, which mean timely payloads need dedicated launchers. If you could guarantee a launch within six months, you might attract more business as well… outlawpoet


Ja I think there is a market there, not a huge one.  But if DARPA has a practical nozzles-forward control system I can see getting the Navy to practically give you a Phantom, and there are still guys around who know how to get those engines running.  It occurred to me that we could even recover the control section if you did it right.  One of the advantages of a nozzles forward design is that you can drop off tanks from the aft end with the engines still firing, and perhaps mount the compressor turbines such that you get them back.  Maybe.  If you’re lucky.










From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Kelly Anderson
Sent: Sunday, February 08, 2015 11:57 PM
To: ExI chat list
Subject: Re: [ExI] darpa's notion of using a retrofitted fighter jet to launch payloads


>…Looks like a rip off of Virgin Galactic's basic concept. My question is why would this cost a million dollars?? -Kelly



I can think that a lot of the cost of this would be in the inertial reference gear in the guidance system.  For typical satellite work, that stuff doesn’t come cheap.  But given some kind of standard bus, there would be mass production, thousands of units perhaps.  I can imagine a standardized thousand unit production run of guidance and control systems including thrust vector control getting down below a million clams, and everything else combined below 100k.


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Justin Corwin
outlawpoet at gmail.com

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