Author Topic: DARPA ALASA  (Read 27572 times)

Offline simonbp

Re: DARPA ALASA
« Reply #20 on: 04/08/2014 07:59 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!

Offline RanulfC

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Re: DARPA ALASA
« Reply #21 on: 04/08/2014 08:48 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!

...And currently for all we know it could drop a couple engines with the tank/1st stage :)

Randy
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Offline Zed_Noir

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Re: DARPA ALASA
« Reply #22 on: 04/09/2014 02:35 AM »
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.

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.
Technically the 1st stage as I described it would not be classified as a drop tank since there will be propellant pumps aboard.

Online ChrisWilson68

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Re: DARPA ALASA
« Reply #23 on: 04/09/2014 04:58 AM »
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

No.  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.

Offline RanulfC

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Re: DARPA ALASA
« Reply #24 on: 04/09/2014 02:43 PM »
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

No. Whether the Eagle is under acceleration or not is irrelevant.

uhm, not really actually. Part of the whole "80,000ft" issue is the F-15 doesn't do WELL at that altitude. In a zoom-climb it would be almost completely out of energy with little aerodynamic authority. It does much better at Mach-2 and 40,000ft. Sorry I wasn't clear about that.

Quote
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.

And of the two, altitude and velocity, the velocity at the time of "launch" is the more important factor from all the air-launch research I've read. Mach-2 at 40,000ft is much more of an advantage than Mach-0.98 at 80,000ft. In addition AoA is also a huge factor in Air Launch and the fact the F-15 will have a high AoA will help a lot.

Quote
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.

I have no doubt of that considering it probably masses around the same as the ASM-ASAT missile: (http://en.wikipedia.org/wiki/ASM-135_ASAT) which means the F-15 will be lucky to launch at supersonic speed at all.

Which as I said before, means they are wasting far to much mass on a manned/aircraft launch platform :) Guess I should get "back-to" playing around with the jet engine launch assist concept again...

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline gosnold

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Re: DARPA ALASA
« Reply #25 on: 06/30/2014 07:41 PM »
Jeff Foust has more info on ALASA:
http://www.spacenews.com/article/military-space/40769darpa-developing-operational-pathfinder-for-alasa-air-launch-system
Quote
The engines are powered by an unusual mixture of nitrous oxide and acetylene.

Offline catdlr

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Re: DARPA ALASA
« Reply #26 on: 02/05/2015 09:30 PM »
ALASA concept Video

Published on Feb 5, 2015
DARPA’s Airborne Launch Assist Space Access program (ALASA) seeks to propel 100-pound satellites into low Earth orbit (LEO) within 24 hours of call-up, all for less than $1 million per launch. The current ALASA design envisions launching a low-cost, expendable launch vehicle from conventional aircraft. Serving as a reusable first stage, the plane would fly to high altitude and release the launch vehicle, which would carry the payload to the desired location. The program is moving ahead with rigorous testing of new technologies that one day could enable revolutionary satellite launch systems that provide more affordable, routine and reliable access to space.


« Last Edit: 02/05/2015 11:16 PM by catdlr »
Tony De La Rosa

Offline Saltvann

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Re: DARPA ALASA
« Reply #27 on: 02/05/2015 09:42 PM »
Here's their press release:

http://www.darpa.mil/NewsEvents/Releases/2015/02/05.aspx

A test flight in late 2015 and 12 orbital test flights in 2016.

Offline Skyrocket

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Re: DARPA ALASA
« Reply #28 on: 02/05/2015 11:04 PM »
ALASA concept Video





According to the video, the drop-tank concept apparently has been dropped.

Offline RanulfC

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Re: DARPA ALASA
« Reply #29 on: 02/06/2015 07:44 PM »
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
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Online kevin-rf

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Re: DARPA ALASA
« Reply #30 on: 02/06/2015 08:02 PM »
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?
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Offline RanulfC

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Re: DARPA ALASA
« Reply #31 on: 02/06/2015 08:09 PM »
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?

"Cheaper" may actually be relative here, remember who's (and ultimatly who the user is) program this is :)

Mechanically less complex but I suspect not as flexible (no pun intended but then again there it is :) ) as a single gimbled motor. "Cheap" 3D printed nozzles/engines maybe?

Randy
From The Amazing Catstronaut on the Black Arrow LV:
British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Offline Zed_Noir

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Re: DARPA ALASA
« Reply #32 on: 02/07/2015 07:16 AM »
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?

IMO the 4 engines reduce the interstage separation distance resulting in a more compact vehicle.


...

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 way they mounted the engines in the video avoids a tailcone ejection event and changes to the vehicle center of gravity and aerodynamics drag profile. Beside they need to place the drogue chute in the tail.

Offline dchill

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Re: DARPA ALASA
« Reply #33 on: 02/07/2015 06:00 PM »
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).
« Last Edit: 02/07/2015 06:00 PM by dchill »

Offline Zed_Noir

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Re: DARPA ALASA
« Reply #34 on: 02/08/2015 02:33 AM »
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).

The drogue chute is quite similar to the units used for stabilizing various ordnance drop by the various US military forces for decades. Your fin stabilization idea would require pop-out and active control features for the vehicle IMO. 

The F-15 Strike Eagle might not be physically able to accommodate a larger three stage vehicle. Also there is a weight limitation to how much the fuselage hardpoint/bomb rack can carry.
« Last Edit: 04/16/2015 09:32 AM by Zed_Noir »

Offline fast

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Re: DARPA ALASA
« Reply #35 on: 04/16/2015 08:37 AM »
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

exactly. first stage tractor is a total nonsense if no drop tanks.
why just don't use this traditional approach???

Offline john smith 19

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Re: DARPA ALASA
« Reply #36 on: 04/16/2015 09:41 AM »
From the Faust article

"The engines are powered by an unusual mixture of nitrous oxide and acetylene."

Acetylene?

That's quite interesting as it's been a perennial possible fuel for decades.

I wonder how they've managed to curb it's tendency to explode.
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Offline Steven Pietrobon

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Re: DARPA ALASA
« Reply #37 on: 05/23/2015 05:26 AM »
They probably mix it with another chemical, quite possibly acetone.
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Offline Skyrocket

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Re: DARPA ALASA
« Reply #38 on: 05/23/2015 09:28 AM »
Generally i am wondering about the safety and stability of a monopropellant mixture of nitrous oxide and acetylene.

Offline john smith 19

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Re: DARPA ALASA
« Reply #39 on: 06/17/2015 08:44 AM »
They probably mix it with another chemical, quite possibly acetone.
Doubtful.

Acetylene tanks use this with IIRC powdered rare earth to absorb the Acetylene.

This is way too heavy for flight weight tanks for a pump fed engine, not to mention the performance loss.
[EDIT2 Opps. I may have been premature thinking of pump feds. Checking physical properties I note N2O2 liquifies around -88c and Ethyne solidifies at about -80c.

This suggests a sort of "aerosol can" architecture, with tanks at a few bar feeding pumps or higher pressure systems running a few 10s of bar, all running around -70 to -80c to keep the propellants dense ]


[EDIT obvious question but does anyone have any idea what sort of Isp you could get out of this propellant at a viable engine chamber pressure? My instinct is 30-100 atm, maybe as low as 10, but that's just a feeling and I can't back it up. Obviously higher pressure --> small chamber(s) --> lower mass but also harder driven pumping system.

It's interesting the US military don't like cryogenics but are OK with things that will vaporize at room temperature and remain dangerous (like a cloud of Ethyne) ]

 
« Last Edit: 06/17/2015 09:42 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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