Any idea about the kind of propellant used? Liquid would probably need to be pumped to the top of the rocket, but swapping from one solid motor compartment to another with the same nozzle seems complicated.
If you really wanted to use solids, maybe you could use the same trick as Orion's LAS: essentially have the solids fire forward into a U-shaped duct.
If you had to pump it 2 m forward at 10 Gs acceleration, the hydrostatic head would be on the order of 2 atm.
Another illustration by Boeing
Off-Topic note: Those engines are stolen from KSP! I recognize the "radial" engine set!On-Topic: I thought I'd suggested such a set up before and seem to recall that I was told it wouldn't work "well" for an LV. I was under the impression that "tractor" rocket designs had some significant issues?Randy
I don't see how that can put 100lbs into orbit and considering how much even an AIM-120 costs, how they expect to do it for $1mil/flt. Article mentions a launch at 40,000ft (well below an F-15's ceiling) with the first two stages using common tractor engines. There's a lot missing here, including an adequate payload bay, so I can only conclude Boeing through Phantom Works got a chunk of cash to do some PR shots (like with the CST-100).In that regard, this is a success as I've always dug the McDonnell Douglas F-15
Well if you put them close to the fuselage you have to put them at an angle, which is less efficient (you have "cosine losses"). An interesting aspect of tractor configuration is that you can save mass on structural elements since you pull instead of pushing, so you don't have to worry about buckling.
Are all four engines burning after it drops the drop tank? I hope the payloads are rated for 10+ g acceleration...
Can the 1st stage burn be pump-feed and the 2nd stage burn be pressure-fed? Presumably the pump gets discarded with the 1st stage. It would be something like the propellants gets pumped from the 1st stage tankage to the 2nd stage tankage to the combustion chambers for the 1st stage burn.
but I can't think of any flown vehicles with drop tanks.
Quote from: simonbp on 04/07/2014 09:43 pm but I can't think of any flown vehicles with drop tanks. Proton-M Briz-M uses a drop tank on the Briz-M upperstage.
Quote from: Skyrocket on 04/07/2014 10:36 pmQuote from: simonbp on 04/07/2014 09:43 pm but I can't think of any flown vehicles with drop tanks. Proton-M Briz-M uses a drop tank on the Briz-M upperstage.Did not know that; thanks!
Quote from: Zed_Noir on 04/07/2014 01:30 amCan the 1st stage burn be pump-feed and the 2nd stage burn be pressure-fed? Presumably the pump gets discarded with the 1st stage. It would be something like the propellants gets pumped from the 1st stage tankage to the 2nd stage tankage to the combustion chambers for the 1st stage burn.I'm not clear on terminology. By staging, you're referring to the Boeing proposal, not traditional staging (like I proposed a few posts back), right? Are drop tanks stages? Wiki says no, Boeing (or at least Steve Johnston) says yes...huh.
The launch altitude is probably significant in that at 40,000ft in a near vertical climb the Eagle is still under acceleration so is providing more significantly towards the total Delta-V budget than if it launched at 80,000ft and almost no airspeed or engine thrust left
Quote from: RanulfC on 04/04/2014 07:52 pmThe launch altitude is probably significant in that at 40,000ft in a near vertical climb the Eagle is still under acceleration so is providing more significantly towards the total Delta-V budget than if it launched at 80,000ft and almost no airspeed or engine thrust leftNo. Whether the Eagle is under acceleration or not is irrelevant.
All that matters is the altitude and velocity at the time of separation. And a lower altitude will only be a win if the velocity is enough to reach the higher altitude at a coast -- which it will not even be close to for the 40kft versus 80kft you're talking about. So it would in fact be far better to launch at low airspeed at 80kft than mach 2-3 at 40kft.
The reason they're planning to launch at 40kft is probably that the launch vehicle weighs so much that the F-15 can't get much higher than that while carrying it.
The engines are powered by an unusual mixture of nitrous oxide and acetylene.
ALASA concept Video
Stupid question, I watched with the sound off, but four engines on the first and second stage. Does that mean they are hoping to reduce costs by eliminating the engine gimbals and use differential thrust for steering?Four engines is really cheaper and more controllable than one engine per stage with gimbals?
...As for the change from the drop-tank to intergrated "first-stage" it makes me wonder how long before the rockets get moved to the tail as per "normal"
The ballute looks like a single point failure to me, if that's their way of guaranteeing stability prior to the start of powered flight. Passive stability (when there are two humans a few feet away) shouldn't require an active device like an inflation system. My guess would be before it gets through safety review they'll need to add something like fins (and maybe end up going to 3 stages due to the added weight).
Uhm, it drops off the F-15 and deploys a ballute so it then goes HORIZONTAL where the engine ignites and THEN has to do another PULL-UP manuever?(banging my head on the desk several times)Nope, STILL doesn't make any sense to me.IF (as I suspect is the case) the AF is worried about a "launch incident" with a liquid propellant LV on the F-15 drop the ballute and use a small solid "seperation" stage to allow the F-15 to pull away. The ballute would even be "ok" if they ignited the main stage BEFORE it looses the critical launch AoA but the video doesn't inspire me that this will get much futher as is.As for the change from the drop-tank to intergrated "first-stage" it makes me wonder how long before the rockets get moved to the tail as per "normal"Randy
They probably mix it with another chemical, quite possibly acetone.
Jeff Foust @jeff_foust 3m3 minutes ago[DARPA's Pam] Melroy: doing static ground tests of ALASA’s mixed monopropellant now. First launch? “more to tell” in the spring. #ispcs
WASHINGTON – The U.S. Defense Advanced Research Projects Agency has scrapped plans to launch small satellites from a modified F-15 fighter jet after two tests of a new rocket fuel ended in explosions this year.
Has any thought been given to using a drone rather than a manned aircraft, for these launches? They fly F-4s converted to QF-4s as aerial targets at Tyndall. These can apparently either auto-land or be controlled by a remote pilot for landing if needed. - Ed Kyle
Air launch plans shelved due to safety concerns:http://spacenews.com/darpa-airborne-launcher-effort-falters/QuoteWASHINGTON – The U.S. Defense Advanced Research Projects Agency has scrapped plans to launch small satellites from a modified F-15 fighter jet after two tests of a new rocket fuel ended in explosions this year.
As a result, DARPA has abandoned plans, described in the agency’s 2016 budget request, to conduct as many as a dozen ALASA test flights during the upcoming year.
Boeing, subcontractor Orbital ATK of Dulles, Virginia, and DARPA nonetheless plan to continue developing the technology. A third propellant test is imminent.
Has any thought been given to using a drone rather than a manned aircraft, for these launches? They fly F-4s and F-16s converted to QF-4s and QF-16s as aerial targets at Tyndall. These can apparently either auto-land or be controlled by a remote pilot for landing if needed. - Ed Kyle
So I'm confused. Is it canceled?
BTW: here is a patent application: NITROUS OXIDE FUEL BLEND MONOPROPELLANTS http://www.faqs.org/patents/app/20090133788
Can we conclude that a monopropellant system is necessary for ALSA to adequately reduce cost and complexity?
Quote from: edkyle99 on 11/30/2015 03:10 pmHas any thought been given to using a drone rather than a manned aircraft, for these launches? They fly F-4s converted to QF-4s as aerial targets at Tyndall. These can apparently either auto-land or be controlled by a remote pilot for landing if needed. - Ed KyleI thought the last QF-4's where retired this year, leaving only the smaller QF-16's.http://www.airforcetimes.com/story/military/2015/05/30/qf4-targeting-drone-last-flight/28015077/
Quote from: kevin-rf on 11/30/2015 05:22 pmQuote from: edkyle99 on 11/30/2015 03:10 pmHas any thought been given to using a drone rather than a manned aircraft, for these launches? They fly F-4s converted to QF-4s as aerial targets at Tyndall. These can apparently either auto-land or be controlled by a remote pilot for landing if needed. - Ed KyleI thought the last QF-4's where retired this year, leaving only the smaller QF-16's.http://www.airforcetimes.com/story/military/2015/05/30/qf4-targeting-drone-last-flight/28015077/ QF-4s are still flying at Holloman AFB. https://www.flightglobal.com/news/articles/usaf-qf-4s-set-for-2017-out-of-service-date-418868/... - Ed Kyle
How does that affect SALVO which was supposed to be a sort of pathfinder ?http://spacenews.com/40769darpa-developing-operational-pathfinder-for-alasa-air-launch-system/
Does anybody know about the dimensions of the ALASA rocket ? all I can find is 24 ft length. also maximum payload of a F-15E in 24500 pounds.